User`s manual

160 • Vacon apfiff09 marine
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6
Set then the midpoint voltage to 2 * Zero Point Voltage
and
the midpoint frequency to (Zero Point Voltage/100%)*Nominal frequency of motor)
Step 2 (If needed): Activate speed control or U/f optimization (Torque boost).
Step 3 (If needed): Activate both speed control and U/f optimization.
NOTE!
In high torque low speed applications it is likely that the motor will
overheat. If the motor has to run long times under these conditions,
special attention must be paid to cooling of the motor. Use external
cooling for the motor if the temperature tends to rise too high.
P2.8.3.1 U/f optimisation ID109
Automatic
torque boost
The voltage to the motor changes proportionally to required torque
which makes the motor produce more torque at start and when running
at low frequencies. Automatic torque boost can be used in applications
where starting torque due to starting friction is high, e.g. in conveyors.
Even with linear U/f curve, the torque boost has an affect but the best
result will be achieved after the identification run when programmable
U/f curve is activated.
P2.8.3.2 U/f ration selection ID108
Linear:
0
The voltage of the motor changes linearly from zero point voltage to the field
weakening point where the voltage at FWP is supplied to the motor.
Squared:
1
The voltage of the motor changes from zero point voltage following the
squared curve form zero frequency to the field weakening point. The motor
runs undermagnetised below the field weakening point and produces less
torque. Squared U/f ratio can be used in applications where torque demand
is proportional to the square of the speed, e.g. in centrifugal fans and pumps.
Programmable U/f curve:
2
The U/f curve can be programmed with three different points.
1. Zero point voltage
2. Midpoint frequency and Midpoint voltage.
3. Field weakening point and field weakening point voltage.
Programmable U/f curve can be used if more torque is needed at low
frequencies. Make the Identification run for optimal setting (ID631).
Linear with flux optimisation:
3
The frequency converter starts to search for the minimum motor current in
order to save energy. This function can be used in applications with constant
motor load, such as fans, pumps etc.