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Original question:

Field Weakening for PMSM motors

Field Weakening for PMSM motors

David Palombo
Prodigy 100 points


I have a question or the TI Applications Engineer.  Can field weakening be performed on motors with a low saliency ratio, i.e. motors that have surface mounted permanent magnets?

  • 0
    TI__Guru** 116090 points
    FWC can be implemented on both surface PM or interior PM motors, and maybe using the same algorithm.
  • 0 in reply to Yanming Luo
    Prodigy 100 points

    Yanming,

    Are there any guidelines as to what we can expect to achieve in terms of how much we could run over the base speed (in terms of ratio or %) in the Field Weakened mode on a rotor with a low saliency ratio?

    Thank you,

    David

  • 0 in reply to David Palombo
    TI__Guru** 116090 points

    In general, the field weakening control (FWC) algorithm set the reference Id based on a motor specification, input voltage, load, and motor speed. It's not necessary to implement FWC if the input voltage is enough high although the motor speed is higher than rated speed. You might have a look at the FWC technical paper that should be easily searched on the website.

    There is an example project (lab09) in Automatic Field Weakening Control in motoWare, you might refer to lab project code and guide.
    www.ti.com/.../motorware

  • 0 in reply to Yanming Luo
    Prodigy 100 points

    Yanming, yes, I understand that.  I am looking at a case where under normal circumstances, the peak BEMF voltage would exceed the DC link voltage.  I am trying to get some guidelines on how much we could drive over the max no-load speed (without FWC) on a PMAC motor with surface mounted magnets, i.e. a motor with a very low salience ratio, when using  FWC.

    Thank you,

    David Palombo

  • 0 in reply to Yanming Luo
    Prodigy 100 points
    I would like an answer to the questions below, i.e. guidelines on how much we could drive over the max no-load speed (without FWC) on a PMAC motor with surface mounted magnets, i.e. a motor with a very low salience ratio, when using FWC.
  • 0 in reply to David Palombo
    TI__Guru** 116090 points
    The maximum speed depends on dc-link voltage and the spec. of a motor like BEMF constant. It's limited to the maximum stator voltage as below equation, and the maximum speed will be limited to Vs also. Maybe, you could find a more detailed description of this in some papers.
    Vs=sqrt(vd^2_vq^2) <= Vsmax, and Vsmax=Vdc/sqrt(3).