code to change the motor amp limit

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devin
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Re: code to change the motor amp limit

Postby devin » 10 Jun 2017, 07:42


rew
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Re: code to change the motor amp limit

Postby rew » 10 Jun 2017, 10:41

KV is essentially the voltage induced when using the motor as a generator. The voltage in each turn depends on the change in magnetic flux. This is measured at zero current, so there is no drop due to I*R. So the voltage over the motor is Nturns * <stuff that depends on the motor> * rotation speed.

devin
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Re: code to change the motor amp limit

Postby devin » 10 Jun 2017, 17:10


devin
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Re: code to change the motor amp limit

Postby devin » 15 Jun 2017, 22:33

Image

devin
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Re: code to change the motor amp limit

Postby devin » 27 Jun 2017, 19:05

[post removed by author]
Last edited by devin on 28 Jun 2017, 17:38, edited 1 time in total.

devin
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Re: code to change the motor amp limit

Postby devin » 28 Jun 2017, 17:37

I made a mistake in the drawing of the wye motor stator magnetic field vectors yesterday....

If one looks closely at yesterday's overlay of the rotor and stator fields it becomes apparent that not all of the energized stator phases would contribute to rotor torque in the same direction.

So I re-drew & I believe this stator magnetic field vector drawing and stator/rotor magnetic field overlay more accurately represent the proper field vectors at one point in the rotor's rotation:

Where:

Red Area = Phase "A" -- Energized
Green Area = Phase "B" -- Energized
Blue Area = Phase "C" -- Not Energized
Black Line = 12 Pole Wye Stator Magnetic Field Vectors w/ 2 Energized Phases
White Line = 14 Pole Rotor Magnetic Field Vectors

Image

Image
Commutation Sequence Source: http://m.eet.com/media/1179124/bldc2tab1.jpg

Image

Image
Wye Diagram Source: the internet

Image

devin
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Re: code to change the motor amp limit

Postby devin » 29 Jun 2017, 00:10

Just finished the Delta version of the stator magnetic field vector diagram...

Image

Image

Image
Delta Diagram Source: the internet

Image

...notice all 12 stator teeth are energized and generating rotor torque in the same (clockwise) direction.

rew
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Re: code to change the motor amp limit

Postby rew » 29 Jun 2017, 07:50


devin
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Re: code to change the motor amp limit

Postby devin » 04 Jul 2017, 03:12

Last edited by devin on 04 Jul 2017, 08:48, edited 1 time in total.

rew
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Joined: 25 Mar 2016, 12:29
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Re: code to change the motor amp limit

Postby rew » 04 Jul 2017, 07:10

A full sine cycle is 2*pi. So a third of that is 2/3 PI

Phase A is energized with the voltage: Va = Vs * sin (f * t + 0*2/3PI);
Phase B is energized with the voltage: Vb = Vs * sin (f * t + 1*2/3PI);
Phase C is energized with the voltage: Vc = Vs * sin (f * t + 2*2/3PI);

here Vs is the "duty cycle" dependent voltage scale. and f is the RPM (in the proper units).

Now the question is: what does it mean that a phase is energized with a voltage: We can only drive either to V+ or to V-?

Well, when the target voltage is 0, we alternate the highside and the lowside switch in a 50/50 fashion. 50% PWM. So now by varying the PWM percentage we can apply (effective) voltages anywhere between -Vbat/2 to +Vbat/2.


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