A Path-Following Preview Controller for Autonomous Air Vehicles

This paper addresses the path-following problem of steering an autonomous air vehicle along a predefined 3-D path, while tracking a desired velocity profile. The presented solution relies on the definition of a path-dependent error space to express the dynamic model of the vehicle, which exhibits a high degree of directional accuracy. The proposed methodology adopts a polytopic Linear Parameter Varying (LPV) representation with piecewise affine dependence on the parameters to accurately model the error dynamics over a wide flight-envelope. The synthesis problem is stated as a discrete-time H2 control problem for LPV systems and solved using Linear Matrix Inequalities (LMIs). To achieve better path-following performance, a preview control technique is adopted, which amounts to introducing a feedforward term driven by future path disturbances. Implementation of the nonlinear controller is addressed within the framework of gain-scheduling control theory using the D-methodology. The effectiveness of the proposed controller is assessed in simulation using the full nonlinear model of a small-scale helicopter.