A Unified Virtual Battery Model for Responsive Assets

We propose a unified virtual battery (VB) model for the flexibility of various responsive assets including batteries, thermostatically controllable loads (TCLs), deferrable loads, shiftable loads, and photovoltaics (PVs), Such a unified model lays a foundation to apply transactive control to responsive assets for ancillary service provision. We generalize the VB model to shiftable loads and PVs and make changes to the VB model of TCLs to make them more suitable to ancillary service provision with transactive control methods. In the unified model, we select a set of parameters to represent the flexibility of different responsive assets to provide ancillary services related to active power. The set of parameters includes an energy state, an energy upper bound, an energy lower bound, a power upper bound, and a power lower bound. These parameters are selected to be as few as required to represent the ancillary service provision flexibility of different responsive assets. We explain the meaning of these parameters to those responsive assets. We provide simulation examples to show the efficacy of the general model to deal with various responsive assets in a unified way.