JP2017123706A - Power conversion device and control method thereof - Google Patents

Abstract

A power conversion device capable of continuing operation even when a short-time unbalance accident occurs and a control method therefor are provided. According to an embodiment, a power conversion device including first and second converters and a control unit is provided. The first converter includes a plurality of switching elements connected in a bridge and a plurality of rectifying elements connected in antiparallel to each switching element, and the first three-phase input by switching of each switching element Converts AC voltage to DC voltage. The second converter converts the DC voltage into a second three-phase AC voltage. The control unit detects the phase of the first three-phase AC voltage, controls each switching element by a fixed pulse pattern method with a modulation rate of 1.2 or more based on the phase, and the angular velocity of the first three-phase AC voltage. When the deviation between the angular velocity and the reference value is a certain value or more, each switching element is turned off. [Selection] Figure 1

Description

  Embodiments described herein relate generally to a power conversion device and a control method thereof.

  There is a power conversion device including a voltage source converter that converts AC power into DC power, and an inverter that converts the DC power into AC power having a desired frequency and voltage and supplies the AC power to a load such as an electric motor. Such a power converter is used in, for example, a rolling plant.

  In a rolling plant, the load current of a power converter for a rolling mill is large. For this reason, if the control of the converter is continued when an unbalanced accident such as a short 1-wire ground fault or a 2-wire short-circuit occurs, the phase information of the power supply will be shifted, and the converter will have a DC overload in a short time. It may lead to current failure.

  On the other hand, when the short-time AC power supply abnormality occurs, if the control of the converter is stopped and simultaneously the output of the electric motor that is the load of the inverter is suppressed, the rolling mill stalls and rolling cannot be continued. In order to continue rolling, a power conversion device that does not restrict the output of the inverter is required even when the control of the converter is stopped for a short time.

  For example, in Patent Document 1, when the DC voltage output from the converter is lower than the lower limit value, the switching element of the converter is turned off and switched to diode rectification. When the converter is in a power running operation, the output power of the load motor is set to zero so that the DC voltage does not drop. When the load of the electric motor is a rolling mill, a reduction in the output of the electric motor leads to a stall of the rolling mill. Therefore, the operation cannot be continued.

  For this reason, in a power converter, it is desired to be able to continue operation even when an unbalanced accident such as a short 1-wire ground fault or a 2-wire short-circuit occurs.

Japanese Patent No. 3158212

  Embodiments of the present invention provide a power converter that can continue operation even when an unbalanced accident such as a short-circuit 1-wire ground fault or 2-wire short-circuit occurs, and a control method thereof.

  According to the embodiment of the present invention, a power converter including a first converter, a plurality of smoothing capacitors, a second converter, a voltmeter, and a control unit is provided. The first converter includes a plurality of bridge-connected switching elements, a plurality of rectifying elements connected in antiparallel to the plurality of switching elements, three AC terminals, and at least three DC terminals, And the first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of a positive potential, a negative potential, and a neutral point potential by switching of the plurality of switching elements. The DC voltage is output from the at least three DC terminals. The plurality of smoothing capacitors are provided between each of the at least three DC terminals. The second converter is connected to the at least three DC terminals and connected to an AC load, converts the DC voltage to a second three-phase AC voltage corresponding to the AC load, and the second three-phase An alternating voltage is supplied to the alternating load. The voltmeter detects a voltage value of each phase of the first three-phase AC voltage. The control unit detects a phase of each phase of the first three-phase AC voltage based on a detection result of the voltmeter, and a line voltage of the first three-phase AC voltage based on the detected phase. And switching of the plurality of switching elements of the first converter is controlled by a fixed pulse pattern method in which a modulation rate between the DC voltage and the DC voltage is 1.2 or more, and the first phase is determined based on the detected phase. (1) The angular velocity of each phase of the three-phase AC voltage is detected, and when the deviation between the detected angular velocity and the angular velocity reference value is a predetermined value or more, the plurality of switching elements are turned off.

  Provided are a power conversion device and a control method thereof that can continue operation even when an unbalanced accident such as a short-time 1-wire ground fault or 2-wire short-circuit occurs.

