Q:

Do stator windings on a permanent-magnet synchronous three-phase ac motor have sinusoidal distributions?

In motor-drives textbooks (e.g Ned Mohan's Electric Motor Drives), the text states that the stator windings on ac machines (e.g. PMAC three-phase motors and induction machines) are, in theory, sinusoidally distributed in the air gap. That is, the conductor density as a function of the mechanical angle (for a two-pole motor) can be written 
$$ n_s(\theta)=\frac{N_s}{2} \sin(\theta) $$
where \$N_s\$ is the number of turns. This is not possible in practice due to the slots, but it is approximated.
Is this true for modern PMAC motors ? If we consider one of the three phases, are there more conductors per angle at 90 and 270 degree angles from the magnetic axis than there are at f.ex 60 and 120 degrees ? I tried to find photos, but could not so easily see this...

A:

Yes:
A PMAC motor has an (approximately) sinusoidally distributed stator winding to produce sinusoidal back EMF waveforms. (Similarly a 3-phase AC induction motor does as well).
A "brushless DC" motor intended for six-step commutation may have trapazoidally distributed windings.
A good summary is Here
An interesting graphical representation with animation is Here

