Siemens SINAMICS S120 Function Manual page 211

Figure 5-2
Closed-loop operation to approx. 0 Hz (can be set using parameter p1755) and the
possibility to start or reverse at 0 Hz directly in closed-loop operation (can be set using
parameter p1750) result in the following benefits:
● No changeover operation required within closed-loop control (bumpless behavior, no
frequency dips, no discontinuities in the torque).
● Closed-loop speed control without encoder down to and including 0 Hz
● Passive loads down to a frequency of 0 Hz
● Steady-state closed-loop speed control down to approx. 0 Hz possible
● Higher dynamic performance when compared to open-loop controlled operation
Note
If, in the closed-loop controlled mode, start from 0 Hz or reversing takes longer than 2 s, or
the time set in p1758 - then the system automatically changes over from closed-loop
controlled into open-loop controlled operation.
Note
Operation in encoderless torque control only makes sense if, in the speed range below the
changeover speed of the motor model (p1755), the setpoint torque is greater than the load
torque. The drive must be able to follow the setpoint and the associated setpoint speed
(p1499 , FBD 6030).
Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
Zero crossover and when induction motors start in closed-loop or open-loop controlled
operation
5.2 Vector control without encoder (SLVC)
Vector control
211