It is a block diagram showing typically the power converter concerning a 1st embodiment. It is a block diagram showing typically the converter concerning a 1st embodiment. It is a graph showing an example of the pulse pattern concerning a 1st embodiment. It is a flowchart which represents typically operation | movement of the power converter device which concerns on 1st Embodiment. It is a block diagram showing typically the power converter concerning a 2nd embodiment. It is a flowchart which represents typically the operation | movement of the power converter device which concerns on 2nd Embodiment.

Each embodiment will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
Note that, in the present specification and each drawing, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

(First embodiment)
FIG. 1 is a block diagram schematically illustrating the power conversion apparatus according to the first embodiment.
As shown in FIG. 1, the power conversion device 10 includes a first converter 11, a second converter 12, a pair of smoothing capacitors 13 and 14, a control unit 15, a voltmeter 16, and an ammeter 17. And comprising.

  The first converter 11 has three AC terminals 11r, 11s, and 11t, and at least three DC terminals 11p, 11n, and 11c. Each AC terminal 11r, 11s, 11t is connected to the AC power source 2 via the transformer 4. The AC power source 2 is a three-phase AC power source. Each AC terminal 11r, 11s, 11t is connected to each phase of the three-phase AC voltage of the AC power supply 2. As a result, a three-phase AC voltage is input to the first converter 11 via the AC terminals 11r, 11s, and 11t. The transformer 4 may be provided in the power conversion device 10 or may be provided separately from the power conversion device 10.

  The first converter 11 converts the input three-phase AC voltage (first three-phase AC voltage) into a DC voltage having at least three levels of a positive potential P, a negative potential N, and a neutral point potential C. In this example, a case where a three-phase AC voltage is converted into the above three levels will be described. Hereinafter, the DC terminals 11p, 11n, and 11c are referred to as a positive potential terminal 11p, a negative potential terminal 11n, and a neutral point terminal 11c, respectively. The first converter 11 may convert a three-phase AC voltage into a DC voltage having a greater number of levels without being limited to three levels. In this case, the number of DC terminals may be four or more.

  The first converter 11 sets the positive potential terminal 11p to the positive potential P, sets the negative potential terminal 11n to the negative potential N, and sets the neutral point terminal 11c to the neutral point potential C. The neutral point potential C is an intermediate potential between the positive potential P and the negative potential N. Thus, the first converter 11 generates the DC voltage Vd between the positive potential terminal 11p and the neutral point terminal 11c and between the neutral point terminal 11c and the negative potential terminal 11n. Therefore, the voltage between the positive potential terminal 11p and the negative potential terminal 11n is 2Vd.

  The smoothing capacitor 13 is provided between the positive potential terminal 11p and the neutral point terminal 11c. The smoothing capacitor 13 is electrically connected between the positive potential terminal 11p and the neutral point terminal 11c. The smoothing capacitor 14 is provided between the neutral point terminal 11c and the negative potential terminal 11n. The smoothing capacitor 14 is electrically connected between the neutral point terminal 11c and the negative potential terminal 11n. Smoothing capacitors 13 and 14 smooth the DC voltage Vd. When the first converter 11 is provided with four or more DC terminals, the smoothing capacitor is provided between the DC terminals. A plurality of smoothing capacitors are provided according to the number of DC terminals.

  The second converter 12 is connected to the DC terminals 11p, 11n, and 11c, and is connected to the induction motor 6. The induction motor 6 is a three-phase induction motor. The second converter 12 converts the DC voltage input from the first converter 11 into a three-phase AC voltage (second three-phase AC voltage) having a desired frequency and voltage value according to the induction motor 6, and A three-phase AC voltage is supplied to the induction motor 6. Thereby, the second converter 12 drives the induction motor 6.

