Study on predictive functional control of an expansion valve for controlling the evaporator superheat

Abstract

A new method is proposed to control the evaporator superheat with an electronic expansion valve. The conventional proportional-integral-derivative (PID) control with invariable parameters cannot show good performance because of the variation of refrigeration unit parameters under disturbances. To solve this problem, this paper presents a method for the use of predictive functional controllers (PFCs) on superheat of an evaporator. This method is based on a physical model of the appliance studied to allow calculation of parameters needed for the use of PFCs. The control system created is incorporated into an industrial programmable logic controller and used for experiments on a refrigerating machine containing a shell and tubes evaporator with R410A as refrigerant fluid. The comparison between the two types of controller, i.e. PID and PFC, indicates that superheat may be more efficiently controlled by using the latter type of controller: the setting value is only slightly exceeded, there are only small oscillations of measured superheat, and the energy efficiency of the refrigeration unit may be improved.