Missile control design considering aerodynamic uncertainties and actuator saturation and fault

Abstract

In this thesis, a missile control design considering aerodynamics uncertainties and actuator saturation and fault is proposed. A general controller is composed of control logic and control distribution logic. Many compensation techniques of control logic and the control distribution for uncertainties and actuator problem are devised and checked by numerical simulations. Contents can be divided into 3 parts. A backstepping process combined with adaptive parameters in the form of sliding model control is applied to obtain a simple and robust controller for tracking the commanded path angle. The features introduced for adaptation and robustness in this work can handle the nonminimum phase effects as well as tracking errors induced by aerodynamic uncertainties. However, this control logic can not handle the system having unhealthy actuators. Thus, the adaptive sliding mode pitch rate control logic with EKF (Extended Kalman Filter) estimator is developed for a missile with highly nonlinear aerodynamics and unhealthy actuators. Conventional sliding mode control algorithms have inherent robustness to system model errors, but they often induce chattering of the actuator commands. An adaptive switching gain varying with respect to the distance from the sliding surface is proposed to cope with system model error and unexpected changes in aerodynamic coefficients. The adaptive sliding gain helps to mitigate the chattering in the steady state. We propose a control command generation method which uses the estimated actuator characteristics by EKF. The proposed method mitigates the control performance degradation caused by actuator fault or model disagreement. However, the performance degradation by actuator saturation is not avoided by using this control logic. The compensation of control distribution logic makes it possible to get out of this trouble. Accordingly, two on-line control allocation methods are proposed to effectively distribute the control command u...