JPH10145973A - Control of active filter for electric power - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the highest compensation effect in a prescribed value range of output current by conducting control so that the effective value of a compensation current command value may be always a prescribed one, and the waveform of the compensation current command value obtained after an inverse number is multiplied may be similar to that of the compensation current command value obtained before the multiplication. SOLUTION: An effective value calculation circuit 601 finds the effective value of a compensation current command, and if it is within a prescribed value range, a limiter circuit 602 outputs '1'. If the effective value is in excess of the prescribed value range, an inverse number is outputted at a excess rate. A multiplication circuit 603 receives the output of a limiter circuit 602 and the output of two-phase/three-phase conversion circuit 67 to conduct mutual multiplication for output. If the output of the effective value calculation circuit 601 is in the prescribed value range, a value obtained by multiplying the output of two-phase/three-phase conversion circuit 67 by '1', that is, the compensation current command of the output of two-phase/three-phase conversion circuit 67 is outputted from the multiplication circuit 603. It is thus possible to provide the highest compensation effect in the prescribed value range of output current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an active power filter.

[0002]

2. Description of the Related Art As the application of a power converter using a power semiconductor device expands, the adverse effect of reactive power and harmonics generated by the power converter on other devices installed in a power system becomes a problem. It has become to. As a countermeasure against these adverse effects, an LC filter has conventionally been used, but there has been a problem that a sufficient compensation effect cannot be obtained when resonance occurs with the system impedance or when the frequency of a harmonic wave fluctuates.

In order to solve the problem of the LC filter, an active power filter using a PWM converter has recently been used. FIG. 4 shows an example of the main circuit configuration of the active power filter. The active power filter 10 includes a capacitor 3, a reactor 4, and a converter unit 5.
It is composed of The converter unit 5 is a transistor
51, a three-phase bridge composed of a diode 52 and a capacitor 53 for DC power supply. A load device 2 that generates harmonics and reactive power is connected to a commercial power supply 1,
An active power filter 10 is connected to the commercial power supply 1 in parallel with the load device 2. Examples of the load device 2 include a thyristor leonard device and a capacitor input type diode rectifier.

The active power filter 10 detects a current flowing into the load equipment 2 by a control circuit (not shown), operates to cancel harmonics and reactive power contained in the current, and supplies a power to the commercial power supply 1. A sinusoidal current with a rate of 1 flows. FIG. 5 shows a configuration example of a control circuit of a conventional power active filter. The control circuit 6 includes three-phase / two-phase conversion circuits 61 and 62, a P / Q conversion circuit 63, a filter circuit 64,
65, a P / Q inverse conversion circuit 66, a two-phase / three-phase conversion circuit 67, an adder 68, and a transistor drive circuit 69.
Further, current detectors 7 and 8 for taking in signals necessary for control are connected to the main circuit.

Next, the operation of the control circuit 6 will be described. The control circuit 6 takes in the voltage of the commercial power supply 1 and the load current flowing through the load device 2 via the current detector 7 and converts each of the voltages into two-phase signals at three-phase / two-phase conversion circuits 61 and 62. Furthermore, P, Q
The conversion circuit 63 separates the power into active power and reactive power, and the filter circuits 64 and 65 take out the harmonic active power and the harmonic reactive power to be compensated. The obtained harmonic active power and harmonic reactive power to be compensated are returned to a two-phase signal by the P / Q inverse conversion circuit 66, and a two-phase / 3-phase conversion circuit 67 is used as a compensation current command for three phases. . The compensating current command and a signal obtained by detecting the output current of the converter unit 5 with the current detector 8 are compared by an adder 68, and a transistor driving circuit 69 generates a drive signal for each transistor 51 of the converter unit 5. The conversion is performed to control the power active filter.

[0006]

The current to be output from the power active filter 10 is determined by harmonics and reactive power generated by the load device 2. Further, since converter unit 5 is formed of a power semiconductor, there is a limit on the current that can be output. If a current exceeding this limit is passed, the power semiconductor and other main circuit components that make up the converter section may be damaged, or the power active filter 10
Will shorten the life of the device. To avoid such a problem, a specified value is set for the output current of the power active filter 10. If the harmonics or reactive power generated by the load device 2 exceeds the specified value of the power active filter 10, some limitation must be provided.

In general, the output current is limited by detecting the instantaneous waveform of the output current and limiting the output current to a value exceeding a certain value so that the output current does not flow any more. When the output current is limited by this method, for example, when the effective value of the output current is sufficiently within the specified value range of the power active filter 10, but the compensation is performed such that the peak current flows only for a moment. However, if only the value exceeding a certain value is uniquely limited, not only the sufficient compensation effect by the power active filter 10 cannot be obtained, but also the power active filter 10 itself becomes a harmonic generation source. There is also. In addition, the utilization rate of the converter unit 5 becomes poor.

