基于动态冗余度的模块化多电平换流器子模块投入策略

Optimized Control Strategy Based on Dynamic Redundancy for Modular Multilevel Converter

为了提升子模块利用率,同时降低子模块电容电压应力,提出了一种基于动态冗余度的模块化多电平换流器子模块投入策略。该方法考虑了交流系统与直流系统的综合影响,提出了动态冗余度以及子模块利用率2项调节指标。在给定工况下,该策略根据桥臂输出电压的最大值以及人为设定的安全裕度来确定子模块电容电压参考值,进而采用最近电平逼近策略进行调制。该方法可以有效提升换流器运行灵活性,扩大系统抵御子模块故障的能力。基于本策略在PSCAD/EMTDC中搭建了仿真平台,并针对多种工况进行了研究分析。仿真结果表明:该策略可以对换流器冗余度进行实时动态调整并实现故障情况下的冗余保护,调整过程中各项指标均无明显波动,验证了本策略的有效性和可行性。

In order to improve the utilization ratio of sub-modules and reduce the capacitor voltage stress on the sub-modules for modular multilevel converter, we proposed a control strategy of modular with redundant sub-modules based on dynamic redundancy. Considering the synthetical effects of the AC and DC system, we proposed two indexes, namely, the dynamic redundancy and the utilization ratio of the sub-modules. In this strategy, under the given working conditions, the reference value of the capacitor voltage is derived according to the maximum output voltage of each con- vener arm and the adjustable safety margin. This method can improve the flexibility of the converter, and enhance the fault ride-through capability of the system. Moreover, we built a model of two-terminal MMC-HVDC system in PSCAD/EMTDC, and analyzed several operation modes of the system. Simulation results show that, by using the pro- posed strategy, the redundancy of the converter is adjustable dynamically and the redundancy protection under fault conditions is valid without obvious fluctuation of any index. Hence, the proposed strategy is valid and feasible.