AAC uses two algorithms, one to measure the motor's
characteristics and one to control the motor. The MCD 500
uses the first start to determine the motor's characteristics
at zero speed and at maximum speed. During each
subsequent start and stop, the starter dynamically adjusts
its control to ensure the motor's actual performance
matches the selected profile throughout the start. The
starter increases power to the motor if the actual speed is
too low for the profile, or decreases power if the speed is
too high.
5.3 Starting Modes
5.3.1 Constant Current
Constant current is the traditional form of soft starting,
which 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 particular 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
Illustration 5.2
1:
1-5 Initial current
2:
1-4 Current limit
3: Full voltage current
Table 5.1
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 of time (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
1-5 Initial Current
to a level that will start the
motor with a light load, and
1-4 Current Limit
to a
level that will start the motor with a heavy load.
•
the load breaks away easily, but starting time
needs to be extended (for example a centrifugal
pump where pipeline pressure needs to build up
slowly).
•
the electricity supply is limited (for example a
generator set), and a slower application of load
will allow 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)
Illustration 5.3
5.3.3 AAC Adaptive Acceleration Control
To use AAC Adaptive Acceleration Control to control
starting performance:
1.
Select Adaptive Control in
1-3 Start Mode
.
2.
Set
1-6 Start Ramp Time
.
3.
Select the desired profile in
1-13 Adaptive Start
Profile
.
4.
Set
1-4 Current Limit
sufficiently high to allow a
successful start. The first AAC start will be a
Constant Current start. This allows the MCD 500
to learn the characteristics of the connected
motor. This motor data is used by the MCD 500
during subsequent AAC Adaptive Acceleration
Control starts.
Application Examples
MCD 500 Operating Instruction
MG17K402 - VLT
®
is a registered Danfoss trademark
31
5
5