[0008]

As means for solving the above problems, a compensation current command value to be compensated by the power active filter in a power active filter including a converter, a capacitor, and a reactor is calculated. Calculating the effective value of the compensation current using the compensation current command value, and when the effective value is within the range of the specified value of the power active filter, outputs the computed compensation current command value as it is, If the effective value exceeds the specified value of the active power filter, calculate the reciprocal of the ratio that became larger than the specified value, multiply this reciprocal by the compensation current command value, and the effective value of the compensation current command value is always the specified value. In addition, control can be performed by controlling the waveform of the compensation current command value after multiplication by the reciprocal to be similar to the waveform of the compensation current command value before multiplication. That.

As another solution, a compensation current command value to be compensated by the power active filter is calculated, a current output from the converter is detected, and an effective value of the compensation current is calculated using the current. If the effective value is within the specified range of the power active filter, the calculated compensation current command value is output as it is, and if the effective value exceeds the specified value of the power active filter, the specified value is output. The reciprocal of the larger ratio is calculated, the reciprocal is multiplied by the compensation current command value, and the effective value of the compensation current command value is always a specified value, and the waveform of the compensation current command value after multiplying the reciprocal is , Can be realized by controlling the waveform so as to be similar to the waveform of the compensation current command value before performing the multiplication.

[0010] Further, a compensation current command value to be compensated by the power active filter is calculated, a current output from the converter is smoothed by the capacitor and the reactor, and a current is detected. Calculates the effective value of the current, and if the effective value is within the range of the specified value of the active power filter, outputs the calculated compensation current command value as it is, and sets the effective value to the specified value of the active power filter. If it exceeds, calculate the reciprocal of the ratio that is larger than the specified value, multiply this reciprocal by the compensation current command value, the effective value of the compensation current command value is always the specified value, and after multiplying the reciprocal It can also be realized by controlling the waveform of the compensation current command value to be similar to the waveform of the compensation current command value before performing the multiplication.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The output current of a power active filter is determined according to the compensation capacity. By expressing this output current as an effective value, it is possible to indicate the capability of the output current of the power active filter regardless of the output current waveform. In addition, by expressing the effective value, it is possible to determine the thermal use state of the converter and other components constituting the main circuit of the power active filter. By determining the specified value of the output current of the power active filter by the effective value, the capability of the output current of the power active filter can be properly evaluated. If the power active filter operates within the range of the output current specified by the effective value, sufficient compensation can be performed regardless of the output current waveform.

When the effective value of the output current exceeds a specified value, the current command value to be compensated is multiplied by a coefficient such that the effective value becomes the specified value, and the effective value of the output current falls within the specified value range. In this case, the output current has a waveform similar to the current waveform of the output current that the power active filter originally needs to perform the compensation and has a specified value. Therefore, if the effective value of the output current exceeds the specified value, the harmonics and reactive power generated by the load equipment cannot be completely compensated, but without stopping the power active filter, the output current Can be performed while maintaining the compensation operation in the state of the specified value.

[0013]

FIG. 1 is a block diagram showing a first embodiment of the present invention. In FIG. 1, components having the same reference numerals as those in FIG. 5 have the same configuration and function. In FIG. 1, an effective value calculation circuit 601, a limiter circuit 602, and a multiplication circuit 603 are added to the conventional control circuit in FIG. Note that 6
A is a control circuit, and 10A is a power active filter, which are portions corresponding to 6 and 10 in FIG. 5, respectively. 2
Up to the point where the phase / 3-phase conversion circuit 67 outputs a compensation current signal for three phases, it is the same as the conventional circuit, but immediately thereafter, the output current of the converter section 5 is compared with the signal of the current detector 8. First, the effective value calculation circuit 601 obtains the effective value of the compensation current command. If the effective value is within the specified value range, the limiter circuit 602 outputs “1”. Also,
If the effective value exceeds the specified value range, the reciprocal of the ratio of the excess is output. For example, if the output of the effective value calculation circuit 601 is equivalent to 200% of the specified value, the limiter circuit 602 operates to output 0.5, which is the reciprocal of 2.0.

The multiplication circuit 603 receives the output of the limiter circuit 602 and the output of the two-phase / three-phase conversion circuit 67, multiplies each other, and outputs the result. If the output of the effective value calculation circuit 601 is within the specified value range, a value obtained by multiplying the output of the two-phase / three-phase conversion circuit by “1”, that is, the compensation current command as it is as the output of the two-phase / three-phase conversion circuit 67 Is output from the multiplication circuit 603. If the output of the effective value calculation circuit 601 exceeds the specified value range, the multiplication circuit
From 603, a compensation current command in which the result of the multiplication is always a specified compensation current command value is output. As a result, the current detector 8
Is equal to or less than 100% of the specified value in any case.

