JPH05209903A - Measurement of asymmetric component of ac current - Google Patents

Abstract

PURPOSE:To measure an asymmetric component with accuracy even if a DC current is superimposed on an AC current to be measured by acquiring a DC current addition value to make a zero-cross time difference of the AC current zero and a DC current component of the AC current and by carrying out calculation based on them. CONSTITUTION:After an AC current to be measured is converted to an AC voltage signal at a current voltage conversion circuit 2, it is sent to a zero-cross time difference detection circuit 4 and a peak detection circuit 5. The circuit 4 measures a zero-cross time difference of an AC current and the circuit 5 measures a peak value and they put out the values to a calculation circuit 7. The circuit 7 calculates a DC voltage to make the zero-cross time zero and sends it to a DC voltage addition circuit 3. The circuit 3 adds this to the AC voltage signal and records a DC current and a measurement time when the zero-cross time becomes zero. Here, a switch 1 sends the AC current to an LPF 9, puts out only a DC component to the circuit 7 after A/D conversion and has its DC current and the measurement time recorded. From these current values and times, the DC current of an asymmetric component is acquired using a predetermined equation. By repeating this measurement, measurement accuracy can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring an asymmetrical component of an alternating current, and more particularly to measuring an asymmetrical component of an alternating current obtained based on a subtraction result of a direct current containing an asymmetrical component and a direct current containing no asymmetrical component. Regarding the method.

[0002]

2. Description of the Related Art As a conventional method for measuring an asymmetric component of an alternating current, there is a method of rectifying an alternating current to be measured and converting it into a direct current, and detecting the obtained direct current as an asymmetric component.

Further, when the direct current is superimposed on the measured alternating current, the direct current which makes the zero-cross time difference caused by the superimposed direct current zero is superimposed on the measured alternating current, and the zero-cross time difference becomes zero. There is a method of detecting the direct current value at that time as a superimposed direct current (Japanese Patent Application No. 2-82289).

[0004]

However, in the conventional method for measuring the asymmetric component of the alternating current, if the direct current component is superimposed on the alternating current in addition to the asymmetric component, the rectified signal becomes the sum of the two. It is not possible to detect only the asymmetric component. Further, according to the latter detection method, only the superimposed DC component is detected, and the asymmetric component cannot be detected. Therefore, an object of the present invention is to provide a method for measuring an asymmetric component of an alternating current, which can measure the asymmetric component with high accuracy even when the direct current is superimposed on the measured alternating current.

[0005]

According to the present invention, in order to measure an asymmetrical component with high accuracy even if a direct current is superposed on the alternating current to be measured, the alternating current to be measured including the direct current is converted into an alternating voltage. To generate a first AC voltage signal; measure a zero-crossing time difference of the first AC voltage signal; add a DC voltage that makes the measured zero-crossing time difference to zero to the first AC voltage signal Converting the added DC voltage to generate a first DC current; passing an AC current to be measured through a DC component through a low-pass filter to generate a second DC current; Provided is a method for measuring an asymmetric component of an alternating current, in which the asymmetric component in the alternating current is measured by subtracting the direct current of 1.

[0006]

The measuring method of the asymmetric component of the alternating current according to the present invention is as follows.
From the zero-cross time difference of the alternating current and its peak value, the direct current to be added to make the zero-cross time difference of the alternating current zero is calculated. On the other hand, the alternating current is passed through a low pass filter to obtain a signal of the sum of the asymmetric component and the superimposed direct current. Next, the asymmetric component is detected by subtracting the DC signal to be added from the sum signal.

[0007]

[Embodiment 1] Hereinafter, a method for measuring an asymmetric component of an alternating current according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of the asymmetric component measuring apparatus according to the present invention, in which a switch 1 for switching the input of the measured alternating current and the input measured alternating current are converted into an alternating voltage signal corresponding to the level thereof. A current-voltage converting circuit 2 for converting, a DC voltage adding circuit 3 for adding a DC voltage to the converted AC voltage signal of the measured AC current, a zero-cross time difference measuring circuit 4 for measuring a zero-cross time difference of the AC voltage signal, and an AC Peak detection circuit 5 for detecting the peak value of the voltage signal, A / D conversion circuit 6 for A / D (analog / digital) converting the detected peak value, zero-cross time difference and peak value of the detected AC voltage signal The calculation circuit 7 calculates the DC voltage to be added based on the above, and records the measurement time of the zero-cross time difference. The output signal from the calculation circuit 7 is D /
D / A conversion circuit 8 for A (digital / analog) conversion
And a low-pass filter 9 that passes the direct-current component of the measured alternating current switched by the switcher 1, and an A / D conversion circuit 10 that A / D-converts the direct-current component that has passed through the low-pass filter 9.

