Power Optimal Current Control Scheme for Bearingless PM Motors

Bearingless motors offer new possibilities in drive technology and open up new design approaches to applications where conventional bearings can hardly be employed. However, especially for low power applications a very cost-effective and highly efficient motor design is desirable. In this paper a current control scheme is presented that ensures operation of the bearingless motor with minimized resistive power losses. Moreover, for motor designs where all the winging systems are used both for radial force and torque generation this control scheme may also ensure production of arbitrary radial forces and torque even if the sum of the phase currents is equal to zero. As a result, star connection of the motor phases is possible and hence the number of required power switches for driving the motor can be reduced.