Download The Danfoss Harmonic Filter AHF 005 and AHF 010

The Danfoss Harmonic Filter AHF 005 and AHF 010
We offer Drives Solutions – with our specialist
knowledge on applications and drives we can offer drive
solutions that guaranties minimum harmonic current
emission and can comply with IEEE 519-1992 and stage
1 of future EN 61000-3-12.
General information on “harmonics”?
The term ”harmonics” is often used in connection with
variable speed drives. But what are harmonics anyway?
Basically, any periodic signal can be represented as a sum
of sin-functions with frequencies equal to an integer
number of the fundamental frequency as shown in the
figure below where the sum of a signal with the
fundamental frequency and signals with frequencies 5,
7,11 and 13 times higher the fundamental is resulting in a
near square waveform. The signal with a frequency 5
times the fundamental is called the 5th harmonic.
1
5
4
3
Ih [A]
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2
1
0
0
5
10
15
20
25
Harmonic order h
30
35
40
The effects of harmonics?
In variable speed drives applications both the harmonic
current distortion and the harmonic voltage distortion are
of interest. The harmonic current and voltage distortion
have different effects on the power system and it is
therefore important to separate these two when discussing
the effects of ”harmonics”.
0.5
0
-0.5
-1
0
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
0.5
0
-0.5
-1
0
Thus for a non-sinusoidal current, as the input current of a
variable speed drive, a harmonic analysis is referring to
the decomposition of the current into the fundamental
current (50Hz or 60Hz) and into currents with frequencies
equal to a integer number times the fundamental
frequency. This decomposition is also called a Fourier
analysis. An example of such a Fourier analysis can be
seen on the figures below, where the current of a VFD
(only half a period is shown) is decomposed into the
harmonic currents.
10
8
Isa [A]
6
4
The harmonic current distortion is caused by the rectifier
part of the variable speed drive, typically a 6-pulse diode
rectifier. The harmonic currents can be described as a
reactive current adding to the active current.
Consequently the harmonic current distortion is
increasing the rms current and if not taking into account
can result in overheating of components such as the
supply transformer or cables. The amount of harmonic
current distortion is often described in percent of the
fundamental current also known as the total harmonic
current distortion (THID).

THID 
I
h2
2
h
I1
The harmonic current is normally flowing from the
harmonic current generator (e.g. the diode rectifier) into
the mains. The voltage drop caused by the harmonic
currents over the supply impedance causes then the
harmonic voltage distortion. I.e. the harmonic voltage
distortion is a product of the harmonic current distortion
and the supply impedance, where a grid with the largest
impedance yields the highest voltage distortion.
The harmonic voltage distortion can interfere with
equipment connected to the same line such as direct online motors or electronic equipment and eventually cause
this equipment to fail. The amount of harmonic voltage
distortion is often described in percent of the fundamental
voltage also known as the total harmonic voltage
distortion (THVD).

2
0
THVD 
U
h2
U1
2
h
Harmonic reduction techniques
To avoid potential problems or to comply with standard
and recommendations such as the IEEE 519-1992 or the
future EN 61000-3-12 several different harmonic
reduction techniques for variable speed drives exist. The
most well known solutions are:





