With increasing adoption of intermittent renewable generation

challenges to maintain stable frequencies for power systems are increasing. Demand-side resources

such as thermo-statically 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 resource for this purpose. A DCS usually has significant regulation flexibility because its rated power capacity is large (up to 100 MW) and it can utilize 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 heterogeneity of buildings to balance temperature impacts. Numerical studies illustrate effectiveness of the proposed model and control strategy.