Research On Attitude Control Technology Of Optical Satellite Platform Based On Single Gimbal Control Moment Gyros

In recent years,with the rapid development of small and medium optical remote sensing satellites,they have shown a wide range of application prospects in military and civil fields.The optical imaging system is the core equipment of the optical remote sensing satellite,and the optical imaging system on the satellite platform with agile attitude enables the optical remote sensing satellite to have more functions and advantages,such as strip splicing,stereo imaging,stronger single orbit data acquisition ability,shorter revisit period and so on.Therefore,it is of great significance to improve the attitude agility of the satellite.Improving the agility of satellite attitude maneuver depends on the attitude control executive part which can output large moments.Compared with the traditional attitude control components such as flywheel and magnetic torque converter,Single gimbal control moment gyroscope(SGCMG)has the advantages of large output torque,accurate output torque,clean and pollution-free.However,according to the requirements of the optical imaging system for the stability and accuracy of the satellite attitude control,the overall technology of the attitude control of the optical satellite platform based on the single gimbal control gyro group(SGCMGs)still faces the following two key technologies to be solved,one is the design of the steering law of the SGCMGs,the other is the high-precision dynamic control of the SGCMG gimbal motor.This paper focuses on these two issues.The first task is to model SGCMGs system.This paper introduces how SGCMG works and gives its dynamic equation.Based on the above analysis,the dynamic simulation model of SGCMGs is established and the permanent magnet synchronous motor(PMSM)is adopted as the driving motor of SGCMGs frame.Besides,this paper points out the disturbance of PMSM in operation and establishes the drive and control model of PMSM.Finally,the theoretical driving and control model of PMSM is tested by the simulation in Matlab/Simulink based on PI control.Secondly,the singularity problems in SGCMGs are analyzed based on the analysis of the dynamics model of SGCMGs.Through theoretical analysis and simulation,the specific performance and function of zero motion in various cases are discussed.The closure of the trajectory of zero motion in nonsingular state and hyperbolic singularity is revealed.On this basis,the existing steering laws are analyzed from the aspects of the design ideas,advantages,and disadvantages.Then,according to the in-depth analysis of system singularities and the overall grasp of SGCMG steering technology,it is pointed out that a steering law with excellent performance and competent in engineering application should have strong singularity avoidance ability,accurate torque output ability,and fast singularity escape ability simultaneously.In order to meet these demands,a novel hybrid control law of SGCMGs is proposed.In our steering law,the evaluation index of the system angular momentum state of the command moment is designed firstly.Then a set of expected gimbal angular velocity is designed according to the effective residual angular momentum evaluation index of each SGCMG for the command torque.The expected gimbal angular velocity can drive the SGCMGs away from the singular states.In the process of singularity avoidance,the steering law determines the appropriate zero motion according to the desired gimbal angular velocity to avoid singularity.In the process of singularity escape,the desired gimbal angular velocity with a certain weight will be directly introduced into the final command of the steering law.Although this will introduce a certain torque error,it can help the system to get rid of the singular state quickly.Finally,there is a smooth switch between the singularity avoidance steering strategy and the singularity escape steering strategy.Compared with other typical steering laws,the simulation results show that the proposed steering law has strong singularity avoidance ability,accurate torque output ability and fast singularity escape ability.In addition,the angular velocity instruction given by the algorithm is more traceable(the relative change is more slowly)by the gimbal motor.The above simulation results show that the proposed hybrid steering law has a better comprehensive performance.Finally,according to the dynamic analysis of SGCMGs and the characteristics of the speed command given by the steering law in the previous simulation,it is concluded that the servo control of the gimbal motor is a high-precision variable-speed servo control.Aiming at the high precision variable speed servo control of the motor,considering the problems and demands of cogging moment disturbance,motor parameter disturbance,motor load moment variation disturbance,speed calculation error,and high dynamic required by the control system,this paper proposes a comprehensive control scheme to improve the dynamic speed tracking accuracy of PMSM.The integrated control method includes five aspects: a)speed loop nonlinear error feedback controller;b)disturbance torque compensator based on extended state observer;c)current loop deadbeat controller;d)motor parameter disturbance compensator;e)tracking differentiator used to obtain high-precision speed.Finally,compared with the simulation and experiment of PI controller,the proposed control structure has better anti disturbance ability and dynamic current and speed tracking ability.The experimental results show that compared with PI controller,the tracking ability of dynamic current and speed is improved by 23.3% and 30% respectively.In order to improve the agility of the optical remote sensing satellite,according to the stability and accuracy requirements of the optical imaging system for satellite attitude control,two key technologies of SGCMGs based optical satellite platform attitude control are studied in-depth,a hybrid steering law with better comprehensive performance and a PMSM control scheme with higher dynamic performance are proposed.The two technical schemes can better meet the stability and accuracy requirements of the optical imaging system for the satellite platform during the imaging period.