Estimation of single-sinusoidal disturbances using back recursive output-based observer

A novel disturbance estimation approach is presented for a class of single-input-single-output (SISO) systems subjected to single-sinusoidal disturbance with unknown frequency. The exogenous modeled disturbance is represented in a parametric uncertainty form by series of virtual disturbances. Especially the unknown parameter related to disturbance frequency can be reduced to a scalar, and is estimated through construction of auxiliary filter based on system output. Resultantly the observer framework asymptotic stability property can be guaranteed, simulations demonstrate the effectiveness of the proposed scheme.