Total efficiency of a deeply buried permanent magnet type bearingless motor equipped with 2-pole motor windings and 4-pole suspension windings

Various kinds of permanent magnet type bearingless motors, which can be characterized by integration of permanent magnet synchronous motors and magnetic bearings, have been proposed and developed. These motors can realize magnetic suspension of rotor shafts by themselves without mechanical contacts or lubrication. However, these motors cannot generate suspension force effectively, because suspension flux necessary for generating suspension force passes through permanent magnets which have large magnetic reluctance. Accordingly, a novel deeply-buried permanent magnet type bearingless motor with 2-pole motor windings and 4-pole suspension windings has been proposed by the principal authors. In the proposed motor, the suspension flux does not pass through the permanent magnets. Thus, it was shown that the proposed motor can generate suspension force effectively in previous papers. In addition, it was confirmed experimentally that the proposed motor has the desired characteristic of high total efficiency considering suspension input power at rated speed. However, irrespective of the proposed motor, no studies have ever tried to make clear the total efficiency of the bearingless motors in wide speed range to the authors' knowledge. Therefore, this paper introduces the total efficiency of the proposed motor in the wide speed range, along with loading test results of a prototype motor.