4 optimising the stalling behaviour, Optimising the stalling behaviour, 5motor control (mctrl) – Lenze 8400 User Manual
Page 192
5
Motor control (MCTRL)
5.7
Sensorless vector control (SLVC)
192
Lenze · 8400 protec HighLine · Reference manual · DMS 3.0 EN · 03/2013 · TD05
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5.7.4.4
Optimising the stalling behaviour
Motor stalling due to a torque overload in the field weakening range is prevented in sensorless
vector control by means of an inverter-internal stalling current monitoring. In the field weakening
range, hence at frequencies above the base frequency, it reduces the maximum current to prevent
the motor from stalling. The reduction depends on the current field frequency, the base frequency,
the DC-bus voltage and the maximum current (
). Generally it applies that a higher field
frequency causes a stronger limitation of the maximum current.
The field weakening behaviour of the sensorless vector control depends on the setting of the reset
time Ti of the torque controller (
).
The following applies to the reset time Ti (
) > 15 ms:
The behaviour in the field weakening range can be adapted via the override point of field weakening
(
). This parameter serves to shift the frequency-dependent maximum current characteristic:
•
> 0 Hz:
• The maximum current characteristic is shifted by the entered frequency to higher field
frequencies.
• The maximally permissible current and the maximum torque increase in the field weakening
range.
• The risk of motor stalling increases.
•
< 0 Hz:
• The maximum current characteristic is shifted by the entered frequency to lower field
frequencies.
• The maximally permissible current and the maximum torque are reduced in the field
weakening range.
• The risk of motor stalling is reduced.
The following applies to the reset time Ti (
) <= 15 ms:
The reduction of the magnetising current in the field weakening range can be adapted via the
override point of field weakening (
•
> 0 Hz:
The reduction of the magnetising current is shifted to higher field frequencies. Here, there is a
risk of the motor being magnetised too much and having too little voltage reserve for the
torque-creating current.
•
< 0 Hz:
The reduction of the magnetising current is shifted to lower field frequencies.
Note!
We recommend to keep the Lenze setting (0 Hz).
Note!
A function for enabling a stable operation can only be implemented to a limited extent
with a reset time Ti <= 15 ms For applications with speeds above the 2-fold rated speed,
we recommend a reset time Ti (
) > 15 ms.