[JAC314] Torque Analysis of an SPM Motor Using a Halbach Array

Overview

SPM motor designs strive to maximize the average torque and minimize the torque ripple to mitigate vibrations. Selection of the right orientation direction for the magnets can improve the average torque and torque ripple characteristics.
A Halbach array is one example for orienting the directions of magnets in an SPM motor. The Halbach array is a unique magnet arrangement that produces a smooth sinusoidal distribution of magnetic flux by orienting the magnets in a helical pattern. JMAG can use magnetization patterns to set the orientation direction of the magnets without running a magnetization analysis (simulation used to magnetize non-magnetic materials).
This case study sets the magnetization pattern for a Halbach array to a two-dimensional SPM motor, and then compares it against a standard magnet arrangement. The results demonstrate that a Halbach array provides at least equivalent torque and a lower torque ripple than a standard magnet arrangement.

Magnetization Pattern Settings

Table 1 outlines the magnetization pattern settings.
Fig. 1 presents the magnetization direction for the [Number of Divisions per Pole] settings. One division per pole matches the existing parallel pattern (circular direction) when [Number of Divisions per Pole] is set to 1.
The magnetization direction varies more consistently as the number of divisions per pole increases.

Torque Characteristics

Fig. 2 illustrates the torque waveform for each magnetization pattern. The torque waveforms can show whether a magnetization pattern helps suppress torque ripple. Table 2 outlines the average torque and torque ripple rate of each magnetization pattern. All three cases using a Halbach array have an average torque of at least 53.7 compared to the average torque of 52.7 for the existing parallel pattern (circular direction). We can also see that a higher number of divisions per pole increases the average torque. The torque ripple drops to 0.138 or less when using a Halbach array compared to 0.541 for the existing parallel pattern (circular direction). This equates to an at least 40% reduction in the torque ripple. These results indicate an SPM motor using a Halbach array can significantly decrease the torque ripple while maintaining the average torque.