Rockwell Automation 20B PowerFlex 70, PowerFlex 700 Reference Manual - Manual (Page 62)

Carrier (PWM) Frequency
62 Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
Carrier (PWM) 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 14 and Figure 15 . Note the
output current at 2 kHz and 4 kHz. The “smoothing” of the current waveform
continues all the way to 10 kHz.
Figure 14 Current at 2 kHz PWM Frequency
Figure 15 Current at 4 kHz 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 thus,
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.