FIG. 2 shows a flow chart of the measuring operation of the asymmetric component measuring apparatus having the above-mentioned configuration. The AC current to be measured input to the measuring device is sent to the current-voltage conversion circuit 2 by the switcher 1, converted into an AC voltage signal according to the level of the AC current, and then passed through the DC voltage addition circuit 3 to the zero-cross time difference detection circuit. 4 and the peak detection circuit 5 directly.

The zero-cross time difference detection circuit 4 measures the zero-cross time difference caused by the DC current superimposed on the AC current signal, and the peak detection circuit 5 measures the peak value of the AC voltage signal and outputs it to the arithmetic circuit 7. The arithmetic circuit 7 is
A DC voltage at which the zero-cross time of the AC voltage signal becomes zero is calculated based on the measured zero-cross time difference and the peak value, and the DC voltage is converted by the D / A conversion circuit 8 and output to the DC voltage addition circuit 3. To do.

The DC voltage adding circuit 3 adds the DC voltage to the AC voltage signal based on the signal that makes the zero-cross time difference zero, and as a result, the DC current I ₁ (n) and the measured value when the zero-cross time becomes zero. Record time T ₁ (n).

When the direct current I ₁ (n) and the measurement time T ₁ (n) are recorded, the switching device 1 is switched to the circuit for measuring the sum of the superimposed direct current and the direct current due to the asymmetric component. A signal is input, a direct current component is passed through the low-pass filter 9, and then the direct current component is converted into a digital signal corresponding to the analog level in the A / D conversion circuit 10 and input to the arithmetic circuit 7, and a direct current I ₂ ( Record n) and measurement time T ₂ (n).

DC current I ₁ (n), measurement time T ₁ (n), DC current I ₂ (n), measurement time T measured by the above method
Based on ₂ (n), the direct current I ₃ (n) due to the asymmetric component can be obtained by the following formula. Where I ₁ : DC current that is superimposed based on the zero-cross time difference I ₂ : DC current that is the sum of the superimposed DC current and the DC current due to the asymmetric component I ₃ : DC current due to the asymmetric component T ₁ : I ₁ (n ) Time of measurement T ₂ : I ₂ (n) Time of measurement n: Number of measurements

The DC current due to the asymmetric component is measured n times by the above equation, and the switching device 1 is switched each time to input the AC current signal. In this way, the accuracy of the measurement can be improved by repeating the measurement. That is, since the time at the time of measuring the direct current is recorded, the asymmetric component can be measured with high accuracy in response to the temporal fluctuation of the superimposed direct current.

[0014]

As described above, according to the method for measuring the asymmetrical component of the alternating current of the present invention, the measured alternating current including the direct current is converted into the alternating voltage to generate the first alternating voltage signal; A zero-cross time difference of the first AC voltage signal is measured; a DC voltage that makes the measured zero-cross time difference zero is added to the first AC voltage signal; the added DC voltage is converted to generate a first DC current. Generate a second direct current by passing a direct current component through the low-pass filter through the measured alternating current; by subtracting the first direct current from the second direct current, the asymmetric component in the alternating current is generated. Since the measurement is performed, the asymmetric component can be measured with high accuracy even if the direct current is superposed on the measured alternating current.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an apparatus for measuring an asymmetric component of an alternating current according to the present invention.

FIG. 2 shows a flowchart of a method for measuring an asymmetric component of an alternating current according to the present invention.

[Explanation of symbols]

1 Switching device 2 Current-voltage conversion circuit 3 DC voltage addition circuit 4 Zero-cross time difference detection circuit 5 Peak detection circuit 6, 10 A / D
Conversion circuit 7 Operation circuit 8 D / A conversion circuit 9 Low-pass filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Otani 5-1-1, Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Power Systems Co., Ltd. Power Systems Laboratory (72) Inventor Kenichiro So, 5 Hidaka-cho, Hitachi-shi, Ibaraki 1-1-1 Hitachi Cable Co., Ltd. Power Systems Laboratory

Claims (1)

[Claims] 1. A method for measuring an asymmetrical component of an alternating current including a direct current, wherein the measured alternating current including the direct current is converted into an alternating voltage to generate a first alternating voltage signal, Measuring the zero-crossing time difference of the AC voltage signal, adding a DC voltage that makes the measured zero-crossing time difference to zero to the first AC voltage signal, converting the added DC voltage to obtain a first DC current. A second direct current is generated by passing a direct current component through the measured alternating current through a low pass filter, and a second direct current is subtracted from the second direct current A method for measuring an asymmetric component of an alternating current, characterized by measuring an asymmetric component.