JPH08263154A - Control method for self-excited reactive power compensation device - Google Patents

Abstract

PURPOSE: To provide the control method for the self-excited reactive power compensation device(SVC) which evades adverse influence of the voltage error component between the output voltage of a large-capacity inverter and a bus voltage on the compensating current control system of a small-capacity inverter. CONSTITUTION: A pulse generator 12 is placed in operation according to the bus voltage VA similar to the output voltage VB of the large-capacity inverter to generate a large-capacity inverter gate signal. The small-capacity inverter, on the other hand, finds a current control signal VI from a control signal performing feedback control so that the difference between a compensating current command value Ic REF from a load current IL and an actual compensating current Ic becomes small, finds an SVC output voltage command value VVREF by adding the bus voltage VA thereto, and subtracts the large capacity inverter output voltage VB from it to calculate a small-capacity inverter output voltage command value VFREF.

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 self-excited reactive power compensator in which a large capacity low speed switching rectangular wave inverter and a small capacity high speed switching PWM inverter are connected in series to a power system.

[0002]

The present application as a self-excited reactive power compensator installed between a grid power supply and a variable load in a power grid having a grid power supply such as a substation and a variable load such as a large-capacity arc furnace or electric railway load. A person previously proposed a structure in which a large-capacity low-speed switching rectangular wave inverter and a small-capacity high-speed switching PWM inverter are serially multiplexed in a power system [Japanese Patent Application No. 6-5522].

A main circuit of this self-excited reactive power compensator (hereinafter referred to as a self-excited SVC) is shown in FIG. 4 and its equivalent circuit is shown in FIG. 5. The self-excited SVC 4 in FIG. It is installed on the system bus 2 between the variable loads 3. S
The VC 4 includes a large-capacity low-speed switching rectangular wave inverter (hereinafter, referred to as large-capacity inverter) 5 and a small-capacity high-speed switching PWM inverter (hereinafter, referred to as small-capacity inverter) 6 as a transformer corresponding to each inverter capacity. It is connected to the system bus 2 in series via 7 and 8. still,
Reference numeral 10 in FIG. 4 is a circuit breaker that interconnects the SVC 4, and reference numeral 11 in FIG. 5 is an equivalent inductance of the transformers 7 and 8.

The large capacity inverter 5 has an output voltage V _B equal to the bus voltage _VA of the system bus 2 on the primary side of the transformer 7.
Is controlled to generate. In this case, the large-capacity inverter 5 draws active power from the system bus 2 and automatically adjusts the DC voltage charged in the DC capacitor 9 to adjust the amplitude of the output voltage V _B to be equal to the bus voltage V _A. .

On the other hand, the small-capacity inverter 6 generates an output voltage V _F of about 10 to 20% of the bus voltage V _A on the primary side of the transformer 8. The output voltage V _F is a voltage component for generating a reactive current based on the compensation reactive current command value according to the load variation in the system bus 2. By varying the amplitude of the reactive component to follow the load variation, the variation occurs. Compensation current (SVC output current) I _{C of} opposite phase to the reactive current generated in load 3
Are generated in the system, and fluctuations in the bus voltage _VA due to load fluctuations are suppressed.

The self-excited SVC 4 has an output voltage V _B of the large capacity inverter 5 and an output voltage V _{F of the} small capacity inverter 6.
Is controlled by independently calculating and outputting, and its control system will be described with reference to the control block of FIG.

In the large-capacity inverter 5, the pulse generator 1 responds to the bus voltage V _A equivalent to its output voltage V _B.
2 is operated to generate a large capacity inverter gate signal. A large-capacity inverter gate signal controls on / off of a switching element such as a thyristor (not shown) of the large-capacity inverter 5. When the output voltage V _B of the large-capacity inverter 5 becomes equal to the bus voltage V _A , the circuit breaker 1 in the off state
0 is turned on, and the SVC 4 is connected to the system bus 2.

On the other hand, the small capacity inverter 6 is connected to the system bus 2
The difference between the compensation current command value I _C ^REF obtained by calculating the load current I _L detected by the compensation current calculation circuit 13 and the actual compensation current I _C calculated by the subtractor 14 becomes small. The output voltage command value V _F ^REF of the small capacity inverter 6 is obtained from the control signal feedback-controlled by the output current control circuit 15. The output voltage command value V _F ^REF is passed through the PWM circuit (pulse width modulation circuit) 16 to generate a small capacity inverter gate signal for turning on / off the switching element of the small capacity inverter 6, and the small capacity inverter 6 is controlled. .

