I am struggling with the calculation of the motor flux for a RPX22-042V24 PMSM. I know back EMF, Torque constant and several other values from the datasheet. But I found different ways to calculate the flux and I am not sure if its correct to use back EMV in V/kRPM or V/RPM.

With the equation at the end of this page I get a flux of 4.15 mWb. Does this value make sense for this parameter?

  • \$\begingroup\$ I found two ways for calculating the magnetic flux of a motor, but the results are very different. Maybe someone knows why? Option 1: According to the formula in the end of this page de.mathworks.com/help/sps/ug/… flux1=Kt/N=16.6mNm/A/4pole pairs=4.15mWb with Kt = torque constant Option 2: According to the formula from the SPMSM page de.mathworks.com/help/mcb/ref/surfacemountpmsm.html flux2=(2/3)*Kt/N=(2/3)*16.6 mNm/A/4pole pairs=2.77mWb The flux's unit is in both cases correct but whats the reason for the factor2/3 \$\endgroup\$
    – hanss
    Commented Sep 19, 2023 at 10:20
  • \$\begingroup\$ This was helpful, do you have any literature where we can establish a relation between Motor speed and phase current at constant load? \$\endgroup\$
    – AK47
    Commented Apr 17 at 6:15

1 Answer 1


If anybody faces the same problem:

In my case the datasheet's values must be converted from line to line to phase values and the formula for flux1 is for a BLDC. For a PMSM the formula for flux2 = (2/3)*Kt/N=(2/3)*16.6 mNm/A/4pole pairs suits better. The other one (via back-EMF) proposed in the link can also be used with a slightly different result.



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