Design Of On-board Charger Based On Totem Pole And LLC Topology

Electric vehicle that is environmentally friendly becomes the development direction of automobile industry gradually.At the same time,on-board charger(OBC),which is a key device in electric vehicle charging system,is also widely used.With the popularization of electric vehicle,new requirements such as miniaturization,high reliability and high efficiency are proposed for the OBC.In this thesis,the overall performance,hardware circuit and control strategy of the OBC are researched.The contents are divided into three parts shown as follows:(1)The overall performance of the OBC is researched.Firstly,the function of each device in charging system and the relationship between them are analyzed,and the main performance indexes of the OBC are given.Then,the connection process between the OBC and the AC charging post and the charging mode of the OBC are studied.Finally,the topology and control strategy of the OBC are analyzed and discussed.In order to meet the requirement of high efficiency,the bridgeless totem pole Boost PFC circuit and the full bridge LLC resonant converter are selected as the main power circuit of the OBC.(2)The hardware circuit of the OBC is designed.On the one hand,the working principle of totem pole Boost PFC circuit and the variation of duty cycle of switch tube driving signal in the circuit are studied,the input inductance and output capacitance parameters of the circuit are calculated and the power devices are selected.One the other hand,the working principle of the soft switching of the full-bridge LLC resonant converter is studied,the characteristics of voltage gain and input impedance are analyzed,and the parameters of resonant network are designed according to its optimal working range.(3)The control strategy of the OBC is designed.First,the transfer function of the controlled object is obtained by establishing the small-signal model of the totem pole Boost PFC circuit,and the controllers of current loop and voltage loop in double loop series control structure are designed.Then,according to the constant current and constant voltage charging requirement of the battery,the control strategy of the full bridge LLC resonant converter is designed,and the parameters of Pi controller are calculated according to the stability index.Finaly,this thesis builts the Saber simulation models of totem pole Boost PFC circuit and full bridge LLC resonant converter,and analyses the simulation data.The simulation results show that the OBC based on totem pole and LLC topology meets the requirements of power factor,voltage ripple and efficiency with low loss and high switching frequency,and verify the effectiveness of the circuit parameters and control strategy designed in this thesis.At the same time,it is verified that compared with the traditional topology,the efficiency of the OBC in this paper is improved and the comprehensive performance is better.In addition,the parameter design method adopted in this paper is more scientific and effective,and improves the efficiency of parameter matching in engineering application.