Disturbance Observer Based Sliding Mode Controller Design for Large Civil Aircraft

Abstract

The design and application of a disturbance observer based sliding mode controller for a linearparameter-varying model of a large aircraft is presented in this paper. A reason why sliding mode control has seen increased interest is its insensitivity to matched uncertainty. The application presented here utilises this property together with the controller’s nonlinearity to provide a degree of robustness to changes in flight conditions over an aircraft’s wide flight envelope without resorting to gain scheduling. It was found that the direct application of sliding mode control resulted in control surface chattering. This was resolved via the implementation of a disturbance observer that treats the mismatch between nominal and actual flight conditions as external disturbance. The estimate was used to compensate for the real disturbance. This resulted in a reduction of the nonlinear controller gain, which in turn decreased the magnitude of chattering. The improvement have been made evident via a comparison between the time domain performance of the original sliding mode controller and the disturbance observer based controller.