Energy efficient control of a refrigeration plant

This paper proposes a novel method for superheat and capacity control of refrigeration systems. The new idea is to control the superheat by the compressor speed and capacity by the refrigerant flow. A new low order nonlinear model of the evaporator is developed and used in a backstepping design of a nonlinear controller. The stability of the proposed method is validated theoretically by Lyapunov analysis and experimental results shows the performance of the system for a wide range of operating points. The method is is compared to a conventional method based on a thermostatic superheat controller and the methods are evaluated with respect to energy efficiency.