During the last three decades, several active damping strategies have been proposed, based on the so-called passivity concept, or equivalently, on the power port concept. One of them, known as Integral Force Feedback (IFF) is reviewed in this paper. Actually, the main drawback of the IFF is that high active damping is obtained at the cost of a degradation of the compliance at low frequency, compromising the capability of disturbance rejection. Classically, a trade-off between damping and stiffness can be reached by adequately high pass filtering the control signal. However, the high pass filter poles and zeros often interfere with the plant dynamics, which in turn compromises the guaranteed stability of the IFF. In this paper, a novel type of high pass filter is proposed. It is shown that this modification makes the controller unconditionally stable, and increases drastically the achievable modal damping. Analytic formulas are derived, and illustrated using simple numerical models. The characteristics of the proposed controller are discussed in terms of maximum modal damping and transmissibility.
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