Siemens SINAMICS S120, Function Manual

Page: 604 / 1094

Function modules
8.14 Advanced Position Control (including Active Vibration Suppression)
Drive functions
604
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
8.14.4 APC with encoder combination and differential position feedback:
Description
The control loop for the speed control can be influenced using these two functions. The
encoder combination acts on the zero positions (quenching frequencies) of the system - and
the differential position feedback on the pole (resonant frequencies). Frequently, it makes
sense to use both functions together.
The encoder combination and the differential position feedback are always optimized
together with the speed control optimization. Generally, it makes sense to first parameterize
the differential position feedback and then the encoder combination.
Application examples:
● The ratio between the load moment of inertia and the motor moment of inertia is very
high. The oscillation frequency is relatively low. In this case, frequently only a very low
speed controller gain can be set.
Using the encoder combination, the zero position can be shifted towards higher
frequencies. The effective moment of inertia on the motor side is increased, and as a
consequence, a higher speed controller gain can be set. This effect can be reinforced by
combining with the differential position feedback.
● The effect of a natural oscillation at the motor is only very low (e.g. as a result of a high
gearbox ratio). This means that the speed controller has no influence on the oscillation.
The effects of the oscillation at the motor can be made more obvious by using a
combination of encoders and differential position feedback. The speed controller can be
set so that optimum damping is achieved. This especially makes sense if no additional
APC functions are being used.
The oscillation can be shifted to higher frequencies by combining encoders and differential
position feedback. The speed controller can then be set with a high gain to optimally respond
to disturbances. An additional APC function is used to dampen oscillations, e.g. acceleration
feedback (see Chapter "APC with acceleration feedback (Page 609)").
Note
By using an encoder combination and the differential position feedback, not only are the
dominant natural oscillations shifted in the control loop, but all natural oscillations originating
from the mechanical system between the two measuring systems. It is possible that a natural
oscillation, which actually should not be influenced, negatively influences the speed control.
This must be carefully observed when optimizing.