Hitachi SJ7002 Series Instruction Manual page 99

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.
Constant torque
Output
voltage
100%
0
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.
Output
voltage
100%
a.
0
Maximum 10% of
frequency base
frequency
V
A042 = 10
100%
Torque boost
A
10%
0
6.0Hz 30.0Hz
A043 = 10%
3–15
SJ700 Inverter
2
Variable torque
b. c.
Base Maximum
frequency frequency
frequency
f base =
60Hz