Brushless Permanent Magnet Motor Design - 2nd Edition - Duane Hanselman

smallest value of n that satisfies (9.20), describes the relative harmonic frequency of the cogging torque.

• The middle of the left hand page shows a cross section of the motor design.

This figure illustrates the relative dimensions of the design.

• The bottom of the left hand page contains motor winding information. The table shown identifies each coil in each phase. The coil angle describes the relative angle of each coil in a given phase. This information is used to compute the winding factor Kwn. As described in Chapter 6, for each phase, In and Out describes the slot number and direction for each coil making up each phase winding.

• Motor back EMFs are shown at the top of the right hand page. The figure depicts the phase back EMF e }lh (0) (6.11). In addition, the figure shows the line-to-line back EMF, which appears across two windings when the phases are connected in the Y-connection as shown in Fig. 8-6. In all designs, the back EMF amplitudes are normalized by the peak value of the line-to-line back EMF. • The relative harmonic content of the phase back EMF eph(0) is shown in the middle of the right hand page. That is, the amplitude of the higher harmonics in epft(8) are shown relative to that of the fundamental component at harmonic index n=1. For example, if the third harmonic is shown at a level of 20%, then the third harmonic has an amplitude 20% of that of the fundamental. This plot provides information about back EMF harmonic distortion.

• At the bottom of the right hand page, the amplitude of the winding factor Kwll (6.13) as a function of harmonic index is shown. This distribution describes how the harmonics of the coil back EMFs add when all coils are connected in series.

Notes • Not all valid combinations of magnet pole and slot counts are considered.

• Some performance data exhibits slight variability because the tooth body width and rotor and stator yoke widths have not been iteratively adjusted to produce identical magnetic circuit reluctance factors.

• The designs illustrated are simply that—illustrations. They may be good starting points for actual designs, but they are not necessarily optimal in any way.