Research On Half-Bridge LLC On-Board Charging Power Supply Based On Transformer Switching Control

Traditional LLC resonant converter takes the rated power point as the design requirement to calculate the resonant parameters.Although the voltage gain in the full load range is guaranteed to meet the requirements,the problem of low efficiency of the converter under light load is ignored at the same time.Aiming at the application of LLC resonant converter in variable power working conditions such as On-Board charging power supply for Electric Vehicle?EV?,etc.This thesis adopts the design thought of variable inductance ratio k,and proposes a Switching Transformer-Based Half Bridge LLC Resonant Converter?STHB-LLC?.The converter efficiency in the light load stage is improved by controlling the switching of the transformer.At the same time,an optimal load partition control strategy is proposed to further broaden the optimized range of light load efficiency,so that the overall efficiency level of the converter can be improved in a large range.Firstly,the basic topology of the proposed STHB-LLC resonant converter is introduced.The equivalent model is theoretically deduced based on the First Harmonic Analysis?FHA?,and the working mode and characteristics of voltage gain are analyzed in detail from the perspective of frequency partitioning.At the same time,the principle of the proposed optimal load partition control strategy is introduced,and the detailed derivation process of the maximum power point P_switchmaxwitch_max for transformer switching control is given.Therefore,the whole load range is divided into two parts:light load region and heavy load region,which provides a theoretical basis for the optimal selection of transformer switching point.Secondly,by analyzing the soft-switching characteristics of the converter and the working characteristics of the staged charging power supply,a 1kW charging power supply for EV is designed based on the proposed STHB-LLC resonant converter.The calculation of resonant parameters of main circuit has carried on the detailed analysis and the concrete design steps are given,also the design and selection of main circuit components has made the introduction.At the same time,the closed loop control scheme of the designed charging power supply is presented,and the control strategy from single closed loop with Constant Current?CC?to double closed loop with Constant Voltage?CV?is adopted to realize the suppression of instability caused by multiple switching at stage of CV.Finally,the charging power simulation model is built with the platform of PSIM,the design parameters and the proposed control strategy are preliminary simulated and verified.On the basis of theoretical analysis and simulation verification,the hardware and software of the prototype were designed,and the experimental platform was built.The simulation and experimental results show that the designed charging power supply can work stably in the ideal working area.In the working stage of CC or CV,it can realize both the ZVS of the primary MOSFET and the ZCS of the secondary rectifier diode.At the same time,the proposed scheme has a significant effect on improving the overall efficiency of the converter,which verifies the correctness of the proposed topology and the optimal load partition control strategy.