Application of two-stage fuzzy PID control in variable refrigerant volume air conditioning systems

The variable refrigerant volume (VRV) air conditioning systems have been employed in small and medium sized buildings recently for its advantages of comfort, energy conservation and easy maintenance. However, the optimal control of VRV air conditioning systems is very difficult due to cross-coupling system parameters and time-variant operating conditions. In this paper, the indoor temperatures are taken as the controlled variables to regulate the openings of individual electronic expansion valve (EEV) and the suction pressure is taken to modulate the speed of inverter-driven compressor, a robust and self-adaptive two-stage Fuzzy Proportional Integral Derivative (PID) controller is proposed. The controllability is tested in a triple evaporator VRV air conditioning system, experimental results show that the proposed two-stage fuzzy PID controller could achieve desired control accuracy and guarantee good robustness for room temperature control.