Disturbance Observer Based Fast Control In Attitude Control System Of Ultra-low Orbit Satellite

This thesis takes the ultra-low-orbit satellite as the research object.Compared with the traditional satellites,their orbits altitude belongs to the space between the thermosphere and the outer atmosphere,and the aerodynamic interference torque during orbiting is higher,which cannot be ignored for the design of attitude control system.In addition,the ultra-low orbit means that the satellite has short overhead time when performing reconnaissance of a fixed target on the ground,so the ultra-low orbit satellite is required to have fast maneuverability.In order to solve the above problem,ensure the stability of attitude control system of ultra-low orbit satellite,and strengthen the satellite’s rapid maneuverability,this thesis focuses on the observation and compensation of large disturbance torque and at the same time carried out the design of reasonable fast attitude control method,the following three parts are included:A fast attitude control based on disturbance sliding mode observer is proposed.Modelling of external aerodynamic interference makes the setting of external interference in the simulation more reasonable,to ensure the rapidity of the satellite’s large-angle attitude maneuvering process,a trigonometric function path planning method is designed.To observe the external aerodynamic interference suffered by the satellite,a disturbance sliding mode observer is designed.To ensure the stability of the ultra-low orbit satellite attitude control system,a modified PD control law with interference estimation compensation is designed.A finite-time attitude control method for ultra-low orbit satellites based on disturbance observer is designed.Effects of the observer are discussed in detail,a kind of disturbance observer with a low-order power term in the deviation correction function is designed.A disturbance observer with finite-time convergence is designed.Both observers have improved the estimation of speed and accuracy.To quickly track the actual satellite attitude to the designed path,a terminal sliding mode control method is designed.Based on the concurrent learning(CL)strategy,a method for estimating and compensating disturbances and faults is proposed.A new idea of disturbance estimation is provided.The CL adaptive identification strategy is introduced into disturbance estimation and the observation module is replaced by the identification module.The external disturbance is regarded as the unknown dynamic part of the system,and the multiplicative fault and additive fault of the actuator are considered.Based on CL strategy,the disturbance and fault are estimated and compensated simultaneously.In order to ensure the stability of the closed-loop system,a modified sliding mode controller with disturbance and fault estimates is designed.