Inertia Emulation through Supercapacitor Energy Storage Systems

To establish a more reliable, sustainable and high-efficiency smart grid, renewable energy sources (RESs) have been increasingly integrated into modern power systems. Since RESs are normally coupled to electrical grids through grid-connected power converters, which do not possess any rotational inertia as conventional synchronous generators do, modern power systems will face frequency control challenges as the power system inertia continues to decrease. To address the lack of inertia concern, supercapacitor energy storage systems (SESSs) are implemented in this paper to generate virtual inertia by proportionally linking the grid frequency to the voltage references of supercapacitors. In this way, the improvements of inertia and frequency control can be achieved. More importantly, this paper discloses that the basic inertia control scheme introduces inertia emulation errors under large frequency disturbances. As a solution, this paper presents a nonlinear inertia control scheme, which ensures fair inertia emulation even under large frequency disturbances. Simulation and experimental results are finally presented to verify the effectiveness of the virtual inertia and the control schemes.