Influence of neutral line to optimal drive current of PM AC motor

The optimal drive current (ODC) can reduce the torque ripple and power loss of the permanent magnetic AC motor (PMACM). The paper presents an analytical model for calculating the optimal drive current of the PMACM with surface mount PM rotor. Both the motors with and without the neutral line are analyzed. Analysis shows that, when the back-emf of the windings contains trip-order harmonics, the neutral line can let the ODC be different from the one without the neutral line, and it can also make the ODC be more effective in loss and torque ripple reduction. Two spindle motors used in Hard disk drive are used to show the effectiveness of the optimal model presented.