Danfoss VLT AutomationDrive FC 301 Programming Manual page 124

Parameter Descriptions
3.8.2 Speed PID Droop
This feature implements precise torque sharing between
multiple motors on a common mechanical shaft.
Speed PID droop is useful for marine and mining
3 3
applications, where redundancy and higher dynamics are
required. Speed PID droop allows to reduce inertia by
utilizing multiple small motors instead of 1 big motor.
External Set-point
Illustration 3.47 Speed PID Droop
The value in parameter 7-01 Speed PID Droop ensures that
the load is shared equally between the motors. If the
torque on the motor is 100% of nominal motor torque, the
frequency converter reduces its output to this motor by
100% of the value in parameter 7-01 Speed PID Droop. If the
torque is 50% of nominal motor torque, the frequency
converter reduces its output to this motor by 50% of the
value in parameter 7-01 Speed PID Droop. This ensures that
the motors share the load evenly.
A side effect of using speed PID droop is that the actual
shaft speed does not match the reference exactly. Speed
PID droop is not efficient in low-speed applications
because the adjustment range may be insufficient.
122
®
VLT AutomationDrive FC 301/302
VLT 1
Set-point
Ramp
Calculation
VLT 2
Set-point
Ramp
Calculation
VLT 3
Set-point
Ramp
Calculation
Danfoss A/S © 01/2018 All rights reserved.
Illustration 3.47 shows the concept of the feature:
Speed
-
PID
Droop
Speed
-
PID
Droop
Speed
-
PID
Droop
Use speed trim if the application requires the following
features:
•
Accurate speed (the actual shaft speed matches
the reference speed).
•
Precise speed adjustment down to 0 RPM.
Torque
M1
PID
Torque
M2
PID
Torque
M3
PID
MG33MO02