Application Of LLC Resonant Converter Based On SiC Devices In The Charger Of Urban Rail

The charger in the auxiliary power supply system of urban rail transit vehicles is an important device for the DC power supply.Improving the power density and efficiency of a charger has an important and direct impact on the optimization of its performance.In recent years,the emergence of Silicon Carbide(SiC)wide bandgap semiconductor devices has provided the possibility to achieve this goal,and LLC resonant soft switch technology will further improve the efficiency.Based on the high-frequency characteristics of silicon carbide semiconductor devices,the principle and characteristics of LLC resonant converter are studied in detail,and the combination of the two is applied in the development of urban rail vehicle charger.Firstly,this paper analyzes the main circuit structure of LLC resonant converter and the principle of three operating modes in detail.The equivalent model of the circuit and voltage gain function are obtained through fundamental wave analysis.Besides,the characteristics of voltage gain,ZVS characteristics and implementation conditions are described.The design flow of resonant element parameters(resonant inductance,resonant capacitance and excitation inductance)is completed by combining analytical method and graphic method,and the resonant parameters are designed based on the actual parameters of the charger.Then,the simulation model of LLC resonant converter charger is established to verify the effectiveness of the resonant parameter design.Secondly,the LLC resonant converter is modeled using the extended description function(EDF)method and the control mode of the system is selected based on the characteristics of the resonant converter.The stability of the system is analyzed based on the output-control transfer function obtained from the modeling,and then the controller design is completed through the frequency-domain analysis method.The steady-state and dynamic control performance of the controller is verified in Matlab simulation software.At last,the three charging strategies are compared and the feasibility of constant current and constant voltage charging method is verified by simulation.Finally,an experimental prototype of a full-SiC LLC resonant converter charger are built.On the experimental prototype of charger,the rationality of the design of the LLC resonant converter parameters is verified and the soft-switching of devices is realized.Besides,experiments verify the correctness of the controller design based on the small signal model of the extended description function.Then the process of charging the battery is simulated by using electronic load,and the constant current and constant voltage charging process is completed,which verify the simulation of charging mode.