DickDV
Member
I agree with what Doug Adams wrote except about reducing harmonics. Changing carrier frequency can SHIFT harmonics but rarely reduces them.
As I mentioned earlier, the general rule is to use the lowest carrier frequency you can without getting objectionable motor whine.
There is one other benefit for using higher carrier frequencies that hasn't been mentioned. If you are going to operate at a very low motor speed, a higher carrier will provide smoother shaft rotation (less cogging) and somewhat better torque, but only at very low speeds.
With today's technology, struggling to make a V/Hz or scalar drive produce low speed torque seems almost primitive. Far better to use a sensorless vector drive and, even better, an ABB drive with DTC. I use these frequently and routinely develop full motor torque at zero speed without any speed feedback device.
Back to shaft cogging, I've run into a few buffing and polishing applications where the slightest variation in shaft speed puts a pattern in the polished finish. I've even seen precision DC drives fail in these applications due to the commutator bars being reflected in the polished pattern. Usually, an AC motor with a high frequency carrier inverter is good enough to do this tough job.
As I mentioned earlier, the general rule is to use the lowest carrier frequency you can without getting objectionable motor whine.
There is one other benefit for using higher carrier frequencies that hasn't been mentioned. If you are going to operate at a very low motor speed, a higher carrier will provide smoother shaft rotation (less cogging) and somewhat better torque, but only at very low speeds.
With today's technology, struggling to make a V/Hz or scalar drive produce low speed torque seems almost primitive. Far better to use a sensorless vector drive and, even better, an ABB drive with DTC. I use these frequently and routinely develop full motor torque at zero speed without any speed feedback device.
Back to shaft cogging, I've run into a few buffing and polishing applications where the slightest variation in shaft speed puts a pattern in the polished finish. I've even seen precision DC drives fail in these applications due to the commutator bars being reflected in the polished pattern. Usually, an AC motor with a high frequency carrier inverter is good enough to do this tough job.