The University of Southampton
Engineering and the Environment

Research project: Compensation filters for feedback control units with proof-mass electrodynamic actuators

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Proof-mass electrodynamic-actuator and accelerometer-sensor pairs with time integrator and fixed gain controller are an effective way to implement velocity feedback control, where stability limits arise as a result of the actuator fundamental resonance. In contrast to previous studies, in this project the response of such a control unit is discussed in terms of its open and closed-circuit base impedance, which can be expressed as the sum of passive and active frequency response functions, where the active part depends on both the actuator dynamics and the response of the analogue controller. It is demonstrated that the control stability could be enhanced by implementing an appropriate control compensator.

Project Overview

Control units comprising proof-mass electrodynamic-actuator and collocated velocity-sensors are an effective way to implement feedback control. Above the actuator fundamental resonance frequency such control units produce active damping on the structure where they are mounted. Control stability limits arise as a result of the actuator fundamental resonance, which introduces a 180° phase lag in the control unit response below this resonance. When the control unit is mounted on a flexible structure, this results in a circle in the left-hand plane of the Nyquist plot of its open loop response function, thus causing the feedback loop to be only conditionally stable.

Two important factors for the control stability are the internal damping, which determines the sharpness of the actuator response at resonance, and the ratio between the fundamental resonance of the actuator and that of the flexible structure on which they are mounted.

This project investigates the design of a compensation filter that shifts the apparent fundamental resonance of the control unit towards lower frequencies and also restricts the actuator peak response at this design frequency.

The response of a control unit with proof-mass electrodynamic-actuator is expressed in terms of the open and closed-circuit base impedance that it exerts to the structure. This base impedance can be described as the sum of passive and active frequency response functions, where the active term depends on both the actuator dynamics and the feedback control law including the complex frequency response function of the compensator. These formulations allow for a straight-forward physical interpretation of both stability and control performance.

Aim of the project is to investigate and demonstrate how the control stability and control performance may be improved by implementing an appropriate phase compensation filter.
CollaborationsThis research is part of the 'Green City Car' project which is funded by the European Union within the SEVENTH FRAMEWORK PROGRAM, THEME 7, ‘Sustainable Surface Transport’, Project Reference: SCP8-GA-2009-233764

Related research groups

Signal Processing and Control Group

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