Feed Forward Control

Figure 23.9: Feed forward control

On Feed-forward Control

• Due to disturbance in the process, the input X(s) to an actuator may generate an output X(s) D(s) which may destabilize the system.
• In such cases if the input X(s) is passed through a feed-forward compensator C_FF (s), and compared with the output X(s)D(s) then with correct estimation of D(s) one may alleviate the effect of the disturbance on the plant G(s).
• The response of the plant may be sensed by monitoring the signal C(s)H(s). However, such responses are used only to monitor the performance of the filter and not fed back in the loop.
• It has been shown by Hansen et al ([11-3]) that optimal gain of the filter C_FF (s) is
  C_FF (s) = - S _FF -1 S _DF , Where, S_FF denotes the power spectral density of the ref signal X(s) and S_DF is the cross spectral density between the disturbance and the filter output.