Hybrid Control of a Supermarket Refrigeration Systems

This paper presents a non-linear model predictive control (NMPC) of a supermarket refrigeration system. This is a hybrid process involving switching nonlinear dynamics and discrete events, on/off manipulated variables, like valves and compressors, continuous controlled variables like goods temperatures and finally, several operation constraints. The hybrid controller is based on a parameterization of the on/off control signals in terms of time of occurrence of events instead of using directly binary values, on this way, we can reformulate the optimization problem as a NLP problem. A rigorous model of a real supermarket refrigeration system provided by Danfoss is presented as well as results of the hybrid controller operating on it. The paper describes the hybrid process, presents the control problem formulation and provides some results of the proposed approach and comparisons with the traditional control.