
188
• VACON®
apfiff09 marine
Local contacts: http://drives.danfoss.com/danfoss-drives/local-contacts/
7.8 Motor Control
Open Loop control
Open loop control controls the motor without encoder feedback from the motor shaft. Control mode
selections 0, 1 and 2 are open loop control modes.
Slip
Induction motor torque is based on slip. When the load increases, also slip will increase. Slip is the
speed that the rotor is left behind the stator electrical frequency.
The below picture presents the torque that is produced by the induction motor when connected
directly on line.
1. Motor Synchronous speed. Motor is taking only magnetization current.
2. Motor nominal operation point. Motor is producing 100% of rated torque and power. Actual
shaft speed is the motor nominal speed. The motor takes nominal current.
3. Pull out torque. This is the point where the motor produced torque starts to decrease when
slip increases. After this point, the motor will stop if load is not reduced.
1
2
3
Torque
100 %
100 %
~600 %
In frequency control, the load will determine the actual shaft speed.
Freq. Out 50 Hz
&
Freq. Ref 50 Hz
T
N
100 %
T
N
50 %
Nominal Slip
Slip
”Shaft
Freq”
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