Research And Design Of Half-bridge Three-Level LLC Resonant Converter Based On Hybrid Control Strategy

At present,the promotion and application of electric vehicles are reversing the construction of charging facilities,and quickly promote the research and development of charging system.On the current technology and market demand,the charging voltage level of charging system can be divided into three categories including high pressure(More than 600V),medium pressure(300V~600V)and low pressure(below 300V).The research of converters for medium and high voltage levels is not only extensive but also relatively mature,but for the low-voltage high-current one is relatively less.And because the charge voltage span is so large that the converters whic are generally suitable for medium or high voltage can not be applied to low voltage applications.Moreover,as the demand of current market for low-voltage high-current type of charging system is quite large(such as site patrol cars,electric logistics vehicles,etc.),it is so significan to research the low-voltage high-current type of converter.Therefore,this research is about the low-voltage high-current charging system,by considering the cost and the difficulty of realization,the half-bridge three-level LLC resonant converter topology has been selected as the main circuit of this system.This paper uses frequency conversion and phase shift combined control strategy in order to facilitate optimized the design of the magnetic device,the converter can work in a narrow frequency range to obtain a wide DC voltage gain and output stably at very low load rates.Firstly,the working principle of the basic half-bridge three-level is briefly introduced,and the circuit of the LLC resonant circuit is modeled and analyzed.After combining the two,the topology of the half-bridge three-level LLC resonant converter is obtained.Secondly,the phase shift control and frequency conversion control are studied respectively,and the control method of the hybrid control strategy is obtained,On this basis,the corresponding control method is put forward for the no-load stable operation.Thirdly,this paper completes the design of the hardware circuit and software system of the half-bridge three-level LLC resonant converter,including the calculation and selection of the main circuit power device parameters,design of Control Circuit with TMS320F28035 as Core,design of drive circuit,sampling circuit,auxiliary power supply.Finally,a half-bridge three-level LLC resonant converter with frequency range of 80 k Hz~120k Hz,output power of 10 k W is developed.Through the debugging and experiment on the main circuit and control circuit of the prototype,the correctness of the circuit theory is verified.The resonant converter developed has good performance,which can achieve stable output under low power consumption,even the load rates are extremely low.