Combining Flexible Loads with Energy Storage Systems to provide Frequency Control

This paper proposes a method of using flexible loads which switch on and off to provide frequency control based on a probability function. The proposed control strategy combines flexible loads with an energy storage system (ESS) in such a way that the flexible loads are responsible for providing support to larger power imbalances whereas the ESS compensates smaller ones. Simulation results based on the well-known WSCC 9-bus system indicate that the controller improves the overall frequency response of the system while maintaining acceptable voltage profiles, and allows for better use of the capacity of the ESS.