State Space Modeling and Control of Aggregated TCLs for Regulation Services in Power Grids

Abstract: Thermostatically controlled loads (TCLs), which possess thermal inertia, have attracted additional attention for providing ancillary services to power systems. In this regard, the aggregation model for TCLs is critical for evaluating the performance and optimizing the control of a population of TCLs. We learn by theoretical analyses and simulations that the accuracy of the state space model in most cases is deteriorated by applying longer TCL dispatch periods. Thus, a modified aggregated TCL model is proposed and a new state transition matrix is derived in this paper to improve the TCL modeling accuracy for the provision of grid regulation services. The proposed control model for the aggregated TCL accounts for compressor time delays that would enhance the collective TCL behavior. A probabilistic control strategy is presented to reduce the adverse impacts on the durability of TCL compressors and communication requirements for implementing the TCL control signal. Simulation results demonstrate that the proposed aggregated TCL model with control signals can closely follow actual TCL behavior and the proposed control strategy can reduce the number of TCL switching for providing ancillary services to power systems.