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How to measure Ls on spinning motor?

Alexandros Amargianos
Prodigy 125 points

Other Parts Discussed in Thread: MOTORWARE

Hello,

I am using the DRV8301-69M-KIT with the latest motorware (1_01_00_12) and i want to drive a pmsm motor under load with the maximum efficiency possible. In order to do that, and since the Ls changes wiith speed and load, i have to measure the Ls and create a lookup table.

Is there any way to do the measurements through the instaspin projects? I mean can i use a function already created for the initial identification while program is already running? I was thining something like that: In main function on a project (e.g lab4)

if (gMotorVars.Speed_krpm>some_value){

measurement_1_for_lookup_table = EST_computeLr_H(handle, USER_MOTOR_IND_EST_CURRENT(?))

}

Is this the correct function that does the computation of the inductance and can i use it like this? Is there any precaution that i may need to consider?

I cannot afford to damage the motor, that is why i post prior to experimenting.

Thank you in advance, 

Alexandros Amargianos

  • 0
    TI__Guru** 119680 points

    Alexandros Amargianos said:
    In order to do that, and since the Ls changes wiith speed and load, i have to measure the Ls and create a lookup table

    You would typically only need to do this if you had a highly salient motor where the Ls_d and Ls_q differences can introduce an angle estimation error vs. just using a single Ls.

    And if you do have a highly salient motor there are things you can do at the current controller level to improve efficiency as well.

    I don't think you will get much out of trying to do this for a non-salient machine.

    Alexandros Amargianos said:
    I mean can i use a function already created for the initial identification while program is already running?

    No, we can not estimate stator inductance while the motor is running.

    To use the method you are describing would require an intimate knowledge of the motor, by design and by testing.  There are companies who obviously have this technology, but for the layperson it is not attainable.