WO2024164811A1 - 微电网系统、功率变换器及其控制方法 - Google Patents

微电网系统、功率变换器及其控制方法 Download PDF

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Publication number
WO2024164811A1
WO2024164811A1 PCT/CN2024/072527 CN2024072527W WO2024164811A1 WO 2024164811 A1 WO2024164811 A1 WO 2024164811A1 CN 2024072527 W CN2024072527 W CN 2024072527W WO 2024164811 A1 WO2024164811 A1 WO 2024164811A1
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Prior art keywords
power converter
voltage
control mode
grid
value
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PCT/CN2024/072527
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English (en)
French (fr)
Inventor
张美清
王硕
董明轩
辛凯
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Huawei Digital Power Technologies Co Ltd
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Huawei Digital Power Technologies Co Ltd
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Priority to EP24710010.0A priority Critical patent/EP4439902A4/en
Priority to US18/667,399 priority patent/US12555999B2/en
Publication of WO2024164811A1 publication Critical patent/WO2024164811A1/zh
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/001—Arrangements for handling faults or abnormalities, e.g. emergencies or contingencies
    • H02J3/0012—Arrangements for handling faults or abnormalities, e.g. emergencies or contingencies characterised by the contingency detection means in AC networks, e.g. using phasor measurement units [PMU], synchrophasors or contingency analysis
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/001—Arrangements for handling faults or abnormalities, e.g. emergencies or contingencies
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/12—Arrangements for adjusting voltage in AC networks by changing a characteristic of the network load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/28—Arrangements for balancing of the load in networks by storage of energy
    • H02J3/32—Arrangements for balancing of the load in networks by storage of energy using batteries or super capacitors with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/388—Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2101/00—Supply or distribution of decentralised, dispersed or local electric power generation
    • H02J2101/20—Dispersed power generation using renewable energy sources
    • H02J2101/22—Solar energy
    • H02J2101/24—Photovoltaics
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2105/00—Networks for supplying or distributing electric power characterised by their spatial reach or by the load
    • H02J2105/10—Local stationary networks having a local or delimited stationary reach
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P80/00—Climate change mitigation technologies for sector-wide applications
    • Y02P80/10—Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier
    • Y02P80/14—District level solutions, i.e. local energy networks

Definitions

  • the present application relates to the field of power supply technology, and in particular to a microgrid system, a power converter and a control method thereof.
  • Microgrids are composed of distributed power generation, power loads, monitoring, protection and automation devices (including energy storage devices when necessary), and are small power supply and consumption systems that can basically achieve internal power balance. Microgrids have two operating modes: grid-connected and off-grid. Grid-connected mode means that under normal circumstances, the microgrid is connected to the large grid and operates in parallel, providing excess power to the large grid or the large grid supplies power to local loads and charges batteries. Off-grid mode means that when a large grid fault is detected or the power quality does not meet the requirements, the microgrid is disconnected from the large grid to form an island state, and the distributed power sources and energy storage batteries in the microgrid supply power to the local loads.
  • Grid-connected mode means that under normal circumstances, the microgrid is connected to the large grid and operates in parallel, providing excess power to the large grid or the large grid supplies power to local loads and charges batteries.
  • Off-grid mode means that when a large grid fault is detected or the power quality does not meet the requirements, the microgrid is disconnected from the large grid to
  • microgrids and all their distributed power sources and energy storage have become an important part of the safety and stability of the power system.
  • the microgrid When a voltage drop occurs in a fault in the large power grid, the microgrid will immediately switch to off-grid mode and operate independently, which will cause a large power disturbance to the large power grid.
  • most of the voltage drops in the large power grid are temporary, that is, most of the faults that occur are not permanent faults, and the system can operate normally after the circuit breaker is disconnected and automatically reclosed. Therefore, in the event of a fault in the large power grid, it is particularly important for the microgrid to provide voltage support for the large power grid and complete the off-grid mode switch before the circuit breaker is disconnected.
  • the power grid includes an external power grid or a microgrid system
  • the first current source control mode is a current source fault ride-through control mode
  • the first voltage source control mode is a voltage source fault ride-through control mode.
  • the grid-connected switch is disconnected after a second duration in the event of a power grid fault, and the second duration is greater than the first duration. It can be understood that when each power converter in the microgrid system detects a grid fault, it controls itself to be in the current source fault ride-through control mode, and controls itself to switch to the voltage source fault ride-through control mode before the grid-connected switch is disconnected.
  • the power converter in a first current source control mode, controls the output voltage of the power converter based on the voltage drop value of the microgrid bus when a grid fault occurs, thereby providing reactive current support to the external grid, and realizing the current source fault ride-through support characteristic of the microgrid system.
  • the power converter controls the output voltage of the power converter based on the maximum preset current amplitude in the preset current amplitude range, thereby providing voltage and frequency support to the external grid, and realizing the voltage source fault ride-through support characteristic of the microgrid system.
  • the power converter obtains a first reference output current value based on the voltage drop value of the microgrid bus when a grid fault occurs, obtains a first reference output modulation voltage value based on the first reference output current value and the first reference angular frequency value, and controls the output voltage of the power converter based on the first reference output modulation voltage value so that the power converter is in a first current source control mode, thereby enabling the power converter to provide a certain voltage support for the external grid based on the voltage drop value, thereby enabling the microgrid system to provide voltage support for the external grid when a grid fault occurs, thereby realizing the current source fault ride-through support characteristic.
  • the power converter obtains a second reference output current value based on the maximum preset current amplitude and the equivalent impedance angle of the external power grid, obtains a second reference output modulation voltage value based on the second reference output current value and the second reference angular frequency value; and controls the output voltage of the power converter based on the second reference output modulation voltage value so that the power converter is in the first voltage source control mode.
  • the power converter switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode, which can reduce the risk of instability of the microgrid system caused by the power converter not switching to the voltage source control mode before the grid-connected switch is disconnected, thereby improving the stability of the microgrid system.
  • the initial reference output current value and the initial reference angular frequency value of the power converter in the first voltage source control mode are respectively the first reference output current value and the first reference angular frequency value of the power converter in the first current source control mode at the switching moment, which can reduce the fluctuation degree of current and voltage during mode switching and improve the smoothness of current and voltage during mode switching.
  • the power converter is also in a second current source control mode before a grid failure occurs, wherein in the second current source control mode, the power converter controls the output voltage of the power converter based on a reference output active current value and a reference output reactive current value.
  • the microgrid system is in a grid-connected mode, and each power converter is in a second current source control mode, i.e., a normal control mode under the current source control mode, which is conducive to improving the stability of the microgrid system.
  • the power converter determines the reference output active current value and the reference output reactive current value as a third reference output current value, and obtains a third reference output modulation voltage value based on the third reference output current value and the third reference angular frequency value; and controls the output voltage of the power converter based on the third reference output modulation voltage value so that the power converter is in a second current source control mode.
  • the power converter further obtains a reference output active current value based on the reference output active power value and the actual output active power value of the power converter. It can be understood that the reference output active current value is obtained in a simple manner, which is conducive to improving the working efficiency of the power converter, thereby improving the working efficiency of the microgrid system.
  • the power converter includes a direct current (DC)/direct current (DC) circuit, a direct current (DC) bus, and a direct current (DC)/alternating current (AC) circuit, and the output end of the DC/DC circuit is connected to the input end of the DC/AC circuit through the direct current (DC) bus.
  • the power converter also obtains a reference output active current value based on a reference bus voltage and an actual bus voltage of the DC bus. It is understandable that the reference output active current value can also be obtained based on the bus voltage of the DC bus, and the reference output active current value can be obtained in various ways with high flexibility.
  • the power converter further obtains a reference output reactive current value based on the reference output reactive power value and the actual output reactive power value of the power converter. It can be understood that the reference output reactive current value is obtained in a simple manner, which is conducive to improving the working efficiency of the power converter, thereby improving the working efficiency of the microgrid system.
  • the power converter further obtains a reference output reactive current value based on a reference output voltage and an actual output voltage of the power converter. It is understandable that the reference output reactive current value can also be obtained based on the output voltage of the power converter, and the reference output reactive current value can be obtained in various ways with high flexibility.
  • the eleventh possible implementation after the power converter is in the first voltage source control mode, when the power grid returns to normal, it switches from the first voltage source control mode to the second voltage source control mode, wherein in the second voltage source control mode, the power converter controls the output voltage of the power converter based on the reference voltage amplitude and the reference frequency value. Furthermore, after the power grid returns to normal, the microgrid system can actively provide preset voltage frequency support and preset voltage amplitude support for the external power grid.
  • the power converter obtains a fourth reference output modulation voltage value based on a reference voltage amplitude and a reference frequency value, and controls the output voltage of the power converter based on the fourth reference output modulation voltage value so that the power converter is in a second voltage source control mode.
  • the power converter determines that a power grid fault occurs when its output voltage is less than a voltage threshold or its output current is greater than a current threshold. It is understandable that the power converter can determine whether the power grid is faulty by its own output voltage or output current. This method does not require communication with the microgrid controller, and can effectively improve the efficiency of the power converter in fault detection of the power grid.
  • the power converter determines that a power grid fault occurs when the voltage of the microgrid bus is less than a voltage threshold. It is understandable that the power converter can also determine whether the power grid is faulty by the voltage of the microgrid bus, and the power grid fault judgment method is diverse and flexible.
  • the microelectronic The grid system also includes a microgrid controller.
  • the microgrid controller detects a grid failure, it controls the grid-connected switch to disconnect after a second period of time.
  • the power converter also sends the control mode of the power converter to the microgrid controller after switching to the second voltage source control mode, wherein in the second voltage source control mode, the power converter controls the output voltage of the power converter based on the reference voltage amplitude and the reference frequency value.
  • the microgrid controller When the grid-connected switch is in the disconnected state and the control mode of the received power converter is the second voltage source control mode, the microgrid controller sends a synchronous control instruction to the power converter, the synchronous control instruction is used to control the amplitude difference between the output voltage amplitude of the power converter and the voltage amplitude of the external power grid to be less than the amplitude difference threshold, and the phase difference between the output voltage phase of the power converter and the voltage phase of the external power grid to be less than the phase difference threshold; and when the amplitude difference between the voltage amplitude of the first end of the grid-connected switch and the voltage amplitude of the second end is less than the amplitude difference threshold, and the phase difference between the voltage phase of the first end of the grid-connected switch and the voltage phase of the second end is less than the phase difference threshold, the microgrid controller controls the grid-connected switch to close.
  • the microgrid controller adjusts the control mode of each power converter based on the switching state of the grid-connected switch and the control mode of each power converter, so that each power converter operates in the current source control mode when the microgrid system is in the grid-connected mode, and operates in the voltage source control mode when the microgrid system is in the off-grid mode, thereby improving the stability of the microgrid system.
  • the microgrid controller also sends a mode switching instruction to the power converter after a third period of time when the grid-connected switch is in a closed state and the control mode of the received power converter is the second voltage source control mode, and the mode switching instruction is used to control the power converter to switch to the second current source control mode, and in the second current source control mode, the power converter controls the output voltage of the power converter based on the reference output active current value and the reference output reactive current value.
  • the microgrid controller adjusts the control mode of each power converter based on the switching state of the grid-connected switch and the control mode of each power converter, so that each power converter operates in the current source control mode when the microgrid system is in the grid-connected mode, and operates in the voltage source control mode when the microgrid system is in the off-grid mode, thereby improving the stability of the microgrid system.
  • the present application provides a power converter, the input and output ends of which are respectively connected to a DC power supply and a microgrid bus, and the microgrid bus is connected to an external power grid through a grid-connected switch.
  • the power converter detects that a fault has occurred in the power grid, it is in a first current source control mode; after the duration of the grid fault reaches a first duration, it switches from the first current source control mode to the first voltage source control mode, wherein the power grid includes an external power grid or a microgrid system where the microgrid bus is located, the first current source control mode is a current source fault ride-through control mode, the first voltage source control mode is a voltage source fault ride-through control mode, the first duration is less than the second duration, and the second duration is the time interval between the moment when the power grid fault occurs and the moment when the grid-connected switch is disconnected.
  • the power converter when the power converter detects that a fault has occurred in the power grid, it controls itself to be in a current source fault ride-through control mode, and controls itself to switch to a voltage source fault ride-through control mode before the grid-connected switch is disconnected, so that the power converter provides voltage support for the external power grid when the power grid fails, and completes the on-grid and off-grid mode switching before the grid-connected switch is disconnected, so that the power converter takes into account both the fault ride-through support function and the on-grid and off-grid switching function.
  • the power converter in a first current source control mode, controls the output voltage of the power converter based on the voltage drop value of the microgrid bus when a grid fault occurs, thereby providing reactive current support to the external grid, and realizing the current source fault ride-through support characteristic of the power converter.
  • the power converter controls the output voltage of the power converter based on the maximum preset current amplitude in the preset current amplitude range, thereby providing voltage and frequency support to the external grid, and realizing the voltage source fault ride-through support characteristic of the power converter.
  • the power converter obtains a first reference output current value based on the voltage drop value of the microgrid bus when a power grid fault occurs, obtains a first reference output modulation voltage value based on the first reference output current value and the first reference angular frequency value, and controls the output voltage of the power converter based on the first reference output modulation voltage value so that the power converter is in a first current source control mode, thereby enabling the power converter to provide a certain voltage support for the external power grid based on the voltage drop value when a power grid fault occurs, thereby realizing the current source fault ride-through support characteristics of the power converter.
  • the power converter obtains a second reference output current value based on the maximum preset current amplitude and the equivalent impedance angle of the external power grid, and obtains a second reference output modulation voltage value based on the second reference output current value and the second reference angular frequency value; the output voltage of the power converter is controlled based on the second reference output modulation voltage value, so that the power converter is in a first voltage source control mode.
  • the power converter switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode, which can reduce the risk of instability of the microgrid system caused by the power converter not switching to the voltage source control mode before the grid-connected switch is disconnected, thereby improving the stability of the power converter.
  • the initial reference output current value and the initial reference angular frequency value of the power converter in the first voltage source control mode are respectively the first reference output current value and the first reference angular frequency value of the power converter in the first current source control mode at the switching moment, which can reduce the fluctuation degree of current and voltage during mode switching and improve the current and voltage.
  • the smoothness of the voltage during mode switching is improved, thereby improving the stability of the power converter during mode switching.
  • the power converter is also in a second current source control mode before a grid failure occurs, wherein in the second current source control mode, the power converter controls the output voltage of the power converter based on a reference output active current value and a reference output reactive current value. It can be understood that before the grid failure, the microgrid system is in a grid-connected mode, and the power converters are all in the second current source control mode, that is, a normal control mode under the current source control mode, which is conducive to improving the stability of the power converter.
  • the power converter determines the reference output active current value and the reference output reactive current value as a third reference output current value, and obtains a third reference output modulation voltage value based on the third reference output current value and the third reference angular frequency value; and controls the output voltage of the power converter based on the third reference output modulation voltage value so that the power converter is in a second current source control mode.
  • the power converter further obtains a reference output active current value based on the reference output active power value and the actual output active power value of the power converter. It can be understood that the reference output active current value is obtained in a simple manner, which is conducive to improving the working efficiency of the power converter.
  • the power converter includes a direct current (DC)/direct current (DC) circuit, a direct current (DC) bus, and a direct current (DC)/alternating current (AC) circuit, and the output end of the DC/DC circuit is connected to the input end of the DC/AC circuit through the DC bus.
  • the power converter also obtains a reference output active current value based on a reference bus voltage and an actual bus voltage of the DC bus. It can be understood that the reference output active current value can also be obtained based on the bus voltage of the DC bus, and the reference output active current value can be obtained in various ways with high flexibility.
  • the power converter further obtains a reference output reactive current value based on the reference output reactive power value and the actual output reactive power value of the power converter. It can be understood that the reference output reactive current value is obtained in a simple manner, which is conducive to improving the working efficiency of the power converter.
  • the power converter further obtains a reference output reactive current value based on a reference output voltage and an actual output voltage of the power converter. It is understandable that the reference output reactive current value can also be obtained based on the output voltage of the power converter, and the reference output reactive current value can be obtained in various ways with high flexibility.
