Practical implementation of dual purpose no voltage drives for bearingless motors

Practical implementations of the power electronics required to operate bearingless machines with so-called 'dual purpose no voltage' (DPNV) windings are proposed. These windings enable a bearingless machine to use the same coils to produce both radial suspension forces and torque, which has been shown in the literature to enable better machine performance. In this paper, the use of two-level inverters is investigated for the two configurations of DPNV windings: the 'parallel' and 'bridge' configurations. The investigation is valid for conventional p±1 pole-pair bearingless motors (i.e. bearingless permanent magnet and induction motors) and p = 1 bearingless motors (bearingless ac homopolar and consequent-pole motors). The advantages and disadvantages of each configuration are explored in terms of control complexity and required hardware; potential paths for circulating currents are identified along with mitigation strategies; and experimental results are presented to validate the proposed power electronic implementation.