Siemens Sinamics S120 Function Manual page 148

Vector control
4.1 Sensorless vector control (SLVC)
Figure 4-3 Vector control without an encoder
Blocking drives
If the load torque is higher than the torque limiting of the sensorless vector control, the drive
is braked to zero speed (standstill). In order that the open-loop controlled mode is not
selected after the time p1758, p1750.6 can be set to 1. Under certain circumstances the
"Motor blocked delay time" (p2177) must be increased.
NOTICE
Exception for reversing drives
It is not permissible to use this setting if the load can force the drive to reverse.
Active loads
Active loads, which can reverse the drive, e.g. hoisting gear, must be started in the open-
loop speed control mode. In this case, bit p1750.6 must be set to 0 (open-loop controlled
operation when the motor is blocked). The static (steady state) torque setpoint p1610 must
be greater than the maximum occurring load torque.
Note
Loads that can drive the motor
For applications with high regenerative load torques at low speeds, p1750.7 can also be set
to 1 As a result, the speed changeover limits of the motor model are increased and a faster
changeover can be made into open-loop controlled operation.
146
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Drive functions