  • the eleventh possible implementation after the power converter is in the first voltage source control mode, when the power grid returns to normal, it switches from the first voltage source control mode to the second voltage source control mode, wherein in the second voltage source control mode, the power converter controls the output voltage of the power converter based on the reference voltage amplitude and the reference frequency value. Furthermore, after the power grid returns to normal, the power converter can actively provide a preset voltage frequency support and a preset voltage amplitude support for the external power grid.
  • the power converter obtains a fourth reference output modulation voltage value based on the reference voltage amplitude and the reference frequency value, and controls the output voltage of the power converter based on the fourth reference output modulation voltage value so that the power converter is in a second voltage source control mode.
  • the power converter determines that a power grid fault occurs when its output voltage is less than a voltage threshold or its output current is greater than a current threshold. It is understandable that the power converter can determine whether the power grid is faulty by its own output voltage or output current. This method does not require communication with the microgrid controller, and can effectively improve the efficiency of the power converter in fault detection of the power grid.
  • the power converter determines that a power grid fault occurs when the voltage of the microgrid bus is less than a voltage threshold. It is understandable that the power converter can also determine whether the power grid is faulty by the voltage of the microgrid bus, and the power grid fault judgment method is diverse and flexible.
  • the present application provides a control method for a power converter, wherein the input and output ends of the power converter are respectively connected to a DC power supply and a microgrid bus, and the microgrid bus is connected to an external power grid via a grid-connected switch.
  • the method comprises: when a power converter detects a grid fault, the power converter is in a first current source control mode; after the duration of the grid fault reaches a first duration, the power converter switches from the first current source control mode to the first voltage source control mode, wherein the power grid includes an external power grid or a microgrid system where the microgrid bus is located, the first current source control mode is a current source fault ride-through control mode, the first voltage source control mode is a voltage source fault ride-through control mode, the first duration is less than the second duration, and the second duration is the time interval between the moment when the grid fault occurs and the moment when the grid-connected switch is disconnected.
  • the power converter in the first current source control mode, controls the output voltage of the power converter based on the voltage drop value of the microgrid bus when a grid failure occurs. In the first voltage source control mode, the power converter controls the output voltage of the power converter based on the maximum preset current amplitude in the preset current amplitude range.
  • the power converter obtains a first reference output current value based on the voltage drop value of the microgrid bus when a power grid fault occurs, obtains a first reference output modulation voltage value based on the first reference output current value and the first reference angular frequency value, and controls the output voltage of the power converter based on the first reference output modulation voltage value so that the power converter is in a first current source control mode.
  • the power converter obtains a second reference output current value based on the maximum preset current amplitude and the equivalent impedance angle of the external power grid, and obtains a second reference output modulation voltage value based on the second reference output current value and the second reference angular frequency value; and controls the output voltage of the power converter based on the second reference output modulation voltage value so that the power converter is in a first voltage source control mode.
  • the initial reference output current value and the initial reference angular frequency value of the power converter in the first voltage source control mode are respectively the first reference output current value and the first reference angular frequency value of the power converter in the first current source control mode at the switching moment.
  • the power converter in a fifth possible implementation manner, is also in a second current source control mode before a grid fault occurs, wherein in the second current source control mode the power converter controls the output voltage of the power converter based on a reference output active current value and a reference output reactive current value.
  • the power converter determines the reference output active current value and the reference output reactive current value as a third reference output current value, and obtains a third reference output modulation voltage value based on the third reference output current value and the third reference angular frequency value; and controls the output voltage of the power converter based on the third reference output modulation voltage value so that the power converter is in a second current source control mode.
  • the power converter also obtains a reference output active current value based on the reference output active power value and the actual output active power value of the power converter.
  • the power converter includes a direct current (DC)/direct current (DC) circuit, a direct current (DC) bus, and a direct current (DC)/alternating current (AC) circuit, and the output end of the DC/DC circuit is connected to the input end of the DC/AC circuit through the DC bus.
  • the power converter also obtains a reference output active current value based on a reference bus voltage and an actual bus voltage of the DC bus.
  • the power converter also obtains a reference output reactive current value based on the reference output reactive power value and the actual output reactive power value of the power converter.
  • the power converter in combination with the fifth possible implementation of the third aspect or the sixth possible implementation of the third aspect, in a tenth possible implementation, the power converter also obtains a reference output reactive current value based on the reference output voltage and actual output voltage of the power converter.
  • the power converter is also in the first voltage source control mode, and when the power grid returns to normal, the power converter switches from the first voltage source control mode to the second voltage source control mode, wherein in the second voltage source control mode the power converter controls the output voltage of the power converter based on a reference voltage amplitude and a reference frequency value.
  • the power converter obtains a fourth reference output modulation voltage value based on a reference voltage amplitude and a reference frequency value, and controls the output voltage of the power converter based on the fourth reference output modulation voltage value so that the power converter is in a second voltage source control mode.
  • the power converter determines that a power grid fault has occurred when its output voltage is less than a voltage threshold or its output current is greater than a current threshold.
  • the power converter determines that a grid fault occurs when a voltage of a microgrid bus is less than a voltage threshold.
  • FIG1 is a schematic diagram of an application scenario of a microgrid system provided by the present application.
  • FIG2a is a schematic diagram of a structure of a microgrid system provided by the present application.
  • FIG2b is another structural schematic diagram of the microgrid system provided by the present application.
  • FIG3 is a schematic diagram of the control timing of the microgrid system provided by the present application.
  • FIG5 is another simulation schematic diagram of the microgrid system provided by the present application.
  • FIG6 is another simulation schematic diagram of a microgrid system provided by the present application.
  • FIG7 is a schematic diagram of a flow chart of a control method for a power converter provided by the present application.
  • FIG8 is another schematic flow chart of a control method for a power converter provided by the present application.
  • FIG9 is a flow chart of a control method for a microgrid controller provided in the present application.
  • FIG. 1 is a schematic diagram of an application scenario of a microgrid system provided by the present application.
  • the microgrid system provided by the present application may be the microgrid system shown in FIG. 1
  • the power converter provided by the present application may be the energy storage converter or photovoltaic inverter shown in FIG. 1 .
  • the microgrid system includes energy storage battery clusters a1, ..., energy storage battery cluster an, photovoltaic strings b1, ..., photovoltaic strings bm, energy storage converters 11, ..., energy storage converters 1n, photovoltaic inverters 21, ..., photovoltaic inverters 2m, microgrid bus BUS, grid-connected switches and household appliances.
  • the input end of the energy storage converter 11 is connected to the energy storage battery cluster a1, ..., the input end of the energy storage converter 1n is connected to the energy storage battery cluster an, and the output end of the energy storage converter 11, ..., the output end of the energy storage converter 1n are all connected to the microgrid bus BUS.
  • the input end of the photovoltaic inverter 21 is connected to the photovoltaic string b1, ..., the input end of the photovoltaic inverter 2m is connected to the photovoltaic string bm, and the output end of the photovoltaic inverter 21, ..., and the output end of the photovoltaic inverter 2m are all connected to the microgrid bus BUS.
  • Household appliances are connected to the microgrid bus BUS.
  • the microgrid bus BUS is connected to the external power grid through a grid-connected switch.
  • each of the last n energy storage inverters inverts the direct current provided by the energy storage battery cluster connected to its input end to obtain alternating current, and outputs the inverted alternating current to the microgrid bus BUS.
  • the above-mentioned m photovoltaic inverters invert the direct current provided by the photovoltaic strings connected to their input ends to obtain alternating current, and output the inverted alternating current to the microgrid bus BUS.
  • each energy storage converter, each photovoltaic inverter and the microgrid controller detects in real time whether a fault occurs in the power grid, wherein the power grid includes an external power grid or a microgrid system.
  • the power grid includes an external power grid or a microgrid system.
  • each energy storage converter and each photovoltaic inverter switches from the first current source control mode to the first voltage source control mode, wherein the first current source control mode is a current source fault ride-through control mode, the first voltage source control mode is a voltage source fault ride-through control mode, the first duration is less than the second duration, and the second duration is the time interval between the moment when the power grid fault occurs and the moment when the grid-connected switch is disconnected.
  • each energy storage converter and each photovoltaic inverter in the microgrid system detects a grid fault, they control themselves to be in the current source fault ride-through control mode, and control themselves to switch to the voltage source fault ride-through control mode before the grid-connected switch is disconnected, so that the microgrid system provides voltage support for the external grid when the grid fails, and completes the on-grid and off-grid mode switching before the grid-connected switch is disconnected, so that the microgrid system takes into account both the fault ride-through support function and the on-grid and off-grid switching function.
  • the above is only an example of the application scenarios of the microgrid system provided by this application, not an exhaustive list, and this application does not limit the application scenarios.
  • FIG. 2a is a schematic diagram of a structure of a microgrid system provided in the present application.
  • the microgrid system 1 includes a DC power supply 101, ..., a DC power supply 10n, a power converter 111, ..., a power converter 11n, a microgrid bus BUS and a grid-connected switch S1.
  • the input end of the power converter 111 is connected to the DC power supply 101, ..., the input end of the power converter 11n is connected to the DC power supply 10n, the output end of the power converter 111, ..., the output end of the power converter 11n is connected in parallel to the microgrid bus BUS, and the microgrid bus BUS is connected to the external power grid through the grid-connected switch S1.
  • the power converter in the present application can be an energy storage converter, a photovoltaic inverter or an electromechanical converter, etc.
  • each power converter in the power converters 111, ..., 11n starts to detect whether a fault occurs in the power grid, wherein the power grid includes the microgrid system 1 or the external power grid.
  • each power converter In the case of detecting a fault in the power grid, each power converter is in a first current source control mode, and after the duration of the power grid fault reaches a first duration, it switches from the first current source control mode to the first voltage source control mode, wherein the first current source control mode is a current source fault ride-through control mode, the first voltage source control mode is a voltage source fault ride-through control mode, the first duration is less than the second duration, and the second duration is the time interval between the moment when the power grid fault occurs and the moment when the grid-connected switch S1 is disconnected.
  • each power converter in the microgrid system 1 when each power converter in the microgrid system 1 detects a grid fault, it controls itself to be in the current source fault ride-through control mode, and controls itself to switch to the voltage source fault ride-through control mode before the grid-connected switch is disconnected, so that the microgrid system 1 provides voltage support for the external grid when the grid fails, and completes the on-grid and off-grid mode switching before the grid-connected switch S1 is disconnected.
  • the microgrid system 1 takes into account both the fault ride-through support function and the on-grid and off-grid switching function.
  • FIG. 2b is another structural schematic diagram of the microgrid system provided by the present application.
  • the microgrid system 1 shown in FIG. 2b also includes a microgrid controller 12, a local load 131 and a local load 132.
  • the local load 131 and the local load 132 are both connected to the microgrid bus BUS.
  • the microgrid controller 12 and the power converter 111, ..., the power converter 11n, the grid-connected switch S1, the local load 131 and the local load 132 are all provided with a communication line represented by a dotted line in FIG. 2b to establish a communication connection.
  • the local load 131 and the local load 132 are respectively a general load and a critical load, and the general load is not always in a grid-connected state.
  • the microgrid controller 12 can disconnect the general load from the microgrid system 1 to ensure the normal power supply to the critical load.
  • each power converter starts to detect whether the power grid is faulty.
  • each power converter is in a current source fault ride-through control mode.
  • the duration of the power grid fault reaches a first duration, each power converter switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • the microgrid controller 12 starts to detect whether the power grid is faulty.
  • the microgrid controller 12 controls the grid-connected switch S1 to disconnect after a second duration. Among them, the second duration is greater than the first duration.
  • each power converter controls its own output voltage based on the voltage drop value of the microgrid bus BUS when the power grid fails; in the voltage source fault ride-through control mode, each power converter controls its own output voltage based on the maximum preset current amplitude in the preset current amplitude range.
  • the grid-connected switch S1 is in a closed state, and the microgrid system 1 is connected to the external grid for operation.
  • each power converter starts to obtain its own output voltage or output current to detect whether the grid fails.
  • the microgrid controller 12 starts to obtain the voltage of the microgrid bus BUS to detect whether the grid fails. Since the working principles of each power converter in the microgrid system 1 are the same, for the sake of convenience, the power converter 111 is used as an example for introduction.
  • the power converter 111 determines that the power grid has failed.
  • the power converter 111 determines that the power grid has failed when the voltage of the microgrid bus BUS is less than the voltage threshold.
  • the power converter 111 When it is determined that the power grid has failed, the power converter 111 obtains a first reference output current value based on the voltage drop value of the microgrid bus when the power grid fails, and obtains a first reference output modulation voltage value based on the first reference output current value and the first reference angular frequency value, thereby controlling the output voltage of the power converter based on the first reference output modulation voltage value, so that the power converter 111 is in a current source fault ride-through control mode, that is, a fault ride-through control mode under the current source control mode.
  • the power converter 111 obtains the first reference output current value I ref1 corresponding to the voltage drop value by querying the preset corresponding table between the voltage drop value and the first reference output current according to the voltage drop value of the microgrid bus BUS when the power grid fails (i.e., the difference between the voltage threshold and the voltage of the microgrid bus BUS when the power grid fails ).
  • the first reference output current value I ref1 includes the first reference output active current value I dref1 and the first reference output reactive current value I qref1 .
  • the larger the voltage drop value of the microgrid bus BUS is, the larger the first reference output current value I ref1 is.
  • the power converter 111 inputs the first reference output active current value I dref1 , the first reference output reactive current value I qref1 , the actual output active current value I d and the actual output reactive current value I q into the current control loop to obtain the first reference q-axis voltage value V qref1 and the first reference d-axis voltage value V dref1 .
  • the current control loop may be any one of a PI controller, a PD controller and a PID controller.
  • the power converter 111 When it is determined that a power grid fault occurs, the power converter 111 further transforms the collected three-phase output voltages Va , Vb , Vc of the power converter 111 from the three-phase stationary coordinate system to the two-phase rotating coordinate system, i.e., performs abc/dq coordinate transformation on the collected three-phase output voltages Va , Vb , Vc of the power converter 111 to obtain a q-axis voltage component Vq , thereby inputting the q-axis voltage component Vq into a phase-locked control loop to obtain a first reference angular frequency value ⁇ 1 .
  • the power converter 111 generates a first reference voltage phase ⁇ 1 based on the first reference angular frequency value ⁇ 1 , and performs dq/abc coordinate transformation based on the first reference voltage phase ⁇ 1 , the first reference q-axis voltage value V qref1 and the first reference d-axis voltage value V dref1 to obtain a first reference output modulation voltage value, and compares the first reference output modulation voltage value with the triangular wave to obtain a first pulse width modulation wave, thereby outputting the first pulse width modulation wave to a switch tube of a power conversion circuit (such as a DC/AC circuit) in the power converter 111 to control the output voltage of the power converter 111, thereby placing the power converter 111 in a current source fault ride-through control mode, thereby enabling the power converter 111 to control its own output reactive current and active current based on the voltage drop value of the microgrid bus when a power grid fault occurs, so as to provide voltage support for the external power grid
  • the power converter 111 switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • the power converter 111 determines a second reference output current value based on the equivalent impedance angle of the external power grid and the maximum preset current amplitude in the preset current amplitude range, and obtains a second reference output modulation voltage value based on the second reference output current value and the second reference angular frequency value, thereby controlling the output voltage of the power converter 111 based on the second reference output modulation voltage value, so that the power converter 111 is in an electrical Voltage source fault ride-through control mode, that is, the fault ride-through control mode under the voltage source control mode.
  • the power converter 111 inputs the second reference output active current value I dref2 , the second reference output reactive current value I qref2 , the actual output active current value I d and the actual output reactive current value I q into the current control loop to obtain the second reference q-axis voltage value V qref2 and the second reference d-axis voltage value V dref2 .
  • the power converter 111 After the duration of the grid fault reaches the first duration, the power converter 111 also obtains a second reference angular frequency value ⁇ 2 based on the reference output active power Pref and the actual output active power P, and generates a second reference voltage phase ⁇ 2 based on the second reference angular frequency value ⁇ 2 .
