SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

phase winding of Figure C.4 will have coilsides of all three phases in each slot. When a slot is
occupied by coilsides from only two phases—such as in Figure C.7-b—the winding is said to be a
double-layer winding. According to one motor designer, the double-layer lap winding is the most
common winding in brushless permanent magnet motors [68, p.130]. The other windings can be
similarly checked for practicality by adding the other phases. The windings of Figure C.5-a and
Figure C.6-a would be double-layer but not all slots would be filled thus these configurations are
not practical. The winding in Figure C.5-b would fill all slots but it would only be a single-layer
winding. These results are particular to the slot and pole configuration of the example. They do
not indicate, for example, that the CFP winding of Figure C.5 always leads to a single-layer
winding with some empty slots. These are all motor design considerations and are not relevant
here but have been pointed out to show how a sinusoidal winding can be approximated by the use
of chorded and distributed windings.
Stator MMF
Per Figure C.1, the impact of the winding function on MMF production is to be studied next. The
total MMF produced by stator current is found by using Ampère’s law which is defined by
Equation (C.3) [44, p.202].
Hdl Ienclosed
path
(C.3)
Assuming the stator and rotor steel have infinite permeability, the magnetic field is confined to
the airgap. Assuming the field is radial and taking advantage of stator symmetry, the integral
reduces to a scalar multiplication of product of H and total airgap length 2·G. A suitable
Ampèrian loop is shown in Figure C.8 with an arbitrary, symmetric conductor distribution; c.f.
[42, p.172], [73, p.9.5].
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