Implementation of the Generalized Complementary Flux Constraint for Low-Loss Active Magnetic Bearings

This paper explores the experimental issues associated with the implementation of the recently developed generalized complementary flux constraint (GCFC) flux-biasing scheme on a spacecraft reaction wheel that is magnetically suspended by a low-loss active magnetic bearing (AMB). Implementation of the GCFC depends fundamentally on the ability to estimate the electromagnet flux. Once addressed, other fundamental issues including the synthesis of a (possibly time-varying) bias flux and the realization of the state-dependent, voltage-switching rule that imposes the GCFC are studied. Significant filtering is required to obtain clean flux measurements and avoid spurious voltage switchings. Open-loop tests experimentally verify that the voltage-switching rule imposes the GCFC flux constraints on the operation of the electromagnets. A passivity-based control algorithm is used to illustrate the closed-loop functioning of the GCFC in large-bias and zero-bias modes of operation to demonstrate the effect of the bias flux on the closed-loop bearing stiffness, damping, and flux slew-rate.