Design And Control Of Two-stage On-board Charger Based On GaN Device

Under the background of "carbon peak and carbon neutrality",new energy vehicles have ushered in rapid development.As one of its core components,the onboard charger also ushered in a new direction of development,such as miniaturization and high efficiency.However,at present,most on-board chargers use common Si MOS as switching devices,which results the charger works on low switching frequency,and the overall volume is larger.Therefore,in this thesis,a new type of semiconductor GaN is used as the main power switch device to design and control the two-stage vehicle charger.Firstly,this thesis analyzes the advantages and disadvantages of the common converter topology of two-stage on-board charger,and determines the overall structure of the two-stage on-board charger in this thesis.The totem pole bridgeless PFC converter is the AC/DC converter,and the CLLLC resonant converter is the DC/DC converter.Then,the working principle and control strategy of the front and rear converters are analyzed.For the totem pole bridless PFC,the working principle and control strategy in the discontinuous current mode are analyzed.It is pointed out that although the discontinuous current mode can realize zero voltage opening of the switching tube,its application is limited due to its large input current peak value and low output power level.To solve this problem,the totem pole bridgless PFC based on GaN device is introduced,and its working principle and control strategy in continuous current mode are analyzed.Then,the causes of input current distortion in continuous current mode are analyzed,and the corresponding control algorithm is adopted to optimize the distortion.For CLLLC resonant converter,firstly,the working principle is analyzed,and then the circuit characteristics are analyzed by establishing the equivalent circuit model and the control strategy is given.In order to achieve a wide range of voltage output,and let the rear stage work near the resonant point,this thesis adopts the control method of varying DC bus voltage,through the coordination between the front and rear stages,the conversion efficiency of the whole machine has been improvedFinally,the overall hardware design scheme of the vehicle charger designed in this thesis is given,including the main circuit parameters design and selection,sampling circuit design,soft start circuit design,auxiliary power supply design and so on.Aiming at the application of GaN devices,the influence of parasitic parameters on the performance of GAN devices is analyzed,and a specific optimization scheme is given.The effectiveness of the control scheme was verified by Simulink simulation software,and a prototype with rated power of 2000 W was built for experimental verification.There are 123 figures,14 tables and 95 references in this thesis.