A Comparison between Current and Flux Control in Magnetic Bearing Systems

A comparison between current and flux control in magnetic bearing systems is made. The system dynamics were modeled in two different forms. In the first form, the magnetic force and electric circuit equations were expressed in terms of airgap flux and gap displacement. In the second form both equations were expressed in terms of coil current and gap displacement. A controller was designed using the Q-parameterization theory and CONSOLE [14] (an optimization software developed at the University of Maryland) to stabilize the system which without control is unstable in nature. The time and frequency responses for both models were compared. The comparison is based on the same values of the respective controller Q-parameters. The results show that magnetic bearing systems can have better performance if they are modeled using airgap flux.