JPH05299972A - Higher harmonic wave detecting circuit - Google Patents

Abstract

PURPOSE:To provide a higher harmonic wave detecting circuit by which only higher harmonic wave components can be detected. CONSTITUTION:This circuit is equipped with a phase locked loop circuit 51 which inputs an alternating voltage or an alternating current as an alternating signal, and detects the phase of the alternating signal, amplitude detecting circuit 52 which detects the amplitude of the alternating signal, basic wave arithmetic circuit 53 which computes the basic wave components of the alternating signal from the phase detected value of the phase locked loop circuit 51, and the amplitude detected value of the amplitude detecting circuit 52, and outputs a basic wave signal, and subtracting circuit 54 which outputs the higher harmonic wave components of the alternating signal as a higher harmonic wave signal by subtracting the basic wave signal from the basic wave arithmetic circuit 53 from the alternating signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic detecting circuit for detecting a harmonic component of an AC voltage or an AC current.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional harmonic wave detection circuit.

Reference numeral 1 is an AC power source, 2 is a load connected to the AC power source 1, 3 is a load current detecting AC device for detecting a load current iL flowing in the load 2, and 4 is a band for blocking a wave in the fundamental frequency band. An elimination filter (hereinafter referred to as BEE), 6 is a current / voltage converter. Next, the operation of the conventional harmonic detection circuit having such a configuration will be described.

Power is supplied from the AC power source 1 to the load 2, and the load current iL flowing through the load 2 is detected by the current transformer 3. The BEF 4 removes the fundamental wave component of the load current iL detected by the current transformer 3, and the harmonic current waveform ih can be detected.

FIG. 4 shows an example of the current waveform shown in FIG. 3. FIG. 4A shows an output current waveform obtained by detecting the load current iL flowing in the load 2 by the current transformer 3, and FIG. ) Indicates a harmonic current waveform obtained by removing the fundamental wave from the load current waveform. FIG. 5 shows a characteristic diagram of BEF4.

[0006]

When a conventional harmonic detection circuit is used for an active power filter or the like for compensating for a harmonic component, BEF4 is used, which causes the following problems. FIG. 5 is a diagram showing the characteristics of the BEF 4, and as shown in the gain characteristics, the BEF 4 not only blocks the fundamental wave component, but also attenuates it up to the frequency band before and after the fundamental wave with a certain gain. Moreover, the phase characteristic also causes a phase shift around the fundamental frequency. Therefore, the low-order harmonic components are detected with attenuation and phase shift, and it is not possible to accurately detect only the harmonic components. The present invention has been made to solve such a problem, and an object of the present invention is to provide a harmonic detection circuit that can detect only harmonic components.

[0007]

In order to achieve the above object, the invention corresponding to claim 1 is a phase locked loop circuit for inputting an AC voltage or an AC current as an AC signal and detecting the phase of the AC signal. And an amplitude detection circuit that detects the amplitude of the AC signal, and a fundamental wave component of the AC signal is calculated from the phase detection value of the phase locked loop circuit and the amplitude detection value of the amplitude detection circuit, and a fundamental wave signal is output. A fundamental wave calculation circuit and a subtraction circuit that subtracts the AC signal and the fundamental wave signal from the fundamental wave calculation circuit to output a harmonic component of the AC signal as a harmonic signal.

[0008]

According to the invention corresponding to claim 1, the AC signal is input to the phase locked loop circuit and the amplitude detection circuit, and the basic value is detected from the phase detection value of the phase locked loop circuit and the amplitude detection value of the amplitude detection circuit. In the arithmetic circuit, the fundamental wave component of the alternating current signal is calculated, and the subtraction circuit subtracts the fundamental wave component from the alternating current signal to obtain the phase and amplitude of the source signal for the low-order harmonic line segment of the detected value. It is possible to take out only the harmonic component of the AC signal without changing it.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the harmonic wave detection circuit of the present invention. The difference from the conventional example of FIG.
In place of the above, the harmonic wave output means 5 is provided. The harmonic output means 5 is a phase locked loop circuit (hereinafter referred to as P
LL circuit) 51, an amplitude detection circuit 52 for detecting an amplitude value of a current waveform, a fundamental wave arithmetic circuit 53 for arithmetically outputting a fundamental wave component from the phase of the PLL circuit 51 and the output of the amplitude detection circuit 52, and an alternating current signal , A subtraction circuit 54 that subtracts the fundamental wave component and outputs a harmonic signal.

