JPH0732539B2 - Harmonic current detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a harmonic current detection method for detecting a high frequency current of a phase current supplied to a load.

[Conventional technology]

In recent years, many industrial and household devices are equipped with a device that generates a large amount of harmonic current, such as a semiconductor rectifier device. Harmonic current is increasing and damage due to harmonic current is becoming a problem.

Conventionally, a passive filter device consisting of a capacitor and a reactor or a resistor is used to shunt a specific harmonic current of the phase current of each phase that is supplied to the load of the system and reduce the harmonic current of the system. It is being appreciated.

However, when using the passive filter device described above,
(I) The harmonic currents of a plurality of orders cannot be reduced by one filter device, (II) the frequency characteristic of the system is changed by the filter device, and (III) the filter current increases when the harmonic current increases. There are various inconveniences such as overloading of the device.

Therefore, an active filter device provided with an inverter is devised, and the active filter device injects a harmonic current formed by the inverter into a fundamental wave current of an angular frequency ωo supplied from a system to a load, Reduce harmonic currents.

In the case of the active filter device, the inverters can form harmonic currents of a plurality of orders, and since the filter device is independent of the system, each of the inconveniences described above when the passive filter device is used occurs. Will be resolved.

By the way, in the above-mentioned active filter device or the like, it is necessary to accurately detect the harmonic current of each phase supplied to the load.

On the other hand, the band elimination filter (notch filter) is generally a quadratic transfer function. (Ωx is the angular frequency of the band to be removed, Q is the resonance frequency, S
Is a complex variable filter and is obtained by transforming the transfer function As is clear from the equation, the angular frequency ωx from the input signal
The signal in the band is removed by subtraction and output.

Since the angular frequency of the fundamental wave current of each phase is constant, it is conceivable to use the band elimination filter for detecting the harmonic current of each phase.

By the way, the band elimination filter is the electronic science series “Design of Active Filter” by Sangpo Publishing Co., Ltd. (1973
As described in, for example, the first edition issued on December 10, the state variable filter circuit is used, for example, as shown in FIG.

And in FIG. 2, (1) is a filter input terminal,
(2) is a first adder that adds an input signal of the input terminal (1) and an output signal of a second integrator described later, and (3) is a first integration into which the output signal of the adder (2) is input. And (4) is a constant circuit that reduces the output signal of the integrator (3) to 1 / Q (Q is the resonance speed) and feeds it back to the input side of the integrator (3).
(5) is a second integrator that integrates the output signal of the integrator (3) and outputs it to the adder (2), (6) is the adder (2),
It is a state variable type filter circuit formed by the integrators (3), (5) and the constant circuit (4), and the output signal of the constant circuit (4) forms the output signal of the filter circuit (6).

(7) is an inverting amplifier that inverts the output signal of the constant circuit (4), and (8) is a current-transformed signal at the input terminal (1) and an amplifier (7).
Is a second adder for adding the output signal of the second output signal, and (9) is a filter output terminal connected to the adder (8).

When the input signal of the input terminal (1) is composed of the fundamental wave component and the harmonic component of the angular frequency ωo, in order to remove the fundamental wave component, the adder (2) and the integrator (2) of the filter circuit (6) The resonance angular frequency ωx of the loops 3) and (5) is set to ωo, and at this time, the output signal of the integrator (3) is the quadratic transfer function. With the bandpass filter signal set in,
The output signal of the integrator (5) is the quadratic transfer function It becomes the low pass filter signal set by.

The signal output from the constant circuit (4) to the amplifier (7) is a signal obtained by multiplying the output signal of the integrator (3) by 1 / Q, that is, a quadratic transfer function. It becomes the extraction signal of the fundamental wave component set in 1. At this time, the phase of the output signal of the constant circuit (4) matches the phase of the input signal of the input terminal (1).

Further, the amplifier (7) inverts the output signal of the constant circuit (4), and the amplifier (7) outputs the sign inversion signal of the output signal of the constant circuit (4) to the adder (8). , The sign inversion signal and the input signal of the input terminal (1) are added by the adder (8), and the signal output from the adder (8) to the output terminal (9) is the input terminal (1 ) The signal obtained by subtracting and removing the fundamental wave component from the input signal, that is, the signal of the harmonic component of the input signal, and the harmonic component of the input signal of the input terminal (1) is detected by the signal of the output terminal (9). .

When the band elimination filter of FIG. 2 is used to detect the harmonic current of each phase, a band elimination filter is provided for each phase, and the phase current of each phase is applied to the input terminal (1) of each band elimination filter. A signal formed by being detected by a current transformer, that is, a phase current detection signal having a waveform of each phase current of each phase may be input.

