JP2001033501A - Method for analyzing inverse-phase component in power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize an error caused by frequency asynchronous property by obtaining a negative-phase component vector for two data rows being separated by a specific phase angle each other and adding them for obtaining the negative-phase component vector after correction. SOLUTION: LPFs 1a, 1b, and 1c input three-phase current detections signals 1a, 1b, and 1c and perform low-pass filtering. A sample/hold circuit 3 samples and holds an input signal being selected by a multiplexer 2 at a fixed period, and an A/D converter 4 converts it into digital data. A CPU 6 extracts two data rows where phase angles are separated by 90 deg. and obtains a negative-phase component with a positive-phase component as a reference for each two data rows. By adding the two negative-phase component vectors, negative-phase component vectors after correction can be obtained, thus canceling out an error caused by frequency asynchronous property and analyzing an accurate negative- phase component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing a reverse phase component in a power system.

[0002]

2. Description of the Related Art Generally, in a power system, in order to manage or control the quality of a power supply, it is required to measure a harmonic component and a reverse phase component.

Conventionally, when analyzing a harmonic component or a negative phase component of a power system, since the frequency of the commercial power supply on the system side fluctuates, sampling is performed in accordance with the fluctuation, and a predetermined operation is performed on the sampling data sequence. By doing so, a harmonic component and a negative phase component are calculated.

[0004]

However, when evaluating the harmonic component and the negative phase component on the real time axis, the sampling period must be constant. When analyzing a harmonic component and a negative-phase component using a data stream obtained by fixed sampling that is not synchronized with the commercial power frequency, an error occurs due to frequency asynchrony. An object of the present invention is to provide a method for analyzing an anti-phase component in a power system, which minimizes an error caused by frequency asynchrony.

[0005]

Means for Solving the Problems Now, the harmonic component of Ia, which is one phase of a balanced three-phase alternating current, is converted to a rated system frequency (50%).
Hz), sampling at 1800 Hz which is 36 times
Fourier transform is performed based on the sampling data for one cycle at every 10 ° of the phase angle, and the analysis is performed. The fifth harmonic component of 5% with respect to the fundamental wave is injected at a phase of 0 °, and the fundamental wave frequency is Is 0.5 Hz. Then, as shown in FIG. 1, when the sampling start position or the cutout start position from the already sampled data (hereinafter referred to as sampling phase angle α) is changed, the apparent fifth harmonic component of the fifth harmonic component is changed. Vector trajectory
It becomes as shown in. Here, the reference of the vector is the fundamental wave phase. In FIG. 2, each plot point is an apparent vector of the fifth harmonic component when the sampling phase angle α is changed every 10 ° from 0 ° to 350 °. As described above, while changing the sampling phase angle α from 0 ° to 350 °, the vector locus shown in FIG. 2 makes two rounds, during which the apparent fifth harmonic component content is ± 0.5.
It fluctuates by about%.

Consider a case in which the reverse phase component of the balanced three-phase current is obtained under the above conditions. First, the current Ia, Ib, respectively Fourier transform for each phase of Ic, determined each phase vector, determined the positive phase component and negative phase components by symmetry coordinates method, positive phase current I a vector of reverse-phase current I ₂ Expressed based on ₁ .
Then, if the sampling phase angle α shown in FIG. 1 is changed every 10 ° and the frequency f is changed every 0.1 Hz within a range of 49.5 to 50.5 Hz, the negative-phase current vector I ₂ The trajectory is as shown in FIG. That is, Δf = ±
At 0.5 Hz, a negative phase current component of about 0.5% is generated, and the vector of the vector has a sampling phase angle α without changing its magnitude.
Rotates the phase. It should be noted that α = 0
The rotation of the concentric circle shown in FIG.

From this relationship, based on two sampling data strings having a phase angle of 90 ° apart, a negative phase component vector is determined based on the normal phase component, and both vectors are added to obtain a frequency variation or sampling. It is presumed that the influence of the phase angle fluctuation can be offset.

