10/05 AWB8230-1541GB
Motor control
65
Motor control
U/f characteristic
With a linear U/f characteristic the ratio of output voltage to
output frequency remains linear in the range from 0 Hz to the
rated frequency (PNU A003, a page 66) a constant torque
curve. This facilitates constant load torques also during
acceleration and deceleration.
In the range from the motor’s rated frequency (PNU A003) up to
the manufacturer’s specified maximum frequency (speed,
PNU A004 a page 66), the output voltage remains constant as
the frequency increases.
If you select the square-law torque curve, the U/f ratio changes in
a square-law pattern. This results in a reduced starting torque in
the lower frequency/speed range.
Examples:
a Linear U/f characteristic:
• For parallel operation of several motors at the frequency
inverter’s output.
• For changeovers at the frequency inverter’s output.
• When operating motors with a low rating.
b Quadratic U/f characteristic:
• Energy-optimized operation of pumps, fans, etc.
• Application requiring a reduced starting torque.
PNU Name RUN b031
= 10
Value Function DS
A044 U/f
characteristic
– – By default, the DF51 uses a linear U/f
characteristic (constant torque curve) to
accelerate and brake the motor.
00
00 Constant torque curve
01 Reduced torque curve
a
b
0
100
[%]
U
f
a Linear
b Quadratic
Figure 66: PNU A044 = 00, constant torque characteristic
f
1
: Transition frequency, motor rated frequency (H004)
f
2
: End frequency, highest permissible motor frequency
0
f
1
f
2
100
[%]
U
f
[Hz]
A004A003
Figure 67: PNU A044 = 01, square-law torque characteristic
f
1
: Transition frequency, motor rated frequency (H004)
f
2
: End frequency, highest permissible motor frequency
0
f
1
f
2
100
[%]
U
f
[Hz]
A003 A004
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