一种模块化直流变压器调制策略研究

隔离型模块化多电平直流变换器（IMMDC）是船用中压直流电力系统的关键部件，论文分析了IMMDC方波调制下桥臂压降与直流母线电压、交流侧方波电压幅值之间的关系。在此基础上，推导了IMMDC的平均等效模型，实现了电路直流回路与交流回路的解耦，针对IMMDC直流回路电流振荡问题，在方波调制的基础上提出了一种改进调制策略，在IMMDC系统中增加一个新的可控量来校正直流电流波形，进而稳定模块直流侧电容电压，提高系统的稳定性。最后，搭建了实验样机并完成了实验验证，结果表明改进调制策略能够有效地抑制直流电流的振荡，减小模块电容电压的波动，验证了所提调制策略的可行性与有效性。

A Modular DC Transformer Modulation Strategy Research

Isolated modular multilevel dc converter (IMMDC) is a promising topology in medium voltage dc grid. This paper study the relationship of arm voltage, dc grid voltage and ac voltage amplitude when the IMMDC operates in square wave modulation. On this basis, the average equivalent mode of IMMDC is derived. Decoupling of dc loop and ac loop in MMC is realized. The dc current oscillation of dc loop is mainly analyzed and a novel modulation strategy is proposed to supress this oscillation. Finally, a down scale prototype of IMMDC is established. The experimental results show that this improved modulation can effectively control the oscillation of dc current and decrease the fluctuation of sub-module capacitance voltage, which verify the feasibility and effectiveness of this strategy.