JPH09128072A - Method for controlling self-excited reactive power compensating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a loss by reducing zero-phase voltage or zero-phase current generated in an inverter or a linking transformer in a self-excited reactive power compensating device by zero-phase components generated in compensating current command signals for three phases by a compensating current computing circuit. SOLUTION: Compensating current command signals Ic (U phase), IcR (V phase), IcR (W phase) found out from the load currents IL of three phases are added by an adder 9, the added value is multiplied by 1/3 through a 1/3 multiplier 10 to find out a signal I0 only for a zero-phase component and signals obtained by subtracting the signal I0 from each of the signals IcR (U phase), IcR (V phase), IcR (W phase) are defined as final compesating current command signals IcREF (U phase), IcREF (V phase), IcREF (W phase) for controlling respective single phase inverters 5 for the three phases. Since any zero-phase component is not included in the final compensating current command signals IcREF for three phases, an unnecessary loss due to a zero-component is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase three-phase power system.
A control method for a self-excited reactive power compensator installed on the system bus of the power line. Specifically, the compensation current command signal for each of the three phases obtained from the load current due to the unbalanced load of each of the three phases of the power system is used. The present invention relates to a control method for a self-excited reactive power compensator that controls three single-phase inverters to compensate for the generated reactive power in each of the three phases of the power system.

[0002]

2. Description of the Related Art As a reactive power compensator (hereinafter referred to as SVC) for rapidly compensating the reactive power generated in a system bus of an electric power system from an unbalanced load such as an arc furnace load, a welding machine load, an electric railway load, etc. A self-excited SVC that uses a single-phase inverter is a prize. The main circuit configuration of the power system in which the self-excited SVC is installed is shown in FIG. 2 and will be described.

The self-excited SVC 4 of FIG. 2 comprises three single-phase inverters 5 and one interconnection three-phase transformer 6, and a transformer 6
Is connected to the system bus 2 of the three-phase three-wire system. A load 3 such as an arc furnace is connected to a system bus 2 having a system power supply 1. A compensating current command signal I _C ^REF for each of the three phases is obtained based on the signal detected by the transformer 7 for the load current I _L generated in the system bus 2 of each of the three phases due to the load fluctuation. The corresponding single-phase inverter 5 for each of the three phases is independently controlled by the compensation current command signal I _C ^REF , and the compensation current I _C flows from the self-excited SVC 4 to the system bus 2 of each of the three phases to load the system bus 2. Reactive power compensation due to fluctuations is performed.

The load 3 is usually an unbalanced load such as an arc furnace, a welding machine, or an electric railway. The self-excited SVC 4 for dealing with such an unbalanced load 3 cancels the unbalanced component of the load current. It is necessary to output unbalanced current. Therefore, in the self-excited SVC 4, the compensation current command signal I _C ^REF for controlling the single-phase inverter 5 for each of the three phases is
Three phases are calculated for each phase. That is, as shown in FIG. 3, the load current I _{L of} each of the U-phase, V-phase, and W-phase of the system bus 2
(U phase), _IL (V phase), and _IL (W phase) are calculated for each phase by the corresponding compensation current calculation circuits 8a, 8b, 8c, and 3
Phase compensation current command signal for each phase I _C ^REF (U phase), I _C ^REF (V
Phase) and I _C ^REF (W phase).

[0005]

By the way, as shown in FIG. 3, load currents I _L (U phase), I _L (V phase) of each of the three phases,
Compensation current command signals I _C ^REF (U phase), I _C ^REF (V) from I _L (W phase) to compensation current calculation circuits 8a, 8b and 8c for each phase.
Phase) and I _C ^REF (W phase) are calculated, the compensation currents of the three phases for each phase are output depending on the responsiveness in the compensation current operation circuits 8a, 8b, 8c for each phase and the operation method. Zero-phase components may occur in the command signals I _C ^REF (U phase), I _C ^REF (V phase), and I _C ^{R EF} (W phase).

