Integrating large shares of heterogeneous thermal loads in power system frequency control

Thermal loads can, in principle, provide ancillary services to power systems. In this paper, we propose a new, practical frequency control scheme that allows different types of thermal loads to collaboratively offer reserves in parallel to generators. Primary reserves are provided by residential refrigerators in a decentralized fashion based on local frequency measurements. Secondary reserves come from centralized control of a pool of residential electric water heaters and heating, ventilation, and air conditioning systems of commercial buildings. The scheme accounts for the loads' electrical and thermal dynamics, and allocates the reserves among them using optimization and signal filtering to achieve the desired responses without compromising user comfort. We demonstrate the scheme's performance via dynamic simulations with a linearized two-area power system model and show that load control improves the system's response to sudden losses of generation and fluctuating power in-feeds.