Challenges with Delta Wound Motor in Torque Control: Seeking Guidance on MTPA Reference Block for reference Id and Iq generation.

I have a quick question that I hope the community can help me with. I'm working on a torque control model with a delta wound motor and I'm using the 'MTPA Reference' blok or 'IPMSM Control Reference' block for generating Id and Iq references. However, I'm facing an issue where the Id and Iq reference values generated by these blocks do not follow the MTPA curve/Flux Weakeing curve, except for the first operating point which is on MTPA curve.

Here's some additional context: I'm using Ld, Lq, and flux values obtained from electromagnetic software specifically designed for delta motors. Strangely, these blocks work perfectly when I use them with other star-connected motors in torque control.

I'd greatly appreciate it if anyone could shed some light on why this discrepancy might be occurring. If I'm unable to resolve this issue, I'm also in the process of creating my own Id and Iq references. However, I'm struggling with determining the base speed and Flux weakening zone. Does anyone have any reference materials or advice that could assist me in this endeavor?

Thank you in advance for your help! Please look at the attached images for more clarity !!

Answer 1

[Darshan Pandit]

hi aditya,

you may refer to following paper for reference where authors conclude that Any delta connected motor can be analysed in terms of its star equivalent for dynamic studies.[1]

The block you're referring to, will work correctly when either star wound motor parameters are used or MTPA & FOC are implemented to control an equivalent star connected motor for your delta would motor. You can use the parameter estimation tool to find the Ld & Lq parameters for an equivalent start connected motor and use them in your studies.

If you wish us to have a details look at the model, please contact us and we have a team who would be glad to help you out.

Hope this helps.

Have a good day.

[1] P. Pillay, R.G. Harley, E.J. Odendal, A comparison between star and delta connected induction motors when supplied by current source inverters, Electric Power Systems Research, Volume 8, Issue 1, 1984, Pages 41-51, ISSN 0378-7796, https://doi.org/10.1016/0378-7796(84)90032-4.

[Aditya]

Dear Mr. Pandit,

I trust you are doing good.

I wanted to extend my heartfelt gratitude for your swift response. Your generosity in answering my questions is greatly appreciated. Unfortunately, I currently lack some of the necessary toolboxes to execute the model. The process of generating Ld, Lq, and flux parameters using an equivalent star-connected motor for a delta-connected motor is a new concept for me. If it's okay, I plan to initiate a service request via the 'Contact us' link that you kindly provided. I will make sure to keep you informed about the progress of this endeavor - If you are able to hop on the call with them, that would be great! It would be nice to get some facetime with you and clarify my questions, but if you're busy, I will make sure to keep you updated here!

Once again, thank you for your kind assistance!

[Darshan Pandit]

Sure aditya. you're welcome.

[Aditya]

Thank you! I have created a service request - case# 06468049. How do you suggest I proceed?!

[Darshan Pandit]

thanks. Our team will get in touch with you.

Answer 2

[Raghunath Rachabattuni]

Hi Aditya,

In addition, check the following link for using delta parameters for a motor plant model.

One of the options (the last one) for the plant model selection includes 3-phase switching inverter with Delta-wound pmsm.

This should give you a direction to conduct your simulations using the delta-wound motor's data. You may also include LUT based PMSM Control Reference block or MTPA Control Reference block in the model.

The related example file's name is mcb_ee_pmsm_foc.slx

This selection is available in R2022b onwards.

Model Switching Dynamics in Inverter Using Simscape Electrical - MATLAB & Simulink Example (mathworks.com)

Best,

RaghuNath

[Aditya]

Hello Raghu,

I wanted to express my appreciation for your prompt response and for sharing the example model. I had the opportunity to look into it, and it aligns with my own model albiet mine is a simpler version of the example. Following your suggestion, I incorporated the 'MTPA Reference' block and 'IPMSM Control Reference' block into the example model. However, when I input Ld, Lq, and flux values for a delta motor, I encountered an issue where it didn't generate reference Id and Iq values that align with the MTPA or Flux weakening curve.

I'm aware that these blocks may not be suitable for Delta motors. Do you happen to know of any other blocksets or methods that support Delta motors for Id and Iq generation?

Once again, thank you for your invaluable assistance!

[Raghunath Rachabattuni]

I hope you correctly used the mcbGenerateTables and the resulting output into the Delta-wound PMSM plant model. Did you use the function as it was used in the example file?

[Aditya]

I did! I do not have star equivalent motor parameters, I believe that is what I need to find out to input in my FOC model. I understand that the mcbGenerateTables has two use cases: star2star and star2delta and it works by giving inputs of star equivalent (Ld, Lq, Rs, and flux) and depending on the two cases, I would get either star or Delta (Rs, fluxD and fluxQ) values for my FEM motor. All my Ld, Lq and flux are for a Delta motor - so can you tell me how will this help me out? Is my understanding of this wrong?

[Raghunath Rachabattuni]

As communicated over the emails through techSupport, in your calculations you did not consider voltage constraints while computing the id iq operating points. This results in assuming all the points to be on the MTPA line. However, in reality, with the voltage constraints in place, the points are along the torque line, as predicted by the LUT based PMSM Control Reference block. From the constraint curves that were shared with you, you can observe this. In this case, the delta or star winding configuration doesnt matter. Only the Ld and Lq values matter.

For more ways to plot the constraint curves, you can go to the following link:

PMSM Drive Characteristics and Constraint Curves - MATLAB & Simulink (mathworks.com)

Best,

RaghuNath

[Aditya]

Dear RaghuNath,

I want to express my gratitude for your assistance with this matter. Thanks to your help, I successfully plotted the constraint curves and was able to validate the results sent to me by your tech support - But are the Voltage limit curves plotted for a 'DELTA' wound motor? The website that you have referred me to seems to calculate 'Vmax' for a 'STAR' wound motor since we are dividing V_dc by SQRT(3) to get Phase-Peak. My understanding of DELTA motor is V_dc = line/phase Peak. (I have attached a screenshot of the segment).

Is my understanding of this correct? And if so, is there a way for me to change the connection to 'DELTA' wound in the 'mcbPMSMCharacteristics' code to get the right voltage limit curves?

Thank you once again for your invaluable assistance!

Sincerely,

Aditya Sai