[Problems to be solved by the invention]

By the way, in the case of the band elimination filter shown in FIG. 2, the transient response characteristic and the steady characteristic vary depending on the Q value.
When the Q value is set to 1, 5 and a square wave signal of 120 ° conduction is input to the input terminal (1), the output signals of the amplifier (7) and integrator (5) are shown in Fig. 3 during the transition period. , As shown in FIG. 4, respectively. In addition, FIG. 3 (a), (b),
(C) shows the square wave signal of the input terminal (1), the output signal of the amplifier (7) and the integrator (5) when the Q value is set to 1, and FIGS. 4 (a) and 4 (b). , (C) are square wave signals when the Q value is set to 5, amplifier (7), integrator (5)
The output signal of is shown.

On the other hand, in the steady state, the output signals of the amplifier (7) and the integrating circuit (5) are as shown in FIGS. 5 and 6, respectively. 5 (a), (b) and (c) show the square wave signal of the input terminal (1), the output signal of the amplifier (7) and the integrator (5) when the Q value is set to 1. 6 (a), (b) and (c) show the square wave signal, the output signal of the amplifier (7) and the integrator (5) when the Q value is set to 5.

As is clear from the comparison between FIG. 3 (b) and FIG. 4 (b), increasing the Q value deteriorates the transient response.

Further, as is clear from the comparison between FIG. 5 (b) and FIG. 6 (b), when the Q value is reduced, the removal rate of the fundamental wave component in the steady state is lowered and waveform distortion occurs.

That is, in the band elimination filter shown in FIG. 2, if the Q value is reduced to increase the response speed, waveform distortion occurs in the steady state, and conversely, if the Q value is increased to reduce the waveform distortion in the steady state, the response is increased. The speed becomes slow, and it becomes difficult to improve both transient response characteristics and fundamental wave component removal characteristics.

Therefore, when the band elimination filter shown in FIG. 2 is used to detect the harmonic current of each phase, either the transient response characteristic or the fundamental current elimination characteristic deteriorates, and good detection cannot be performed. There is a problem.

The present invention provides a technique for detecting a harmonic current of a phase current supplied to a single-phase or multi-phase load quickly, with good transient response characteristics and fundamental wave current removal characteristics, with reduced waveform distortion. Subject.

[Means for solving problems]

According to the present invention, a phase current detection signal having a waveform of a phase current supplied to a load is converted into a secondary transfer function. (Ωo is the angular frequency of the fundamental wave current, Q is the resonance frequency, S is a complex variable), and a low-pass filter signal set by the transfer function is obtained, and the low-pass filter signal is obtained. Is delayed by 90 ° to form a fundamental current detection signal of the waveform of the fundamental current, and the harmonic current is detected by subtracting the fundamental current detection signal from the phase current detection signal. This is a method of detecting harmonic current.

[Action]

And the quadratic transfer function Is formed by using, for example, the output signal of the integrator (5) of the filter circuit (6) of FIG. 2, in which case the output signal of the integrator (5) is of the integrator (3). Since the phase of the output signal is advanced by 90 °, the low-pass filter signal of the filter circuit is a signal of which the phase of the fundamental current in the phase current is advanced by 90 °.

Further, as is clear from the waveforms of FIGS. 3 (c) and 5 (c), the low-pass filter signal has little waveform distortion in the steady state even if the Q value is made small and the transient response speed is made fast. It changes faithfully according to the fundamental wave current.

Therefore, the fundamental current detection signal obtained by delaying the low-pass filter signal by 90 ° becomes a signal with the same phase and waveform as the fundamental current, and the fundamental current is subtracted from the phase current detection signal to obtain the phase current. The harmonic current in the current is detected.

By reducing the Q value of the filter circuit, the fundamental current increases the transient response speed and is detected with low waveform distortion, which makes the harmonic current improve both the transient response characteristics and the fundamental current removal characteristics. Detected.

〔Example〕

Next, the present invention will be described in detail with reference to FIG. 1 showing one embodiment thereof.

In FIG. 1, (10) is a filter input terminal to which a phase current detection signal is input, (11) is a filter circuit configured the same as the state variable filter circuit (6) of FIG. 2,
(7), (8), (9) and (10) are the adder (2), integrator (3), constant circuit (4) and integrator (5) of FIG.
Corresponding to the third adder, the third integrator, the 1 / Q constant circuit, and the fourth integrator.

The filter circuit (11) is different from the filter circuit (6) in that the output signal of the integrator (10), that is, the low-pass filter signal is used as the output signal of the filter circuit (11).

Further, (12) is a delay element for delaying the phase of the low-pass filter signal of the integrator (10) by 90 ° and outputting it, and is formed by a BBD (bucket preguard device) or the like.

(13) is an inverting amplifier for inverting and outputting the output signal of the delay element (12), and (14) is a fourth addition circuit for adding the output signal of the amplifier (13) and the phase current detection signal of the input terminal (1). It is an adder. (15) is a filter output terminal connected to the adder (14).

