Adaptive compensation of sensor runout for magnetic bearings with uncertain parameters: Theory and experiments

The problem of sensor runout in magnetic bearing systems has been largely o verlooked due to similarities with mass unbalance in creating periodic dist urbances. While the effect of mass unbalance cart be significantly reduced, if not eliminated, through rotor balancing, sensor runout disturbance is u navoidable since it originates from physical nonconcentricity between rotor and stator. Sensor runout is also caused by nonuniform electrical and magn etic properties around the sensing surface. To improve performance of magne tic bearings, we present an adaptive algorithm for sensor runout compensati on. It guarantees asymptotic stability of the rotor geometric center and on -line feedforward cancellation of runout disturbances using persistent exci tation. Some of the advantages of our algorithm include simplicity of desig n and implementation, stability, and robustness to plant parameter uncertai nties. The stability and robustness properties are derived from passivity o f the closed-loop system. Numerical simulations are presented to demonstrat e efficacy of the algorithm and experimental results confirm stability and robustness for large variation in plant parameters.