Enhanced Robust Control of a 3-DOF Helicopter System Utilizing an Unknown Input Observer

Abstract-In this paper, a generalized matrix inverse-based unknown input observer (UIO) has been developed for a benchmark 3-DOF helicopter system to manage unknown, time-varying nonlinear dynamics and disturbances. The goal is to ensure the helicopter accurately follows the specified elevation and pitch references. To achieve this, we introduce a novel, simplified UIO to estimate the combined unknown dynamics, which are subsequently incorporated into the control design as a compensator. By introducing an auxiliary system, an invariant manifold is derived and utilized in the UIO design. The full-order observer, constructed using the g-inverse, is expanded and implemented to achieve this purpose. This new estimator requires setting only a single scalar and achieves exponential convergence. Consequently, the proposed control design utilizing the estimator can achieve precise output tracking. This control method is implemented on a benchmark 3-DOF helicopter, and its efficacy is validated through simulations and results.