ABB ACS880 Series, Firmware Manual

Page: 75 / 764

Note:
• The function can be enabled only when the drive is a speed-controlled follower
in remote control mode.
• Drooping ( 25.8 ) is ignored when the load share function is active.
• The master and follower should have the same speed control tuning values.
• The speed correction term is limited by the speed error window parameters
24.44 and 24.43 . An active limitation is indicated by 6.19 .
• For a reliable ramp stop of a follower,
•
both parameters 24.43 and 24.44 must be set smaller than parameter 21.6
(or speed error window control disabled altogether by 24.41 ), and
• parameter 24.11 must be set smaller than parameter 21.6 .
Communication
A master/follower link can be built by connecting the drives together with fiber
optic cables (may require additional equipment depending on existing drive
hardware), or by wiring together the XD2D connectors of the drives. The medium
is selected by parameter
60.1 .
Parameter 60.3 defines whether the drive is the master or a follower on the
communication link. Typically, the speed-controlled process master drive is also
configured as the master in the communication.
The communication on the master/follower 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 using parameters
61.1 … 61.3 . 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.
The default setting of parameter 61.1 is Follower CW . With this setting in the
master, a word consisting of bits 0…11 of 6.1 and four bits selected by parameters
6.45 … 6.48 is broadcast to the followers. However, bit 3 of the follower control
word is modified so that it remains on as long as the master is modulating, and
its switching to 0 causes the follower to coast to a stop. This is to synchronize the
stopping of both master and follower.
Note: When the master is ramping down to a stop, the follower observes the
decreasing reference but receives no stop command until the master stops
modulating and clears bit 3 of the follower control word. Because of this, the
maximum and minimum speed limits on the follower drive should not have the
same sign – otherwise the follower would be pushing against the limit until the
master finally stops.
Program features 75