In the case of this embodiment, control can be performed only by signals in the control circuit without adding any components to the main circuit side. Further, since the effective value calculation circuit 601 performs calculation in units of the cycle of the commercial power supply 1, a high-speed calculation speed for performing instantaneous waveform control is not required. In the case of this embodiment, the input of the effective value calculation circuit 601 is a two-phase / three-phase conversion circuit 67.
However, it is naturally possible to calculate the effective value of the compensation current command from the output of the P and Q inverse conversion circuit 66.

FIG. 2 shows a second embodiment of the present invention. FIG.
The difference from this embodiment is that the input of the effective value calculation circuit 601 is 2
This is where the signal output from the current detector 8 is not the output from the phase / 3-phase conversion circuit 67. 6B is a control circuit, and 10B is a power active filter, which are portions corresponding to 6 and 10 in FIG. 5, respectively. The difference from the first embodiment is that the effective value is not calculated by the control signal but is calculated by using the effective value of the actual output current of the power active filter. Therefore, it is not necessary to consider an error between the control signal and the actual output current.
Also in the case of this embodiment, similarly to the embodiment of FIG. 1, control can be performed only by signals in the control circuit without adding any components to the main circuit side.

FIG. 3 shows a third embodiment of the present invention. The effective value calculation circuit 601 calculates the effective value of the actual output current of the converter unit 5 as in the embodiment of FIG. However, a current detector 604 is newly provided at a point where the detection point of the output current of the converter unit 5 has a ripple current removed by the reactor 4 and the capacitor 3, and an output signal of the current detector 604 is used as an effective value calculation circuit 601. To calculate the effective value. 6C is a control circuit, and 10C is a power active filter, which are portions corresponding to 6 and 10 in FIG. 5, respectively. In the case of the present embodiment, it is necessary to newly provide a current detector 604 on the main circuit side. However, since the ripple current due to the switching of the transistor 51 is removed by the reactor 4 and the capacitor 3, the signal here is Detection is easy even when a current having a high peak value flows due to the transient fluctuation of 2.

[0018]

According to the control method of the active power filter according to the present invention shown in FIGS. 1, 2 and 3, the load device 2 generates unexpected harmonics and reactive power and compensates them. When it becomes necessary to flow a compensation current exceeding a specified value that can be output from the power active filter, the effective value of the output current of the power active filter becomes 10% of the specified value.
Since it is controlled so that it is equivalent to 0% and is output with a waveform similar to the current waveform originally required for compensation, it is uniquely compared with a control method that cuts a certain current or more of the instantaneous current waveform to limit the current. However, the highest compensation effect can be obtained within the specified range of the output current without stopping the power active filter. Further, the converter unit 5 can be used most efficiently. Of course, if the output current of the power active filter required for compensation is within the specified value range,
It goes without saying that control can be performed at a compensation rate of 100% regardless of the peak value of the output current waveform.

[Brief description of the drawings]

FIG. 1 is a block diagram of a control circuit according to the present invention.

FIG. 2 is a block diagram of a second control circuit according to the present invention.

FIG. 3 is a block diagram of a third control circuit according to the present invention.

FIG. 4 is a main circuit configuration example of an active power filter.

FIG. 5 is a block diagram of a conventional control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Load equipment 3,53 Capacitor 4 Reactor 5 Converter part 6,6A, 6B, 6C Control circuit 7,8,604 Current detector 10,10A, 10B, 10C Power active filter 51 Transistor 52 Diode 61,62 3 phase / 2 phase conversion circuit 63 P / Q conversion circuit 64, 65 filter circuit 66 P / Q inverse conversion circuit 67 2 phase / 3 phase conversion circuit 68 Adder 69 Transistor drive circuit 601 Effective value calculation circuit 602 Limiter circuit 603 Multiplication circuit

Claims (3)

[Claims] 1. A power active filter comprising a converter section, a capacitor, and a reactor, calculates a compensation current command value to be compensated by the power active filter, and calculates an effective value of the compensation current using the compensation current command value. If the effective value is within the range of the specified value of the current of the power active filter, the calculated compensation current command value is output as it is, and if it exceeds the specified value, it becomes larger than the specified value. The reciprocal of the ratio is calculated, and the reciprocal is multiplied by the compensation current command value. The effective value of the compensation current command value is always a specified value, and the waveform of the compensation current command value after multiplying the reciprocal is multiplied. A control method for a power active filter, wherein the control is performed so that the waveform is similar to the waveform of the compensation current command value before performing. 2. The method according to claim 1, wherein an effective value of the compensation current is calculated using a current output from the converter instead of calculating an effective value of the compensation current using the compensation current command value.
The control method of the active power filter described in the above. 3. The electric power according to claim 1, wherein instead of calculating the effective value of the compensation current using the compensation current command value, the effective value of the compensation current is calculated using the current smoothed by the capacitor and the reactor. How to control the active filter.