I had an interesting thought whilst I was munching my sandwich the other day. Supposing I have some kind of motor and I feed it a phase to each lead. So, if the 2 leads are 180 out of phase, the motor will run at full power. If the 2 leads are in phase, that brakes the motor because it acts like a short. But if I can adjust one of the phases so it is some other amount then a variable amount of current can flow through the motor. If I do it using a square wave, the current starts to look like an AC version of PWM.
So the question is, is there a useful application for this? Is it actually done anywhere? Or did I just have a sandwich-induced brain fart?