JPS61125628A - Method and device for compensating reactive electric power - Google Patents

Abstract

PURPOSE:To minimize losses in a transformer and a snubber circuit by compensating a large capacity basic wave component and a small capacity one by a low frequency PWN control and a high frequency PWN control, respectively. CONSTITUTION:A basic wave reactive current is added to a compensation current given from a voltage control circuit 12, and a difference between currents in a basic wave reactive power compensating device 14 is given to a PWN control circuit 11 from an adder/subtractor 16, whereby said device 14 compensates the basic wave reactive power. On the other hand, a high frequency reaction current can be available by obtaining a difference between outputs of a reactive current converting circuit 10 and a band-pass filter 13 by means of an adder/subtractor 17. This high frequency reactive current is added to a subject for keeping the DC voltage of the compensation current (capacitor 5') given from the voltage control circuit 12, and the difference between the currents (output of a current detector 7') in a high frequency reactive power compensating device 14' is given to the PWN control circuit 11. Thus said device 14' compensates the reactive current of the high frequency component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a reactive power compensation method and apparatus for controlling the total power factor of a power supply system to approximately 1.

[Technical background of the invention]

In order to operate the grid economically and improve stability, reactive power compensators have been widely used. Especially in recent years! , II A reactive power compensator using a pulse width modulation type (hereinafter referred to as PWM type) self-help converter with good titability is attracting attention. The conventional device will be described below with reference to FIGS. 3 and 4 of the accompanying drawings. In addition, in the description of the drawings, the same elements are indicated by the same reference numerals.

FIG. 3 is a configuration diagram of an example of a conventional device. Connected to the power supply system 1 are a load 2 serving as a source of reactive power, and a transformer 3 for insulating the system 1 from the reactive power compensator. In addition, the transformer 3 has a P
The WM converter 4 is connected to a capacitor 5 which serves as a direct current voltage source, and a direct current voltage detector 6 which detects the voltage across the capacitor 5. Furthermore, a current detector 7 is inserted between the converter 3 and the PWM converter 4 to detect the current of the reactive power compensator itself. A voltage detector 9 that detects the voltage of the ratio detector 8 system 1 is provided, and these outputs are invalid 1! It is given to the flow variation circuit 10.

The P W M i/I I11 circuit 11 has a voltage fI11
w Circuit 12 output and invalidity! ! Based on the output of the current conversion circuit 10 and the output of the current detector 7, the PWM converter 4 is
IXlt6° Next, the operation of the configuration example shown in FIG. 3 will be explained.

Reactive current conversion circuit 1 based on load current and grid voltage
0 determines the reactive current to be compensated. Furthermore, the voltage of the capacitor 5 constituting the DC power supply is detected by a voltage detector 6,
It is matched with the reference value E by the adder/subtractor 15 and inputted to the voltage control W circuit 12. In this way, a supplementary current is obtained that keeps the DC voltage constant. Furthermore, this compensation 71i current (voltage I
The sum of the reactive current to be compensated (output of the I control circuit 12), the reactive current to be compensated for (output of the reactive current conversion circuit 10), and the current generated by the reactive power compensator itself (output of the 111% E detector 7). It is matched by the adder/subtractor 16, and P
90 circuit 11. As a result, each element constituting the PWM converter is turned on and off, and a reactive current to be compensated is generated.

FIG. 4 is a waveform diagram of compensation 1: flow in the configuration example shown in FIG. The current flowing through load 2 is as shown by curve A.

On the other hand, the compensation current supplied from the reactive power compensator is like a sawtooth broken line B. Therefore, the reactive current is compensated and the overall power factor is made approximately 1.

[Problems with background technology]

Incidentally, the current flowing through the load generally includes a harmonic reactive current component and a fundamental wave reactive current component. Therefore, in order to always keep the overall power factor at 1, the reactive current of the 14th harmonic and the reactive current of the fundamental wave must be supplied by the reactive power compensator. The harmonic frequency that is the problem here is
These are often the 5th, 7th, 11th, and 13th orders of the fundamental wave, so to 611611 these 1 & harmonics, use PW
Satisfactory characteristics cannot be obtained unless the switching frequency of the self-extinguishing element constituting the M-type converter is made sufficiently high.

Also of load? Since the ti current generally contains more fundamental wave reactive current than harmonic reactive current, the capacity of the reactive power compensator ends up being large.

Therefore, in order to simultaneously compensate for the reactive current of the fundamental wave and the reactive current of the harmonics, it is necessary to operate at a high frequency, and in addition, a large capacity is required, so the number of parallel elements that make up the PWM converter is increased. or multiplex the converters. Therefore, the switching loss of the element increases, and furthermore, the loss of the snubber circuit and the loss of the transformer used to protect the element increase significantly.

As described above, the conventional technology has the problem that the device itself becomes large and the efficiency is low.

(Object of the Invention) The present invention has been made to overcome the drawbacks of the above-mentioned prior art, and it is possible to achieve high efficiency with less loss in the transformer and snubber circuit, and to reduce the size of the W1 system. An object of the present invention is to provide a reactive power compensation method and a device therefor.

[Summary of the invention]

In order to achieve the above object, the present invention separates the reactive N81 generated by the load connected to the grid into a fundamental (low frequency) component and a harmonic (high frequency) component, and for the former, the low frequency P W M The present invention provides a reactive power compensation method in which compensation is performed using IJ III, and the latter is compensated using high frequency PW Mill III, and a device therefor.

