Dynamics Modeling And Flight Control For A Stratospheric Airship

Near space is quantitatively defined as the range of earth altitudes from20km to100km, below which aerial aircraft can produce sufficient lift for steady flight, andabove which the atmosphere is rarefied enough for satellites to orbit with meaningfullifetimes. There is a growing worldwide interest in a new concept consisting of usingautonomous fight vehicles as platforms operating for extended periods of time at analtitude around20km to accomplish various missions. As a typical lighter-than-airvehicle, the stratospheric airship has an enormous, yet untapped potential as low-speed,or even steady platforms for many different applications, such as reconnaissance,surveillance, telecommunication, broadcasting relays, region navigation, environmentalmonitoring, disaster aid, scientific exploration, and so on.With the rapid progress of airship technologies, advanced flight control system playsa key role in the development of the stratospheric airship. Dynamic nonlinearity, modeluncertainties, and external disturbances contribute to the difficulty in maneuvering anairship to accomplish various missions. Therefore, flight control remains a keytheoretical and technical challenge for the stratospheric airship. For the purpose ofsolving the flight control application problems and further developing the new theoryand methods, this dissertation studies the dynamic model, the dynamic characteristics,the attitude regulation problem, the trajectory-tracking problem, and the station-keepingproblem of the stratospheric airship. The main results achieved in this dissertation aresummarized as follows.1. The dynamic model of the stratospheric airship is derived, the mode analysismethod based on eigenvalue and eigenvector of the state equations is proposed, and thedynamic characteristics of the airship are investigated.1) A conceptual design for thestratospheric airship is presented; reference frames and motion variables of the airshipare defined, and the nonlinear dynamic model of the airship is derived by using theNewton-Euler formulation.2) The approximate linear model is derived from thenonlinear dynamic model under the “small perturbation” assumption, and stability of theairship is analyzed by means of Lyapunov stability theorem.3) The mode analysismethod is proposed, and the motion modes of the airship are investigated. Thelongitudinal motion includes the heave mode, surge mode and pendulum mode, whereasthe lateral motion includes the yaw mode, slideslip mode and roll oscillation mode.2. A novel attitude control approach for the stratospheric airship using feedbacklinearization and terminal sliding mode control (TSMC) is proposed.1) The attitudemotion equations of the airship is derived, and expressed as an affine nonlinear system.2) The nonlinear attitude control system is decoupled into three single-inputsingle-output linear subsystems via feedback linearization.3) The attitude controller is designed based on the new linear systems using TSMC, and the global stability of theclosed-loop system is proven by using the Lyapunov stability theorem. Simulationresults demonstrate that the attitude control system tracks the commanded angleprecisely in the presence of model uncertainty and external disturbance. Contrastingsimulation results indicate that the proposed control approach enables the control errorconverges to zero in a finite time, and has better performance against the SMC.3. A fuzzy parameter-tuning sliding mode control (FPTSMC) approach fortrajectory-tracking control of the stratospheric airship is proposed.1) The problem oftrajectory-tracking control of the airship is formulated, and the model of trajectorycontrol system is derived.2) The SMC is designed to track a time-varying referencetrajectory for its robustness against parametric uncertainty.3) To attenuate thechattering results from SMC, a FPTSMC is proposed in which the control parametersare tuned according to the fuzzy rules, with switching sliding surface function as fuzzycontrol inputs and control parameters as fuzzy control outputs. The stability of theclosed-loop control system is proven using the Lyapunov stability theorem. Simulationresults demonstrate that the FPTSMC performs well in terms of the stability androbustness of trajectory-tracking control despite of model uncertainty and externaldisturbance. Contrasting simulation results indicate that the FPTSMC attenuates thechattering effectively and has better performance against the SMC.4. A fuzzy adaptive sliding mode control (FASMC) approach for station keepingcontrol of the stratospheric airship is proposed.1) The station-keeping control problemof the airship is formulated, and the model of station-keeping control system is derived.2) The SMC is designed under the assumption that the airship model is accuratelyknown.3) In order to solve the problem of model uncertainty, a fuzzy system is used toapproximate the uncertain model of the airship, and an adaptive law is adopted to tunethe optimal parameter vector. The stability of the closed-loop control system is provenvia the Lyapunov stability theorem. The effectiveness and robustness of the proposedcontrol approach is demonstrated via simulation studies. Contrasting simulation resultsindicate that the FASMC has better performance against the SMC.This dissertation expands the research domain of the current flight control theory bydeveloping the dynamic model, control theory, methods and approaches, which haveboth theoretical innovation and technique significance, and provides a promisingapproach for flight control system design of the stratospheric airship. The research workhas high application value in near space aerostatic vehicle and other near spaceapplication projects.