Set Oscillation Damping - Lenze i950 Commissioning Manual

13.4.8

Set oscillation damping

The oscillation damping serves to reduce the oscillations during no-load operation which are
caused by energy oscillating between the mechanical system (mass inertia) and the electrical
system (DC bus). Furthermore, the oscillation damping can also be used to compensate for
resonances.
Damping is possible only for constant oscillations at a steady-state operating
point.
Oscillations occurring sporadically cannot be damped.
Oscillation damping is not suitable for oscillations occurring during dynamic pro-
cesses (e.g. accelerations or load changes). Oscillation damping is only active if
the setpoint speed is greater than 10 rpm and the DC-bus voltage exceeds a
value of 100 V.
The determination of the oscillation is based on the active current. In order to obtain the
alternating component of the active current, this current is differentiated. This signal is then
passed through a PT1 filter.
Istwert Wirkstrom
0x2DD1:002
Identification of the oscillation
Before the oscillation damping can be parameterised, the oscillation must be identified. One
option is to look at the motor current when the oscillation damping is switched off (gain = 0
%). The oscilloscope function of the »PLC Designer« enables to record the following currents:
Q current
•
Total current
•
A passive load and continuous operation with constant speed (steady-state operation) result
in a constant current. If the drive oscillates, the motor current oscillates as well. This makes it
possible to detect the frequency and amplitude of the oscillation by means of the AC compo-
nent in the motor current. Hereinafter this AC component will be referred to as "current oscil-
lation".
Parameter setting
The gain of the oscillation damping is to be set according to the following equation:
The time constant must be set so that the oscillation can be dampened, but that higher-fre-
quency components are filtered from the signal. The time constant is determined from the
reciprocal value of the double current oscillation frequency:
The calculated oscillation frequency can be limited before being added to the rotating field
frequency. The maximum frequency can be derived from the amplitude of the current oscilla-
tion, the rated motor current and the slip frequency of the connected motor:
V/f characteristic control for asynchronous motor (VFC open loop)
Pendeldämpfung
Zeitkonstante
0x2B0A:002
Sollwert
Drehfrequenz
Verstärkung
0x2B0A:001
Rampen-Endfrequenz
0x2B0A:004
Verstärkung der Schwingungsdämpfung
Zeitkonstante
×
2 Amplitude der Stromschwingung
=
max. Frequenz
-
Motor Bemessungsstrom
Configuring the motor control
Begrenzung
0x2B0A:002
Stromamplitude
=
×
2 Gerätemaximalstrom
1
=
×
2 Schwingfrequenz
×
Nennschlupffrequenz
Set oscillation damping
×
100%
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