Research On Several Technical Problems Of SiC-based Hybrid Control LLC Resonant Converter

With the continuous updating of today's rail transit technology and the continuous iteration of products,the on-board DC-DC converters are required to improve their performance in terms of volume,power density and power conversion efficiency.Because of its advantages in power density and conversion efficiency,LLC resonant converters stand out in applications such as automotive power supplies.The control method of LLC resonant converter at a phase-shifted fixed frequency is to change the total output voltage of the converter by changing the phase-shift angle.And in the frequency conversion control process,the entire charger can realize the zero voltage(ZVS)of the primary power switch of the converter within the fluctuation range of the entire frequency band.What's more,in order to further improve the power conversion efficiency.The secondary rectifier enables zero current shutdown(ZCS).The inverter-controlled resonant converter has a high working efficiency,and fixed frequency control can be used as a soft-start process to start the converter.By combining the two control strategies of fixed frequency phase shift control and variable frequency control,the work conversion efficiency of the system will be further improved.In addition,compared with traditional Si devices,SiC power semiconductor devices have a series of advantages such as high breakdown field strength,wide band gap,excellent heat dissipation performance,and high saturated electron drift rate.Therefore,a new type of SiC power semiconductor device is used instead of the Si device in the traditional car charger to apply to the LLC controlled hybrid buck transformer.In this paper,SiC MOSFET C2M0080120 D is selected as the main power switch and applied to the prototype of a 200 W full-bridge LLC converter.And,the DSP28335 digital signal processing control chip is used as the central controller of the power supply system.Experiments show that the mixed control mode of fixed frequency phase shifting and variable frequency control is completely feasible and effective.