[0009]

One of the preconditions for the compensation current control system of FIG. 6 to operate normally is that the output voltage V _B of the large capacity inverter 5 and the bus voltage V _{A have} the same amplitude. However, when the large-capacity inverter 5 which is a rectangular wave inverter automatically controls the amplitude of the output voltage V _B to be equal to the bus voltage _VA by controlling the DC voltage of the DC capacitor 9 with active power from the grid. There is a slight response delay during the voltage feedback control, and the output voltage V _B may not be equal to the bus voltage V _A during this response delay. While such a voltage error of V _B ≠ V _A occurs, the voltage error component [V _A −V _B ] of both voltages is small capacity inverter 6
Acts as a disturbance that disturbs the compensation current control system of
The compensation current control performance of No. 4 may be deteriorated.

Therefore, the object of the present invention is to
_A self-excited SVC with stable operation in which adverse effects on the compensation current control system of the small capacity inverter 6 due to voltage error components of the output voltage V _B of the large capacity inverter 5 and the bus voltage _VA are suppressed.
It is to provide a control method of.

[0011]

DISCLOSURE OF THE INVENTION The present invention provides a large capacity rectangular wave inverter for outputting to a system bus having a variable load a voltage equivalent to the bus voltage of the system bus through a large capacity transformer, and a system. A control method for a self-excited SVC in which small-capacity inverters that output a compensating voltage for suppressing load fluctuations of a busbar are connected in series to each other by a small-capacity transformer, wherein an output voltage command signal of the small-capacity inverter and a busbar voltage are provided. Add and SV
The output voltage command value signal of the entire C is obtained, and the output voltage component of the large capacity inverter or the voltage component corresponding to this output voltage component is subtracted from this output voltage command value signal to obtain the final value of the small capacity inverter. The above object is achieved by obtaining the output voltage command value.

Further, according to the present invention, when the self-excited SVC is started, the output voltage command value of the small-capacity inverter is set to zero for a fixed time until the output voltage of the large-capacity inverter reaches a steady state, and after this fixed time. By adjusting the startup gain so that it returns to the rated value, the startup characteristics are improved.

[0013]

Operation: The output voltage command value of the small capacity inverter is subtracted from the output voltage command value signal of the entire SVC obtained by adding the bus voltage to the output voltage command signal of the small capacity inverter to obtain the final output voltage command value of the small capacity inverter. By asking
The error component between the bus voltage and the large-capacity inverter output voltage is automatically included in the small-capacity inverter output voltage command value, and the disturbance of the compensation current control system of the small-capacity inverter is suppressed.

Further, by adjusting the starting gain so that the output voltage command value of the small capacity inverter is zero during a certain period of time until the output voltage of the large capacity inverter reaches a steady state at the time of starting the SVC, the small capacity is started at the time of starting the SVC. Since the output voltage command value of the inverter is not generated, the load on the transformer of the small capacity inverter is lightened.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention applied to the self-excited SVC 4 of FIG. 4 will be described below with reference to the control block of FIG. 1 and a partially modified control block of FIG.

As shown in FIG. 1, in the method of the present invention, an adder 1 is provided between the output current control circuit 15 and the PWM circuit 16.
7 and a subtractor 18 are additionally provided, and the bus voltage V _A is added to the adder 17.
Is applied to the subtractor 18 with the large-capacity inverter output voltage V _B , and the following SVC control is performed.

In the large-capacity inverter 5, the pulse generator 1 responds to the bus voltage V _A equivalent to its output voltage V _B.
2 is operated to generate a large capacity inverter gate signal. In this case, the circuit breaker 10 of FIG. 4 is turned on when the output voltage V _B of the large capacity inverter 5 becomes equal to the bus voltage _VA .

In the compensation current control system for the small-capacity inverter 6, first, the compensation current command value I _C ^REF obtained by computing the load current I _L by the compensation current computing circuit 13 and the actual compensation current I _C are calculated. The output current control circuit 15 reduces the difference.
Current control signal V from the control signal feedback-controlled by
_I is obtained, and the current control signal V _I and the bus voltage V _A are added by the adder 17 to obtain the SVC output voltage command value V _V ^REF . The SVC output voltage V _V is a voltage V _V = V _B + V _F corresponding to a voltage component to be output by the entire SVC 4. The SVC output voltage command value V _V ^REF is given by the following equation.

