The Soft-Switching Of High-Frequency DC Charger System

Higher frequency, modular construction and digitalization will be the main development tendency in power electronics. To reduce the switching loss with higher frequency, it will be a trend to make research on Soft-Switching technique. The paper is based on the research of charger used in automobile, which belongs to the project of Zhuzhou Electric Locomotive Research Institute. This paper apply soft-switching technique in high-power high-frequency direct power and design a charging system for lead-acid batteries. The main contents include:On the base of research on the topological structure, operation principle and course of full bridge converter, an improved full bridge phase-shift ZVZCS-PWM DC/DC converter is adopted. The converter utilizes leakage inductance of transformer and parallel capacitor of power switches as resonance units, to realize zero-voltage-switching (ZVS) for leading-leg. And it realizes ZCS for lagging-lag by using one clamping capacitor and two discharging diodes to reset the primary current. Based on the analysis of the operation principle, switching course and the condition of soft-switching, parameters of the circuit have been designedand the main circuit has load been simulated by Saber.Because of the slow change of battery load and charge characteristic, single close-loop PI control strategy has been adopted.This paper introduced a digital control system based on digital signal processor IC (TMS320F2812).At last, based on the theoretical research and simulation, the high-frequency direct power charger, 36Kw and 18kHz, has been developed. The state of ZVS for leading bridge and ZCS for lagging bridge have been tested.The testing result has been compared with simulation's, and the efficiency has been measured.The simulation analysis and experiment show the feasibility of the scheme, which apply soft-switching technique in high-power high-frequency direct converter. The topological structure, parameters of the circuit and control method are correct. The switching loss has been reduced effectively and the efficiency of the converter has been improved.