Inertia Emulation by Flywheel Energy Storage System for Improved Frequency Regulation

To alleviate air pollution and energy shortage issues, an increasing amount of renewable energy sources (RESs), such as wind power and solar photovoltaics (PVs), has been integrated into modern power systems. However, the large penetration level of renewable energies leads to the reduction of inertia as RESs are normally connected to the power grid through power electronics converters, which do not inherently provide the inertia as synchronous generators do. To solve the lack of inertia issue, this paper proposes the method of using flywheel energy storage systems (FESSs) to provide the virtual inertia and frequency support. As compared with batteries, flywheels have a much longer lifetime and higher power density. By regulating the speed of the flywheel in proportion to the grid frequency, the flywheel serves as an energy buffer that absorbs and releases its kinetic energy to provide inertia support. Furthermore, the design methods of the virtual inertia emulated by FESSs are described in detail. Finally, the feasibility of the proposed method is verified by simulations, and the simulation results validate the improvement of frequency regulation in terms of frequency nadir and rate of change of frequency (RoCoF).