Supplementary frequency regulation with multiple virtual energy storage system aggregators

High intermittency renewable generation reduces the system inertial and increase system uncertainties introducing new challenges for frequency regulation of future grid, including primary, secondary, and tertiary ancillary services. Residential air-conditioning contributes to electric utility critical peak load where the frequency regulation reserves are low. This article proposes a construction to turn such thermostatic load into a virtual energy storage system (VESS) and provides an algorithm to enable ancillary frequency regulation services by coordinating multiple groups of aggregated VESS. Based on the thermal modeling of individual VESS, the response behavior can be predicated and scheduled by an aggregator control. In primary frequency regulation scheme, the VESS aggregators communicate to share the frequency deviation signals and response according to a droop strategy under constraints of room temperatures and switching time. In secondary frequency regulation scheme, the VESS aggregators communicate and compete with each other to provide supplementary spinning reserve and reduce the generation cost. The ability of VESS is quantified to share the automatic generation control (AGC) responsibility optimally. Case studies are conducted to validate the effect and feasibility of the proposed frequency regulation schemes. The results show that it can provide technical and economic benefits to both participating residences and power system operators.