JPH02262840A - Controller for active filter - Google Patents

Abstract

PURPOSE:To reduce switching loss of main switching element without sacrifice of higher harmonic suppressing effect by automatically resulting PWM carrier frequency of a PWM converter based on comparison result between detected higher harmonic and voltage distortion and preset operating conditions. CONSTITUTION:A carrier frequency (fc) controlling circuit 9C is preset to vary the carrier frequency on some conditions, and when a specific order harmonic is a problem because of the character of load setting is made according to the character of the system or the load. In this case, the fc controlling circuit 9C responds quickly to the conditions for increasing fc while responds to the conditions for decreasing fc such that operation is started upon continuation of that condition for a predetermined time. When a main circuit element 10 is switched with as low fc as possible within such range as voltage distortion at system side and the amount of higher harmonics to be produced from the load satisfy preset conditions, an active filter can be functioned effectively with minimum switching loss.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is directed to the control of a PWM converter type active filter connected to the output end of a power system in order to remove harmonics generated from a load. It is related to the device.

(Conventional technology) In recent years, as various power electronics devices have become widespread in the industrial field, the power electronics devices have become increasingly popular.

A problem has arisen in that the generated harmonics flow into the power system.

As one of the effective means to solve this problem, GTO,
A PWM converter type that uses high-speed switching of a self-extinguishing semiconductor power device such as an SI thyristor to inject a compensation current in the opposite phase to the harmonics generated by the load into the load connection line or bus bar to cancel out the generated harmonics. Active filters are attracting attention.

The configuration of a conventional PWM converter type active filter is shown in Figure 2.The main circuit type includes a voltage type that uses a DC voltage source and a current type that uses a DC current source.Here, an example of the voltage type is shown. It is shown.

In Fig. 2, 1 is the power system, 2 is the harmonic generation load,
3 is an active filter main circuit, and 4 is an active filter control circuit. For simplicity, only one phase of the control circuit is shown.

The main circuit 3 of the active filter is constructed by assembling a module 12 in which a self-extinguishing semiconductor element 10 (hereinafter simply referred to as a main circuit element) and a diode 11 are connected in antiparallel to form a bridge. 13 is a reactor, and 14 is a DC capacitor.

The compensation current command value calculation circuit 5 has a function of detecting a harmonic component Ih from the load current If taken in by the CT 15 and calculating a current command value 8 to be compensated by the active filter.

The constant current control circuit 6 performs constant current control so that the current command value and the output current IACF of the active filter taken in by the CT 16 match, and outputs the reference voltage signal E. Output.

Since this reference voltage signal EC is a continuous quantity, it must be converted into an on/off signal for the main circuit elements. Each main circuit element 10 is compared in size.
By determining the on/off timing of the gate pulse, that is, the phase of the gate pulse of each element, and operating each element according to this gate pulse, the DC voltage Vd across the DC capacitor 14 is controlled by PWM, and the active filter is Outputs a compensation current that cancels out the load harmonic Ih.

Fig. 3 shows the PWM control operation of the gate pulse generation circuit 7 using a single-phase active filter as an example, where X is a carrier wave, Y is a carrier wave obtained by inverting X, and EC is a reference voltage signal. By comparing X, EC, and Y, the on/off patterns of the main circuit elements 10A to 100 are determined.

The output terminal voltage vc' of the active filter becomes a strip-shaped pulse train as shown in the lower part of FIG.
The output voltage VC that has passed through has a waveform isometrically shown by a dotted line. Also, the switching frequency of the main circuit elements is PWMII
It is determined by the transmission frequency fc.

(Problem to be Solved by the Invention) Generally, as the PWM carrier frequency fC increases, the harmonic compensation effect of the active filter increases, so the active filter is operated with fc fixed at a constant value as high as possible within the range allowed by the element characteristics. It is normal to do so.

However, if fc is increased, the switching loss will increase and the efficiency of the device will deteriorate.Also, if the harmonics generated by the load change and each harmonic component decreases, a higher carrier frequency is required. There is no need to operate the device as it is.

