ABB ACS880 Firmware Manual page 31

The master drive is typically speed-controlled and the other drives follow its torque or
speed reference. In general, a follower should be
• torque-controlled when the motor shafts of the master and the follower are rigidly
coupled by gearing, chain etc. so that no speed difference between the drives is
possible
• speed-controlled when the motor shafts of the master and the follower are flexibly
coupled so that a slight speed difference is possible. When both the master and
the follower are speed-controlled, drooping is also typically used (see parameter
25.08 Drooping
In some applications, both speed control and torque control of the follower are
required. In those cases, an "on-the-fly" change between speed and torque control
can be performed via a digital input of the follower. With torque control, follower
parameter 26.15 Load share
optimal load sharing between the master and the follower. Pulse encoders are
recommended to be used in all torque-controlled followers.
If a drive needs to quickly switch between master and follower statuses, one user
parameter set (see page 70) can be saved with the master settings, another with the
follower settings. The suitable settings can then be activated using eg. digital inputs.
Communication
The communication on the fiber optic link is based on the DDCS protocol, which
employs data sets (specifically, data set 41). One data set contains three 16-bit
words. The contents of the data set are freely configurable, but the data set broadcast
by the master typically contains the control word, speed reference and torque
reference, while the followers return a status word with two actual values.
Three words of additional data can optionally be read from each follower. The
followers from which data is read are selected by parameter
selection in the master. In each follower drive, the data to be sent is selected by
parameters 61.01...61.03. The data is transfered in integer format over the link, and
then displayed by parameters
To indicate faults or warnings in the followers, external events (see parameter group
31 Fault functions) can be used. For example, use bit 3 (Fault) of the status word
received from a follower (typically parameter
trigger an external event.
Block diagrams of the master/follower communication are presented on pages
and 406.
Construction of the fiber optic link
The master/follower link is formed by connecting the drives together using fiber optic
cables. Drives with a ZCU-11 or ZCU-13 control unit require an additional FDCO
DDCS communication module; drives with a BCU-x2 control unit require an RDCO
module.
rate).
can be used to scale the incoming torque reference for
62.04...62.12
60.14 M/F follower
in the master.
62.04 Follower node 2 data 1
Program features 31
sel) to
405