# Three phase AC power measurement

I am trying to measure the output power for BLDC controller, in order to calculate the efficiency of the controller. I came to know that two watt-meter method is one of the method used to calculate the three phase AC power.

But instead of using two wattmeters, i have.....

• Two clamp meters (AC/DC clamp meter) for measuring Ir and IY.

• Two multimeters (AC/DC) for measuring VRB and VYB.

• My input power is DC 48 volt. P = V × I will give me the input power.

• But to calculate the output power has complexity.

W1 = IR × VRB and W2 = IY × VYB

W1 + W2 gives the output power.

For voltage measurement VRB and VYB:

My bldc controller output is trapezoidal waveform with variable output frequency, Vrb and Vyb can be calculated by using ac multi meter. Because ac voltage does not depends on the Frequency, whatever the Output frequency the Vrms will be the same i guess. Correct me friends if i am wrong.

For current measurement Ir and Iy : Since the AC current must not be same for different frequency at all time. How to calculate the AC current at my output frequency say (eg: 100 Hz).

Edited... Sorry i forgot to say something, I am driving the bldc controller with bldc motor in a load setup.

• I've fixed some of the random and missing capitalisation and shown how to write subscripts (<sub>...</sub>) but ran out of energy to finish them all. – Transistor Aug 25 '20 at 14:28