Design of fractional order PID controller using IMOPSOA for degree of superheating of refrigerant at evaporator outlet

This paper proposes a fractional order PID control scheme to regulate temperature of refrigerant at evaporator outlet, that is, degree of superheating, that is closely related to both refrigerating capacity and running safely for a vapor compression refrigeration apparatus. Since this fractional order PID control effect on degree of superheating is mainly depended on tuning parameters of fractional order PID controller for degree of superheating (DS-FOPIDC), an improved multi-objective particle swarm optimization algorithm (IMOPSOA) is firstly established by the combination a modification of single-objective particle swarm optimization algorithm and Gaussian variation. And then, by selecting three control performance indexes on degree of superheating as the corresponding objective function for this IMOPSOA, an algorithm is designed to continuously find out the optimized values of five parameters of DS-FOPIDC for upgrading the regulating effect on degree of superheating. Finally, by means of performing the simulation model of this fractional order PID control system and the designed algorithm simultaneously, the corresponding results show that this control system including DS-FOPIDC is feasible in application and the designed algorithm can find out Pareto optimal solutions of five parameters of DS-FOPIDC, which can obviously reduce the fluctuation of degree of superheating and further improve its control quality including zero steady state error, the smaller overshoot, the appropriate damping ratio and the shorter regulating time, etc. These findings in this research may also provide the reference guides for controlling the other performance or process parameters in HVAC&R engineering.