Equivalent system model of district cooling system in frequency domain to provide primary frequency regulation

With the increasing adoption of intermittent renewable generation, challenges to maintain stable frequencies for power systems are increasing. Demand-side resources, such as thermostatically controlled loads (TCLs), have been proven capable of providing regulation services. The district cooling system (DCS), a type of centralized TCL that provides cooling services for a group of buildings, is an ideal such resource. A DCS usually has significant regulation flexibility because its rated power capacity is large (up to 100 MW) and it can utilize the thermal inertia of an aggregation of buildings. However, as a large-scale system with complex thermal dynamics, its effective regulation is nontrivial, and its traditional demand-driven control scheme has difficulty considering regulation signals from power systems. To address these challenges, we propose a bidirectional-driven control scheme in a DCS for the first time. On this basis, we formulate the thermal and electricity model of a DCS in the frequency domain and derive an equivalent model to control it like a traditional generator. Furthermore, we propose a sensitivity-based control strategy for a DCS to allocate mass flow adjustments among buildings, which effectively considers the heterogeneity of buildings to balance temperature impacts. Numerical studies illustrate the effectiveness of the proposed model and control strategy.