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In the practical operation, as the network would have instantaneous power drop or loss. When VFD detects
the network loss, VFD will run decelerating, this is equivalent to charging to the grid side. The VFD can run
normally within [MOMENTARY POWER-OFF TIME] (0~1 sec); If the grid side does not restore the power over
[MOMENTARY POWER-OFF TIME], see 6.5.5.
The purpose is to compensate the voltage drop consumed on the motor rotor resistor during the low frequency
running, to improve the motor output torque. For the running state of the large torque load (such as Compressor,
Slurry Pump and Belt Conveyor, etc.), by setting VFD “Torque Lifting” parameters, it can solve the difficult
problems. The torque lifting value should be based on the load conditions, if lifts too much, there will be large
current impact during the start. The parameter setting range is 0%~15%, if 0%, it will no lifting; if 15%, it will be the
max lifting.
6.7 Torque Lifting
6.6 Instantaneous Power Loss Function
Figure 6-5 U/F curve
U
N
: VFD reference voltage F
N
: VFD reference frequency U
C
: Voltage of torque boost gain.
When the torque rise is set to 0%, the basic U/f line is similar as a straight line passing the origin. When the
torque boost gain is U
C
/U
N
*100%, the starting point of the basic U/f curve is U
C
, which increases the U/f value
and improves the output torque of the VFD.
