JPH0732538B2 - Three-phase circuit harmonic current detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a three-phase circuit harmonic current detection method for detecting a harmonic current of each phase of a balanced three-phase circuit.

[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.

In the past, it was possible to reduce the harmonic current of the system by shunting a specific harmonic current of the phase current of each phase supplied to the load of the system with a passive filter device consisting of a capacitor and a reactor or resistor. Has been done.

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 current of an angular frequency ωo supplied from a system to a load, Reduce harmonic currents.

In the case of an active filter device, harmonic currents of a plurality of orders can be formed by the inverter, and since the filter device is independent of the system, each of the inconveniences described above when using the passive filter device is eliminated. 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.

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 a constant frequency of ωo, it can be considered 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 “Designing an active filter” by Koho Publishing Co., Ltd. (1973
As described in, for example, the first edition issued on December 10, the state variable filter circuit is used, as shown in FIG. 4, for example.

And in FIG. 4, (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 the input signal of the input terminal (1) and the 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. 4 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. It suffices to input, for example, a signal formed by detection by a current transformer or the like, that is, a phase current detection signal of each waveform of the phase current of each phase.

[Problems to be solved by the invention]

By the way, in the case of the band elimination filter shown in Fig. 4, the transient characteristics and steady-state characteristics change depending on the Q value, and the Q value is set to 1 and 5, respectively, and the input terminal (1) is energized at 120 °. When the square wave signal of is input, the amplifier (7),
The output signal of the integrator (5) is 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.

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. 7 and 8, respectively. In addition,
7 (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. , FIG. 8 (a), (b),
(C) shows the square wave signal when the Q value is set to 5, the output signal of the amplifier (7) and the integrator (5).

As is clear from the comparison between FIG. 5 (b) and FIG. 6 (b), the transient response is deteriorated when the Q value is increased.

Further, as is clear from the comparison between FIG. 7 (b) and FIG. 8 (b), if the Q value is made smaller, 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. 4, if the Q value is made small in order to increase the response speed, waveform distortion occurs in the steady state, and conversely, if the Q value is made large in order to reduce the waveform distortion in the steady state, the response is made. 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 of FIG. 4 is used to detect the harmonic current of each phase, either transient response characteristic or fundamental current elimination characteristic deteriorates, and good detection cannot be performed. There is a problem.

The present invention makes both transient response characteristics and fundamental current removal characteristics good, particularly in the case of a three-phase balanced load, that is, a balanced three-phase circuit, to quickly and reduce waveform distortion to improve harmonics of each phase. The technical problem is to detect the wave current.

[Means for solving problems]

According to the present invention, a phase current detection signal having a waveform of each phase current of each phase of a balanced three-phase circuit 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 low-pass filter signals of each phase set by the transfer function are obtained, A fundamental wave current detection signal of each waveform of the fundamental wave current of each phase is formed by subtractive synthesis of the low-pass filter signals of each two phases, and the fundamental wave current of each phase is formed from the phase current detection signal of each phase. A method for detecting a harmonic current of a three-phase circuit, which is characterized by detecting a harmonic current of each phase by subtracting a detection signal.

[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. 4, in which case the output signal of the integrator (5) is of the integrator (3). Since the output signal has a phase advanced by 90 °, the low-pass filter signal of each filter circuit has a waveform obtained by advancing the phase of the fundamental current of each phase by 90 °.

Further, as is clear from the waveforms of FIG. 5 (c) and FIG. 7 (c), the output signal of the integrator (5) remains constant even if the Q value is made small to increase the transient response speed. There is little waveform distortion at all times, and it changes faithfully according to the fundamental wave current.

On the other hand, in the case of a balanced three-phase circuit, the phase currents of the three phases supplied to the load are 120 ° out of phase.

Therefore, the signal formed by subtracting and combining the low-pass filter signals of each two-phase has the phase of the fundamental current of each two-phase of 90.
° It becomes a vector composite signal of the advanced signal, that is, the fundamental current detection signal of the waveform of the fundamental current of each phase. In this case, by reducing the Q value of each filter circuit,
The fundamental wave current of each phase is detected with high transient response speed and without waveform distortion, whereby the harmonic current of each phase is detected with good transient response characteristics and fundamental wave current removal characteristics.

