Linear Quadratic Regulator Controller to Improve Transient Frequency Stability Through Virtual Inertia

Abstract

The increased penetration of photovoltaics (PV) and wind energy resources has raised awareness to the maintenance of the future grid's stability and reliability. One emerging issue is the susceptibility to frequency instability when facing substantial generation-load imbalances due to decrease in rotational inertia of the grid. As a possible solution for frequency instability issues, virtual inertia (VI) is implemented using energy storage systems (ESSs). It is shown that, through a Linear Quadratic Regulator (LQR) controller, frequency change and the rate of change of frequency (ROCOF) of a system are optimally reduced. The designed LQR controller is further tested for the system with decreased inertia and it is able to maintain frequency change for up to 90% of decreased inertia and ROCOF only for up to 10% within the standards. The ROCOF was found to be more sensitive to decreased inertia than change in frequency, which suggests the use of an adaptive controller, instead of a fixed gain LQR controller, in the presence of significant parametric changes.