A feedforward controller by modified series approximation

A new pole-zero cancellation technique using a modified series approximation is proposed for the feedforward controller. The gain of the system with the proposed feedforward controller is close to 1 for up to relatively high frequency. The tracking error of this method depends on the pth-order difference of the desired trajectory. The method is effective when the closed-loop system has unstable zeros in the left-half plane of the z plane close to the unit circle. The tracking errors are analyzed in terms of the location of an unstable zero and the reference trajectory. The effectiveness of the proposed method is shown in the simulation.