how to calculate power of three-phase PWM which drive BLDC

Discussion in 'General Electronics Chat' started by hitbuyi, Nov 3, 2012.

  1. hitbuyi

    Thread Starter New Member

    May 20, 2011
    5
    0
    i have a bldc drive board, it has three wires to connect a bldc motor, now i want to calculate the efficiency of the drive board according to following 2 steps

    1, measure input power, using DSO to measure voltage V and current I ,Pi =V*I
    2, measure output power, i think if i can get power of one wire Po, the total
    power is 3*Po,and

    efficiency = 3*Po/ Pi
    but i found the voltage wave of the wire is 20k PWM, and current is square,

    how to calculate the Power Po?

    thank u in advance.
     
  2. ScottWang

    Moderator

    Aug 23, 2012
    4,848
    767
    Assuming PWM duty cycle is 50%/50%.
    3*Po/ Pi → 3*Po/V*(I/2)
     
  3. hitbuyi

    Thread Starter New Member

    May 20, 2011
    5
    0

    i still do not know how to decide U, I, since V is pwm, and I is exponential,not DC
     
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