  As described above, the power conversion device 10 performs the power running operation of the induction motor 6. The first converter 11 is a three-level voltage source converter. The second converter 12 is a voltage-type inverter. Moreover, the power converter device 10 converts the three-phase AC voltage generated by the induction motor 6 into a three-phase AC voltage corresponding to the AC power source 2, and supplies the converted three-phase AC voltage to the power supply system. That is, the power conversion device 10 can also perform the regenerative operation of the induction motor 6. In this case, the first converter 11 functions as an inverter, and the second converter 12 functions as a converter. The AC load to which the second converter 12 supplies the three-phase AC voltage is not limited to the induction motor 6 and may be another AC load. In addition to operating the induction motor 6, the power conversion device 10 also operates, for example, a synchronous motor.

  The voltmeter 16 detects the voltage value of each phase of the three-phase AC of the AC power supply 2. The voltmeter 16 inputs the detected voltage value of each phase to the control unit 15. The ammeter 17 detects the current value of each phase of the three-phase AC of the AC power supply 2. The ammeter 17 inputs the detected current value of each phase to the control unit 15.

  The control unit 15 controls the operations of the first converter 11 and the second converter 12 based on the detection results of the voltmeter 16 and the ammeter 17. The control unit 15 controls the conversion from the three-phase AC voltage to the DC voltage by the first converter 11. The control unit 15 controls the conversion from the DC voltage to the three-phase AC voltage by the second converter 12. The operation of the second converter 12 may be controlled by a control unit different from the control unit 15.

FIG. 2 is a block diagram schematically illustrating the converter according to the first embodiment.
As illustrated in FIG. 2, the first converter 11 includes a plurality of switching elements 21 that are bridge-connected and a plurality of rectifying elements 22 that are connected in antiparallel to each of the switching elements 21. In this example, the first converter 11 further includes a plurality of rectifying elements 23.

  The switching element 21 has a pair of main terminals and a control terminal. The control terminal is used for switching between an on state in which a current flows between the main terminals and an off state in which no current substantially flows between the main terminals. As the switching element 21, for example, a self-extinguishing element such as a GTO (Gate Turn Off thyristor) or an IGBT (Insulated Gate Bipolar Transistor) is used. The control terminal is, for example, a gate terminal.

  The first converter 11 is a three-phase bridge type and has six arms AR, AS, AT, AX, AY, and AZ. The configurations of the phase arms AR, AS, AT, AX, AY, and AZ connected to the AC terminals 11r, 11s, and 11t are substantially the same. Therefore, here, the two arms AR and AX connected to the AC terminal 11r (R phase) will be described as an example.

  The positive-side arm AR includes two switching elements SR1 and SR2 connected in series, rectifying elements DR1 and DR2 connected in antiparallel to each of these switching elements SR1 and SR2, and a series of switching elements SR1 and SR2. And a rectifying element DR3 connected between the connection point and the neutral point terminal 11c.

  Similarly, the negative arm AX includes two switching elements SX1, SX2 connected in series, rectifying elements DX1, DX2 connected in antiparallel to each of these switching elements SX1, SX2, and each switching element SX1, And a rectifying element DX3 connected between the series connection point of SX2 and the neutral point terminal 11c.

  Both arms AR and AX are connected in series between a positive potential terminal 11p and a negative potential terminal 11n, and a series connection point of both arms AR and AX is connected to an R-phase AC terminal 11r. The potential at the series connection point of the switching elements SR1 and SR2 is clamped to the neutral point potential C via the rectifying element DR3. Similarly, the potential at the series connection point of the switching elements SX1 and SX2 is clamped to the neutral point potential C via the rectifying element DX3. The rectifying elements DR1, DR2, DX1, DX2 (each rectifying element 22) are so-called free-wheeling diodes. The rectifying elements DR3 and DX3 (each rectifying element 23) are so-called clamp diodes.

  The configuration of the arms AS and AT is substantially the same as the configuration of the arm AR. The configuration of the arms AY and AZ is substantially the same as the configuration of the arm AX. Thereby, the potential of the AC terminals 11r, 11s, and 11t is clamped to any one of the three levels of the positive potential terminal 11p, the negative potential terminal 11n, and the neutral point terminal 11c in accordance with the switching of each switching element 21. Is done.