  • the power converter 111 performs dq/abc coordinate transformation based on the second reference voltage phase ⁇ 2 , the second reference q-axis voltage value V qref2 and the second reference d-axis voltage value V dref2 to obtain a second reference output modulation voltage value, and compares the second reference output modulation voltage value with the triangular wave to obtain a second pulse width modulation wave, thereby outputting the second pulse width modulation wave to the switch tube of the power conversion circuit in the power converter 111 to control the output voltage of the power converter 111, so that the power converter 111 switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • the power converter 111 when the power converter 111 is in the voltage source fault ride-through control mode, it completes the active current and reactive current distribution based on the maximum preset current amplitude, provides voltage and frequency support for the external power grid, and realizes the voltage source fault ride-through support characteristics.
  • the microgrid controller 12 controls the grid-connected switch S1 to disconnect.
  • each power converter in the microgrid system 1 completes the switching from the fault ride-through control mode under the current source control mode to the fault ride-through control mode under the voltage source control mode, so that the microgrid system 1 can take into account both the grid-connected and off-grid switching functions and the fault ride-through support functions during the fault ride-through period (i.e., the time period from the start of the grid fault to the disconnection of the grid-connected switch S1), and significantly reduce the reliance on communication delay performance, thereby avoiding the power converter from injecting disturbance signals into the external grid to detect the off-grid state, thereby solving the problem of instability of the microgrid system 1 caused by the large delay in power converter mode switching (i.e., some power converters did not switch to the voltage source control mode before the grid-connected switch S2 was disconnected), thereby improving the stability and market competitiveness of the microgrid system 1.
  • the power converter 111 inputs the initial reference output active current value I dref20 , the initial reference output reactive current value I qref20 , the actual output active current value I d and the actual output reactive current value I q into the current control loop to obtain the second reference q-axis voltage value V qref2 and the second reference d-axis voltage value V dref2 .
  • the power converter 111 generates a second reference voltage phase ⁇ 2 based on the initial reference angular frequency value.
  • the power converter 111 performs dq/abc coordinate transformation based on the second reference voltage phase ⁇ 2 , the second reference q-axis voltage value V qref2 and the second reference d-axis voltage value V dref2 to obtain a second reference output modulation voltage value, and compares the second reference output modulation voltage value with the triangular wave to obtain a second pulse width modulation wave, thereby outputting the second pulse width modulation wave to the switch tube of the power conversion circuit in the power converter 111 to control the output voltage of the power converter 111, thereby placing the power converter 111 in a voltage source fault ride-through control mode, and completing the switching from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • the power converter 111 may continue to control its own output voltage based on the second reference output voltage determined by the initial reference output current value I ref20 and the initial reference angular frequency value ⁇ 20 , so that the power converter 111 remains in the voltage source fault ride-through control mode; or, after the power converter 111 switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode based on the initial reference output current value I ref20 and the initial reference angular frequency value ⁇ 20 , the power converter 111 may also control the output voltage of the power converter 111 based on the second reference angular frequency value and the second reference output current value determined by the maximum preset current amplitude and the equivalent impedance angle of the external power grid, so that the power converter 111 remains in the voltage source fault ride-through control mode
  • the power converter 111 inputs the third reference output active current value Idref3 , the third reference output reactive current value Iqref3 , the actual output active current value Id and the actual output reactive current value Iq into the current control loop to obtain the third reference q-axis voltage value Vqref3 and the third reference d-axis voltage value Vdref3 .
  • the power converter 111 also performs abc/dq coordinate transformation on the collected three-phase output voltages Va , Vb , and Vc of the power converter 111 to obtain a q-axis voltage component Vq , and then inputs the q-axis voltage component Vq into the phase-locked control loop to obtain a third reference angular frequency value ⁇ 3 .
  • the power converter 111 when the power grid returns to normal, it switches from the voltage source fault ride-through control mode to the second voltage source control mode (normal control mode under the voltage source control mode), wherein in the second voltage source control mode, the power converter 111 controls its output voltage based on the reference voltage amplitude and the reference frequency value. Conversely, after the power converter 111 is in the voltage source fault ride-through control mode, if the power grid still fails, the power converter 111 remains in the voltage source fault ride-through control mode.
  • the second voltage source controller can be a virtual synchronous generator (VSG) control mode.
  • the power converter 111 obtains a fourth reference output modulation voltage value according to the reference voltage amplitude and the reference frequency value, and controls its own output voltage according to the fourth reference output modulation voltage value, so that the power converter 111 switches to the second voltage source control mode.
  • the power converter 111 After switching to the second voltage source control mode, the power converter 111 sends its own control mode to the microgrid controller 12.
  • the microgrid controller 12 receives the control modes sent by each power converter and detects the switching state of the grid-connected switch S1.
  • the microgrid controller 12 when the control mode of the power converter 111 is the second voltage source control mode and the grid-connected switch S1 is in the disconnected state, the microgrid controller 12 sends a synchronization control instruction to the power converter 111.
  • the power converter 111 controls the amplitude difference between its own output voltage amplitude and the voltage amplitude of the external power grid to be less than the amplitude difference threshold value based on the received synchronization control instruction, and its own The phase difference between the output voltage phase and the voltage phase of the external power grid is less than the phase difference threshold, so that the output voltage of the power converter 111 is synchronized with the voltage of the external power grid.
  • the microgrid controller 12 controls the grid-connected switch S1 to close when the amplitude difference between the voltage amplitude of the first terminal (i.e., the voltage amplitude at the first terminal a1) and the voltage amplitude of the second terminal (i.e., the voltage amplitude at the second terminal a2) of the grid-connected switch S1 is less than the amplitude difference threshold, and the phase difference between the voltage phase of the first terminal (i.e., the voltage phase at the first terminal a1) and the voltage phase of the second terminal (i.e., the voltage phase at the second terminal a2) of the grid-connected switch S1 is less than the phase difference threshold.
  • the microgrid controller 12 when the control mode of the power converter 111 is the second voltage source control mode and the grid-connected switch S1 is in a closed state, the microgrid controller 12 sends a mode switching instruction to the power converter 111 after a third time period. The power converter 111 switches from the second voltage source control mode to the second current source control mode based on the received mode switching instruction.
  • the microgrid controller 12 adjusts the control mode of each power converter based on the switching state of the grid-connected switch S1 and the control mode of each power converter, so that each power converter operates in the current source control mode when the microgrid system 1 is in the grid-connected mode, and operates in the voltage source control mode when the microgrid system 1 is in the off-grid mode, thereby improving the stability of the microgrid system 1.
  • FIG. 3 is a control timing diagram of the microgrid system provided by the present application.
  • the grid voltage V mag of the external grid does not drop, that is, the external grid does not fail.
  • the grid-connected switch S1 is in a closed state, and the power converter 111 is in the second current source control mode CS2.
  • the grid voltage V mag of the external grid has not recovered, the external grid is still faulty, and the power converter 111 is in the first current source control mode CS1.
  • the grid-connected switch S1 is still in the closed state.
  • the external grid still fails, and the power converter 111 switches from the first current source control mode CS1 to the first voltage source control mode VS1.
  • the grid-connected switch S1 is still in the closed state.
  • the external power grid is still faulty, the power converter 111 is in the first voltage source control mode VS1 , and the grid-connected switch S1 is still in the closed state.
  • the microgrid controller 12 controls the grid-connected switch S1 to be disconnected, the voltage of the microgrid system 1 is restored, and the power converter 111 is still in the first voltage source control mode VS1 .
  • the external power grid is still faulty, the power converter 111 is still in the first voltage source control mode VS1, and the grid-connected switch S1 is in the disconnected state.
  • the grid voltage V mag of the external grid is restored, the external grid returns to normal, and the power converter 111 switches from the first voltage source control mode VS1 to the second voltage source control mode VS2.
  • the grid-connected switch S1 is in the disconnected state.
  • the power converter 1111 is in the second voltage source control mode VS2, and controls its own output voltage based on the synchronous control instruction sent by the microgrid controller 12.
  • the grid-connected switch S1 is in the disconnected state.
  • the external power grid is normal, and the power converter 111 is in the second voltage source control mode VS2 .
  • the microgrid controller 12 controls the grid-connected switch S1 to close, and determines the switching state of the grid-connected switch S1 and the control mode of the power converter 111 .
  • the external power grid is normal, the power converter 111 is still in the second voltage source control mode VS2, and the grid-connected switch S1 is in a closed state.
  • the microgrid system 1 adopts a "bottom-up main, top-down auxiliary" grid-connected and off-grid switching control mode, that is, during a grid fault, each power converter in the microgrid system 1 first determines whether the grid is faulty and then performs a control mode switch.
  • the microgrid controller 12 reissues a grid-connected and off-grid switching control mode of a mode control instruction to each power converter based on the switching state of the grid-connected switch S1 and the control mode of each power converter, so that each power converter takes into account the grid-connected and off-grid switching function and the fault-crossing support function during the fault ride-through period, and significantly reduces the reliance on communication delay performance, avoiding the power converter from injecting a disturbance signal into the external grid to detect the off-grid state, thereby solving the problem of instability of the microgrid system 1 caused by a large power converter switching delay, thereby improving the stability and market competitiveness of the microgrid system 1.
  • the grid-connected and off-grid switching control mode provided in the embodiment of the present application does not require high communication delays between the microgrid controller 12 and each power converter, and even if the communication delay is large, it will not cause instability of the microgrid system 1, and has good delay robustness.
  • the closing or shutting down of the grid-connected switch S1 may be controlled by the microgrid controller 12. It can also be directly controlled by the controller included in the grid-connected switch S1.
  • the control logic of the controller of the grid-connected switch S1 to control the grid-connected switch S1 to open or close is consistent with the control logic of the microgrid controller 12 to control the grid-connected switch S1 to open or close, which will not be described in detail here.
  • the microgrid system provided by the present application is verified to have both the on-grid and off-grid switching function and the fault ride-through support function during fault ride-through.
  • Figure 4 is a simulation schematic diagram of the microgrid system provided by the present application.
  • the upper and lower curves in Figure 4 (a) respectively represent the three-phase output voltage Vabc and the three-phase output current Iabc of each energy storage converter
  • Figure 4 (b) is an enlarged schematic diagram of the curve corresponding to the time period 7.46s-7.54s in Figure 4 (a).
  • each energy storage converter when the operation time does not reach 7s, each energy storage converter is connected to the grid in the normal control mode under the current source control mode.
  • the operation time is 7s, a three-phase grounding fault occurs in the external power grid.
  • each energy storage converter performs fault ride-through in the current source mode, that is, each energy storage converter is in the current source fault ride-through control mode.
  • the operation time is 7.5s, each energy storage converter switches from the current source control mode to the voltage source control mode. Specifically, each energy storage converter switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • each energy storage converter When the operation time is between 7.5s and 7.8s, each energy storage converter performs fault ride-through in the voltage source mode, that is, each energy storage converter is in the voltage source fault ride-through control mode.
  • the operation time is 7.8s, the grid-connected switch is disconnected, the microgrid system and the external power grid are restored, and each energy storage converter operates off-grid.
  • the operating time is greater than 7.8s, each energy storage converter operates independently with load in the normal control mode under the voltage source control mode.
  • each energy storage inverter in the microgrid system can switch from the first current source control mode to the first voltage source control mode during fault ride-through when a fault occurs in the external power grid, taking into account both the fault ride-through support function and the grid-connected and off-grid switching function.
  • Figure 5 is another simulation schematic diagram of the microgrid system provided by the present application.
  • the upper and lower curves in Figure 5 (a) respectively represent the three-phase output voltage Vabc and the three-phase output current Iabc of each energy storage converter
  • Figure 5 (b) is an enlarged schematic diagram of the curve corresponding to the time period 7.46s-7.54s in Figure 5 (a).
  • each energy storage converter when the operation time does not reach 7s, each energy storage converter is connected to the grid in the normal control mode under the current source control mode.
  • the operation time is 7s, a three-phase grounding fault occurs at a certain point inside the microgrid system.
  • each energy storage converter performs fault ride-through in the current source mode, that is, each energy storage converter is in the current source fault ride-through control mode.
  • the operation time is 7.5s, each energy storage converter switches from the current source control mode to the voltage source control mode. Specifically, each energy storage converter switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • each energy storage converter When the operation time is between 7.5s and 7.8s, each energy storage converter performs fault ride-through in the voltage source mode, that is, each energy storage converter is in the voltage source fault ride-through control mode.
  • the operation time is 7.8s, the grid-connected switch is disconnected, and each energy storage converter operates off-grid.
  • the operation time is between 7.8s and 8s, the two energy storage converters continue to perform fault ride-through in voltage source mode.
  • the operation time When the operation time is 8s, the fault is removed and the voltage of the microgrid system is restored.
  • each energy storage converter When the operation time is greater than 8s, each energy storage converter operates independently with load in normal control mode under voltage source control mode.
  • each energy storage inverter in the microgrid system provided by the present application can still switch from the first current source control mode to the first voltage source control mode during the fault ride-through period when a fault occurs in the microgrid system, taking into account both the fault ride-through support function and the grid-connected and off-grid switching function.
  • FIG. 6 is another simulation schematic diagram of the microgrid system provided by the present application.
  • the two curves in the upper left corner of Figure 6 respectively represent the three-phase output voltage Vabc and the three-phase output current Iabc of the energy storage converter PCS1, and the two curves in the lower left corner are respectively enlarged schematic diagrams of the curves corresponding to the time period 7.45s-7.6s of the two curves in the upper left corner of Figure 6.
  • the two curves in the upper right corner of Figure 6 respectively represent the three-phase output voltage Vabc and the three-phase output current Iabc of the energy storage converter PCS2, and the two curves in the lower right corner are respectively enlarged schematic diagrams of the curves corresponding to the time period 7.45s-7.6s of the two curves in the upper right corner of Figure 6.
  • each energy storage converter when the operation time does not reach 7s, each energy storage converter is connected to the grid in the normal control mode under the current source control mode.
  • the operation time is 7s, a three-phase grounding fault occurs in the external power grid.
  • each energy storage converter performs fault ride-through in the current source mode, that is, each energy storage converter is in the current source fault ride-through control mode.
  • the energy storage converter PCS1 switches from the current source control mode to the voltage source control mode. Specifically, each energy storage converter switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • the energy storage converter PCS1 When the operation time is between 7.5s and 7.55s, the energy storage converter PCS1 performs fault ride-through in the voltage source mode, and the energy storage converter PCS2 performs fault ride-through in the current source mode.
  • the operation time is 7.55s, the energy storage converter PCS2 switches from the current source fault ride-through control mode to the voltage source fault ride-through control mode.
  • the operation time is between 7.55s and 7.8s
  • the energy storage converters PCS1 and PCS2 both perform fault ride-through in voltage source mode.
  • the operation time is 7.8s, the grid-connected switch is disconnected, the fault is removed, and each energy storage converter operates off-grid.
  • each energy storage converter When the operation time is greater than 7.8s, each energy storage converter operates independently with load in the normal operation mode under the voltage source control mode.
  • FIG. 7, is a flow chart of a control method for a power converter provided by the present application.
  • the control method of the power converter is applicable to each power converter in the microgrid system 1 shown in Figures 2a and 2b.
  • the control method of the power converter may include the steps of:
  • the power grid includes an external power grid or a microgrid system
  • the first current source control mode is a current source fault ride-through control mode.
  • the power converter when the output voltage of the power converter is less than a voltage threshold or the output current of the power converter is greater than a current threshold, the power converter obtains a first reference output current value according to the voltage drop value of the microgrid bus during a power grid failure, and obtains a first reference output modulation voltage value according to the first reference output current value and the first reference angular frequency value, thereby controlling its own output voltage based on the first reference output modulation voltage value to put the power converter in a first current source control mode.
  • the power converter controls the output voltage of the power converter based on a maximum preset current amplitude in a preset current amplitude range.
  • the power converter after the duration of the grid fault reaches a first duration, the power converter will switch from the first current source control mode to the first voltage source control mode.
  • the first reference output current value and the first reference angular frequency value of the power converter in the first current source control mode at the switching moment are respectively determined as the initial reference output current value and the initial reference angular frequency value of the power converter in the first voltage source control mode, and the second reference output modulation voltage value is obtained based on the initial reference output current value and the initial reference angular frequency value, so as to control the output voltage of the power converter based on the second reference output modulation voltage value, so that the power converter switches from the first current source control mode to the first voltage source control mode.
  • the power converter in the event of a grid fault, controls itself to be in a current source fault ride-through control mode upon detecting a grid fault, and controls itself to switch to a voltage source fault ride-through control mode before the grid-connected switch is disconnected.