Therefore, the method of analyzing a negative phase component in a power system according to the present invention provides a data sequence by sampling a signal under measurement at a fixed period that is an integer fraction of one period of the rated system frequency of the power system. Two data strings with a phase angle of 90 ° apart are extracted, a negative-phase component vector based on the normal-phase component is obtained for each of these two data strings, and these two negative-phase component vectors are added to obtain the corrected It is characterized in that an inverse phase component vector is obtained. In the method for analyzing a negative-phase component in a power system according to the present invention, a data string is obtained by sampling a signal to be measured at a fixed period that is an integer fraction of one period of the rated system frequency of the power system, and the phase angles of the data lines are 90 ° with each other.
Two separated data strings are extracted, and a negative-phase component vector based on the normal-phase component is obtained for each of the two data strings. The two opposite-phase component vectors have a point symmetrical positional relationship among the vector trajectories on the concentric circles shown in FIG. The vector locus makes two rounds on a concentric circle by one round). Therefore, by adding the two opposite-phase component vectors obtained in this way, an error due to frequency asynchronism is canceled out, and accurate analysis of the opposite-phase component becomes possible.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 is a block diagram showing the configuration of a measuring apparatus according to an embodiment of the present invention. In FIG. 4, low-pass filters 1a, 1b, and 1c receive three-phase current detection signals (Ia), (Ib), and (Ic), and perform low-pass filtering. The cutoff frequency is usually determined so that no aliasing error based on the sampling frequency occurs. The multiplexer 2 selects one of the low-pass filters 1a, 1b, 1c. The sample and hold circuit 3 samples and holds the input signal selected by the multiplexer 2 at a constant period, and
Converter 4 converts this into digital data. C
The PU 6 executes a program written in the ROM 7 in advance, and performs analysis of a harmonic component and analysis of a negative-phase component by processing described later. The CPU 6 outputs a control signal to the multiplexer 2, the sample and hold circuit 3, and the A / D converter 4 via the I / O port 5, and reads digital data obtained by the A / D converter 4. The RAM 8 is used as a working area for storing sampling data and performing various arithmetic processing. The operation panel 10 includes a keyboard including a mode changeover switch for measuring a harmonic component and a measurement of a reverse phase component, and a display for displaying a measurement result. The CPU 6 reads a key via the interface 9 and outputs a display of the measurement result. Perform control. The printer 12 is a device that records and records the measurement results, and the CPU 6 controls the printing of the measurement results via the interface 11.

Next, the CP in the measuring device shown in FIG.
The processing procedure of U6 is shown in FIGS. FIG. 5 shows a processing procedure at the time of measuring a harmonic component. First, an input signal which is a detection signal of a predetermined phase current is sampled by a certain number of data. For example, if the rated system frequency is 50 Hz, sampling is performed at a cycle of every 10 ° of the phase angle, that is, at a frequency of 1800 Hz. Thereafter, a data sequence for each 180 ° is shifted for every 10 ° of the phase angle and extracted over one cycle of the fundamental frequency. As a result, 36 kinds of data strings are obtained. Thereafter, a discrete Fourier transform (DF
T) is performed to obtain a vector of the fundamental wave component and each harmonic component. Then, the vector of the target harmonic component (here, the fifth harmonic component) is rotated based on the vector of the fundamental component. Thereafter, the vector of the fifth harmonic component obtained for the 36 kinds of data strings in this manner is vector-averaged, and the vector of the fifth harmonic component without error caused by frequency asynchronism is obtained.

In the above-described example, sampling is performed at a phase angle of every 10 °, and 36 kinds of data strings are extracted by changing the cutout start phase angle every 10 °. The phase angle shift interval does not need to be equal to the sampling period, for example, 30 °
It may be different for each case, and 12 types of data strings may be extracted.

FIG. 6 shows a processing procedure at the time of measuring the reversed-phase component.
First, a fixed number of data are sampled for each of three input signals which are detection signals of a three-phase current. For example, if the rated system frequency is 50 Hz, sampling is performed at a cycle of every 10 ° of the phase angle, that is, at a frequency of 1800 Hz. After that, each phase has a phase angle of 90 ° apart from each other.
One data string is extracted, and a vector of an antiphase component is calculated for both data strings by the target coordinate method. Then, by adding the vectors of the two negative-phase components based on the normal-phase components, respectively, a negative-phase component having no error due to frequency asynchrony is obtained.

[0013]

According to the method for analyzing a negative-phase component in a power system of the present invention, a data string obtained by sampling a signal under measurement at a fixed period equal to an integral number of one period of the rated system frequency of the power system is used. Thus, regardless of the fluctuation of the commercial power supply frequency of the system, the error due to the frequency asynchrony can be minimized to obtain the negative phase component.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a three-phase alternating current waveform, a sampling phase angle, and sampling data for one cycle.

FIG. 2 is a diagram illustrating an example of a vector locus of a fifth harmonic.

FIG. 3 is a diagram illustrating an example of a vector trajectory of an antiphase component.

FIG. 4 is a block diagram illustrating a configuration of a measurement device according to an embodiment.

FIG. 5 is a flowchart illustrating a processing procedure when measuring a harmonic component.

FIG. 6 is a flowchart showing a processing procedure at the time of measuring a negative-phase component.

Claims (1)

[Claims] 1. A data sequence is obtained by sampling a signal under measurement at a fixed period that is an integral fraction of one period of a rated system frequency of a power system, and two data sequences having a phase angle of 90 ° apart from each other are extracted. In each of the two data sequences, a negative-phase component vector based on the normal-phase component is obtained, and the two negative-phase component vectors are added to obtain a corrected negative-phase component vector. Analysis method for reversed phase components.