Siemens SINAMICS G120XA - Encoderless Vector Control; Structure of Vector Control Without Encoder (Sensorless)

6.6.3 Encoderless vector control
6.6.3.1 Structure of vector control without encoder (sensorless)
Overview
The vector control comprises closed-loop current control and a higher-level closed-loop speed
control.
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1)
for induction motors
2)
Settings that are required
Figure 6-64 Simplified function diagram for sensorless vector control with speed controller
Using the motor model, the converter calculates the following closed-loop control signals from
the measured phase currents and the output voltage:
● Current component I
q
● Current component I
q
● Speed actual value
The setpoint of the current component I
d
(flux setpoint) is obtained from the motor data. For
speeds above the rated speed, the converter reduces the flux setpoint along the field
weakening characteristic.
When the speed setpoint is increased, the speed controller responds with a higher setpoint for
current component I
q
(torque setpoint). The closed-loop control responds to a higher torque
setpoint by adding a higher slip frequency to the output frequency. The higher output frequency
also results in a higher motor slip, which is proportional to the accelerating torque. I
q
and
Advanced commissioning
6.6 Motor control
SINAMICS G120XA converter
288 Operating Instructions, 03/2019, FW V1.0, A5E44751205B AB