  • This allows the power converter to provide voltage support for the external grid when a grid fault occurs, and completes the on-grid and off-grid mode switching before the grid-connected switch is disconnected, thereby allowing the power converter to take into account both the fault ride-through support function and the on-grid and off-grid switching function.
  • the microgrid system is in a grid-connected operation mode, and the power converter is in a second current source control mode.
  • the power converter controls the output voltage of the power converter based on the reference output active current value and the reference output reactive current value.
  • the power converter determines the reference output active current value and the reference output reactive current value as the third reference output current value, and obtains the third reference output modulation voltage value based on the third reference output current value and the third reference angular frequency value; the output voltage of the power converter is controlled based on the third reference output modulation voltage value so that the power converter is in the second current source control mode.
  • S202 The power converter determines whether a power grid fault occurs.
  • the power converter determines that the power grid is faulty when its output voltage is less than a voltage threshold or its output current is greater than a current threshold.
  • the power converter determines that the power grid is faulty when the voltage of the microgrid bus is less than a voltage threshold.
  • the power grid includes an external power grid or a microgrid system.
  • the power converter is in a first current source control mode.
  • the power converter obtains a first reference output current value according to a voltage drop value of a microgrid bus when a power grid fails, and obtains a first reference output modulation voltage value according to the first reference output current value and a first reference angular frequency value, thereby controlling the power supply voltage based on the first reference output modulation voltage value.
  • the output voltage of the power converter is controlled so that the power converter is in a first current source control mode.
  • S204 The power converter determines whether the power grid has returned to normal.
  • the power converter determines that the power grid has returned to normal when its output voltage is greater than or equal to a voltage threshold.
  • the power converter determines that the power grid has returned to normal when its output current is less than or equal to a current threshold.
  • the power converter determines that the power grid has returned to normal when the voltage of the microgrid bus is greater than or equal to a voltage threshold.
  • step S201 the power converter executes step S201 if it is determined that the power grid has returned to normal, and executes step S205 otherwise.
  • S205 The power converter determines whether the duration of the grid fault reaches a first duration.
  • the first time length is shorter than the second time length, and the second time length is the time interval between the moment when the grid fault occurs and the moment when the grid-connected switch is disconnected.
  • the power converter executes step S206 , otherwise, executes step S203 .
  • the power converter switches from the first current source control mode to the first voltage source control mode.
  • the power converter controls the output voltage of the power converter based on the maximum preset current amplitude in the preset current amplitude range.
  • the power converter determines a second reference output current value based on the maximum preset current amplitude and the equivalent impedance angle of the external power grid, and obtains a second reference output modulation voltage value based on the second reference output current value and the second reference angular frequency value; the output voltage of the power converter is controlled based on the second reference output modulation voltage value so that the power converter is in a first voltage source control mode, thereby completing the switching from the first current source control mode to the first voltage source control mode.
  • the first reference output current value and the first reference angular frequency value of the power converter in the first current source control mode are respectively determined as the initial reference output current value and the initial reference angular frequency value of the power converter in the first voltage source control mode, and a second reference output modulation voltage value is obtained based on the initial reference output current value and the initial reference angular frequency value, thereby controlling the output voltage of the power converter based on the second reference output modulation voltage value, so that the power converter switches from the first current source control mode to the first voltage source control mode.
  • the power converter determines whether the power grid returns to normal.
  • step S208 the power converter executes step S206 .
  • the power converter switches from the first voltage source control mode to the second voltage source control mode, and sends the control mode of the power converter to the microgrid controller.
  • the power converter controls the output voltage of the power converter based on the reference voltage amplitude and the reference frequency value.
  • the power converter obtains a fourth reference output modulation voltage value according to the reference voltage amplitude and the reference frequency value, and controls the output voltage of the power converter according to the fourth reference output modulation voltage value, so that the power converter is in the second voltage source control mode, and the switching from the first voltage source control mode to the second voltage source control mode is completed.
  • the power converter sends its own control mode to the microgrid controller.
  • S209 The power converter determines whether a mode switching instruction is received.
  • step S210 When the power converter receives the mode switching instruction, it executes step S210 , otherwise it executes step S208 .
  • S210 The power converter determines whether the mode switching instruction is a second current source control mode switching instruction.
  • the power converter executes step S212 , otherwise, executes step S211 .
  • the power converter switches from the second voltage source control mode to the second current source control mode.
  • the power converter controls the output voltage of the power converter based on the reference output active current value and the reference output reactive current value.
  • the power converter determines the reference output active current value and the reference output reactive current value as the third reference output current value, and obtains the third reference output modulation voltage value based on the third reference output current value and the third reference angular frequency value; controls the output voltage of the power converter based on the third reference output modulation voltage value, so that the power converter is in the second current source control mode, and completes the switching from the second voltage source control mode to the second current source control mode.
  • the power converter is in the second voltage source control mode.
  • step S212 please refer to the description of step S201, which will not be repeated here.
  • each power converter in the microgrid system completes the switching from the fault ride-through control mode under the current source control mode to the fault ride-through control mode under the voltage source control mode, so that each power converter can take into account the grid-connected and off-grid switching function and the fault ride-through support function during the fault ride-through period, and significantly reduce the communication delay.
  • the performance dependence requirement is to avoid the power converter injecting disturbance signals into the external power grid to detect the off-grid state, thereby solving the instability problem of the microgrid system caused by the large switching delay of the power converter.
  • FIG. 9 is a flow chart of a control method for a microgrid controller provided in the present application.
  • the control method for a microgrid controller provided in an embodiment of the present application is applicable to the microgrid controller 12 shown in Figures 2a and 2b.
  • the control method for a microgrid controller may include the following steps:
  • the microgrid controller controls the grid-connected switch to disconnect after a second period of time.
