Research On LLC Resonant Converter Applied To DC Charging Pile

Electric vehicle is a hot spot in the world,and the DC charging pile is very important to the development of electric vehicle.At the same time,it is also the key part of electric vehicle energy supply.The electric vehicle DC charging pile adopts the structure of two stages,the first stage is a three-phase PFC circuit,the output is about 800 V of the DC voltage,and the second stage is a DC-DC converter with wide voltage output,which is used to charge the car battery.In this paper,the DC-DC circuit of the DC charging pile is studied.In order to shorten the charging time,reduce the volume of charging pile and improve the power density,it is necessary to realize the high frequency.With the high frequency,the switching loss is serious.In order to reduce the switching loss,the circuit must realize soft switching.By analysis,the half bridge three level LLC resonant converter is adopted as the main circuit of the post-circuit of the DC charging pile.The control mode of LLC resonant converter is frequency modulation and phase shift control.Based on the advantages and disadvantages of the two control methods,this paper adopts the hybrid control strategy which combines frequency modulation and phase shift control.This paper analyzes the working principle and characteristics of frequency modulated mode and phase shift mode of half bridge three level LLC resonant converter.On this basis,the main circuit parameters of the converter are analyzed and designed.Because the analog control circuit has many disadvantages,such as various components,poor portability,and poor anti-interference ability,this paper uses DSP28335 as the control unit to design the hardware and software of the control circuit.A prototype of 15 kW was made in the laboratory,and the theoretical analysis was verified by experiments.The experimental results confirm the correctness of the theoretical analysis and the feasibility of the design scheme.