4.1.5 Automatic Motor Adaptation (AMA)
AMA is an algorithm to measure the electrical motor
parameters on a motor at standstill. This means that AMA
itself does not supply any torque.
AMA is useful when commissioning systems and
optimising the adjustment of the frequency converter to
the applied motor. This feature is particularly used where
the default setting does not apply to the connected motor.
1-29 Automatic Motor Adaptation (AMA)
allows a choice of
complete AMA with determination of all electrical motor
parameters or reduced AMA with determination of the
stator resistance Rs only.
The duration of a total AMA varies from a few minutes on
small motors to more than 15 minutes on large motors.
Limitations and preconditions:
•
For the AMA to determine the motor parameters
optimally, enter the correct motor nameplate
data in
1-20 Motor Power [kW]
to
1-28 Motor
Rotation Check
. For asynchronous motor, enter
the correct motor nameplate data in
1-24 Motor
Current
and
1-37 d-axis Inductance (Ld)
.
•
For the best adjustment of the frequency
converter, carry out AMA on a cold motor.
Repeated AMA runs may lead to a heating of the
motor, which results in an increase of the stator
resistance, Rs. Normally, this is not critical.
•
AMA can only be carried out if the rated motor
current is minimum 35% of the rated output
current of the frequency converter. AMA can be
carried out on up to one oversize motor.
•
It is possible to carry out a reduced AMA test
with a Sine-wave filter installed. Avoid carrying
out a complete AMA with a Sine-wave filter. If an
overall setting is required, remove the Sine-wave
filter while running a total AMA. After completion
of the AMA, reinsert the Sine-wave filter.
•
If motors are coupled in parallel, use only
reduced AMA if any.
•
The frequency converter does not produce motor
torque during an AMA. During an AMA, it is
imperative that the application does not force the
motor shaft to run, which is known to happen
with e.g. wind milling in ventilation systems. This
disturbs the AMA function.
•
Only Complete AMA can be activated when
running a PM motor (when
1-10 Motor
Construction
is set to
[1] PM non salient SPM
).
4.1.6 Fan Application with Resonance
Vibrations
In the following applications resonant vibrations can arise,
which can result in damage to the fan:
•
motor with fan mounted directly on the motor
shaft,
•
running point in field weakening area, and
•
running point close to or above nominal point.
Overmodulation is a way to increase the motor voltage
delivered by the frequency converter for f
mot
between 45
Hz and 65 Hz.
•
Advantages of overmodulation:
-
Lower currents and higher efficiency are
achievable in the field weakening area.
-
The frequency converter can give
nominal grid voltage at nominal grid
frequency.
-
When the mains voltage occasionally
falls below the correct motor voltage,
for example, at 43 Hz, then overmodu-
lation can compensate up to the
required motor voltage level.
•
Disadvantage of overmodulation: The non-
sinusoidal voltages increase the harmonics of the
voltages. This increase results in torque ripples,
which can damage the fan.
Solutions to avoid fan damage
•
The best solution is to disable the overmodu-
lation, reducing vibrations to a minimum.
However, this solution can also cause derating of
the applied motor in the range 5–10%, due to
the missing voltage no longer applied by the
overmodulation.
•
An alternative solution for applications where it is
not possible to disable the overmodulation, is to
skip a small frequency band of the output
frequencies. If the motor is designed to the limit
of the fan application, the voltage losses in the
frequency converter result in inadequate torque.
In these situations, the problem of vibration can
be reduced significantly by skipping a small
frequency band around the mechanical resonance
frequency, for example at the sixth harmonic. This
skip can be performed by setting parameters
(parameter group
4-6* Speed Bypass
) or by using
the semi auto bypass set-up
4-64 Semi-Auto
Bypass Set-up
. However, there is no general
design rule for making an optimal skip of
frequency bands as this is highly dependent on
Application Examples
VLT
®
DriveMotor FCP 106 and FCM 106 Design Guide
MG03M102 -
08/2015
37
4
4
Summary of Contents for VLT DriveMotor FCM 106
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