Operating Instructions ACU
Magnetization
+ current
impr.+ I*R-Comp.
In this operation mode, the current set with the parameter Current
during Flux-Formation 781 is impressed into the motor for
magnetization after release. The output frequency is kept at 0 Hz for the
Max. Flux-Formation Time 780. Once this time has elapsed, the output
frequency is increased according to the set acceleration. Once the
output frequency reaches the value set with parameter Frequency Limit
624, the Starting Current 623 is withdrawn. There is a smooth
transition to the V/f characteristic, and a load-dependent output current
is obtained. At the same time, the increase of the output voltage by the
IxR compensation becomes effective as from this output frequency. The
V/f characteristic is displaced by the portion of voltage which depends
on the stator resistance.
Magn.+
Curr.Imp.
w. Ramp Stop
Operation mode 12 contains an additional function to guarantee a
starting behavior under difficult conditions. The magnetization and
starting current impression are done according to operation mode 2. The
ramp stop takes the current consumption of the motor at the
corresponding operating point into account and controls the frequency
and voltage change by stopping the ramp. The Controller Status 275
signals intervention of the controller by displaying message “RSTP”.
Magn.+
Curr.Imp.
w. RS.+
I*R-Comp.
In this operation mode, the functions of operation mode 12 are
extended by the compensation of the voltage drop across the stator
resistance. When the output frequency reaches the value set with
parameter Frequency Limit 624, the increase of the output voltage by
the IxR compensation becomes effective. The V/f characteristic is
displaced by the portion of voltage which depends on the stator
resistance.
In contrast to field-oriented control systems, sensorless control systems feature a current controller
which controls the starting behavior. The PI controller controls the current impress of parameter
Starting Current 623. The proportional and integrating part of the current controller can be set via
parameters Amplification 621 and Integral Time 622. The control functions can be deactivated by
setting the parameters to 0.
13.1.1.1 Starting current
The Starting Current 623 ensures, particularly for high-torque start, a sufficient torque until the
Frequency Limit624 is reached.
Applications in which high current is permanently needed at a low speed are to be realized using
forced-ventilated motors to prevent thermal overload.
I
FIN
= Rated frequency inverter output current
o: Overload capacity of frequency inverter.
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