MMC柔性直流输电系统网侧故障时紧急功率支援控制

Emergency power support control for MMC flexible HVDC transmission system during AC fault

为了解决MMC-HVDC(Modular Multilevel Converter Based on HVDC,MMC-HVDC)交流侧系统故障时的过流问题,以及增强MMC换流器的低压穿越能力,通过对换流器功率数学模型及控制方式进行分析,发现了换流器有功和无功功率解耦的PI控制方式。提出了当交流侧发生对称和不对称故障时,通过控制PI值限制功率输出,同时由交流电压偏差有效值生成正负序补偿电流的紧急功率支援控制策略。将这种控制策略添加到电磁暂态仿真系统当中,当系统网侧发生对称或不对称故障时,利用数值仿真技术分析了换流器阀侧的电能质量。仿真结果验证了所提出的控制方法对故障时过流抑制的有效性,同时增强了换流器的低压穿越能力。

In order to solve the over current problem of MMC-HVDC during AC fault, while enhance the low voltage ride through capability of the MMC converter, this paper finds that the converter active and reactive power control mode is decoupling PI control through researching converter power mathematical model and control mode. And it proposes a kind of emergency power support control strategy, which controls the PI value to limit the power output, at the same time, generates positive and negative sequence current compensation through the deviation of the AC voltage RMS when symmetric or asymmetric faults occur in AC side. The control strategy is added to the electromagnetic transient simulation system. When symmetric and asymmetric faults occur in network side, power quality of the valve side is analyzed by using numerical simulation method. Simulation results verify the validity of fault over current suppression of the proposed control method, at the same time it can enhance the low voltage converter through ability.