Fighter Aircraft Cabin Temperature Control by Variable Time-Delay in Loop with Control Input Normalization

Aircraft cabin temperature is controlled by regulating the cabin supply air temperature. This supply air temperature is a critical parameter which varies with respect to aircraft altitude and to be maintained properly to the required value corresponding to that altitude to have a good comfortable condition inside the cockpit. It is affected by many internal factors like engine bleed air flow rate, pressure, and temperature and also with external factors like ambient temperature, pressure, and attitude. Due to huge variations in these parameters especially in a fighter aircraft, the cabin temperature control system of this aircraft is often experience limit cycle oscillations and subsequent cabin temperature fluctuations. To minimize the cabin temperature fluctuations, suitable control logic needs to be considered at the design stage itself to avoid future tuning of such control system which makes additional flight-tests and generates large expenses. This paper focuses in developing the control strategies for a fighter aircraft cabin temperature control system using simulation model of ECS system presented in the previous work. The electronic controller of the system, using its control strategies, drives the actuator or Temperature Control Valve (TCV) to maintain the required temperature. The control architecture in the model has been modified to analyze different control strategies. Most of the conventional control0 methods or schemes do not take account the effect of variation in the input parameters on system performance in their control logic. This paper compares three different control strategies viz. PID, Time-delay control and a novel Variable Time-delay control along with control input normalization. The control strategies along with system architecture are modeled in LMS AMESim and transient responses of temperature control system have been studied for different control strategies. Finally, the novel control strategy using variable time-delay control with Control Input Normalization (CIN) is proposed, which minimizes the actuator movement, reduces temperature fluctuations and improves the system performance.