Rockwell Automation Publication PFLEX-RM003E-EN-E - January 2011 81
Detailed Drive Operation Chapter 1
drives. The PLL is used in conjunction with SynchLink, the speed loop, and the
position loop in order to synchronize drives together in an ELS system.
Figure 18 - Phase Locked Loop Block Diagram
Position Reference
Parameter 721 [PLL Position Ref ] should be linked to the encoder position. The
encoder Edges Per Revolution (EPR) value, parameter 725 [PLL EPR Input],
must be specified for the feedback device used.
Speed Reference (Feed Forward)
By default, parameter 720 [PLL Control], bit 0 “Vel FdFwd En” = 0 and the feed-
forward branch is disabled. Even when feed forward is disabled, the PLL
effectively tracks the reference encoder and should be considered first. There will
be zero position error at constant ramp and in steady-state speed. The PLL will
not track to zero error during a change in acceleration.
If the desired performance cannot be achieved without feed forward, set
parameter 720 [PLL Control], bit 0 “Vel FdFwd En” = 1. The encoder speed is
calculated automatically by the “X to V” conversion block. However, for systems
with relatively high mechanical disturbances it may be advantageous to link
parameter 728 [PLL Ext Spd Ref ] to a speed input that is less noisy and then
select that path by setting Parameter 720 [PLL Control], bit 1 “Ext Vel In” = 1.
When [PLL Ext Spd Ref ] is used, parameter 729 [PLL Ext SpdScale] can be used
to calibrate the external speed reference.
Lpf
Loop
Filter
X to V
Conv
0
0
0
VE
[ ]
[ ]
EGR
X X
727
726
724
725
723
722
721
728
X
729
720
720
720
730
147
2
0
1
24
734
735
731
732
733
PLL Position Ref
PLL Ext Spd Ref
PLL Bandwidth
PLL Rev Input
PLL EPR Input
PLL Rev Output
PLL EPR Output
PLL VirtEncdrRPM
PLL LPFilter BW
PLL Control
(Trckng AComp)
PLL Control
(Vel FdFwd En)
PLL Control
(Ext Vel In)
PLL Ext SpdScale
PLL Speed Out
PLLSpeedOut Adv
PLL Posit Out
PLL Posit OutAdv
PLL FiltPosit Out
+
+
+
-
FW Functions En
(PhaseLockLp)
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