A Comparative Analysis of Cross Coupling Estimations Using Disturbance Observers for Twin Rotor MIMO System

This paper presents an in-depth investigation into disturbance/uncertainty estimation within the intricate and highly coupled nonlinear Twin Rotor MIMO System (TRMS). Unlike numerous existing studies that decouple system dynamics and pseudo-linearize them, this paper maintains a holistic approach to system treatment. The accurate estimation of disturbances plays a vital role for compensating in control law, thus enhancing system robustness. By addressing cross-coupling effects as uncertainties along with exogenous disturbances, three distinct disturbance observers are introduced and their convergence is analyzed. Given the unpredictable nature of actual disturbances, minimizing mathematical constraints remains pivotal for effective design. A significant aspect of the sliding mode disturbance observers proposed in this study is their relaxation of the assumption that external disturbances must remain constant or change slowly, a typical requirement in disturbance observer (DO) design problems that is challenging to ensure from a practical engineering perspective. In addition to simulations, a numerical comparison of disturbance estimation is provided, with a focus on the Root Mean Square (RMS) error value as a performance index to evaluate the effectiveness of the estimators.