Levitation and torque control of internal permanent magnet type bearingless motor

A general solution for levitation control applicable to permanent magnet (PM) synchronous and induction type rotating motors is presented. Levitation force is generated by the superposition of P+2 or P-2 pole magnetic flux with the usual motoring magnetic flux (pole number P). PM synchronous motors have the advantage that the control of rotation and levitation are independent, however, the levitation force is weak. Conversely, induction motors produce a strong levitation force, but their efficiency is poor and the control of rotation and levitation are coupled. This paper introduces an internal permanent magnet (IPM) type bearingless motor which has the merits of strong levitation force and relatively easy control properties. A simple experimental apparatus is made to confirm the properties of the proposed motor. The results obtained are discussed in detail.