The configuration of the PLL circuit 51 divides an input signal into two orthogonal phase components as shown in FIG. A phase difference that calculates an analog phase difference signal Δθ from the three-phase / two-phase conversion circuit 511, the output of the three-phase / two-phase conversion circuit 511, and the orthogonal two-phase fundamental wave component that is the output of the PLL circuit 51. The comparator circuit 512, the low-pass filter 513 that removes the harmonic component of the phase difference comparison circuit 512, the variable frequency oscillator 514 whose oscillation frequency changes according to the input voltage, and the output pulse of the variable frequency oscillator 514 are counted. Then, the counter 515 that outputs the phase data of the fundamental wave, and the ROM table 516 and the ROM table 516 that have two-phase sine (sin θ) and cosine (cos θ) that are orthogonal to the digital count signal θ of the counter 515. PLL circuit 5 from digital / analog converters (hereinafter referred to as D / A converters) 517a and 517b for converting the data into analog sine and cosine data. It has been configured.

Next, the operation of the harmonic detection circuit configured as described above will be described. In FIG. 1, an AC power supply 1
The load current iL flowing through the load is detected by the current transformer 3. The detected load current iL is converted into an AC voltage signal by the current / voltage converter 6. Input to the PLL circuit 51 and the amplitude detection circuit 52. The PLL circuit 51 is orthogonal to the three-phase AC voltages R, S, T input as shown in FIG.
The unit fundamental wave AC voltages VFd and VFq of the phase are calculated and output.

The amplitude detection circuit 52 can detect the amplitude by converting the three-phase AC voltage into two-phase voltage components orthogonal to each other, squaring each of them, taking the square root of the sum, and filtering.

The fundamental wave calculation circuit 53 multiplies the two-phase unit AC voltage synchronized with the load current iL from the PLL circuit 51 by the output value of the amplitude detection circuit 52, and converts it by two-phase / 3-phase conversion. The fundamental wave component in the load current signal can be output. From the load current signal iL to the fundamental wave calculation circuit 5
The subtraction circuit 54 subtracts the fundamental wave component with the output of 3. Therefore, by removing only the fundamental wave component from the load current iL, it is possible to detect only the harmonic wave component. Here, referring to FIG. 2, P for detecting the phase of the load current iL
LL circuit 51, amplitude detection circuit 52, fundamental wave calculation circuit 5
The operation of No. 3 will be described in detail. In FIG. 2, the three-phase / two-phase conversion circuit 511 inputs the three-phase AC signals R, S, T and outputs the two-phase AC voltages V1d, V1q represented by the following equation. V1d = V1 cos θ1 (1) -1 V1q = V1 sin θ1 (1) -2 where V1 is the amplitude and θ1 is the phase.

The two-phase AC signal converted into the two-phase AC voltages V1d and V1q by the three-phase / two-phase conversion circuit 511 is PLL.
A phase difference comparison circuit 512 calculates a phase difference signal Δθ from the analog phase detection signals VFd and VFq of the two orthogonal fundamental wave components which are the outputs of the circuit 51. VFd and VFq are output as in the following equation. VFd = cos θ2 (2) -1 VFq = sin θ2 (2) -2 where θ2 is the detection phase. In addition, the phase difference comparison circuit 5
12 performs the calculation of the following equation to calculate the two-phase AC voltages V1d and V1q.
And the analog phase difference signal Δθ (θ1 − θ2) are output.

