Single temperature sensor superheat control using a novel maximum slope-seeking method

Abstract

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 slopeseeking 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.

Multivariable Newton-based extremum seeking

“…Hence, rather than optimizing the map itself, they offer a new scheme which can be useful in practice for maximizing the sensitivity of an input-to-output function to improve the signal-to-noise ratio as well as minimizing parameter sensitivity when designing feedforward controllers. For instance, the authors in [15] present a refrigeration system where a suitable operating point is located at the maximum negative slope that is subject to change. This point of zero curvature corresponds to a minimum of the first derivative of the input-output map.…”

Newton-based extremum seeking for higher derivatives of unknown Maps with Delays

“…In [5] the authors represent a refrigeration system where a suitable operating point is located at the maximum negative slope which is subject to change. This point of zero curvature corresponds to a minimum of the first derivative of the input-output map.…”

Explicit model predictive control of split-type air conditioning system

“…The temperature difference in refrigerant between the inlet and outlet of the evaporator is called superheat. The purpose of expansion valves or metering devices in general is to control the superheat for the safe operation of compressors (Vinther et al, 2013). This helps to improve the life cycle of the compressor.…”