Fan Application With Resonance Vibrations; Energy-Saving Examples; Why Use A Drive For Controlling Fans And Pumps; The Clear Advantage - Energy Savings - Danfoss VLT DriveMotor FCP 106 Design Manual

Application Examples
nameplate data in parameter 1-24 Motor Current
and parameter 1-37 d-axis Inductance (Ld).
•
For the best adjustment of the drive, 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 increase is not critical.
•
AMA can only be carried out if the rated motor
current is minimum 35% of the rated output
current of the drive. AMA can be carried out on
up to 1 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 drive 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.
This situation is known to occur with, for
example, windmilling in ventilation systems. The
running motor shaft disturbs the AMA function.
•
When running a PM motor (when
parameter 1-10 Motor Construction is set to [1] PM
non-salient SPM), only [1] Enable complete AMA
can be activated.
4.1.6 Fan Application with Resonance
Vibrations
In the following applications, resonant vibrations can occur,
which can result in damage to the fan:
•
Motor with fan mounted directly on the motor
shaft.
•
Running point in field weakening area.
•
Running point close to or above nominal point.
Overmodulation is a way to increase the motor voltage
delivered by the drive for f
mot
•
Advantages of overmodulation:
-
Lower currents and higher efficiency are
achievable in the field weakening area.
- The drive can give nominal grid voltage
at nominal grid frequency.
-
When the mains voltage occasionally
drops below the correct motor voltage,
for example at 43 Hz, overmodulation
MG03M302
Design Guide
45–65 Hz.
Danfoss A/S © 12/2018 All rights reserved.
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
drive 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 6
Perform this skip by setting parameters
(parameter group 4-6* Speed Bypass) or by using
the semi-auto bypass set-up parameter 4-64 Semi-
Auto Bypass Set-up. However, there is no general
design rule for making an optimal skip of
frequency bands as this depends on the width of
the resonance peak. In most situations, it is
possible to hear the resonance.

4.2 Energy-saving Examples

4.2.1 Why Use a Drive for Controlling Fans
and Pumps?
A drive takes advantage of the fact that centrifugal fans
and pumps follow the laws of proportionality for such fans
and pumps. For further information, see
chapter 4.2.3 Example of Energy Savings.

4.2.2 The Clear Advantage - Energy Savings

The clear advantage of using a drive for controlling the
speed of fans or pumps lies in the energy savings.
When comparing with alternative control systems and
technologies, a drive is the optimum energy control system
for controlling fan and pump systems.
4
th
harmonic.
41
4