PI parameter setting of compressor refrigerating capacity test systems adopting the unified modeling language

Mathematical models based on the Modelica language are built to solve the problem that the compressor test system is a dynamic system with the characteristics of great inertia, pure time-delay, strong coupling and multiple disturbances,and cannot rapidly reach a stable state. The Ziegler-Nichols method is applied to the simulation software Dymola to obtain initial PI parameters. The step excitation is given in the expansion valve under the condition that the parameters of other elements are fixed to constants, and then the PI controller is added after removing the step excitation. The influences of PI parameters on the discharge pressure, the suction superheat, the suction pressure and the subcooled temperature are concluded. It is found that increasing the proportional gain or decreasing the integrating gain could be used to solve the overshoot problems of the discharge pressure and the suction superheat, and that decreasing the integrating gain is also beneficial to the shock condition. When the suction pressure is overshoot, the proportional gain should be decreased. If the response time is too long, the proportional gain should be increased or the integrating gain should be decreased. Moreover, the subcooled suction could be improved by decreasing both the proportional gain and the integrating gain. These results could be considered as a reference for the practical engineering.