This paper describes the analysis and robust control of a one-stage refrigeration cycle. Using the compressor speed and the expansion valve opening as control variables, the outlet temperature of evaporator secondary flux and the superheating degree of refrigerant at evaporator outlet are controlled. The main dynamics of the system are identified at various operating points and a controllability analysis is carried out in order to highlight existing constraints in its closed-loop performance. A multivariable robust H ∞  controller is designed and applied, using the S/KS/T Mixed Sensitivity Problem approach. Simulation results prove that the robust controller has better performance than a decentralized PID controller, agreeing with the controllability analysis conclusions and the control design specifications.
['José A. Alfaya', 'Guillermo Bejarano', 'Manuel G. Ortega', 'Francisco R. Rubio']
Multi-operating-point robust control of a one-stage refrigeration cycle