〔Example〕

Next, the present invention will be described in detail with reference to FIGS. 1 to 3 showing one embodiment thereof.

Now, assuming that the load of the balanced three-phase circuit forms the source load of the harmonic current, the phase currents of the three phases supplied to the source load are 120 ° out of phase and The harmonic current is superimposed on the wave current.

Then, in order to detect the harmonic current of each phase, first, the phase current of each phase is detected by a current transformer to form a phase current detection signal of each waveform of the phase current of each phase.

Next, the current detection signals for each phase are shown in FIG. 1 (a), (b),
As shown in (c), the phase current detection signal input terminal (10
a), (10b), (10c) through each filter circuit (11
Input a), (11b), and (11c) respectively.

By the way, each of the filter circuits (11a) to (11c) is formed in the same manner as the state variable type filter circuit (6) of FIG. 4, and (12a), (12b) and (12c) in the figure are adders (2 ) Corresponding to the third adder, (13a), (13b) and (13c) corresponding to the third integrator corresponding to the integrator (3), (14a), (14b) and (14).
c) is a 1 / Q constant circuit corresponding to the constant circuit (4), (15
a), (15b), (15c) are the fourth equivalent to the integrator (5)
It is an integrator.

Note that the filter circuits (11a) to (11c) differ from the filter circuit (6) in that the output signals of the integrators (15a) to (15c), that is, the low-pass filter signals are transferred to the filter circuits (11a) to (11a). (11c) is the output signal.

The adder (12) of each of the filter circuits (11a) to (11c)
a) to (12c), integrators (13a) to (13c), (15a) to (1
The loop of 5c) resonates at the angular frequency ωo of the fundamental wave current of each phase, and at this time, the bandpass filter signals output from the integrators (13a) to (13c) are quadratic transfer functions. The signal is set by the integrator (15a) ~ (15a
c) further integrates the band pass filter signals of the integrators (13a) to (13c), so that the integrators (15a) to (1
The low-pass filter signal in 5c) is a quadratic transfer function It becomes the signal set by.

By the way, as is apparent from FIGS. 5 (c) and 7 (c), the low-pass filter signals of the integrators (15a) to (15c) can be obtained even if the Q value is reduced and the transient response speed is increased. ,
There is little waveform distortion in the steady state, and the signal has a waveform that is faithful to the fundamental current of each phase.

On the other hand, since the phase of the bandpass filter signals of the integrators (13a) to (13c) matches the phase of the fundamental wave current of each phase, the lowpass filter signals of the integrators (15a) to (15c) are The signal has a waveform that advances the phase of the fundamental current by 90 °.

Further, since the phases of the fundamental wave currents of the respective phases are shifted by 120 °, the low-pass filter signals of the integrators (15a) to (15c) are also signals whose phases are shifted by 120 °.

Therefore, the vector relationship between the phase currents a, b, c of each phase and the low-pass filter signals a ', b', c'is as shown in FIG.

Then, for example, a two-phase low-pass filter signal b ′,
When c'is subtractively combined, its component c'-b 'becomes in phase with the phase current a as shown by the broken line arrow in FIG.
A fundamental wave current detection signal having the waveform of the fundamental wave current in the phase current a is obtained.

Similarly, two-phase low-pass filter signals c ′, a ′,
Is obtained by subtraction synthesis, a fundamental current detection signal of the waveform of the fundamental current in the phase current b is obtained, and by subtraction synthesis of the two-phase low-pass filter signals a ′ and b ′, A fundamental current detection signal having a waveform is obtained.

If only subtractive synthesis is performed, Since the fundamental current is detected at the level of, the signal obtained by subtractive synthesis is actually To form a fundamental current detection signal for each phase.

Then, the harmonic current of each phase can be detected by subtracting the fundamental wave current detection signal of each phase obtained by the above-mentioned subtractive synthesis from the phase current detection signal of each of the input terminals (10a) to (10c). Therefore, the arithmetic circuit (16) shown in FIG. 3 is provided for each phase.

