Decoupled load flow and its feasibility in systems with dynamic topology

Load flow redistribution caused by transmission line outages in an emergency may result in a cascading failure, thus it is important to analyze load flow for systems with dynamic topology. Recently we presented a unified DC power flow method to overcome the following difficulties of existing methods: system topology cannot be fully captured in the formulation, and connected and disconnected systems cannot be handled in a unified way. Based on our previous method, the real power flow feasibility checking problem is formulated as finding feasible solutions of a set of linear inequalities. Since DC power flow is not sufficient in emergency analysis, this paper extends the previous method to the unified decoupled load flow method, and analyzes both real and reactive power. In our new method, load flows are iteratively obtained by using generalized inverse in each iteration. The DC power flow feasibility checking method is also extended to analyze AC flow by simplifying our new load flow method to a non-iterative one and formulating voltage security constraints as a set of linear inequalities. Numerical results on a 9 bus case, the IEEE 30 and 300 bus cases and the Polish 2746 bus system are presented to illustrate the advantages of our method and to analyze its usefulness.