Single-shunt current reading and MAX_CURRENT

Posted on May 17, 2011 at 10:15

Hi Gigi!

in the documentation of the STM3210B-MCKIT

http://www.st.com/stonline/products/literature/um/13031.htm

you can find at page 7 following text:

''In the single-shunt current reading configuration, the current sampling is done only when the value on the shunt resistor is positive. The only positive value read on the shunt resistor allows to set a higher gain for the op-amp than the one set in three-shunt mode.''

So, I think that the current will only be measured when the voltage on the shunt is positive. Are we using a trapezoidal or a sinusoidal control with the ST MC-library? Thank you!

saluti dall'Austria!

Posted on May 17, 2011 at 10:15

Hi Walterma,

In single shunt topology the current flows in both direction in the shunt when the motor is driven sinusoidal.

In case of trapezoidal control the current flows only in one direction.

So using single shunt sinusoidal driving you have to add the offset and read both positive and negative values.

Best regards

Gigi

[ This message was edited by: gianluigi.forte on 11-11-2008 09:11 ]

Posted on May 17, 2011 at 10:15

Hi, I'm using the single-shunt current read method and I'm trying to set the maximal current by setting the constant MAX_CURRENT in MC_State_Observer_param.h

The formula is:

MAX_CURRENT = 3.3/(2*Rs*Av)

Why do you divide by 2 ??? It should be divide by 2 only in a three-shunt topology, or not? In the single-shunt topology you have only to measure positive voltages.

Posted on May 17, 2011 at 10:15

Ciao Walterma

the UM0379 can be generate a little confusion because it refers to a 3 shunt configuration versus a 1 shunt configuration.

It will be better to replace the name ''Three-shunt current reading configuration'' with ''Sinusoidal current reading configuration'' and replace the name ''Single-shunt current reading configuration'' with ''Trapezoidal current reading configuration''

To summarize:

It is possible to use the power board in this way:

1 Shunt Trapezoidal (Set the OP AMP as described in par 3.2) W4 open W5 Closed W10 1-2

1 Shunt Sinusoidal (Set the OP AMP as described in par 3.1) W4 open W5 closed W10 1-2

3 Shunt Sinusoidal (Set the OP AMP as described in par 3.1) W4 closed W5 open W10 2-3

The drive developed for STM32 MC Kit is single or three shunts sinusoidal so you have to select the second or third configuration.

Driving in sinusoidal mode single or three shunt resitor configuration the current in the shunt flows in both directions.

Driving in trapezoidal mode (not supported by the library for the moment) the current flows only in one direction.

Ciao

Gigi