Robust discrete time output feedback sliding mode control with application to aircraft systems
This thesis describes the development of robust discrete time sliding mode controllers where only output information is available. A connection between discrete time sliding mode controllers and so-called min-max controllers is described. New conditions for the existence of stabilizing output feedback discrete time sliding mode controllers are given for non-square systems with bounded matched uncertainties. A novel sliding surface is described; this in itself is not realizable through outputs alone, but it gives rise to a control law which depends only on outputs. An explicit procedure is also described which shows how a Lyapunov matrix, which satisfies both a discrete Riccati inequality and a structural constraint, can be obtained using LMI optimization. This Lyapunov matrix is used to calculate the robustness bounds associated with the closed-loop system.;For systems which are not static output feedback stabilisable, a compensation scheme is proposed and a dynamic output feedback discrete time sliding mode controller is described with a simple parameterisation of the available design freedom.;Initially, a regulation problem, to drive all plant states to zero, is considered. Then a new scheme which incorporates tracking control using integral action is proposed for both the static and dynamic output feedback discrete time sliding mode controller. The scheme requires only that the plant has no poles or zeros at the origin and therefore with an appropriate choice of surface, the controller can be applied to non-minimum phase systems.;The theory described is demonstrated for various engineering systems including implementation on a DC-motor rig in real-time and simulations on a nonlinear, non-minimum phase model of a Planar Vertical Take-Off and Landing aircraft. The effectiveness of the controller is further proven by its application for control of the longitudinal dynamics of a detailed combat aircraft model call the high Incidence Research Model, a benchmark problem used by the Group for Aeronautical Research and Technology in Europe. Simulations with real-time pilot input commands have been carried out on a Real Time All Vehicle Simulator and good results obtained.