中文摘要：

提出了一种考虑暂态电压跌落限制的直接法，快速求取保证故障后电力系统电压高于限值的故障临界清除时间（CCT）。根据带约束动力系统稳定域理论，其受限稳定边界由边界上不稳定平衡点、周期轨和半鞍点的稳定流形以及部分可行域边界构成。半鞍点的稳定流形是系统受限稳定边界的重要部分，并且可以用半鞍点处的等能量面来近似。暂态电压跌落限制可以考虑为对故障后电力系统的一个约束。基于电力系统结构保持模型，寻找到了和故障相关的一个半鞍点，将持续故障轨迹和可行域边界交点的发电机角速度变为0后，就得到一个半鞍点。然后，以该点能量作为临界能量确定CCT，保证故障后系统满足暂态电压跌落约束。采用了迭代方法提高计算精度。仿真结果验证了所提出方法的有效性。

英文摘要：

A direct method considering transient voltage dip is proposed to calculate the critical clearing time （CCT） ensuring that voltages of post fault power system are higher than limit. According to the stability region theory of constrained dynamic system, the restricted stability boundary is composed of stable manifolds of unstable equilibrium points, periodic orbits and semi saddles on the boundary, and portions of the boundary of the feasible region. The stable manifolds of semi saddles are significant part of the restricted stability boundary and they can be approximated by equal energy surface of semi-saddles. The restriction of transient voltage dip is a constraint on post fault power system. Based on the structure preserving model of power system, a semi-saddle point relevant to the fault is found. The intersection point of fault-on trajectory and feasible region boundary becomes a semi-saddle when the angular speeds of generators are set to zero. The critical clearing time satisfying the constraint of transient voltage dip can be determined using the energy of this point as critical energy. Iteration is used to improve the accuracy. The validity of the method proposed is verified by simulation.