Robust attitude control for an unmanned helicopter in near-hover flights

In this paper, a systematic procedure for designing robust attitude controllers for unmanned helicopters, based on mixed H
₂
/H
_∞
methodologies, is presented. Firstly, a family of linearized models describing the near-hover flight dynamics is derived which can be compactly formulated as a nominal plant perturbed by norm bound uncertainties on the system, control and wind matrices. It is then shown that a single robust controller can be designed guaranteeing stability, robustness and gust disturbance rejection for the whole near-hover flight envelope. Performance analysis and simulation results show that the proposed attitude control strategy can also satisfy the handling qualities defined in ADS-33E specification requirements. Finally, the attitude controller is used as a module in a total control scheme offering position tracking capabilities which is implemented in a real embedded system. The efficacy of the total control structure is proved by Hardware-In-the-Loop simulations on an accurate nonlinear helicopter model.