A novel approach for rejection of cosine disturbances

In this paper the disturbance rejection problem is investigated for a class of linear systems in a new online disturbance-observer-based control framework. The external disturbances are supposed to be cosine harmonic signal with the known frequency. First for the system without disturbances, an output feedback controller is designed via LMI. Based on Fourier transformation algorithm, a modified algorithm is proposed to compute the harmonic component of the output of the closed-loop control system. By using the phaser method, one can estimate the disturbance excitation signal, and then modify the control signal to reject the original disturbance. If the output also has fluctuation, the rejection procedure can be applied again. Finally, simulations is given to demonstrate the effectiveness of the proposed method.