Based On The Variable Step Size LMS Algorithm Research On Harmonic Detection Of Urban Rail Power Supply System

In recent years,China’s urban rail transit industry has developed rapidly.The power supply system of urban rail transit is a key link in the urban power grid,which provides electric energy for the rail transit system.Its main task is to provide stable and reliable electric power for urban rail transit vehicles and lighting equipment.Because the urban rail transit system is a hybrid AC/DC system,a large number of rectifiers,inverters and other nonlinear power electronic equipment will produce harmonics,which will bring some negative effects to the urban distribution network.Therefore,it is of great significance to study the influence of the urban rail power supply system and the harmonics generated on the urban distribution network.In this paper,the structure and power supply mode of urban rail power supply system are analyzed in detail,and several main harmonic detection methods are introduced in detail.Then it analyzes the source of harmonics of urban rail power supply system and introduces the concept of harmonics of power system and the standard of harmonics of public power network.This paper mainly analyzes the main harmonic source rectifying unit and lighting equipment system of urban rail power supply system,then deduces and analyzes the working principle of 24 pulse rectifier and its characteristic harmonics and non-characteristic harmonics theoretically.Secondly,based on the research on the harmonic characteristics of urban rail power supply system,this paper designs a new harmonic detection algorithm based on the improvement of the existing inverse cosine function variable step size LMS algorithm.In this algorithm,the average of the expected error estimates is obtained by using the autocorrelation average estimation of the error signals,and then the inverse cosine is used as the core function to adjust the step size updating.The interference of error signal to step size updating is eliminated,and the steady state error is small.The derived third order weight iteration formula is used to replace the traditional weight iteration formula to obtain faster convergence speed.Finally,the model of each component of the subway power supply system is established based on Matlab/Simulink platform,and then the simulation model is run to verify.Simulation results show that the improved variable step size LMS algorithm can not only effectively improve the accuracy of the original algorithm,but also maintain the convergence and calculation speed of the original algorithm.And the algorithm has achieved good results in the harmonic detection of urban rail power supply system,which provides a good solution for the subsequent harmonic control.