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Rockwell Automation Publication 2198-UM002E-EN-P - February 2018
Appendix D
Motor Control Feature Support
Current Limiting for
Frequency Control
The current limiting module prevents the OutputCurrent value from
exceeding the OperativeCurrentLimit value when the drive is configured in
Frequency Control mode.
Figure 161 - Current Limiting Module
In Frequency Control mode, OperativeCurrentLimit is the minimum value of
the motor-thermal current limit, inverter-thermal current limit, motor-peak
current limit, drive-peak current limit, and the CurrentVectorLimit value.
The Effects of Current Limiting
Indirect current limiting is available for induction motors configured for
frequency control. You can use this feature to help prevent overcurrent faults
due to aggressive acceleration/deceleration profiles or impact loads. The
Current Limiting attribute uses a PI regulator to control the OutputCurrent
by adjusting the velocity reference.
Figure 162 - Effects of Current Limiting on an Aggressive Acceleration
+
–
+
–
Velocity from Planner
(MAJ)
Fine
Command
Velocity
Velocity
Reference
PI
Operative
Current Limit
Output
Current
IMPORTANT
When configured for Frequency Control (induction motors only), select the
Decel and disable stopping action only when the Current Limiting feature is
enabled.
16
14
12
10
8
6
4
2
0
O
utpu
t C
urr
en
t (
Arms), O
pe
ra
tiv
e
Cu
rr
en
t Limit
(rms)
Aggressive Acceleration, No Current Limiting
70
60
50
40
30
20
10
0
-10
Fr
eq
ue
nc
y (
H
z)
Time (ms)
Output Current
Operative Current Limit
Output Frequency
16
14
12
10
8
6
4
2
0
O
utpu
t C
urr
en
t (
Arms), O
pe
ra
tiv
e
Cu
rr
en
t Limit
(rms)
Aggressive Acceleration, Current Limiting Active
70
60
50
40
30
20
10
0
-10
Fr
eq
ue
nc
y (
H
z)
Time (ms)
Output Current
Operative Current Limit
Output Frequency
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0
200
400
600
800
1000
1200
1400
1600
1800
2000