Torque Control - Siemens SIRIUS 3RW44 User Manual

6.2.2 Torque Control

Start torque
Limiting torque
Starting time
Maximum starting
time
Internal run-up
recognition
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 06
The motor speed and torque are calculated using the voltage and current r.m.s.
values, as well as the associated phase information between the line voltage
and the motor current (= cos  = sensorless control), and the motor voltage is
controlled accordingly.
Torque control means that the torque generated in the motor is linearly
increased from a parameterizable start torque up to a parameterizable end
torque within an adjustable starting time.
The advantage over the voltage ramp is the improved mechanical run-up
behavior of the machine.
The soft starter controls the torque generated at the motor continuously and
linearly according to the set parameters until the motor has completely run up.
For optimum torque control during the starting procedure, the motor data of the
motor connected to the soft starter should be entered in the selected parameter
set using the menu item "Setting".
The height of the start torque determines the switch-on torque of the motor. A
smaller start torque results in a smaller run-up torque and smaller starting
current. The start torque should be high enough so that the motor starts
immediately and softly when the start command is sent to the soft starter.
The level of the limiting torque determines which maximum torque should be
generated in the motor during run-up. This value can thus also act as an
adjustable torque limitation.
In order to achieve a successful run-up, the parameter value should be set to
approx. 150 %. It should, however, be at least high enough so that the motor
does not get stuck during run-up. This ensures that enough acceleration torque
is generated throughout the entire motor run-up phase.
The length of the starting time determines the time in which the start torque is
increased to the end torque.
A longer starting time results in a smaller acceleration torque over the motor run-
up. This results in a longer and softer motor run-up. The length of the starting
time should be selected in such a way that the motor accelerates softly until it
reaches its nominal speed.
If the starting time ends before the motor has completely run up, the torque is
limited to the set limiting torque until the soft starter recognizes the run-up
process and closes the internal bypass contacts.
The "Maximum starting time" parameter can be used to determine the time after
which the drive must have completed its run-up. If the drive is not in nominal
operation upon completion of the set time, the starting procedure is aborted and
an error message is generated.
The soft starter features an internal run-up recognition. If a completed motor run-
up is recognized within the set starting time, the ramp will be aborted and the
motor voltage will immediately be increased to 100 % of the line voltage. The
internal bypass contacts close and the thyristors are bridged.
Device Functions
6-5