The Control Strategy Of Aircraft Vapour Compression Cooling System

In order to improve the comprehensive performances of aircraft, more and more advanced electronic devices have been applied to various airplanes, this inevitably contributes to the sharp increasing of heat load in airplanes. By using the traditional air cycle cooling system to remove such huge heat load would increase the amount of the bleed air due to the low utilization rate and have bad influence on the engine of the aircraft. To overcome this problem, the American have developed integrated thermal management system with vapour compression cooling system included for their advanced fighter. Compared with the system on the ground, the aircraft vapour compression cooling system has the characteristics of fast and wide change with the working condition and heat load, so doing some deep research about the system performance and control strategy is necessary.The present studies focus on the vapour compression cooling system and do a series of experimental research related to the open loop performance and control strategy based on cooling capacity and overheat or evaporator pressure. The detailed works are summarized as follows:(1) In order to simulate the real situation of aircraft vapour compression system, an experimental bench with the function of fast and broad regulation of cooling capacity, heat load and condenser water inlet temperature was designed and built. The cooling capacity was adjusted by variable speed compressor and electronic expansion valve(EEV), heat load and condenser water inlet temperature was regulated by controlled electronic heater in the evaporator water loop and electronic three valve in the condenser water loop respectively.(2) By using the experimental bench, the open loop performance of the system was studied. The effects of compressor speed, EEV opening, evaporator and condenser water flow rate and temperature on various parameters, such as evaporator, condenser pressure and overheat, were studied systematically(3) Heat load of the system and condenser water inlet temperature were selected as the disturbance variable, two series of parameters: overheat and evaporator water outlet temperature or evaporator pressure and evaporator water outlet temperature respectively were chosen as the control variables. Two PID controllers were used to regulate the speed of the compressor and opening of the electronic expansion valve in order to keep the evaporator water outlet temperature, overheat or evaporator pressure at the set valve. The experimental results show that the suggested control strategy in the present study can adjust the evaporator outlet water temperature near the set valve, but due to the instability at the outlet of the evaporator, the control of overheat may vibrate sharply sometimes, and this of course results to the bad performance of the control algorithm. Compared to the overheat control, the evaporator pressure control processing works more smoothly and steadily without the worrying about dramatic fluctuations.