JPH0965660A - Method for controlling system interconnection inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a DC overvoltage which is generated when active power flows in during the transitional period of the interconnection of an inverter to a power system by setting a mode in which active power is outputted from the inverter during the transitional period by advancing the phase of the output voltage of the inverter when the inverter is interconnected to a power system by a specific amount against a system voltage. SOLUTION: A multiplier 12 generates an control signal VE which controls the active power of an inverter by multiplying the sum signal gE(gE or gE+gC) of the output signal gE of a DC voltage control circuit 11 and a phase bias signal GC by a phase signal VS obtained by delaying the phase of a system voltage VS by 90 deg. by means of a phase shifter 13. Since the phase bias signal g. is added. the inverter always operates from a state where the inverter is advanced from the output voltage VS of the inverter at the interconnecting time when the inverter is interconnected to a power system. Therefore, the generation of a DC overvoltage from the inverter is prevented during the transitional period of the interconnection, because the inverter is set to a mode in which the inverter outputs active power and suppresses the flowing in of active power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for a grid-connected inverter used in a self-excited reactive power compensator, an active filter, a distributed power source, etc.

[0002]

2. Description of the Related Art An example of a main circuit of a grid-connected inverter used in a self-excited reactive power compensator for suppressing voltage fluctuations due to load fluctuations of a power system will be described with reference to FIG. An inverter DC power supply unit 5 is provided on the DC side. The inverter DC power supply unit 5 is a rectification circuit for initial charging and a distributed power supply circuit for solar cells. In FIG. 2, the AC voltage of the auxiliary power supply 9 is rectified only when the switch 8 is closed, and the DC capacitor 6 is rated. An initial charging rectifier circuit 7 is shown which charges the inverter DC voltage E _D. The inverter 4 is
The power system having the system power supply 1 is interconnected via the interconnection breaker 3 as follows.

When the circuit breaker 3 is opened and the switch 8 is closed, the DC capacitor 6 is charged by the rectifier circuit 7 and the rated inverter DC voltage E _D is established, the inverter 4 is started and the inverter output voltage When V _I has the same phase and the same amplitude as the system voltage V _S , the circuit breaker 3 is closed to establish interconnection. After this interconnection, the switch 8 is opened, and the active power P determined by the inverter output voltage V _I and the inverter current I
Flows into the inverter 4, the inverter DC voltage E _D is controlled to the rated value, and the inverter internal power loss is replenished.

That is, the system impedance 2 of the power system
(Resistance R and reactance jX), R << j
In relation to X, the active power P flowing into the inverter 4 is controlled by adjusting the voltage ΔV having a 90 ° phase difference with respect to the system voltage V _S by the inverter output voltage V _I.
The inverter DC voltage E _D is adjusted to the rating. Here, if the phase difference between the system voltage V _S and the inverter output voltage V _I is θ, the relationship of I∝P∝θ∝ΔV is maintained, and the active power P is controlled by the phase adjustment. The DC voltage E _D is adjusted.

FIG. 3 for adjusting the inverter DC voltage E _D
The control system of FIG. 1 starts controlling the inverter DC voltage E _{D after} the circuit breaker 3 is turned on and the inverter 4 is system-interconnected. The error signal between the inverter DC voltage E _D and its DC voltage command signal E _D ^REF is obtained by the subtractor 10, and this error signal is calculated by the DC voltage control circuit 1
Enter 1 The DC voltage control circuit 11 controls so that the input error signal becomes small, and outputs the amplitude adjustment output signal g _E corresponding to the input to the multiplier 12. on the other hand,
The phase signal V _S ′ obtained by delaying the phase of the system voltage V _S by 90 ° by the 90 ° phase shifter 13 is input to the multiplier 12, and the inverter active power control signal V whose amplitude is adjusted by the amplitude adjustment output signal g _E. We obtain _E [V _E = g _E V _S ']. The inverter active power control signal V _E corresponds to the voltage ΔV for adjusting the phase difference θ.

Thus, the inverter active power control signal V _E
And the system voltage V _S and the voltage signal V _C for obtaining the inverter output current are added by the adder 15 to obtain the inverter output voltage command signal V _I ^REF . The voltage signal V _C is a signal of V _C = (R + jX) I ^REF obtained by converting the inverter current command signal I ^REF into voltage by the voltage signal conversion circuit 14. The inverter output voltage command signal V _I ^REF from the adder 15 is output to a PWM circuit (pulse width modulation circuit) not shown, and the inverter 4 is activated.

In the above inverter control, the inverter DC voltage E _D falls below the rated value and the DC voltage command signal E _D
^When the error with ^REF increases, the inverter active power control signal V _E increases in accordance with the error, and the active power P flowing into the inverter 4 increases. The result is DC voltage E _D
Is reflected in the increase of ED and is finally feedback-controlled so that E _D = E _D ^REF .

[0008]

When the circuit breaker 3 is turned on to connect the inverter 4 to the system, the inverter output voltage V _I and the system voltage V _S are in phase with each other. The inverter output voltage V _I and the inverter output voltage command signal V _I ^REF do not match due to the on / off operation shift of the switching element of the above, and the phase of the inverter output voltage V _I may be slightly behind the phase of the system voltage V _S. . If the inverter 4 is grid-connected at the stage where there is such a phase error, the inverter output voltage V will be changed during the transition period until the DC voltage control circuit 11 enters the steady state and the feedback control of E _D = E _D ^REF works. _I and system voltage V _S
The active power due to the phase difference of 1 may flow into the inverter 4, causing a problem that the DC side of the inverter 4 is brought into an overvoltage state.

