Torque Limits; Speed Dependant Current Limitation - ABB DCS 500B Description

Functional Software description

Torque Limits

Speed Depend-
ant Current Limi-
tation
38
Scaling of these limit values is 4095 = nominal current of the motor
I MOTN A (502)
ARM CURR LIM P (2307), scale: 4095 = I MOTN A (502)
ARM CURR LIM N (2308), scale: 4095 = I MOTN A (502)
Example. If the nominal current of the motor is 200A and the maximum
current is set to +/-230A, the limits are set to 230A/200A*4095=+/-4709.
Torque limits for the speed controller and the external torque refer-
ence chain are set by means of the parameters. The program
takes care that these limits cannot exceed the final torque limits,
which are based on the given armature current limit and flux refer-
ence. This ensures that, e.g. the speed controller does not ask for
a larger torque than the current limits allow.
The torque limitation outputs 12301...12306 are internally con-
nected to torque reference chain and speed controller.
The armature current limits are calculated for the torque limits by
means of the flux reference in such a way that the nominal current
of the motor with nominal flux gives nominal torque of the motor,
scaling: 4000 = T N(motor) . The final torque limits can be read out
from signals TORQMAX2 (12305) and TORQMIN2 (12306).
TORQ MIN (2306), scale: 4000==T N(motor)
TORQ MAX (2305), scale: 4000==T N(motor)
With the help of this function the load (motor´s shaft, coupling, gear
box and load machine) or the motor itself (commutation problems
at high speed) can be protected against overload.
If the drive is used in the field weakening range, the torque pro-
duced is lower than in the base speed range. Because of this and
together with the design criteria of the mechanics sometimes the
current needs to be lowered to avoid damage.
Some motors (most often at high speed motors) the current needs
to be reduced depending on the speed because of their electrical
design. Especially above the field weakening point the loading cur-
rent needs to be reduced according to instructions of motor cata-
logue.
The speed dependant current limitation function is described by 5
(x,y) coordinates. The pairs are:
1. ... _LIM_SPEED
2. point 1/4
3. point 2/4
4. point 3/4
5. 100% / 20000 point
Linear interpolation is used for values between these coordinates.
- ... _LIM_N1
- ... _LIM_N2
- ... _LIM_N3
- ... _LIM_N4
- ... _LIM_N5
DCS 500 Software Description