Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 25)

Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013 25
Detail Drive Configuration and Operation Chapter 1
Carrier (PWM) Frequency See the PowerFlex 700S Drives with Phase II Control, Technical Data,
publication
20D-TD002 , for derating guidelines as they travel to carrier
frequency.
Parameter 402 [PWM Frequency] sets the switching frequency. In general, the
lowest possible switching frequency that is acceptable for any particular
application is the one that should be used. There are several benefits to increasing
the switching frequency. Refer to
Figure 1 and Figure 2 on page 25 . Note the
output current at 2 kHz and 4kHz. The “smoothing” of the current waveform
continues all the way to 10 kHz.
Figure 1 - Current at 2kHz PWM Frequency
Figure 2 - Current at 4kHz PWM Frequency
The benefits of increased carrier frequency include less motor heating and lower
audible noise. An increase in motor heating is considered negligible and motor
failure at lower switching frequencies is very remote. The higher switching
frequency creates less vibration in the motor windings and laminations making
lower audible noise. This may be desirable in some applications. Some
undesirable effects of higher switching frequencies include derating ambient
temperature vs. load characteristics of the drive, higher cable charging currents
and higher potential for common mode noise.
A very large majority of all drive applications will perform adequately at
2…4 kHz.