基于真双极接线的VSC-MTDC系统功率转代策略

随着国内柔性直流输电技术的快速发展,基于真双极接线的多端柔性输电技术将被越来越多地应用到实际工程中。不同于单极线路或换流器退出运行时,伪双极系统下会出现的线路过载和切机切负荷现象,对于运行方式更为灵活的真双极系统,由于非故障极可转代故障极的部分功率,使得电网可靠性和整体输电能力的提升成为可能。提出了一种适用于真双极多端柔性直流输电(VSC-MTDC)系统的功率转代策略:基于真双极系统正负极电网可独立控制功率的特点,当直流系统在非正常运行状况下出现非对称拓扑时,在确保各元件不越限的前提下使非故障极电网转代故障极电网部分功率,以提高VSC-MTDC系统的总传输容量。同时,基于张北±500 k V柔性直流输电示范工程,搭建了真双极四端柔性直流输电PSCAD/EMTDC仿真系统,对所提策略进行了有效性验证。

Power Conversion Strategy of VSC-MTDC System Based on Real Bipolar Wiring Mode

In China, with the rapid development of voltage source converter based multi-terminal direct current(VSC-MTDC)transmission technology, the real bipolar wiring mode has become increasingly popular in actual multi-terminal direct current(MTDC)projects. In the pseudo bipolar mode, line overload, generator tripping or load shedding may occur if a direct current line or a converter quits operation, while in the more flexible real bipolar mode, power conversion from fault grid to the non-fault one is permissible under similar conditions. A power conversion strategy for bipolar operation VSC-MTDC system is proposed. Since the positive and negative grid can be independently controlled in the bipolar mode, power surplus of the fault grid can be transferred to the non-fault one by using the proposed strategy under abnormal operating conditions. This strategy has improved the reliability and transmission capability of power grid within the limits of each element capacity. The simulation model based on Zhangbei ±500 kV MTDC demonstration project is established in PSCAD/EMTDC. The validity of the proposed strategy has been proved by the simulation results.