A method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device

Abstract

The present invention discloses a method for measuring the amplitude and phase angle of an electrical signal of a low-voltage protection device, which comprises: obtaining the original sampling point electrical signal of the low-voltage protection device; filtering the original sampling point electrical signal with a filter to obtain the filtered sampling point electrical signal; performing discrete Fourier transform on the filtered sampling point electrical signal to obtain the calculated amplitude and calculated phase angle of the sampling point electrical signal; and correcting the calculated amplitude and calculated phase angle of the sampling point electrical signal with the amplitude compensation coefficient and the phase compensation coefficient of the filter to obtain the corrected amplitude and phase angle. The present invention can improve the accuracy of the amplitude and phase angle while filtering out interference signals, so that the low-voltage protection device will not malfunction when performing electromagnetic compatibility tests.

Description

Technical Field

[0001] The invention relates to a method for measuring the amplitude and phase angle of an electric signal of a low-voltage protection device, and belongs to the technical field of signal measurement of secondary equipment of a power system. Background Art

[0002] Embedded microcomputer protection devices are currently widely used in various plants, stations and other places in the power system. During the operation of the protection device, it is necessary to accurately measure the voltage and current signals in the power system. Currently, the discrete Fourier algorithm (DFT) is commonly used to process the voltage and current signals and measure the voltage and current amplitude and phase angle, so that the protection device can effectively trip the faulty part when a fault occurs in the power system (overcurrent, overvoltage, undervoltage, etc.), protecting the entire power system from safe and stable operation.

[0003] When conducting electromagnetic compatibility tests, low-voltage protection devices need to superimpose high-frequency, high-voltage interference signals on AC sampling signals, requiring the low-voltage protection devices to be put into various protection functions and the delay to be set to 0ms. At this time, if the discrete Fourier algorithm is used to measure the voltage and current amplitude and phase angle in the low-voltage protection device, the peaks and glitches in the signal may affect the measurement results, and inaccurate measurement results may cause the low-voltage protection device of the power system to malfunction, etc. Summary of the invention

[0004] In view of the problem that DFT in the prior art cannot accurately measure the amplitude and phase angle of the electrical signal in the low-voltage protection device, the present invention proposes a method for measuring the amplitude and phase angle of the electrical signal of the low-voltage protection device. The electrical signal of the low-voltage protection device is filtered, DFT and corrected without changing the original sampling frequency. While ensuring the accuracy of amplitude and phase angle measurement, the peaks and burrs in the signal are filtered out, thereby suppressing the possibility of malfunction of the low-voltage protection device from the source.

[0005] In order to solve the above technical problems, the present invention adopts the following technical means:

[0006] The present invention proposes a method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device, comprising the following steps:

[0007] Acquire an original sampling point electrical signal of the low voltage protection device, wherein the original sampling point electrical signal is voltage or current;

[0008] The original sampling point electrical signal is filtered by using a filter to obtain a filtered sampling point electrical signal;

[0009] Performing discrete Fourier transform on the filtered sampling point electrical signal to obtain the calculated amplitude and calculated phase angle of the sampling point electrical signal;

[0010] The calculated amplitude and calculated phase angle of the electrical signal at the sampling point are corrected using the amplitude compensation coefficient and the phase angle compensation coefficient of the filter to obtain the corrected amplitude and phase angle.

[0011] Furthermore, the filter includes a differential filter and an integral filter; when the original sampling point electrical signal is a voltage, the differential filter is used to filter the original sampling point electrical signal; when the original sampling point electrical signal is a current, the integral filter is used to filter the original sampling point electrical signal.

[0012] Furthermore, the expression for filtering the original sampling point electrical signal using a differential filter is as follows:

[0013] (1)

[0014] in, express The sampling point electrical signal after differential filtering at the jth sampling point at time, Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time , k is the filter time interval, and the value range of k is [ 1 , f / 50 ] , f is the sampling frequency of the low voltage protection device, , N is the number of sampling points in one cycle.

[0015] Furthermore, the expression for filtering the original sampling point electrical signal using an integral filter is as follows:

[0016] (2)

[0017] in, express The sampling point electrical signal after the integral filtering of the jth sampling point at the moment, Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time , k is the filter time interval, and the value range of k is [ 1 , f / 50 ] , f is the sampling frequency of the low voltage protection device, , N is the number of sampling points in one cycle.

