Hitachi L100 Series Instruction Manual page 84

Torque Control Algorithms
The inverter generates the motor output
according to the V/f algorithm selected.
Parameter A_44 selects the inverter algorithm
for generating the frequency output, as shown
in the diagram to the right. The factory
default is 00 (constant torque).
Review the following description to help you
choose the best torque control algorithm for
your application.
The built-in V/f curves are oriented toward developing constant torque or variable torque
characteristics (see graphs below). You can select either constant torque or reduced
torque V/f control.
Constant and Variable (Reduced) Torque – The graph below (left) shows the constant
torque characteristic from 0Hz to the base frequency A_03. The voltage remains
constant for output frequencies higher than the base frequency. The graph below (right)
shows the general variable (reduced) torque curve. The range from 0Hz to the base
frequency is the variable characteristic.
V
A_44 = 00
100%
0
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 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 A_42 and A_43. 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.
Constant torque
Hz
Base
Max.
freq.
freq.
L100 Inverter
Inverter Torque Control Algorithms
V/f control,
constant torque
V/f control,
variable torque
V
A_44 = 01 Variable torque
100%
0
Base
freq.
A_42 = 11
V
100%
Torque boost
A
11.8%
0
6.0Hz 30.0Hz
A_43 = 10 (%)
3–13
A44
00
Output
01
Hz
Max.
freq.
Hz
f base =
60Hz