  Since the configuration of the second converter 12 is substantially the same as the configuration of the first converter 11, detailed description thereof is omitted. In the second converter 12, the side connected to each of the smoothing capacitors 13 and 14 is a direct current side (corresponding to the positive potential terminal 11p, the negative potential terminal 11n, and the neutral point terminal 11c), and the side connected to the induction motor 6 is On the AC side (corresponding to AC terminals 11r, 11s, 11t) The control unit 15 controls the conversion from the DC voltage to the three-phase AC voltage by the second converter 12 by controlling the switching of each switching element of the second converter 12.

  The control unit 15 includes a phase detector 30, an effective / ineffective current detector 32, and a gate control unit 34. The detection result of the voltmeter 16 is input to the phase detector 30. The phase detector 30 detects the phase of each phase of the three-phase AC voltage of the AC power supply 2 based on the detection result of the voltmeter 16.

  Further, the phase detector 30 detects the angular velocity of each phase of the three-phase AC voltage of the AC power supply 2 based on the detected amount of change per unit time of the phase. In other words, the phase detector 30 detects the frequency of each phase of the three-phase AC voltage of the AC power supply 2. The phase detector 30 inputs the detected phase information and angular velocity information of each phase to the gate control unit 34.

  The detection result of the voltmeter 16 and the detection result of the ammeter 17 are input to the effective / ineffective current detector 32. The effective / ineffective current detector 32 is based on the detection results of the input voltmeter 16 and ammeter 17 and the effective current Ip and the ineffective current supplied to the first converter 11 from the AC power supply 2 side. The current Iq is calculated. The effective / ineffective current detector 32 inputs the calculated effective current Ip and reactive current Iq to the gate control unit 34.

  The gate control unit 34 generates a control signal (for example, a gate signal) for controlling switching of each switching element 21 of the first converter 11 by a fixed pulse pattern method. The gate control unit 34 inputs the generated control signals to the control terminals of the switching elements 21. Accordingly, the gate control unit 34 switches on / off of each switching element 21 and controls the operation of the first converter 11.

  The fixed pulse pattern method is a method of continuously generating the same pulse pattern every cycle. The basic frequency of the pulse pattern is synchronized with the frequency of the AC power supply 2. The gate control unit 34 synchronizes the fundamental frequency of the pulse pattern with the frequency of the AC power supply 2 based on the phase information detected by the phase detector 30. The fixed pulse pattern method is described in detail in, for example, Japanese Patent No. 3630621, Japanese Patent No. 4015795, Japanese Patent No. 5411031, and the like.

  Further, the gate control unit 34 sets the deviation between the effective current Ip and the reactive current Iq to zero based on the effective current Ip and the reactive current Iq detected by the effective / reactive current detector 32, for example. A phase correction amount for calculating the phase is calculated. Then, the gate control unit 34 generates a pulse pattern whose phase is shifted from the phase of the AC power supply 2 by the correction amount. Note that the phase of the pulse pattern may be determined only by the phase information of the phase detector 30.

FIG. 3 is a graph showing an example of a pulse pattern according to the first embodiment.
FIG. 3 is an example of the control signals GR1, GR2, GX1, GX2 and the R-phase voltage waveform Vsr input to the R-phase switching elements SR1, SR2, SX1, SX2. As shown in FIG. 3, the waveform of the ¼ period of the pulse pattern is symmetrical with respect to 90 °. The positive and negative pulses for the three-level converter are vertically symmetrical. Furthermore, the pulse patterns of the three phases are the same pulse patterns that are shifted from each other by 120 °. Therefore, if a ¼ period pulse pattern is determined, all pulse patterns are determined. Although FIG. 3 illustrates the case of 3 pulses per half cycle of the AC power supply, the number of pulses may be arbitrary.

The gate control unit 34 sets the modulation rate between the line voltage of the AC power supply 2 and the positive or negative DC voltage Vd to 1.2 or more in the control of the fixed pulse pattern method. When the modulation factor is m and the line voltage of the AC power supply 2 is Va, the modulation factor m can be obtained by the following equation (1).
m = (√2 / √3) Va / Vd (1)
That is, the DC voltage Vd is made smaller than the line voltage Va. Thereby, the modulation factor m can be 1.2 or more.

