Environmental Engineering Reference
In-Depth Information
configuration shows that the two rotor discs have been phased such that the flux
linkages in the stator are diminished. The net voltage induced into the stator coils is
the vector sum of voltages due to flux from each rotor disc magnet, but the flux
linkages are now out of phase, resulting in lower net induced voltage, hence the
equivalent of field weakening. The conceptual lever arm shown at the right in
Figure 5.32 is meant to illustrate a mechanical cam and spring assembly that
actuates the rotor disc phasing.
As a point of reference, this technique can be traced back to work performed
by Dr Izrail Tsals,
c.
1989, while he was with the PA Consulting Group, High-
tstown, NJ. Dr Tsals later joined the Arthur D. Little Company in Cambridge, MA.
In a mechanical field weakening scheme devised by Dr Tsals, the two layers of
permanent magnets in a drum machine were phased in a manner very similar to the
scheme illustrated in Figure 5.32. Mechanical springs and counterweights attached
to the rotor hub were used to effect field weakening by masking off magnet flux as
speed increased.
5.3.4 Multilayer designs
Single buried layer IPM designs were the first to be implemented and put into
production for white goods, industrial use, and electric and hybrid vehicle propul-
sion. Many investigators have since implemented various multilayer designs in
which the magnets are inserted into radial cavities separated by soft iron and sup-
ported by iron bridges and posts. In some of this work, it has been reported that
torque was improved by 10% and the high efficiency contour was also expanded by
10% when the total rotor magnet volume was held constant [25].
Figure 5.33 illustrates the improvement over a single buried magnet layer, total
magnet volume constant, ferrite magnets are used. The test machines were 3-phase,
4-pole, 24-slot IPM designs having 60 mm rotor OD, a 0.5 mm mechanical airgap
and remanence of 0.42 T and 280 kA/m (3.5 kOe) coercivity.
210
180
Double layer
Single layer
93%
90%
0 2 4 6 8 10
Speed (krpm)
Figure 5.33 Multiple layer IPM machines for battery electric and hybrid
propulsion
The power curve for the single and double layer designs considered here are for
x >
2 so that high speed power is somewhat lower than peak power at the corner point
