Study On Modeling Of Heat-stop And Temperature Control Strategy For Open Ground-based Solar Telescope

Temperature control system is an important part of open ground-based solar telescopes.It is one of the core systems to ensure the safe and stable operation of ground-based solar telescope and obtain clear solar image.Through the implementation of the active temperature control system,the mirror seeing and the internal seeing effect of the heat stop can be minimized,so as to improve the quality of the solar observation image.However,with the increasing aperture of the open ground-based solar telescope,its condensing ability is becoming stronger and stronger.At the same time,it also faces many problems,especially the increasing thermal load,which will seriously affect the safe operation of the ground-based solar telescope.Therefore,the research on the thermal control technology of the ground-based solar telescope has become one of the key research technologies of the ground-based large aperture solar telescope in various countries.The CLST(Chinese Lager Solar Telescope),an open ground-based solar telescope developed in China,also needs to solve the thermal control problem of the solar telescope.This paper mainly aims at the heat stop,the core component of the 1.8m CLST ground-based large aperture solar telescope,establishes its mathematical model according to the law of energy conservation,and verifies the correctness and feasibility of the modeling through experiments,which lays a theoretical foundation for the theoretical and application research of the control strategy of the heat stop temperature control system.At the same time,according to the characteristics of the reflective heat stop,the control methods of the temperature control strategy of the large time-delay system are studied,and different control strategies are used to analyze and compare the models,so as to provide a reference for the follow-up research of the control strategy of the heat stop active temperature control system.Firstly,starting from the overall heat stop active temperature control system,this paper discusses the composition of the heat stop active temperature control system,introduces the structure and function of each component in detail,and analyzes the control method of the heat stop temperature control system.Secondly,for the reflective heat stop,the mathematical model of the heat stop is established through the law of energy conservation,and the main factors affecting the surface temperature of the heat stop are analyzed according to the temperature control target of the heat stop,so as to reasonably simplify the mathematical model of the heat stop.At the same time,relying on the 1.8 m CLST ground-based large aperture solar telescope experimental platform of the Institute of Optics and Electronics,Chinese Academy of Sciences,to verify the correctness of the established reflective heat stop model.The experimental results show that under the same input conditions,the temperature difference between the theoretical modeling calculation result and the experimental measurement result of the heat stop surface temperature is less than 2 ℃,and the maximum error between the theoretical calculated heat stop surface temperature and the ambient temperature is 1.49℃,The maximum error between the actual measured surface temperature of the heat stop and the ambient temperature is 0.89 ℃.It can meet the requirements of temperature control target of heat stop of solar telescope.Thirdly,the mathematical model of electric heater is established based on the principle of heat balance,the mathematical model of transmission pipeline is established based on the finite element method,and combined with the established mathematical model of heat stop,the mathematical model of the whole heat stop active temperature control system is preliminarily formed.Fourthly,according to the established mathematical model of the heat stop temperature control system,PID(Proportion Integration Differentiation)control strategy,PID + Smith predictive control strategy,internal model control strategy and adaptive PI control strategy based on model reference are mainly used to simulate and analyze the established heat stop active temperature control system model.The results show that,the adaptive PI control based on model reference is optimal in terms of response speed and reducing overshoot.Finally,in order to ensure the accuracy of temperature measurement,the temperature sensor to be used is calibrated.After calibration,the measurement error is reduced from more than 1.5 ℃ to less than 0.05 ℃,which can meet the requirements of temperature measurement.The calibrated temperature sensor is used to measure the surface temperature of the heat stop.For the 1.8m CLST ground-based solar telescope of Institute of Optics and Electronics,Chinese Academy of Sciences,the active temperature control system of the whole telescope is designed,including the active temperature control system of the main mirror and the active temperature control system of the heat stop.According to the actual situation,the PID control strategy is adopted to adjust,which can control the temperature difference between the surface temperature of the heat stop and the ambient temperature within ±2℃,At the same time,the temperature difference between the surface temperature of the main mirror and the ambient temperature can also be controlled within ±2℃ to meet the requirements of the active temperature control target of the whole solar telescope.