A Wide Bandwidth Model for the Electrical Impedance of Magnetic BearingS

Magnetic bearings are often designed using magnetic circuit theory. When these bearings are built, however, effects not included in the usual circuit theory formulation have a significant influence on bearing performance. Two significant sources of error in the circuit theory approach are the neglect of leakage and fringing effects and the neglect of eddy current effects. This work formulates an augmented circuit model in which eddy current and flux leakage and fringing effects are included. Through the use of this model, eddy current power losses and actuator bandwidth can be derived. Electrical impedance predictions from the model are found to be in good agreement with experimental data from a typical magnetic bearing

An Appraisal of Power-Minimizing Control Algorithms for Active Magnetic Bearings

Active magnetic bearings consume much less power than conventional passive bearings, especially when power-minimizing controllers are employed. Several power-minimizing controllers have been proposed, such as variable bias controllers and switching controllers. In this paper, we present an appraisal of the power-minimizing control algorithms for active magnetic bearings in an attempt to provide an objective guideline on the merits of the control algorithms. In order for the appraisal, we develop an unified and consistent model of active magnetic bearing systems. The performances of the power-minimizing controllers are assessed through this model. The results show that the power-minimizing controllers indeed save considerable power when the machine state is relatively steady. However, a simple proportional-derivative type controller is on a par with the much more complex powerminimizing controllers in terms of power consumption when the machine is experiencing transient loads

Self-Sensing Magnetic Bearings Driven by a Switching Power Amplifier

Active magnetic bearings require some form of control, based on feedback of the position of the suspended object, to overcome open--loop instability and to achieve targeted system performance by modifying the bearing dynamics. In many applications of magnetic bearings, a need to eliminate discrete position sensors may arise either from economic or reliability considerations. Magnetic bearings which estimate the position from the information available in the electromagnet signals are referred to as "self--sensing"

A wide bandwidth model for the electrical impedance of magnetic bearings

Magnetic bearings are often designed using magnetic circuit\ud theory. When these bearings are built, however, effects not\ud included in the usual circuit theory formulation have a\ud significant influence on bearing performance. Two\ud significant sources of error in the circuit theory approach\ud are the neglect of leakage and fringing effects and the\ud neglect of eddy current effects. This work formulates an\ud augmented circuit model in which eddy current and flux\ud leakage and fringing effects are included. Through the use\ud of this model, eddy current power losses and actuator\ud bandwidth can be derived. Electrical impedance predictions\ud from the model are found to be in good agreement with\ud experimental data from a typical magnetic bearing