Servo-Inverter i950 FW: from V01.06.04.2154
Response of the new version:
Parameter filter time constant (0x2DE0:26) newly implemented: Filtering of the actual velocity value for use in the pre-control path of field and field weakening controller now separately adjustable, independent of the actual velocity value filtering for the velocity controller.
The default setting of the new parameter (0x2DE0:26 = 10ms) is adapted to commonly used resolver types. The disturbing signals excited via the resolver error curve are thus sufficiently attenuated for the pre-control paths of the field controllers. 0x2DE0:26 can be increased if unsteady behavior should occur nevertheless.
Additionally, it is recommended to execute the commissioning function "Resolver Error Compensation".
See also the FAQ article linked at the end of this article.
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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