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What is the gain of inverter?

Vigneshwar V
Prodigy 180 points
Part Number: DRV8301
Other Parts Discussed in Thread: TMS320F28069M, CONTROLSUITE, MOTORWARE

Hello everyone

I am trying to build FOC algoritham using TMS320f28069M and DRV8301 as iverter module. The output of current loop is Vd and Vq and I converted this into 3 phase voltages using anti Park& Clarke transformations. Now these voltages has to be converted into duty i.e equivalent pwm register values. I am using below formula to convert into duty values.

Duty=(((Va/Vdc)+1)*Pwm_register/2).....[ 1 ] 

Va is the voltage from transformation.
Vdc is the bus voltage.
Pwm register is value calculated for 20khz  

 Duty=(((Va/Vdc/2)+1)*Pwm_register/2)....[ 2 ]
In above two equations which one is correct?

What is the gain of inverter? Can someone explain with equation.

Thank You
Vigneshwar V

  • 0
    TI__Guru** 115480 points
    What example project did you refer in controlSUITE or motorWare? And what modulation strategy are you using? SPWM or SVPWM?
    Generally, we used 2-level for a 3-phase inverter, so the 50% pwm duty is zero point for spwm or svpwm. More detailed description on FOC and SVPWM, you may download controlSUITE and find related documents in the folder as below.
    C:\ti\controlSUITE\libs\app_libs\motor_control\math_blocks\v4.3\~Docs
  • 0 in reply to Yanming Luo
    Prodigy 180 points

    I haven't referred any example file. I am using SVPWM. Yes 50% duty is zero point thats why i used PWM_Register/2.

    Thank You

    Vigneshwar V

  • 0 in reply to Vigneshwar V
    TI__Guru** 115480 points
    Got. It's difficult to say which equation is correct which depends on pwm count mode, modulation technique and scale unit in your system. The equation 1 is right to calculate the duty cycle of pwm for SPWM if the pwm count mode is up/down mode. And the GAIN or Modulation Index equals to Vref/(Vdc/2), the Vref is vector voltage from the FOC. You may refer to a application notes (spra524, can be found in TI website) to get more detail about SVPWM.
  • 0 in reply to Yanming Luo
    Prodigy 180 points

    Thanks Yanming for replying.

    Can you tell me what is the gain of inverter?it would be better if you explain with equations.

    I am using up down mode in pwm. As you told modulation index is Vref/(Vdc/2 ) then in equation I need to use the same right? Then how come equation 1 is correct?

    What do you mean by modulation technique and scale unit? If you can explain briefly I can provide you required information.

    Thank You

    Vigneshwar V

  • 0 in reply to Vigneshwar V
    TI__Guru** 115480 points
    Actually, I can't fully understand the gain of inverter you mentioned, I didn't use this concept in my former FOC project. You may have a look at the reference document first since these terminologies are difficult to explain clearly in a few words. And let me know if you have any questions again.
  • 0 in reply to Yanming Luo
    Prodigy 180 points
    Thank you Yanming.
    Can you please answer my orher two questions too ?
    I have heard people saying gain of inverter is Vdc/2, I didn't understand how is this?
  • 0 in reply to Vigneshwar V
    TI__Guru** 115480 points
    As replied above, more details about modulation technique and scale unit can be in found in the user's guide of FOC example project in controlSUITE. The gain concept is often used for signal sampling or power amplifier, we don't use it in FOC of motor.
    Modulation technique includes SPWM, SVPWM, DPWMMIN, DPWMMAX...., there is many pwm strategies, you may find very detailed explain in some motor control books.
    Scale unit means there is a scale value for current, voltage, or speed which equal to 1, to divide this scale value for other current/voltage/speed setting or feedback value.