船舶中压直流系统中模块化多电平变换器的并联拓扑与控制优化

Parallel topology and control optimization of modular multilevel converter in ship MVDC system

在船舶中压直流(medium voltage direct current,MVDC)电力系统中,并联式模块化多电平变换器(modular multilevel converter,MMC)因可以承担较大的桥臂电流逐渐受到关注,但MMC并联存在环流问题,会导致功率损耗和系统成本增加。为减少并联MMC的环流,首先对并联结构中子模块数对输出电压、交流侧总谐波畸变率(total harmonic distortion,THD)、传输效率的影响进行研究,找到最优子模块数,然后在分析MMC环流产生机理的基础上设计一种基于内模控制(internal model control,IMC)的并联协调控制策略,以此建立并联MMC-MVDC电力整流系统模型。MATLAB/Simulink的仿真结果表明,采用基于IMC的协调控制策略可有效减少并联MMC的环流,并提高桥臂承担电流的能力。

In the ship medium voltage direct current(MVDC)power system,the parallel modular multilevel converter(MMC)has attracted more and more attention because it can bear the larger bridge arm current.However,there exists the circulating current in the parallel MMC,which leads to the power loss and the system cost increase.To reduce the circulating current in the parallel MMC,the influence of the number of sub-modules on the output voltage,the total harmonic distortion(THD)of alternating current side and the transmission efficiency is studied to find out the optimal number of sub-modules.Then,based on the analysis on the generation mechanism of MMC circulating current,a parallel coordinated control strategy based on the internal model control(IMC)is designed,and a parallel MMC-MVDC power rectifier system model is established by the control strategy.The MATLAB/Simulink simulation results show that the IMC-based coordinated control strategy can effectively reduce the circulating current of parallel MMC,and improve the ability of the bridge arm to bear the current.