The PMSM Current Reference Generator block is implementing equations for both MTPA and FW. However, this approach may not always provide a solution. The equations for the two modes are given in the documentation page:
When no feasible solution can be found it usually means that the algorithm was not able to find a pair of currents (id,iq) that would satisfy the voltage constraint for the given parameters. Sometimes increasing the nominal voltage will help. Depending on the machine under test, the constant parameters Ld, Lq, psim might make it impossible to find a solution. In a real system machine parameters will have some variations related to magnetic saturation and other phenomena (at different d-q currents will have different parameters).
I hope this helps.
