Order Reduction Approach to Velocity Sensorless Performance Recovery PD-Type Attitude Stabilizer for 2-DOF Helicopter Applications

In this article, we exhibit an order reduction output-feedback attitude stabilization scheme for 2-degree-of-freedom (2-DOF) helicopters by considering system nonlinearity and parameter variations in the controller and observer design tasks. As the first merit, the proposed observer for the angular velocity contains the disturbance estimation mechanism as a subsystem assisting the main estimator, which is independent of the system parameter information. As the second advantage, the resultant observer renders it possible to design an improved proportional-derivative-type controller that includes the active damping term and nonlinearly structured design parameters, reducing the closed-loop system order to 1. The Quanser 2-DOF helicopter system experimentally validates the practical merit of the proposed technique.