Optimization and Cascade Robust Temperature Control of a Refrigerated Chamber

This paper addresses the temperature control of a refrigerated chamber, using a vapour-compression refrigeration system. A cascade control strategy is proposed, where the outer controller regulates the chamber temperature by generating a reference on the cooling power to be satisfied by the inner controller, which manipulates the actual manipulated variables: the compressor speed and the expansion valve opening. Since two control variables are available to satisfy only a certain cooling demand, energy efficiency is addressed to generate the required cooling power as efficiently as possible. A simple decoupling strategy is applied to reduce the high coupling between both controlled variables, while the PID parameters are calculated applying affine parameterisation and considering a certain condition for robust stability. The performance of the proposed control strategy is evaluated in simulation, concerning reference tracking and disturbance rejection.