| Large reflector antenna has been widely used in radio astronomy,satellite communications,deep space exploration and other fields for the characteristics of high gain and narrow beam.In order to improve the gain and resolution of antenna,on the one hand,it is required that increasing its diameter is a way which resulting in narrow beam,as a consequence,the antenna pointing accuracy is required to be higher and higher;On the other hand,it is required to improve working frequency band,which leads to a phenomenon that the influence of the structural and environmental factors on the performance is more significant.However,the increase of antenna aperture makes antenna structure stiffness reduced,at the same time,large windward area lead to wind interference effect more prominent.The combination of the two factors often causes the flexible oscillation of antenna,resulting in the performance dropped significantly.Considering the randomness of the wind disturbance,the pointing error is difficult to predict accurately and compensate in real-time;Although the way of building large radome can avoid wind influence on antenna,large antenna cover not only cost much,but also the impact on the performance will be more remarkable,especially for high frequency band antenna.So,effective inhibition of wind interference on antenna performance has become one of the most key and difficult problems in antenna development.In view of the typical large reflector antenna,this paper aims to improve the pointing accuracy under wind disturbance.It discusses from the perspective of model,control and structure design,and makes a further study of the large reflector antenna and the key technologies of wind interference design.In this paper,the main work and achievements are as follows:1.A dynamic model of the large reflector antenna was built.Firstly,based on the finite element model,using the generalized modal coordinates and the modal superposition method,the structure elastic deformation is transformed to inherent vibration mode as the base of space vector,dynamic model of flexible oscillation of large reflector antenna had been established.On this basis,the impacting mechanism of the antenna pointing accuracy from the vibration modal is analyzed.According to the extent of the pointing influenced by vibration modal,the order of the dynamic model is reduced,thus the pointing control-oriented large antenna dynamic model is established.The simulation results of 7.3 m diameter Ka-band antenna show that:under the condition of keeping the same order number,the above methods could reduce the model error from 21.51%to 7.35%,the correctness of the model laid a foundation for the control of the large reflector antenna pointing.2.This paper analyzes the impact on the large reflector antenna pointing accuracy caused by the wind disturbance.Using davenport wind spectrum,it discussed the impact on the antenna rotation angle caused by wind torque and on the beam pointing from the reflector deformation caused by wind pressure respectively.For the former,the rotation angle error is derived by introducing the equivalent wind torque into servo control system;For the latter,dynamic model oriented to control the large reflector antenna will discrete wind for different nodes of input forces,and will get pointing error under different wind,namely flexible pointing error.7.3 m and 110 m diameter antenna simulation results show that,with the increase of diameter,the pointing error caused by the flexible deformation increased from 0.93 times to 2 times comparing angle error.Therefore,it should be effectively suppressed in order to improve the pointing accuracy.3.In order to suppress the influence of pointing error caused by flexible deformation effectively,it puts forward the feedforward compensation control method based on disturbance observation and wind resistance control method based on the Linear-Quadratic-Gauss(LQG).The former treats pointing error caused by structure deformation as a disturbance torque,at the same time,it involves the model perturbation and the nonlinear disturbance uncertainty factors in observation of the torque,and uses the feedforward compensation;The latter treats pointing error caused by structure deformation disturbance as a state disturbance,it uses the quadratic performance index to get optimal control effect.The 7.3 m diameter antenna simulation results show that:In average wind speed of 10 m/s,it could reduce pointing error to 25.4%based on feedforward compensation control,which is the same effect under the traditional Propotion Integration Differentiation(PID)control.The LQG control scheme could further reduce to 23.3%.4.In order to effectively suppress the influence of wind gusts and further improve the pointing accuracy,it puts forward the wind disturbance predictive control method based on the wind speed prediction.Using least squares support vector machine regression function,the antenna location of the wind speed prediction model was established to estimate the antenna location after a number of sampling period of wind speed,and then to forecast the pointing error which is introduced into model predictive control algorithm,the optimal control input is derived by using the quadratic programming problem transformed by optimal estimation problem.The 7.3 m diameter antenna simulation results show that:In average wind speed of 10 m/s,the anti-wind disturbance predictive control method based on wind speed forecasting could reduce maximum pointing error to 17.5%which is the same percentage caused by the traditional PID control,meanwhile,in the initial stage of the control compensation,the maximum pointing error is only a half the error of the system with LQG controller.5.In order to solve the problem of slow response of large reflector antenna for large inertia,this paper proposes a beam waveguide antenna wind interference adaptive active compensation control method.Using the fast response and high accuracy active plate mirror,and an angle amplification factor is designed to ensure that the displacement of the active plate mirror should fall within the driving stroke range,which laid a foundation for that the active mirror adjustment could compensate point deviation caused by the wind disturbance in time.65 m diameter beam waveguide antenna simulation results show that:At the average wind speed of 10 m/s,based on the active mirror adjustment,wind interference adaptive active compensation control method could reduce maximum pointing error to 5.4%which normally generated by the traditional PID control.This method could be applied to not only newly developed large reflector antenna but also completed antenna upgrade.It could have the effect of getting twice the result with half the effort to improve the performance of large reflector antenna and observation ability. |
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