This is for the first time I am using this forum to solve my actual problem.
Well, I've got an AC drive and Induction motor.
U=230V AC (line-to-line; in delta connection)
I=6.9A (in delta connection)
V/Hz control (open loop, no optimization, no slip or IR drop compensation)
Motor is coupled to a freely rotating DC motor (not powered).
I apply 230V AC (rms) on the output of inverter (line-to-line voltage) and 50Hz. I would expect a no-load current about 30% of nominal (maybe 40% for a 6-pole motor) - it means about 2.5A. But the current RMS is 5A (70%)!
Is that normal? I think it isn't. And that's the reason I am asking WHY.
Some questions and suggestions:
- Motor is dedicated for operation condition described above.
- PWM is 16kHz, but the situation is the same for any PWM frequency.
- I think, the motor is overexcited. Line currents are not purely sinusoidal but distorted on the top of sine-waves.
- The 1-st harmonic of AC (line-to-line) voltage applied to the motor is indeed 230V AC. I checked it using RC filter and scope.
Hope, my description is not too confusing.
Thanks for any comment.