Robust Control Technology For Near Space Vehicles With Input Constraint

The near space vehicle (NSV) has become a prior and important air vehicle around the worlddue to its potential value, and it has been widely applied to both military and civilian aeras. Toobtain the optimal aerodynamic performance during its supersonic status, NSV usually adopts theconfiguration with low wing span and large wing skew angle. However, such configuration can notmake the aerodynamic performance achieve the best when it is in subsonic and transonic status. Tosolve this problem, the concept of oblique wing is proposed and attacts the increasing interest andresearch. Besides, the rudder saturation is a common problem for any vehicle which can not beignored arbitrarily. Otherwise, it will degrade the system control performance, even leading to aserious accident. Therefore, the robust flight control for near space vehicles with the oblique wing(NSVOW) and input saturation is an innovative and challenging project. This dissertation studiesthe model of NSVOW, and its robust attitude control is investigated by considering parameteruncertainty, external disturbance and input saturation. The main works are given as follows:Firstly, the six-degree-of-freedom and twelve-state kinematic equations of NSVOW areestablished according to references, and the stability and coupling of the open-loop system areanalysed through simulation. For the convenience of further research, the attitude model equationsof NSVOW are transformed into the form of affine nonlinear equations in accordance withsingularly perturbed theory and time-scale separation principle.Then, the attitude control scheme is designed for NSVOW with parameter uncertainty andexternal disturbance based on sliding mode control (SMC). The nonlinear disturbance observer(NDO) is employed to approximate the parameter uncertainty as well as the external disturbance.Radial basis function neural networks (RBFNNs) are constructed as a compensator to overcome thesaturation nonlinearity. The stability of the closed-loop system is proved through the Lyapunovanalysis. Simulation results are presented to demonstrate the effectiveness of the proposed flightcontrol scheme.Thirdly, the control design is studied for a class of uncertain multi-input and multi-output(MIMO) nonlinear systems with input saturation. The dynamic surface control (DSC) is proposedto solve the problem of calculation expansion in the conventional backstepping technique byintroducing a first-order filter at each step. As a result, the derivative of the virtual control law isavoided to be calculated, simplifying the design process. The nonlinear disturbance observer is applied to approximate the compounded disturbance. In addition, an auxiliary system is constructedto eliminate the effect of input saturation. It is proved that all signals of the closed-loop system areuniformly ultimately bounded through Lyapunov analysis. Satisfactory results are obtained forNSVOW based on the proposed control scheme.Following, a hyperbolic tangent function is used to transform the original MIMO nonlinearsystem into an equivalent form in order to solve the problem of input saturation, and a new robustcontrol scheme is proposed. Namely, a subsystem is added in the last step of the conventionalbackstepping control which we can use a Nussbaum function to tackle the input saturation. Besides,a kind of new intelligent disturbance observer is designed which is called recurrent wavelet neuralnetwork disturbance observer (RWNNDO). The control scheme is proposed for a class of uncertainMIMO nonlinear systems based on the backstepping technique and the dynamic surface method. Thestability of the closed-loop system is rigorously analyzed through Lyapunov method. The applicationto NSVOW shows the satisfactory performance.Finally, the fault tolerant control (FTC) scheme is developed for a class of uncertain MIMOnonlinear systems with actuator faults and input saturation based on sliding mode control andnonlinear disturbance observer. Neural networks are employed to deal with actuator faults.Considering input saturation, a compensated term is constructed in the control law. The stability ofthe closed-loop system is proved and all closed-loop signals are uniformly ultimately bounded viaLyapunov analysis. Simulation results are given to demonstrate the effectiveness of the proposedfault tolerant control scheme.