"Peak Efficiency" Control Mode?

General topics and discussions about the VESC and its development.
devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 29 Aug 2017, 06:40


rew
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Re: "Peak Efficiency" Control Mode?

Postby rew » 29 Aug 2017, 18:38

Yes.

devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 29 Aug 2017, 19:42

This is the way I conceptualize what is happening at no load rpm and how it involves the drift velocity.

At no load rpm, if we choose the spinning rotor magnets as the "stationary" frame of reference, then both the stator winding copper & the copper's free electrons have kinetic energy relative to the "stationary" rotor magnetic moment reference frame at no load rpm. At this RPM, if the voltage applied by the battery is 50V, the back voltage (Back EMF) caused by the relative motion of the free electrons through the rotor magnetic moment is also 50V in the opposite direction, leading to 0w electrical in the copper winding and no net rotor acceleration.

At stall @ 100% duty cycle in a copper wye motor, if the battery voltage is doubled, the drift velocity of the electrons is doubled, but their kinetic energy (& electrical wattage) is quadrupled. As a result of this quadrupled kinetic energy & doubled drift velocity at stall, the windings must have 4 times as much kinetic energy relative to the "stationary" reference frame of the rotor magnetic moment in order for the battery voltage to equalize with the back emf voltage resulting in net 0 watts and net 0 acceleration at no load rpm (& exactly 4 times as much rotor kinetic energy equates to exactly 2 times as much rotor velocity).

^Thus, doubling the battery voltage (or halving the number of turns) doubles the rotor's rpm at no load rpm.

Addy
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Re: "Peak Efficiency" Control Mode?

Postby Addy » 30 Aug 2017, 00:22

Not sure why you're trying to think of this in terms of drift velocity. Current is a simpler concept to think about instead of drift velocity.

To maximize efficiency like you're talking about you would have to keep the motor at the speed at which it is the most efficient, and that speed is determined by how the motor is wound / constructed. I don't think you could dynamically change that. You could perhaps limit the motor speed to keep the efficiency high, but a lot of people do this manually by not blasting around at full throttle all the time.

For the question of aluminum vs copper windings, for the same wire gauge and number of turns, aluminum would have a higher resistance, which would reduce the maximum current of the motor and reduce the maximum speed, so the kV rating would not be the same.

rew
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Re: "Peak Efficiency" Control Mode?

Postby rew » 30 Aug 2017, 07:46

If you keep talking about kinetic energy in electrons, one day I'll calculate that kinetic energy for you. It's going to be less than you expect. For all practical purposes the kinetic energy in the electrons is zero. You should also stop talking about 100% duty at stall.

The hobbyking motor I linked simply allows 1.5V of effective voltage above the BEMF. So if the rotor is stalled, you're allowed 1.5V or 3% duty cylce (at 50V battery voltage). If the rotor is doing 150RPM, (1V BEMF) you're allowed to do 2.5V or 5% dutycycle.

devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 30 Aug 2017, 09:38


devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 31 Aug 2017, 16:36


rew
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Re: "Peak Efficiency" Control Mode?

Postby rew » 01 Sep 2017, 12:17


devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 01 Sep 2017, 18:42


devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 01 Sep 2017, 22:35



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