1 Department of Electronic Systems, The Faculty of Engineering and Science (ENG), Aalborg University, VBN2 Automation & Control, The Faculty of Engineering and Science (ENG), Aalborg University, VBN3 The Faculty of Engineering and Science (TECH), Aalborg University, VBN4 Strategic Research Centre on Zero Energy Buildings, The Faculty of Engineering and Science (ENG), Aalborg University, VBN5 Aalborg University Space Center, The Faculty of Engineering and Science (ENG), Aalborg University, VBN6 Aalborg U Robotics, The Faculty of Humanities, Aalborg University, VBN
Superheating of refrigerant in the evaporator is an important aspect of safe operation of refrigeration systems. The level of superheat is typically controlled by adjusting the flow of refrigerant using an electronic expansion valve, where the superheat is calculated using measurements from a pressure and a temperature sensor. In this paper we show, through extensive testing, that the superheat or filling of the evaporator can actually be controlled using only a single temperature sensor. This can either reduce commissioning costs by lowering the necessary amount of sensors or add fault tolerance in existing systems if a sensor fails (e.g. pressure sensor). The solution is based on a novel maximum slope-seeking control method, where a perturbation signal is added to the valve opening degree, which gives additional information about the system for control purposes. Furthermore, the method does not require a model of the system and can be tuned automatically.
International Journal of Refrigeration, 2013, Vol 36, Issue 3, p. 1118-1129
Refrigeration systems; Evaporator; Superheat; Maximum slope-seeking; Harmonics; Control