That is, with respect to the line voltage Va, the DC voltage Vd is made smaller than the value of the following expression (1A). Thereby, the modulation factor m can be 1.2 or more.
Vd = (√2 / √3 / 1.2) Va (1A)

  The modulation factor m can be changed, for example, by adjusting the timing of the pulse P1 in FIG. If the timing of the pulse P1 is delayed, the central pulse width decreases, and the modulation factor m decreases accordingly. Conversely, if the timing of the pulse P1 is advanced, the central pulse width increases and the modulation factor m also increases. Thereby, the modulation factor m can be set arbitrarily. Further, the gate control unit 34 sets the modulation rate m to 1.5 or less, for example.

  When the power control operation of the induction motor 6 is performed, the gate control unit 34 determines whether the deviation between the detected angular velocity and the angular velocity reference value is equal to or greater than a certain value based on the angular velocity information input from the phase detector 30. Determine whether. The gate control unit 34 performs the above determination for each phase of the three-phase AC voltage. The angular velocity reference value is determined according to the frequency of the AC power supply 2, for example. For example, when the frequency of the AC power supply 2 is 50 (Hz), the angular velocity reference value is 100π (rad / s). The gate control unit 34 determines, for example, by setting ± 10% of the angular velocity reference value as a constant value. For example, when the frequency of the AC power supply 2 is 50 (Hz), the gate control unit 34 is equal to or greater than a certain value when the deviation between the detected angular velocity and the angular velocity reference value is ± 10π (rad / s) or more. Is determined.

  When the gate control unit 34 determines that each phase is less than a certain value, as described above, the switching of each switching element 21 of the first converter 11 is performed in a fixed pulse pattern method with a modulation rate of 1.2 or more. To control.

  On the other hand, if the gate control unit 34 determines that at least one of the phases is equal to or greater than a certain value, the gate control unit 34 turns off the switching elements 21 of the first converter 11. The gate control unit 34 generates a control signal for turning off each switching element 21 and inputs the control signal to the control terminal of each switching element 21 to turn off each of the switching elements 21. Thereby, the gate control unit 34 operates the first converter 11 using the first converter 11 as a diode converter by the rectifying elements 22.

  As described above, the gate control unit 34 includes a converter mode in which the first converter 11 is operated as a voltage source converter by a fixed pulse pattern method having a modulation rate of 1.2 or more, and a diode in which the first converter 11 is operated as a diode converter. And a rectification mode.

  When the gate control unit 34 determines that the deviation is equal to or greater than a certain value and then returns to a state less than the certain value, the operation of the first converter 11 is returned from the diode rectification mode to the converter mode. That is, the gate control unit 34 restarts control of the plurality of switching elements 21 by the fixed pulse pattern method when the deviation returns to a state below a certain value after turning off the plurality of switching elements 21.

FIG. 4 is a flowchart schematically showing the operation of the power conversion device according to the first embodiment.
FIG. 4 schematically shows an operation when the induction motor 6 is in a power running operation.
As shown in FIG. 4, in the power conversion device 10, when performing the power running operation of the induction motor 6, the gate control unit 34 of the control unit 15 performs the first converter with a fixed pulse pattern method with a modulation factor of 1.2 or more. The switching of each of the 11 switching elements 21 is controlled, and the first converter 11 is operated in the converter mode. Thereby, the gate control unit 34 converts the three-phase AC voltage of the AC power supply 2 into a DC voltage. In addition, the control unit 15 controls the operation of the second converter 12 and converts the DC voltage output from the first converter 11 into a three-phase AC voltage corresponding to the induction motor 6. The second converter 12 supplies the converted three-phase AC voltage to the induction motor 6. Thereby, the induction motor 6 is power-run.

  When powering the induction motor 6, the gate control unit 34 controls the operation of the first converter 11, and the deviation between the detected angular velocity and the angular velocity reference value is determined for each phase of the three-phase AC voltage. It is determined whether or not it is a certain value or more.

  If the gate control unit 34 determines that each phase is less than a certain value, the gate control unit 34 continues the operation of the first converter 11 in the converter mode.

