Research On Nonlinear Correction Of Current Transformer

The stable operation of the current transformer is of great significance to the monitoring and protection of the power system,but the nonlinear problem of the current transformer will distort the secondary current,causing the relay protection to malfunction and delay,and seriously affect s the stable operation of the power system.Aiming at the nonlinear problem caused by the hysteresis characteristics of the current transformer,this paper analyzes the nonlinear characteristics of the current transformer and the reasons for the current transformer output distortion waveform,and proposes a Support Vector Machine(SVM)nonlinear correction based on parameter adaptive adjustment method.The output voltage waveform of the current transformer is modeled,parameter optimization and nonlinear regression.Finally,it realizes the correction of the amplitude and phase of the distortion waveform and improves the measurement accuracy of the current transformer through the hardware circuit.And the specific research content is as follows:1.This article analyzes the working principle of current transformers and classifies them according to their functions.The principle of fiber Bragg grating sensing,the characteristics of Giant Magnetostrictive Material(GMM),the demodulation principle of fiber Bragg gratings and the nonlinear reasons of current transformers are analyzed in detail,which lays a theoretical foundation for exploring new nonlinear correction methods.2.Due to the hysteresis characteristics of the iron core material and the nonlinear characteristics of the GMM,the output error of the current transformer is relatively large.Based on the analysis of the nonlinear model,respectively,using the SVM and BP neural network method to build a model of the normalized error function,and the experimental results show that SVM models the error function better.3.After establishing the error normalization model,it starts to determine the linear relationship between the adaptive parameters and then builds the nonlinear correction model of the current transformer.4.Designed a hardware system with Field Programmable Gate Ar ray(FPGA)as the control core,the software is programmed with Verilog HDL language and the nonlinear correction algorithm is embedded in the soft core of FPGA.Finally,the experimental test shows that the nonlinear correction model based on the SVM algorithm improves the measurement precision of the current transformer.