Originally Posted by
SystemTheory
Access,
These diagrams show DC/Battery voltage on VBus, and six control signals to the transistors. This suggests PWM signal is integrated with the frequency modulation signal within the phase control signals.
(Just saw your waveforms as I posted this question, maybe it is resolved there, check on it later).
If PWM is 100% at 70% throttle, does that mean 30% of the throttle is not accelerating the motor to greater rpm, or that frequency modulation takes over to enable further acceleration?
Yes, the same MOSFETs that do the phase switching can naturally also do the PWM. There are 3 phase wires and the ESC has to be able to connect each of those phase wires (through the digital switches / MOSFETS) to either +V or GND.
With brushed the only way the ESC could control the speed of the motor was to vary the PWM duty cycle. Any PWM duty cycle other than 100% causes switching losses which means less efficiency. With brushless the ESC has more tools with which to control rotor speed, like variable forward advance / phase switching speed. So the idea in designing an ESC to work efficiently is to get to 100% PWM as early as possible and then to control farther acceleration with the latter two. Forward advance is important because coils do not 'turn on' or 'turn off' instantly, the inductance is a factor.
You also have Back-EMF in the picture and I'm honestly not exactly sure how that fits in or is properly modeled.