Temperature Control of Combat Aircraft Environmental Control System by Time-delay in loop with Control Input Normalization

Environmental Control System (ECS) of a fighter aircraft operates classically in an air standard refrigeration cycle. ECS takes engine bleed air and supplies conditioned air to the cockpit or cabin, controls the cabin temperature and pressure for crew comfort and provides cooling for avionics equipment. Cockpit temperature is regulated by controlling the temperature of supply air which needs to be controlled properly to maintain a good comfortable condition inside the cockpit. It is affected not only by the bleed air flow rate, pressure, and temperature but also with external factors like ambient temperature, altitude, pressure, and attitude. Due to large variations in these parameters, the cabin temperature control system is often likely to experience limit cycle fluctuations. To minimize this oscillation and subsequent cabin temperature fluctuations, suitable control logic needs to be conceived at the design stage itself since tuning of such a control system makes additional flight-tests and generates large expenses. The control logic applied to the system drives the actuator or Temperature Control Valve (TCV) to maintain the required temperature. Most of the conventional control methods or schemes do not take into account the effect of the input parameters on system performance in their control logic. This paper explains about two different control strategies, PID and a novel method, and the importance of transient input characteristics on ECS performance. The control strategies along with system architecture were modeled using LMS AMESim and transient responses of the system were analyzed. Subsequently, the control system has been enhanced from control input normalization to avoid overshooting from known disturbances. The result indicated that the chosen novel control strategy minimizes the actuator movement, reduces temperature fluctuation and improves the system performance.