FOC library V2.0 Current sense

jgil · ‎2009-04-02

Posted on April 03, 2009 at 05:52

jgil · ‎2011-05-17

Posted on May 17, 2011 at 10:15

Hello

I have a doubt with this topic. I am designing a power driver.

Application note UM0492

IMAX= 3.3/(2*rshunt*Av) Where for the kit MB459B Av=2.57 and rshunt 0.22 ohms.

at another line

Alignment final phase A current = (I_ALIGNMENT * 0.64)/(32767*Rshunt)

where 0.64 = 3.3/(2*2.57)

Application note UM0492

G = s / v = (R + r)/r

The relation between the input signal e and the signal v on the positive input of the follower

is:

v = (U/(k*r3) + e/(k*r1))

where k =(1/r1+1/r2+1/r3)

The resistor values implemented on the MB549B board are:

R=5400Ω \ r=1000Ω \ r1=660Ω \ r2=560Ω \ r3=4700Ω

and

U=5V

Therefore, the gain is:

G = 6.4

Vout = 0.302*6.4 + e*0.431*6.4=e*2.75+ 1.93

The gain is 2.75 instead of 2.57. The software fogui puts es default 2.57.

Is it a error?

The coefficient 32767 I think that it is because the A/D justifies the conversion to the left side not?

I need to clarify it.

Thank you

jgil · ‎2011-05-17

Posted on May 17, 2011 at 10:15

Sorry.

The second application note is UM0379 not UM0492

ok

stello · ‎2011-05-17

Posted on May 17, 2011 at 10:15

Hello,

you are right, the right Av should be 2.75. In fact, due to some problem in the layout of the MB459B board, we've measured an Av of 2.57.

The coefficient 32767 is because this is the maximum value for all the software variables containing the motor current info.

Cheers,

Billino