FAULT-TOLERANCE OF MAGNETIC BEARINGS BY GENERALIZED BIAS CURRENT LINEARIZATION

The mathematical basis for bias linearization of quadratic magnetic ac tuators, as typified by magnetic bearings, is developed. The approach generalizes prior ad hoc methods of linearizing the relationship betwe en actuator force and electromagnet current, obviating the earlier ass umptions of stator symmetry. This relationship is fundamentally quadra tic in the regime where the magnetic material is unsaturated and flux is essentially proportional to magnet current. Growing from the proper ties of a fundamental representation for the current-force relationshi ps in magnetic bearings, conditions are determined under which lineari zation may be possible. A numerical optimization problem is posed whos e solution provides a linearization scheme which maximizes the availab le force capacity of the actuator. A corollary result is a method for obtaining coil-fault tolerant in magnetic bearings without adding coil s to existing actuators. Several paper examples are presented to illus trate linearization of asymmetric actuators, actuators with failed coi ls, and force/moment actuators.