In particular, recently, as the current and voltage ratings of main circuit elements have increased, the operating frequency has also improved from several kHz to several tens of kHz, and the switching loss has also become considerable, so the switching frequency (i.e. carrier frequency) has to be adjusted depending on the situation. It is necessary to reduce switching loss by adjusting the switching loss.

SUMMARY OF THE INVENTION An object of the present invention is to provide a rational control device for a PWM converter type active filter that reduces switching loss of main circuit elements without impairing the harmonic suppression effect and thereby improves operating efficiency.

[Structure of the invention]

(Means and effects for solving the problem) The present invention provides a control device for a PWM converter type active filter that is connected in parallel to a harmonic generating load connected to an electric power system and compensates for harmonics generated in the load. ,
A harmonic detection circuit that detects each harmonic generated in the load, a voltage distortion detection circuit that detects voltage distortion at the time of load input, and a comparison of the detected harmonics and voltage distortion with preset operating conditions, Based on the comparison results, PWM
Equipped with a carrier frequency control circuit that automatically adjusts the PW and M carrier frequencies of the converter, it performs PWM control of the PWM converter at the lowest carrier frequency within the range that satisfies the operating conditions, thereby reducing switching loss of the main circuit elements of the PWM converter. This is aimed at improving the operating efficiency of the active filter by minimizing the amount of noise.

(Example) An example of the present invention is shown in FIG. In Figure 1, the second
The same parts as in the figures are given the same symbols and their explanations are omitted.

In Figure 1, 9A is a circuit that measures the voltage distortion rate of the grid, 9B is a circuit that measures each harmonic included in the load current, and 9C is a circuit that determines whether to raise or lower the carrier frequency from the measurement results of 9A and 9B above. This is a carrier frequency control circuit.

The carrier wave frequency control circuit 9C is set in advance under what conditions the carrier wave frequency is to be changed. The carrier frequency is lowered under the condition that it is less than B% of the

If harmonics of a specific order are a problem due to the nature of the load,
Settings are made according to the characteristics of the system and load, such as ``increase the carrier frequency when the N-order harmonic becomes 0% or more of the fundamental wave.''

In this case, the carrier wave frequency control circuit 9C responds quickly to the condition of increasing the carrier wave frequency, and starts operating after the condition continues for a certain period of time to the condition of decreasing the carrier wave frequency.

This is to avoid frequent increases and decreases in the carrier wave frequency in the case of a load in which harmonics vary randomly. give a signal.

In this way, by switching the main circuit element IO at the lowest possible carrier frequency within the range where the voltage distortion on the grid side and the amount of harmonic generation in the load satisfy the preset conditions, the active filter can be made effective with minimum switching loss. It becomes possible to operate it.

〔Effect of the invention〕

As explained above, according to the control device for the PWM converter type active filter of the present invention, the switching of the main circuit elements is performed at the lowest possible carrier frequency within the preset conditions, so that the desired harmonic suppression effect can be achieved. Switching loss was reduced without any loss. Highly efficient active filter operation can be achieved.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an example of an active filter control device according to the present invention, FIG. 2 is a system diagram showing an example of a conventional active filter control device, and FIG. 3 is an explanation of PWM control of an active filter. It is a diagram. 1... Power system ja2... Harmonic generation load 3... Active filter main circuit 4... Active filter control circuit 5... Compensation current command value calculation circuit 6... Constant current control circuit 7. ...Gate pulse generation circuit 8...Carrier wave generation circuit 9A...Voltage distortion detection circuit 9B...
・Harmonic detection circuit 9C...carrier frequency control circuit
10. l0A-100...Main circuit element 11...Diode 12...Module 13...
Reactor 14...DC capacitor 1
5, 16...CT (8733) Agent Patent attorney Yoshiaki Inomata (and 1 other person) Figure 1 +3121011

Claims (1)

[Claims] Harmonic detection detects each harmonic generated by the load in a control device for a PWM converter type active filter that is connected in parallel to a harmonic generating load connected to the power system and compensates for harmonics generated by the load. A voltage distortion detection circuit that detects voltage distortion at the load input terminal compares the detected harmonics and voltage distortion with preset operating conditions, and automatically adjusts the PWM carrier frequency of the PWM converter based on the comparison results. 1. A control device for an active filter, comprising a carrier frequency control circuit for adjusting.