JPH1051956A - Active filter control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the operation accuracy of an active filter control circuit by obtaining the integral multiple signals of inputted first and second detected digital values, by comparing a compensating current command obtained by computing higher harmonics contained in the first detected digital value with the second detected digital value which is the compensating current of an active filter. SOLUTION: In a CPUm 343', a compensating current computing section 3436 inputs signals through an integral multiplier 3439 and a subtractor 3438 generates compensating current commands ICU*' and ICV*'. In a CPUs 344', compensating currents ICU' and ICV' are supplied to a subtractor 3441 through an integral multiplier 3432. The subtractor 3441 compares the commands ICU*' and ICV*' with the currents ICU' and ICV' and generates a gate command Sg'. The integral multipliers 3439 and 3442 are signal generators which raise the signal levels of input digital values to signal levels which are 2n times as high as the original. levels. Thus, the level of a feedback signal which is compared with the signal of a higher harmonic component in an arithmetic circuit is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter which intervenes between a power supply system and a load to perform harmonic compensation, and more particularly to an active filter control circuit in which the calculation accuracy in a control circuit is improved. , It is about.

[0002]

2. Description of the Related Art FIG. 2 shows an application example of an active filter, 1 is a power supply system, 2 is a load, 3 is an active filter (hereinafter referred to as ACF), 41 is a current transformer for detecting load current,
Reference numeral 42 denotes a current transformer for detecting a power supply current. In the ACF 3, 31 is a power transformer, 32 is an AC reactor, 33 is a power converter, 34 is a control circuit, 35 is a ripple filter, 36 is a voltage detecting transformer, and 37 is a compensation current detecting current transformer. It is.
Furthermore, VCD is a DC voltage supplied from the power converter 33 to the control circuit 34, Eu and Ev are system voltages detected by the voltage detecting transformer 36, and ILU and ILV are detected by the load current detecting current transformer 41. The detected load currents ISU and ISV are the power supply currents ICU and ICU detected by the power supply current detection current transformer 42, respectively.
CV is a compensation current detected by the compensation current detection current transformer 37. Such an ACF 3 is commonly used, and a detailed description thereof is omitted here. Next, a control circuit of the ACF is shown in FIG.

FIG. 3 shows an example of a typical control circuit of an ACF. Reference numerals 341 and 342 denote A / D converters for performing analog-to-digital signal conversion. Reference numeral 343 denotes a CPU m which is a CPU having a compensation current calculation function. Here, CPUs, which are CPUs having a comparison operation function, and Sg are power converters of FIG.
Gate command for 33. In CPUm 343,
Reference numerals 3431 and 3432 denote 3φ / 2φ converters, 3433 denotes an instantaneous power calculation unit, 3434 denotes a low-pass filter, 3435 denotes an adder, 3436 denotes a compensation current calculation unit, 3437 denotes a 2φ / 3φ converter, and 3438 denotes a subtractor. . In the CPUs 344, 3441 is a subtractor.

That is, although such a control circuit is also known, the DC voltage VCD, the system voltages Eu and Ev and the load current
The LU and ILV (or power supply currents ISU and ISV) are converted into digital signals via the A / D converter 341 and taken in by the CPU m 343. The CPU m 343 roughly indicates the load current (or power supply current) to be compensated and the system. Voltage and instantaneous power calculations are performed, and compensation current calculations are performed using harmonic components from which fundamental components have been removed. Compensation current commands ICU * and ICV
* Is obtained. Further, the compensation currents ICU and ICV are converted into digital signals via the A / D converter 342 and taken into the CPUs 344, and the subtractor 3441 compensates for the compensation current commands ICU * and ICU *.
CV * is compared with compensation currents ICU and ICV, and gate command S
g is obtained. Thus, the ACF 3 is connected to the power supply system 1,
The control circuit 34 intervenes between the loads 2 and the gate command Sg
Is generated in the power converter 33, and the compensation currents ICU, ICU * and ICV * are adjusted so that the power converter 33 becomes the compensation current commands ICU *, ICV *.
It controls CV to compensate for harmonics.