Then, a detection signal formed by detecting the phase current supplied to the load by a current transformer or the like, that is, a phase current detection signal having a waveform of the phase current is input to the input terminal (1).

By the way, the angular frequency of the fundamental current included in the phase current is ωo
If so, the loop of the adder (7), the integrators (8), and (10) of the filter circuit (11) resonates at the angular frequency ωo of the fundamental current, as in the filter circuit (6). The bandpass filter signal output from the integrator (8) is a quadratic transfer function. Since the bandpass filter signal of the integrator (8) is further integrated by the integrator (10), the lowpass filter signal of the integrator (8) becomes 2
Transfer function It becomes the signal set by.

By the way, as is apparent from FIGS. 3 (c) and 5 (c), the low-pass filter signal of the integrator (10) is Q
Even if the value is made small and the transient response speed is made fast, there is little waveform distortion in the steady state, and the signal has a waveform faithful to the fundamental current.

On the other hand, since the phase of the bandpass filter signal of the integrator (8) matches the phase of the fundamental wave current of each phase, the integrator (10)
The low-pass filter signal of is a signal having a waveform obtained by advancing the phase of the fundamental current of each phase by 90 °.

That is, the low-pass filter signal of the integrator (10) is 90 ° of the fundamental wave current component of the phase current detection signal of the input terminal (1).
The signal has advanced phase.

Since the phase of the low-pass filter signal of the integrator (10) is delayed by 90 ° by the delay element (12), the output signal of the delay element (12) is the signal of the fundamental wave current component of the phase current detection signal, That is, the fundamental wave current detection signal has the same waveform and the same phase as the fundamental wave current.

Further, the sign of the fundamental wave current detection signal is inverted by the amplifier (13), and the output signal of the amplifier (13) and the phase current detection signal of the input terminal (1) are added by the adder (14). Therefore, from the adder (14) to the output terminal (15), the delay element (1
A signal obtained by subtracting the fundamental wave current detection signal of 2), that is, a harmonic current detection signal of the waveform of the harmonic current is output, and the harmonic current is detected by the harmonic current detection signal of the output terminal (15). .

Even if the Q value of the filter circuit (11) is decreased to increase the transient response speed, the low-pass filter signal will not be distorted in a steady state. Therefore, by decreasing the Q value, good transient response characteristics can be obtained. The harmonic current is detected by reducing the waveform distortion, the transient response characteristic and the fundamental current removal characteristic are both improved, and the harmonic current is detected. For example, when applied to an active filter device, the harmonic current is detected by the inverter. Is faithfully formed, and the harmonic current can be satisfactorily reduced.

By the way, since the self-phase harmonic current is detected using only the self-phase current, the load is a single-phase or multi-phase balanced load,
Even with an unbalanced load, the harmonic current of each phase is detected by providing the block of FIG. 1 for each phase.

The filter circuit (11) is, for example, a constant circuit (9).
The output signal may be inverted in sign and fed back to the input side of the adder (7), and it goes without saying that it can be formed by a filter having various configurations.

Further, it is needless to say that it can be applied not only to the active filter device but also to various devices such as a device for detecting a harmonic current.

〔The invention's effect〕

As described above, according to the harmonic current detection method of the present invention, the Q value of the filter circuit (11) is set to a small value, the waveform distortion is reduced with good transient response characteristics, and the phase current detection signal of its own phase is detected. Since the fundamental wave current of its own phase can be detected, it is possible to detect the harmonic current by improving both the transient response characteristic and the fundamental wave current removal characteristic regardless of the type of load.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of a method for detecting a harmonic current according to the present invention, FIG. 2 is a block diagram of a conventional band elimination filter, and FIGS. 3 (a)-(c) and 4 (a). ) To (c) are waveform diagrams for explaining the transient response characteristic of FIG. 2 when the Q value is set to 1, 5 respectively, FIG. 5 (a) to (c), and FIG. 6 (a) to ( 3C is a waveform diagram for explaining the steady-state characteristic of FIG. 2 when the Q value is set to 1, 5 respectively. (11) …… Filter circuit, (12) …… Delay element, (13)
…… Inverting amplifier, (14) …… Adder.

Claims (1)

[Claims] 1. A phase transfer current detection signal having a waveform of a phase current supplied to a load is converted into a quadratic transfer function. (Ωo is the angular frequency of the fundamental wave current, Q is the resonance frequency, S is a complex variable), and a low-pass filter signal set by the transfer function is obtained, and the low-pass filter signal is obtained. Is delayed by 90 ° to form a fundamental current detection signal of the waveform of the fundamental current, and the harmonic current is detected by subtracting the fundamental current detection signal from the phase current detection signal. Harmonic current detection method.