SOC-aware Primary Frequency Control of Low-inertia Power Systems with Battery Energy Storage

The state of charge (SOC) of battery energy storage system (BESS) is modeled and integrated into the primary frequency control of a low-inertia power system. This is achieved by developing a new state-space model of the system, which includes the SOC dynamics, and using it to design a piece-wise linear SOC controller that prohibits the BESS depletion beyond the minimum allowable range. The controller design and its effect on the system stability are studied based on Popov/circle criterion, which is commonly used for piece-wise linear systems. The developed system model is validated by MATLAB simulations, and the real-time implementation feasibility of the proposed SOC-aware primary frequency control is verified through real-time simulations of a low-inertia power system with varying load conditions.