| Nowadays,the global energy crisis and climate change are becoming increasingly serious.The promotion of electric vehicles(EVs)has become an important choice for countries to achieve energy conservation and pollution emissions reduction.This means that plenty of EVs will be connected to the grid through chargers,and fast chargers with high power are widely used.As a typical high-frequency power electronic equipment,harmonic and supraharmonic emission caused by fast charger cannot be ignored.In order to have a more comprehensive grasp of the harmonic and supraharmonic emission characteristics of fast charger,this paper conducted a large amount of field measurement at several fast charging stations and an in-depth analysis of measurement data.The main research work of the thesis is presented as follows.Firstly,fast charging stations are investigated in a city.A complete field measurement process is designed based on the measurement purpose,with consideration of the loads and structure of the stations.Three measurement points are selected in the distribution boxes.Plenty of field measurements were implemented in 4 different charging stations.Lots of measurement data were obtained to provide the data basis for subsequent analysis.Secondly,based on the field measurement results,the charging power characteristics of the charger under different operating conditions and its influence on the RMS and phase angle of the harmonic current are analyzed.The similarities and differences of the harmonic emission characteristics of different brands of chargers are compared.Based on the method of prevailing harmonic phasor,the harmonic current cancellation characteristics between chargers in the charging station is analyzed to propose the advice about the configuration of the charger during the planning and construction stage.Besides,the measurement results are compared with the harmonic limits of the standards,and recommendations on harmonic limits for EV charger are presented.Finally,a comprehensive analysis of the supraharmonics characteristics,as well as the impact of charger brand,charging power on the emission characteristics are presented.And the voltage unbalance and secondary emission problem in the charging station is discovered.The phenomenon of frequency and amplitude fluctuation of the supraharmonics found in the measurements are analyzed in theory and testified by experiments.With the field measurements of EV chargers,the characteristics of harmonics and supraharmonics are achieved under the actual operation,which provides the guidance for the planning of charging stations,the elimination of harmonics and supraharmonics,as well as the improvement of related standards. |
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