Environmental Engineering Reference
In-Depth Information
compares the efficiency of the mechanical field weakening method with that of
electronic field weakening IPM. There are obvious mechanical disadvantages with
a scheme such as that shown in Figure 5.30 (such as lubrication, striction, unba-
lance and oscillation if not properly damped).
100
90
Mechanical
80
70
Electronic
Speed
Figure 5.31 Efficiency comparison of mechanical versus electronic field
weakening
The second mechanical field weakening method has been more recently
described [24] for which a mechanical spring and cam assembly is employed to
shift the relative position of the magnet discs in an axial flux permanent magnet
(AFPM) machine. Figure 5.32 illustrates the cam and spring mechanism as well as
the implementation on an AFPM rotor.
Rotor
Stator
Rotor
Phasor
Low speed
Rotor
Stator
Rotor
Phasor
High speed
Figure 5.32 Cam spring method of mechanical field weakening ( from
Reference 23)
In this mechanical field weakening scheme, the airgap flux density is not
altered, so no mechanical work is done by the rotor phasing. The cam and spring
mechanism need only phase the two rotor sections as a function of mechanical
speed to realize field weakening. Output regulation due to loading will, of course,
need to be accomplished using electronic controls. In Figure 5.32 the high speed