  On the other hand, if the gate control unit 34 determines that at least one of the phases is equal to or greater than a certain value, the gate control unit 34 turns off each switching element 21 and switches the operation of the first converter 11 from the converter mode to the diode rectification mode. .

  When it is determined that the deviation between the detected angular velocity and the angular velocity reference value is greater than or equal to a certain value in one or two phases of the three-phase AC voltage of the AC power source 2, an unbalanced accident occurs in the AC power source 2 it seems to do. When an unbalanced accident occurs in the AC power supply 2, there is a possibility that the phase detection by the phase detector 30 is shifted. For this reason, if the first converter 11 is continuously operated in the converter mode at the time of an unbalanced accident, the first converter 11 and the second converter 12 may fail due to a direct current overcurrent.

  Further, the modulation factor m when the first converter 11 is operated in the diode rectification mode is, for example, about 1.21. For this reason, when the difference between the modulation factor m in the converter mode and the modulation factor m in the diode rectification mode is large, the DC voltage may become excessively large when the first converter 11 is switched to the diode rectification mode. Or get smaller.

  For example, if the modulation factor m in the converter mode is smaller than 1.2, when the first converter 11 is switched to the diode rectification mode, the DC voltage Vd becomes small and the power running operation of the induction motor 6 can be continued. It becomes impossible. For example, when the first converter 11 is operated by PWM control, it is considered that the modulation factor m is maximized during so-called two-phase modulation in which one of the three phases is kept on for a period of 120 °. The modulation factor m at this time is 1.15, which is smaller than 1.2.

  On the contrary, if the modulation factor m in the converter mode is larger than 1.5, the DC voltage Vd increases when the first converter 11 is switched to the diode rectification mode, and the first converter 11 and the second converter. There are concerns about 12 failures.

  In the power conversion device 10 according to the present embodiment, the first converter 11 is operated in a converter mode by a fixed pulse pattern method having a modulation rate of 1.2 or more. Thereby, the fluctuation | variation of the DC voltage Vd when the 1st converter 11 is switched to the diode rectification mode can be suppressed. Therefore, in the power converter 10, even when a short-time imbalance accident occurs, the power running operation of the induction motor 6 can be continued by switching the first converter 11 to the diode rectification mode.

  Moreover, in the power converter device 10 which concerns on this embodiment, the modulation factor m at the time of a converter mode shall be 1.5 or less. Thereby, the fluctuation | variation of DC voltage Vd when the 1st converter 11 is switched to the diode rectification mode can be suppressed more appropriately. When the DC voltage Vd in the converter mode is made larger than the DC voltage Vd in the diode rectification mode, the modulation factor m is, for example, 1.2 or more and less than 1.35.

  After switching the first converter 11 to the diode rectification mode, the gate control unit 34 determines whether or not the deviation between the detected angular velocity and the angular velocity reference value has returned to a state below a certain value. When the gate control unit 34 opposes returning to a state of less than a certain value, the operation of the first converter 11 is returned from the diode rectification mode to the converter mode.

  Further, the control unit 15 determines whether or not a predetermined time has elapsed from the switching timing to the diode rectification mode after switching the first converter 11 to the diode rectification mode. If the unbalance accident has continued for a predetermined time or more, it is considered that an abnormality has occurred in the AC power supply 2. Therefore, if the control unit 15 determines that the predetermined time has elapsed, that is, if the state where the deviation is equal to or greater than a predetermined value is continued for the predetermined time, the operation of the second converter 12 is stopped and the power running operation of the induction motor 6 is performed. To stop. Thereby, the power converter device 10, the induction motor 6, etc. can be protected from abnormality of the alternating current power supply 2, for example.

