Dynamic Virtual Inertia Control for Inverter-Interfaced Distributed Energy Resources

In this paper, a novel dynamic virtual inertia control scheme is proposed to improve the frequency dynamic response of grid forming inverters. The proposed controller dynamically calculates the virtual inertia constant as a function of the gradient of the output voltage frequency, in order to prevent large frequency deviation and large values of rate of change of frequency (RoCoF) after load variations. Meanwhile, without altering the controller dynamics, the proposed control scheme accomplishes short settling times and intercepts frequency oscillations around the equilibrium point. Inspired by the concept of the bounded integral controller, the proposed solution adopts the simple structure of the integral controller to achieve the desired control tasks and to ensure that the inertia constant will remain within predefined limits, independently of the frequency deviation. The boundedness property of the proposed controller is analytically proven using vector field theory and the stability of an inverter-interfaced distributed energy resource (DER) equipped with the proposed controller is proven using the Routh-Hurwitz criterion. Finally, the effectiveness of the proposed controller in achieving the desired control tasks (i.e. RoCoF and frequency deviation restriction, fast convergence to the rated frequency) under scenarios of external disturbances (e.g. variations in load demand) is validated, in a simulation environment created in Typhoon HIL real time simulator for a microgrid consisting of 4 buses and 4 inverter-interfaced DERs.