Design And Research Of GaN Power Device Based Two-stage EV On-board Charger

Under the background of the deteriorating global environment and environment and the depletion of fossil energy.Governments around the world have introduced corresponding policies to stimulate the development of the electric vehicle industry.Electric vehicles have gradually become the mainstream of future automobile development.The on-board charger,as a key device for electric vehicle electric energy supplement,directly affects the car’s range and charging time.Therefore,designing a car charger that meets the requirements of high reliability,high efficiency,and high power density plays an important role in increasing the penetration rate of electric vehicles.After investigating the relevant technical indicators of the car charger,a two-stage on-board charger based on Ga N power device was designed and analyzed.Its front stage uses the totem pole Boost PFC topology.After analyzing the circuit principle and working mode of the totem pole Boost PFC,it replaces the traditional Si MOSFET switch with a Ga N power device,so that the totem pole PFC can run in continuous current mode To match the power level,working efficiency and current harmonic requirements of the on-board charger.In order to maintain the stability of the output voltage,a voltage outer loop and a current inner loop control method are adopted.According to the small-signal model of the circuit,the transfer function of the control object is derived,and the controller in the double-loop structure is designed in turn.The second stage uses a dual active full bridge topology.The operating mode of the dual active full-bridge circuit under single phase shift is analyzed,and the limiting conditions for soft switching of the switch are given.Based on this principle,a model-based variable frequency control strategy is proposed.After detecting the input voltage value,the set output voltage value and the soft switching current value,the controller can calculate the phase shift angle and operating frequency required by the converter in real time.Meanwhile,the voltage loop is used to compensate the calculation errors caused by the dead time,converter loss,etc.This control strategy greatly expands the soft switching range of the converter under a single phase shift,and reduces the return power under heavy load conditions.Considering the strong electromagnetic interference problem of the two-stage converter at high switching frequency,corresponding EMI filters were designed.Experimental results prove that the filter can effectively suppress common mode and differential mode interference.The simulation model was built on Matlab / Simulink software,which verified the feasibility of totem pole PFC and dual active full bridge parameter design and control strategy.Finally,an experimental prototype of 1 k W based on Ga N power device was built.The prototype uses TI ’s TMSF28335 floating-point controller to achieve full digital control.The experimental results show that the totem pole PFC can output a stable DC voltage and has a high power factor.The dual active full bridge can output a voltage matching the battery pack.After the soft switching current is adjusted by means of frequency conversion,the soft switching of all the switching tubes is realized.