Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 56)

56 Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013
Chapter 1 Detail Drive Configuration and Operation
There is a second order low pass filter in the Speed Control-Regulator. This filter
is located after the speed error signal. The break frequency is set by parameter 89
[Spd Err Filt BW]. The break frequency is set to five times (5x) the Speed Loop
Bandwidth. This filter is used to attenuate any high frequency noise that the
speed loop would not be able to control.
Lead-Lag Filter
The PowerFlex 700S incorporates a generic lead lag filter. The filter has the
following Laplace transfer function:
Kn is the gain term for the filter and Wn is the frequency term for the filter.
Lead-Lag Filter “lag”
When Kn is less than one (Kn<1) the filter behaves like a low pass filter.
Figure 15 shows the lead lag in a “lag configuration.” The unique aspect of this
filter is that the gain stops once the input frequency is equal to Wn/Kn. Another
aspect to this filter is that there is a mild phase shift during the attenuation.
Figure 15 - Kn < 1 “Lag Filter”
Figure 16 on page 57 shows the bode plot of the lag configuration. Kn is set to 0.7
and Wn is set to 35 rad/sec. The time domain shows a 100 rad/sec sinusoidal
input. Notice that the phase shift between input and output are marginal.
Kn s wn +
×
s wn +
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