Torque Control - Siemens 3RW44 Manual

Figure 7-2
Typical applications for voltage ramps
The voltage ramp function principle is suitable for all types of application.
If test runs with the application are carried out using motors that are smaller than those to be
used in the actual system, we recommend using the "Voltage ramp" startup mode.
For machines requiring a breakaway pulse (inverse load response, e.g. in mills or crushers),
the breakaway pulse must be set as described in chapter Breakaway pulse in combination
with the voltage ramp or torque control startup mode (Page 124). The "Voltage ramp+current
limiting (U+current limiting)" startup mode is recommended for heavy starting.
7.2.2

Torque control

The motor speed and torque are calculated using the voltage and current rms 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 starting 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
"Setting" menu item.
3RW44 soft starters
Manual, 03/2017, NEB535219502000/RS-AB/008
Principle of the voltage ramp for the torque characteristic
Device functions
7.2 Startup modes
121