Development of evaporation pressure-capacity control strategy for aircraft vapor cycle system

The conventional superheat-capacity control strategy fails to regulate the superheat steadily because of the violent oscillation at certain situations. This paper newly proposed an evaporation pressure-capacity control strategy to simulate the vapor cycle system by modulating the EEV opening to control the evaporation pressure rather than the superheat. A dual SISO expert PID controller with a feedforward compensator was employed to compare the control performance of the conventional superheat-capacity control strategy with the developed strategy. Experimental results showed both control strategies could regulate the capacity satisfactorily, but the new strategy could maintain the evaporation pressure stably. The conventional method failed to maintain the superheat around the target because of the violent oscillation observed. The developed strategy could regulate the aircraft vapor cycle system smoothly and reliably even under fast and widely changing environment. In addition, violent oscillation of superheat with big change width and quick frequency was observed and reported.