Reduced-order implementation of disturbance observers for robust tracking of non-linear systems

The disturbance-observer-based control (DOBC) is a well-known robust control scheme and recently its non-linear version has been developed. Observing that two components (so-called Q-filters) in the conventional DOBC structure have the same transfer function, the authors propose a reduced-order DOBC for uncertain non-linear systems. It is shown that the proposed controller also guarantees the same robust transient response as those developed before. Numerical simulations using a magnetic levitation system are included to illustrate the detailed design procedure and validate the performance of the proposed controller.