Re: permanent magnet AC synchronous motors from China
The optimal waveform for an AC motor's coils depends on both how the
windings are positioned, and how the iron is shaped. The easiest way to
see the optimal waveform for a given motor is to spin it as a generator,
and look at the waveform it generates.
Let's say you have a 2-pole motor. As you go in a circle around the air
gap between rotor and stator, the magnetic field produced by the rotor
magnets is all North poles for half of the circle, and all South poles
for the other half. If we "unwrap" these poles and lay them
horizontally, you get something like
NNN...SSS... (one complete revolution)
As they rotate, these magnetic poles pass each wire in the stator once
per revolution. Passing the North pole raises the voltage; passing the
South pole lowers the voltage. Passing the gaps leaves the voltage constant.
If the strength of the magnetic field is the same across the pole faces,
and the width of the gaps between poles is the same as the with of the
poles themselves, then you get this kind of waveform.
/ \ /
/ \ /
This is called a trapezoidal waveform.
To make it more square, you make the poles very narrow and the gaps
between the very wide. This waveform is easy for the electronics to
produce, but hard on the motor because all the magnetic flux is