Adaptive cancellation of sinusoidal disturbances for unknown stable plants

The design of a local adaptive output feedback compensator is addressed to reject biased multiple sinusoidal disturbances of unknown amplitude, phase and frequency, acting on an unknown stable single-input single-output linear or nonlinear system. Sufficient conditions on the phase uncertainty of the system transfer function at the frequencies contained in the disturbance are provided, which lead to the compensator design. This result is generalized to the case of stable nonlinear systems.