What happens?
Vibrations occurring during operation in the field-weakening range, with some combinations of motor and inverter, especially with powerful asynchronous motor types (ASM).
They are caused by interference signals contained in the actual speed value and caused by the feedback system.
Background:
The actual speed value is filtered by the filter time constant 0x2904 before it is used in the various control loops.
In order for an ASM drive to respond dynamically (servo) even when operating in field-weakening mode, the control loops of the field axis (field controller and field-weakening controller) must be matched to the motor in addition to the speed and position control loops. In Lenze motors, this is ensured by the motor parameters set in the motor data catalog and the corresponding equations. Nevertheless, there are combinations of motor and inverter that behave very unsteadily at high speeds.
This is due to the interference signals contained in the recorded actual speed, which affect the pre-control paths of the field control, despite correctly set control loops.
The reason for this is the so-called resolver error curve, which causes a harmonic disturbance component on the actual speed. The resulting speed ripple propagates via the mentioned pre-control paths into the field control loops, so that they become "unsteady".
This results in the following contrast: For the field control, a stronger filtering is required, whereas for the speed controller, a lower filtering is to be applied in order to ensure dynamic drive behavior. However, only the one filter time constant 0x2904 is available.
When does the behaviour occur?
In the following combination:
powerful asynchronous motor (ASM)
Resolver feedback
small actual speed value filter time ( 0x2904 < 2ms)
Resolver error curve not determined (0x2C44:1..9 on default).
Which products are affected?
Servo-Inverter i950 FW
Short term measures / evaluation / recommendations:
Set the actual speed value filter time (0x2904) to values > 2ms or have the resolver error curve identified by the device (0x2822:25 = 1) and thus activate resolver error compensation.
Alternatively, although not recommended, the gain of the field control loop (0x29C0:1) can be reduced. This has a similar damping effect as the use of speed filtering, but the control loop may tend to low-frequency oscillation ("pumping").
See also FAQ article:
i950 with ASM: operation at high speeds (field weakening range) - settings to reduce any vibrations that may occur
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