Droop Function - Siemens SINAMICS S120 Function Manual

Operating Modes
Vector control
3.2.6

Droop function

The droop function (enabled via p1492) ensures that the speed setpoint is reduced
proportionally as the load torque increases.
Droop injection
r1490
0
0 1
p
1492
r1084
--
Speed setpoint
r1087
Actual speed value
*) Only active if pre --control is active (p1496 > 0)
**) only active with SLVC
Fig. 3-31 Speed controller with droop function
Drooping is the most straightforward way of controlling load balancing. This type of
control can only be applied, however, if the drives are operated in motor mode and
the speed is steady state. This method is only suitable to a limited extent for drives
that are accelerated and braked with significant changes in speed.
This simple type of load balancing control is used, for example, in applications in
which two or more motors are connected mechanically or operate with a common
shaft and fulfill the above requirements. The droop function compensates for
torque differences that can occur as a result of the mechanical connection between
the motors by modifying the speeds of the individual motors (drive is relieved when
the torque becomes too great).
Preconditions
S All connected drives must be operated with vector control and speed control
(with or without an encoder).
S The ramp-function generator ramp-up and ramp-down times must be the same
for all drives.
3-122
p1 489
150 ms
**)
--control
Pre
K
T
p
n
*)
PI speed
controller
--
T
i
SLVC
VC
p1488
0
0
1
2
r1508
3
r1482
r1547 [0] r1538
r1547 [1] r1539
T K
i p
: p1452 p1470
: p1442 p1460
© Siemens AG, 2005. All rights reserved
SINAMICS S120 Function Manual, 06/05 Edition
r0079
Torque
setpoint
T
n
p1472
p1462