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

#### Laphrase

Joined Jul 8, 2019
3
Hello all,
My question is quite similare as this post :
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.

Joined Jul 18, 2013
27,657
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.

#### Laphrase

Joined Jul 8, 2019
3
I am using a H-bridge with SVPWM. So There is always current flowing in the phases.

Joined Jul 18, 2013
27,657
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.