Research On Temperature Control Algorithm Of Mechanical Cryocooler

At present, the infrared detecting technology is widely applied to many areas which includes weather forecasting, environmental monitoring, disaster warning, resources exploration, agricultural planting, fishery breeding and military remote sensing. It is closely related to the national development.In the field of remote sensing in aerospace, mechanical cryocoolers is an important component of infrared detectors since its small size, light weight and high stability. The accuracy and stability of mechanical cryocooler temperature control is important to the high definition imaging system. The method based on Proportion-IntegrationDifferentiation(PID) is commonly adopted in active temperature control in the world at present. Because of the lack of knowledge of the mathematical model of cryocooler components, the deep analysis of PID control algorithm is hard to be made with the consideration of the controlled objects. Furthermore, there is less simulation study on cryocooler close-loop temperature control system. The design of PID parameter highly depend on the engineering experiences, and it is time and effort consuming. To solve these problems, the following works focused on PID control algorithm of mechanical cryocooler were carried out.Firstly, according to the theories of heat transfer and electronic circuits, the model structure and order was determined through theoretical modeling. Simultaneously, the unknown parameters could be estimated through Parameter Identification. Then, a closed-loop control model of mechanical cryocoller temperature control system was built.Secondly, the analysis of the influence of incremental digital PID control parameters on system stability was given, based on the PID principle and the mathematical model of cryocooler components.Subsequently, combining the transfer function of the mechanical cryocooler component with incremental PID controller, a calculation method of incremental PID parameter stable regions based on stability margins was put forward. The simulation results demonstrated effectiveness of this method.Eventually, the unknown parameters in the mathematical model of mechanical cryocooler component was estimated through Parameter Identification. Also the change law of cryocooler component transfer function was summarized with the consideration of different thermal load. Then the Simulink simulation platform of the temperature control system was constructed. Considering the constraints in the practical application, the tuning law of each parameter and some typical cases were summarized using a method of both experiment and simulation. Ultimately the temperature stability of this mechanical cryocooler temperature control system achieved ± 0.1K / 30 min.