Hi, reducing the id will effectively bring down the stator-rotor flux linkage. This results in reduced torque output in some conditions. However, this is subjected to the voltage constraint at the given operating speed. To understand the relevance of id and iq in optimal operation of the motor, we need to consider the constraints, and then try to derive the optimal currents for the given operating point(speed and load torque).
The following link explains the relationship between id, iq and the operating points. It also explains meaning of all the PMSM constraint curves.
All the computations that are shown in the above link are also to be done for a non-linear motor (with core saturation). The block "LUT based PMSM Control Reference" considers both linear and non-linear behavior of the motor and the computes the optimal reference currents. These id iq LUTs can be used in simulation, or code-generation also when this block is used in the Simulink model.
This block considers not only MTPA operation of the motor, but also includes Field-weakening region, and MTPV (deep field weakening) region too.
Hope this helps.
RaghuNath
