SJ700
2
Inverter
Configur
ing Dr
iv
e
P
a
ra
met
e
rs
3–15
Constant and Variable Torque –
The graph below (left) shows the constant torque character-
istic from 0Hz to the base frequency A003. The voltage remains constant for output frequencies
higher than the base frequency.
The graph above (right) shows the general characteristic for variable torque. The curve may be
best described in three sections, as follows:
a.
The range from 0Hz to 10% of the base frequency is the constant torque characteristic.
For example, a base frequency of 60Hz ends the constant torque characteristic segment
at 6Hz.
b.
The range from 10% of the base frequency to the base frequency is the variable
(reduced) torque characteristic. The voltage is output in the curve of frequency to the 1.7
power.
c.
After reaching the base frequency, the characteristic maintains a constant output voltage
for higher frequencies.
Using parameter A045 you can modify the voltage gain of the inverter. This is specified as a
percentage of the full-scale setting AVR (Automatic Voltage Regulation) in parameter A082.
The gain can be set from 20% to 100%. It must be adjusted in accordance with the motor
specifications.
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 character-
istics by boosting the voltage above the
normal V/f ratio (shown at right). The
boost is applied from zero to 1/2 the
base frequency. You set the breakpoint
of the boost (point A on the graph) by
using parameters A042 and A043. The
manual boost is calculated as an
addition to the standard straight V/f line (constant torque 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.
NOTE:
Manual torque boost applies only to constant torque (A044=00) and variable torque
(A044=01) V/f control.
NOTE:
The motor stabilization parameter H006 is effective for constant torque (A044=00) and
variable torque (A044=01) V/f control.
Constant torque
Variable torque
Maximum
frequency
Base
frequency
100%
100%
Maximum
frequency
Base
frequency
Output
voltage
Output
voltage
10% of
base
frequency
a.
b.
c.
0
0
f base =
60Hz
Torque boost
A042 = 10
A043 = 10%
frequency
100%
10%
0
V
A
6.0Hz
30.0Hz
