Analysis and Mitigation of the Impacts of Asymmetrical Virtual Inertia

The potential of plug-in (hybrid) electric vehicles (PHEVs) to participate in power system control, via the vehicle-to-grid program, is increasing rapidly. In several recent studies, PHEVs are employed to participate in system frequency regulation; however, no attention has been paid to the impact of single-phase connection of these distributed energy sources. This paper addressed the use of PHEVs to stabilize the frequency in microgrids and/or weak grids which lack enough inertia considering the single-phase nature and communication delays. Small-signal analysis is used to evaluate the performance of both droop and virtual inertia control methods, and show how time delay of a centralized control could impact system stability. Advantages and disadvantages of distributed control are studied, and a new method based on a combination of both centralized and distributed control is proposed to mitigate the impact of asymmetrical virtual inertia while it allows the utilization of all available PHEVs for active power however asymmetric they are. Time-domain simulations are used to verify the analytical studies.