[0018] Furthermore, the calculation method of the calculated amplitude and calculated phase angle of the electrical signal at the sampling point is as follows:

[0019] Put the filtered sampling point electrical signal into the FFT loop area to obtain the sine and cosine parts of the sampling point electrical signal:

[0020] (3)

[0021] (4)

[0022] in, The filtered sampling point electrical signal of the jth sampling point in the low voltage protection device is put into the sinusoidal part of the FFT cycle, N is the number of sampling points in one cycle, represents the filtered sampling point electrical signal of the jth sampling point, The electric signal of the filtered sampling point representing the jth sampling point is put into the cosine part of the FFT cycle;

[0023] The calculated amplitude and phase angle of the electrical signal at the sampling point are obtained through discrete Fourier transform:

[0024] (5)

[0025] (6)

[0026] in, represents the calculated amplitude of the sampling point electrical signal at the jth sampling point, Represents the calculated phase angle of the sampling point electrical signal of the jth sampling point.

[0027] Furthermore, the calculation formula of the amplitude compensation coefficient of the differential filter is as follows:

[0028] F ' = 1 [cos( f ) − 1 ] 2 + [sin( f )] 2 (7)

[0029] in, represents the amplitude compensation coefficient of the differential filter, is the theoretical value of phase angle difference;

[0030] The calculation formula of the phase angle compensation coefficient of the differential filter is as follows:

[0031] ψ ' = f + arctan[ cos( f ) − 1 sin( f ) ] (8)

[0032] in, Represents the phase compensation coefficient of the differential filter.

[0033] Furthermore, the calculation formula of the amplitude compensation coefficient of the integral filter is as follows:

[0034] F " = 1 [cos( f ) + 1 ] 2 + [sin( f )] 2 (9)

[0035] in, represents the amplitude compensation coefficient of the integral filter, is the theoretical value of phase angle difference;

[0036] The calculation formula of the phase angle compensation coefficient of the integral filter is as follows:

[0037] ψ " = 90 + f + arctan[ cos( f ) + 1 sin( f ) ] (10)

[0038] in, Indicates the phase compensation coefficient of the integration filter.

[0039] Furthermore, the theoretical value of the phase angle difference The calculation formula is as follows:

[0040] (11)

[0041] Among them, k is the filter time interval, and the value range of k is [ 1 , f / 50 ] , f is the sampling frequency of the low voltage protection device.

[0042] Furthermore, the corrected amplitude is:

[0043] (12)

[0044] in, represents the corrected amplitude of the jth sampling point in the low voltage protection device, represents the calculated amplitude of the sampling point electrical signal at the jth sampling point, Represents the amplitude compensation coefficient of the filter.

[0045] Furthermore, the corrected phase angle is:

[0046] (13)

[0047] in, represents the corrected phase angle of the jth sampling point in the low voltage protection device, represents the calculated phase angle of the sampling point electrical signal of the jth sampling point, Represents the phase compensation coefficient of the filter.

[0048] The following advantages can be obtained by using the above technical means:

[0049] The present invention proposes a method for measuring the amplitude and phase angle of an electrical signal of a low-voltage protection device. The method of the present invention adds a compensation correction method based on a filter on the basis of a traditional discrete Fourier transform. Without changing the original sampling frequency and the hardware structure of the low-voltage protection device, interferences such as spikes and glitches in the electrical signal of the original sampling point are filtered out by a filter. In order to avoid inaccurate measurement values ​​of the filtered signal, the present invention also corrects the calculated amplitude and calculated phase angle through an amplitude compensation coefficient and a phase angle compensation coefficient to improve the accuracy of the corrected amplitude and phase angle, thereby ensuring that the voltage and current measurement results of the low-voltage protection device will not be distorted, thereby suppressing the possibility of malfunction of the low-voltage protection device from the source.

[0050] The method of the present invention is mainly used for voltage and current measurement when a low-voltage protection device is subjected to an electromagnetic compatibility test. It can improve the accuracy of the amplitude and phase angle while filtering out interference signals, and can prevent the low-voltage protection device from malfunctioning when subjected to an electromagnetic compatibility test. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A flow chart of the steps of a method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device according to the present invention;

[0052] Figure 2 The following is an operation flow chart of the method for measuring the amplitude and phase angle of an electrical signal in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below in conjunction with the accompanying drawings:

[0054] The present invention proposes a method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device. Figure 1 As shown, the specific steps include:

[0055] Step A, obtaining an original sampling point electrical signal of the low voltage protection device, wherein the original sampling point electrical signal is voltage or current;

[0056] Step B: filtering the original sampling point electrical signal using a filter to obtain a filtered sampling point electrical signal;

[0057] Step C, performing discrete Fourier transform on the filtered sampling point electrical signal to obtain the calculated amplitude and calculated phase angle of the sampling point electrical signal;

[0058] Step D: using the amplitude compensation coefficient and the phase angle compensation coefficient of the filter to correct the calculated amplitude and the calculated phase angle of the sampling point electrical signal to obtain the corrected amplitude and phase angle.

