Design Of Superheat Controller And Research On Its Control Performance For Refrigeration System

Electronic Expansion Valve (EEV) has been increasingly used in refrigeration system recently in order to run the refrigeration system efficiently. EEV with reasonable control strategy applied is the key to reduce energy consumption and improve operating efficiency. Therefore the research has far-reaching significance for environmental protection and sustainable development of society.This paper investigates EEV, EEV controllers and control algorithm development in the world. It introduces domestic air-conditioning refrigeration system operating principle and thermodynamic properties, EEV working principles and its advantages, the controller’s working principle and common algorithms. Basing on this, a superheat controller was designed and developed. The hardware design includes main control unit (MCU), human-machine interaction (HMI) unit, EEV driver unit, storage and communications unit, etc. The software design consists of analog acquisition, serial communication, display and key module, fuzzy control algorithm, etc.Home air conditioning and refrigeration experiment platform was designed to verify the control performance. The hardware combines data acquisition units, a variety of sensors and industrial computer. Supporting software was programmed for the experiment platform, providing real-time acquisition, display, data storage, parameter calculation, and other features for the control strategy, which bring great convenience for the research of control strategy.Final analysis starts from the minimum stable superheat mechanism, introducing minimum stable superheat curve. The minimum stable superheat according to the compressor was obtained on the basis of experiments. Due to the refrigeration system has the characteristic of parameter tuning difficulty, slow time variability, uncertainty, nonlinear, fuzzy control technique was proposed to the superheat control. Through self-designed controller and refrigeration platform, a large number of experiments were done, showing that the superheat can be well controlled with the control accuracy at±1℃.