Stability Of The Speed Control Loop - Siemens SINAMICS S120 Function Manual

Start value of the adaptation
The frequency with which the adaptation starts at the pulse enable, i.e. the start value of the
adaptation, is always the current blocking frequency of the filter. It can be read in r5285 and
in the filter frequency parameters. After a pulse inhibit and renewed pulse enable, this
starting frequency is the blocking frequency last determined before the pulses were inhibited.
After switching the drive off and on, the adaptation starts with the frequency stored in the
frequency parameters of the adapted filter.
You have the following options in order to find a suitable start value for the frequency of the
adaptation:
● Use the current position of the resonance frequency as start value.
– To do this, read the current resonance frequency from the frequency response
– Determine the current resonance frequency from one cycle of the "One button tuning".
OR
● Use 500 Hz as start value.
The start value may be above or below the sought resonance frequency. This value should
be set as blocking frequency of the respective bandstop filter before the adaptation is
activated and the pulse enable set.
4.8.3.3

Stability of the speed control loop

Moving the bandstop filter changes the phase and amplitude frequency response of the
speed control loop. The stability of the speed control loop is not checked by the current
setpoint filter adaptation. If the current setpoint filter adaptation is operated with activated
online tuning (p5300 = 2), parameter settings are made automatically that guarantee the
stability.
If the autotuning is not activated, you have to make settings yourself that prevent an
instability. You must ensure a sufficiently large phase reserve. Note the following points:
● The phase and amplitude frequency response of the adapted filter
● The lower limit frequency of the adaptation (p5282)
A resonance frequency can be moved by the active closed-loop control. An instability of the
controller can be provoked by too high a controller gain that has a higher amplitude than the
mechanical resonance frequency and therefore influences the adaptation.
Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
measurement or
Servo control
4.8 Autotuning
131