Danfoss MCO 305 Operating Instructions Manual page 28

MCO 305 Operating Instructions
Position
Reference
Setpoint
generator
CP
AV is the actual velocity
AP is the actual position (calculated from encoder feedback) in qc (Quad Counts).
CP is the current position set point in qc.
CV is the velocity set point in qc/ms
(Position deviation) is calculated by CP–AP.
CA is the acceleration set point
The PID filter works according to the following formula:
1 = FFVEL * (Setpoint Velocity)
2 = FFACC * (Setpoint Acceleration)
3 = KPROP * (Position Deviation)
4 = KINT * (Sum of all previous Position Deviations) (limited by KILIM)
5 = KDER * (Difference of Position Deviation)
6 = 3 + 4 + 5 (Limited by BANDWIDTH)
NB!:
In SYNCV mode the PID controller is working with speed deviation instead of position deviation.
Speed deviation is calculated by CV–AV.
The controller in the MCO 305 utilizes two control strategies at the same time:
1. An open-loop feed-forward control. Since the asynchronous motor inherently has a good open loop
performance the feed-forward control is a very important part of the controller in most applications.
Benefits from using feed-forwards control is a very fast and accurate response to changes in the
setpoint reference.
2. A closed-loop PID control. The PID controller monitors the difference between the actual position and
the setpoint position. Based on this information it calculates a control signal to minimize the position
deviance. Thus the MCO is able to compensate for changes in load or friction. The PID controller is also
necessary to compensate for any position deviance caused by inaccurate setting of the open-loop feed-
forward controller.
28
__ Optimizing the PID Controller __
FFVEL
CV
FFACC
CA
KPROP
+
–
AP
KINT
KILIM
KDER
MG.33.K2.02 – VLT is a registered Danfoss trademark
+
+
+
+
Motor and
+
–
BANDWIDTH
FC300