Ok, I just couldn't contain my curiosity anymore, so I tried it:
I connected a 3 ph PM servo motor to a V/Hz VFD. I set max frequency (= maximum motor frequency), max voltage frequency (= rated motor frequency), and max voltage (= motor rated voltage), and also something called "electronic thermal relay" which is supposed to turn the motor off in case of an overcurrent situation. I set this to the rated current of the motor (2 A).
I set the frequency to 15 Hz and pressed "Run". Ok, the motor started to turn, but sounded kind of bad (squeaking noise). I checked the current, and saw that the *stupid* VFD pushed some 10-12 A into the poor motor! I turned it off before it burnt the windings, but I guess I now have a motor that's a lot weaker than before (max peak current for this motor is 6 A - poor magnets!).
I have no idea why the overcurrent protection didn't work. Perhaps the VFD performs some kind of integration of current over time to allow for short term overcurrent?
Well, at least now I know how well it works...
Arvid  |