A brief tutorial overview of disturbance observers for nonlinear systems: application to flatness-based control

The paper presents a brief overview of the most popular disturbance estimation techniques together with their application to flatness-based control. Two disturbance estimation approaches, the basic disturbance observer and the extended state observer, are described in a tutorial manner. Positive and negative aspects of both approaches are pointed out. Open research questions on disturbance estimation are presented. In the second part of the paper it is demonstrated how to integrate disturbance estimation into flatness-based control. The basic feedback linearization based approach, but also a novel event-based approach for differentially flat systems, are described. It is shown that disturbance estimation can be integrated easily into both of these control approaches. Finally, the results are demonstrated on three models: a heating, ventilation and air-conditioning; an active magnetic bearing; and an underwater vehicle models.