Author Description

"Preface Unknown disturbances originating from various sources exist in all practical controlled systems, where unmodeled dynamics and uncertainties can also be formulated as an equivalent disturbance. As such, disturbance attenuation and rejection for nonlinear systems is a challenging objective in the area of control. Analysis and synthesis for non-linear control systems with disturbances has been one of the most active research fields in the past few decades. There are several drawbacks to be overcome in future studies on non-linear antidisturbance control. First, in engineering applications, the disturbance may originate from various sources and can be described by a composite form rather than a single variable. In this case, the H8 control may be too conservative to provide highly accurate control performance. On the other hand, disturbance rejection approaches usually need precise models for both the controlled system and the disturbance system. This confines their applications since the disturbance is also described by a single output variable from a precise exo-system and robustness is difficult to guarantee. For example, although disturbance observer based control is a valid disturbance rejection strategy for non-linear systems with harmonic disturbances, the performance of the system will deteriorate if the disturbance model cannot be described precisely. In filtering problems, both external noises, measurement noises and structure vibrations, and also unmodeled, nonlinear and uncertain dynamics are usually merged into the disturbance variable."--