Offset-Free Model Predictive Control of a Heat Pump

This work presents an offset-free model predictive control (OF-MPC) design for energy-efficient control of a heat pump. A model developed from a combination of first-principles and empirical components with parameters estimated using real heat pump data is used as a test bed for the implementation of the MPC design. Open-loop system dynamics are examined first to design and implement the appropriate control structure. Next, a linear model is identified using appropriate step test simulations on the detailed heat pump model. Subsequently, a model predictive controller formulation, which eliminates the tradeoff between tracking and energy objectives, is designed. The MPC includes an augmented model (including disturbance states) and an associated Luenberger observer to estimate the disturbance (plant-model mismatch at steady state). Simulation results subject to realistic disturbances and measurement noise demonstrate that energy savings can be achieved (anywhere between 1.7% and 1.9%), while preserving a safer operating window (a 43% improvement, with respect to a safe operation measure) with the proposed OF-MPC design that achieves tighter tracking regulation (improvement of 40% and above), compared to a traditional control approach.