[0059] N sampling points are set within one cycle of the low voltage protection device, and the voltage signal and current signal of each sampling point are collected according to the sampling frequency as the original sampling point electrical signal of the low voltage protection device.

[0060] In step B of the method of the present invention, the filter includes a differential filter and an integral filter. When the original sampling point electrical signal is a voltage, the differential filter is used to filter the original sampling point electrical signal; when the original sampling point electrical signal is a current, the integral filter is used to filter the original sampling point electrical signal.

[0061] The expression for filtering the original sampling point electrical signal using a differential filter is as follows:

[0062] (14)

[0063] in, express The sampling point electrical signal after differential filtering at the jth sampling point at time, Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time , k is the filter time interval, and the value range of k is [ 1 , f / 50 ] , f is the sampling frequency of the low voltage protection device, , N is the number of sampling points in one cycle.

[0064] The expression for filtering the original sampling point electrical signal using an integral filter is as follows:

[0065] (15)

[0066] in, express The sampling point electrical signal after integral filtering of the jth sampling point at time.

[0067] In step C of the present invention, the calculation method of the calculated amplitude and calculated phase angle of the electrical signal at the sampling point is as follows:

[0068] Step C01, put the filtered sampling point electrical signal into the FFT loop area to obtain the sine part and cosine part of the sampling point electrical signal:

[0069] (16)

[0070] (17)

[0071] in, The filtered sampling point electrical signal of the jth sampling point in the low voltage protection device is put into the sinusoidal part of the FFT cycle, represents the filtered sampling point electrical signal of the jth sampling point. When the sampling point electrical signal is a voltage, = , when the electrical signal at the sampling point is current, = , The filtered sampling point electrical signal representing the jth sampling point is placed into the cosine part of the FFT cycle.

[0072] Step C02: Based on and , the calculated amplitude and phase angle of the electrical signal at the sampling point are obtained through discrete Fourier transform. The specific expressions are as follows:

[0073] (18)

[0074] (19)

[0075] in, represents the calculated amplitude of the sampling point electrical signal at the jth sampling point, Represents the calculated phase angle of the sampling point electrical signal of the jth sampling point.

[0076] In step D of the present invention, the filter time interval and the sampling frequency of the low voltage protection device can be calculated. and Theoretical value of the phase angle difference between :

[0077] (20)

[0078] According to the phase angle difference theoretical value The amplitude compensation coefficient and phase angle compensation coefficient of the filter can be obtained through the modified formula of trigonometric function. The specific operation is as follows:

[0079] Step D01: For the differential filter, according to the AC signal expression and formula (14), it can be known that:

[0080] (twenty one)

[0081] in, is the amplitude, is the angular frequency, is the initial phase angle.

[0082] By rearranging formula (21), the calculation formula of the amplitude compensation coefficient of the differential filter is as follows:

[0083] F ' = 1 [cos( f ) − 1 ] 2 + [sin( f )] 2 (twenty two)

[0084] in, Represents the amplitude compensation coefficient of the differential filter.

[0085] The calculation formula of the phase angle compensation coefficient of the differential filter is as follows:

[0086] ψ ' = f + arctan[ cos( f ) − 1 sin( f ) ] (twenty three)

[0087] in, Represents the phase compensation coefficient of the differential filter.

[0088] Step D02: For the integral filter, according to the AC signal expression and formula (15), it can be known that:

[0089] I i + k , j = 1 2 ( X i + k , j + X i , j ) = 1 2 [ A cos( oh t + i + f ) + A cos( oh t + i )] (twenty four)

[0090] By rearranging formula (24), the calculation formula of the amplitude compensation coefficient of the integral filter is as follows:

[0091] F " = 1 [cos( f ) + 1 ] 2 + [sin( f )] 2 (25)

[0092] in, Represents the amplitude compensation coefficient of the integration filter.

[0093] The calculation formula of the phase angle compensation coefficient of the integral filter is as follows:

[0094] ψ " = 90 + f + arctan[ cos( f ) + 1 sin( f ) ] (26)

[0095] in, Indicates the phase compensation coefficient of the integration filter.

