Research On Contactless Charging System And Battery Charger For Electric Vehicles

Environmental-friendly and pollution-free,the electric vehicles have gradually become the trend of the automobile industry in various countries.But the vehicle charging by wire has also brought some drawbacks,such as the high costs of maintenance,the leakage of electric,and so on.The contactless charging method,on the other hand,implements electrical isolation between the transmitting side and receiving side while transferring electric power,and therefore it can get rid of the charging line.Compared to the wired charging,the contactless charging is more secure,more convenient,and more flexible;it has great application prospect.This thesis focuses on the field of wireless charging for electric vehicles.Through mathematical modeling,simulation analysis,software and hardware design,and the debugging work,a wireless power transfer(WPT)system and battery charger for an electric vehicle is developed.The main contents are as follows:(1)The mutual inductance coupling models of three compensation topology of SS,SP and LCL-S are established.The voltage and current output property of each topology is studied;the characteristics of the output voltage gain,system impedance angle,and power transfer efficiency are studied with respect to the variation of load resistance,coupling coefficient,and system working frequency of SS,SP and LCL-S compensation topology.Curves and surfaces are drawn.Through comparison,the LCL-S compensation topology has more stable voltage gain,and is not prone to bifurcation phenomena.Therefore,the LCL-S topology becomes the compensation topology designed for this thesis.(2)The topology structure of WPT system and battery charger and the constant current constant voltage charging mode for electric vehicles are determined.The soft switching condition of the WPT system and DC/DC full bridge converter are analyzed.Finally,the above analyses are verified by the simulation model of PSIM.(3)The design goals and the overall design scheme of WPT system and battery charger are determined.The parameters of loosely coupled transformer,compensation capacitors,filter inductor,filter capacitor,and other key components according to the design goals are confirmed.(4)The principle diagram and hardware circuit of WPT system and battery charger are designed by Altium Designer.The hardware circuits include the full bridge inverter circuit,MOSFET drive circuit,protection circuit,voltage and current sampling circuit,signal conditioning circuit,and rectifier circuit.The selection of key components in the circuits are given.(5)The TI floating-point DSP TMS320F28335 is selected as the control chip to design the control for WPT system and battery charger.The ePWM module is used to generate a drive signal;the ADC module is used as the sampling of the voltage and current;the DMA module is used to process the sampling data.The control methods include bipolar mode control for WPT system and phase shift for charger control.Finally,the prototype of the WPT system and battery charger are built,and the soft switching of the WPT system and battery charger are analyzed.The constant current charging mode and constant voltage charging mode of the charger are tested.The test shows that the designed prototype achieves soft switching,and the charger realizes the designed charging strategy.When the load is full,the transferred power and power transfer efficiency of the WPT system and the battery charger meet the design requirements.