直流充电桩后级变换器软启动控制策略研究

Soft start of full bridge LLC resonant converter of charging module control strategy research

随着国家对节能减排的深入推进,电动汽车行业迅速发展。直流充电桩的充电模块作为充电桩的核心,其后级DC-DC环节选用全桥LLC谐振拓扑,使充电桩可以工作在高频大功率条件下,大大提升了充电桩的功率密度。针对该拓扑在启动时存在较大冲击电流的缺陷,详细分析了变换器启动过程中各参数的变化,在原有传统软启动策略的基础上提出了一种先移相后降频的软启动策略,该控制策略结合了移相软启动和降频软启动的优点,在25 ms内即可完成软启动,且工作波形畸变较小,仍可保持全负载范围的软开关特性。搭建了一台实验样机,验证了软启动策略的可行性,并检测稳定工作后的波形畸变情况,实验结果表明,该软启动策略可有效抑制启动冲击电流,具有更佳的启动效果。

With the country’s deepening of energy conservation and emission reduction,the electric vehicle industry develops rapidly.The charging module in the DC charging pile is the core.The selection of the full-bridge LLC resonant topology enables the charger to work under high-frequency and high-power conditions,which improves the power density of the charger greatly.In order to limit the large inrush current during startup,the changes of various parameters during the startup process were analyzed in detail,and a control strategy was proposed that performs phase-shifting first and then reduces the frequency.This strategy integrated the advantages of both phase-shifting control and frequency control,which could start the converter within 25 ms.Under this control strategy,the distortion of the converter's working waveform is small,and all the switches can realize zero-voltage switching from nearly zero to full load.An experimental prototype was built to verify the feasibility of the soft-start strategy,and to detect the waveform distortion after stable operation.Experimental results show that the soft-start strategy proposed in the article can effectively suppress the starting inrush current and has a better starting effect.