I'm playing with the brushless motor controller from my flying toy, and I see what they're doing and I'm curious if the technique has a special name, other than just PWM. It's a 3 phase DC motor. To send a pulse to each coil, instead of one DC pulse they're actually sending a bunch of smaller DC pulses, to simulate a sine wave I think. Perhaps to make the motor run smoother than if they sent one bigger pulse. It reminds me a little bit of a Class-D audio amplifier. To make the motor spin faster they shorten the time between the smaller pulses, which makes the groups of pulses arrive faster. To change the power output they're changing the duty cycle of the individual little pulses, like regular PWM. It's also interesting that instead of pulsing high, they raise the voltage high and pulse low. I'm guessing because N-channel MOSFETs tend to be more efficient than P-channel (less heat)?
I copied some screen shots below. I only have a 2 channel scope, but you can see the phasing of the groups of pulses between the coils. Ground reference for my scope is the negative on the power supply.
Slow:
Fast:
Slow (low power):
Fast (high power):
I copied some screen shots below. I only have a 2 channel scope, but you can see the phasing of the groups of pulses between the coils. Ground reference for my scope is the negative on the power supply.
Slow:
Fast:
Slow (low power):
Fast (high power):
It's wrapped up in shrink wrap and feels like it's potted. Google shows me that there are IC's specifically for controlling brushless DC motors, for example: 
