模块化多电平换流器子模块故障时中性点移位容错控制策略

模块化多电平换流器(MMC)发生子模块故障后,由于桥臂子模块数目的改变,将使故障相的相电压输出能力发生改变,导致三相输出不对称。针对MMC子模块故障下容错控制问题,以保证子模块故障后线电压平衡为控制目标,提出了一种MMC中性点移位控制(NPSC)容错控制策略。其通过修正故障后各相调制波控制中性点在故障相的相电压矢量方向上进行移位,在完成子模块故障容错运行的同时简化了传统中心点偏移控制算法的复杂程度,易于实现。同时,文中分析了NPSC下对MMC系统运行的影响,指出了该种控制方式下桥臂电流工频分量与直流分量的分配特性。最后,通过仿真与实验进行验证,表明了理论分析与该容错控制策略的有效性。

Fault-tolerant Control Strategy of Neutral Point Shift for Sub-module Faults of Modular Multilevel Converters

After the occurrence of fault with sub-modules of modular multilevel converter(MMC), the fault-phase voltage output capacity will be changed since the changed number of sub-modules of the fault bridge, which will make the system neutral point shift. For the fault-tolerant control problem following the sub-module fault of MMC, this paper proposes a fault-tolerant control strategy based on neutral point shift control(NPSC)to ensure the line-to-line voltage of the system symmetrical output. It controls the neutral point shift in the fault phase by correcting each phase modulation wave after the fault. It can complete the sub-module fault ride-through while reducing the complexity of the traditional neutral-offset control algorithm at the same time. The influence of MMC system operating characteristic under the NPSC fault-tolerant control is analyzed, and the distribution characteristics of fundamental frequency component and direct current component of bridge current are pointed out. Finally, simulation and experiment results verify the feasibility of the theoretical analysis and the proposed scheme. This work is supported by Application Technology Research and Engineering Demonstration Program of National Energy of China(No. NY20150302).