[0096] In step D of the present invention, the specific operation of correcting the calculated amplitude and calculated phase angle of the sampling point electrical signal using the amplitude compensation coefficient and phase angle compensation coefficient of the filter is as follows:

[0097] (27)

[0098] (28)

[0099] in, represents the corrected amplitude of the jth sampling point in the low voltage protection device, represents the amplitude compensation coefficient of the filter, , represents the corrected phase angle of the jth sampling point in the low voltage protection device, represents the phase compensation coefficient of the filter, .

[0100] In order to verify the effect of the method of the present invention, the present invention provides the following examples:

[0101] In the embodiment of the present invention, the sampling frequency of the low voltage protection device is 1.2 kHz, the number of sampling points in one cycle is 24, the angle difference between each sampling point is 360 / 24=15°, the filter time interval k of the differential filter is 2, and the filter time interval k of the integral filter is 1.

[0102] like Figure 2 As shown, the process of measuring amplitude and phase angle based on the method of the present invention is as follows:

[0103] (1) Obtain the original sampling point electrical signal of the low-voltage protection device, and use a differential filter to filter the voltage signal, and use an integral filter to filter the current signal to obtain the filtered voltage signal and current signal: , .

[0104] (2) Perform discrete Fourier transform on the filtered voltage signal and current signal respectively to obtain the calculated amplitude and calculated phase angle of the voltage signal and current signal.

[0105] (3) According to formula (20), we can get Theoretical value of the phase angle difference between , points processing Theoretical value of the phase angle difference between .

[0106] (4) The correction coefficient of the differential filter is calculated according to formula (21). The specific derivation process of the 30° difference is as follows:

[0107] D i + 2 , j = A cos( oh t + i + 30 0 ) − A cos( oh t + i ) = A [ cos( oh t + i + 30 0 ) ¯ ¯ − cos( oh t + i )] = A [ cos( oh t + i )cos( 30 0 ) − sin( oh t + i )sin( 30 0 ) ¯ ¯ − cos( oh t + i )] = A [cos( oh t + i ) 3 2 − sin( oh t + i ) 1 2 − cos( oh t + i )] = A [ 3 − 2 2 cos( oh t + i ) − 1 2 sin( oh t + i )] = A ( − 1 2 ) 2 + ( 3 − 2 2 ) 2 sin( oh t + i + ψ ) (29)

[0108] in, ,therefore .

[0109] (30)

[0110] According to formula (30), the gain of the amplitude after the difference and the original Fourier algorithm is 0.5176380902, so the amplitude compensation coefficient of the differential filter is =1 / (0.5176380902)=1.931851653.

[0111] The phase angle -75° in formula (30) differs from the original Fourier algorithm phase angle of 30° by 105°, so the phase angle compensation coefficient of the differential filter is =105°.

[0112] (5) The correction coefficient of the integral filter is calculated according to formula (24). The specific derivation process of the 15° integral is as follows:

[0113] I i + 1 , j = 1 2 ( A cos( oh t + i + 15 0 ) + A cos( oh t + i )) = ( A 2 )[ cos( oh t + i + 15 0 ) ¯ ¯ + cos( oh t + i )] = ( A 2 )[ cos( oh t + i )cos( 15 0 ) − sin( oh t + i )sin( 15 0 ) ¯ ¯ + cos( oh t + i )] = ( A 2 )[cos( oh t + i ) 6 + 2 4 − sin( oh t + i ) 6 − 2 4 + cos( oh t + i )] = ( A 2 )[ − 6 − 2 4 sin( oh t + i ) + 6 + 2 + 4 4 cos( oh t + i )] = ( A 2 ) ( − 6 − 2 4 ) 2 + ( 6 + 2 + 4 4 ) 2 sin( oh t + i + P ) (31)

[0114] in, ,therefore .

[0115] (32)

[0116] According to formula (32), the gain of the amplitude after integration and the original Fourier algorithm is 0.9914448614, so the amplitude compensation coefficient of the integral filter is =1 / (0.9914448614)=1.008628961.

[0117] The phase angle of -172.5° in formula (32) differs from the original Fourier algorithm phase angle of 15° by 187.5°. Therefore, the phase angle compensation coefficient of the differential filter is =187.5°.

[0118] (6) The amplitude compensation coefficient and phase angle compensation coefficient obtained in steps (4) and (5) are used to correct the calculated amplitude and calculated phase angle of the voltage signal and the current signal, respectively, to obtain the corrected amplitude and phase angle.

[0119] According to the above specific embodiments, if no correction processing is performed, the calculated amplitude obtained by DFT differs from the correct result by 1.931851653 times or 1.008628961 times, and the calculated phase angle differs from the correct result by 105° or 187.5°. Therefore, the method of the present invention can well correct the measured value of the signal after filtering and ensure the accuracy of the amplitude and phase angle measurement.

