Voltage Characteristics of a Consequent-Pole Bearingless PM Motor With Concentrated Windings

A bearingless permanent magnet (PM) motor combines functions of non-contact magnetic suspension and torque generation together, thus it can drive without mechanical contact. Unlike conventional bearingless PM motors, such as a surface-mounted PM motor, a consequent-pole type of bearingless PM motor has inherent advantages. It can regulate the radial rotor positions independently of the motor drive and has no tradeoff between radial suspension force and torque. In the consequent-pole bearingless PM motors, distributed or concentrated windings can be employed to the motor winding structure. However, relationship between voltage characteristics and the winding design has not yet been revealed. In this paper, the induced electromotive force (EMF) of the consequent-pole bearingless PM motor is numerically calculated on the basis of the magnetic flux distribution in the airgap around the rotor. It is found that the EMF is distorted by the second harmonic at a specific slot number in a consequent-pole rotor. The calculated EMFs are confirmed with the experimental results in the fabricated test machines.