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On the difficulty of globally optimally controlling refrigeration systems

Author(s) : BEJARANO G., ALFAYA J. A., ORTEGA M. G., et al.

Type of article: Article

Summary

This paper describes in detail some key aspects of the modelling and the global optimization of vapour compression refrigeration systems, which reveal some intrinsic difficulties in controlling such systems when a steady-state optimal operation is intended. Concerning dynamic modelling a control-oriented simplified model based on the moving boundary approach is presented, which has only three state variables. Global optimization of a one-stage, one-load-demand cycle is also addressed, which shows that not all the optimal operating points are achieved with minimum degree of superheating at the evaporator outlet, but it depends on the cooling load. As a result of the global optimization it is found out that optimal cycles are defined by three variables, whereas only two manipulated variables are available, which leads to an underactuated control problem. A study of the controllability of the previously presented simplified model is carried out and some difficulties which arise when optimally controlling these systems are highlighted by means of some control simulations carried out using a model-based control strategy from the literature.

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