  • the power grid includes an external power grid or a microgrid system.
  • the microgrid controller controls the grid-connected switch to be disconnected after a second period of time.
  • the microgrid controller detects the switching state of the grid-connected switch and obtains the control mode of each power converter.
  • the microgrid controller detects the switching state of the grid-connected switch, and sends a control mode acquisition instruction to each power converter to acquire the control mode of each power converter.
  • step S304 When the grid-connected switch is disconnected, the microgrid controller executes step S304, otherwise, it executes step S306.
  • the mode switching instruction for switching to the second voltage source control mode is used to control each power converter to switch to the second voltage source control mode.
  • the microgrid controller sends a synchronization control instruction to each power converter.
  • the synchronous control instruction is used to control the amplitude difference between the output voltage amplitude of the power converter and the voltage amplitude of the external power grid to be less than the amplitude difference threshold, and the phase difference between the output voltage phase of the power converter and the voltage phase of the external power grid to be less than the phase difference threshold.
  • the microgrid controller determines whether the control mode of the power converter is the second voltage source control mode.
  • the microgrid controller executes step S307 , otherwise, executes step S302 .
  • the second mode switching instruction for switching to the second current source control mode is used to control the power converter to switch to the second current source control mode.
  • the microgrid controller adjusts the control mode of each power converter based on the switching state of the grid-connected switch and the control mode of each power converter, so that each power converter operates in a current source control mode when the microgrid system is in a grid-connected mode, and operates in a voltage source control mode when the microgrid system is in an off-grid mode, thereby improving the stability of the microgrid system.

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Abstract

本申请提供了一种微电网系统、功率变换器及其控制方法，该微电网系统包括至少一个功率变换器、微电网母线和并网开关，功率变换器的输出端连接微电网母线，微电网母线通过并网开关连接外部电网。功率变换器在检测到电网发生故障的情况下，处于第一电流源控制模式；在电网故障的持续时长达到第一时长后，从第一电流源控制模式切换至第一电压源控制模式。第一电流源控制模式为电流源故障穿越控制模式，第一电压源控制模式为电压源故障穿越控制模式，第一时长小于第二时长，第二时长为电网发生故障的时刻至并网开关断开的时刻之间的时间间隔。采用本申请，可使微电网系统在电网故障时为外部电网提供电压支撑，并在并网开关断开前完成并离网模式切换。

Description

微电网系统、功率变换器及其控制方法
本申请要求在2023年02月07日提交中国国家知识产权局、申请号为202310150573.1的中国专利申请的优先权，发明名称为“微电网系统、功率变换器及其控制方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电源技术领域，尤其涉及一种微电网系统、功率变换器及其控制方法。
背景技术
微电网由分布式发电、用电负荷、监控、保护和自动化装置等组成(必要时含储能装置)，能够基本实现内部电力电量平衡的小型供用电系统。微电网有并网和离网两种运行模式。并网模式是指在正常情况下，微电网与大电网并网运行，向大电网提供多余的电能或由大电网向本地负载供电并向电池充电。离网模式是指当检测到大电网故障或电能质量不满足要求时，微电网与大电网断开形成孤岛状态，由微电网内的分布式电源和储能电池向本地负荷供电。
随着微电网接入大电网的配电电压等级和容量提高，微电网及其所有的分布式电源和储能已成为电力系统安全稳定的重要组成部分。在大电网出现故障发生电压跌落时，微电网就立即切换为离网模式独立运行，将会给大电网造成较大的功率扰动。此外，大电网大部分的电压跌落都是暂时性的，即所发生的故障大部分不是永久性故障，在线路断路器断开再自动重合闸后系统可以正常运行。因此，在大电网出现故障的情况下，微电网能够为大电网提供电压支撑，并在线路断路器断开之前完成并离网模式切换尤为重要。
发明内容
本申请提供了一种微电网系统、功率变换器及其控制方法，可使微电网系统在电网故障时为外部电网提供电压支撑，并在并网开关断开前完成并离网模式切换。
第一方面，本申请提供了一种微电网系统，该微电网系统包括至少一个功率变换器、微电网母线和并网开关，功率变换器的输入端和输出端分别连接直流电源和微电网母线，微电网母线通过并网开关连接外部电网。功率变换器在检测到电网发生故障的情况下，处于第一电流源控制模式；并在电网故障的持续时长达到第一时长后，从第一电流源控制模式切换至第一电压源控制模式。其中，电网包括外部电网或者微电网系统，第一电流源控制模式为电流源故障穿越控制模式，第一电压源控制模式为电压源故障穿越控制模式。并网开关在电网发生故障的情况下经过第二时长后断开，第二时长大于第一时长。可以理解的，微电网系统中的各功率变换器在检测到电网发生故障的情况下，通过控制自身处于电流源故障穿越控制模式，并在并网开关断开前控制自身切换至电压源故障穿越控制模式的方式，使得微电网系统在电网故障时为外部电网提供电压支撑，并在并网开关断开前完成并离网模式切换，从而使微电网系统兼顾故障穿越支撑功能和并离网切换功能，保证微电网系统的稳定运行。
结合第一方面，在第一种可能的实施方式中，在第一电流源控制模式下功率变换器基于电网发生故障时微电网母线的电压跌落值控制功率变换器的输出电压，从而对外部电网提供无功电流支撑，实现微电网系统的电流源故障穿越支撑特性。在第一电压源控制模式下功率变换器基于预设电流幅值范围中的最大预设电流幅值控制功率变换器的输出电压，从而对外部电网提供电压和频率支撑，实现微电网系统的电压源故障穿越支撑特性。
结合第一方面第一种可能的实施方式，在第二种可能的实施方式中，功率变换器根据电网发生故障时微电网母线的电压跌落值获得第一参考输出电流值，根据第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值，并基于第一参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电流源控制模式，从而使得功率变换器基于电压跌落值为外部电网提供一定的电压支撑，进而使得微电网系统在电网故障时能够为外部电网提供电压支撑，实现电流源故障穿越支撑特性。
结合第一方面第一种可能的实施方式或者第一方面第二种可能的实施方式，在第三种可能的实施方式中，功率变换器基于最大预设电流幅值和外部电网的等效阻抗角获得第二参考输出电流值，基于第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值；基于第二参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电压源控制模式。可以理解的，在电网故障的持续时长达到第 一时长后，功率变换器从电流源故障穿越控制模式切换至电压源故障穿越控制模式，可减小由于功率变换器在并网开关断开之前没切换至电压源控制模式而导致的微电网系统失稳的风险，从而提高微电网系统的稳定性。
结合第一方面第三种可能的实施方式，在第四种可能的实施方式中，功率变换器处于第一电压源控制模式下的初始参考输出电流值和初始参考角频率值分别为切换瞬间功率变换器处于第一电流源控制模式下的第一参考输出电流值和第一参考角频率值，可减小模式切换时电流和电压的波动程度，提高电流和电压在模式切换时的平滑度。
结合第一方面至第一方面第四种可能的实施方式中的任一种，在第五种可能的实施方式中，功率变换器还在电网发生故障之前处于第二电流源控制模式，其中，在第二电流源控制模式下功率变换器基于参考输出有功电流值和参考输出无功电流值控制功率变换器的输出电压。可以理解的，在电网发生故障之前，微电网系统处于并网模式，各功率变换器均处于第二电流源控制模式，即电流源控制模式下的正常控制模式，有利于提高微电网系统的稳定性。
结合第一方面第五种可能的实施方式，在第六种可能的实施方式中，功率变换器将参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，基于第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值；基于第三参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电流源控制模式。
结合第一方面第五种可能的实施方式或者第一方面第六种可能的实施方式，在第七种可能的实施方式中，功率变换器还基于功率变换器的参考输出有功功率值和实际输出有功功率值获得参考输出有功电流值。可以理解的，参考输出有功电流值的获取方式简单，有利于提供功率变换器的工作效率，进而提高微电网系统的工作效率。
结合第一方面第五种可能的实施方式或者第一方面第六种可能的实施方式，在第八种可能的实施方式中，功率变换器包括直流DC/直流DC电路、直流母线和直流DC/交流AC电路，DC/DC电路的输出端通过直流母线连接DC/AC电路的输入端。功率变换器还基于直流母线的参考母线电压和实际母线电压获得参考输出有功电流值。可以理解的，参考输出有功电流值还可以基于直流母线的母线电压获得，参考输出有功电流值的获取方式多样，灵活性高。
结合第一方面第五种可能的实施方式或者第一方面第六种可能的实施方式，在第九种可能的实施方式中，功率变换器还基于功率变换器的参考输出无功功率值和实际输出无功功率值获得参考输出无功电流值。可以理解的，参考输出无功电流值的获取方式简单，有利于提供功率变换器的工作效率，进而提高微电网系统的工作效率。
结合第一方面第五种可能的实施方式或者第一方面第六种可能的实施方式，在第十种可能的实施方式中，功率变换器还基于功率变换器的参考输出电压和实际输出电压获得参考输出无功电流值。可以理解的，参考输出无功电流值还可以基于功率变换器的输出电压获得，参考输出无功电流值的获取方式多样，灵活性高。
结合第一方面至第一方面第十种可能的实施方式中的任一种，在第十一种可能的实施方式中，功率变换器还在自身处于第一电压源控制模式后，在电网恢复正常的情况下，从第一电压源控制模式切换至第二电压源控制模式，其中，在第二电压源控制模式下功率变换器基于参考电压幅值和参考频率值控制功率变换器的输出电压。进而，在电网恢复正常后，微电网系统能够主动为外部电网提供预设电压频率支撑和预设电压幅值支撑。
结合第一方面第十一种可能的实施方式，在第十二种可能的实施方式中，功率变换器根据参考电压幅值和参考频率值获得第四参考输出调制电压值，并根据第四参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电压源控制模式。
结合第一方面至第一方面第十二种可能的实施方式中的任一种，在第十三种可能的实施方式中，功率变换器在自身的输出电压小于电压阈值或者自身的输出电流大于电流阈值的情况下，确定电网发生故障。可以理解的，功率变换器可以通过自身的输出电压或者输出电流的方式判断电网是否故障，该方式无需与微电网控制器通信，可有效提高功率变换器对电网进行故障检测时的效率。
结合第一方面至第一方面第十二种可能的实施方式中的任一种，在第十四种可能的实施方式中，功率变换器在微电网母线的电压小于电压阈值的情况下，确定电网发生故障。可以理解的，功率变换器还可以通过微电网母线的电压判断电网是否故障，电网故障判断方式多样，灵活性高。
结合第一方面至第一方面第十四种可能的实施方式中的任一种，在第十五种可能的实施方式中，微电 网系统还包括微电网控制器，微电网控制器在检测到电网发生故障的情况下，经过第二时长后控制并网开关断开。
结合第一方面第十五种可能的实施方式，在第十六种可能的实施方式中，功率变换器还在切换至第二电压源控制模式后，向微电网控制器发送功率变换器的控制模式，其中，在第二电压源控制模式下功率变换器基于参考电压幅值和参考频率值控制功率变换器的输出电压。微电网控制器在并网开关处于断开状态且接收到的功率变换器的控制模式为第二电压源控制模式的情况下，向功率变换器发送同期控制指令，同期控制指令用于控制功率变换器的输出电压幅值与外部电网的电压幅值之间的幅值差值小于幅值差值阈值，以及功率变换器的输出电压相位与外部电网的电压相位之间的相位差值小于相位差值阈值；并在并网开关的第一端电压幅值与第二端电压幅值之间的幅值差值小于幅值差值阈值，且并网开关的第一端电压相位与第二端电压相位之间的相位差值小于相位差值阈值的情况下，微电网控制器控制并网开关闭合。可以理解的，微电网控制器基于并网开关的开关状态和各功率变换器的控制模式，对各功率变换器的控制模式进行调整，以使各功率变换器在微电网系统处于并网模式时运行在电流源控制模式，在微电网系统处于离网模式时运行在电压源控制模式，从而提高微电网系统的稳定性。
结合第一方面第十六种可能的实施方式，在第十七种可能的实施方式中，微电网控制器还在并网开关处于闭合状态且接收到的功率变换器的控制模式为第二电压源控制模式的情况下，经过第三时长后向功率变换器发送模式切换指令，模式切换指令用于控制功率变换器切换至第二电流源控制模式，在第二电流源控制模式下功率变换器基于参考输出有功电流值和参考输出无功电流值控制功率变换器的输出电压。可以理解的，微电网控制器基于并网开关的开关状态和各功率变换器的控制模式，对各功率变换器的控制模式进行调整，以使各功率变换器在微电网系统处于并网模式时运行在电流源控制模式，在微电网系统处于离网模式时运行在电压源控制模式，从而提高微电网系统的稳定性。
第二方面，本申请提供了一种功率变换器，该功率变换器的输入端和输出端分别连接直流电源和微电网母线，微电网母线通过并网开关连接外部电网。功率变换器在检测到电网发生故障的情况下，处于第一电流源控制模式；在电网故障的持续时长达到第一时长后，从第一电流源控制模式切换至第一电压源控制模式，其中，电网包括外部电网或者微电网母线所在的微电网系统，第一电流源控制模式为电流源故障穿越控制模式，第一电压源控制模式为电压源故障穿越控制模式，第一时长小于第二时长，第二时长为电网发生故障的时刻至并网开关断开的时刻之间的时间间隔。进而，功率变换器在检测到电网发生故障的情况下，通过控制自身处于电流源故障穿越控制模式，并在并网开关断开前控制自身切换至电压源故障穿越控制模式的方式，使得功率变换器在电网故障时为外部电网提供电压支撑，并在并网开关断开前完成并离网模式切换，从而使功率变换器兼顾故障穿越支撑功能和并离网切换功能。
结合第二方面，在第一种可能的实施方式中，在第一电流源控制模式下功率变换器基于电网发生故障时微电网母线的电压跌落值，控制功率变换器的输出电压，从而对外部电网提供无功电流支撑，实现功率变换器的电流源故障穿越支撑特性。在第一电压源控制模式下功率变换器基于预设电流幅值范围中的最大预设电流幅值，控制功率变换器的输出电压，从而对外部电网提供电压和频率支撑，实现功率变换器的电压源故障穿越支撑特性。
结合第二方面第一种可能的实施方式，在第二种可能的实施方式中，功率变换器根据电网发生故障时微电网母线的电压跌落值获得第一参考输出电流值，根据第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值，并基于第一参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电流源控制模式，从而使得功率变换器在电网故障时基于电压跌落值为外部电网提供一定的电压支撑，进而实现功率变换器的电流源故障穿越支撑特性。
结合第二方面第一种可能的实施方式或者第二方面第二种可能的实施方式，在第三种可能的实施方式中，功率变换器基于最大预设电流幅值和外部电网的等效阻抗角获得第二参考输出电流值，基于第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值；基于第二参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电压源控制模式。可以理解的，在电网故障的持续时长达到第一时长后，功率变换器从电流源故障穿越控制模式切换至电压源故障穿越控制模式，可减小由于功率变换器在并网开关断开之前没切换至电压源控制模式而导致的微电网系统失稳的风险，从而提高功率变换器的稳定性。
结合第二方面第三种可能的实施方式，在第四种可能的实施方式中，功率变换器处于第一电压源控制模式下的初始参考输出电流值和初始参考角频率值分别为切换瞬间功率变换器处于第一电流源控制模式下的第一参考输出电流值和第一参考角频率值，可减小模式切换时电流和电压的波动程度，提高电流和电 压在模式切换时的平滑度，从而提高功率变换器在模式切换时的稳定性。
结合第二方面至第二方面第四种可能的实施方式中的任一种，在第五种可能的实施方式中，功率变换器还在电网发生故障之前处于第二电流源控制模式，其中，在第二电流源控制模式下功率变换器基于参考输出有功电流值和参考输出无功电流值控制功率变换器的输出电压。可以理解的，在电网故障之前，微电网系统处于并网模式，功率变换器均处于第二电流源控制模式，即电流源控制模式下的正常控制模式，有利于提高功率变换器的稳定性。
