Institute of Space and Astronautical Science Achievable Robustness Comparison of Position Sensed and Self-Sensing Magnetic Bearing Systems

Two options for the control of a magnetic bearing system are considered and compared for achievable robustness. The first of these, the position sensed configuration: uses a measurement of the position of the rotor for feedback. The second configuration, the self-sensing configuration, attempts to achieve closed-loop stability and robustness using only a measurement of the electromagnet coil currents. We derive limits, independent of the choice of linear. time-invariant controller, on the achievable robustness in each case. We also consider how these limits change with changing bearing physical parameters as well as closed-loop system bandwidth and controller relative degree. Finally, we consider an example magnetic bearing system in order to determine the magnitude of these bounds for a real system.