Hitachi CONVENTION 14 Instruction Manual page 99

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Torque Control Algorithms
The inverter generates the motor output according
to the V/f algorithm selected. Parameter A044
selects the inverter algorithm for generating the
frequency output, as shown in the diagram to the
right (A244 for 2nd motor). 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 at right shows the constant torque
characteristic from 0Hz to the base frequency
A003. The voltage remains constant for output
frequencies higher than the base frequency. The
graph below (left) shows the general variable
(reduced) torque curve. The range from 0Hz to
the base frequency is the variable characteristic.
V
100%
The graph above (right) shows the variable (reduced) torque curve, which has a
constant torque characteristic from 0Hz to 10% of the base frequency. This helps to
achieve higher torque at low speed with reduced torque curve at higher speeds.
Manual Torque Boost – The Constant
and
feature an adjustable
curve. When the motor load has a lot of
inertia or starting friction, you may
need to increase the low frequency
starting
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 A042 and A043. The manual boost is
calculated as an addition to the standard V/f curve.
Variable torque
A044 = 01
0
Base
freq.
Variable Torque
torque boost
torque characteristics
Hz
Max.
freq.
A042 = 5 (%)
algorithms
100%
5% voltage
boost
by
(100%=A082)
Inverter Torque Control Algorithms
Variable freq. control,
constant torque
Variable freq. control,
reduced torque
Variable freq. control,
reduced torque1
V Constant torque
A044 = 00
100%
0
Base
freq.
V Variable torque
A044 = 06
100%
0
10% Base Base
freq. freq.
V
A
0
1.8Hz 30Hz
A043 = 3 (%)
A044
00
Output
01
06
Hz
Max.
freq.
Hz
Max.
freq.
Hz
fbase = 60Hz