Feedforward Control for Disturbance Rejection: Model Matching and Other Methods

Feedforward control can improve disturbance rejection performance of a system when the measurement of the disturbance is available. This paper discusses the design of feedforward control in the discrete-time domain using the model matching methods that compute optimal and stable feedforward controllers. It is shown that the existence of a non-zero solution to the model matching problem depends on the difference between the relative degrees of the plant dynamics and the disturbance dynamics. A number of approximate dynamic inversion techniques commonly used for feedforward control design are reviewed and compared with the model matching methods. These feedforward control design methods are then applied to the application of an example tape head track-following servo system where the feedforward controller aims at reducing the position error caused by the lateral tape motion. Simulation results are presented to demonstrate the effectiveness of the feedforward control.