Digital Filtering Method of Measured Data in Three-phase AC System

Abstract

Provided is a digital filtering method for three-phase alternating current system measurement data. The method includes the steps that a three-phase voltage signal VA, a three-phase voltage signal VB and a three-phase voltage signal VC are converted into a voltage signal V alpha and a voltage signal V beta under a two-phase alpha beta coordinate system; lowpass filtering is respectively carried out on the voltage signal V alpha and the voltage signal V beta according to a set transfer function to obtain a voltage signal V' alpha and a voltage signal V' beta; fundamental frequency phases delta of the voltage signal V' alpha and the voltage signal V' beta are calculated; fundamental frequency phase delay angle delta 0 of the lowpass filtering is calcauted according to the transfer function; the voltage signal V' alpha and the voltage signal V' beta are converted into direct current voltage Vd and direct current voltage Vq under a rotating dq two-phase coordinate system according to the fundamental frequency phases delta; the direct current voltage Vd and the direct current voltage Vq are converted into a voltage signal V'A, a voltage signal V'B and a voltage signal V'C under a three-phase coordinate system making delta-delta 0 as a coordinate system angle. The digital filtering method for the three-phase alternating current system measurement data can effectively solve the problem of fundamental frequency phase delay of a traditional filtering mode, and improves phase control precision of an electric system.

Description

Technical field [0001] The invention relates to the technical field of digital filtering, in particular to a digital filtering method for measurement data of a three-phase AC system. Background technique [0002] With the application of high-power switching devices in the fields of wind power generation, photovoltaic power generation, and flexible AC transmission, the power system has shown more and more significant nonlinearity, especially in the voltage source converter based on pulse width modulation (PWM) technology ( VSC) application occasions, the amplitude of high-order characteristic harmonics is close to or may even exceed the amplitude of the fundamental frequency. In order to solve the above problems, a filter can be installed on the primary side of the system. However, due to the wide spectrum of high-order harmonics , Uncertainty, and the high cost of filtering equipment, the effect obtained by this technology is extremely unsatisfactory. [0003] Because the waveform...

AI Technical Summary

Problems solved by technology

[0002] With the application of high-power switching devices in wind power generation, photovoltaic power generation, flexible AC power transmission and other fields, the power system presents more and more significant non-linearity, especially in voltage source converters based on pulse width modulation (PWM) technology ( In VSC) applications, the amplitude of the high-order characteristic harmonics is close to or even exceeds the amplitude of the fundamental frequency. In order to solve the above problems, a filter can be installed on the primary side of the system. , uncertainty, and high cost of filtering equipment, the effect obtained by this technology is extremely unsatisfactory

[0003] Due to the waveform distortion caused by high-order harmonics, the system cannot be normally controlled and accurately measured. Therefore, the existing power system generally performs first-order or high-order low-pass digital filtering on the sampled data in the measurement link on the secondary side of the system. The current main research is on the parameter design of the transfer function H(s)

However, any physically realizable system will have a delay in practice. No matter how the coefficients in the transfer function H(s) are designed, after the three-phase AC system measurement data is filtered, it is difficult to avoid the fundamental frequency phase delay before and after filtering. The harmonic distortion rate (THD) of the measurement data of the three-phase AC system is still high, which makes the phase control of the power system have serious deviations

Images