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Original question:

Inertia Estimation with InstaSPIN-MOTION

CCS/TMS320F28027F: Issue with disabling FAST

Shubham Joshi
Prodigy 90 points

Part Number: TMS320F28027F

Tool/software: Code Composer Studio

Hi,

I am working on a small BLDC motor and trying to run it with Instaspin.

Struggling with startup of this motor. Force angle module is enabled and set to rotate at 1Hz, USER_ZEROSPEEDLIMIT limit is set to 0.9. So ideally FAST should not give angle output till estimated speed reached 0.9*USER_IQ_FULL_SCALE_FREQ_Hz. USER_IQ_FULL_SCALE_FREQ_Hz = 800Hz, FAST must not be active before estimated speed reaches 720Hz. During my test speed never increases beyond 100Hz.

Yet by observing estimated angle frequency, it is always greater than 1Hz and corresponds exactly to estimated speed. It can be concluded that FAST is calculating angle using current measurements and not traking input from force angle.

USER_ZEROSPEEDLIMIT was increased just to see if force angle keeps control all the time. For motor startup, motor is being run in speed control mode before switching to final control algorithm. During the startup phase motor spins reverse few times. If speed controller at startup is removed and a constant vq is provided, still motor spins reverse many times.

Appreciate your help.

  • 0
    TI__Guru** 117080 points
    Typically, the USER_ZEROSPEEDLIMIT and USER_FORCE_ANGLE_FREQ_Hz should be set to 1~5Hz. A motor is difficult to run smoothly higher than its rated speed, especially for a PMSM under a load since the rotor angle will be not correct. The FAST is working always when you enable the estimator, but its generated angle will be not used if the motor speed is lower than USER_FORCE_ANGLE_FREQ_Hz.
    Please have a look at Chapter 14 of instaSPIN user's guide (SPRUHJ1G) that should help you on the motor startup.
    Btw, the force angle is just used for startup and a very low speed, it can't work well for full speed range since the angle will be not correct and its error can't be ignored.
  • 0 in reply to Yanming Luo
    Prodigy 90 points

    According to the user manual. angle feedback from FAST will be used when speed is above USER_ZEROSPEEDLIMIT, I am experimenting with motor by giving a constant frequency excitation signal and hence need FAST to be disabled. If USER_ZEROSPEEDLIMIT is set high enough then FAST should never give angle feedback and controller should work with angle feedback from force angle module.

    Am I missing something here?

  • 0 in reply to Shubham Joshi
    TI__Guru** 117080 points
    As replied to you, the FAT is just an estimator that works always if you enable the control flag in the project, but the position angle and speed will not be used for FOC modules if the motor speed is lower than USER_FORCE_ANGLE_FREQ_Hz.
    Btw, you could have a look at the lab21 or lab11e that don't use the FAST during low speed.