Spatial Distribution of Grid Inertia and Dynamic Flexibility: Approximations and Applications

Dynamic grid flexibility is a new paradigm in power system flexibility studies which incorporates grid flexibility with grid stability. This paper explores the two metrics that are used to define the dynamic flexibility framework - inertial index and dynamic flexibility index, and aims to improve their computational efficiency, robustness, and develop smoothing strategies to mitigate the impact of fluctuating power injection from renewable energy sources (RES) on the inter-area oscillatory mode of the system. A novel and robust approximate flexibility index is formulated analytically, which provides a faster yet reliable alternative to the existing flexibility indexing method. The accuracy and computational efficiency of the improved index is compared against previous method through simulation studies performed on the 39-bus system. Application of these indices to understand the implications of RES sitting strategies on grid dynamics, and to develop local mitigation strategies for cost-effective smoothing controller placements, are discussed for the Indian Northern Regional Power Grid (NRPG).