M^(2)S^(2)DCT的阀串支路电流优化控制策略

A sub-module branch current optimization strategy for M^(2)S^(2)DCT

具有模块化多电平结构的串联开关直流变压器(direct current transformer, DCT)在使用传统单移相控制时,存在中压侧全桥换流时阀串支路产生电流尖峰的问题,器件承受额外的电流应力。基于该新型DCT的工作原理与电流波形,提出一种基于中压侧全桥换流移相的阀串支路电流优化调制方法。文中对阀串支路的电流应力进行详细分析,结合电路可靠工作移相角范围,确定中压侧全桥换流移相角最优值的计算方法,从而确立优化控制策略。该优化控制策略独立于原有的功率控制环路运行,不改变DCT功率传输状态,不影响功率的调节控制,易于投入实际应用。仿真与样机实验的结果验证了该优化控制策略降低电流应力的有效性,同时样机实验结果显示效率得到提升。综合原理分析与效果验证可知,该优化控制策略对设备的安全运行与器件选型具有借鉴意义。

A hybrid direct current transformer(DCT) with modular multilevel structure and series-connected switches experiences current spike in sub-module branch when using original control method. The existence of current spike causes extra current stress on components. Based on the operating principle and current waveforms, an optimization modulation method is proposed, which is based on the phase shift of medium-voltage side full-bridge. The current stress of series-connected switches branch is analyzed, combined with limitation of phase shift angle for operation safety, the algorithm for the optimum phase shift angle is determined, and the optimized control strategy is established. This strategy is independent of the original power control loop, so it does not change the power transmission status and interfere with power control, which makes it easy to be put into practical application. The effectiveness of current stress reduction is verified by simulation and prototype test, and a certain improvement of efficiency is shown by the results of prototype test. Based on the analysis of operation principle and simulation and test results, the optimal control strategy is proved to have positive significance for the safe operation of equipment and selection of components.