Behaviour and control of an inverter-fed three-pole active radial magnetic bearing

Nowadays active magnetic bearings (AMB) are used as heteropolar ones with three or four pole-pairs. Newer evolutions strive therefore for the commitment of magnetic bearings that can be practiced with traditional three-phase inverters. Such unipolar radial bearing consists of an iron ring with three concentrated poles wounded by magnetic coils. The magnetic field lines are closed over the other poles and the keeper. There exists a radial crossing of the air gaps. For such a unipolar magnetic bearing the sum of all fluxes must be zero. The pole-fluxes and pole-forces are all dependent on the three-phase m.m.f. To project a position control-loop in two axes a strong current- and low position-dependent decoupling are necessary. Further investigations concerning the biasing is discussed which is necessary to linearize the force current characteristic.