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Compute Back EMF

mingjiang li
Prodigy 30 points

 

Dear Sirs,

 

In manual spruhj1f, Page 411 Figure 11-19, Decoupled PI Controllers for a PMSM

 

Vq = PID_q_out + id * ω * Ls + ω * KE ;

 

 

I want to use “USER_MOTOR_RATED_FLUX * ω(rad/s) * 2 * 3.1415 “to substitute for “ω * KE”, is it right？

 

If I use ω * KE （Vpeak/KPRM）, do I need to use

“ω(KPRM) * KE / (PolePaires * sqrt(3))” or others?

 

I am not sure. Please Help.

 

Thanks a lot.

 

  • 0
    TI__Expert 4760 points
    Hello Mingjiang Li,
    The second term (w*KE) accounts for the back-emf voltage, which is the largest component of the compensation voltage term in most cases. The equation assumes KE is in units of peak volts, line-to-neutral per electrical radians/second, and speed is in units of electrical radians/seconds. If you use a KE or speed value in any other units, you must correct the scaling to get it back to these units.
    Let's take a look at your example. Since USER_MOTOR_RATED_FLUX is in units of Volts/Hz, you must convert it to Volts per radian per second. To do this, you need to DIVIDE by 2*pi, not multiply by it.
    If you use w*KE (Vpeak/KRPM), then you once again need to convert KE to the correct units. If Vpeak is line-to-line (it's not clear from your comments), then you need to convert it to line-to-neutral. To convert from KRPM to electrical radians/sec, you need to multiply by 1000*pole-pairs*2*pi/60.
    Hope that helps,Dave
  • 0 in reply to Dave (Wisconsin) Wilson
    Prodigy 30 points

    Dave,

       Thanks for your response. This solve my problems.

       Really appreciate.