Feedfoward control is a strategy of implementing a control action based on some known disturbance to minimize the effect of that disturbance on the process variable. The Feedfoward effect bypasses the closed loop PID algorithm.
As it's name implies, the disturbance is measured and transmitted, i.e. Feedfoward, ahead of the PID algorithm to add in an Output effect that is summed with the closed loop PID algorithm. The summation of the closed loop PID output and the Feedfoward equation is then transmitted to the final control output.
Feedfoward Requirements:
- The disturbance must be measurable
- You must know in how much that you wish to move to Output based upon the disturbance, i.e. Knowledge of the process.
- You must know in what direction to move the Output based upon the disturbance.
Feedfoward control can result in closer control by eliminating the influence long before closed loop PID can, because the PID loop can not react until after the error is measured. Since the effect of Feedfoward is a "Open Loop system", i.e. no feedback, it is never perfect and it's effect should be used with caution.
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