That is, when active power flows into the inverter 4 during the transition period during interconnection, the active power that has flowed in is cut off by the rectifier circuit 7 to charge up the DC capacitor 6, resulting in inverter DC. The DC overvoltage state in which the voltage E _D rises abnormally causes the overvoltage protection relay to operate, which may cause a device failure such as a reactive power compensator. There was a problem.

Therefore, the object of the present invention is to
It is an object of the present invention to provide a control method for always stabilizing and interconnecting a grid interconnection inverter.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a grid-connected inverter for AC-converting a rated inverter DC voltage provided by an inverter DC power supply unit such as an initial charging rectifier circuit. In order to prevent the delay in the system voltage phase, a manually adjustable phase bias signal that advances the inverter output voltage phase from the system voltage before the interconnection is added to the output signal of the DC voltage control circuit that constantly controls the inverter DC voltage. By adding this signal and multiplying this added signal by a signal that is 90 ° phase delayed from the system voltage, and using it as an inverter active power control signal, the mode in which active power flows out within the capacity range of the inverter DC power supply during interconnection is set. It is characterized in that

Here, the above phase bias signal is added to the output signal of the DC voltage control circuit as needed by measuring the phase error between the inverter output voltage and its command signal before interconnection, and this addition is performed. Therefore, the inverter output voltage at the time of interconnection becomes a phase state advanced with respect to the system voltage, and a mode is set in which active power flows out at the time of interconnection.

[0013]

FIG. 1 shows a control block of a grid interconnection inverter 4 according to the method of the present invention, which may be basically the same as the control block of FIG. In the present invention,
An adder 17 is additionally installed between the DC voltage control circuit 11 and the multiplier 12, and a manually adjustable phase bias signal g _C is added to the output signal g _E of the DC voltage control circuit 11 by the adder 17 as required. It is characterized by adding. The output signal g _E of the DC voltage control circuit 11 and the phase bias signal g _C
The addition signal g _E '[g _E or (g _E + g _C )] is multiplied by the phase signal V _S ′ obtained by delaying the phase of the system voltage V _S by 90 ° by the 90 ° phase shifter 13 by the multiplier 12. And the amplitude-adjusted inverter active power control signal V _E is obtained.

Phase bias signal g_C Of the inverter 4
Inverter output voltage V during grid connection _I Is the system voltage
V_S It is a phase adjustment signal that does not delay the phase of
Inverter output voltage V during interconnection_I Is later in phase than the system voltage
In this state, the phase bias signal g_C Add in
Barter output voltage V_I Is the system voltage V_S Match the phase of
To proceed. Output signal of DC voltage control circuit 11
No. g_E Phase bias signal g to_C Addition of the inverter
After manufacturing, for example, when the inverter is shipped,
It is done as needed.

That is, at the stage of shipping the inverter, the presence / absence of a phase shift between the inverter output voltage V _I and the inverter output voltage command signal V _I ^REF is measured and checked. In this investigation, the phase of the inverter output voltage V _I during grid connection is the system voltage V _I.
If it is determined that the value of _S coincides with _S , it is determined that the addition of the phase bias signal g _C is unnecessary, and the product is shipped without addition. Further, if it is determined in the above survey that the phase of the inverter output voltage V _I is delayed from the system voltage V _S during system interconnection,
The phase bias signal g _C is added manually, and the phase bias signal g _C is added and shipped.

The addition of the phase bias signal g _C causes the inverter 4 to operate from the state in which the phase of the inverter output voltage V _I is always advanced with respect to the system voltage V _S during interconnection. Therefore, the inverter 4 is in a mode in which active power flows out during the transition period of the interconnection, so that the inflow of active power during the interconnection transition period is suppressed and the generation of the inverter DC overvoltage is avoided. The active power output from the inverter 4 during the interconnection transition period by adding the phase bias signal g _C is manually set within the capacity of the inverter DC power supply unit 5.

[0017]

According to the present invention, in addition to the existing DC voltage control circuit, the phase of the inverter output voltage can be adjusted by manual adjustment of the manually adjustable phase bias signal. By advancing the inverter output voltage phase at the desired time by a desired amount with respect to the system voltage and setting the mode to output active power from the inverter during the transition period of interconnection, DC overvoltage due to active power inflow during the transition period of interconnection is set. It is possible to prevent it, and to always realize stable grid interconnection.

Further, since it can be implemented only by additionally installing a simple adder circuit for adding the phase bias signal by manual to a part of the existing inverter device, it can be easily applied to the existing equipment and is advantageous in terms of equipment investment. Can be carried out.

[Brief description of drawings]

FIG. 1 is a control block diagram in the control method of the present invention.

FIG. 2 is a main circuit diagram of a grid interconnection inverter.

FIG. 3 is a control block diagram of a conventional method for controlling a grid interconnection inverter.

[Explanation of symbols]

 4 system interconnection inverter 5 inverter DC power supply unit 11 DC voltage control circuit

Claims (1)

[Claims] 1. In a system interconnection inverter for converting an inverter DC voltage of a rating given by an inverter DC power supply unit into an AC, the output signal of a DC voltage control circuit for controlling the inverter DC voltage at a constant level is output to the inverter output before interconnection. Add a manually adjustable phase bias signal that advances the voltage phase from the system voltage, and add this added signal and the system voltage to 90
° The AC active signal that is multiplied by the phase-delayed signal is used as the inverter active power control signal so that the active power can be discharged in the capacity range of the inverter DC power supply during interconnection. System inverter control method.