JPH04352014A - Instantaneous reactive power compensating device - Google Patents

Abstract

PURPOSE:To obtain an instantaneous reactive power compensating device capable of removing an unnecessary ripple current due to the swiching of a power converter when a compensating current value is small. CONSTITUTION:Reactive power and a higher harmonic current out of a load current are computed by an instantaneous current computing element and a compensating current for canceling the reactive power and the higher harmonic current are found out. The obtained compensating current value is compared with a certain reference value by an output controller 15, and when the compensating current is small, a voltage command from the controller 15 is outputted to a power conversion controller 14 to control the power converter 3 so as to stop it. When the compensating current is small and compensation is unneccessary, the flowing of an unnecesary ripple current due to the swiching of the power converter 3 into a system line can be suppressed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instantaneous reactive power compensator for compensating for reactive power consumed by a load and harmonic current flowing through the load.

0002

[Background Art] An instantaneous reactive power compensator is installed in a system line between a power source and a load, and compensates for reactive power and harmonic current of the load from the instantaneous values of three-phase voltage and current sent from the power source. By calculating an instantaneous compensation current for the current and using this instantaneous compensation current to compensate for reactive power and harmonic current, good power is supplied to the load.

Conventionally, a device as shown in FIG. 2 has been proposed as an example of the instantaneous reactive power compensator as described above. Figure 2 is, for example, a document from the Semiconductor Power Conversion Study Group of the Institute of Electrical Engineers of Japan, 1984 (SPC-84-80) "PWM
1 is a block diagram showing the configuration of a conventional instantaneous reactive power compensation device disclosed in "About Non-Interference Control of Instantaneous Reactive Power Compensation Using a Controlled Power Converter." In the figure, 1 is a three-phase AC power supply, 2 is a load to which power is supplied from the AC power supply 1,
Reference numeral 3 denotes a power converter that generates a voltage for causing a compensation current to flow through a reactor 4 in the system line between the AC power source 1 and the load 2, and this power converter 3 is constructed using a self-extinguishing element. There is. 5 and 6 are load current detectors and compensation current detectors for detecting load current and compensation current; 7
is an AC function that is required when converting the three-phase signal detected by the load current detector 5 and the compensation current detector 6 into a two-phase signal in the synchronous rotation coordinate system, and when performing the inverse conversion. a voltage synchronization signal generator that generates synchronization with the voltage of the power supply 1, 8
and 9 is a 3-phase/2-phase converter that converts the 3-phase signals detected by the load current detector 5 and the compensation current detector 6 into 2-phase signals in a synchronous rotation coordinate system represented by the γ-axis and the δ-axis. and
In particular, the three-phase/two-phase converter 8 is an instantaneous power calculator that calculates reactive power and harmonic current from the load current detected by the load current detector 5 and the voltage synchronization signal detected by the voltage synchronization signal generator 7. Acts as a vessel. 10 is a high-pass filter for cutting off the DC component; 11 is a voltage detector for detecting the DC bus voltage of the power converter 3;
2 is a current control circuit that calculates the output voltage of the power converter 3 for causing a compensation current to flow through the reactor 4; 13 is a current control circuit that converts a two-phase signal in a synchronous rotation coordinate system output from the current control circuit 12 into a three-phase signal; 2-phase/3-phase converter for converting, 1
Reference numeral 4 denotes a power conversion controller for generating, using the power converter 3, a voltage according to the three-phase voltage command output from the two-phase/three-phase converter 13.

Next, the operation of the above-mentioned conventional instantaneous reactive power compensator will be explained. The three-phase signals detected by the load current detector 5 and the compensation current detector 6 are converted into two-phase signals of a synchronous rotation coordinate system represented by the γ-axis and the δ-axis using the 3-phase/2-phase converters 8 and 9. Convert to signal. In this synchronous rotation coordinate system, the direction of the composite voltage of the three-phase voltage of the AC power supply 1 is the δ axis, and the direction counterclockwise π/2 rad (radian) is the γ axis. This is a coordinate system that rotates clockwise at the angular frequency ω of the power supply voltage. In this coordinate system, the effective current is expressed only by the DC component of the δ-axis current, and the other δ
All of the alternating current component of the axis current and the γ-axis current become instantaneous reactive currents. Therefore, by passing the δ-axis component of the load current through the high-pass filter 10 and removing the DC component, an instantaneous reactive current can be obtained.

[0005] The instantaneous reactive current obtained in this way,
The current control circuit 12 controls the voltage generated in the power converter 3 so that it matches the compensation current flowing to cancel this instantaneous reactive current. The current control circuit 12 simultaneously performs control such that the DC bus voltage of the power converter 3 is constant in order to stabilize the output voltage of the power converter 3. The control command obtained by the current control circuit 12 is converted into a voltage command, which is a two-phase signal in a synchronous rotation coordinate system, by using a two-phase/three-phase converter 13.
Obtain phase voltage command.

In order to cause the power converter 3 to output a voltage according to the voltage command output from the two-phase/three-phase converter 13, the power conversion controller 14 operates the power converter at a time according to the voltage command. The self-extinguishing elements of the positive side arm and the negative side arm of each phase of No. 3 are controlled to be turned on alternately.

