电力电子装置和直流输电系统接入交流系统后，现有的故障分析计算方法鲜有考虑交直流的相互作用对交流故障特性的影响。针对这一问题，提出了适用于交流系统故障分析的直流系统等值模型。首先，基于交流系统不对称故障情况下换流器的特性，采用开关函数法和序分量法建立了换流器的等值模型，该模型能够充分考虑换流器的谐波特性对计算结果的影响，提高了计算精度，同时，与交流系统接口方便，计算简单；其次，分析了交流故障期间直流控制器的响应特性，建立了直流控制器的模型；最后，提出了交直流互联系统统一计算的故障计算方法。对比计算结果与EMTDC仿真结果，证明元件模型和算法是准确有效的。%Fault behaviors of the AC system interconnected by HVDC system cannot be studied by conventional fault algorithms. The effects of interaction of the hybrid systems on the AC fault features are often ignored for the sake of analytical simplicity. In this paper, a mathematical model for HVDC system which is suitable for analyzing faults in the AC system is presented. First, for analysis of HVDC converter under the asymmetric AC system, an equivalent model of the converter based on the switching function method and sequence components method is put forward. Because it has taken the important harmonic characteristics into account, it can improve the calculation accuracy. Meanwhile, it has a convenient interface with the AC system and a simple calculation. Then, the response performances of HVDC control system during the AC fault period are discussed and its model is established. Finally, a general algorithm is developed to incorporate the proposed HVDC model into the conventional AC short-circuit calculation algorithm. The effectiveness of the proposed HVDC model and the algorithm has been verified by using simulation studies and by comparing the results with those obtained from the EMTDC simulation.
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