Environmental Engineering Reference
In-Depth Information
Comparison of machine types
Brushed-dc
IPM
SPM-dc
SPM-ac
VRM
SREL
IM
0
20
40
60
80
100
Torque (Nm)
Figure 5.26 Relative ranking of machine types based on peak torque
( from Reference 21)
In Figure 5.26 the IPM machine compares very favourably with the surface PM
designs operating with sinusoidal flux (ac) and trapezoidal flux (dc) for a fixed
frame size and total electromagnetic volume. The torque for these designs is given
in absolute terms.
Torque ripple is a major consideration in hybrid propulsion and must be
included in any comparison of machine types. In Figure 5.27 the corresponding
torque ripple is plotted, again from data presented in Reference 21.
Comparison of machine types
Brushed-dc
IPM
SPM-dc
SPM-ac
VRM
SREL
IM
0
20
40
60
80
Torque ripple (%)
Figure 5.27 Machine comparison based on output torque ripple
( from Reference 20)
It is much clearer from the discussion above and by reviewing Figure 5.27 that
the IPM machine has the torque ripple character of a VRM, since it in essence is a
reluctance machine. This characteristic has significant bearing on its application in
hybrid propulsion not only because of its high ratings but also because driveline
inertia will suppress torque ripple to be a minor issue. But the fact remains that
IPMs still have more torque ripple than brushless ac machines and certainly more
ripple torque than an IM.
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