In FIG. 3, (17) is the input terminal for the phase current detection signal, (18) and (19) are the input terminals for the two-phase low-pass filter signals, and (20) is the low-pass filter for the input terminal (19). An amplifier that inverts the sign of the signal, (21) is an adder that adds the low-pass filter signal of the input terminal (18) and the low-pass filter signal of the input terminal (19) whose sign is inverted by the amplifier (20), (22) is the output signal of the adder (21) A constant circuit for reducing the constant current, (23) a subtractor for subtracting the output signal of the constant circuit (22) from the phase current detection signal of the input terminal (17), (24) a harmonic connected to the subtractor (24) This is a current detection signal output terminal.

When the harmonic current of the phase current a is detected by the arithmetic circuit (16), the input terminal (17) is connected to the input terminal (10a).
Input the phase current detection signal of and input terminal (18),
The low-pass filter signals of the filter circuits (11b) and (11c) are input to (19), and at this time, the sign of the low-pass filter signals of the filter circuit (11c) is inverted by the amplifier (20). (21) subtracts and synthesizes the low-pass filter signals of both filter circuits (11b) and (11c).

Furthermore, the output signal of the adder (21) is fed by the constant circuit (22). As a result, the constant circuit (22) outputs the fundamental wave current detection signal of the phase current a to the subtractor (23).

Then, since the output signal of the constant circuit (23) is subtracted from the current transformation signal of the input terminal (17) by the subtractor (23), the waveform of the harmonic current in the phase current a is output to the output terminal (16). The harmonic current detection signal is output, and the harmonic current in the phase current a is detected.

The harmonic currents of the remaining phase currents b and c are also
Each is detected in the same manner as described above.

Even if the Q values of the filter circuits (11a) to (11c) are set small and the transient response speed is increased, the fundamental wave current of each phase with less waveform distortion is detected in the steady state, so the Q value is set small. By doing so, the fundamental current is removed almost completely from each phase current of each phase with good transient response characteristics, both transient response characteristics and fundamental current removal characteristics are improved, and harmonic currents are detected. When applied to an active filter device, a harmonic current of each phase is faithfully formed by the inverter, and the harmonic current can be satisfactorily reduced.

Each of the filter circuits (11a) to (11c), for example, inverts the output signals of the constant circuits (14a) to (14c) and feeds them back to the respective input sides of the adders (12a) to (12c). Of course, it may be configured, and it is needless to say 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 for a three-phase circuit of the present invention, the transient response speed is increased and the waveform distortion is increased by setting the Q value of each of the filter circuits (11a) to (11c) small. Is reduced to detect the fundamental wave current of each phase of the balanced three-phase circuit, improve both transient response characteristics and fundamental wave current removal characteristics, and detect the harmonic current of each phase.

[Brief description of drawings]

1 to 3 show an embodiment of a method for detecting harmonic currents of a three-phase circuit according to the present invention. FIGS. 1 (a) to 1 (c) are block diagrams of a filter circuit, and FIG. Phase current of each phase and vector diagram of low-pass filter signal of each phase, FIG. 3 is a block diagram of an arithmetic circuit, FIG. 4 is a block diagram of a conventional band elimination filter, and FIGS. 5 (a) to 5 (c), 6 (a) to 6 (c) are waveform diagrams for explaining the transient characteristics of FIG. 4 when the Q value is set to 1, 5 respectively, and FIG. 7 (a) to
(C) and FIGS. 8 (a) to 8 (c) are waveform diagrams for explaining the steady-state characteristics of FIG. 4 when the Q value is set to 1,5, respectively. (11a), (11b), (11c) ... Filter circuit, (16)
…… Arithmetic circuit.

Claims (1)

[Claims] 1. A phase transfer current detection signal of each phase current of each phase of a balanced three-phase circuit 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 low-pass filter signals of each phase set by the transfer function are obtained, A fundamental wave current detection signal of each waveform of the fundamental wave current of each phase is formed by subtractive synthesis of the low-pass filter signals of each two phases, and the fundamental wave current of each phase is formed from the phase current detection signal of each phase. A method for detecting a harmonic current in a three-phase circuit, which comprises detecting a harmonic current of each phase by subtracting a detection signal.