Research On Harmonic Detection Methods For Electric Vehicle Charging Piles

The emergence of electric vehicles has freed traditional cars from the constraints of fossil fuels and achieved true energy conservation and emission reduction to a certain extent.Nowadays,with the promotion of national policies and the stimulation of market demand,the number of electric vehicles is increasing day by day,and the trend of occupying the market is becoming increasingly evident.However,new problems brought about by it have also emerged.As a nonlinear load,the introduction of electric vehicle charging piles in large quantities will inevitably pose a threat to the power quality of the power system and bring a large amount of harmonic interference to the power grid.Due to the complexity of the charging station’s own structure and the uncertainty of the working environment,traditional harmonic detection methods are difficult to present its harmonic interference well.For this reason,this thesis optimizes the phase of Adaline network,and then introduces wavelet transform into it to get a new combinatorial optimization algorithm.This algorithm is applied to the charging pile model to detect harmonic current,and has achieved good detection results.The research content of this article mainly includes the following aspects:(1)Analyzing the charging characteristics of electric vehicles under constant current charging,constant voltage charging,and two-stage charging methods,research has found that two-stage charging is the most efficient.Build equivalent models of different types of charging piles and conduct theoretical analysis on them.The results show that the six pulse rectifier type charging piles and the twelve pulse rectifier type charging piles generate 6k ± 1st harmonic and 12 k ± 1st harmonic,respectively,and the total harmonic content of the latter is lower than that of the former.Compared to uncontrolled rectifier charging piles,the harmonics generated by PWM rectifier charging piles can be suppressed to a certain extent,but the requirements for controllers are higher.(2)Compare three traditional harmonic analysis methods,namely,fast Fourier transform,wavelet transform and Hilbert Huang transform,and build different signal models for harmonic detection and analysis according to different methods.The detection results indicate that Fast Fourier Transform is good at frequency domain analysis of stationary signals,but its performance in time domain is poor;Wavelet transform has advantages in non-stationary signal processing and strong time-domain analysis ability;The Hilbert Huang transform effectively combines time and frequency domains,but there is a problem of endpoint effects and modal aliasing,which affects the detection results.(3)Optimize the phase of the Adaline network to better meet practical needs.A harmonic detection method combining wavelet transform with Adaline improved network is proposed,which not only retains the time-domain analytical ability of wavelet transform,but also introduces the advantages of high efficiency,low error,and all phase detection of Adaline improved network.Through experimental model validation,the comprehensive error of this method is only 0.766%,which improves the accuracy by 28.642% compared to traditional Adaline networks.(4)Build simulation models for six pulse rectification type charging piles and twelve pulse rectification type charging piles,extract the AC side current signal,and use the method of combining wavelet transform and Adaline network to detect harmonics.The amplitude and phase of harmonics are obtained,and the detection results are in line with reality.A harmonic suppression method based on active power filter(APF)is proposed to reduce the harmonic content and ensure that the current waveform meets the standard for the form of harmonics.In conclusion,compared with other traditional harmonic analysis methods,the wavelet Adaline improved network harmonic analysis method described in this paper has obvious advantages,and this method performs well in the harmonic detection of the charging pile model,which can provide some reference for the field of harmonic analysis,and has certain promotion significance.