Understanding ESC

[PowerRocks]

For brush less is the ESC basically a VFD? Or is it a fixed frequency output with variable RMS voltage per half cycle? ie PWM

If PWM why did esc not go the VFD way? Theoretically if you could adjust frequency and peak voltage you could adjust torque at any speed.

I hope that question makes sense, else I did a bad job putting my thoughts down to words. I am an engineer, drives and power are my specialty. In industry all I see is induction motors and control of induction motors.

I have learned how to do theoretical calculations on synchronous, induction and DC motors. I know that the inrunner brushless is a variation of a synchronous motor with a permanent magnetic field on the inside as opposed to having to create a magnetic field on the inside using coils and brushes. Now can anyone point me in the direction so I may obtain formulas to do calculations on a brushless setup.

So far I think what I said is right, someone please correct me if I'm wrong. I'm not even a year out of school, but when in school motors, drives, and power were my favorite subjects.

For those who don't have a great grasp of the various types of motors and drives here is a website you should definitely study. The professor there is definitely a guru. http://www.ece.ualberta.ca/~knight/
His notes and animation definitely make understanding the concepts a whole lot easier.