Δθ = sin ⁻¹ (VFd · V1q−VFq · V1d) ÷ {(V1d) ² + (V1q) ² } ^1/2 … (3)

This phase difference signal Δθ is passed through a low frequency filter 513 which removes a harmonic component, and a variable frequency oscillator 5
14 and counts the number of output pulses of the variable frequency oscillator 514, and outputs the phase data of the fundamental wave. Counter 515 and digital count signal θ of the counter 515
On the other hand, the ROM table 516 having orthogonal two-phase sine and cosine, and the D / A converter 5 for converting the data of the ROM table 516 into analog sine and cosine data.
17a and 517b, the analog phase detection signal VFd,
The phase difference signal Δθ is output so that VFq is output as the phase axis.
The feedback loop is configured so that the output signal becomes zero, and as a detected signal, the three-phase AC voltage R,
S, T, that is, a synchronized signal of the three-phase AC currents R, S, T is output from the PLL circuit 51 as a phase axis.

Next, in order to make the amplitudes of the analog phase detection signals VFd and VFq equal to the fundamental wave component of the load current iL, the detected signal is subjected to 3-phase / 2-phase conversion in the amplitude detection circuit 52, Absolute value I (= | I from the two-phase AC voltages V1d and V1q
|) Is calculated by the following equation. │I│ = {(V1d) ² + (V1q) ² } ^1/2 (4) The fundamental wave operation circuit 53 multiplies the orthogonal phase two-phase fundamental wave components VFd and VFq output from the PLL circuit 51 and the output | I | = | I | cos θ2 (5) -1 | I | q = | I | sinz θ2 (5) -2. By performing the two-phase / three-phase conversion calculation of the equation (5), the output of the fundamental wave arithmetic circuit 53 becomes the fundamental wave component.

In the block diagram of the embodiment of FIG. 1, instead of the load current detecting current transformer 3, a system voltage detecting transformer can be connected and the current / voltage converter 6 can be eliminated.
This makes it possible to detect the harmonic component contained in the system voltage.

[0020]

As described above, according to the harmonic detecting circuit of the present invention, it is possible to detect only the harmonic component of the AC voltage or the AC current without shifting the phase. As a result, by injecting the harmonic current using this detection circuit in the opposite direction, the active filter for canceling the harmonic current generated by the load exerts the ability to sufficiently compensate for the harmonic on the load side. It is possible to prevent harmonics from flowing out to the grid.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of a portion that outputs a fundamental wave component of FIG.

FIG. 3 is a block diagram showing a conventional harmonic wave detection circuit.

FIG. 4 is a waveform diagram in the case of removing a fundamental wave component from a load current iL and a load current iL and using only a harmonic component.

5 is a characteristic diagram of the band elimination filter of FIG.

[Explanation of symbols]

1 ... AC power supply, 2 ... Load, 3 ... Current transformer, 4 ... Band elimination filter, 5 ... Harmonic output means, 6 ... Current / voltage converter, 51 ... Phase locked loop circuit,
52 ... Amplitude detection circuit, 53 ... Fundamental wave operation circuit, 54 ... Operation circuit, 511 ... Three-phase / 2-phase conversion circuit, 512 ... Phase difference comparison circuit, 513 ... Low-pass filter, 514 ... Variable frequency oscillator, 515 ... Counter 516 ... ROM table,
517a, 517b ... Digital / analog converters.

Claims (1)

[Claims] 1. A phase-locked loop circuit for inputting an AC voltage or an AC current as an AC signal to detect the phase of the AC signal, an amplitude detection circuit for detecting the amplitude of the AC signal, and a phase-locked loop circuit. A fundamental wave calculation circuit that calculates a fundamental wave component of an AC signal from a phase detection value and an amplitude detection value of the amplitude detection circuit and outputs a fundamental wave signal, and a fundamental wave signal from the fundamental wave calculation circuit from the AC signal And a subtraction circuit that outputs a harmonic component of the AC signal as a harmonic signal by subtracting.