Base impedance of velocity feedback control units with proof-mass electrodynamic actuators

Rohlfing, J., Gardonio, P. and Elliott, S.J. (2010) Base impedance of velocity feedback control units with proof-mass electrodynamic actuators. Brennan, M.J., Kovacic, Ivana, Lopes, V., Murphy, K., Petersson, B., Rizzi, S. and Yang, T. (eds.) In Recent Advances Structural Dynamics: Proceedings of the X International Conference. University of Southampton. 12pp .

Abstract

Control units comprising a proof-mass electrodynamic actuator and accelerometer-sensor pair with a time integrator and fixed gain controller are an effective way to implement velocity feedback control on panels. The control units produce active damping provided the fundamental resonance frequency of the actuator is well below that of the structure under control. Control stability limits arise from the actuator fundamental resonance which introduces a 180° phase lag in the control unit response, thus causing the feedback loop to be only conditionally stable.

In contrast to previous studies, this paper discusses the response of the control unit in terms of the open and closed-circuit base impedance that it exerts on the structure. This allows for a straight forward physical interpretation of both stability and control performance. Experimental and simulation results show that the base impedance can be described as the sum of passive and active frequency response functions, where the active part of the control unit response depends on the actuator dynamics and also on the response of the analogue controller circuit.

It is demonstrated that the control stability could be enhanced by implementing an appropriate compensator that shifts the fundamental resonance of the control units towards lower frequencies.

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