Selection Of Advanced Harmonic Filter; How To Select The Correct Ahf; Calculation Of The Correct Filter Size Needed; Calculation Example - Danfoss AHF005 Design Manual

Selection of Advanced Harmo...
5 Selection of Advanced Harmon-
ic Filter
This chapter will provide guidance about how to choose the
right filter size and contains calculation examples, electrical
data and the general specification of the filters.

5.1 How to Select the Correct AHF

For optimal performance the AHF should be sized for the
mains input current to the frequency converter. This is the
input current drawn based on the expected load of the
frequency converter and not the size of the frequency
converter itself.
5.1.1 Calculation of the Correct Filter Size
Needed
The mains input current of the frequency converter (I
be calculated using the nominal motor current (I
displacement factor (Cos φ) of the motor. Both values are
normally printed on the name plate of the motor. In case the
nominal motor voltage (U ) is unequal to the actual mains
M,N
voltage (U ), the calculated current must be corrected with the
L
ratio between these voltages as shown in the following
I FC I M cos
equation: = 1.1 × ×
L N
. ,
The AHF chosen must have a nominal current (I
or larger than the calculated frequency converter mains input
current (I ).
FC,L
NOTE
Do not oversize the AHF. The best harmonic perform-
ance is obtained at nominal filter load. Using an
oversized filter will most likely result in reduced THiD
performance.
If several frequency converters are to be connected to the
same filter, the AHF must be sized according to the sum of the
calculated mains input currents.
NOTE
If the AHF is sized for a specific load and the motor is
changed, the current must be recalculated to avoid
overloading the AHF.
AHF005/010 Design Guide
) can
FC,L
) and the
M,N
U M
N
,
( ρ ) ×
U L
) equal to
AHF,N
®
MG.80.C3.02 - VLT is a registered Danfoss trademark

5.1.2 Calculation Example

System mains voltage (U ):
L
Motor name plate power(P ):
M
Motor efficiency (ƞ ):
M
FC efficiency (ƞ ):
FC
AHF effiency (ƞ )(worst case estimate):
AHF
Maximum line current (RMS):
P M
× 1000
=
U L × η × η × η × 3 380 × 0.96 × 0.97 × 0.98 × 3
M FC AHF
In this case a 96 A filter must be chosen.
380 V
55 kW
0.96
0.97
0.98
55 × 1000
= 91.57 A
15
5 5