[0005]

In this type of ACF, that is, an ACF in which a compensation current command is obtained from an output of a current transformer of a system current and a compensation current is injected into the system, a case where a load current is obtained by a control circuit thereof. If the conversion ratio of the A / D converter that converts the detected value of the load current is an analog input (± 2 V) with reference to the fundamental wave, the output at the time of 8 bits is (±
128) Steps. Therefore, when the harmonic component in the load current is as small as 5% of the fundamental wave, the conversion ratio output is (± 100) steps for the fundamental wave and (± 5) steps for the harmonic component. The result is a fairly rough control level. Therefore, when the calculation is performed using such values, the compensation performance of the ACF deteriorates due to an error in detection accuracy. In addition, when the power supply current is obtained, since the system current after compensation by the ACF is detected, similarly, the number of steps corresponding to the harmonic of the conversion ratio output decreases, and the compensation performance of the ACF deteriorates. Further, when the signal level is low, the signal level is liable to be affected by noise, and the calculation error increases.

An object of the present invention is to improve the operation accuracy in the control circuit and improve the compensation performance even when the A / D conversion ratio output based on the current detection current transformer output is low. To provide a special device.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has the following structure. That is, a control circuit of an ACF that obtains a compensation current command from a current transformer output of a system current and injects a compensation current into the system calculates a harmonic component included in a first detection digital value that is a load current or a power supply current. And a comparing means for obtaining a second detected digital value which is a compensation current of the ACF to be compared with the compensated current command.
And a signal generating means for obtaining an integer multiple signal of the detected digital value input.

According to this solution, an integer multiplier for increasing the signal level of each of the harmonic component input of the compensation current calculation means and the compensation current input of the comparison means by 2n times is provided. By comparing the current command with the compensation current, a gate command to the power converter can be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a main part of an embodiment of the present invention in a manner similar to FIG.
m and 344 'are CPUs and Sg' is a gate command for the power converter 33 of FIG. That is, in the CPU m 343 ′, the compensation current calculation unit 3436 inputs a signal via the integer multiplier 3439, and eventually, the subtractor 3438 outputs the compensation current commands ICU * ′, ICV
* 'Occurs. In the CPUs 344 ', compensation currents ICU' and ICV 'are given to the subtractor 3441 via the integer multiplier 3442, and the subtractor 3441 generates compensation current commands ICU *' and ICV.
* 'And the compensation currents ICU' and ICV are compared, and a gate command Sg 'is generated. Here, the integer multiplier 3439 and the integer multiplier 3442 are signal generators for increasing the signal level by 2n times the input digital value. Thus, in the example of FIG. 1, by increasing the signal level of the harmonic component in the arithmetic circuit and further increasing the level of the feedback signal to be compared with it, the arithmetic accuracy is improved, and as a result, the compensation performance is improved. It is clear.

[0010]

As described in detail above, according to the present invention, even if the A / D conversion ratio output based on the current detection current transformer output is low, the calculation accuracy in the control circuit is improved and the compensation performance is improved. Thus, it is possible to provide an apparatus having a simple configuration.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a configuration of a main part of an embodiment of the present invention.

FIG. 2 is a system diagram showing an application example of an active filter.

FIG. 3 is a system diagram showing a conventional example of a typical control circuit of an active filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply system 2 Load 3 Active filter 31 Power transformer 32 AC reactor 33 Power converter 34 Control circuit 341 A / D converter 343 'CPUm 3431 3φ / 2φ converter 3433 Instantaneous power calculator 3434 Low-pass filter 3436 Compensation Current calculation part 3437 2φ / 3φ converter 3439 Integer multiplier 344 'CPUs 3442 Integer multiplier 35 Ripple filter 36 Voltage detection transformer 37 Compensation current detection current transformer 41 Load current detection current transformer 42 Power supply current detection Current transformer VCD DC voltage Eu System voltage ILU Load current ISU Power supply current ICU Compensation current ICU 'Compensation current ICU * Compensation current command ICU *' Compensation current command Sg Gate command Sg 'Gate command

Claims (1)

[Claims] An active filter interposed between a power supply system and a load for compensating for harmonics by a power converter, wherein a harmonic component included in a first detection digital value that is a load current or a power supply current is calculated. The first detected digital value and the second detected digital value, the second detected digital value being a compensation current of the active filter to be compared with the compensation current command. An active filter control circuit comprising signal generation means for obtaining an integer multiple signal of the detected digital value input.