5.2 Adaptive Control
Adaptive control is motor control based on the
performance characteristics of the motor. With adaptive
control, select the starting or stopping profile that best
matches the load type. The soft starter automatically
controls the motor to match the profile. The VLT
®
Soft
Starter MCD 500 offers 3 profiles:
•
Early acceleration and deceleration.
•
Constant acceleration and deceleration.
•
Late acceleration and deceleration.
Adaptive control uses 2 algorithms; 1 to measure the
motor characteristics, and 1 to control the motor. The soft
starter uses the first start to determine the motor charac-
teristics at zero speed and at maximum speed. During each
subsequent start and stop, the soft starter dynamically
adjusts its control to ensure that the actual motor
performance matches the selected profile throughout the
start. If the actual speed is too low for the profile, the soft
starter increases power to the motor. If the speed is too
high, the soft starter decreases power.
5.3 Starting Modes
5.3.1 Constant Current
Constant current is the traditional form of soft starting. It
raises the current from zero to a specified level and keeps
the current stable at that level until the motor has
accelerated.
Constant current starting is ideal for applications where the
start current must be kept below a specific level.
700%
600%
500%
300%
100%
400%
200%
10%
20% 30% 40% 50%
Rotor speed (% full speed)
60% 70% 80% 90% 100%
17
7
H
A
2
8
9
.1
1
Cur
re
nt
(%
mo
tor
f
ull
loa
d
c
ur
re
nt
)
1
3
2
1
Parameter 1-5 Initial current
2
Parameter 1-4 Current limit
3 Full voltage current
Illustration 5.2 Example of Constant Current
5.3.2 Current Ramp
Current ramp soft starting raises the current from a
specified starting level (1) to a maximum limit (3), over an
extended period (2).
Current ramp starting can be useful for applications where:
•
The load can vary between starts (for example a
conveyor which may start loaded or unloaded).
Set
parameter 1-5 Initial Current
to a level that
starts the motor with a light load. Set
parameter
1-4 Current Limit
to a level that starts the motor
with a heavy load.
•
The load breaks away easily, but starting time
must be extended (for example a centrifugal
pump where pipeline pressure must build up
slowly).
•
The electricity supply is limited (for example a
generator set), and a slower application of load
allows greater time for the supply to respond.
700%
600%
500%
300%
100%
400%
200%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
177HA290.
10
CURRENT (% Mo
tor F
ull Load Cur
rent)
ROTOR SPEED (% Full Speed)
Full Voltage Stator Current
Current Limit (e.g. Par. 2 = 400% x FLC)
Initial Current (e.g. Par. 3 = 250% x FLC)
Ramp Time
(eg Par. 4 = 10 secs)
1
Parameter 1-5 Initial current
2
Parameter 1-6 Start ramp time
3
Parameter 1-4 Current limit
4 Full voltage current
Illustration 5.3 Example of a 10 s Current Ramp Time
Product Features
VLT
®
Soft Starter MCD 500
36
Danfoss A/S © 05/2016 All rights reserved.
MG17K602
5
5
