Nonlinear Robust Control of an Highly Manoeuvrable Missile

Introduction Automatics and control theory should be considered at the top of modern engineering science. Control systems are everywhere and, over time, they are going to be more and more essential (not just incidental, as happens now) for the proper functioning of any system. This thesis is about control system design for a generic air-to-air missile autopilot and guidance system. For the autopilot, a nonlinear recursive approach is proposed, beginning from a simpler, nominal, implementation to arrive, in the end, to a more complicated robust one. The rst two control systems proposed are based on a wiser version of Backstepping, which uses a non-quadratic Lyapunov function to achieve in a more natural way some necessary dynamic cancellations. A faster version of these two autopilots is also designed, including nonlinear damping terms. Then, nonlinear robust control theory is introduced, highlighting the structure of the generic nonlinear uncertain system. A nonlinear robust roll autopilot is designed, including in the robust recursive approach, that shall represent the baseline for the robust versions of the autopilot, also a revisited version of Lyapunov redesign, which has no counterpart in control theory literature. For pitch and yaw dynamics are, nally, proposed the static and dynamic robust recursive designs, two rigorous and systematic approaches to the problem of controlling a nonlinear uncertain system, which seem to be well suited to handle the structure of the missile vector-elds. To derive the equations of all the nonlinear controllers, a complete, nonlinear dynamical model of the missile is necessary: this is very important, because nonlinear control represents a model based design methodology. The simulation model was developed in the rst part of the work, together with the simplied models used for control design. Also, an accurate and very physical-oriented open-loop analysis of the missile behaviour is presented, with some simulations regarding the statically unstable dynamics, the phenomenon of peaking related to nite time explosions and the non-minimum phase. The nal part of the work is dedicated to the guidance system design. A nonlinear, Lyapunov-based, approach is used to guarantee the nite-time convergence to zero of the line-of-sight angular rates. The guidance loop is closed around the dynamic robust recursive controller, which in simulation will show the best performance. In this way, the guidance system and the autopilot will be both of energetic and nonlinear nature, and 9