结合第二方面第五种可能的实施方式，在第六种可能的实施方式中，功率变换器将参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，基于第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值；基于第三参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电流源控制模式。
结合第二方面第五种可能的实施方式或者第二方面第六种可能的实施方式，在第七种可能的实施方式中，功率变换器还基于功率变换器的参考输出有功功率值和实际输出有功功率值获得参考输出有功电流值。可以理解的，参考输出有功电流值的获取方式简单，有利于提供功率变换器的工作效率。
结合第二方面第五种可能的实施方式或者第二方面第六种可能的实施方式，在第八种可能的实施方式中，功率变换器包括直流DC/直流DC电路、直流母线和直流DC/交流AC电路，DC/DC电路的输出端通过直流母线连接DC/AC电路的输入端。功率变换器还基于直流母线的参考母线电压和实际母线电压获得参考输出有功电流值。可以理解的，参考输出有功电流值还可以基于直流母线的母线电压获得，参考输出有功电流值的获取方式多样，灵活性高。
结合第二方面第五种可能的实施方式或者第二方面第六种可能的实施方式，在第九种可能的实施方式中，功率变换器还基于功率变换器的参考输出无功功率值和实际输出无功功率值获得参考输出无功电流值。可以理解的，参考输出无功电流值的获取方式简单，有利于提供功率变换器的工作效率。
结合第二方面第五种可能的实施方式或者第二方面第六种可能的实施方式，在第十种可能的实施方式中，功率变换器还基于功率变换器的参考输出电压和实际输出电压获得参考输出无功电流值。可以理解的，参考输出无功电流值还可以基于功率变换器的输出电压获得，参考输出无功电流值的获取方式多样，灵活性高。
结合第二方面至第二方面第十种可能的实施方式，在第十一种可能的实施方式中，功率变换器还在自身处于第一电压源控制模式后，在电网恢复正常的情况下，从第一电压源控制模式切换至第二电压源控制模式，其中，在第二电压源控制模式下功率变换器基于参考电压幅值和参考频率值控制功率变换器的输出电压。进而，在电网恢复正常后，功率变换器能够主动为外部电网提供预设电压频率支撑和预设电压幅值支撑。
结合第二方面第十一种可能的实施方式，在第十二种可能的实施方式中，功率变换器根据参考电压幅值和参考频率值获得获得第四参考输出调制电压值，并根据第四参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电压源控制模式。
结合第二方面至第二方面第十二种可能的实施方式中的任一种，在第十三种可能的实施方式中，功率变换器在自身的输出电压小于电压阈值或者自身的输出电流大于电流阈值的情况下，确定电网发生故障。可以理解的，功率变换器可以通过自身的输出电压或者输出电流的方式判断电网是否故障，该方式无需与微电网控制器通信，可有效提高功率变换器对电网进行故障检测时的效率。
结合第二方面至第二方面第十二种可能的实施方式中的任一种，在第十四种可能的实施方式中，功率变换器在微电网母线的电压小于电压阈值的情况下，确定电网发生故障。可以理解的，功率变换器还可以通过微电网母线的电压判断电网是否故障，电网故障判断方式多样，灵活性高。
第三方面，本申请提供了一种功率变换器的控制方法，该功率变换器的输入端和输出端分别连接直流电源和微电网母线，微电网母线通过并网开关连接外部电网。该方法包括：功率变换器在检测到电网故障的情况下，处于第一电流源控制模式；在电网故障的持续时长达到第一时长后，从第一电流源控制模式切换至第一电压源控制模式，其中，电网包括外部电网或者微电网母线所在的微电网系统，第一电流源控制模式为电流源故障穿越控制模式，第一电压源控制模式为电压源故障穿越控制模式，第一时长小于第二时长，第二时长为电网发生故障的时刻至并网开关断开的时刻之间的时间间隔。
结合第三方面，在第一种可能的实施方式中，在第一电流源控制模式下功率变换器基于电网发生故障时微电网母线的电压跌落值，控制功率变换器的输出电压。在第一电压源控制模式下功率变换器基于预设电流幅值范围中的最大预设电流幅值，控制功率变换器的输出电压。
结合第三方面第一种可能的实施方式，在第二种可能的实施方式中，功率变换器根据电网发生故障时微电网母线的电压跌落值获得第一参考输出电流值，根据第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值，并基于第一参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电流源控制模式。
结合第三方面第一种可能的实施方式或者第三方面第二种可能的实施方式，在第三种可能的实施方式中，功率变换器基于最大预设电流幅值和外部电网的等效阻抗角获得第二参考输出电流值，基于第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值；基于第二参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电压源控制模式。
结合第三方面第三种可能的实施方式，在第四种可能的实施方式中，功率变换器处于第一电压源控制模式下的初始参考输出电流值和初始参考角频率值分别为切换瞬间功率变换器处于第一电流源控制模式下的第一参考输出电流值和第一参考角频率值。
结合第三方面至第三方面第四种可能的实施方式中的任一种，在第五种可能的实施方式中，功率变换器还在电网发生故障之前处于第二电流源控制模式，其中，在第二电流源控制模式下功率变换器基于参考输出有功电流值和参考输出无功电流值控制功率变换器的输出电压。
结合第三方面第五种可能的实施方式，在第六种可能的实施方式中，功率变换器将参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，基于第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值；基于第三参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电流源控制模式。
结合第三方面第五种可能的实施方式或者第三方面第六种可能的实施方式，在第七种可能的实施方式中，功率变换器还基于功率变换器的参考输出有功功率值和实际输出有功功率值获得参考输出有功电流值。
结合第三方面第五种可能的实施方式或者第三方面第六种可能的实施方式，在第八种可能的实施方式中，功率变换器包括直流DC/直流DC电路、直流母线和直流DC/交流AC电路，DC/DC电路的输出端通过直流母线连接DC/AC电路的输入端。功率变换器还基于直流母线的参考母线电压和实际母线电压获得参考输出有功电流值。
结合第三方面第五种可能的实施方式或者第三方面第六种可能的实施方式，在第九种可能的实施方式中，功率变换器还基于功率变换器的参考输出无功功率值和实际输出无功功率值获得参考输出无功电流值。
结合第三方面第五种可能的实施方式或者第三方面第六种可能的实施方式，在第十种可能的实施方式中，功率变换器还基于功率变换器的参考输出电压和实际输出电压获得参考输出无功电流值。
结合第三方面至第三方面第十种可能的实施方式中的任一种，在第十一种可能的实施方式中，功率变换器还在自身处于第一电压源控制模式后，在电网恢复正常的情况下，从第一电压源控制模式切换至第二电压源控制模式，其中，在第二电压源控制模式下功率变换器基于参考电压幅值和参考频率值控制功率变换器的输出电压。
结合第三方面第十一种可能的实施方式，在第十二种可能的实施方式中，功率变换器根据参考电压幅值和参考频率值获得第四参考输出调制电压值，并根据第四参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电压源控制模式。
结合第三方面至第三方面第十二种可能的实施方式中的任一种，在第十三种可能的实施方式中，功率变换器在自身的输出电压小于电压阈值或者自身的输出电流大于电流阈值的情况下，确定电网发生故障。
结合第三方面至第三方面第十二种可能的实施方式中的任一种，在第十四种可能的实施方式中，功率变换器在微电网母线的电压小于电压阈值的情况下，确定电网发生故障。
应理解的是，本申请上述多个方面的实现和有益效果可互相参考。
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图1是本申请提供的微电网系统的应用场景示意图；
图2a是本申请提供的微电网系统的一结构示意图；
图2b是本申请提供的微电网系统的另一结构示意图；
图3是本申请提供的微电网系统的控制时序示意图；
图4是本申请提供的微电网系统的一仿真示意图；
图5是本申请提供的微电网系统的另一仿真示意图；
图6是本申请提供的微电网系统的又一仿真示意图；
图7是本申请提供的功率变换器的控制方法的一流程示意图；
图8是本申请提供的功率变换器的控制方法的另一流程示意图；
图9是本申请提供的微电网控制器的控制方法的流程示意图。
具体实施方式
本申请提供的微电网系统和功率变换器可适用于新能源智能微网领域、输配电领域、新能源领域(如光伏并网领域、风力并网领域)、光伏发电领域、风力发电领域等多种应用领域。本申请提供的微电网系统和功率变换器可适用于不同的应用场景，比如，兼顾并网和离网功能的大型工商业微电网场景、中小型分布式微电网场景等，具体来讲，微电网场景包括光伏供电场景、储能供电场景、光储混合供电场景、光风混合供电场景等。下面以中小型分布式光储混合供电场景为例对微电网系统进行说明。
参见图1，图1是本申请提供的微电网系统的应用场景示意图。如图1所示，在中小型分布式光储混合供电场景下，本申请提供的微电网系统可以为图1所示的微电网系统，本申请提供的功率变换器可以是图1所示的储能变流器或者光伏逆变器。该微电网系统包括储能电池簇a1、……、储能电池簇an、光伏组串b1、……、光伏组串bm、储能变流器11、……、储能变流器1n、光伏逆变器21、……、光伏逆变器2m、微电网母线BUS、并网开关和家电设备。储能变流器11的输入端连接储能电池簇a1，……，储能变流器1n的输入端连接储能电池簇an，储能变流器11的输出端、……、储能变流器1n的输出端均连接至微电网母线BUS。光伏逆变器21的输入端连接光伏组串b1，……，光伏逆变器2m的输入端连接光伏组串bm，光伏逆变器21的输出端、……、以及光伏逆变器2m的输出端均连接至微电网母线BUS。家电设备连接至微电网母线BUS。微电网母线BUS通过并网开关连接外部电网。在微电网系统并入外部电网开始工作后，上个n个储能变流器中的各储能变流器将各自输入端相连的储能电池簇所提供的直流电，进行逆变后得到交流电，并将逆变后的交流电输出至微电网母线BUS。上述m个光伏逆变器将各自输入端相连的光伏组串所提供的直流电，进行逆变后得到交流电，并将逆变后的交流电输出至微电网母线BUS。从而实现对家电设备和外部电网的供电。此外，在微电网系统并入外部电网开始工作后，各储能变流器、各光伏逆变器和微电网控制器均实时检测电网是否发生故障，其中，电网包括外部电网或者微电网系统。各储能变流器和各光伏逆变器在检测到电网发生故障的情况下，处于第一电流源控制模式。在电网故障的持续时长达到第一时长后，各储能变流器和各光伏逆变器从第一电流源控制模式切换至第一电压源控制模式，其中，第一电流源控制模式为电流源故障穿越控制模式，第一电压源控制模式为电压源故障穿越控制模式，第一时长小于第二时长，第二时长为电网发生故障的时刻至并网开关断开的时刻之间的时间间隔。可以理解的，微电网系统中的各储能变流器和各光伏逆变器在检测到电网发生故障的情况下，通过控制自身处于电流源故障穿越控制模式，并在并网开关断开前控制自身切换至电压源故障穿越控制模式的方式，使得微电网系统在电网故障时为外部电网提供电压支撑，并在并网开关断开前完成并离网模式切换，从而使微电网系统兼顾故障穿越支撑功能和并离网切换功能。上述只是对本申请提供的微电网系统的应用场景进行示例，而非穷举，本申请不对应用场景进行限制。
下面结合图2a至图6对本申请提供的微电网系统和功率变换器的工作原理进行示例说明。
参见图2a，图2a是本申请提供的微电网系统的一结构示意图。如图2a所示，微电网系统1包括直流电源101、……、直流电源10n、功率变换器111、……、功率变换器11n、微电网母线BUS和并网开关S1。功率变换器111的输入端连接直流电源101，……，功率变换器11n的输入端连接直流电源10n，功率变换器111的输出端、……、功率变换器11n的输出端均并联至微电网母线BUS，微电网母线BUS通过并网开关S1连接外部电网。其中，本申请中的功率变换器可以是储能变流器、光伏逆变器或者机电变流器等。
在一可选实施方式中，在微电网系统1并入外部电网工作后，功率变换器111、……、功率变换器11n中的各功率变换器开始检测电网是否发生故障，其中，电网包括微电网系统1或者外部电网。在检测到电网发生故障的情况下，各功率变换器处于第一电流源控制模式，并在电网故障的持续时长达到第一时长后，从第一电流源控制模式切换至第一电压源控制模式，其中，第一电流源控制模式为电流源故障穿越控制模式，第一电压源控制模式为电压源故障穿越控制模式，第一时长小于第二时长，第二时长为电网发生故障的时刻至并网开关S1断开的时刻之间的时间间隔。
在本申请实施例中，微电网系统1中的各功率变换器在检测到电网发生故障的情况下，通过控制自身处于电流源故障穿越控制模式，并在并网开关断开前控制自身切换至电压源故障穿越控制模式的方式，使得微电网系统1在电网故障时为外部电网提供电压支撑，并在并网开关S1断开前完成并离网模式切换， 从而使微电网系统1兼顾故障穿越支撑功能和并离网切换功能。
参见图2b，图2b是本申请提供的微电网系统的另一结构示意图。如图2b所示，与图2a所示的微电网系统1相比，图2b所示的微电网系统1还包括微电网控制器12、本地负荷131和本地负荷132。本地负荷131和本地负荷132均连接至微电网母线BUS。微电网控制器12与功率变换器111、……、功率变换器11n、并网开关S1、本地负荷131和本地负荷132之间均设置有图2b中用虚线表示的通讯线，以建立通信连接。其中，本地负荷131和本地负荷132分别为一般负荷和关键负荷，一般负荷并不是一直处于并网状态，具体来讲，一般负荷在微电网母线BUS的电压小于供电电压阈值时，微电网控制器12可以将一般负荷从微电网系统1中断开，以保证对关键负荷的正常供电。
在一可选实施方式中，在微电网系统1并入外部电网开始运行后，各功率变换器开始检测电网是否故障。在电网发生故障的情况下，各功率变换器处于电流源故障穿越控制模式。并在电网故障的持续时长达到第一时长后，各功率变换器从电流源故障穿越控制模式切换至电压源故障穿越控制模式。同时，在微电网系统1并入外部电网开始运行后，微电网控制器12开始检测电网是否故障。在电网发生故障的情况下，微电网控制器12经过第二时长后控制并网开关S1断开。其中，第二时长大于第一时长。在电流源故障穿越控制模式下各功率变换器基于电网故障时微电网母线BUS的电压跌落值，控制各自的输出电压；在电压源故障穿越控制模式下各功率变换器基于预设电流幅值范围中的最大预设电流幅值，控制各自的输出电压。
具体的，并网开关S1处于闭合状态，微电网系统1并入外部电网工作。在微电网系统1并入外部电网开始运行后，各功率变换器开始获取各自的输出电压或者输出电流，检测电网是否发生故障。同时，在微电网系统1并入外部电网开始运行后，微电网控制器12开始获取微电网母线BUS的电压，检测电网是否发生故障。由于微电网系统1中各功率变换器的工作原理均一致，为了便于介绍，下面以功率变换器111为例进行介绍。
在功率变换器的输出电压小于电压阈值或者功率变换器的输出电流大于电流阈值的情况下，功率变换器111确定电网发生故障。可选的，功率变换器111在微电网母线BUS的电压小于电压阈值的情况下，确定电网发生故障。在确定电网发生故障的情况下，功率变换器111根据电网故障时微电网母线的电压跌落值获得第一参考输出电流值，并根据第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值，从而基于第一参考输出调制电压值控制功率变换器的输出电压，以使功率变换器111处于电流源故障穿越控制模式，即电流源控制模式下的故障穿越控制模式。
具体来讲，功率变换器111根据电网发生故障时微电网母线BUS的电压跌落值(即电压阈值与电网故障时微电网母线BUS的电压之间的差值)，通过查询电压跌落值与第一参考输出电流之间的预设对应表格的方式，获得该电压跌落值对应的第一参考输出电流值Iref1。其中，第一参考输出电流值Iref1包括第一参考输出有功电流值Idref1和第一参考输出无功电流值Iqref1。在上述预设对应表格中，微电网母线BUS的电压跌落值越大则第一参考输出电流值Iref1越大。之后，功率变换器111向电流控制环输入第一参考输出有功电流值Idref1、第一参考输出无功电流值Iqref1、实际输出有功电流值Id和实际输出无功电流值Iq后得到第一参考q轴电压值Vqref1和第一参考d轴电压值Vdref1。其中，电流控制环可以是PI控制器、PD控制器和PID控制器中的任意一种。
在确定电网发生故障的情况下，功率变换器111还将采集到的功率变换器111的三相输出电压Va,Vb,Vc从三相静止坐标系变换到两相旋转坐标系，即对采集到的功率变换器111的三相输出电压Va,Vb,Vc进行abc/dq坐标变换，得到q轴电压分量Vq，从而将q轴电压分量Vq输入锁相控制环后得到第一参考角频率值ω1。之后，功率变换器111基于第一参考角频率值ω1，生成第一参考电压相位θ1，并基于第一参考电压相位θ1、第一参考q轴电压值Vqref1和第一参考d轴电压值Vdref1，进行dq/abc坐标变换后得到第一参考输出调制电压值，并将第一参考输出调制电压值与三角波进行比较得到第一脉冲宽度调制波，从而将该第一脉冲宽度调制波输出至功率变换器111中的功率变换电路(如DC/AC电路)的开关管，以控制功率变换器111的输出电压，从而使功率变换器111处于电流源故障穿越控制模式，进而使得功率变换器111基于电网故障时微电网母线的电压跌落值控制自身的输出无功电流和有功电流以为外部电网提供电压支撑，实现电流源故障穿越支撑特性。
之后，在电网故障的持续时长达到第一时长后，功率变换器111从电流源故障穿越控制模式切换至电压源故障穿越控制模式。
在一可选实施例中，功率变换器111基于外部电网的等效阻抗角和预设电流幅值范围中的最大预设电流幅值确定第二参考输出电流值，并基于第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值，从而基于第二参考输出调制电压值控制功率变换器111的输出电压，以使功率变换器111处于电 压源故障穿越控制模式，即电压源控制模式下的故障穿越控制模式。
具体的，在电网故障的持续时长达到第一时长后，功率变换器111获取外部电网的等效阻抗角，并基于最大预设电流幅值IM和外部电网的等效阻抗角σ，计算得到第二参考输出电流值Iref2,即第二参考输出有功电流值Idref2＝IM*cosσ和第二参考输出无功电流值Iqref2＝IM*sinσ。之后，功率变换器111向电流控制环输入第二参考输出有功电流值Idref2、第二参考输出无功电流值Iqref2、实际输出有功电流值Id和实际输出无功电流值Iq后得到第二参考q轴电压值Vqref2和第二参考d轴电压值Vdref2。
在电网故障的持续时长达到第一时长后，功率变换器111还基于参考输出有功功率Pref和实际输出有功功率P得到第二参考角频率值ω2，并基于第二参考角频率值ω2，生成第二参考电压相位θ2。之后，功率变换器111基于第二参考电压相位θ2、第二参考q轴电压值Vqref2和第二参考d轴电压值Vdref2，进行dq/abc坐标变换后得到第二参考输出调制电压值，并将第二参考输出调制电压值与三角波进行比较得到第二脉冲宽度调制波，从而将该第二脉冲宽度调制波输出至功率变换器111中的功率变换电路的开关管，以控制功率变换器111的输出电压，从而使功率变换器111从电流源故障穿越控制模式切换至电压源故障穿越控制模式。进而，使得功率变换器111在处于电压源故障穿越控制模式下时基于最大预设电流幅值完成有功电流和无功电流分配，为外部电网提供电压和频率支撑，实现电压源故障穿越支撑特性。
之后，在微电网控制器12在检测到电网故障时(即在检测到微电网母线BUS的电压小于电压阈值时)经过第二时长后，微电网控制器12控制并网开关S1断开。
可以理解的，由于第一时长小于第二时长，因此可以保证在并网开关S1断开之前，微电网系统1中的各功率变换器完成从电流源控制模式下的故障穿越控制模式切换至电压源控制模式下的故障穿越控制模式，以使微电网系统1在故障穿越期间(即从电网故障开始至并网开关S1断开之间的时间段)兼顾并离网切换功能和故障穿越支撑功能，并显著降低对通讯延时性能的依赖需求，避免功率变换器为检测离网状态而向外部电网注入扰动信号，从而解决功率变换器模式切换延时较大(即在并网开关S2断开之前有些功率变换器没切换至电压源控制模式)导致的微电网系统1失稳问题，进而提升微电网系统1的稳定性和市场竞争力。