V _V ^REF = V _I + V _A ...

Next, the subtractor 18 subtracts the large-capacity inverter output voltage V _B from the SVC output voltage command value V _V ^REF .
The signal [V _V ^REF −V _B ] remaining after the subtraction corresponds to the small-capacity inverter output voltage V _F , and the small-capacity inverter output voltage command value V _F ^REF is obtained from this signal and output to the PWM circuit 16. , The small capacity inverter gate signal is generated to control the small capacity inverter 6.

The large-capacity inverter output voltage V _B subtracted from the SVC output voltage command value V _V ^REF is determined by the voltage value detected by the transformer (not shown) of the primary side voltage of the transformer 7 of the large-capacity inverter 5. Alternatively, the pulse width and the amplitude of the control pulse for driving the large-capacity inverter 5 may be obtained by a simulated voltage signal obtained by Fourier analysis.

The small capacity inverter output voltage command value V _F ^REF obtained in the above manner is given by the following equation.

V _F ^REF = V _V ^REF -V _B ...

Substituting the equation into the equation, the small capacity inverter output voltage command value V _F ^REF is given by the following equation.

V _F ^REF = V _I + V _A −V _B

= V _I + (V _A −V _B ) ...

Therefore, the large-capacity inverter 5 which is the rectangular wave inverter of FIG. 4 controls the DC voltage of the DC capacitor 9 by the active power from the grid so that the amplitude of the output voltage V _B becomes equal to the bus voltage V _A. Even if the output voltage V _B does not become equal to the bus voltage V _A due to a response delay or the like in the automatic adjustment so that the voltage error component [V _A − V _B ] is included in the small capacity inverter output voltage command value V _F ^{R EF} , and the voltage error component [V
So _{that A} -V _B] is automatically corrected. As a result, the disturbance due to the voltage error component [V _A -V _B] in the compensation current control system of the small-capacity inverter 6 is surely suppressed, the better the compensation current control performance SVC4.

By the way, in the SVC control method of FIG. 1, the following problems may occur when the SVC is started.

Since the self-excited SVC 4 is connected to the system bus 2, it is necessary to turn on the circuit breaker 10 after making the large-capacity inverter output voltage V _B equal to the bus voltage V _A at the time of startup. When the bus voltage V _A is output at the instant when the SVC is started, there is a possibility that the large-capacity inverter 5 is stopped due to an overcurrent due to the excitation characteristic of the transformer 7 of the large-capacity inverter 5. As a solution to this problem, a soft start control method in which the large-capacity inverter output voltage V _B is gradually increased as shown in the graph of FIG.

In such soft start control, an overcurrent of the large capacity inverter 5 at the time of starting the SVC can be prevented, but the output voltage command value V _F ^{REF of the} small capacity inverter 6 is prevented.
Is given by the above formula V _F ^REF = V _V ^REF -V _B , the transformer 8 of the small capacity inverter 6 may be overexcited from the moment the SVC starts to the time when the circuit breaker 10 is turned on and enters a steady state. Comes out.

That is, the compensation current command value I _C at the time of starting the SVC
^{Since REF} is zero and the current control signal V _I output from the output current control circuit 15 is zero,

V _F ^REF = V _V ^REF -V _B = V _A -V _B

The relationship is as follows. Therefore, the command value V _F ^REF of the small-capacity inverter output voltage V _F , which is about 10 to 20% of the bus voltage V _A , appears as a waveform close to a rectangular wave as shown in FIG. The small-capacity inverter output voltage command value V _F ^REF at the time of SVC startup need not be generated in the SVC startup period T until the large-capacity inverter output voltage V _B becomes equal to the bus voltage _VA and the circuit breaker 10 is turned on. However, from the relation of the above equation, SV
It occurs in the C activation period T. Then, the fundamental wave effective value of the small-capacity inverter output voltage V _F due to the rectangular-wave-shaped small-capacity inverter output voltage command value V _F ^REF as shown in FIG. 3B exceeds the rating of the transformer 8, and the SVC start-up period T Therefore, the transformer 8 may unnecessarily be overexcited.

The occurrence of such a problem at the time of starting the SVC is prevented by the control method of the present invention described in FIG.

