An Integrated Model for Frequency Control of Power Grid Through Aggregated Variable Speed Air-Conditioning System

Flexible loads can adjust their operating power in response to the changes in the power grid’s demand or supply, making them an ideal demand-side measure for regulating the grid’s frequency. In the present study, a homogeneously aggregated Variable Speed Air-Conditioning (VSAC) system is integrated into a single area power system model considering its reset control action. The operating power of the VSAC system is evaluated based on the lumped parameter models which have been widely used to evaluate the heat transfer rate of a VSAC system. Mathematical formulations are derived to establish the relationship between the VSAC system’s operating power, compressor frequency, and grid frequency. Closed loop transfer functions are obtained by incorporating the internal temperature controller and an external grid frequency regulation controller. Simulation results show that the dynamic responses of the power grid’s frequency and power deviation of the grid were steady-state stable. Considering 30,000 homogeneous VSACs with 1.5 tonnes capacity, the rated power of the aggregated VSACs is 59 MW (approx.). The grid’s frequency reached a minimum which is around 0.5% of the nominal base frequency and a maximum which is around 0.3% other nominal frequency, within 2 s of the load perturbation. Studies conducted in this paper provide an interesting approach in Buildings-to-Grid integration research by considering the VSAC systems as virtual storage.