Research On Integrated Robust Flight Control Design For Ducted-fan Vehicle

Rotorcraft based vehicles with vertical take-off and landing(VTOL),hovering and various maneuvering capabilities could accomplish a large number of important missions,such as surveillance,transportation and data acquisition in areas that are dangerous for human operators and inaccessible to ground vehicles.Over the last two decades,the flight control of under-actuated unmanned aerial vehicles(UAVs)and related applications have attracted a great deal of interest from the University,the industry,and the military community.This thesis focuses more specifically on the automatic flight control system design for a novel duct-fan vehicle,and provides a comprehensive methodology to design,implement,and test ducted-fan unmanned aerial vehicles(DUAVs).We choose the ducted-fan based vehicle as the main research object because it offers higher security and aerodynamic efficiency and thus is suitable for development of future flying-driving vehicles.However,there are only a handful of reported examples of ducted-fan vehicle in real-world applications,which is mainly due to the poor flight performance that can be achieved.This work attempts to explore and provide an effective integrated solution incorporating modeling and control.In this thesis,a multi-loop cascaded control system design is solved by modern multivariable robust control techniques combined with various mixed performance specifications and non-smooth optimization algorithm in order to provide rapidity,accuracy,robustness,disturbances rejection and input-energy saving.Robust control under controller structure constraint,large envelope flight control problem and actuators anti-windup problem are systematically solved by the application of non-smooth optimization approach.The main content of this thesis can be summarized as follows:1.This thesis investigates the integrated modeling of the ducted-fan vehicle flight dynamics,which combines the benefits of first-principles and system identification techniques.Firstly,a comprehensive nonlinear model with minimum structural complexity is derived.The simplified model not only includes some essential dynamics of this particular vehicle,reduces the burden of model analysis,the difficulties in model identification and model correction,but also facilitates the high-performance controller design and implementation.2.The thesis shows how the use of identified linear model of near hovering condition and robust_?strategy solves robust hover control problem.First,robust control scheme is proposed based on separating the system dynamics into two time scales referred to as fast inner-loop attitude dynamics and slow outer-loop translational dynamics in order to provide stabilization,robustness on control inputs and gust attenuation.Then,a simple controller structure only including static output feedback gain matrix and forward-path loop-shaping weights is presented,in which static output feedback algorithm based on LMI is applied to rapidly tuning the free parameters under various constraints.3.This part shows how to use effectively the identified multi-models around different operating points with the nonsmooth_?general controller design framework to produce robust large envelope controllers.A single linear controller cannot cope with the nonlinear behavior of the flight vehicle,and thus controller parameters need to be re-tuned,which is usually known as gain scheduling.The target flight envelope is represented by forward flight speed.A compact linear or quadratic formula expressing the dependence on the scheduling variable is proposed and the controller parameters are tuned via nonsmooth optimization algorithm,which provides smooth transition between flight conditions without post-processing or interpolation.Sometimes,the input efforts commanded by the control law is approaching the saturation levels in maneuvering flight or in presence of wind gust disturbances,which may lead to performance degradation or even instability.Different from classic anti-windup scheme based on two-step design procedure,the proposed anti-windup compensator combined with the feedback controller are obtained simultaneously as the minimizer of the_?norm of corresponding loop transfer.