Get power supply current from 3-phase current (BLDC)

Thread Starter

Laphrase

Joined Jul 8, 2019
3
Hello all,
My question is quite similare as this post :
https://forum.allaboutcircuits.com/threads/how-to-add-3-phase-currents-for-total.51874/#2
The problem is that I could not reply on this post because it is too old, and it does not really answer the main question of the topic. So here I go:

Scope:
I use a BLDC motor controlled by the Space Vector Pulsed Width Modulation (SVPWM) driving method.
The motor is 3-phases Y configuration.
I have a 3 current sensors on each 3 phases (The sum of the 3 values are equal to 0).
I do not have a current sensor on the power supply line.

Problem:
What I would like to get is the value of the current given to the motor from the power supply. I can not find the relation between the current I measure on the phases and the current of the power supply.

My hypothesis:
I get the maximum current value over the 3 phases and apply a coefficient to compute the input current. But if I change the motor, this coefficient does not fit anymore. So maybe there is a relation with the motor parameters (Impedance, inductance ...)

Do you have any idea to guide me please.
 

MaxHeadRoom

Joined Jul 18, 2013
19,400
Keep in mind that although a BLDC motor generates a 3phase sinusoidal voltage, for motor operation, only two winding's are energized at any one time.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
19,400
That is not by definition a BLDC motor, although a 3 phase synchronous motor or SVPWM is virtually identical, in the 3ph version it is fed with 3phase, in the BLDC version only two windings energized at any one time.
Max.
 

Thread Starter

Laphrase

Joined Jul 8, 2019
3
Yes I agree, this is the shape of the current on all the phase:
PrrcB.png

So all the power supply current flow from one phase to the other (the 3rd is idle). Why this phase current is not the image of the power supply current ?
 
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