To improve the lightweight level of auxiliary converters for urban rail vehicles, full SiC intermediate frequency auxiliary converters have become a trend. Aiming at its core component, a full SiC intermediate frequency isolated DC-DC converter using Boost + LLC topology is studied in this paper. The working principle and characteristics of the converter are analyzed in detail. Based on the operating characteristics of the LLC resonant converter and the realization mechanism of soft switching, an optimization design method of the resonant parameters is proposed, which can make LLC resonant converters exhibit the characteristics of DC transformers and realize soft switching in the full load range. Considering the power losses of the converter and the voltage stress of SiC MOSFET, the design method of the intermediate bus voltage is given. Finally, the correctness of the parameter design method is verified by simulation and experiment, and the performance of the full SiC intermediate frequency isolated DC-DC converter is analyzed. When the input voltage is 1500V and the output power is 15kW, the efficiency of the converter reaches 96.21%. Compared with the Si intermediate frequency isolated DC-DC converter, the power density is improved by 80.62%.

With greater power density, a hybrid power source that combines supercapacitors and batteries has a wide range of applications in pulse-operated power systems. In this paper, a supercapacitor/battery semi-active hybrid energy storage system (HESS) with a full current-type control strategy is presented. The studied HESS is composed of batteries, supercapacitors, and a bidirectional buck–boost converter. The converter is controlled such that supercapacitors supply load power pulses, and batteries provide the power in steady state. To realize the fast compensation of the supercapacitors to the load power pulses, a power distribution module based on hysteresis control theory is designed in the control system. Moreover, the control strategy does not require the model parameters of the converter and supercapacitors, so the control system is simplified. A complete configuration scheme and cost analysis of the proposed HESS are also presented. Obtained results show that the proposed supercapacitor/battery semi-active HESS has good performance in terms of dynamic response, weight, and energy utilization coefficient (EUC).