For example, in the unbalanced load 3, sporadic reactive power exceeding the rated capacity of the single-phase inverter 5 for each of the three phases is generated, and the compensation current I _{C of} each of the three phases of the SVC 4 corresponds to the single. The current upper limit value determined by the rated capacity of the phase inverter 5 may be exceeded. In such a case, the compensating current I _{C of} each of the three phases is amplitude-cut by the corresponding current upper limit value of the single-phase inverter 5 to increase the apparent capacity of the entire inverter, which causes a single unbalanced load fluctuation. Although the reactive power compensation effect is enhanced, the compensation current command signal I _C ^{R EF} (U phase) of each of the three phases of FIG. 3 is processed by the amplitude cut processing of the compensation current I _C of each of the three phases. I _C ^REF (V phase), I
Zero phase component may occur in _C ^REF (W phase).

As described above, when zero-phase components are generated in the compensation current command signals I _C ^REF (U phase), I _C ^REF (V phase) and I _C ^REF (W phase) of each of the three phases, the three phases are generated. Zero-phase voltage and zero-phase current are generated in the single-phase inverter 5 of each phase and the three-phase transformer 6 for interconnection,
There is a problem that unnecessary power loss occurs, and in particular, there is a problem in the three-phase transformer 6 that heat is undesirably generated by a zero-phase current.

An object of the present invention is to control a single-phase inverter for each of the three phases by a compensating current command signal that does not generate a zero-phase voltage or a zero-phase current, so that an inverter or a transformer for interconnection. It is an object of the present invention to provide a control method for a self-excited SVC that reduces unnecessary loss in the.

[0009]

The technical means for achieving the above object of the present invention is to obtain a compensating current command signal for each of the three phases from the load current of each of the three phases of the power system, and to compensate for each phase. In the control of the self-excited reactive power compensator, which independently controls the three single-phase inverters of each of the three phases by the current command signal to compensate the generated reactive power of each of the three phases of the power system, Compensation current command signals obtained from each of the three phases are added, and a signal obtained by multiplying the added value by 1/3 is subtracted from each of the compensation current command signals of each of the three phases.
It is characterized in that the signals of the respective phases are the final compensation current command signals for controlling the corresponding single-phase inverters of the respective three phases.

Here, when the load is an unbalanced load, the compensation current command signal for each of the three phases calculated from the load current of each of the three phases of the power system includes a zero phase component. The zero-phase component is 1/3 by adding the compensation current command signals for each of the three phases.
It is detected by multiplying by. Therefore, the signals obtained by adding the compensation current command signals for each of the three phases and multiplying by 1/3 are subtracted from the signal compensation current command signals for each of the three phases to obtain the signals for each of the three phases. Does not include zero-phase component,
If the final compensation current command signal for controlling the single-phase inverter of each phase is used as the final compensation current command signal, unnecessary loss due to the zero-phase component is reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A control method according to the present invention for a self-excited SVC 4 shown in FIG. 2 will be described with reference to a control circuit example shown in FIG.
The same or corresponding parts as those in FIG. 3 of FIG. 1 are designated by the same reference numerals.

In the present invention, the load currents I _L (U phase), I _L (V phase) and I _L (W
Phase) is calculated for each phase by the corresponding compensation current calculation circuits 8a, 8b, 8c to obtain a compensation current command signal for each of the three phases.
In order to avoid confusion between the obtained signals of the three phases and the compensation current command signal of FIG. 3, I _C ^R (U phase), I _C ^R (V
Phase) and I _C ^R (W phase). In this case, the responsiveness in the compensation current calculation circuits 8a, 8b and 8c for each phase is the same as in the conventional case,
Calculation scheme compensation current command signal three phases output by the I _C ^R (U-phase), I _C ^R (V-phase), there is the zero-phase component is generated in the I _C ^R (W-phase).

