| As a space vehicle developed by many countries,spacecraft plays an important role in military and civil fields.For saving fuel and increasing on orbit operation time,the spacecraft structure has been replaced by light weight materials,which introduced the vibration by flexible appendance(such as solar panels,antennas,etc.).In addition,there are some disturbances,such as liquid slosh,gravity gradient,solar light pressure,etc,which would do a damage on spacecraft system.Then,the spacecraft model exhibits strong nonlinearity and strong coupling.Moreover,due to the influence of actuators and the measurement components,there would be actuator saturation and unmeasurable angular velocity of spacecraft,which would reduce the control performance and even destroy the stability of the control system.Therefore,this paper is investigated on flexible vibration and attitude control to achieve fast and high-precision attitude control of spacecraft.The main contributions of this paper are given as follows.Firstly,the arctangent function mode is designed to realize the fast quaternion control.And the improved super-twisting sliding mode controller is proposed to estimate the comprehensive uncertainty including flexible vibration,liquid fuel sloshing and external disturbance.Furthermore,the saturated super-twisting sliding mode controller is designed by adding feedback term to realize finite-time high precision attitude control under input constraints.Secondly,since the flexible vibration treated as disturbance is a passive solution and the flexible vibration still exists,an improved input shaper and continuous terminal sliding mode controller are proposed to realize active vibration suppression and attitude control.Considering the contradiction between the impulse sequence time and the robustness of input shapers,a fast robust input shaper is proposed to effectively suppress the flexible vibration,and a second order adaptive continuous terminal sliding mode controller is proposed to realize finite time high accuracy attitude control without the information of disturbance high order derivative.Thirdly,since the input shaper is the feedforward filter which introduces the problem of time delay,the integrated control method combined of positive position feedback controller,angular velocity observer and terminal sliding mode controller is proposed to realize active vibration suppression and finite time attitude control.Based on the estimated frequency of flexible vibration,a positive position feedback method is designed to suppress the flexible vibration.The angular velocity observer is designed to estimate the angular velocity in finite time without the assumption that the second derivative of quaternion is bounded or semi-global convergence.Based on the estimated angular velocity,a terminal sliding mode controller is designed to realize attitude control by adding the item of quaternion estimation error.The influence of angular velocity estimated system on attitude control accuracy is reduced.It can be obtained that flexible vibration suppression and attitude control in finite time by the proposed controller.Finally,since the positive position feedback method is based on intelligent materials which would increase the complexity of spacecraft structure,an integrated control method combined of flexible vibration observer,disturbance observer and attitude controller is proposed by taking the flexible vibration as a state variable.The flexible vibration observer and disturbance observer are designed to estimate the flexible vibration and disturbance.Based on the estimated flexible vibration and disturbance,the attitude controller based on state feedback is designed to realize finite time flexible vibration suppression and attitude control simultaneously without intelligent materials. |
