How to measure PWM voltage (10k)?


Thread Starter

Eric Sun

I want to build up a testbed for measuring pwm-fed motor efficiency used in electrical vehicle. I can use pz4000 power analyzer to measure, but now i want to build a automated acquisition system to measure 10k carrier frequecy's pwm voltage. i cannot find a good way, can you give me some suggestion? Thank you very much!
1) You can "demodulate" the phase voltages. This simply means that you put a low pass filter on the phase voltages (often a single pole RC filter).

2) Internal to the drive there is always some number or signal that represents the PWM ratio. That number combined with the B+ voltage will allow you to calculate the phase voltage.

Actually, due to fast voltage hops due to the motor inductance, you cannot see the "exact motor terminal voltage" but for efficiency calculations they are usually unimportant.
The cut-off frequency of low-pass filter must be significantly lower than PWM frequency - it must be less than 1k for your application.