Rockwell Automation 20D PowerFlex 700S AC Drives with Phase II Control Reference Manual - Manual (Page 52)

52 Rockwell Automation Publication PFLEX-RM003E-EN-E - January 2011
Chapter 1 Detailed Drive Operation
Lead-Lag Filter “Lead”
When Kn is greater than one (Kn>1), the lead-lag filter operates as lead filter. The
original equation is re-written into a term that can be used to utilize the lead
function. Wn is divided throughout the equation. Two new terms are developed.
The lead term (Wld) is used to display the lead of the filter. The lag term (Wlg) is
used to show the lag of the filter.
Figure 11 - Kn > 1 “Lead Filter”
Figure 11 above shows the bode plot of the lead function. The lead term is used to
counteract lags in the system. The speed loop bandwidth appears to the position
loop as a low pass filter or a lag. The lead filter can be used to cancel the speed
loop lag and replace it with a faster lag.
In the following example:
• The system appears as a lag with a 5 radians/second response.
• The lead filter was set to compensate for the 5 radians/second response
(Wld=5)
• The lag filter was set to 50 radians/second response (Wlg=50)
• Kn is set to Wlg/Wld (50/5) = 10
• Wn is set to Wlg = 50
Kn s wn +
×
s wn +
------------------------------
Kn s wn 1 +
( ) ⁄ ×
s wn 1 +
( ) ⁄
---------------------------------------------
s Wld 1 +
( ) ⁄
s Wlg 1 +
( ) ⁄
----------------------------------
wn Wlg =
Kn
Wlg
Wld
---------- =
g a in
kn
1
wn
kn
wn
“ Le a d ” (kn >1)