(Embodiment of the Invention) Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2 of the accompanying drawings. FIG. 1 is a block diagram of the same embodiment. As is clear from a comparison with FIG. 3, the fundamental wave reactive power compensator 14 surrounded by the dotted line is the same as the circuit shown in FIG. Further, the basic configuration of the harmonic reactive power compensator 14' is the same. Unlike FIG. 3, in FIG. 1, a bandpass filter 13 is connected to the output side of the reactive current conversion circuit 10, and the output of the reactive current conversion circuit 10 and the signal passed through the bandpass filter 13 are subtracted by an adder/subtractor 17. Ru.

Next, the operation of the embodiment shown in FIG. 1 will be explained. Current detector 8 and voltage detection! Based on the load current and system voltage obtained in step i9, the reactive current to be compensated for is determined by the reactive current conversion circuit 10. This reactive current is input to a band pass filter 13 that allows only the fundamental frequency component to pass, and only the fundamental reactive current is extracted. This fundamental wave reactive current is added to the compensation current given from the voltage 617111 circuit 12 (which keeps the DC voltage of the capacitor 5 constant), and the difference with the current of the fundamental wave reactive power compensator [14] is added to the compensation current given by the voltage 617111 circuit 12. is applied to the PWMM 11 circuit 11, and the fundamental wave reactive power is compensated by the fundamental wave reactive power compensator 114. In this case, the fundamental frequency component is invalid 1! Since only the current needs to be compensated for, the switching frequency of the elements constituting the PWM converter 4 can be lowered.

On the other hand, the harmonic reactive current is obtained by calculating the difference between the output of the bandpass filter 13 and the output of the reactive current conversion circuit 10 using the adder/subtractor IJ device 17.

This harmonic reactive power if current is added to the compensation N current given from the voltage control circuit 12 (which keeps the DC voltage of the capacitor 5' constant), and the current of the harmonic reactive power compensator 14' itself (i current detected The difference between the output of unit 7' and
' to the PWM ill a11 circuit 11. In this way, the at14-wave reactive power supplementary device 14'
compensates for the reactive current of all waves.

In this case, since the reactive current of harmonic components is compensated for, the switching frequency of the elements constituting the PWM converter 4' needs to be sufficiently high.

Fig. 2 is a waveform diagram of the compensation current, Fig. 2 <a> shows the conventional example by Takamae that separates the fundamental wave component and the harmonic component, and Fig. 2 (b) shows the waveform of the present embodiment. Only the fundamental wave component is shown, and FIG. 2(C) shows only the harmonic component according to this embodiment. As shown in FIGS. 2(b) and 2(c), the fundamental wave reactive current A1 is compensated by the compensation current B1 by the fundamental wave reactive power compensator 14, and the a-harmonic reactive current A2 is compensated by the harmonic reactive power compensator 14. ' is compensated by compensation current B2. In this way, the overall power factor of the system is 1
is maintained.

As described above, according to this embodiment, it is possible to set the switching frequency of the fundamental wave reactive power compensator M14 that compensates for the fundamental wave reactive power, which generally has a larger capacity than the harmonic reactive power, sufficiently low, so that the switching It is possible to reduce the switching loss of the element, which is proportional to the frequency, and the loss of the snubber circuit that protects the element from overvoltage (generally, this loss accounts for the largest proportion of the total loss). Further, transformer loss due to harmonics caused by the switching frequency can also be sufficiently reduced.

Note that although a voltage-type PWM converter is used in the above embodiment, it goes without saying that a current-type PWM converter can also be used.

(Effects of the Invention) As described above, according to the present invention, the reactive current generated by the load connected to the grid is separated into the fundamental wave (low frequency) component and the harmonic (II frequency) component, and the capacity is relatively small. The former is compensated for by the low frequency P W M III ilD,
Since the latter, which has a relatively small capacity, is compensated by high-frequency PWM control, we have developed a reactive power compensation method that has low loss in transformers and snubber circuits, is highly efficient, and can reduce the size of the device. equipment can be provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of compensation current according to the conventional example and the embodiment shown in FIG. 1, and FIG.
This figure is a configuration diagram of an example of a conventional device, and FIG. 4 is a waveform diagram of a compensation current in the configuration example shown in FIG. 3. 1...Power system, 2...Load, 3.3'...Transformer, 4.4'・PWM'aafi, 5, 5'-
D nt:/sa, 6.6'...DC voltage detector, 7
．． 7' 8...Current detector, 9...Voltage detector, 1
0...Reactive current conversion circuit, 11.11'...P
W M i control circuit, 12... Voltage lll111 circuit, 13... Bandpass filter, 14... Fundamental wave reactive power compensator, 14'... High wave reactive power compensator M
.

Claims (1)

[Claims] 1. In a reactive power compensation method for compensating for a reactive current generated by a load connected to a grid by supplying a compensation current to the grid, the fundamental frequency component of the reactive current is The compensation is performed by supplying the fundamental frequency component of the compensation current to the system through low frequency PWM control by the first PWM converter, and the harmonic component of the reactive current is A reactive power compensation method, characterized in that compensation is performed by supplying harmonic components of the compensation current to the system through high-frequency PWM control using a second PWM converter having a different frequency. 2. Reactive current conversion means for determining the reactive current to be compensated based on the voltage supplied to the grid and the current flowing through the load, and passing only the fundamental reactive current that is the fundamental frequency component of the reactive current to be compensated. filter and subtracting the fundamental reactive current from the reactive current to be compensated,
It has means for outputting a harmonic reactive current that is a harmonic component of the reactive current to be compensated, and a first PWM converter, and controls the first PWM converter based on the fundamental reactive current. By this, fundamental wave reactive power compensating means for supplying the fundamental frequency component of the compensation current to the system, and the second PW
A harmonic reactive power compensation means having an M converter and supplying harmonic components of the compensation current to the system by controlling the second PWM converter based on the harmonic reactive current. Reactive power compensator.