# AC motor phase current vs Battery pack current?



## jddcircuit (Mar 18, 2010)

Need some help with understanding the relationship of sinusoidal phase currents created using sinusoidal PWM battery voltage switching and how it relates to battery pack current.

My PWM duty cycle for each motor phase varies sinusoidally to create sinusoidal phase currents 120 degrees out of phase. I am unsure how to calculate or approximate battery pack current given my peak dutycycle and my peak phase current.

For DC motor and PWM controller:
Imotor * Duty% = IBattery

This is my guess for AC motor and Sinusoidal PWM controller:

(IPhasePeak * .707) * (DutyPeak% *.707) = IBattery 

Am I guessing correctly?

Thanks
Jeff


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## peggus (Feb 18, 2008)

Using the variables you specified I believe this is the answer.

Motor RMS voltage = (Duty peak * V batt ) / sqrt(2)
Phase-N RMS voltage = motor RMS voltage / sqrt(3)
Motor power = 3 * Phase-N RMS voltage * Iphase_pk / sqrt(2)
I_batt = motor power / V batt

Or simplified

I_batt = Duty_RMS * 0.57 * 3 * Iphase_RMS


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## jddcircuit (Mar 18, 2010)

peggus said:


> Using the variables you specified I believe this is the answer.
> 
> Motor RMS voltage = (Duty peak * V batt ) / sqrt(2)
> Phase-N RMS voltage = motor RMS voltage / sqrt(3)
> ...


 
Thank you very much


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