Fault tolerance of homopolar magnetic bearings

• Published in: Journal of sound and vibration Vol. 272; no. 3; pp. 495 - 511
• Main Author: Na, Uhn Joo
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 06.05.2004; Elsevier
• Subjects: Exact sciences and technology; Fundamental areas of phenomenology (including applications); Physics; Solid mechanics; Structural and continuum mechanics; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...); Orbit; Rupture; Magnetic force; Numerical method; Coil; Constrained optimization; Fault tolerance; Lagrange multiplier; Load capacity; Magnetic bearing; Permanent magnet; Power amplifier; Actuator
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/S0022-460X(03)00379-1

This paper develops the theory for a fault-tolerant, permanent magnet biased, homopolar magnetic bearing. If some of the coils or power amplifiers suddenly fail, the remaining coil currents change via a novel distribution matrix such that the same magnetic forces are maintained before and after failure. Lagrange multiplier optimization with equality constraints is utilized to calculate the optimal distribution matrix that maximizes the load capacity of the failed bearing. Some numerical examples of distribution matrices are provided to illustrate the new theory. Simulations show that very much the same dynamic responses (orbits or displacements) are maintained throughout failure events (up to any combination of 5 coils failed for the 8 pole magnetic bearing) while currents and fluxes change significantly. The overall load capacity of the bearing actuator is reduced as coils fail. The same magnetic forces are then preserved up to the load capacity of the failed bearing.