Torque Control - Siemens SIRIUS 3RW44 System Manual

6.2.2 Torque Control

Start torque
Limiting torque
Starting time
Maximum starting
time
Internal run-up
recognition
SIRIUS 3RW44 System Manual
GWA 4NEB 535 2195-02 DS 04
The motor speed and torque is 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 ϕ = 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 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 stopping process, the motor data of the
motor connected to the soft starter should be entered in the selected parameter.
This can be specified using the "Setting" menu item.
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 running up. This value can thus also act as an
adjustable torque limitation.
In order to obtain a successful run-up, the parameter value should be set to
about 150 %. It should be at least high enough so that the motor does not get
stuck during startup. 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 such 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 is used to determine the time after which
the drive should have fully 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 defined 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 will close and the thyristors are bridged.
Device Functions
6-5