VFD training class was awesome! Question about Carrier Frequency...

The training class I just finished today was really great. I now have a good understanding of vfds.
I cannot wait to take this knowledge into the field.

One question though: Carrier Frequency. From the class my understandning is that by changing the frequency I will basically alter the 'sound' of the motor.
Is that the only thing that will occur when the carrier frequency is changed? Any tips on finding an 'ideal' frequency (if there is such a thing).
I have an 460vac 800HP motor that sounds fine to me, but the customer doesn't like the sound (thinks it's too high pitched). Though its running fine. I figured that by changing the way it sounds a bit, it might relieve some undue stress from my customers shoulders. (silly I know, but it does bother him, so if I can help then why not).

The carrier frequency is the frequency at which the pulses in your pulse width modulation switch at. The rapid switching on and off produces a "hum" in your machine at the same frequency of this carrier as well as at the odd harmonics. This produces the classic "whine" associated with VSD drives.

Many brands seem to have settled on 4kHz for their carrier frequency. This is within the human audiable range, and can be annoying to some people. You can often change the setting, commonly to 8kHz or 16kHz. This can make the whine less annoying or even, in the case of 16kHz, inaudiable for some people. Another reason for changing the carrier frequency is sometimes it produces resonance in some components.

The down side to this is that each switching event has an associated switching loss. This loss is directly proportional to the switching frequency. Doubling the frequency will double the switching losses.
This will result in additional heating of the VSD, and possibly less power available at the motor.

Hope this helps,

Doug

Another problem with increasing the carrier is that the cables and motor are absorbing (or reflecting) the associated changes in voltage (dv/dt). Because of this, if you increase the carrier frequency too much it is possible to damage the cables, motor, or even the drive.

You can get dv/dt protection networks to be placed on the motor to absorb this, protecting the rest of the system.

One advantage of the Perfect Harmony series of drives is the low level of voltage they are actually switching with each pulse, essentially getting the dv/dt of a low voltage drive in a medium voltage application.

Did you try the wings while you were up there?