向无源网络供电的LCC-MMC混合直流输电系统控制策略

电网换相换流器和模块化多电平换流器(LCC-MMC)混合直流输电系统兼顾了两种换流器的技术优势和经济优势,具有较好的应用前景。无源网络装设容性滤波装置能够起到平滑交流电压波形、提供电压支撑等作用。首先通过理论推导,建立了含容性滤波装置的模块化多电平换流器数学模型,基于dq理论,提出了模块化多电平换流器的无源解耦控制策略。针对送端电网换相换流器侧交流故障可能导致的功率中断等问题,从电网换相换流器和模块化多电平换流器的控制机理出发,分析了故障阶段及故障后的系统响应特性,并进而提出了送端交流故障穿越附加控制策略。为验证上述控制策略的有效性,在PSCAD/EMTDC内建立了一个LCC-MMC混合直流输电模型。通过受端电压频率变化和送端交流故障仿真,验证了所提控制策略的可行性和有效性。

Control Strategies for LCC-MMC Hybrid DC System Connected to Passive Networks

The line commutated converter-modular multilevel converter(LCC-MMC)hybrid DC system has good application prospects for combining the technical and economic advantages of two kinds of converters. The capacitive filtering device installed on the passive network can smooth the AC voltage waveform, provide voltage support, etc. Firstly, a mathematical model of the modular multilevel converter(MMC)containing the capacitive filtering device is developed through theory deduction, and the decoupling control strategy of the MMC is proposed based on the dq theory. For the problem of power transmission interruption during AC fault at the sending end of line commutated converter(LCC), the system fault response characteristic is analyzed by proceeding from the control mechanism of LCC and MMC. Then an additional control strategy for the sending-end AC fault ride-through is put forward. In order to verify the effectiveness of the control strategies, a LCC-MMC hybrid DC transmission model is established in PSCAD/EMTDC. The feasibility and effectiveness of the proposed control strategies are verified by the simulation of the voltage/ frequency variation at the receiving end and the AC fault at the sending end.