Application of PLC and HMI in the CO₂ transcritical refrigeration experimental platform

The paper adopted SIMATIC PLC as the control center and cooperates with SIMATIC KTP900 basic touch screen and GRM533YW-C IOT module to design a CO₂ transcritical refrigeration experiment platform (EXP). The EXP acquired analog signals from sensors through PLC expansion modules. The PLC communicated with the touch screen and the IoT module through PROFINET to achieve data interaction. In the EXP, the touch screen and the remote devices had separate control interfaces, both of which can perform system control and real-time data display. The control strategy and abnormal alarm of CO₂ transcritical refrigeration system was accomplished in PLC. In the cooling experiment, the maximum deviation value of temperature was less than 0.4 °C in the refrigeration container. In the 750 W load step experiment, the static error of the temperature was ± 0.2 °C in the refrigeration container, and the static error of the superheat was ± 0.17 K. This indicated that the EXP had excellent control quality. The different control strategies for the compressor, gas cooler fan, auxiliary cooler fan, EEV and pressure regulating valve can be realized in the EXP. Therefore, the performance optimization of CO₂ transcritical refrigeration system in different operating conditions can be studied.