Sizing of Energy Storage Systems for Grid Inertial Response

Although the deployment of renewable energy sources (RES) alleviates several concerns related to energy, natural resources, and climate change, their lack of rotational kinetic energy is a key challenge to the stability and resilience of future power grids. Energy storage systems (ESS) hold the potential to compensate for this lack of rotational kinetic energy with virtual inertia—such a system is called a virtual synchronous generator (VSG). Determining optimal sizes of VSGs is a key factor to develop strategies that efficiently assure the capability of VSGs in maintaining the stability of future power systems. This paper proposes an approach for sizing ESS for grid inertial response in the presence of RES. Time domain simulations are used to determine the minimum inertia required by a power system to maintain its stability. A stochastic method involving Monte Carlo simulation is developed and utilized to determine the low frequency events for a given time period. A stability index is also developed to quantify the probability of occurrence of low inertia events in the system. The ESS is then sized accordingly to compensate for the lost inertia. The proposed method is demonstrated on the reduced Western System Coordinating Council 9-bus test system. The results show that VSG can compensate for the lack of rotational kinetic energy for a wide range of fault clearing times and penetration of RES.