Pardon me if this question covers too many elements;

I am not yet informed enough to fully comprehend what would be the important parameters which must be matched for such a system to work, which is based on:

An internal combustion petrol engine, whose output shaft drives a BLDC generator, which in turn generates power for a BLDC motor.

Essentially, what is confusing is that I find information regarding BLDCs that they are actually (perhaps only some of them; but the ones I was looking at) 3-phase AC motors which then have rectifiers to change AC to DC (if a generator), or a converter to transform DC input power to 3-phase AC, if used as a motor. Also, as far as I understood, to power the correct sequence of coils, if using a DC power from a battery, an ESC electronic speed controller is necessary.

So, would a Petrol>Generator>Motor setup be possible without such power conversion (directly 3-phase AC from the generator to the motor) and without electronic speed controllers?

[That is, if the petrol engine has a throttle, would that be sufficient as a means of controlling how much power the generator is providing to the electrical motor, therefore directly controlling the electrical motor power output, by the speed of the petrol engine? Or do the generator and motor have to be identical for that to work, that is, which parameters need to be matched between them? The kV of the electric generator and motor (RPM/V)? or maybe their rated RPM, or pole numbers, need to be the same?

I was trying to understand this setup with the following example parameters:

Engine: 2-stroke petrol

  • 35kW @ 6000 RPM

Generator: BLDC permanent magnet synchronous motor (PMSM), axial flux, sinusoidal three-phase, out-runner

  • 33kW @ 6000 RPM, 120V

Motor: BLDC PMSM, in-runner

  • 33kW @ 8400 RPM, 120V

the generator efficiency at the mentioned RPM is 90-96% depending on torque, but let’s ignore the efficiency for the sake of clarity.

So, what I would be very grateful to understand, is what are the requirements for this system to work properly when starting the petrol engine & changing its speed/power?

Thank you

  • $\begingroup$ I expect the diesel/electric locomotive industry has worked out the best solutions to your questions . $\endgroup$ Dec 6 '20 at 20:56
  • $\begingroup$ @blacksmith37 true, the locomotive applications is where the drivetrains most often employ CE-electric transmissions; although I was wondering more about the schematic perspective, and the underlying rules of motor physics; perhaps I should post this question in electrical engineering site $\endgroup$
    – ivanantuns
    Dec 6 '20 at 21:03

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