负序电流补偿对提高电网电能质量至关重要，可改善三相负荷不平衡度和支撑不平衡电网电压。星形级联H桥(CHB)STATCOM是新一代中高压有源补偿装置，具有模块化，器件少等优点。但其三相直流母线相互分离，相间有功功率无法直接转移，在补偿负序电流时需兼顾三相有功功率平衡，严重限制了负序电流的补偿范围。针对CHB拓扑结构的不足，本项目综合共直流母线变换器与CHB的优势，提出利用共直流母线变换器为CHB相间有功功率提供新的平衡路径，以期拓宽负序电流的补偿范围。本项目研究混合CHB的关键技术主要包括：揭示相间有功功率的平衡机理，提出CHB相间直流电压均衡策略；分析负序电流范围与共直流母线电压的关系，提出负序电流范围的计算算法和共直流母线电压的设计依据；进一步挖掘混合型CHB的优势，提出基于共直流母线变换器的容错控制策略。通过本项目的探索，为提高中高压电网的电能质量和安全可靠运行提供理论和技术基础。

Negative sequence current compensation is very important for the grid to improve the power quality, which can reduce the imbalance of the load current and also support the unbalanced grid. Cascaded H-bridge (CHB) STATCOM is an advanced reactive power compensation device for medium and high-voltage power system because of its modular structure and fewer components. Due to the separated DC-links among three phases, the cluster active power cannot exchange directly. Hence, the negative sequence current control should take the balance of three cluster active powers into account, which seriously limits the negative sequence current range of CHB STATCOM. To solve this problem, this proposal combines the CHB and the converter with common DC-link which can be used to transfer and counteract the imbalanced active powers from the CHB, thus the negative sequence current compensation range can be widened. For this hybrid CHB STATCOM, we focus on the following key techniques: the balance mechanism of the three-cluster active powers and the balance control of three-cluster DC voltages for CHB; the computational algorithm of negative sequence current range and the design method of the common DC-link voltage; the fault-tolerant control by using the redundancy of the converter with common DC-link. Through the exploration of the hybrid CHB STATCOM, it can offer a brand-new solution to improve the power quality and guarantee the safe operation of medium and high-voltage power system.