Asynchronous motors - Special functions
Function description12
Version: 1.5
3.2 General information
Speed reduction due to sudden load increase at constant speed in one the processing operation (for
example ingression of a drill in solid material) is started with the Firmware v2.03 using the break down
protection controller (BPC).
Specific characteristic asynchronous motors
This function is only suitable for asynchronous motors without feedback system. The BPC is replaced the
current regulator. The max. torque of an asynchronous motor is simultaneously the break down moment. Will
that max. an uncontrolled state of the motor occurs. The result is an overcurrent error F2A1.
Typical torque / speed characteristic of an asynchronous motor
The diagram shows the course of a characteristic
curve a rotating field frequency. When operating with
a break down protection controller, always attempts
to avoid the prohibited area, possibly this does not
result in a setpoint specification respected. If so, your
PLC must take appropriate measures to ensure the
permissible Operation.
Optimal way to dimensioning from application and motor
If this application requires more current (torque) (e.g.,
dull milling tool), the current value travels along the
curve to the left
The left image shows a rotating field frequency when
the current is applied over the rotational speed. This
is mainly true for the linear range (Rated to cut-off
current). The area after the break down current is not
relevant (not permissible).
With the AX5000, the values:
• P-0-0093 (rated current) and
• P-0-0092 (peak current)*
* is calculated from P-0-0093 and the Overload factor
(for ASM mostly 1.5) from the motor data files.
The response of the BPC with respect to the current limit (P-0-0115) would be:
• The break down protection controller is activated.
• The rotating field frequency is reduced. As a result, the current value does not exceed the current limit
value (P-0-0115) and thus prevents the breaking current * from being reached.
* The servo drive turns the motor torque-free. It would lead to an uncontrolled stand still.
Operation in field weakening
In the field weakening follows the envelope of the
function M = 1 / n. In the linear range (Mk4 / Mk5), a
reduction in the rotational field frequency causes a
significant increase in the torque.
During the operation of an asynchronous motor,
different torque courses result depending on the
rotational field frequency (f).
Behavior of the break down moments with
changed field weakening:
• The break down moments (Mk1 - Mk3) are the
same to reach the field weakening.
• The break down moments (Mk4 and Mk5)
decrease almost linearly at the beginning of the
field weakening.
• As the field weakening (Mk6 and others)
increases, the break down moment is very low
and almost constant.
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