中文摘要：

在中长期电压稳定过程中，发电机可能会由于无功短缺导致过励磁限制器（over-excitation limiter，OXL）启动，使得将发电机保持为PV节点的这一传统做法面临一定问题。该文对常规多端口网络等值方法进行了改进，将可描述OXL 作用下的发电机模型应用到多端口网络中，给出了发电机OXL启动的在线判定方法，使得改进后的多端口等值网络能够有效计及发电机OXL的动态变化。进一步，基于计及发电机动态的多端口等值网络，推导出可辨识负荷功率最大值点的电压稳定性指标。仿真结果表明，该文方法对即将发生的中长期电压崩溃能起到有效的预警作用。

英文摘要：

During the mid-long term voltage stability, the generator may, due to reactive power shortages, start its over-excitation limiter （OXL）, leading the conventional approach that keeps the generator asPV node faces some problems. This paper improved the traditional multi-port network equivalent method by applying the generator model which can describe the action of OXL to the multi-port network, and provided an approach for online identification of OXL startup, thus the dynamic conversion of generator OXL can be considered in the improved multi-port equivalent network. Further, a voltage stability index was, based on the proposed multi-port equivalent network, derived to identify the maximum load power point. Simulation results show that the proposed method can provide a good early warning for the impending mid-long term voltage collapse.