7.3.5. 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.
Preconditions
The function is only effective in the motor control type "V/f characteristic control (VFC
open loop)".
Restrictions
Observe the following restrictions:
• 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 processes
(e.g. accelerations or load changes).
• Oscillation damping is only active if the setpoint speed is greater than 10 rpm and the
DCbus voltage exceeds a value of 100 V.
Details
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.
Identification of the oscillation
Before the oscillation damping function can be parameterised, the oscillation has to be
identified. One way to do this is to examine the motor current while oscillation damping is
switched off (gain = 0 %). At steady-state operation, a constant current flows. If the drive
oscillates, these oscillations are also visible on the motor current. It is therefore possible
to determine the frequency and the amplitude of the oscillation from the alternating
component of the motor current. In the following, this alternating component is referred
to as "current oscillation".
Parameter setting
The gain of the oscillation signal is to be set according to the following equation:
0x2B0A:001 (P318.01) = current amplitude * 100 % / (√2 * maximum device current)
The default time constant of the PT1 filter should be sufficient for most applications. If
required, it is only possible to adapt the time constant via »Emotron Easy starter«.
Generally, the time constant must be set so that the oscillation can be dampened, but that
higher-frequency components are filtered from the signal. The time constant is
determined from the reciprocal value of the double current oscillation frequency:
0x2B0A:002 (P318.02) = 1 / (2 * oscillation frequency)
Name / value range / [default setting]
(P318.01)
(Gain)
Gain of the oscillation signal.
•
With the setting 0, oscillation damping is deactivated.
0x2B0A:002
(P318.02)
Filter time
(Filter time)
Time constant of the PT1 filter.
Axis information: Maximum current
•
Read only: x.xx A
Display of the maximum current of the axis.
(P104.00)
(Motor current)
Display des present current-r.m.s. value.
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