"Peak Efficiency" Control Mode?

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

Postby markorman » 05 Sep 2017, 06:55

First of all stop posting this graph, which has nothing to do with 3 phase BLDC or PMSM motors.

rew
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Re: "Peak Efficiency" Control Mode?

Postby rew » 05 Sep 2017, 07:34


pf26
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Re: "Peak Efficiency" Control Mode?

Postby pf26 » 05 Sep 2017, 09:01

@devin: your graph assumes the motor torque/current decreases linearly with RPM, which is obviously a wrong assumption in all practical applications. RPM and torque/amps can both be varied depending upon the motor load and ESC control parameters. For a given motor, the efficiency varies with both RPM and current. Highest efficiencies are obtained at high RPM and moderate currents, and can exceed 90% for good quality motors. At higher RPM, the iron losses become predominant though but motor datasheets generally don't specify this clearly.

devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 05 Sep 2017, 12:24


markorman
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Re: "Peak Efficiency" Control Mode?

Postby markorman » 05 Sep 2017, 13:07

Again your graphs are not for 3-phase BLDC or PMSM motors, which can have efficiency around 90-95%. Don't know where you got your 85% theoretical limit.

If you want to maintain desired speed you need to apply proper torque to counteract all the forces braking you. This torque will be dependent on the load. Depending on the speed and desired torque regulator will set proper duty cycle to achieve this required torque. If your "algorithm" calculates different duty cycle, you will either accelerate (if duty cycle is higher than needed) or decelerate (if duty is lower than needed) since you will apply different torque than needed. In almost all applications, especially in EV's you want to control the speed or the torque.

devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 05 Sep 2017, 14:15


markorman
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Re: "Peak Efficiency" Control Mode?

Postby markorman » 05 Sep 2017, 14:49

Stop thinking about controlling the motor with watts. Nobody nowhere is controlling the motor with watts. The only time you care about watts consumed by motor is when you have to limit the power drained from battery.
Almost are motors are in torque control mode (at least in automotive world) since the torque is the force the motor produces and force you feel when accelerating/decelerating. In BLDC and PMSM motor you have to limit the torque because the mechanical limits, and limits due to current in copper windings.

This is typical graph for PMSM motors. You have to limit the torque (motor current) and then limit the power.

Image

At this is graph for Tesla's model S

Image

Both graphs shows maximum Output the motor can achieve, without destroying it. Torque and current (motor current) have the same shape.

devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 05 Sep 2017, 19:00


markorman
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Re: "Peak Efficiency" Control Mode?

Postby markorman » 05 Sep 2017, 19:31

Well if you think this is better than what all of the industry and automotive field is using go ahead and work with useless watts. But please read more about motor control techniques since i believe you don't understand it and it doesn't look anybody on this forum can explain it to you.

Over and out.

devin
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Re: "Peak Efficiency" Control Mode?

Postby devin » 05 Sep 2017, 19:42



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