Research On Disturbance Compensation Control Technology Based On High Precision Tracking And Pointing System

The research of satellite laser communication has developed rapidly in recent years and has broad development prospects.Among them,the high-precision tracking system plays a key role in the establishment and maintenance of the laser communication link.Tracking and aiming system is a complex system integrating optics,mechanics and electronics,in order to meet the design needs of the satellite laser communication system,the tracking accuracy of the tracking system must reach the micro-radian standard.Based on the engineering background of satellite laser communications,the subject conducts research on its acquisition,pointing,and tracking processes,focusing on the issue of disturbance compensation control for tracking and targeting systems.How to eliminate the effects of internal friction disturbance,platform jitter and some non-linear disturbances on the tracking accuracy of the tracking system is the key to achieving high-precision robust servo control of the satellite-based tracking system.Due to the long communication distance of the inter-satellite laser communication system,the narrow beam divergence angle for communication,and the complicated space environment,it is very difficult to establish a stable communication link at both ends of the communication.In order to eliminate the influence of unfavorable factors,this subject conducts research on several contents of the satellite tracking system.(1)This paper introduces the composition of the tracking and aiming system and analyzes the workflow of the tracking and aiming system,the establishment and maintenance of a laser communication link generally requires three stages: acquisition,pointing,and tracking,describe in detail how each phase works.The system of satellite laser communication terminal to realize the whole process of APT is called tracking and aiming subsystem,which is mainly divided into coarse tracking system and fine tracking system.In order to conveniently describe the attitude and orbital movement of the ATP process,the commonly used coordinate system and coordinate transformation are calculated and analyzed.Then,the establishment process of the satellite laser communication link,that is,the working process of the ATP subsystem,is introduced.The capture mode and scanning mode are analyzed,the capture time formula is deduced,and the capture scheme is determined.The composition and principle of compound axis tracking are introduced in detail,which lays the foundation for the control algorithm design in the following chapters.Finally,the redundant power of the inter satellite communication link is calculated.Combined with the optical power equation of the system link,the influence of each parameter in the process of establishing the communication link is analyzed,and the accuracy index of the tracking and aiming system is proposed.(2)In order to achieve high precision tracking performance,the complex axis control structure is used in this project.The relationship between the stability of the coarse tracking system and the fine tracking system and the stability of the compound axis of the tracking and aiming system is analyzed theoretically.Based on the composite axis tracking structure,the coarse tracking system and the fine tracking system are studied and designed separately.In order to establish the motion model of the tracking system,the traditional scanning method was used to identify the control model of the coarse tracking system,and the classic PID control strategy was used to design the three-loop controller for the coarse tracking system.In order to establish the motion model of the tracking system,the traditional scanning method was used to identify the control model of the coarse tracking system,and the classic PID control strategy was used to design the three-loop controller for the coarse tracking system.On this basis,the disturbance factors affecting the tracking accuracy of the coarse tracking system are analyzed.Several commonly used disturbance compensation methods are introduced,this project decided to adopt a compensation method based on dynamic LuGre friction model.The parameters of the LuGre friction model were identified through experimental data,and the experimental data of position error and velocity error before and after compensation were compared to prove the effectiveness of disturbance compensation.In order to improve the low-speed stability of the system and the noise amplification phenomenon that the system uses the encoder differential method to obtain speed information,this topic uses a Kalman filter-based speed estimation algorithm based on the kinematics model of the tracking system to enhance the lowspeed resolution and response speed of the system.(3)For the identification problem of fine tracking control system,an adaptive differential evolution algorithm with improved population initialization is proposed.Through the optimization of population initialization and the improved adaptive mutation factor,the improved algorithm can improve the global search ability and convergence speed of the traditional differential evolution algorithm.The Benchmark test evaluation function set is used to compare the test results with other intelligent identification algorithms,and the advantages of the improved differential evolution algorithm in convergence accuracy and iteration speed are reasonably verified.In addition,a set of experimental schemes for a precise tracking experiment platform is proposed.Based on the experimental data,a differential evolution algorithm is used to identify the system,and a control model of the precise tracking system is obtained.The identification results show that the output of the two algorithms is basically consistent with the actual results of the experimental system.However,the root mean square error value of the identification results of the improved differential evolution algorithm was reduced by 54.1%,which verified the effectiveness and feasibility of the algorithm in the experimental system.(4)The tracking accuracy of the satellite-based tracking and pointing system ultimately depends on the tracking accuracy of the fine tracking system,and the disturbance of the fine tracking system mainly comes from the jitter of the platform and the nonlinear disturbance caused by the piezoelectric ceramics.The subject studies the platform jitter power spectrum analysis of the fine tracking system and analyzes the nonlinear disturbances of the piezoelectric ceramics.Due to the complex and difficult to model the disturbance model of the fine tracking system,this issue proposes that this kind of situation can not be accurately modeled.This subject proposes an advanced control strategy that improves ADRC combined with iterative learning methods.This control strategy combines the advantages of the two methods.It does not require an accurate disturbance model and has strong robustness.It can effectively suppress platform vibration and nonlinear disturbances caused by piezoelectric ceramics.The effectiveness of the control strategy is verified by simulation tests and desktop platform experiments,which improves the tracking accuracy of the tracking system and meets the indicators proposed by the project design.