Active magnetic bearings

Background

Compared to roller bearings active magnetic bearings provide some interesting advantages:

  • contact free; means no friction, wear or lubrication
  • low-maintenance
  • allows for very high rotating speeds.

These come along with some disadvantages compared to roller bearings, such as higher costs, a higher size ratio caused by the control- and power-electronics and the lower specific bearing capacity. Furthermore auxiliary bearings are needed in case of a system failure.

Approach

The mechatronic system active magnetic bearing already contains information about the rotor displacements and the bearing forces in form of sensor signals. Hence the system calls for the implementation of additional functions besides its basic function ‘bearing of the rotor’. Examples for additional functions are:

  • determination of the balancing quality
  • active unbalance compensation and isolation
  • adaption of the systems dynamic on the operating conditions
  • determination of the systems transfer behavior during operation
  • online fault detection and diagnosis

Current Research

Magnetic bearings offer the possibility to estimate the rotor position required for the control out of the electric currents of the bearings. This functional integration of the position sensor by an extension of the software leads to a considerable cost saving. An expensive position sensor is no longer required. Furthermore the installation space of the position sensors is eliminated and the important property of collocation is inherently given.

With regard to a system failure, backup bearings are examined with a focus on fast-rotating rotors with high surface speeds. Reliability and durability are research goals. The technical limits are analytically and experimentally investigated and design improvements are derived.