A Hybrid Energy Storage System Based on Supercapacitor and Electric Vehicle Batteries for Frequency Stability Improvement of Islanded Microgrids

Abstract

Modern power grids have been continuously integrating renewable energy sources (RESs) to create more sustainable, stable, and high-efficiency small-scale microgrids (MGs). Rotational inertia is greatly reduced in such grids compared to conventional grids that are dominated by synchronous generators (SGs). As a result, the system will encounter higher frequency variations and a greater frequency nadir, which may jeopardize the dynamic performance and thus raises the possibility of system instability. Various energy storage systems (ESSs) are introduced as effective solutions for augmenting the rotational inertia of low-inertia MGs. Therefore, in this study, a hybrid ESS (HESS) composed of a supercapacitor (SC) and electric vehicle (EV) battery is suggested to enhance the frequency stability of an islanded MG. In which, the SC is adopted to provide virtual inertial characteristics as it has a high-power density, and the EV's battery is adopted to provide virtual damping characteristics as it has a high-energy density, that results in improved virtual inertia (IVI) control concept. Through this way, the improvements of an islanded MG frequency stability can be achieved. In order to assess the improvement of both inertial and damping responses, the suggested IVI control concept is compared to the system with/without conventional virtual inertia support through simulation results. It verifies the superiority of the suggested IVI control concept to reduce MG frequency variation and dampen angular oscillation.