Feedback-linearization based robust relatively optimal trajectory tracking controller for 3-DOF helicopter

Abstract

This paper proposes a feedback linearization-based robust trajectory tracking controller for the elevation and pitch axes of three degrees of freedom (3-DOF) helicopter. The 3-DOF helicopter is a benchmark system that operates on the same principle of operation as that of a tandem-rotor helicopter. Accurate control of this laboratory set up in the presence of external disturbances is a sophisticated problem as it is easily affected by external disturbances due to its low weight. Hence, to ensure efficient trajectory tracking performance in the presence of uncertainties and disturbances a nonlinear disturbance observer is integrated with a feedback linearization (FL) based relatively optimal trajectory tracking controller (ROTTC). Feedback linearization of the nonlinear model results in a decoupled linear error dynamics for each axis, which is used for the design of the ROTTC. The stability of the 3-DOF helicopter in the presence of estimation error and parameter uncertainties is analyzed using the Lyapunov method. A comparison study with an FL-based robust linear quadratic regulator (RLQR) method illustrates the superiority of the proposed method in terms of tracking error and disturbance estimation. The efficacy of the proposed controller to accommodate external disturbances is demonstrated with real-time implementation on the 3-DOF helicopter with a strong wind disturbance as well as an impulse disturbance.