With the success of feedforward techniques, feedback control researchers have begun to explore the relationship between these two control paradigms. The goal of the present paper is to further investigate the relationship between feedforward and feedback control techniques by means of the classical Bode integral constraint on achievable performance. These results provide insight into the phenomenon of spillover which has been widely discussed in the vibration control literature. Specifically, it is shown that a particular feedforward controller called the zero spillover controller avoids spillover by producing perfect disturbance cancellation at every frequency. For readability, we derive the approximate zero spillover controller which is shown to be an optimal feedback controller for an LQG problem with suitable cross weights. Finally, the results are illustrated by means of analytical and numerical examples.

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