接入孤岛新能源电场的双极柔直换流站控制策略

Study on Control Strategy of Bipolar VSC Station Connected to Islanded Renewable Power Plant

当新能源电场孤岛接入柔性直流换流站时,需要柔性直流换流站为其提供交流电压。若双极柔性直流换流站的正、负极换流单元均采用定交流电压幅值、定频率控制（简称定U/f控制）,会由于其接入同一交流母线且控制目标相同而导致系统不稳定。因此,针对大容量新能源孤岛接入的柔性直流换流站,提出双极换流单元的交流电压、频率下垂协调控制（简称双U/f下垂控制）,并与一极采用U/f控制,另外一极采用定有功功率、定无功功率控制（简称定P/Q控制）进行了对比分析。在PSCAD/EMTDC仿真环境中建立了4端柔性直流电网模型,以新能源电场出力波动、单极闭锁及受端交流系统短路故障为例对2种控制策略进行了仿真测试,验证了文中所提出控制策略的有效性。

With islanded renewable power plant connected, voltage-sourced converter（VSC） station needs to provide AC voltage. However, if constant AC voltage and frequency（constant U/f） control strategy is applied to both positive and negative VSC converter units, the system will become instable, because the two converter units are connected to the same AC bus with the same control target. This paper proposes an AC voltage and frequency droop control strategy for bipolar VSC station（double U/f droop control） with large-capacity islanded renewable power plant connected, followed by comparison with the strategy of one pole constant U/f control and the other pole constant active power and reactive power（constant P/Q） control. A 4-terminal VSC-HVDC grid model is built in PSCAD/EMTDC and simulation is performed. Simulation results show that the control strategy works well during renewable power plant output fluctuation, after one pole outage, and after a short-circuit in the AC system of the inverter station, validating effectiveness of the proposed control strategy.