Model following flight control system design using quasi-sliding mode control

Abstract

This thesis deals with the model-following flight control system design for a missile employing discrete-time quasi-sliding mode control. In general, the classical PI-type flight control system has been used for the control of missiles. In this thesis, the classical PI-type reference model is constructed for the purpose of designing a model following flight control system and the quasi-sliding mode control law is used to design a robust flight control system to model uncertainties and disturbances. Furthermore, output feedback is used to design a quasi-sliding mode control law and the model states are used for the unmeasured states instead of estimating them. The sampled data systems are used for representing the plant and reference model, since the control law is implemented in the digital computer. The nonlinear missile dynamics are linearized at the equilibrium points within a flight envelope to design a flight control system. The models of the missile and actuator dynamics may contain the model uncertainties. Besides, the external disturbances need to be accounted for in a realistic plant. Hence, the control input of the quasi-sliding mode controller composed of the equivalent control input using the nominal parameters of the plant model and the additive control input compensating for the model uncertainties and disturbances is proposed. In order to enhance the tracking performance within the whole flight envelope, the parameters of the equivalent control are gain scheduled with the state variables of the missile dynamics. Two compensating control inputs, (1) using saturation function, and (2) using adaptive sliding mode control, are proposed and their stability proved. The switching function defining the sliding surface is represented as the linear combination of the error between the states of the reference model and the plant. In the quasi-sliding mode control, the switching function asymptotically converges to zero. The convergence of the switching func...