Field Monitoring When Opti-Torque Changes The Field Direction; Field Current / Flux Linearisation - ABB DCS 500B Description

Functional Software description
Field monitoring
when OPTI-
TORQUE
changes the field
direction
Field current /
FLUX linearisa-
tion
58
Value 100 means that field current is directly proportional to torque
reference. When a 10% torque reference is wanted to produce full
field current, OPTI.REF GAIN (1315) is set to 1000.
Field monitoring differs from normal field changes in that during field
reversal other controllers are not blocked. The bit 5 TC FIELD
CHANGE in TC STATUS (11204) is kept in zero. The minimum
field signal is normally delayed by two seconds, and this is a fixed
delay. Because the time that the field current remains below the
minimum level is also a function of the torque reference, and the
torque reference depends on the process and the speed control-
ler´s gain values, two seconds may be too short a time in some ap-
plications.
For this reason the minimum field monitoring is by-passed, if the
field current reference falls below a certain level. Two parameters
are needed for defining the threshold to the reference when mini-
mum level is by-passed.
OPTI.REF MIN L (1316)
When the field reference falls below this limit, the minimum field
monitoring is by-passed.
OPTI REF MIN TD (1317)
This is an additional delay to keep the by-passing activated after the
field current has again increased above the reference level. The
field reference cannot be below the limit OPTI.REF MIN L (1316)
longer than this time when OPTI-TORQUE function is active or the
field reversal is done.
When an extremely accurate control of torque is needed, e.g. on
unwinder section of winder, the field current has to be linearised.
The reason is that torque is the product of motor armature current
and motor FLUX but motor FLUX is not directly proportional to the
field current.
Flux
Figure 43 Flux of DC-motor as a function of field current
614 = 15% of nominal
1000 = 1s
I exc.
DCS 500 Software Description