José A. Alfaya

Design, automation and control of a two-stage, two-load-demand experimental refrigeration plant

This paper describes the design, implementation and automation of a two-stage, two-load-demand experimental refrigeration plant. The facility is fully configurable, since cycles with one or two compression stages, and one or two load demands can be set up. Detailed description of the experimental facility concerning its physical components, actuators and sensors is addressed, as well as low-level control and communication bus issues. The high-level control environment and its communication with the low-level controller are also approached. Furthermore, a well-known in industry decentralised control strategy is applied to a one-stage, two-load-demand refrigeration cycle, analysing some preliminary control results from an energy efficiency point of view.

Controllability analysis and robust control of a one-stage refrigeration system ☆

Abstract This paper describes the controllability analysis and the design of a multivariable robust controller for a one-stage refrigeration cycle, which is the most used system for cooling issues and whose energy management and control are key factors. The controlled variables are the superheating degree of refrigerant at the evaporator outlet and the outlet temperature of evaporator secondary flux, whereas the control variables are the electronic expansion valve opening and the compressor speed. The system is considered therefore as a MIMO one. Up to eight different operating points are identified in order to design the multivariable H ∞ controller based on the S / KS / T Mixed Sensitivity Problem. Simulation results comparing this controller to a decentralised PID and to a multivariable predictive one are shown, proving a better performance of the robust controller as well as accomplishment with the controllability analysis conclusions.

Steady-state parameter estimation of an experimental vapour compression refrigeration plant

This paper describes the steady-state parameter identification process of the components which constitute a vapour-compression refrigeration cycle. Particularly relevant is the heat exchanger steady-state parameter identification due to the refrigerant phase change which occurs during a typical cycle operation. Experimental results that prove the validity of the considered assumptions are shown and discussed.

Multi-operating-point robust control of a one-stage refrigeration cycle

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.