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Old 09-16-2015, 04:25 PM   #2022 (permalink)
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Originally Posted by e*clipse View Post
The best info I can find is the inductance for the motors I'm using is very low - 1.4mH to about 3mH ( It varies due to phase angle, I think )
Hmm. The motor manufacturer designed the 8 pole motor for 50 Hz and 1500 rpm (as an example). But you want to run it much faster .. 800 Hz and 12,000 rpm was it? The inductance is a part of the impedance of the motor, but it varies by frequency. In fact, it rises with frequency. The resistance does not change. So you have a proportional but slightly non-linear increase in impedance as your frequency increases.

If you are trying to push rated current .. say 100 amps .. through a motor that is rated for 50 Hz and 750 rpm, but you are using 800 Hz and 12,000 rpm ... I would expect that the rise in impedance would come mostly from the inductance and that your power factor would suffer. Not only would you get less amps into the motor, but the work done by the motor would drop because the power factor is worse.

Are you planning/already have rewound the motor for lower voltage so you can get good current at say 5000 rpm? Is the motor rated for this speed and so you already have the correct applied voltage?

... and ... would the carrier frequency have *ANYTHING* to do with how much current you can put through the motor? Does the motor *SEE* carrier frequency or just the averaged frequency?
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