Robust Sliding Mode Control For Near Space Vehicle

Considering the tense international situation and further requirement of national defense security,near space vehicle (NSV) has become a new vehicle which attracts increasing attention of manymilitary powers. Unlike the aeronautic and astonautic vehicles, NSV enjoys a new flight scope whichis formed by the upper limit of aeronautics and lower limit of astronautics. Then, many advantages,such as high mobility, easy maintenance, improved efficiency/cost ratio, wide cover range, can befound in this new vehicle. However, it is also faced with a large number of difficulties. Since its flightscope, working environment and mission mode are different with traditional flight vehicle, NSV hasseverely nonlinear property, fast time variation, strong coupling and uncertainty. Therefore, researchfor NSV control system becomes an important part in this fundamental science project. In thisdissertation, a strongly robust strategy, which is called sliding mode control with unidirectionalauxiliary surface (UAS-SMC), is proposed to solve these problems in NSV project. The main resultsare given as follows:First of all, based on the analysis of aerodynamic configuration, a general structure of controlsystem is given for NSV and then a set of six-degree-of-freedom twelve-state equations are derivedthe motion of NSV in hypersonic mode. After that, we discuss the flight environment, mission, flightmechanics and dynamic characteristics in this project. From the above discussion, this paper focuseson the requirements of strong robustness, damping capacity and coordinated control in NSV control.Secondly, the robust requirement for attitude motion is presented as the fundamental work of thisdissertation. And a new strategy, which is called sliding mode control with unidirectional auxiliarysurface (UAS-SMC), is proposed for this requirement in NSV control research. Based on the modifiedsliding mode structure, unidirectional auxialiry surface and positively invariant set are introduced inthis method. Then, UAS-SMC strategy can enjoy the enhanced robustness when compared withtraditional sliding mode control. And the chattering phenomenon is eliminated with discontinuousapproaching law in UAS-SMC. Unlike the higher order method, the differential information isunnecessary in UAS-SMC method. So it is suitable for the engineering application. Meanwhile, sincechattering-free UAS-SMC controller is designed by discontinuous approaching law, the preciousinvariance and anti-disturbance property is retained. It is noted that this new method is better that thesliding mode control with boundary layer method. Therefore, the UAS-SMC method shows a newway to eliminate the chattering phenomenon.Then, terminal sliding mode control with unidirectional auxiliary surface (UAS-TSMC) ispresented for the critical damping characteristics problem in the short-period motion of NSV. And terminal attractor is used to improve the convergence rate in this method. Then, UAS-TSMC methodhas the advantages of UAS-SMC and terminal sliding mode control at the same time. Based on theenhanced convergence rate of UAS-TSMC method, the damping capacity of control system isimproved here. And the Lyapunov theory and simulation results are used to prove the robustness andchamping capacity in this method.Furthermore, coordinated problem is investigated in the research of NSV control. The discussionfor this problem can be divided into two different parts: longitudinal motion and coordinated turningmotion. For the longitudinal motion, regulatory factor and sliding mode disturbance observer isutilized to solve the coupling and anti-ditsurbance problem. Then, the control problem in coordinatedturning motion is improved with nonaffine nonlinear system in trajectory control loop. And thecontrol system for this part is designed with analytical method, newton iteration method andUAS-SMC strategy. Then, the stable tracking of height, velocity and lateral shift in coordinatedturning motion is guaranteed. The stability of closed-loop system is analysed via Lyapunov methodand the excellent performance is demonstrated by simulation.Finally, the work of this dissertation is summarized and the further work is also discussed.