Comparison of Backstepping-Based Sliding Mode and Adaptive Backstepping for a Robust Control of a Twin Rotor Helicopter

In this contribution, two robust MIMO backstepping control approaches for a twin rotor aerodynamic system (TRAS) test-rig are considered. The TRAS represents a nonlinear system with significant couplings. A nonlinear multibody model of the TRAS with lumped unknown disturbance torques is derived using Lagrange’s equations. Herewith, both a backstepping-based sliding mode control and an adaptive backstepping control are designed to track desired trajectories for the azimuth angle and the pitch angle. An explicit expression is derived for the reaching time in the case of the backstepping-based sliding mode control. In order to estimate immeasurable angular velocities and unknown disturbance torques for the backstepping-based sliding mode control, a discrete-time extended Kalman filter (EKF) is employed. For the adaptive backstepping, a robust sliding mode differentiator is used instead to estimate the angular velocities. Moreover, in the adaptive backstepping control approach, the disturbance compensation is realised with the help of additional adaptive control parts driven by the tracking errors of the controlled variables. The overall stability of the proposed controllers in combination with the corresponding estimator is investigated thoroughly by simulations. Furthermore, in order to validate the proposed control schemes, experiments are performed on the dedicated test-rig and a comparison of the two proposed control structures is provided as well.