摘要
基于MMC的运行基本原理,研究了柔直电网功率不平衡时桥臂电容的充电过程,得到了直流电压与不平衡功率之间的表达式。针对不平衡功率引起的直流过电压问题,现有的故障穿越措施主要有紧急降低风电功率和装设耗能装置2种,该文提出了一种自适应NLM策略实现直流电压的紧急控制,可延长直流电压上升达到保护定值的时间,在换流站闭锁前实现安控有效切机。通过在PSCAD/EMTDC中搭建电磁暂态模型进行仿真分析,验证了该策略的有效性。
Based on basic operation principle of modular multi-level converter(MMC), charging process of bridge arm capacitor with unbalanced power in MMC-HVDC grid is studied, and the expression of relationship between DC voltage and unbalanced power is obtained. Existing fault-ride-through strategies mainly include emergency reduction of wind power and additional installation of energy dissipation devices. This paper proposes an improved emergency modulation strategy to suppress DC overvoltage by adjusting input numbers of sub-module adaptively. This strategy can reserve sufficient time to cut the unbalanced power and achieve fault-ride-through. An electromagnetic transient model is built in PSCAD/EMTDC, and effectiveness of the strategy is verified with simulation.
引文
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