Rearch On On-Board Charger

With the rapid development of new energy electric vehicles,as one of the core parts of new energy electric vehicles,on-board charger(OBC),the batteries charging and power grid have put forward higher requirements for their performance.For the power grid,the AC-DC circuit of the former stage needs to have higher power factor,dynamic performance and lower input current harmonics;for the batteries in electric vehicles,the DC-DC circuit of the latter stage is required to provide stable DC output,and has a wider output voltage range.At the same time,in order to meet the market demand,OBC should have high power density and adapt to different voltage and power levels.Based on this,this paper studies the control strategy of the front-stage AC-DC circuit and the soft-switching characteristics of the latter stage DC-DC circuit of the OBC.Firstly,for the front-stage AC-DC circuit topology,the traditional voltage-current double-closed-loop control is limited by bandwidth and gain,so it is difficult to meet the requirements of low input current harmonics and high dynamic performance at the same time.To solve this problem,a fast dynamic response control strategy is proposed.By simulation comparing with the traditional voltage-current double closed-loop control and load power feed-forward control,The simulation results show that the output voltage overshoot is reduced by 7.5%,the dynamic adjustment time is shortened by 49 ms,and the total Harmonic Distortion(THD)of the input current is maintained at 2.01%.It is verified that the proposed control strategy has better dynamic performance without increasing the outer loop bandwidth and input current harmonics.Secondly,in order to realize the efficient operation of OBC,the working principle of full-bridge LLC resonant converter under Pulse Frequency Modulation(PFM)is studied,its switching mode is analyzed,its unified FHA(Fundamental Harmonic Analysis,FHA)model is established by fundamental wave analysis method,and its DC gain characteristic is utilized.The conditions of full-bridge LLC resonant converter working on zero-voltage switching(ZVS)at the primary side and zero-current switching(ZCS)at the secondary side are described.Finally,the circuit parameters are designed for the technical requirements of the latter DC-DC circuit for the 3kW OBC,and the system simulation is carried out.The simulation results show that the full-bridge LLC resonant converter works on zero-voltage switching(ZVS)at the primary side and zero-current switching(ZCS)at the secondary side.full-bridge LLC resonant converter has a wide output voltage range,and can realize the primary side ZVS and secondary side ZCS.The resonant current is sinusoidal at full load,and the converter works at the highest efficiency.Finally,a vehicle charger experimental platform is built.The experimental results show that the can realized unit power factor rectification,the output voltage can be stabilized at 400 V,the resonant current is sinusoidal when the switching frequency is close to 100 kHZ,and the former ZVS side ZCS can be realized under half load and near full load conditions.verify the correctness of theoretical analysis,control method and parameter selectionFinally,an experimental platform is built.Experiments on full-bridge LLC resonant converter show that the resonant current is sinusoidal when the switching frequency is close to the resonant frequency,the ZVS and ZCS can be realized under half-load and near full-load conditions.The correctness of theoretical analysis,control method and parameter selection in this paper is verified.