MTPA IN IPMSM Performance

I am trying to inplement MTPA in an Ipmsm.To see the effect of idref decrease. What I did was to limit speed to 2000rpm and gave a load of 14Nm and I manually decreased idref in negative direction to see if performance improves .The reference d current is being tracked however the performance actually deteriorates compared to id=0 control (Efficiency) .The constraints imposed are Speed pi out= Isref.Iqref=sqrt(Isref^2-idref^2)..And vqmax=sqrt(Vsmax^2-Vd^2).Keep in mind all values are in per unit .The Actual Ld=0.000055 lq=0.000014 back emf constant=8.43 vrms/krpm and dc voltage =48V.Is there any other factor which i should consider in the control system to make optimal use of the reluctance torque

Answer 1

[Raghunath Rachabattuni]

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.

PMSM Constraint Curves and Their Application - MATLAB & Simulink Example (mathworks.com)

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.

LUT based PMSM Control Reference - Generate lookup-table-based control reference currents for field-oriented control of permanent magnet synchronous motor - Simulink (mathworks.com)

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