Bearingless PM-synchronous machine with axial active magnetic bearing fed by zero-sequence current

Abstract

A novel inverter supply for bearingless PM-synchronous motors with magnetic suspension allows the reduction of the number of power electronic switches. Hence, all six motional degrees of freedom of bearingless AC machines may be controlled via 3-phase inverter topologies. In this paper, instead of a bearingless motor consisting of two half motors, one bearingless motor with an additional radial active magnetic bearing is treated. Bearingless machines with cylindrical rotors in contrast to double cone rotors generate – apart from the electromagnetic torque – only radial magnetic forces. Hence, an axial magnetic bearing is used.For this bearing, there is no need for a feeding converter bridge as the bearing coil is fed by the zero-sequence current of the feeding 3-phase inverters. The bearing coil is placed between the two star points of the motor winding. The zero-sequence current amplitude is adjusted by the 3-phase inverters via pulse width modulation. The feasibility of this kind of axial position control is proven by simulation as well as with an experiment with a 1\xa0kW prototype motor up to 60000\xa0min−1.