Research On The Front Stage Rectifier Of DC-Charging Pile For Electric Vehicles

With The development of electric vehicles is fast and the increment is large.And as the supporting equipment of electric vehicles,the charging pile realizes the connection between the input end and the power grid,and the output end realizes the charging of the vehicle battery,which was usually composed of two-stage circuits,the former rectifier and the latter DC / DC converter.The function of the former rectifier: first,to provide stable DC bus voltage for the later DC / DC converter;second,to meet the requirements of the grid on the grid equipment,namely low harmonic content and unit power factor input.The function of the post DC / DC converter was to transform the DC bus voltage output by the former rectifier into a wide voltage output to provide charging power for various voltage levels of electric vehicles.Therefore,it was of great engineering value and practical significance to study the front stage rectifier of charging pile.In this paper,three-phase three switch three level(Vienna)rectifier were studied.Firstly,the working principle of three-phase Vienna rectifier was analyzed,the equivalent circuit and switch model were derived,and the mathematical model was established by using the state space average method.The transformation from three-phase static coordinate to two-phase rotating coordinate system was completed,and the mathematical model was further simplified.Secondly,the variable index sliding mode control method and precise feedback linearization method were proposed.The feasibility of the proposed control method was verified by mathematical theory.Based on the two methods,the double closed-loop control strategy of current inner loop and voltage outer loop was designed.The neutral point potential balance of capacitor was controlled by positive and negative short vectors.A modulation method of converting three-level SVPWM to two-level SVPWM was presented In this paper.Then,the simulation model of Vienna rectifier was built in Matlab / Simulink software.The simulation results of the traditional PI control strategy and the new control strategy proposed in this paper were analyzed,and the simulation data were compared.It is concluded that the DC output voltage stability,harmonic content and other technical indicators of the sliding mode control strategy were better than the PI control strategy.Finally,TMS320F28335 chip was used as the digital controller to design the hardware circuit and software program of Vienna rectifier,and a prototype of 15 kw power was developed and tested.Through the analysis of the experimental results,it can be seen that the Vienna rectifier can achieve unity power factor correction,low harmonic content and stable DC output voltage.The correctness of the system design was verified,and it had certain engineering application value.