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AC Drive Carrier Frequency
In the AC drives there are parameters called "Carrier Frequency", what is the effect of it on improving the output waveform?
Higher carrier frequency will reduce audible noise but at a cost in losses in the AC drive. Lower carrier means high motor noise and higher losses in the motor. Some AC drives are rated full output at only 2.5kHZ max, others at 4kHz and higher. So, if you push the ac drive carrier higher than its standard output, it has to be derated (unloaded a bit). Take the carrier down, the AC drive likes it and the motor hates it. Motors like pure sinusoidal waves coming from generators - any reconstructed wave form coming off a DC bus (all AC drive outputs) has harmonics that heat up the motor and the lower the carrier, the more the harmonics and motor losses. Finally, be aware these losses are significant. Derate curves in the AC drive instruction books show 5 - 7% losses just to go from 2.5 to 4kHz or 10 to 14HP degradation on a 200HP motor.
The carrier frequency is what the base PWM signal runs at. Typically the higher the carrier frequency, the quieter the motor will run, but at the possible expense of damaging the windings or bearings if there is a lot of cable length, or capacitance in the output circuit. If you have an old motor, or are running a significant length of output cable, choose a lower carrier frequency drive. Now, if your instance has only a couple feet away from the AC drive, you can pretty much choose anything you want and not have to worry about the carrier frequency. For experimentation purposes you can select the different frequencies and notice the audible difference in the motor, and if you have a scope with sufficient voltage isolation probes, you can view the ac drive's output voltage and current waveforms. Low is sometimes around 8kHz, and high is about 15kHz for 230/480V drives. There is also usually another parameter for the carrier frequency as well, that either leaves the frequency constant, or allows the frequency to change as the output frequency varies. That's pretty old school, most machines today just use a fixed frequency.
Higher carrier frequency will reduce audible noise but at a cost in losses in the AC drive. Lower carrier means high motor noise and higher losses in the motor. Some AC drives are rated full output at only 2.5kHZ max, others at 4kHz and higher. So, if you push the ac drive carrier higher than its standard output, it has to be derated (unloaded a bit). Take the carrier down, the AC drive likes it and the motor hates it. Motors like pure sinusoidal waves coming from generators - any reconstructed wave form coming off a DC bus (all AC drive outputs) has harmonics that heat up the motor and the lower the carrier, the more the harmonics and motor losses. Finally, be aware these losses are significant. Derate curves in the AC drive instruction books show 5 - 7% losses just to go from 2.5 to 4kHz or 10 to 14HP degradation on a 200HP motor.
The carrier frequency is what the base PWM signal runs at. Typically the higher the carrier frequency, the quieter the motor will run, but at the possible expense of damaging the windings or bearings if there is a lot of cable length, or capacitance in the output circuit. If you have an old motor, or are running a significant length of output cable, choose a lower carrier frequency drive. Now, if your instance has only a couple feet away from the AC drive, you can pretty much choose anything you want and not have to worry about the carrier frequency. For experimentation purposes you can select the different frequencies and notice the audible difference in the motor, and if you have a scope with sufficient voltage isolation probes, you can view the ac drive's output voltage and current waveforms. Low is sometimes around 8kHz, and high is about 15kHz for 230/480V drives. There is also usually another parameter for the carrier frequency as well, that either leaves the frequency constant, or allows the frequency to change as the output frequency varies. That's pretty old school, most machines today just use a fixed frequency.
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