Siemens SINAMICS S120 Function Manual page 188

Vector control
5.1 Sensorless vector control (SLVC)
Encoderless vector control has the following characteristics at low frequencies:
● Closed-loop controlled operation for passive loads up to approx. 0 Hz output frequency
(p0500 = 2), for p1750.2 = 1 and p1750.3 = 1.
● Start an induction motor in the closed-loop controlled mode (after the motor has been
completely excited), if the speed setpoint before the ramp-function generator is greater
than p1755.
● Reversing without the need to change into the open-loop controlled mode is possible, if
the range of the changeover speed p1755 is passed through in a shorter time than the
changeover delay time set in p1758, and the speed setpoint in front of the ramp-function
generator lies outside the open-loop controlled speed range of p1755.
● In the "Torque control" mode, at low speeds, the system always changes over into the
open-loop controlled mode.
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.
188
Zero crossover and when induction motors start in closed-loop or open-loop controlled
operation
Function Manual, (FH1), 04/2014, 6SL3097-4AB00-0BP4
Drive functions