195NA440.10
Danfoss
MCT 10
PLC
1
2
3
4
1
Start/stop
3
Closed loop process control
2
2 Speed reference
4
Combined fieldbus and traditional control signals
Illustration 3.1 Example of Control Structures
3.2 Mains Input
3.2.1 Mains Supply Interference/Harmonics
3.2.1.1 General Aspects of Harmonics
Emission
A frequency converter takes up a non-sinusoidal current
from mains, which increases the input current I
RMS
. A non-
sinusoidal current is transformed via a Fourier analysis and
split up into sine-wave currents with different frequencies,
that is, different harmonic currents I
n
with 50 Hz as the
basic frequency:
Harmonic currents
I
1
I
5
I
7
Hz
50
250
350
Table 3.1 Harmonic Currents
The harmonic currents increase the heat losses in the
installation (transformer, cables) even though they do not
affect the power consumption directly. Increased heat
losses can lead to overload of the transformer and high
temperature in the cables. Therefore keep the harmonics
at a low level by:
•
using frequency converters with internal
harmonic filters
•
using advanced external filters (active or passive).
175HA034.10
Illustration 3.2 Filters
NOTICE
Some of the harmonic currents can disturb communi-
cation equipment connected to the same transformer or
cause resonance with power-factor correction batteries.
To ensure low harmonic currents, the frequency converter
is equipped with intermediate circuit coils as standard.
These coils normally reduce the input current I
RMS
by 40%.
The voltage distortion on the mains supply voltage
depends on the size of the harmonic currents multiplied
by the mains impedance for the frequency in question.
The total voltage distortion THD is calculated based on the
individual voltage harmonics using this formula:
THD % = U
2
5 + U
2
7 + ... + U
2
N
(U
N
% of U)
System Integration
VLT
®
DriveMotor FCP 106 and FCM 106 Design Guide
MG03M102 -
08/2015
23
3
3
