LUT-based IPMSM Reference Block: Flux-Weakening Id/Iq Too High vs MotorCAD (R2025a)

Issue: PMSM FOC – Flux Weakening Region Current Optimization

I’m using Motor Control Blockset (R2025b) for FOC of a PMSM and facing mismatches in flux-weakening operation compared to MotorCAD/MCIS data.

• Motor setup: 5 pole pairs, Rs = 0.01125 Ω, Ld = 178 µH, Lq = 224 µH, flux = 0.03696 Wb, Vdc = 100 V.
• At low speed (MTPA region): MATLAB’s Id/Iq match MotorCAD well (e.g., 60 Nm @ 1000 rpm).
• At high speed (FW, e.g., 15 Nm @ 7000 rpm): MATLAB selects much higher |Id|, leading to phase currents ≈ 154–161 A, while MotorCAD optimizes at ≈ 96 A. This results in significantly higher copper losses and lower efficiency.
• Tried:
• Single-data model (constant Ld, Lq, flux) → overestimates FW depth.
• LUT-based model (imported MotorCAD Ld/Lq/Flux maps with mcbGenerateTables, idiqLUTs, vclmt method) → closer, but still higher currents vs MotorCAD’s MTPV points.
• Verified constraints (current circle, voltage ellipse, torque hyperbola).

Ask:

How can I configure the PMSM Control Reference block (or supporting functions) to follow MotorCAD’s minimum-current MTPV trajectory in the FW region? Is this a modeling limitation, or do I need custom optimization (e.g., using Model-Based Calibration Toolbox or MotorCAD-MATLAB co-simulation)? Any examples or best practices for accurate FW LUT import would be very helpful.

[Raghunath Rachabattuni]

Hi Adhavan, good to hear from you. If you can share the motor data (for the Ld, Lq and FluxPM tables) and the operating points that are being considered and the corresponding id iq from the other tools, we can have a detailed look. Please feel free to email me directly.

[Raghunath Rachabattuni]

Please note that it would help to create a technical escalation to enable easy data sharing.

[adhavan d]

Down load file and convert this format with extension.

PMSMSpeedCurrentsFcn.p

Royal_LUT_F_Based_Model.slx

RoyalE_LUT_Based_Data.m

Runfile_Royal_LUT_Based.m

Please keep this file PMSMSpeedCurrentsFcn.p whereyou run slx ,.m file in same folder

1.Open and run RoyalE_LUT_Based_Data.m.store all data in workspace.

2. open Royal_LUT_F_Based_Model.slx file

3. finally run file of Runfile_Royal_LUT_Based.m

Answer 1

[Raghunath Rachabattuni]

Hi Adhavan, Thanks for the response. I assume this is the same data as what was shared in the technical escalation. More details are given in the response. To summarize the response, the black star (marked using MotorCAD data) is outside the voltage limit ellipse. Although this point is within the current limit circle, the reference current values given by MotorCAD are not valid under these conditions of operating voltage and speed.

You can read more about the voltage limit curve here: PMSM Constraint Curves and Their Application - MATLAB & Simulink Example

The red star is marked using reference currents from "LUT based PMSM Control Reference" from MCB (Motor Control Blockset). The small deviation from the ideal point is due to the descritization of the speed and torque grids and the resulting interpolation.

Also, if you follow the response to the escalation, you may notice that LUT based PMSM Control Reference block's outputs are with lower current magnitude (compared to MotorCAD's data) even at the other operating condition (1000 rpm, 60Nm).

MCB supports importing the FEA data from electrmagnetic simulation software to derive optimal currents. MCB provides a turn-key solution to most common use-cases while MBC (Model-based Calibration) toolbox caters to more advanced/complex use-cases which involve temperature variations, and efficiency-based optimization, and gives more control to the users. For simpler cases such as the one presented, outputs from MCB and MBC workflows are identical.