[0120] The method of the present invention can filter out interferences such as spikes and burrs in the original sampling point electrical signal without changing the original sampling frequency and the hardware structure of the low-voltage protection device, and obtain accurate and reliable amplitude and phase angle, which can ensure that the voltage and current measurement results of the low-voltage protection device will not be distorted, so that the low-voltage protection device will not malfunction during the electromagnetic compatibility test.

[0121] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device, characterized in that: The steps include: Acquire an original sampling point electrical signal of the low voltage protection device, wherein the original sampling point electrical signal is voltage or current; The original sampling point electrical signal is filtered by using a filter to obtain a filtered sampling point electrical signal; Performing discrete Fourier transform on the filtered sampling point electrical signal to obtain the calculated amplitude and calculated phase angle of the sampling point electrical signal; The calculated amplitude and calculated phase angle of the electrical signal at the sampling point are corrected by using the amplitude compensation coefficient and the phase angle compensation coefficient of the filter to obtain the corrected amplitude and phase angle; The filter includes a differential filter and an integral filter; When the original sampling point electrical signal is a voltage, a differential filter is used to filter the original sampling point electrical signal; When the original sampling point electrical signal is current, the original sampling point electrical signal is filtered using an integral filter; The calculation formula of the amplitude compensation coefficient of the differential filter is as follows: ； in, represents the amplitude compensation coefficient of the differential filter, is the theoretical value of phase angle difference; The calculation formula of the phase angle compensation coefficient of the differential filter is as follows: ； in, Represents the phase angle compensation coefficient of the differential filter; The calculation formula of the amplitude compensation coefficient of the integral filter is as follows: ； in, represents the amplitude compensation coefficient of the integral filter, is the theoretical value of phase angle difference; The calculation formula of the phase angle compensation coefficient of the integral filter is as follows: ； in, Indicates the phase compensation coefficient of the integral filter.

2. The method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device according to claim 1, characterized in that: The expression for filtering the original sampling point electrical signal using a differential filter is as follows: ； in, express The sampling point electrical signal after differential filtering at the jth sampling point at time, Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time , k is the filter time interval, and the value range of k is , f is the sampling frequency of the low voltage protection device, , N is the number of sampling points in one cycle.

3. The method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device according to claim 1, characterized in that: The expression for filtering the original sampling point electrical signal using an integral filter is as follows: ； in, express The sampling point electrical signal after the integral filtering of the jth sampling point at the moment, Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time Indicates that the jth sampling point in the low voltage protection device is The original sampling point electrical signal at time , k is the filter time interval, and the value range of k is , f is the sampling frequency of the low voltage protection device, , N is the number of sampling points in one cycle.

4. The method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device according to claim 1, characterized in that: The calculation method of the calculated amplitude and calculated phase angle of the electrical signal at the sampling point is as follows: Put the filtered sampling point electrical signal into the FFT loop area to obtain the sine and cosine parts of the sampling point electrical signal: ； ； in, The filtered sampling point electrical signal of the jth sampling point in the low voltage protection device is put into the sinusoidal part of the FFT cycle, N is the number of sampling points in one cycle, represents the filtered sampling point electrical signal of the jth sampling point, The electric signal of the filtered sampling point representing the jth sampling point is put into the cosine part of the FFT cycle; The calculated amplitude and phase angle of the electrical signal at the sampling point are obtained through discrete Fourier transform: ； ； in, represents the calculated amplitude of the sampling point electrical signal at the jth sampling point, Represents the calculated phase angle of the sampling point electrical signal of the jth sampling point.

5. The method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device according to claim 1, characterized in that: Phase angle difference theoretical value The calculation formula is as follows: ； Among them, k is the filter time interval, and the value range of k is , f is the sampling frequency of the low voltage protection device.

6. The method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device according to claim 1, characterized in that: The corrected amplitude is: ； in, represents the corrected amplitude of the jth sampling point in the low voltage protection device, represents the calculated amplitude of the sampling point electrical signal at the jth sampling point, Represents the amplitude compensation coefficient of the filter.

7. The method for measuring the amplitude and phase angle of an electrical signal of a low voltage protection device according to claim 1, characterized in that: The corrected phase angle is: ； in, represents the corrected phase angle of the jth sampling point in the low voltage protection device, represents the calculated phase angle of the sampling point electrical signal of the jth sampling point, Represents the phase compensation coefficient of the filter.

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