中文摘要：

充分考虑非对称状态下直流侧二次谐波的影响,建立了适用于交流系统故障计算的直流系统模型,并与传统的交流系统故障分析模型联立,采用具有超线性收敛的弦截法进行统一迭代求解。直流系统作为所连换流母线的正负序电流注入,只需计算一次交流网络节点导纳阵并求解一次诺顿等值电纳,可以方便地与原交流系统故障计算程序接口。在PSCAD上搭建CigreBenchmark直流标准模型和含三条直流馈入的交流系统模型,设置各种故障,验证了故障分析模型的有效性及弦截法的收敛可靠性。

英文摘要：

Considering the impact of the second harmonic on DC side under asymmetric conditions,a DC system model for AC system of fault conditions is proposed.It can be easily embedded into the traditional AC system fault calculation process.The model is solved through utilizing the secant unified iterative method,which is a super linear convergence algorithm.The DC system can be regarded as the positive and negative sequence current inj ected into the AC bus.Therefore,the node admittance matrix and Norton equivalent susceptance of the AC network is calculated only once for interfacing with the original AC system fault calculation program.The CIGRE-Benchmark system and a three-infeed DC system are established in PSCAD.The results of simulation of various faults applied show that the proposed model is efficient and the secant unified iterative method is reliable in convergence.