The self-excited SVC control block shown in FIG. 2 differs from that shown in FIG. 1 only in that a starting gain adjusting circuit 19 is provided between the subtractor 18 and the PWM circuit 16. The start-up gain adjusting circuit 19 sets the start-up gain K to zero only during the SVC start-up period T from the SVC start-up start time T ₀ to the steady-state operation start time T ₁ when the circuit breaker 10 is turned on, and from the steady-state start time T ₁ It is a gain adjustment circuit that allows the starting gain K to be returned to a steady value of 1.

Therefore, the small-capacity inverter output voltage command value V _F ^REF obtained in the same manner as the control method of FIG.

V _F ^REF = K (V _V ^REF -V _B )

It is given by the following equation. In this case, SVC
Large-capacity inverter output voltage V during operation _B Gradually rises
Bus voltage V_A When the steady operation starts, which is equal to₁ become
Since K = 0, there is no voltage output and
There is no possibility that the device 8 will be overexcited. Also, start steady operation
Time point T₁ After passing the time, K = 1
The small-capacity inverter 6 is controlled to be steady as in FIG.
Start driving.

In the case of the control method shown in FIG. 2, the starting gain K of the starting gain adjusting circuit 19 may be gradually brought closer to ₁ from the time T ₁ at which the steady operation is started. Control becomes easy.

[0040]

The present invention has the following effects by the above control method.

According to the control method of the first aspect, from the signal obtained by subtracting the output voltage of the large-capacity inverter from the output voltage command value signal of the whole SVC obtained by adding the bus voltage to the small-capacity inverter output voltage command signal. Since the final output voltage command value of the small capacity inverter was obtained, even if there is a difference between the bus voltage and the large capacity inverter output voltage due to the DC voltage control response delay of the large capacity inverter, this voltage error component By being included in the inverter output voltage command value, the disturbance of the compensation current control system of the small capacity inverter is suppressed, and the compensation current control performance of the self-excited SVC can be improved.

According to the control method of the second aspect,
Since the output voltage command value of the small-capacity inverter is adjusted to zero for a fixed time until the output voltage of the large-capacity inverter reaches a steady state at SVC startup, the SV
The output voltage command value of the small-capacity inverter does not occur from C startup to the steady state, so unnecessary over-excitation of the small-capacity inverter transformer from the SVC startup to the steady state is eliminated, and this transformer receives it. The burden is reduced.

[Brief description of drawings]

FIG. 1 is a control block diagram showing a first embodiment of the present invention.

FIG. 2 is a control block diagram showing a second embodiment of the present invention.

FIG. 3 is a simulated output voltage diagram (a) and an output voltage command value waveform diagram (b) for explaining the problems to be solved by the method of the present invention in the control block of FIG.

FIG. 4 is a circuit block diagram showing a schematic configuration of a self-excited reactive power compensator which is a premise of the method of the present invention.

5 is an equivalent circuit diagram of FIG.

FIG. 6 is a control block diagram for explaining a conventional control method of the self-excited var compensator of FIG.

[Explanation of symbols]

2 System bus 3 Variable load 4 Self-excited reactive power compensator 5 Large capacity low speed switching rectangular wave inverter (large capacity inverter) 6 Small capacity high speed switching PWM inverter (small capacity inverter) 7 Large capacity transformer 8 Small capacity transformer K Start gain

Claims (2)

[Claims] 1. A large-capacity low-speed switching rectangular wave inverter that outputs a voltage equivalent to the bus voltage of the system bus to a system bus having a fluctuating load via a large-capacity transformer, and suppresses load fluctuation of the system bus. A method for controlling a self-excited var compensator in which a small-capacity high-speed switching PWM inverter that outputs a compensation voltage via a small-capacity transformer is connected in series, and an output voltage command signal for the small-capacity high-speed switching PWM inverter is provided. And the bus voltage are added to obtain the output voltage command value signal of the entire reactive power compensator, and the output voltage component of the large capacity low speed switching rectangular wave inverter or the large capacity low speed switching rectangular wave inverter control is obtained from this output voltage command value signal. From the signal obtained by subtracting the voltage component corresponding to the output voltage component calculated from the signal, The method of self-excited reactive power compensation apparatus and obtains the final output voltage command value of the etching PWM inverter. 2. The method for controlling a self-excited var compensator according to claim 1, wherein the output voltage command value of the small capacity high speed switching PWM inverter is set to a large capacity low speed switching rectangular wave inverter when the reactive power compensator is started. A method for controlling a self-excited reactive power compensating device, wherein the output voltage is set to zero for a fixed time until the output voltage reaches a steady state, and the starting gain is adjusted so as to return to the rated value after the fixed time.