AC coils
Built-in DC-coils
Multipulse (12- and 18-pulse)
Active filter
Passive filter
The most common and easiest harmonic reduction
technique is probably the use of AC-coils in front of the
VFD. The AC-coils smoothens the line current drawn by
the converter. Hereby, a significantly lower current
distortion can be achieved compared to a basic VFD
without coils. Similar effects as with AC-coils can be
obtained with DC-coils built-in to the VFD. However, the
DC-coils are, compared to AC-coils, smaller in size, have
higher efficiency and no reduction of the DC-link voltage.
12- and 18-pulse rectifiers have over a long period been
the standard solution to reduce the harmonic distortion
from drives. In theory the 5th and 7th harmonic currents
(for 18-pulse also the 11th and 13th) are cancelled by phase
shifting transformers and the use of two (or three) sixpulse diode rectifiers. However, a significant
disadvantage of the multi-pulse harmonic reduction
technique is the susceptibility to non-ideal supply voltage.
As some voltage unbalance or harmonic background
distortion always is present in reality a complete
cancellation of the 5th and 7th (11th and 13th ) is rarely
achieved.
Active filter is an emerging technique with the potential
to reduce the harmonic distortion to nearly zero.
However, for the active filter to be a successful harmonic
reduction technique for the near future some significant
challenges needs to be taken care of. For example, the
active filter is switching high voltages directly on the
mains with the result of introduction of high frequency
noise. At the time being there are no norms to regulate
the amount of the switching frequency noise (2kHz – 150
kHz) allowed into the mains, thus a major task for the
future is to determine a reasonable level of high frequency
noise to ensure that no damage occurs on other
equipment.
The Danfoss solution
Danfoss offers three levels of harmonic reduction
techniques.
As standard all Danfoss frequency converters are
equipped with built-in dc-link inductances reducing the
harmonics typically by a factor of two compared to
frequency converters without any measures. The built-in
dc-link inductances not only ensure compliances with
harmonic limits in most applications but also ensure a
long lifetime of the dc-link capacitor. Danfoss optionally
also offers the Danfoss harmonic filters AHF 010 and
AHF 005, where the AHF 010 is reducing the harmonic
current to less than 10% and the AHF 005 is reducing the
harmonic current to less than 5%.
The Danfoss AHF 005 and AHF 010 are advanced
harmonic filters not to be compared with traditional
harmonic trap filters. The Danfoss harmonic filters have
been specially designed to match the Danfoss frequency
converters.
Product range
Line Voltage
Filter Current
380 - 415 V AC (50 Hz) or
440 - 480 V AC (60 Hz)
10A – 325A (For higher power modules
can be paralleled)
AHF 010 and AHF 005 characteristics:
 Small compact housing that fits into a panel
 Easy to use in retrofit applications
 AHF 010 reduces the total harmonic current
distortion to 10%
 AHF 005 reduces the total harmonic current
distortion to 5%
 One filter module can be used for several
frequency converters
 High efficiency (> 0.98)
 User-friendly commissioning – no adjustment
necessary
 No routine maintenance required
Compared to other known solutions the Danfoss harmonic
filters offer excellent harmonic performance
Basic three phase six pulse rectifier
Three-phase rectifier with ac input
chokes
Danfoss FC with built-in dc-link
chokes
12-pulse rectifier
Danfoss FC with AHF 010
18-pulse rectifier
Active filters
Danfoss FC with AHF 005
THID
60% – 80%
35% – 45%
< 40%
10% – 15%
< 10%
4% – 7%
3% - 8%
< 5%
Current and Distortion Spectrum at Full Load
AH F 005
AH F 010
AHF 005
AHF 010
4%
6%
3%
5%
3%
4%
2%
3%
2%
2%
1%
1%
1%
0%
0%
5
7
11
13
17
Harmonic order
19
23
25
5
7
11
13
17
Harmonic order
Total Harmonic current distortion (THID) vs. Load
19
23
25
Performance at non-ideal supply voltage
Well knowing that the ideal three-phase supply voltage is
nearly non-existing the Danfoss harmonic filters AHF 005
and AHF 010 are developed in such a way that they are
ensuring values close to or better than 10% THID or 5%
THID also if the pre-existing total harmonic voltage
distortion of the supply voltage is 2% or the voltage
unbalance is 2%.
Furthermore, as shown in the figures below, even at sever
unbalance of 3% or severe background distortion of 5%
significant reduction of the harmonic current emission can
be obtained.
Please note that any other harmonic filter, 12-pulse or 18pulse rectifier is susceptible to non-ideal supply voltage
such as voltage unbalance or voltage background
distortion. The above stated performance levels at nonideal supply voltage should therefore not be seen as a
limiting factor but rather a demonstration of our high
information level when discussing important issues such
as harmonic distortion.