基于电流滞环型调制的模块化多电平变换器容错策略研究

Research on the Hysteresis-band Current Tracking Strategy based on Fault-Tolerant Control for Modular Multilevel Converter

模块化多电平变换器(MMC)是电压源型变换器(VSC)的一种新型的拓扑结构。其子模块故障保护问题,是业内拓扑研究的难点之一。针对这个问题,本文提出一种子模块故障容错策略。实时监测变换器逆变侧输出电流与给定电流的误差以及负载侧两端电压,从而决定逆变侧输出电压,使得输出电流快速、高效地跟踪给定电流。当监测出变换器出现子模块故障时,切除该子模块并且对输出电压进行重构,保证上、下桥臂不会出现过流现象,系统平稳运行直到故障修复。另外,建立虚拟子模块,将其循环映射到实际子模块的驱动信号中,从而实现子模块电容电压均衡。这种控制策略简单可靠、鲁棒性强,易于工程实现。本文通过仿真和实验验证了所提方法的正确性和有效性。

Modular Multilevel Converter（MMC） is a novel topology of Voltage Source Converter（VSC）. The protection issues of the malfunction of the sub-module are difficult to handle with. With regard to this problem, the fault-tolerant control based hysteresis-band current tracking strategy, which is used for the MMC, is proposed in the paper. The output voltage can be determined by real-time monitoring the voltage of the load and the deviation between the output current and the given current. Thus, the output current can track the given current quickly and efficiently. When the malfunction occurs in the sub-module, which then must be cut off, and the output voltage should be restructured. The upper/lower arm will be protected from overcurrent. The whole system can still be running smoothly before the fault has been repaired. In addition, the voltage of the capacitor in the sub-module can be balanced by loop mapping the constructed virtual sub-module into the actual sub-module. The proposed strategy is simple and reliable for the control of MMC. According to the simulation and experimental results, the correctness and validity of the proposed method are verified.