User`s manual

apfiff09 marine vacon • 155
24-
6
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 load increases also slip will increase. Slip is the
speed that rotor is behind of stator electrical frequency.
Below picture presents torque that is produced by 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 motor nominal speed and motor takes nominal current.
3. Pullout torque. This is point where motor produced torque start to decrease when slip
increases. After this point motor will stop if load is not reduced.
12
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”