Compensation filter for feedback control units with proof-mass electrodynamic actuators, simulations and experimental studies

Abstract

This technical memorandum presents studies on velocity feedback control with an electrodynamic proof-mass actuator. It is demonstrated that the stability and performance of the control unit can be substantially improved by implementing an appropriate open-loop compensation filter. In the simulations the control unit is described in terms of the open and closed-loop base impedance it presents to the structure under control. This allows for a straight-forward physical interpretation of the control system and allows a direct derivation of the expression for the proposed compensator.

Studies on the sensitivity of the compensation to uncertainties in the actuator parameters show that even for considerable variations in the actuator response the compensation filter provides significant improvement over the uncompensated cases. The enhanced control stability which results from a detuning of the control actuator passive mechanical and active electromechanical response allows tuning the control unit mechanical resonance such that actuator acts as a passive vibration absorber, a configuration that would lead to poor control stability if direct uncompensated velocity feedback is applied. One draw back of the compensator is the enhancement of the feedback signal at low frequencies. This may lead to stroke/force saturation of the actuator before the optimal control gain can be implemented. This can be addressed by implementing an additional high-pass filter in the feedback loop, which attenuates the low frequency feedback signal and suppresses measurement noise. However, this has to be balanced with a loss in the control stability due to the additional phase-lead that is introduce. Experimental studies were conducted to validate the simulated control performances and it is demonstrate that the proposed compensator can be used in the design of small scale self contained multifunctional feedback control units.

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