Urban Power Grid Planning with Nested Microgrids: Ensuring Continuous Power Supply to Critical Loads Under Extreme Events

Extreme events can damage power infrastructure and cause multiple failures to the power grid. In this case, the power grid can transition into several islanded micro grids supported by local resources to ensure continuous power supply to critical loads. This paper proposes the concept of nested microgrids and the corresponding planning approach to deploy of different types of generation and energy storage resources. First, the islanding ability of a micro grid to maintain the dynamic frequency in a safe range under a large sudden power unbalance is explicitly expressed and linearized as an analytical linear constraint. Then, the planning problem is formulated as a mixed integer linear program, maximizing the weighted number covered critical loads by nested microgrids. Finally, the effectiveness of the proposed method is verified through a case based on a real urban power grid in China. The simulation results show that the proposed method enables the urban power grids to transition smoothly to islanded micro grids under multiple faults caused by extreme events, ensuring continuous power supply to critical loads.