进一步地，由于功率变换器直接从电流源故障穿越控制模式切换至电压源故障穿越控制模式会存在电流扰动，为了减小模式切换时自身的输出电流和输出电压的波动程度，提高输出电流和输出电压在模式切换时的平滑度，可通过设置功率变换器处于电压源故障穿越控制模式下的初始参考输出电流值和初始参考角频率值分别为切换瞬间功率变换器处于电流源故障穿越控制模式下的第一参考输出电流值和第一参考角频率值的方式实现。
具体的，在电网故障的持续时长达到第一时长后，功率变换器111将电网故障的持续时长为第一时长时功率变换器111处于电流源故障穿越控制模式下的第一参考输出电流值Iref1和第一参考角频率值ω1，作为功率变换器111处于电压源故障穿越控制模式下的初始参考输出电流值Iref20和初始参考角频率值ω20。其中，初始参考电流值Iref20包括初始参考输出有功电流值Idref20和初始参考输出无功电流值Iqref20。之后，功率变换器111向电流控制环输入初始参考输出有功电流值Idref20、初始参考输出无功电流值Iqref20、实际输出有功电流值Id和实际输出无功电流值Iq后得到第二参考q轴电压值Vqref2和第二参考d轴电压值Vdref2。功率变换器111基于初始参考角频率值生成第二参考电压相位θ2。之后，功率变换器111基于第二参考电压相位θ2、第二参考q轴电压值Vqref2和第二参考d轴电压值Vdref2，进行dq/abc坐标变换后得到第二参考输出调制电压值，并将第二参考输出调制电压值与三角波进行比较得到第二脉冲宽度调制波，从而将该第二脉冲宽度调制波输出至功率变换器111中的功率变换电路的开关管，以控制功率变换器111的输出电压，从而使功率变换器111处于电压源故障穿越控制模式，完成从电流源故障穿越控制模式切换至电压源故障穿越控制模式。
需要说明的是，在功率变换器111基于初始参考输出电流值Iref20和初始参考角频率值ω20，从电流源故障穿越控制模式切换至电压源故障穿越控制模式后，功率变换器111可以一直基于初始参考输出电流值Iref20和初始参考角频率值ω20所确定的第二参考输出电压控制自身的输出电压，以使功率变换器111保持在电压源故障穿越控制模式；或者，在功率变换器111基于初始参考输出电流值Iref20和初始参考角频率值ω20，从电流源故障穿越控制模式切换至电压源故障穿越控制模式后，功率变换器111也可以基于第二参考角频率值、以及由最大预设电流幅值和外部电网的等效阻抗角所确定的第二参考输出电流值，控制功率变换器111的输出电压，以使功率变换器111保持在电压源故障穿越控制模式。
在微电网系统1并入外部电网开始运行后，功率变换器111还在检测到电网故障之前处于第二电流源控制模式，即电流源控制模式下的正常控制模式。其中，在第二电流源控制模式下功率变换器111基于参 考输出有功电流值和参考输出无功电流值控制自身的输出电压。示例性的，第二电流源控制模式可以为有功功率P/无功功率Q控制模式。
在一可选实施例中，功率变换器111获取自身的实际输出有功功率值，并将自身的实际输出有功功率值和参考有功功率值输入有功无功功率控制环后，得到参考输出有功电流值。
在另一可选实施例中，功率变换器111包括DC/DC电路、直流母线和DC/AC电路，其中，DC/DC电路的输入端连接功率变换器的输入端，DC/DC电路的输出端通过直流母线连接DC/AC电路的输入端，DC/AC电路的输出端连接功率变换器111的输出端。功率变换器111获取直流母线的实际母线电压，并将直流母线的实际母线电压和参考母线电压输入电压控制环后，得到参考输出有功电流值。
在一可选实施例中，功率变换器111还获取自身的实际输出无功功率值，并将自身的参考输出无功功率值和实际输出无功功率值输入有功无功功率控制环后，获得参考输出无功电流值。
在另一可选实施例中，功率变换器还获取自身的实际输出电压，并将自身的参考输出电压和实际输出电压输入电压控制环后，获得参考输出无功电流值。
其中，上述实施例中有功无功功率控制环和电压控制环可以是PI控制器、PD控制器和PI D控制器中的任意一种。
功率变换器111可以基于上述获取参考输出有功电流值的任一实施例，与上述获取参考输出无功电流值的任一实施例的任意组合，获得参考输出有功电流值和参考输出无功电流值。功率变换器111将参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，并基于第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值，从而基于第三参考输出调制电压值控制自身的输出电压，以使功率变换器111处于第二电流源控制模式。
为了便于介绍，下面以基于参考输出有功功率值和参考输出无功功率值分别确定参考输出有功电流值和参考输出无功电流值的方式为例，对功率变换器111处于第二电流源控制模式进行说明。
具体的，功率变换器111获取自身的实际输出有功功率值P和实际输出无功功率值Q，并将自身的参考输出有功功率值Pref、参考输出无功功率值Qref、实际输出有功功率值P和实际输出无功功率值Q输入有功无功功率控制环后，获得第三参考输出有功电流值Idref3和第三参考输出无功电流值Iqref3。之后，功率变换器111向电流控制环输入第三参考输出有功电流值Idref3、第三参考输出无功电流值Iqref3、实际输出有功电流值Id和实际输出无功电流值Iq后得到第三参考q轴电压值Vqref3和第三参考d轴电压值Vdref3。功率变换器111还对采集到的功率变换器111的三相输出电压Va,Vb,Vc进行abc/dq坐标变换，得到q轴电压分量Vq，从而将q轴电压分量Vq输入锁相控制环后得到第三参考角频率值ω3。之后，功率变换器111基于第三参考角频率值ω3，生成第三参考电压相位θ3，并基于第三参考电压相位θ3、第三参考q轴电压值Vqref3和第三参考d轴电压值Vdref3，进行dq/abc坐标变换后得到第三参考输出调制电压值，并将第三参考输出调制电压值与三角波进行比较后得到第三脉冲宽度调制波，从而将该第三脉冲宽度调制波输出至功率变换器111中的功率变换电路的开关管，以控制功率变换器111的输出电压，进而使功率变换器111处于第二电流源控制模式。
此外，在功率变换器111处于电压源故障穿越控制模式后，在电网恢复正常的情况下，从电压源故障穿越控制模式切换至第二电压源控制模式(电压源控制模式下的正常控制模式)，其中，在第二电压源控制模式下功率变换器111基于参考电压幅值和参考频率值控制自身的输出电压。反之，在功率变换器111处于电压源故障穿越控制模式后，若电网仍故障，则功率变换器111保持在电压源故障穿越控制模式。示例性的，第二电压源控制器可以为虚拟同步发电机(Virtual Synchronous Generator,VSG)控制模式。
在一可选实施例中，功率变换器111根据参考电压幅值和参考频率值获得第四参考输出调制电压值，并根据第四参考输出调制电压值控制自身的输出电压，以使功率变换器111切换至第二电压源控制模式。
具体的，功率变换器111在基于参考电压幅值和参考频率值得到第四参考输出调制电压值后，将第四参考输出调制电压值与三角波进行比较后得到第四脉冲宽度调制波，从而将该第四脉冲宽度调制波输出至功率变换器111中的功率变换电路的开关管，以控制功率变换器111的输出电压，进而使功率变换器111处于第二电压源控制模式，完成电压源故障穿越控制模式至第二电压源控制模式的模式切换。
功率变换器111在切换至第二电压源控制模式后，向微电网控制器12发送自身的控制模式微电网控制器12接收各功率变换器发送的控制模式，并检测并网开关S1的开关状态。
在一可选实施例中，在功率变换器111的控制模式为第二电压源控制模式且并网开关S1处于断开状态的情况下，微电网控制器12向功率变换器111发送同期控制指令。功率变换器111基于接收到的同期控制指令控制自身的输出电压幅值与外部电网的电压幅值之间的幅值差值小于幅值差值阈值，以及自身的 输出电压相位与外部电网的电压相位之间的相位差值小于相位差值阈值，从而使得功率变换器111的输出电压与外部电网电压同步。之后，微电网控制器12在并网开关S1的第一端电压幅值(即第一端a1处的电压幅值)与第二端电压幅值(即第二端a2处的电压幅值)之间的幅值差值小于幅值差值阈值，并且，并网开关S1的第一端电压相位(即第一端a1处的电压相位)与第二端电压相位(即第二端a2处的电压相位)之间的相位差值小于相位差值阈值的情况下，控制并网开关S1闭合。
在另一可选实施例中，在功率变换器111的控制模式为第二电压源控制模式且并网开关S1处于闭合状态的情况下，微电网控制器12经过第三时长向功率变换器111发送模式切换指令。功率变换器111基于接收到的模式切换指令，从第二电压源控制模式切换至第二电流源控制模式。
可以理解的，微电网控制器12基于并网开关S1的开关状态和各功率变换器的控制模式，对各功率变换器的控制模式进行调整，以使各功率变换器在微电网系统1处于并网模式时运行在电流源控制模式，在微电网系统1处于离网模式时运行在电压源控制模式，从而提高微电网系统1的稳定性。
进一步地，为了方便理解，请参见图3，图3是本申请提供的微电网系统的控制时序示意图。如图3所示，在t0时刻至t1时刻内，外部电网的电网电压Vmag没有发生跌落，即外部电网没有发生故障。此外，在t0时刻至t1时刻对应的时间段内，并网开关S1处于闭合状态，功率变换器111处于第二电流源控制模式CS2。
在t1时刻，外部电网的电网电压Vmag发生跌落，即外部电网发生故障，功率变换器111从第二电流源控制模式CS2切换为第一电流源控制模式CS1。此外，在t1时刻，并网开关S1仍处于闭合状态。
在t1时刻至t2时刻内，外部电网的电网电压Vmag没有恢复，外部电网仍故障，功率变换器111处于第一电流源控制模式CS1。此外，在t1时刻至t2时刻对应的时间段内，并网开关S1仍处于闭合状态。
在t2时刻，即从t1时刻开始经过第一时长T1后的时刻，外部电网仍故障，功率变换器111从第一电流源控制模式CS1切换至第一电压源控制模式VS1。此外，在t2时刻，并网开关S1仍处于闭合状态。
在t2时刻至t3时刻内，外部电网仍故障，功率变换器111处于第一电压源控制模式VS1，并网开关S1仍处于闭合状态。
在t3时刻，微电网控制器12控制并网开关S1断开，微电网系统1的电压恢复，功率变换器111仍处于第一电压源控制模式VS1。
在t3时刻至t4时刻内，外部电网仍故障，功率变换器111仍处于第一电压源控制模式VS1，并网开关S1处于断开状态。
在t4时刻，外部电网的电网电压Vmag恢复，外部电网恢复正常，功率变换器111从第一电压源控制模式VS1切换至第二电压源控制模式VS2。此外，在t4时刻，并网开关S1处于断开状态。
在t4时刻至t5时刻内，外部电网正常，功率变换器1111处于第二电压源控制模式VS2，并基于微电网控制器12发送的同期控制指令控制自身的输出电压。此外，在t4时刻至t5时刻所对应的时间段内，并网开关S1处于断开状态。
在t5时刻，外部电网正常，功率变换器111处于第二电压源控制模式VS2。微电网控制器12控制并网开关S1闭合，并确定并网开关S1的开关状态和功率变换器111的控制模式。
在t5时刻至t6时刻内，外部电网正常，功率变换器111仍处于第二电压源控制模式VS2，并网开关S1处于闭合状态。
在t6时刻，即从微电网控制器12确定并网开关S1闭合且功率变换器111的控制模式为第二电压源控制模式VS2的t2时刻开始，经过第三时长T3后的时刻,外部电网正常，功率变换器111基于微电网控制器12发送的模式切换指令，从第二电压源控制模式VS2切换至第二电流源控制模式CS2。此外，在t6时刻，并网开关S1处于闭合状态。
在本申请实施例中，微电网系统1采用“从下而上为主，从上而下为辅”的并离网切换控制方式，也即在电网故障期间，微电网系统1中的各功率变换器先自行判断电网是否故障后执行控制模式切换，之后，微电网控制器12基于并网开关S1的开关状态和各功率变换器的控制模式向各功率变换器补发模式控制指令的并离网切换控制方式，从而使得各功率变换器在故障穿越期间兼顾并离网切换功能和故障穿越支撑功能，并显著降低对通讯延时性能的依赖需求，避免功率变换器为检测离网状态而向外部电网注入扰动信号，从而解决功率变换器切换延时较大导致的微电网系统1失稳问题，进而提升微电网系统1的稳定性和市场竞争力。此外，本申请实施例提供的并离网切换控制方式，对微电网控制器12与各功率变换器之间的通讯延时要求不高，即使通讯延时大也不会造成微电网系统1失稳，具有很好的延时鲁棒性。
需要说明的是，在本申请中，并网开关S1的闭合或者关断除了可以是由微电网控制器12控制之外， 还可以由并网开关S1中所包含的控制器直接控制。这里，并网开关S1的控制器控制并网开关S1断开或者闭合的控制逻辑与微电网控制器12控制并网开关S1断开或者闭合的控制逻辑一致，此处不再展开说明。
下面结合图4至图6，以功率变换器为储能变流器为例，对本申请提供的微电网系统在故障穿越期间兼顾并离网切换功能和故障穿越支撑功能进行验证。
参见图4，图4是本申请提供的微电网系统的一仿真示意图。如图4所示，图4中(a)的上下两部分曲线分别表示各储能变流器的三相输出电压Vabc和三相输出电流Iabc,图4中(b)是对图4中(a)的时间段7.46s-7.54s所对应的曲线放大示意图。
如图4所示，在运行时间未达到7s时，各储能变流器以电流源控制模式下的正常控制模式并网。在运行时间为7s时，外部电网发生三相接地故障。在运行时间介于7s-7.5s之间时，各储能变流器以电流源模式进行故障穿越，即各储能变流器处于电流源故障穿越控制模式。在运行时间为7.5s时，各储能变流器由电流源控制模式切换至电压源控制模式，具体来讲，各储能变流器由电流源故障穿越控制模式切换至电压源故障穿越控制模式。在运行时间介于7.5s-7.8s之间时，各储能变流器以电压源模式进行故障穿越，即各储能变流器处于电压源故障穿越控制模式。在运行时间为7.8s时，并网开关断开，微电网系统和外部电网恢复，各储能变流器离网运行。在运行时间大于7.8s时，各储能变流器以电压源控制模式下的正常控制模式带载独立运行。
基于图4可知，本申请提供的微电网系统中的各储能变流器可以在外部电网发生故障的故障穿越期间从第一电流源控制模式切换至第一电压源控制模式，兼顾故障穿越支撑功能和并离网切换功能。
参见图5，图5是本申请提供的微电网系统的另一仿真示意图。如图5所示，图5中(a)的上下两部分曲线分别表示各储能变流器的三相输出电压Vabc和三相输出电流Iabc,图5中(b)是对图5中(a)的时间段7.46s-7.54s所对应的曲线放大示意图。
如图5所示，在运行时间未达到7s时，各储能变流器以电流源控制模式下的正常控制模式并网。在运行时间为7s时，微电网系统内部某一点发生三相接地故障。在运行时间介于7s-7.5s之间时，各储能变流器以电流源模式进行故障穿越，即各储能变流器处于电流源故障穿越控制模式。在运行时间为7.5s时，各储能变流器由电流源控制模式切换至电压源控制模式，具体来讲，各储能变流器由电流源故障穿越控制模式切换至电压源故障穿越控制模式。在运行时间介于7.5s-7.8s之间时，各储能变流器以电压源模式进行故障穿越，即各储能变流器处于电压源故障穿越控制模式。在运行时间为7.8s时，并网开关断开，各储能变流器离网运行。在运行时间介于7.8s-8s之间时，2台储能变流器继续以电压源模式进行故障穿越。在运行时间为8s时，故障切除，微电网系统的电压恢复。在运行时间大于8s时，各储能变流器以电压源控制模式下的正常控制模式带载独立运行。
基于图5可知，本申请提供的微电网系统中的各储能变流器在微电网系统发生故障的故障穿越期间依然可以从第一电流源控制模式切换至第一电压源控制模式，兼顾故障穿越支撑功能和并离网切换功能。
参见图6，图6是本申请提供的微电网系统的又一仿真示意图。如图6所示，图6中的左上方的两部分曲线分别表示储能变流器PCS1的三相输出电压Vabc和三相输出电流Iabc,左下方的两部分曲线分别为对图6中左上方的两部分曲线的时间段7.45s-7.6s所对应的曲线放大示意图。图6中的右上方的两部分曲线分别表示储能变流器PCS2的三相输出电压Vabc和三相输出电流Iabc,右下方的两部分曲线分别为对图6中右上方的两部分曲线的时间段7.45s-7.6s所对应的曲线放大示意图。
如图6所示，在运行时间未达到7s时，各储能变流器以电流源控制模式下的正常控制模式并网。在运行时间为7s时，外部电网发生三相接地故障。在运行时间介于7s-7.5s之间时，各储能变流器以电流源模式进行故障穿越，即各储能变流器处于电流源故障穿越控制模式。在运行时间为7.5s时，储能变流器PCS1由电流源控制模式切换至电压源控制模式，具体来讲，各储能变流器由电流源故障穿越控制模式切换至电压源故障穿越控制模式。在运行时间介于7.5s-7.55s之间时，储能变流器PCS1以电压源模式进行故障穿越，储能变流器PCS2以电流源模式进行故障穿越。在运行时间为7.55s时，储能变流器PCS2从电流源故障穿越控制模式切换至电压源故障穿越控制模式。在运行时间介于7.55s-7.8s之间时，储能变流器PCS1和PCS2均以电压源模式进行故障穿越。在运行时间为7.8s时，并网开关断开，故障切除，各储能变流器离网运行。在运行时间大于7.8s时，各储能变流器以电压源控制模式下的正常工作模式带载独立运行。
基于图6可知，本申请提供的微电网系统中的各储能变流器即使在故障穿越期间从第一电流源控制模式切换至第一电压源控制模式的时间不同步，依然不会影响微电网系统的稳定性。
参见图7，图7是本申请提供的功率变换器的控制方法的一流程示意图。本申请实施例提供的功率变 换器的控制方法适用于图2a和图2b所示的微电网系统1中的各功率变换器。功率变换器的控制方法可包括步骤：
S101，在检测到电网发生故障的情况下，功率变换器处于第一电流源控制模式。
其中，电网包括外部电网或者微电网系统，第一电流源控制模式为电流源故障穿越控制模式。
在一可选实施方式中，在第一电流源控制模式下功率变换器基于电网故障时微电网母线的电压跌落值，控制功率变换器的输出电压。
具体的，功率变换器在自身的输出电压小于电压阈值或者自身的输出电流大于电流阈值的情况下，根据电网故障时微电网母线的电压跌落值获得第一参考输出电流值，并根据第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值，从而基于第一参考输出调制电压值控制自身的输出电压，以使功率变换器处于第一电流源控制模式。
S102，在电网故障的持续时长达到第一时长后，功率变换器从第一电流源控制模式切换至第一电压源控制模式，第一时长小于第二时长，第二时长为电网发生故障的时刻至并网开关断开的时刻之间的时间间隔。
其中，第一电压源控制模式为电压源故障穿越控制模式。
在一可选实施方式中，在第一电压源控制模式下功率变换器基于预设电流幅值范围中的最大预设电流幅值控制功率变换器的输出电压。
在一可选实施例中，在电网故障的持续时长达到第一时长后，功率变换器基于最大预设电流幅值和外部电网的等效阻抗角确定第二参考输出电流值，基于第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值，并基于第二参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电压源控制模式，完成从第一电流源控制模式至第一电压源控制模式的模式切换。
在另一可选实施方式中，在电网故障的持续时长达到第一时长后，功率变换器将从第一电流源控制模式切换至第一电压源控制模式的切换瞬间功率变换器处于第一电流源控制模式下的第一参考输出电流值和第一参考角频率值，分别确定为功率变换器处于第一电压源控制模式下的初始参考输出电流值和初始参考角频率值，并基于初始参考输出电流值和初始参考角频率值获得第二参考输出调制电压值，从而基于第二参考输出调制电压值控制功率变换器的输出电压，以使功率变换器从第一电流源控制模式切换至第一电压源控制模式。
具体实现中，本申请提供的功率变换器的控制方法中功率变换器所执行的更多操作可参见图2a和图2b所示的微电网系统1中的各功率变换器所执行的实现方式，在此不再赘述。
本申请实施例中，在电网发生故障的情况下，功率变换器在检测到电网发生故障的情况下，通过控制自身处于电流源故障穿越控制模式，并在并网开关断开前控制自身切换至电压源故障穿越控制模式的方式，使得功率变换器在电网故障时为外部电网提供电压支撑，并在并网开关断开前完成并离网模式切换，从而使功率变换器兼顾故障穿越支撑功能和并离网切换功能。
