Hitachi WJ200-001L, Instruction Manual

Page: 109 / 680

3

24
Manual Torque Boost
–
The Constant
and Variable Torque algorithms
feature an adjustable
torque boost
curve. When the motor load has a lot of
inertia or starting friction, you may
need to increase the low frequency
starting torque characteristics by
boosting the voltage above the normal
V/f ratio (shown at right). The function
attempts to compensate for voltage
drop in the motor primary winding in
the low speed range.
The boost is applied from zero to the base frequency. You set the breakpoint of the boost
(point A on the graph) by using parameters

and

. The manual boost is
calculated as an addition to the standard V/f curve.
Be aware that running the motor at a low speed for a long time can cause motor
overheating. This is particularly true when manual torque boost is ON, or if the motor
relies on a built-in fan for cooling.
Voltage gain
–
Using parameter

you can
modify the voltage gain of the inverter (see
graph at right). This is specified as a
percentage of the full scale output voltage.
The gain can be set from 20% to 100%. It
should be adjusted in accordance with the
motor specifications. Gain can be changed
even during operation in V/f mode, and while
stopped in SLV mode. When the setting is
changed , reset (RS terminal on/off) is to be
executed so that the motor constants are
re-calculated.
After the setting is done, please be sure to reset (terminal RS on/off) to recalculate
the motor constant.
Refrain from change the setting value suddenly (within 10%). Inverter may
overvoltage trip due to the rapid change of output voltage.
Voltage compensation gain and slip compensation gain
–
Using parameters

and

, you can obtain better performance under automatic torque boost mode (

=

).
See following table for the concept of adjustment, including other parameters.
Symptom Adjustment Adjust item
Motor torque is not enough at low speed
(The motor does not rotate at low speed) Increase the voltage setting for manual torque
boost, step by step 
/

Increase the voltage compensation gain for
automatic torque boost, step by step 
/

Increase the slip compensation gain for
automatic torque boost, step by step 
/

Reduce carrier frequency

Motor speed decreases (stalls) when a Increase the slip compensation gain for 
/

100%
fbase fmax

=100
80%

=80
V
0
0
5% voltage
boost
(100%=

)

= 5 (%)
fbase = 60Hz 30Hz
V
100%
1.8Hz

= 3 (%)
Hz
A