(Second Embodiment)
FIG. 5 is a block diagram schematically illustrating the power conversion apparatus according to the second embodiment.
As shown in FIG. 5, the control unit 15 of the power conversion device 110 further includes a voltage detector 36. Note that substantially the same functions and configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The detection result of the voltmeter 16 is input to the voltage detector 36. Based on the detection result of the voltmeter 16, the voltage detector 36 detects a decrease of the three-phase AC voltage of the AC power supply 2 by a certain value or more. The voltage detected by the voltage detector 36 may be a phase voltage of each phase of the three-phase AC voltage, or may be a line voltage of each phase of the three-phase AC voltage. The voltage threshold is, for example, 20% to 30% of the rated voltage of the three-phase AC voltage of the AC power supply 2. For example, when one of the three-phase AC voltages of the AC power supply 2 becomes 20% or less of the rated voltage, the voltage detector 36 detects a decrease of a certain value or more. When the voltage detector 36 detects a decrease in the three-phase AC voltage above a certain value, the voltage detector 36 inputs a voltage decrease detection signal indicating detection of the voltage decrease to the gate control unit 34.

FIG. 6 is a flowchart schematically showing the operation of the power conversion device according to the second embodiment.
As shown in FIG. 6, the gate control unit 34 has detected the voltage drop by the voltage detector 36 in a state where the first converter 11 is operated in the converter mode and the induction motor 6 is in the power running operation. In this case, each switching element 21 is turned off, and the first converter 11 is switched from the converter mode to the diode rectification mode. That is, in this example, the gate control unit 34 determines that an unbalanced accident has occurred in the AC power supply 2 when any one of the three-phase AC voltages of the AC power supply 2 has dropped by a certain value or more.

  When the voltage detector 36 detects a decrease in the three-phase AC voltage and then returns to a state where the three-phase AC voltage is greater than a certain value, the gate controller 34 changes the operation of the first converter 11 in the diode rectification mode. To return to converter mode. That is, the gate control unit 34 turns off the plurality of switching elements 21 and then switches the plurality of switching elements by the fixed pulse pattern method when the three-phase AC voltage of the AC power supply 2 returns to a state larger than a certain value. 21 control is resumed. Further, when a predetermined time has elapsed since switching to the diode rectification mode, the control unit 15 stops the operation of the second converter 12 and stops the power running operation of the induction motor 6.

  Depending on the condition of the unbalanced accident of the AC power supply 2, the abnormality may be detected by the voltage detector 36 before the abnormality is detected by the phase detector 30. Therefore, in the power converter 110 according to the present embodiment, when a voltage drop is detected during the power running operation, the first converter 11 is switched from the converter mode to the diode rectification mode. Thereby, for example, an unbalanced accident of the AC power supply 2 can be detected more appropriately. For example, failures such as the first converter 11 and the second converter 12 associated with an unbalanced accident of the AC power supply 2 can be more appropriately suppressed.

  Thus, in this example, during the power running operation of the induction motor 6, the AC power source 2 is not activated by at least one of the angular velocity based on the detection result of the phase detector 30 and the voltage based on the detection result of the voltage detector 36. Detect equilibrium accidents. The detection of the unbalanced accident of the AC power supply 2 may be performed only by the angular velocity as shown in the first embodiment, or may be performed only by the voltage as shown in FIG.

  Although the modulation factor is 1.2 or more in the above, if the current rating of the first converter 11 has a margin, the required electric energy can be increased by increasing the current against the decrease in the DC voltage Vd. The second converter 12 can be supplied. In other words, even when the modulation factor is less than 1.2, the current rating of the first converter 11 can have a reciprocal margin of the degree of decrease in the DC voltage Vd when the first converter 11 is in the diode rectification mode. Thus, the present invention can be implemented.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 2 ... AC power source, 4 ... Transformer, 6 ... Induction motor, 10, 110 ... Power converter, 11 ... 1st converter, 12 ... 2nd converter, 13, 14 ... Smoothing capacitor, 15 ... Control unit, 16 Voltmeter, 17 ... ammeter, 21 ... switching element, 22 ... rectifier element, 23 ... rectifier element, 30 ... phase detector, 32 ... active / ineffective current detector, 34 ... gate controller, 36 ... voltage Detector

Claims (7)

