ABB ACQ580, Firmware Manual

Page: 79 / 422

Program features 75

Power loss ride-through
See section Undervoltage control (power loss ride-through) on page 80 .

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 (default), 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 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. Thus using squared mode saves energy.
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
• Menu - Primary settings - Motor - U/f ratio
• Parameter 97.20 U/F ratio (page 290 ).

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.
T
Br
T
N
20
40
60
(%)
Motor
speed
No flux braking
Flux braking
T
Br
= Braking torque
T
N
= 100 Nm
Flux braking
No flux braking
t (s)
f (Hz)