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rahulpillai
Level 1
Level 1
10 sign-ins First reply posted 5 questions asked

Hi there,

I am confused about the field weakening settings for the IMC controller. It seems like there are two different settings affecting the field weakening controller. 

1. In Solution designer setting-> motor control configuration>Control Regulators, there exists field weakening current limit as well as modulation threshold at which field weakening should get activated.

2. In motor control configuration>FOC and inverter setting, there is an SVPWM Over modulation enable/disable setting. 

How do these two settings work together? In other words, if I disable field weakening in 1 above (by setting current limit to 0%), while disabling over modulation in setting 2, will field weakening controller be activated? If yes, at what modulation will it get activated (linear modulation range is until 86.6% motor voltage)

My observation during testing when I set a field weakening current limit of 10% (I also had SVPWM over modulation disabled) was that when I increased speed of the motor, the 10% limit was not respected.  It is very strange that there is no documentation on the field weakening behaviour of the IMC in the reference or the software manual. Hence, I am forced to ask here.

Further question: In 1 above, is the field weakening current limit, the % of Id current allowed during field weakening?

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1 Solution
SarkarSushru
Moderator
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100 replies posted 10 likes received 100 sign-ins

Hi @rahulpillai ,

  • Enabling SVPWM Over Modulation maximizes DC bus utilization. Disabling SVPWM Over Modulation limits the modulation to the linear range. The Field weakening Modulation Threshold specifies the modulation index threshold to start field weakening. It is recommended to set this value below the SVPWM linear range.
  • What is the percentage deviation of the Id current from the limit value set?

Thanks,

Sushruti

View solution in original post

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5 Replies
SarkarSushru
Moderator
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100 replies posted 10 likes received 100 sign-ins

Hi @rahulpillai ,

1. If field weakening is disabled by setting the current limit as 0%, field weakening will not get activated.
2. What was the Field weakening modulation threshold value configured for your testing? Make sure that the threshold was reached, for the field weakening to get enabled.
3. Field weakening current limit specifies the Id current Limit during field weakening as the percentage of the rated current.

Please let us know if you have any further queries.

Thanks,

Sushruti

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rahulpillai
Level 1
Level 1
10 sign-ins First reply posted 5 questions asked

Hi Sushruti,

Could you please explain what is the SVPWM over modulation enable/disable setting and how it interacts with the flux weakening settings?

To your question, in pt.2 above the field weakening modulation threshold was set to 95% and this threshold was hit as seen from the motor voltage number. However, Id current went up more than the limit of 10% which I had set it to. Could you please explain that?

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SarkarSushru
Moderator
Moderator
Moderator
100 replies posted 10 likes received 100 sign-ins

Hi @rahulpillai ,

  • Enabling SVPWM Over Modulation maximizes DC bus utilization. Disabling SVPWM Over Modulation limits the modulation to the linear range. The Field weakening Modulation Threshold specifies the modulation index threshold to start field weakening. It is recommended to set this value below the SVPWM linear range.
  • What is the percentage deviation of the Id current from the limit value set?

Thanks,

Sushruti

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rahulpillai
Level 1
Level 1
10 sign-ins First reply posted 5 questions asked

The Id current went up above the set threshold by around 5%. Is it because of the MTPA Id reference that it is going above the thershold?

I did further tests during field weakening region and could see that if the motor current limit is hit, when the motor voltage is being maintained to the linear modulation range, the motor speed is derated. The behaviour makes sense to me and is useful for our applicatoin. However, it is strange that there is no documentatioon in your software or reference manuals about this behaviour. Do you have any other place where this behavior is documented or can you describe the software behaviour in more detail here in this thread?

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SarkarSushru
Moderator
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100 replies posted 10 likes received 100 sign-ins

Hi @rahulpillai ,

Unfortunately, documentation is not available explaining this phenomenon at this moment.

Thank you for your understanding.

 

Best Regards

Sushruti

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