Nonlinear H∞ Controller for the Quad-Rotor Helicopter with Input Coupling

This paper presents a nonlinear H∞ control law for underactuated mechanical systems with input coupling. Apart from the controlled degrees of freedom (DOF), the proposed controller considers the dynamics of the remaining DOF in the cost variable, which allows to stabilize them. The underactuated mechanical system is normalized to obtain a diagonal inertia matrix allowing to weigh with various criteria different DOF. This controller is applied to the quadrotor helicopter to perform path tracking, whose mechanical structure has been modified in order to obtain coupling between longitudinal and lateral movements with roll and pitch motions. Simulation results in presence of aerodynamic disturbances, structural and parametric uncertainties are presented to corroborate the effectiveness and the robustness of the proposed controller.