模块化多电平开关串联型直流变压器的电流优化控制策略

Current Optimal Control Strategy for DC Transformer with Modular Multilevel Structure and Series-connected Switches

针对模块化多电平开关串联型直流变压器在中压侧端口电压偏低和轻载情况下存在电流应力增大、运行效率降低的问题,提出了一种基于低压侧全桥内移相控制的电流优化控制策略。通过移相控制,在高频变压器端口产生零电平区间,抑制了传输电感电流尖峰,降低了器件电流应力及损耗。通过研究该直流变压器的工作模式,分析电流应力,以电流应力优化为目标制定优化控制策略。该策略采用分段计算移相角的方法,在维持开关管软开关特性的同时达到良好的闭环控制效果。最后,通过仿真和样机实验验证了所提优化控制策略的有效性。

To deal with the problems of high current stress and low operation efficiency of the DC transformer combining modular multilevel structure and series-connected switches under conditions of low voltage on the medium-voltage side and low load,this paper proposes a current optimal control strategy based on the inner-phase-shift control of the low-voltage side full-bridge.By adopting the phase-shift control,the zero-level interval is generated at the port of the high-frequency transformer,and the peak current of the transmission inductor can be suppressed,which reduces the current stress and loss of devices.The current stress is analyzed by studying the operation modes of the DC transformer,and the optimal control strategy is established based on the goal of current stress optimization.This strategy adopts the method of calculating phase-shift angle in segments,which achieves a good closed-loop control effect while maintaining the soft switching characteristics of switch tubes.The effectiveness of the proposed optimal control strategy is verified by the simulation and the prototype experiment.