Asymptotic rejection of a class of periodic disturbances in nonlinear output-feedback systems

Asymptotic rejection of periodic disturbances whose basic wave patterns can be described by odd functions is considered. This class of disturbances covers asymmetric waveforms in a half-period such as sawtooth waveforms, as well as disturbances with symmetric half-period waveforms such as sinusoidal and triangular disturbances. The systems considered can be transformed to a nonlinear output-feedback form. The amplitude and phase of the disturbances are unknown. The newly proposed half-period integration technique is used to estimate the unknown disturbances in the systems, together with observer design techniques to deal with nonlinearity. The proposed control design with disturbance estimation asymptotically rejects the unknown disturbance, and ensures the overall stability of the system