# What is the relationship between feedforward control and bandwidth?

This is a control theory question, but because there is no control theory stack exchange, I thought this was the closest appropriate location:

I've been studying feedforward control system designs, specifically motion stages that use acceleration feedforward control. In this control system, a control signal is generated based on changes in the command signal (as opposed to relying solely on feedback control).

My question, what does feedforward typically do to the system response bandwidth? If done correctly, I would assume it increases the bandwidth? Say for example the feedforward controller is designed as the inverse of the plant, is there a proof that illustrates that bandwidth is increased?

Furthermore, most feedforward control setups combine feedforward control with feedback control. In this scenario, how does the bandwidth between a feedback system and feedback-feedfoward system compare? Assume feedforward control is used in the sense of creating a command signal that attempts to compensate for changes in the reference command.

• Not sure, but I think robotics.stackexchange.com would also be a good place to ask. I personally agree that Control theory questions be asked here, however. – rrz0 Jan 3 '18 at 17:01

Positive acceleration feedback is used to reduce the effective inertia in the system, thereby increasing $\omega_n$ and increasing bandwidth. Check this out with a simple 2nd order system, where positive acceleration feedback will reduce the $s^2$ coefficient in the TF denominator.