IN-24-C046 - Air-Conditioning System Constraint Enforcement Using a Reference Governor

This paper presents a reference governor (RG) for ensuring the safe operation of air conditioning (AC) systems. Our controller is specifically designed to enforce critical constraints regarding refrigerant superheat, thereby preventing potential damage to the AC hardware. While conventional heating, ventilation, and air conditioning (HVAC) controllers prioritize energy efficiency, our RG complements these controllers by preventing harmful scenarios involving the entry of liquid or two-phase refrigerant into the compressor. Our RG dynamically adjusts the thermostat temperature set-point requested by indoor occupants to satisfy the constraint on discharge superheat temperature. In our approach, we first identify a control-oriented model for the AC system using data gathered from high-fidelity simulations in Thermosys. Then, we use this model and associated data to bound the uncertainty of the model. Finally, leveraging the uncertainty-quantified model, we design the RG employing advanced control techniques, including positively invariant sets. This leads to a quadratically constrained quadratic program, for which we provide a computationally efficient solution. We numerically verify our RG using high-fidelity simulations in Thermosys that simulates the working process of a vapor compression AC system. These simulations confirm that certain desired room temperatures lead to constraint violations in the open-loop system. Conversely, when the system is operated in closed-loop with our RG, it consistently operates within safety constraints.