3rd order harmonic distortion with PM alternator

[hogshead]

I have fashioned permanent magnet alternators with air cores and with iron cores. The air core units generate a sine wave (or something close to it), but the iron core units have third order harmonic distortion, (see waveform). Why is this?

 

[jim hardy]

it would be interesting to integrate that voltage wave. Result will be the flux.
That would probably answer your question.

A simple integrator can be easily made with just a series resistor-capacitor, with time constant long compared to period of your wave.
Observe fvoltage across capacitor and add gain to correct for attenuation of the RC filter.

Remember your flux peak is at the voltage zero crossing.

Then remember your Fourier.
Anything that distorts the waves symmetrically, ie shapes top and bottom as in a mirror reflection, is an odd harmonic.
Asymetric distortion is even harmonics.
That's why tube guitar amplifiers sound different than op-amp guitar amplifiers. Good ears pick up on the different overtones.

old jim