直流馈入下交流系统故障特性分析及故障分量电流差动保护改进

由于直流系统的故障响应具有快速非线性特征，基于准稳态的分析方法不再适用于高压交直流互联(HVDC/AC)系统，因此对于交流保护的适应性分析将更为困难。为解决上述问题，在原有HVDC/AC系统动态相量等值方法的基础上，计及直流系统的非线性以及不同故障严重程度下直流系统控制策略切换的影响，提出更为准确的HVDC/AC系统等值计算方法。基于此，分析直流系统的接入对交流线路暂态故障特性的影响，研究该影响与故障分量电流差动保护动作性能之间的关系，并提出基于电流暂降检测的故障分量电流差动保护自适应动作判据。基于PSCAD/EMTDC平台的仿真结果验证了理论分析的正确性及改进策略的有效性。

Fault characteristics analysis and fault component current differential protection improvement of AC system with infeed DC

Because of the fast and nonlinear characteristics of fault response in DC system, the analysis method based on quasi-steady is no more suitable for HVDC/AC(High Voltage DC/AC interconnected) system, which makes the analysis of AC protection adaptability more difficult. In order to solve this pro-blem, based on the original dynamic phasor equivalence method of HVDC/AC system, the effect of nonli-near of DC system and control strategy switching of DC system under faults with different severities is considered, and a more accurate equivalent calculation method of HVDC/AC system is proposed. On this basis, the effect of interconnection of DC system on transient fault characteristics of AC line is analyzed, the relation between which and the operation performance of fault component current differential protection is researched, and a self-adaptive operation criterion of the protection based on current sag detection is proposed. The simulative results based on PSCAD/EMTDC platform verify the correctness of theoretical analysis and the effectiveness of the improved strategy.