Compensated phase method of current for reducing torque ripple of multi-degree of freedom surfaced permanent-magnet motor

In this paper, the torque characteristics of multi degree of freedom surfaced permanent-magnet motor (multi-D.O.F. SPM) are introduced. The multi-D.O.F. SPM can rotate a shaft while the rotor tilts to one side. To decrease the torque ripple, the locus of summed wave forms of motor driving current have to be in an ellipse. Because the axis of electro motive force is generated by many numbers of currents as considering rotor position, the currents have different phase while the rotor is tilting. Therefore the phase of each current is defined as function of rotor position as using compensated phase method in this paper. The modified current is verified by comparison of analytic simulation results to experimentation results.