参见图8，图8是本申请提供的功率变换器的控制方法的另一流程示意图。本申请实施例提供的功率变换器的控制方法适用于图2a和图2b所示的微电网系统1中的各功率变换器。功率变换器的控制方法可包括步骤：
S201，微电网系统处于并网运行模式下，功率变换器处于第二电流源控制模式。
其中，在第二电流源控制模式下功率变换器基于参考输出有功电流值和参考输出无功电流值控制功率变换器的输出电压。
具体的，微电网系统处于并网运行模式下，功率变换器将参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，基于第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值；基于第三参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电流源控制模式。
S202，功率变换器判断电网是否发生故障。
具体的，功率变换器在自身的输出电压小于电压阈值或者自身的输出电流大于电流阈值的情况下，确定电网故障。可选的，功率变换器在微电网母线的电压小于电压阈值的情况下，确定电网故障。其中，电网包括外部电网或者微电网系统。
之后，功率变换器在确定电网发生故障的情况下，执行步骤S203，否则执行步骤S201。
S203，功率变换器处于第一电流源控制模式。
具体的，功率变换器根据电网故障时微电网母线的电压跌落值获得第一参考输出电流值，并根据第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值，从而基于第一参考输出调制电压值控 制功率变换器的输出电压，以使功率变换器处于第一电流源控制模式。
S204，功率变换器判断电网是否恢复正常。
具体的，功率变换器在自身的输出电压大于或者等于电压阈值的情况下，确定电网恢复正常。可选的，功率变换器在自身的输出电流小于或者等于电流阈值的情况下，确定电网恢复正常。可选的，功率变换器在微电网母线的电压大于或者等于电压阈值的情况下，确定电网恢复正常。
之后，功率变换器在确定电网恢复正常的情况下，执行步骤S201，否则执行步骤S205。
S205，功率变换器判断电网故障的持续时长是否达到第一时长。
其中，第一时长小于第二时长，第二时长为电网发生故障的时刻至并网开关断开的时刻之间的时间间隔。
具体的，功率变换器在确定电网故障的持续时长达到第一时长后，执行步骤S206，否则执行步骤S203。
S206，功率变换器从第一电流源控制模式切换至第一电压源控制模式。
其中，在第一电压源控制模式下功率变换器基于预设电流幅值范围中的最大预设电流幅值控制功率变换器的输出电压。
在一可选实施方式中，功率变换器基于最大预设电流幅值和外部电网的等效阻抗角确定第二参考输出电流值，基于第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值；基于第二参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第一电压源控制模式，完成从第一电流源控制模式切换至第一电压源控制模式。
在另一可选实施方式中，功率变换器将从第一电流源控制模式切换至第一电压源控制模式的切换瞬间功率变换器处于第一电流源控制模式下的第一参考输出电流值和第一参考角频率值，分别确定为功率变换器处于第一电压源控制模式下的初始参考输出电流值和初始参考角频率值，并基于初始参考输出电流值和初始参考角频率值获得第二参考输出调制电压值，从而基于第二参考输出调制电压值控制功率变换器的输出电压，以使功率变换器从第一电流源控制模式切换至第一电压源控制模式。
S207，功率变换器判断电网是否恢复正常。
功率变换器在确定电网恢复正常的情况下，执行步骤S208，否则执行步骤S206。
S208，功率变换器从第一电压源控制模式切换至第二电压源控制模式，并向微电网控制器发送功率变换器的控制模式。
其中，在第二电压源控制模式下功率变换器基于参考电压幅值和参考频率值控制功率变换器的输出电压。
具体的，功率变换器根据参考电压幅值和参考频率值获得第四参考输出调制电压值，并根据第四参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电压源控制模式，完成从第一电压源控制模式切换至第二电压源控制模式。功率变换器在切换至第二电压源控制模式后，向微电网控制器发送自身的控制模式。
S209，功率变换器判断是否接收到模式切换指令。
功率变换器在接收到模式切换指令的情况下，执行步骤S210，否则执行步骤S208。
S210，功率变换器判断模式切换指令是否为第二电流源控制模式切换指令。
功率变换器在模式切换指令为第二电流源控制模式切换指令的情况下，执行步骤S212，否则执行步骤S211。
S211，功率变换器从第二电压源控制模式切换至第二电流源控制模式。
其中，在第二电流源控制模式下功率变换器基于参考输出有功电流值和参考输出无功电流值控制功率变换器的输出电压。
具体的，功率变换器将参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，基于第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值；基于第三参考输出调制电压值控制功率变换器的输出电压，以使功率变换器处于第二电流源控制模式，完成从第二电压源控制模式切换至第二电流源控制模式。
S212，功率变换器处于第二电压源控制模式。
这里，步骤S212的具体实现方式请参照步骤S201的描述，此处不再赘述。
在本申请实施中，由于第一时长小于第二时长，因此可以保证在并网开关断开之前，微电网系统中的各功率变换器完成从电流源控制模式下的故障穿越控制模式切换至电压源控制模式下的故障穿越控制模式，以使各功率变换器在故障穿越期间兼顾并离网切换功能和故障穿越支撑功能，并显著降低对通讯延时 性能的依赖需求，避免功率变换器为检测离网状态而向外部电网注入扰动信号，从而解决功率变换器切换延时较大导致的微电网系统失稳问题。
参见图9，图9是本申请提供的微电网控制器的控制方法的流程示意图。本申请实施例提供的微电网控制器的控制方法适用于图2a和图2b所示的微电网控制器12。微电网控制器的控制方法可包括步骤：
S301，在检测到电网发生故障的情况下，微电网控制器经过第二时长控制并网开关断开。
其中，电网包括外部电网或者微电网系统。
具体的，微电网控制器在微电网母线的电压小于电压阈值的情况下，经过第二时长控制并网开关断开。
S302，微电网控制器检测并网开关的开关状态，获取各功率变换器的控制模式。
具体的，微电网控制器检测并网开关的开关状态，并向各功率变换器发送控制模式获取指令以获取各功率变换器的控制模式。
S303，微电网控制器判断并网开关是否断开。
在并网开关断开的情况下，微电网控制器执行步骤S304，否则执行步骤S306。
S304，微电网控制器向各功率变换器发送切换为第二电压源控制模式的模式切换指令。
其中，切换为第二电压源控制模式的模式切换指令用于控制各功率变换器切换为第二电压源控制模式。
S305，微电网控制器向各功率变换器发送同期控制指令。
其中，同期控制指令用于控制功率变换器的输出电压幅值与外部电网的电压幅值之间的幅值差值小于幅值差值阈值，以及功率变换器的输出电压相位与外部电网的电压相位之间的相位差值小于相位差值阈值。
S306，微电网控制器判断功率变换器的控制模式是否为第二电压源控制模式。
在功率变换器的控制模式为第二电压源控制模式的情况下，微电网控制器执行步骤S307，否则执行步骤S302。
S307，微电网控制器经过第三时长后，向功率变换器发送切换为第二电流源控制模式的第二模式切换指令。
其中，切换为第二电流源控制模式的第二模式切换指令用于控制功率变换器切换为第二电流源控制模式。
在本申请实施例中，微电网控制器基于并网开关的开关状态和各功率变换器的控制模式，对各功率变换器的控制模式进行调整，以使各功率变换器在微电网系统处于并网模式时运行在电流源控制模式，在微电网系统处于离网模式时运行在电压源控制模式，从而提高微电网系统的稳定性。
以上，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (30)

  1. 一种微电网系统，其特征在于，所述微电网系统包括至少一个功率变换器、微电网母线和并网开关，所述功率变换器的输入端和输出端分别连接直流电源和所述微电网母线，所述微电网母线通过所述并网开关连接外部电网，其中：
    所述功率变换器，用于在检测到电网发生故障的情况下，处于第一电流源控制模式；在所述电网故障的持续时长达到第一时长后，从所述第一电流源控制模式切换至第一电压源控制模式，其中，所述电网包括所述外部电网或者所述微电网系统，所述第一电流源控制模式为电流源故障穿越控制模式，所述第一电压源控制模式为电压源故障穿越控制模式；所述第一时长小于第二时长，所述第二时长为所述电网发生故障的时刻至所述并网开关断开的时刻之间的时间间隔。
  2. 根据权利要求1所述的微电网系统，其特征在于，在所述第一电流源控制模式下所述功率变换器基于所述电网发生故障时所述微电网母线的电压跌落值，控制所述功率变换器的输出电压；在所述第一电压源控制模式下所述功率变换器基于预设电流幅值范围中的最大预设电流幅值，控制所述功率变换器的输出电压。
  3. 根据权利要求2所述的微电网系统，其特征在于，所述功率变换器用于根据所述电网发生故障时所述微电网母线的电压跌落值获得第一参考输出电流值，根据所述第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值；基于所述第一参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第一电流源控制模式。
  4. 根据权利要求2或3所述的微电网系统，其特征在于，所述功率变换器用于基于所述最大预设电流幅值和所述外部电网的等效阻抗角确定第二参考输出电流值，基于所述第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值；基于所述第二参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第一电压源控制模式。
  5. 根据权利要求4所述的微电网系统，其特征在于，所处功率变换器处于所述第一电压源控制模式下的初始参考输出电流值和初始参考角频率值分别为切换瞬间所述功率变换器处于所述第一电流源控制模式下的第一参考输出电流值和第一参考角频率值。
  6. 根据权利要求1-5任一项所述的微电网系统，其特征在于，所述功率变换器还用于在所述电网发生故障之前处于第二电流源控制模式，其中，在所述第二电流源控制模式下所述功率变换器基于参考输出有功电流值和参考输出无功电流值控制所述功率变换器的输出电压。
  7. 根据权利要求6所述的微电网系统，其特征在于，所述功率变换器用于将所述参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，基于所述第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值；基于所述第三参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第二电流源控制模式。
  8. 根据权利要求6或7所述的微电网系统，其特征在于，所述功率变换器还用于基于所述功率变换器的参考输出有功功率值和实际输出有功功率值获得所述参考输出有功电流值。
  9. 根据权利要求6或7所述的微电网系统，其特征在于，所述功率变换器包括直流DC/直流DC电路、直流母线和直流DC/交流AC电路，所述DC/DC电路的输出端通过所述直流母线连接所述DC/AC电路的输入端；
    所述功率变换器还用于基于所述直流母线的参考母线电压和实际母线电压获得所述参考输出有功电流值。
  10. 根据权利要求6或7所述的微电网系统，其特征在于，所述功率变换器还用于基于所述功率变换 器的参考输出无功功率值和实际输出无功功率值获得所述参考输出无功电流值。
  11. 根据权利要求6或7所述的微电网系统，其特征在于，所述功率变换器还用于基于所述功率变换器的参考输出电压和实际输出电压获得所述参考输出无功电流值。
  12. 根据权利要求1-11任一项所述的微电网系统，其特征在于，所述功率变换器还用于在所述功率变换器处于所述第一电压源控制模式后，在所述电网恢复正常的情况下，从所述第一电压源控制模式切换至第二电压源控制模式，其中，在所述第二电压源控制模式下所述功率变换器基于参考电压幅值和参考频率值控制所述功率变换器的输出电压。
  13. 根据权利要求12所述的微电网系统，其特征在于，所述功率变换器用于根据所述参考电压幅值和所述参考频率值获得第四参考输出调制电压值，并根据所述第四参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第二电压源控制模式。
  14. 根据权利要求1-13任一项所述的微电网系统，其特征在于，所述功率变换器用于在所述功率变换器的输出电压小于电压阈值或者所述功率变换器的输出电流大于电流阈值的情况下，确定所述电网发生故障。
  15. 根据权利要求1-14任一项所述的微电网系统，所述微电网系统还包括微电网控制器，所述微电网控制器用于在检测到所述电网发生故障的情况下，经过所述第二时长后控制所述并网开关断开。
  16. 根据权利要求15所述的微电网系统，其特征在于，所述功率变换器还用于在切换至第二电压源控制模式后，向所述微电网控制器发送所述功率变换器的控制模式，其中，在所述第二电压源控制模式下所述功率变换器基于参考电压幅值和参考频率值控制所述功率变换器的输出电压；
    所述微电网控制器用于在所述并网开关处于断开状态且接收到的所述功率变换器的控制模式为所述第二电压源控制模式的情况下，向所述功率变换器发送同期控制指令，所述同期控制指令用于控制所述功率变换器的输出电压幅值与所述外部电网的电压幅值之间的幅值差值小于幅值差值阈值，以及所述功率变换器的输出电压相位与所述外部电网的电压相位之间的相位差值小于相位差值阈值；并在所述并网开关的第一端电压幅值与第二端电压幅值之间的幅值差值小于所述幅值差值阈值，且所述并网开关的第一端电压相位与第二端电压相位之间的相位差值小于所述相位差值阈值的情况下，控制所述并网开关闭合。
  17. 根据权利要求16所述的微电网系统，其特征在于，所述微电网控制器还用于在所述并网开关处于闭合状态且接收到的所述功率变换器的控制模式为所述第二电压源控制模式的情况下，经过第三时长后向所述功率变换器发送模式切换指令，所述模式切换指令用于控制所述功率变换器切换至第二电流源控制模式，在所述第二电流源控制模式下所述功率变换器基于参考输出有功电流值和参考输出无功电流值控制所述功率变换器的输出电压。
  18. 一种功率变换器，其特征在于，所述功率变换器的输入端和输出端分别连接直流电源和微电网母线，所述微电网母线通过并网开关连接外部电网；
    所述储能变流器，用于在检测到电网发生故障的情况下，处于第一电流源控制模式；在所述电网故障的持续时长达到第一时长后，从所述第一电流源控制模式切换至第一电压源控制模式，其中，所述电网包括所述外部电网或者所述微电网母线所在的微电网系统，所述第一电流源控制模式为电流源故障穿越控制模式，所述第一电压源控制模式为电压源故障穿越控制模式，所述第一时长小于第二时长，所述第二时长为所述电网发生故障的时刻至所述并网开关断开的时刻之间的时间间隔。
  19. 根据权利要求18所述的功率变换器，其特征在于，在所述第一电流源控制模式下所述功率变换器基于所述电网发生故障时所述微电网母线的电压跌落值，控制所述功率变换器的输出电压，在所述第一电压源控制模式下所述功率变换器基于预设电流幅值范围中的最大预设电流幅值控制所述功率变换器的输出电压。
  20. 根据权利要求19所述的功率变换器，其特征在于，所述功率变换器用于根据所述电网发生故障时所述微电网母线的电压跌落值获得第一参考输出电流值，根据所述第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值；基于所述第一参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第一电流源控制模式。
  21. 根据权利要求19或20所述的功率变换器，其特征在于，所述功率变换器用于基于所述最大预设电流幅值和所述外部电网的等效阻抗角确定第二参考输出电流值，基于所述第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值；基于所述第二参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第一电压源控制模式。
  22. 根据权利要求21所述的功率变换器，其特征在于，所处功率变换器处于所述第一电压源控制模式下的初始参考输出电流值和初始参考角频率值分别为切换瞬间所述功率变换器处于所述第一电流源控制模式下的第一参考输出电流值和第一参考角频率值。
  23. 根据权利要求18-22任一项所述的功率变换器，其特征在于，所述功率变换器还用于在所述电网发生故障之前处于第二电流源控制模式，其中，在所述第二电流源控制模式下所述功率变换器基于参考输出有功电流值和参考输出无功电流值控制所述功率变换器的输出电压。
  24. 根据权利要求23所述的功率变换器，其特征在于，所述功率变换器用于将所述参考输出有功电流值和参考输出无功电流值确定为第三参考输出电流值，基于所述第三参考输出电流值和第三参考角频率值获得第三参考输出调制电压值；基于所述第三参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第二电流源控制模式。
  25. 根据权利要求18-24任一项所述的功率变换器，其特征在于，所述功率变换器还用于在所述功率变换器处于所述第一电压源控制模式后，在所述电网恢复正常的情况下，从所述第一电压源控制模式切换至第二电压源控制模式，其中，在所述第二电压源控制模式下所述功率变换器基于参考电压幅值和参考频率值控制所述功率变换器的输出电压。
  26. 一种功率变换器的控制方法，其特征在于，所述功率变换器的输入端和输出端分别连接直流电源和微电网母线，所述微电网母线通过并网开关连接外部电网；
    所述方法包括：
    在检测到电网发生故障的情况下，控制所述功率变换器处于第一电流源控制模式，其中，所述电网包括所述外部电网或者所述微电网母线所在的微电网系统，所述第一电流源控制模式为电流源故障穿越控制模式；
    在所述电网故障的持续时长达到第一时长后，控制所述功率变换器从所述第一电流源控制模式切换至第一电压源控制模式，其中，所述第一电压源控制模式为电压源故障穿越控制模式，所述第一时长小于第二时长，所述第二时长为所述电网发生故障的时刻至所述并网开关断开的时刻之间的时间间隔。
  27. 根据权利要求26所述的方法，其特征在于，在所述第一电流源控制模式下所述功率变换器基于所述电网发生故障时所述微电网母线的电压跌落值，控制所述功率变换器的输出电压，在所述第一电压源控制模式下所述功率变换器基于预设电流幅值范围中的最大预设电流幅值控制所述功率变换器的输出电压。
  28. 根据权利要求27所述的方法，其特征在于，所述基于所述电网发生故障时所述微电网母线的电压跌落值，控制所述功率变换器的输出电压，包括：
    根据所述电网发生故障时所述微电网母线的电压跌落值获得第一参考输出电流值，根据所述第一参考输出电流值和第一参考角频率值获得第一参考输出调制电压值；
    基于所述第一参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第 一电流源控制模式。
  29. 根据权利要求27或28所述的方法，其特征在于，所述基于基于预设电流幅值范围中的最大预设电流幅值，控制所述功率变换器的输出电压，包括：
    基于所述最大预设电流幅值和所述外部电网的等效阻抗角获得第二参考输出电流值，基于所述第二参考输出电流值和第二参考角频率值获得第二参考输出调制电压值；
    基于所述第二参考输出调制电压值控制所述功率变换器的输出电压，以使所述功率变换器处于所述第一电压源控制模式。
  30. 根据权利要求27所述的方法，其特征在于，所述功率变换器处于所述第一电压源控制模式下的初始参考输出电流值和初始参考角频率值分别为切换瞬间所述功率变换器处于所述第一电流源控制模式下的第一参考输出电流值和第一参考角频率值。
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