直流配电网MMC-H型直流变压器回流功率的变频优化

Variable-frequency optimization strategy based on backflow power of MMC-H DC transformer in DC distribution network

研究适用于直流配电网的模块化多电平换流器H桥(MMC-H)型直流变压器,其由模块化多电平(MMC)桥臂、H桥和交流变压器组成。MMC采用阶梯波调制,H桥采用方波调制。推导出基于移相控制的传输功率与回流功率表达式,总结影响回流功率的因素与零回流功率的边界条件。为抑制回流功率,提出了变频优化策略,通过工作频率的变化来调节移相比落入零回流功率区域,减小回流功率与电流应力。最后,搭建实验平台对变频优化控制策略进行验证,实验结果表明变频优化控制策略能够调节移相比,降低电流应力与损耗,提高直流变压器效率。

The MMC-H(Modular Multilevel Converter-H-bridge) DC(Direct Current) transformer suitable for DC distribution system is studies,which is composed of MMC arm,H-bridge and AC transformer. MMC utilizes staircase modulation and H-bridge adopts square-wave modulation. Besides,the formula of transmission power and backflow power based on phase-shift control are derived,and the factors that affect the backflow power and the boundary conditions of zero backflow power are summarized. In order to suppress the backflow power,a variable-frequency optimization strategy is proposed. The phase-shift ratio can be adjusted to fall into the zero backflow power zone through variable operating-frequency strategy,so as to reduce the backflow power and current stress. Finally,an experimental prototype is built to verify the feasibility of variable-frequency optimization strategy. The experimental results show that the variable-frequency optimization strategy can adjust the phase-shift ratio,reduce the current stress and loss,and improve the efficiency of DC transformer.