Remember that we are working in deviation variables. Assume that we are not making a setpoint change, so r(s) = 0. Since we do not want the output variable to change, that is equivalent to saying that we desire y(s) = 0. From Equation (10.6) we can see that the only way to assure y(s) = 0 is for the following relationship to hold

Equation 10.7

In this expression all the transfer functions are determined for a particular system, except for the feed-forward controller, g_{cf}(s). Solving Equation (10.7) for g_{cf}(s), we find

Equation 10.8

If we make the simplifying assumption that the disturbance measurement has ...

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