Sliding Mode Variable Structure Control For The Attitude System Of Rockets During Ascending Stage

In the vehicle launching phase, there remains a substantial degree ofuncertainty regarding the structural dynamics caused by onboard payload motion,rotation of flexible appendages, and fuel consumptions; Meanwhile, the variouskinds of disturbances and measurement noise of inertial navigation systemencountered, the rocket will deviate from the desired trajectory; Moreover, due tophysical limitations, the actuator outputs are constantly bounded or constrained,which will potentially deteriorate the system performance and even destroy thesystem’s stability. These practical problems must be taken into consideration whendesign attitude stabilization controllers. This paper considers the attitudestabilization control problem of rockets. Various controllers are designed to dealwith the upper mentioned disturbances. Specifically, the main contents of this thesisare presented as follows:Firstly, the nonlinear dynamics of the launch vehicle is derived. The smalldeviation attitude dynamics model of the launch vehicle is further derived aftersimplifying and linearization, which significantly facilitates the controller design.Second, two robust control approaches using adaptive terminal sliding modeare developed for the trajectory tracking control problem. In both approaches, theterminal sliding mode control law is designed based on equivalence principle ofsliding mode control which ensures the robustness of the controller. The first methodadopts an online adaptation law for disturbance parameters identification.Meanwhile, the conditional integral is introduced to modify the terminal slidingmode to diminish the stabilization error. Further, a new robust control approachusing adaptive terminal sliding mode is developed to tackle the singularity appearedin conventional terminal sliding mode control method. The terminal sliding modecontroller (SMC) can guarantee the existence of the sliding phase of the closed loopsystem. By appropriately tuning controller parameters, the reaching phase of SMCcan be eliminated. Simulation results verify the feasibility and effectiveness of theproposed controller.Third, two robust control approaches are developed for solving the saturationissue. The first method incorporates an auxiliary system to compensate the effects caused by the saturation. Simulation results show the high effectiveness and goodperformance. Meanwhile, robust adaptive neural network control algorithm isadopted to tackle additional parameter uncertain and unknown external disturbance.Furthermore, an adaptive synchronized control scheme for launch vehicle withbounded input is proposed. The design methodology can be expressed as, for launchvehicle dynamic model with parameter uncertainties, first design an adaptivesynchronized controller in which the external disturbance is temporary ignored.Then considering the existence of disturbance, the controller is improved toattenuate the L2disturbance gain.In the end, the details of system responses are numerically simulated in theconjunction with the above proposed four novel attitude tracking control laws. Thesimulation result indicates that the commands can be tracked effectively in the flightcontrol system and the attitude can be stabilized with satisfactory robustperformances.