No feasible current reference found on PMSM Current reference Generator

Hi,In my model,When I apply [ 1000 2000 3000 ] these speed,The results PMSM Current reference generator works.But When I have set Speed value in Rpm on PMSM Current reference generator. [ 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 ] and Torque in Nm [ 0.48 0.53 0.60 0.68 0.79 0.95 1.19 1.59 2.38 4.76 ] and Voltage in Volt [ 36 40 48 52 ] in Automatically generated lookup table.It shows no feasible current reference found.For 3000 rpm & 1.5 Nm ,It takes -1.5 A id and 30 Iq Amp.

My Question is is PMSM Current reference generator block working in Field Weakening mode for IPMSM.

Answer 1

[Sabin]

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:

https://www.mathworks.com/help/sps/ref/pmsmcurrentreferencegenerator.html

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.

[adhavan d]

Hi ,

I don't know how to select the constant parameters Ld, Lq, psim for The PMSM Current Reference Generator block.How to Select Constant parameters Ld,Lq,psim,Rs for all Condition(Speed,Torque,Voltage).

[Sabin]

The Automatically generated lookup table is only accepting constant machine parameters and that may be a possible reason why no feasible solution can be found. As an alternative you can check the LUT based PMSM Control Reference in Motor Control Blockset or generate the references offline using your own strategy and then use the lookup tables in the PMSM Current Reference Generator.

[Aditya]

Dear Sabin,

Thank you so much for the reply. I have used 'LUT based PMSM Control Reference' block for torque control, I have attached a picture of the block here. Although I have one question regarding the inputs for the block, namely:

When I give my feedback speed in rad/s as input to the block, my torque demand is met, but when I give my feedback spped input as rpm, torque demand is not me. (Documentation on the block says to give the input reference speed in rpm.)

Also, when my feedback speed is in rad/s, my output id and iq values are very close to the values got in my speed control model (using 'MTPA Control Reference') for the same motor parameters.

Any clarifications on this from your end would be a big help! Thank you!!

[Sabin]

The unit of inputs to the LUT based PMSM Control Reference can be in PU or SI. By default it is Per-Unit and the base speed is 4107 rpm. If you have rpm speed probably better to use SI units in the 'Input units' tab.

[Raghunath Rachabattuni]

Hi Aditya, the units for wm input port of the block are rad/s (mechanical). Thanks for pointing out the doc typo, it will be corrected soon.