Influence of Neutral Line to the Optimal Drive Current of PMAC Motors

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

I. Introduction

From the point of view of quantity, a permanent magnetic (PM) AC (PMAC) motor with surface mount PM rotor (SM-PMAC motor) is more popular than other types of PMAC motors. The spindle motor used in hard disk drive is the typical SM-PMAC motor, and the motor with nine slots and six magnetic pole-pair is shown in Fig. 1. for this kind of motor, in linear state, the winding inductance is independent of the rotor position; therefore its and are the same [1]. A concern is how to realize the optimal current in a SM-PMAC motor in many applications.