Sensorless Operation (Without An Encoder) - Siemens SINAMICS S120 Function Manual

Servo control

4.12 Sensorless operation (without an encoder)

4.12 Sensorless operation (without an encoder)
Note
Unstable operation
The operation of synchronous motors without an encoder must be verified in a test
application. Stable operation in this mode cannot be guaranteed for every application.
Therefore, the user will be solely responsible for the use of this operating mode.
Description
Both encoderless and mixed operation (with/without encoder) is possible. Encoderless
operation with the motor model allows a higher dynamic response and greater stability than
a standard drive with V/f control. Compared with drives with an encoder, however, speed
accuracy is lower and the dynamic response and smooth running features deteriorate.
Since the dynamic response in operation without an encoder is lower than in operation with
an encoder, acceleration torque precontrol is implemented to improve the control dynamic
performance. It controls, knowing the drive torque, and taking into account the existing
torque and current limits as well as the load moment of inertia (motor moment of inertia:
p0341 x p0342 + load torque: p1498), the required torque for a demanded speed dynamic
performance optimized from a time perspective.
Note
If the motor is operated with and without an encoder (e.g. p0491 ≠ 0 or p1404 < p1082), the
maximum current during operation without an encoder can be reduced via p0642 (reference
value is p0640) in order to minimize interfering, saturation-related motor data changes during
operation without an encoder.
A torque smoothing time can be parameterized via p1517 for the torque precontrol. The
speed controller needs to be optimized for operation without an encoder due to the lower
dynamic response. This can be achieved via p1470 (P gain) and p1472 (integral time).
In the low-speed range, the actual speed value, the orientation, and the actual flux can no
longer be calculated during operation without an encoder due to the accuracy of the
measured values and the parameter sensitivity of the procedure. For this reason, an open-
loop current/frequency control is selected. The switchover threshold is parameterized via
p1755 and the hysteresis via p1756.
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Function Manual, (FH1), 04/2014, 6SL3097-4AB00-0BP4
Drive functions