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

Thread Starter


Joined May 20, 2011
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.