Improving frequency dynamic response of inverter-interfaced distributed energy resources via dynamic virtual inertia control

In this paper, a novel virtual inertia control algorithm is presented to enhance the frequency dynamic response of inverter-interfaced Distributed Energy Resources (DERs). By utilising the simple integral control structure, the proposed controller dynamically alters the value of the virtual inertia according to the value of the Rate of Change of Frequency (RoCoF), in order to decrease frequency oscillations and achieve fast convergence to the equilibrium point. Using vector field theory, it is shown that the controller structure imposes a lower limit on its output (virtual inertia) while the boundedness of the virtual inertia and the inverter frequency deviation around their nominal values are analytically proven using the ultimate boundedness theory. Furthermore, convergence to the desired equilibrium for the closed loop system consisting of an inverter-interfaced DER is proven using eigenvalue analysis. Finally, the efficacy of the the proposed approach in improving the frequency response of DERs during events of external disturbances (e.g. sudden variations in load demand) is validated for a 4-node and 4-DER microgrid created on the Typhoon HIL real-time simulator.