Abstract: The district cooling system (DCS) belongs to a class of centralized air-conditioning loads and has frequency regulation potential. This paper proposes an auxiliary frequency regulation control strategy of DCS based on model predictive control (MPC) with terminal constraints, which controls the power consumption of the DCS by adjusting the chilled water flow rate and the number of chiller shutdowns. Firstly, the dynamic model of DCS and traditional units considering the relationship between chilled water flow rate and chilled water outlet temperature is established, and the state space expression of the system is constructed. Then, a joint frequency regulation control model for DCSs and traditional units is established based on terminal constrainted MPC method, with the objective function of minimizing frequency deviation, building temperature deviation from human comfort temperature, chilled water flow’s control instructions, and traditional unit’s control instructions. Moreover, the terminal constraints include terminal cost function and terminal set. It has been proven that the terminal constrained MPC problem is asymptotically stable by constructing the Lyapunov function of the system. Finally, simulations on a 10-unit 39-bus system and an actual power system verify that adding terminal constraints can improve system stability, and the use of DCS to assist in grid frequency regulation can help the system to quickly restore the rated frequency and improve regulation performance. In addition, the participation of DCSs in grid frequency regulation would not have a significant impact on comfort.

Key words: district cooling system, secondary frequency regulation, model predictive control, terminal constraints, Lyapunov method