Research On High Efficiency Electric Vehicle Charger Technology Based On GaN Devices

With the development of electric vehicle industry at home and abroad,the development of on-board charger(OBC)technology has played an important role in promoting the popularization of electric vehicle.High efficiency miniaturized OBC technology is becoming a research hotspot.The high efficiency power factor correction(PFC),high efficiency DC-DC converting and miniaturization of vehicle charger based on single-phase household power supply system are the key problems to be solved in the design of the OBC.The traditional Si MOSFET is applied as the switch in OBC topology,which limits the working frequency and efficiency of the OBC.Therefore,the high efficiency two-stage OBC based on the new GaN device for electric vehicle is studied as follows in this thesis.The two-stage OBC based on GaN device is composed of a pre-stage PFC and a post-stage DC-DC converter.The pre-stage PFC converter adopts the topology of totem pole bridgeless PFC circuit based on GaN device,and the GaN device is used as the high frequency bridge arm switch to solve the problem that the traditional Si MOSFET switch can not make the converter work in the CCM mode,and the power level of the converter is improved.The full-hardware control circuit is designed with one-cycle control chip IR1150 as the main control chip,and the synchronous rectifier type control mode is adopted to realize the synchronous rectifier type complementary drive of the high frequency bridge arm switch.The dynamic control enables GaN device to reverse guide current under the condition of forward gate driving voltage,reduces the reverse on-off voltage drop of GaN device,and further improves the efficiency of totem pole bridgeless PFC.The circuit topology and synchronous rectifier control mode are simulated by PSIM simulation software.The simulation results show that the totem pole bridgeless PFC based on synchronous rectifier type control mode can effectively improve the PFC effect.The post-stage DC-DC converter adopts HB-LLC resonant converter,and the control circuit of the converter is designed to realize soft switching control and constant current / constant voltage mode charging control.The HB-LLC resonant converter is designed with UCC25600 as the main control chip.The switching frequency of the HB-LLC resonant converter is controlled near the resonant frequency point,which realizes the primary switch on ZVS and the secondary side output rectifier diode ZCS at the same time,effectively reduces the switching loss.The switchs of HB-LLC resonant converter use cascade GaN device,which makes the operating frequency of this converter further improved,the volume of components is reduced and the overall efficiency is improved.In the control circuit,the current feedback loop and voltage feedback loop are designed to adjust the measured output current and voltage compared with the rated output of the OBC to realize the switching between the constant current/constant voltage charging mode.PSIM simulation results show that the HB-LLC resonant converter realizes primary switch on ZVS and secondary output rectifier ZCS in the full load range,and can enter the constant current charging mode at 8.25 A and the constant voltage charging mode at 400 V.Finally,the 3.3kW experimental prototype based on the GaN device is built to verify.The experimental results show that the design parameters of the prototype can meet the application requirements of the OBC,and realizes 8.25 A constant current and 400 V constant voltage charing.The PFC efficiency can reach 97.9% under full load condition,and the overall efficiency is over 96%,which meets the application requirements of miniaturization and efficiency of the OBC.