A Unified Stochastic Hybrid System Approach to Aggregate Modeling of Responsive Loads
For power system engineers and demand response designers, this provides a more general aggregate load modeling framework that extends beyond first-order TCLs.
The paper develops a unified stochastic hybrid system (SHS) approach for aggregate modeling of responsive loads, including general thermostatically controlled loads and deferrable loads, and derives partial differential equations governing density evolution. The model generalizes existing results and enables new modeling scenarios.
Aggregate load modeling is of fundamental importance for systematic analysis and design of various demand response strategies. Instead of keeping track of the trajectories of individual loads, the aggregate modeling problem focuses on characterizing the density evolution of the load population. Most existing models are only applicable to Thermostatically Controlled Loads (TCL) with first-order linear dynamics. This paper develops a unified aggregate modeling approach that can be used for general TCLs as well as deferrable loads. We propose a deterministic hybrid system model to describe individual load dynamics under demand response rules, and develop a general stochastic hybrid system (SHS) model to capture the population dynamics. We also derive a set of partial differential equations (PDE) that governs the probability density evolution of the SHS. Our results cannot be obtained using the exiting SHS tools in the literature as the proposed SHS model involves both random and deterministic switchings with general switching surfaces in multi-dimensional domains. The derived PDE model includes many existing aggregate load modeling results as special cases and can be used in many other realistic modeling scenarios that have not been studied in the literature.