Robust H₂=H∞ position tracking control of an unmanned helicopter for near-hover flights

In this paper, a systematic procedure for designing Position Tracking controllers for Unmanned Helicopters, based on mature H₂=H∞ methodologies, is presented. Firstly, a family of linearized models describing the near-hover flight dynamics is derived which can be formulated as a nominal plant perturbed by norm bounded uncertainties on the system, control and disturbance (wind gust) matrices. The full system dynamics is then decomposed into rotational (Inner) and translational (Outer) subsystems, and separate controllers are subsequently designed. Each controller guarantees stability, robustness and gust disturbance rejection for the whole near-hover flight envelope while appropriately selected closed-loop pole regions, justify the combination of the two controllers into a composite position control scheme. The efficacy of the proposed total control structure is proved by hardware-in-the-loop simulations on an accurate nonlinear helicopter model.