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.