Next, the compensating current command signal I for each of the three phases
_C ^R(U phase), I_C ^R(V phase), I_C ^R(W phase) with adder 9
Add and multiply the added value by 1/3 with 1/3 multiplier 10
Signal I _OAsk for. The adder 9 and the 1/3 multiplier 10
Calculates the zero-phase component of each of the three phases from the normal three-phase AC
In the circuit, the signal I obtained from the 1/3 multiplier 10_OIs
It is a zero-phase component included in each of the three phases.

Therefore, the compensation current calculation circuits 8a, 8 for each phase are provided.
Compensation current command signal I of each phase output from b and 8c
_{When the} zero phase component signal I _O is subtracted from each of _C ^R (U phase), I _C ^R (V phase), and I _C ^R (W phase) by the subtracters 11a, 11b, and 11c, only the zero phase component is canceled. A signal of each of the three phases consisting of the positive phase component and the negative phase component thus obtained is obtained. The signal in which this zero-phase component is canceled is used as the signal of the self-excited SVC4 3
Phase Compensation current command signals I _C ^REF (U phase), I _C ^REF (V phase), I _C ^REF (W
Phase). In this case, compensation current command signals I _C ^REF (U phase), I _C ^REF (V
Phase) and I _C ^REF (W phase) are represented by the following equations.

I _C ^REF (U phase) = I _C ^R (U phase) −I _O (zero phase) I _C ^REF (V phase) = I _C ^R (V phase) −I _O (zero phase) I _C ^REF (W-phase) = I _C ^R (W-phase) -I _O (zero phase) As a result, compensation current command signal three phases which are removed in the zero-phase component I _C ^REF (U-phase), I _C ^REF ( V phase), I _C ^REF (W
Phase), if the single-phase inverter 5 of each of the three phases is independently controlled, unnecessary zero-phase voltage and zero-phase current do not occur in the single-phase inverter 5 and the three-phase transformer 6 for interconnection, and the zero-phase component No unnecessary loss due to.

[0016]

According to the present invention, even if the compensation current command signal obtained from the load current of the system bus of the three-phase three-wire has a zero-phase component by the compensation current calculation circuit, the compensation of each phase of the three phases is performed. The zero-phase component is canceled from the compensation current command signal by subtracting the signal obtained by adding the current command signals and multiplying by 1/3 from the compensation current command signal of each of the three phases, and the signal in which the zero-phase component is cancelled. Since the inverter is controlled as the final compensation current command signal, the generation of zero-phase voltage and zero-phase current in the self-excited SVC inverter and the interconnection transformer is reduced, and unnecessary loss due to the zero-phase component is reduced. It is possible to provide a self-excited SVC with few compensation efficiencies.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a compensation current command signal calculation circuit for explaining a control method of the present invention.

FIG. 2 is a main circuit diagram of a power system in which a self-excited reactive power compensator is installed.

FIG. 3 is a circuit diagram of a compensating current command signal arithmetic circuit for explaining a control method of a conventional self-excited reactive power compensator.

[Explanation of symbols]

 3 load 4 self-excited reactive power compensator (SVC) 5 single-phase inverter 8a to 8c compensation current operation circuit 9 adder 10 1/3 multiplier 11a to 11c subtractor

Claims (1)

[Claims] 1. A compensating current command signal for each of the three phases is obtained from a load current of each of the three phases of the power system, and three compensating current command signals for each phase are used to independently form three single-phase inverters for each of the three phases. A control method of a self-excited reactive power compensator for controlling and compensating generated reactive power of each of the three phases of a power system, wherein a compensation current command signal obtained from each of the three phases of the power system Is added and the signal obtained by multiplying the added value by 1/3 is subtracted from each of the compensation current command signals of each of the three phases, and the signals of each of the three phases are obtained. The method for controlling a self-excited var compensator, wherein the final compensation current command signal for controlling the single-phase inverter is used.