deciding on upper and lower limit for solving scenario and calculating the losses

Melih Ayyildiz_22506
Melih Ayyildiz_22506 Altair Community Member
edited January 8 in Community Q&A

Hello,

I want to solve a project for an electric machine (PMSM) on Flux2D. I created the machine in FluxMotor first and then exported a Flux2D model with the suitable working point conditions. It is a PMSM with eight poles. 

I am still unsure how to decide on the higher and lower limits of the solving scenario. It seems that for different properties of the machine, I can adjust the higher and lower bound. I am unsure if my observation is correct until now. Could someone verify my observation? It seems that i can control the scenario by time or by the position of the rotor. 

For specific scenarios it could look like this:

  • cogging torque: 
    • rotor initial position for t=0s is 0°
    • lower limit: 0°
    • higher limit: calculate the period of the cogging torque by using the least common multiplier like in this picture:image
  • back emf:
    • rotor initial position for t=0 is 0°
    • lower limit=0°
    • upper limit: mechanical angle that would be equivalent to one full electrical cycle: 360°/(#pole pairs)
  • computation at a specific speed/ losses computation
    • the interval needs to be at least one electrical period; better yet: a bit longer than a electrical period 
    • rotor initial position is not 0°; The initial rotor position is set to xyz degrees so that the phase current is aligned with the phase back
      emf when GAMMA is zero. (This phrase is written in an example inside flux; it is attached to this post and can be read on page 71). If I export a Flux2D Model from FluxMotor, this value is already calculated and saved as a parameter called ROTOR_INIT_POS. 
      • Why is this the case? Is there any literature that I could read? I don't know why all of the sudden this is so important.
    • higher limit: last available time step or mechanical position
    • lower limit: last available time step or mechanical position MINUS the equivalent of an electrical period

Are these assumptions correct?

I want to calculate the losses of my motor. When I export the Flux2D model from FluxMotor in my case, the solving scenario already has two interval definitions in it. I think that one is used internally to determine ROTOR_INIT_POS. The other is defined as :

  • lower limit: ROTOR_INIT_POS = 3.75°
  • upper limit ROTOR_INIT_POS +  180° =183.75°

The electric machine has 8 poles. I would have assumed that I only have to solve the between 0° and ROTOR_INIT_POS+360°/(8/2)=3.75°+90°=93.75°

So I would have set the lower and higher limit of the solving scenario 0° and 93.75°.

While calculating the mean losses I would have set the the higher limit to 93.75° and the lower limit to 3.75°. Because of that, I am quite suprised that the default solving scenario is much higher. WHat's the reason for that?

image

 

 

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Best Answer

  • Letizia_Ferrara
    Letizia_Ferrara
    Altair Employee
    edited January 8 Answer ✓

    Hello Melih,

    Thanks for writing. The rules you wrote are correct.

    The reason is that especially in the examples, the aim is provide a quick computation, so only one period plus 2 /3 steps are solved. Generally, in fact, with current generators and synch machine, one period plus 2/3 steps are sufficient, since the first two steps where the quantities are affected by the initialization state are not considered.

    FluxMotor considers instead 2 periods normally, this is why you found 183.75° [that means 90°x2+INIT_POS].

    The reason because you normally find a starting position in the working point computation, is that we need to align the current with the BEMF, to be able to set the phase difference then (GAMMA parameter), as I underlined in the previous question.

    Please open a support request if you need to have more explanation.. we could arrange a meeting on this and please don't forget to indicate whether my answer is helpful to you and to mark as resolved the questions for which we have resolved your concerns.

    Best regards,

    Letizia

     

Answers

  • Letizia_Ferrara
    Letizia_Ferrara
    Altair Employee
    edited January 8 Answer ✓

    Hello Melih,

    Thanks for writing. The rules you wrote are correct.

    The reason is that especially in the examples, the aim is provide a quick computation, so only one period plus 2 /3 steps are solved. Generally, in fact, with current generators and synch machine, one period plus 2/3 steps are sufficient, since the first two steps where the quantities are affected by the initialization state are not considered.

    FluxMotor considers instead 2 periods normally, this is why you found 183.75° [that means 90°x2+INIT_POS].

    The reason because you normally find a starting position in the working point computation, is that we need to align the current with the BEMF, to be able to set the phase difference then (GAMMA parameter), as I underlined in the previous question.

    Please open a support request if you need to have more explanation.. we could arrange a meeting on this and please don't forget to indicate whether my answer is helpful to you and to mark as resolved the questions for which we have resolved your concerns.

    Best regards,

    Letizia

     

  • Melih Ayyildiz_22506
    Melih Ayyildiz_22506 Altair Community Member
    edited January 8
    Letizia Ferrara_21767 said:

    Hello Melih,

    Thanks for writing. The rules you wrote are correct.

    The reason is that especially in the examples, the aim is provide a quick computation, so only one period plus 2 /3 steps are solved. Generally, in fact, with current generators and synch machine, one period plus 2/3 steps are sufficient, since the first two steps where the quantities are affected by the initialization state are not considered.

    FluxMotor considers instead 2 periods normally, this is why you found 183.75° [that means 90°x2+INIT_POS].

    The reason because you normally find a starting position in the working point computation, is that we need to align the current with the BEMF, to be able to set the phase difference then (GAMMA parameter), as I underlined in the previous question.

    Please open a support request if you need to have more explanation.. we could arrange a meeting on this and please don't forget to indicate whether my answer is helpful to you and to mark as resolved the questions for which we have resolved your concerns.

    Best regards,

    Letizia

     

    Hi Letizia,

    thank you very much for your answer. I am happy that my assumptions were correct.

    I will try to find some literature about the topic regarding the back EMF/ initial rotor position and then I would open up a support case. 

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