Performance enhancement of a class of nonlinear nonminimum phase systems by adaptive observer

An adaptive observer scheme for the estimation of unknown disturbances in a nonlinear nonminimum phase time-invariant, single-input single-output control system is proposed. It is assumed that the disturbances are generated by a system with unknown parameters, which are identified by the adaptive observer. The design is based on coprime factorization of the plant model over the ring of stable rational functions. Comparison between adaptive observers for strictly positive real plant and the proposed scheme is shown, as well. The stability of the overall system is proved. The effectiveness of the proposed scheme is verified through simulation examples