The instantaneous reactive power compensator is constructed so that the potential difference between the output voltage of the power converter 3 and the power supply voltage of the AC power source 1 is applied to a reactor 4, and a compensation current is caused to flow through the reactor 4.

[0008]

Problem to be Solved by the Invention Since the conventional instantaneous reactive power compensator described above is constructed as described above, the compensation current for canceling the reactive power and harmonic current is supplied to the power source.
The power converter 3 continues to operate even when almost no current flows through the grid line between loads, and therefore unnecessary ripple current due to switching in the power converter 3 flows into the grid line, causing deterioration of distortion factor, etc. There was a problem that this could happen.

The present invention has been made to solve the above-mentioned problems, and provides an instantaneous reactive power compensator that eliminates unnecessary ripple current caused by switching in a power converter when the compensation current is small. With the goal.

0010

[Means for Solving the Problems] An instantaneous reactive power compensator according to the present invention includes a load current detector that detects a current flowing through a load, and a voltage synchronization signal generator that generates a voltage synchronization signal whose phase is synchronized with a power supply voltage. an instantaneous power calculator that calculates reactive power and harmonic current from the detected load current and the generated voltage synchronization signal, and a power source that calculates compensation current for canceling the calculated reactive power and harmonic current. This output controller includes a power converter that flows through a grid line between loads, a power conversion controller that controls the power converter to flow a compensation current, and an output controller that operates based on the output of an instantaneous power calculator. The output of the power converter is input to a power conversion controller, and the power conversion controller controls the power converter to stop.

[0011]

[Operation] In the instantaneous reactive power compensator according to the present invention,
An instantaneous power calculator calculates reactive power and harmonic current from the load current detected by the load current detector and the voltage synchronization signal whose phase is synchronized with the power supply voltage generated by the voltage synchronization signal generator. A compensation current for canceling reactive power and harmonic current is made to flow through the grid line between the power source and the load using a power converter. By the way, when the compensation current is small, the output controller uses its output to stop the power converter via the power conversion controller,
Unnecessary ripple current caused by switching in this power converter is controlled so as not to flow into the grid line.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an instantaneous reactive power compensator according to an embodiment of the present invention. Reference numerals 1 to 14 in FIG. 1 are the same as those in the conventional example shown in FIG. is omitted. In the figure, 15 is an output controller that compares the value of compensation current for canceling reactive power and harmonic current with a certain reference value, and controls the stop/operation of the power converter 3 based on the comparison result.

Next, the operation of the instantaneous reactive power compensator according to the embodiment of the present invention will be explained. Reference numeral 1 in Figure 1
14 are the same as those in the conventional example shown in FIG. 2, and their operations are also the same, so detailed explanations will be omitted. Detected by load current detector 5, 3 phase/
The load current converted into the synchronous rotation coordinate system by the two-phase converter 8 has its γ-axis component intact, and its δ-axis component is obtained as the amount of current to be compensated for through the high-pass filter 10. This amount of current to be compensated is not limited to the current control circuit 12;
It is also input to the output controller 15. The output controller 15 compares the input current amount to be compensated with a certain reference value,
When the amount of current to be compensated for is less than a certain reference value, the voltage command is output to the power conversion controller 14. For this purpose, the power conversion controller 14 controls the power converter 3 and closes all of the self-extinguishing elements constituting the power converter 3 to stop the operation of the power converter 3.

[0014]

As described above, according to the instantaneous reactive power compensator of the present invention, there is provided a load current detector that detects the current flowing through the load, and a voltage synchronizer that generates a voltage synchronization signal whose phase is synchronized with the power supply voltage. A signal generator, an instantaneous power calculator that calculates reactive power and harmonic current from the detected load current and the generated voltage synchronization signal, and a compensation current for canceling the calculated reactive power and harmonic current. It is equipped with a power converter that flows through the grid line between the power source and the load, a power conversion controller that controls the power converter to flow compensation current, and an output controller that operates based on the output of the instantaneous power calculator. The output of the controller is input to the power conversion controller, and the power conversion controller controls the power converter to stop, so when the compensation current is small and there is no need to compensate, switching in the power converter is controlled. This provides an excellent effect of providing an instantaneous reactive power compensator that can prevent unnecessary ripple current from flowing through the grid line.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an instantaneous reactive power compensator that is an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a conventional instantaneous reactive power compensator.

[Explanation of symbols]

1 AC power supply 2 Load 3 Power converter 4 Reactor 5 Load current detector 6 Compensation current detector 7 Voltage synchronous signal generator 8 3-phase/2-phase converter 9 3-phase/2-phase converter 10 High pass filter 11 Voltage detector 12 Current control circuit 13 2-phase/3-phase converter 14 Power conversion controller 15 Output controller

Claims (1)

[Claims] 1. A load current detector that detects the current flowing through the load; a voltage synchronization signal generator that generates a voltage synchronization signal whose phase is synchronized with the power supply voltage; An instantaneous power calculator that calculates reactive power and harmonic current from the voltage synchronous signal generated by the voltage synchronous signal generator, and a compensation current for canceling the reactive power and harmonic current obtained by this instantaneous power calculator. a power converter that causes the power converter to flow through the system line between the power supply and the load; a power conversion controller that controls the power converter to flow the compensation current; An instantaneous reactive power compensator comprising: an output controller that controls the power conversion controller.