适应多端直流输电系统直流故障仿真的工程实用模型研究

多端直流输电(Multi-terminalDC,MTDC)已经成为颇具竞争力的跨区域大功率输电技术，但因结构复杂，目前缺乏完整的数学模型。真双极混合桥模块化多电平变流器(Modularmulti-levelconverter,MMC)是特高压MTDC的重要部分。若仍沿用半桥MMC的模型建模，真双极结构中双阀组交流侧的电气联接无法体现。另外，半桥MMC模型中0-1二值开关函数推广到混合桥的合理性也有待证明。为解决MTDC建模中存在的上述问题，以昆柳龙直流工程为例，首先推导真双极混合桥MMC的完整数学模型，并对常规高压直流换流站和直流传输线进行准稳态和集中参数近似。进一步建立了直流故障下MTDC的工程实用数学模型，兼顾了精确性和复杂性。最后针对直流单极接地故障运用该模型进行分析计算，并与PSACD仿真结果进行对比，验证了所提出模型的有效性。

A practical model suitable for DC fault simulation of a multi terminal DC transmission system

Multi terminal DC (MTDC) has become a competitive cross-regional high-power transmission technology, but there has been little research on its complete mathematical model because of its structural complexity. A true bipolar hybrid bridge modular multi-level converter (MMC) is an important part of ultra-high voltage MTDC. If its mathematical model still adopts the simple half-bridge MMC, electrical connection on the AC side of the true bipolar MMC cannot be reflected. Also, the rationality of extending the 0-1 binary switching function of the half-bridge MMC model to the hybrid bridge has yet to be proven. To solve the above-mentioned problems in MTDC modeling, Kun-Liu-Long DC project is taken as an example. First, the complete mathematical model of the true bipolar hybrid bridge MMC is deduced, and the quasi-steady state and lumped parameter approximation of conventional HVDC converter stations and DC transmission lines are carried out. Then, both accuracy and complexity are considered to establish a practical engineering model of MTDC under a DC fault. Finally, the DC unipolar ground fault is calculated and analyzed using the proposed model. Compared with the calculation results of PSACD, the validity of the proposed model is verified. This work is supported by the Science and Technology Project of China Southern Power Grid Co., Ltd. (No. ZBKJXM20180635).