Performance recovery of nonlinear model helicopter using extended high gain observer

Nonlinear control methods are difficult to work on an unmanned helicopter system for its inherently unstable, high-order, and cross-coupled dynamic characters. In order to use experienced linear control methods on nonlinear helicopter system, in this paper, approximate feedback linearization method is used to linearize the nonlinear helicopter system by neglecting the coupling term. Then, we introduce an extended high gain observer to estimate the outputs and their derivatives for rejecting the coupled disturbance. Combining this observer and any linear control strategy the nonlinear helicopter system would be not only to achieve stabilization or regulation, but also to shape the transient response. The main contribution of this method, comparing with other exiting high gain disturbance rejection methods, is in proving transient performance recovery and not just asymptotic stabilization or regulation. Based on the method proposed in this paper, a nonlinear helicopter can be converted into an easily controllable linear system.