CN-121995152-A - Nonlinear load monitoring method and device

CN121995152ACN 121995152 ACN121995152 ACN 121995152ACN-121995152-A

Abstract

The disclosure belongs to the technical field of monitoring instruments, and particularly relates to a nonlinear load monitoring method and device. The method comprises the steps of obtaining preprocessed sampling value signal parameters, calculating the sampling value signal parameters by a zero crossing method to obtain grid fundamental wave frequency, determining sampling points of Fourier transformation according to the grid fundamental wave frequency, establishing orthogonal bases of Fourier transformation according to the sampling points of the Fourier transformation and the grid fundamental wave frequency, determining amplitude values and phases of fundamental waves and integer harmonics through the orthogonal bases of the Fourier transformation, and determining amplitude values and phases of inter-harmonics according to the amplitude values and phases of the fundamental waves and the integer harmonics to realize nonlinear load monitoring. The method can automatically adjust the frequency difference caused by asynchronous sampling, reduce frequency leakage and fence effect caused by an asynchronous algorithm, improve the accuracy by more than 10 times when the frequency deviation is 0.5% compared with the traditional DFT, and increase the calculated amount by only one time of calculation of an orthogonal basis.

Inventors

Yue Xianmin
Teng Qigang
CAI XIAODONG
YANG JIAQI
WANG WEIFENG
XU HUIYAO
HU KAIXIANG
HE QIAOFENG

Assignees

中国石油天然气股份有限公司

Dates

Publication Date: 20260508
Application Date: 20241104

Claims (12)

1. A method of nonlinear load monitoring, the method comprising: Acquiring a preprocessed sampling value signal parameter; calculating sampling value signal parameters by adopting a zero crossing method to obtain fundamental wave frequency of a power grid; determining the sampling point number of the Fourier transform according to the fundamental frequency of the power grid, and establishing an orthogonal basis of the Fourier forward transform according to the sampling point number of the Fourier transform and the fundamental frequency of the power grid; Determining the amplitude and the phase of the fundamental wave and each integer harmonic wave through the orthogonal basis of Fourier positive transformation; And determining the amplitude and the phase of the inter-harmonic according to the amplitude and the phase of the fundamental wave and each integer harmonic, so as to realize nonlinear load monitoring.
2. The method of nonlinear load monitoring in accordance with claim 1, wherein, Acquiring the preprocessed sampling value signal parameters, including: Acquiring a three-phase alternating voltage signal and a three-phase alternating current signal; The three-phase alternating voltage signal and the three-phase alternating current signal are reduced and processed to obtain preprocessed three-phase alternating voltage signal parameters; And transconductance amplifying and shrinking the processed three-phase alternating current signal to obtain the preprocessed three-phase alternating current signal parameter.
3. The method of nonlinear load monitoring in accordance with claim 2, wherein, The sampling value signal parameters comprise sampling values before different times of forward zero crossing, sampling values after different times of forward zero crossing and sampling periods.
4. A nonlinear load monitoring method in accordance with claim 3, wherein, The zero crossing method is adopted to calculate the sampling value signal parameter, obtaining the fundamental frequency of the power grid comprises the following steps: Calculating sampling value signal parameters through a zero-crossing calculation method to obtain a time interval of multiple zero-crossing non-integer sampling; And determining the number of sampling points of an integer between zero crossings, weighting the sampling period, and combining the time intervals of non-integer sampling of a plurality of zero crossings to obtain the fundamental wave frequency of the power grid.
5. The method of nonlinear load monitoring in accordance with claim 1, wherein, Determining the amplitude and phase of the fundamental wave by the quadrature basis of the fourier positive transform, comprising: obtaining Fourier coefficients of 50 periodic fundamental waves through orthogonal basis of Fourier positive transformation and sampling points of Fourier transformation; The amplitude of the fundamental wave is obtained by weighting the Fourier coefficient of the fundamental wave of 50 periods; The phase of the fundamental wave is obtained based on the amplitude of the fundamental wave.
6. The method of nonlinear load monitoring in accordance with claim 1, wherein, Determining the amplitude and phase of each integer harmonic by fourier positive transformed quadrature basis, comprising: Obtaining Fourier coefficients of fundamental waves of 50m periods through orthogonal basis of Fourier positive transformation and sampling points of Fourier transformation; the amplitude of each integer subharmonic is obtained by weighting the Fourier coefficient of the fundamental wave of 50m periods; The phase of each integer harmonic is derived based on the amplitude of each integer harmonic.
7. The method of nonlinear load monitoring in accordance with claim 1, wherein, Determining the amplitude and phase of the inter-harmonics from the amplitude and phase of the fundamental wave and each integer harmonic, comprising: calculating the harmonic amplitude of the inter-harmonic of each frequency point according to the number of sampling points of Fourier transformation; removing the harmonic amplitude of all inter-harmonics in the integer harmonics; Integrating all inter-harmonics larger than a harmonic threshold value to generate an inter-harmonic group set; for the inter-harmonics in the inter-harmonic group set, 10 inter-harmonic orthogonal bases are established according to 1/10 frequency interval of 1 Hz; calculating and acquiring an inter-harmonic subgroup set according to the inter-harmonic orthogonal basis; For the inter-harmonics in the inter-harmonic subgroup set, establishing 10 inter-harmonic orthogonal bases according to a frequency interval of 1/10 of 0.1 Hz; calculating the harmonic amplitude of an inter-harmonic subgroup according to the inter-harmonic orthogonal basis; and selecting the amplitude and the phase of the largest element as the amplitude and the phase of the inter-harmonic.
8. The nonlinear load monitoring device is characterized by comprising an AD conversion circuit (9), wherein the AD conversion circuit (9) is connected with a current-voltage conversion module (3) and a voltage tracking module (7), the current-voltage conversion module (3) is connected with a current transformer (5), and the voltage tracking module (7) is connected with a voltage divider resistor network (4); the AD conversion circuit (9) is used for collecting waveform values of the voltage and current channels and calculating amplitude values and phases of harmonic waves and inter-harmonic waves; the voltage dividing resistor network (4) is used for reducing three-phase alternating-current voltage signals; the current-voltage conversion module (3) is used for amplifying three-phase current.
9. The nonlinear load monitoring apparatus in accordance with claim 8, wherein, The AD conversion circuit (9) is also connected with the reference voltage (1) and the chip (8).
10. The nonlinear load monitoring apparatus in accordance with claim 9, wherein, The chip (8) is connected with the display screen (6) and the keyboard (10).
11. An electronic device, comprising: A processor and a memory; the processor invokes the computer program stored in the memory to perform the nonlinear load monitoring method recited in any one of claims 1 through 7.
12. A computer-readable storage medium comprising, The computer readable storage medium has stored therein a computer program which, when executed by a processor, enables the processor to perform the nonlinear load monitoring method in accordance with any one of claims 1 to 7.

