Approximate feedforward control

Disturbances are inevitable in most control systems. They drive the systems away from their set points. It takes time for feedback control to reject them. The feedforward control offers great potentials for regulation performance if the disturbances are measurable. One obstacle for feedforward control implementation is that the theoretical one is unrealizable for various reasons. In this paper, a new feedforward control design approach based on frequency response approximation is proposed and performs much better than the existing method in the literature. A performance measure is defined to assess if the feedforward control can outperform feedback control alone and analytical conditions are derived to determine such a measure a prior. Simulation is presented for illustration of our method.