Cogging Torque Compensation - Siemens SINAMICS S120 Function Manual

9.15

Cogging torque compensation

Overview
Due to the fixed relationship between absolute position and cogging force for synchronous
motors, the "Cogging torque compensation" function is particularly suited to these motors for
the improvement of radial eccentricity. On the other hand, this function is not suitable for
induction motors.
Requirement
● Synchronous motors
● Servo drive objects
Function description
The cogging torque compensation is executed via a compensation table which, depending on
the position of the motor measuring system, is read out and precontrolled. The cogging torque
compensation can also be performed based on the direction. For this reason, a separate table
can be used for the compensation for each direction of motion (p5260, p5261).
The tables for the cogging torque compensation must be filled out using a "learning process".
During this learning process, the cogging torque can be measured when moving the motor and
stored in the table. If you want to use direction-based cogging torque compensation, you have
to perform corresponding learn runs for each direction of motion.
Note
Activation of the "Cogging torque compensation" function module leads to a significant
increase in the computing time required for each drive axis. The operation of 6 servo axes on
one Control Unit can no longer be guaranteed in all constellations and should be reduced to 5
axes.
Restrictions
● This function can only be applied for servo type drive objects.
● A motor encoder is always required for the cogging torque compensation.
● Transistor-transistor logic or HTL encoders are not suitable for cogging torque
compensation.
● The encoder must have absolute information, thus it must be an absolute value encoder or
have a clear zero mark or be distance-coded. Due to the premature validity message of
absolute information, DQI encoders are only suitable with a bypass (Encoder Data Set
switchover after start-up). SINAMICS encoder evaluations with actual hardware required
(SMC 10/20, SME12x, ≥ 6SL xxxx-xxxxx-xxx3) and SINAMICS firmware > 04.50.22).
● The compensation is then applied to the torque-generating current setpoint. It is only
effective if neither current nor voltage limiting intervenes and the frequency is not higher
than the current controller bandwidth.
Drive functions
Function Manual, 06/2019, 6SL3097-5AB00-0BP2
Function modules
9.15 Cogging torque compensation
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