76 Program features
Settings
Parameter group
37 User load curve
(page
255
).
U/f
ratio
The
U
/f function is only available in scalar motor control mode, which uses frequency
control.
The function has two modes: linear and squared.
In linear mode, the ratio of voltage to frequency is constant below the field weakening
point. This is used in constant torque applications where it may be necessary to
produce torque at or near the rated torque of the motor throughout the frequency
range
In squared mode, the ratio of the voltage to frequency increases as the square of the
frequency below the field weakening point. This is typically used in centrifugal pump
or fan applications. For these applications, the torque required follows the square
relationship with frequency. Therefore, if the voltage is varied using the square
relationship, the motor operates at improved efficiency and lower noise levels in
these applications.
The
U
/f function cannot be used with energy optimization; if parameter
45.11
Energy
optimizer
is set to
Enable
, parameter
97.20
U/F ratio
is ignored.
Settings
Parameter
97.20
U/F ratio
(page
344
).
Flux braking
The drive can provide greater deceleration by raising the level of magnetization in the
motor. By increasing the motor flux, the energy generated by the motor during
braking can be converted to motor thermal energy.
The drive monitors the motor status continuously, also during flux braking. Therefore,
flux braking can be used both for stopping the motor and for changing the speed. The
other benefits of flux braking are:
T
Br
20
40
60
(%)
Motor
speed
No flux braking
Flux braking
T
Br
= Braking torque
= 100 Nm
Flux braking
No flux braking
t
(s)
f
(Hz)
ACS380 FW.book Page 76 Friday, May 4, 2018 4:18 PM
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