Periodic motion planning and nonlinear H∞ tracking control of a 3-DOF underactuated helicopter.

Nonlinear H∞ synthesis is developed to solve the tracking control problem into a 3-DOF helicopter prototype. Planning of periodic motions under a virtual constraints approach is considered prior the controller design in order to achieve our goal. A local H∞ controller is derived by means of a certain perturbation of the differential Riccati equations that appear while solving the corresponding H∞ control problem for the linearised system. Stabilisability and detectability properties of the control system are thus ensured by the existence of the proper solutions of the unperturbed differential Riccati equations, and hence the proposed synthesis procedure obviates an extra verification work of these properties. Due to the nature of the approach, the resulting controller additionally yields the desired robustness properties against unknown but bounded external disturbances. Convergence and robustness of the proposed design are supported by simulation results. [ABSTRACT FROM AUTHOR]