said by Guspaz:
I'm not disagreeing with that, just pointing out that it's not a square wave
I was not disagreeing with what you said either, just pointing out that there is no "low/medium/high", it is alternating rectangular pulses, all or nothing in either direction.
low/medium/high (multiple output levels) sounds more like what a triangular approximation UPS would be doing. These used to be somewhat common about 10 years ago but are largely forgotten today.