FEEDBACK STRUCTURE-BORNE SOUND CONTROL OF A FLEXIBLE PLATE WITH AN ELECTROMAGNETIC ACTUATOR: THE PHASE LAG PROBLEM

Abstract In this paper an experimental study is presented on active control of a clamped plate at audio frequencies by using feedback controller and electromagnetic actuator. The controller is designed with modern control theory on a lumped parameter model of the plate, and is then implemented in experiments to control the real structure. In practice, the optimal control force cannot be generated exactly as desired due to the non-ideal characteristics of the control system. Several factors such as A/D and D/A convertors, velocity estimation through approximate differentiation, and the electromagnetic actuator are examined in respect to their frequency features. An analytical model is developed to predict the phase lag of the actual control force to the designed control force. It is shown that if the phase lag is over 90 degrees, the control system will become unstable. Two techniques are discussed for improving the system performance that is mainly affected by the electromagnetic actuator when the high speed sampling and processing device is used as the controller. The simple and practical method is to employ a phase-lead compensation network in the control circuit. Another one that is more fundamental is to incorporate the characteristics of the actuator into the system by feeding back the current passing through the actuator into the controller. Various experiments are carried out to verify the analysis and the proposed methods, and the potentials of the electromagnetic actuator in controlling the high frequency vibration and noise are therefore demonstrated.