Description

Nonlinear load monitoring method and device Technical Field The disclosure belongs to the technical field of monitoring instruments, and particularly relates to a nonlinear load monitoring method and device. Background With the widespread use of nonlinear devices such as power electronics in power systems, harmonic pollution in the power grid is becoming more and more serious, such as rectifiers, in particular rectifiers with capacitive filtering, which are controlled or not, and which are non-integer multiples of the inter-harmonics of the control signals due to randomness of the control signals for stationary converters, welding machines, arc furnaces and the like. The frequency converter used in petroleum exploitation is an electric equipment using power electronic elements, and the front end of the frequency converter adopts a capacitive filtering rectifier, so that the frequency converter has obvious energy-saving effect in operation, but serious harmonic pollution is brought to a power grid. In general, fourier transform (DFT) is used for harmonics of integer multiples, and N fundamental waves are sampled for harmonics of non-integer multiples, and the period of the fundamental waves is spread to a periodic function, so that the frequency resolution can be improved by N times, which corresponds to a signal capable of measuring 1/N harmonic, but when the number of harmonics is an infinite cyclic fraction m, the fourier transform of the sampling period spread causes an asynchronous error because N/m cannot be satisfied as the periodic function. Disclosure of Invention In view of the foregoing, the present disclosure provides a nonlinear load monitoring method, the method comprising: Acquiring a preprocessed sampling value signal parameter; calculating sampling value signal parameters by adopting a zero crossing method to obtain fundamental wave frequency of a power grid; determining the sampling point number of the Fourier transform according to the fundamental frequency of the power grid, and establishing an orthogonal basis of the Fourier forward transform according to the sampling point number of the Fourier transform and the fundamental frequency of the power grid; Determining the amplitude and the phase of the fundamental wave and each integer harmonic wave through the orthogonal basis of Fourier positive transformation; And determining the amplitude and the phase of the inter-harmonic according to the amplitude and the phase of the fundamental wave and each integer harmonic, so as to realize nonlinear load monitoring. Preferably, acquiring the preprocessed sample value signal parameter includes: Acquiring a three-phase alternating voltage signal and a three-phase alternating current signal; The three-phase alternating voltage signal and the three-phase alternating current signal are reduced and processed to obtain preprocessed three-phase alternating voltage signal parameters; And transconductance amplifying and shrinking the processed three-phase alternating current signal to obtain the preprocessed three-phase alternating current signal parameter. Preferably, the sampling value signal parameters comprise sampling values before different times of forward zero crossing, sampling values after different times of forward zero crossing and sampling periods. Preferably, the zero crossing method is adopted to calculate sampling value signal parameters to obtain the fundamental frequency of the power grid, and the method comprises the following steps: Calculating sampling value signal parameters through a zero-crossing calculation method to obtain a time interval of multiple zero-crossing non-integer sampling; And determining the number of sampling points of an integer between zero crossings, weighting the sampling period, and combining the time intervals of non-integer sampling of a plurality of zero crossings to obtain the fundamental wave frequency of the power grid. Preferably, determining the amplitude and phase of the fundamental wave by the quadrature basis of the fourier positive transform includes: obtaining Fourier coefficients of 50 periodic fundamental waves through orthogonal basis of Fourier positive transformation and sampling points of Fourier transformation; The amplitude of the fundamental wave is obtained by weighting the Fourier coefficient of the fundamental wave of 50 periods; The phase of the fundamental wave is obtained based on the amplitude of the fundamental wave. Preferably, determining the amplitude and phase of each integer subharmonic by fourier-positive-transform quadrature basis includes: Obtaining Fourier coefficients of fundamental waves of 50m periods through orthogonal basis of Fourier positive transformation and sampling points of Fourier transformation; the amplitude of each integer subharmonic is obtained by weighting the Fourier coefficient of the fundamental wave of 50m periods; The phase of each integer harmonic is derived based on the amplitude of each integer