A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in antiparallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals. By switching the switching element, the first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of a positive potential, a negative potential, and a neutral point potential, and the DC voltage is converted into the DC voltage. A first converter that outputs from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
Connected to the at least three DC terminals and connected to an AC load, converts the DC voltage into a second three-phase AC voltage corresponding to the AC load, and converts the second three-phase AC voltage to the AC load. A second converter to supply;
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
The phase of each phase of the first three-phase AC voltage is detected based on the detection result of the voltmeter, and the line voltage of the first three-phase AC voltage and the DC voltage are detected based on the detected phase. And controlling the switching of the plurality of switching elements of the first converter by a fixed pulse pattern method in which the modulation rate of the first converter is 1.2 or more, and based on the detected phase, the first three-phase AC voltage A control unit that detects the angular velocities of each of the phases and turns off the plurality of switching elements when a deviation between the detected angular velocities and the angular velocity reference value is a certain value or more;
The power converter provided with.   The control unit restarts control of the plurality of switching elements by the fixed pulse pattern method when the deviation returns to a state below the predetermined value after turning off the plurality of switching elements. 1. The power conversion device according to 1.   3. The power conversion device according to claim 1, wherein the control unit turns off the plurality of switching elements when the first three-phase AC voltage detected by the voltmeter decreases by a certain value or more.   When the first three-phase AC voltage is returned to a state greater than the constant value after turning off the plurality of switching elements, the control unit is configured to switch the plurality of switching elements according to the fixed pulse pattern method. The power converter according to claim 3 which resumes control. A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in antiparallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals. By switching the switching element, the first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of a positive potential, a negative potential, and a neutral point potential, and the DC voltage is converted into the DC voltage. A first converter that outputs from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
Connected to the at least three DC terminals and connected to an AC load, converts the DC voltage into a second three-phase AC voltage corresponding to the AC load, and converts the second three-phase AC voltage to the AC load. A second converter to supply;
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
The phase of each phase of the first three-phase AC voltage is detected based on the detection result of the voltmeter, and the line voltage of the first three-phase AC voltage and the DC voltage are detected based on the detected phase. The switching of the plurality of switching elements of the first converter is controlled by a fixed pulse pattern method with a modulation rate of 1.2 or more, and the first three-phase AC voltage detected by the voltmeter is constant. A control unit that turns off the plurality of switching elements when the value is reduced by more than a value;
The power converter provided with. A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in antiparallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals. By switching the switching element, the first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of a positive potential, a negative potential, and a neutral point potential, and the DC voltage is converted into the DC voltage. A first converter that outputs from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
Connected to the at least three DC terminals and connected to an AC load, converts the DC voltage into a second three-phase AC voltage corresponding to the AC load, and converts the second three-phase AC voltage to the AC load. A second converter to supply;
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
A method for controlling a power conversion device comprising:
Detecting the phase of each phase of the first three-phase AC voltage based on the detection result of the voltmeter;
Based on the detected phase, the fixed pulse pattern method in which the modulation rate between the line voltage of the first three-phase AC voltage and the DC voltage is 1.2 or more, the plurality of the first converters Controlling the switching of the switching element;
Detecting an angular velocity of each phase of the first three-phase AC voltage based on the detected phase;
A step of turning off the plurality of switching elements when a deviation between the detected angular velocity and an angular velocity reference value is a certain value or more;
A control method for a power conversion device having A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in antiparallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals. By switching the switching element, the first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of a positive potential, a negative potential, and a neutral point potential, and the DC voltage is converted into the DC voltage. A first converter that outputs from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
Connected to the at least three DC terminals and connected to an AC load, converts the DC voltage into a second three-phase AC voltage corresponding to the AC load, and converts the second three-phase AC voltage to the AC load. A second converter to supply;
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
A method for controlling a power conversion device comprising:
Detecting the phase of each phase of the first three-phase AC voltage based on the detection result of the voltmeter;
Based on the detected phase, the fixed pulse pattern method in which the modulation rate between the line voltage of the first three-phase AC voltage and the DC voltage is 1.2 or more, the plurality of the first converters Controlling the switching of the switching element;
A step of turning off the plurality of switching elements when the first three-phase AC voltage detected by the voltmeter has decreased by a certain value or more;
A control method for a power conversion device having

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