Siemens SINAMICS S120 - Vector Control Without Encoder (SLVC); Three-Phase Induction Motor

Vector control
5.2 Vector control without encoder (SLVC)
Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
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5.2
Vector control without encoder (SLVC)
During operation via the "Sensorless vector control" function (SLVC), the position of the flux
and actual speed must be determined using the electric motor model. The motor model is
buffered by the incoming currents and voltages. At low frequencies (approx. 0 Hz), the motor
model cannot determine the speed with sufficient accuracy. For this reason, in this range,
the vector control can be changed over from closed-loop to open-loop control. When using
passive loads, additional limitations and constraints must be taken into consideration (see
Supplementary conditions for the operation of third-party motors).
5.2.1
Three-phase induction motor
The changeover between closed-loop/open-loop control is controlled by means of the time
and frequency conditions (p1755, p1756, p1758). If the setpoint frequency at the ramp-
function generator input and the actual frequency are below p1755 · (1 - (p1756/100 %))
simultaneously, then the system does not wait for the time condition.
Figure 5-1 Changeover conditions for SLVC