EN-TH05-11/2004
Martti Tuomainen
1 (9)
Shunt Active Filters (SAF)
Operation principle of a Shunt Active Filter.
Non-linear loads like Variable Speed Drives, Uninterrupted Power Supplies
and all kind of rectifiers draw a non-sinusoidal current from the network.
Therefore they can be considered to be harmonic current sources. Shunt
Active Filter works as a current source which, when properly designed and
controlled, produces harmonic currents having opposite phase than those
harmonic currents produced by the non-linear load. When such a Shunt Active
Filter is connected parallel with a non-linear load its harmonic currents are
compensated and the network is loaded with almost fundamental current only.
3-phase 400V 50Hz or 60Hz
i1
-Σih
i1+Σih
Variable speed drive or some other
harmonic source
Active filter
Figure 1. Non-linear load with shunt active filter
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
EN-TH05-11/2004
Martti Tuomainen
2 (9)
Shunt Active Filter and harmonic producing load
Considering harmonic current producing load like a typical voltage source
Variable Speed Drive with a 4% line side reactor in Figure 2 its AC-side current
looks like in Figure 3.
L1
L2
L3
AC-motor
4%
M
6-pulse diode rectifier
Inverter
Figure 2. Voltage Source Variable Speed Drive
1 50.00
5th harmonic 32.0%
7th harmonic 9.5%
1 00.00
50.00
11th harmonic 6.4%
0.00
0.1 6000
-50 . 00
-1 0 0 . 0 0
0. 1 6500
0.1 7000
0. 1 7500
0.1 8000
0.1 8500
0. 1 9000
0.1 9500
0.20000
13th harmonic 3.3%
17th harmonic 2.4%
19th harmonic 1.8%
-1 5 0 . 0 0
Figure 3. AC side current of a Voltage Source Variable Speed Drive and its
harmonic content
In Figure 4 there is the current produced by an active filter to compensate
harmonic currents shown in Figure 3. Please note that in this case active filter
is not producing fundamental reactive power and therefore there is no
fundamental current but harmonic currents only.
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
EN-TH05-11/2004
Martti Tuomainen
3 (9)
50.00
40.00
- 5th harmonic 32.0%
- 7th harmonic 9.5%
30.00
20.00
-11th harmonic 6.4%
-13th harmonic 3.3%
-17th harmonic 2.4%
-19th harmonic 1.8%
1 0.00
0.00
0.1 600
0.1 650
0.1 700
0.1 750
0.1 800
0.1 850
0.1 900
0.1 950
0.2000
-1 0 . 0 0
-2 0 . 0 0
-3 0 . 0 0
-4 0 . 0 0
-5 0 . 0 0
Figure 4. Current of an active filter and its harmonic content
Connecting this active filter parallel with the load harmonics are compensated
and the network is loaded by almost fundamental current only like shown in
Figure 5.
1 50.00
1 00.00
3-phase 400V 50Hz or 60Hz
50.00
0.00
0. 1 600
i1
0.1 650
0. 1 700
0. 1 750
0.1 800
0.1 850
0.1 900
0.1 950
0.1 800
0. 1 850
0.1 900
0.1 950
0. 2000
-5 0 . 0 0
-1 0 0 . 0 0
-1 5 0 . 0 0
1 50. 00
50.00
40.00
1 00. 00
30.00
i1+Σih
50. 00
20.00
1 0.00
0. 00
0. 1 6000
0.00
0. 1 6500
0. 1 7000
0. 1 7500
0. 1 8000
0. 1 8500
0. 1 9000
0. 1 9500
0. 20000
0 . 1 6 00
0. 1 650
0.1 700
0.1 750
-1 0 . 0 0
-5 0 . 0 0
-2 0 . 0 0
-Σih
-1 0 0 . 0 0
-1 5 0 . 0 0
-3 0 . 0 0
-4 0 . 0 0
-5 0 . 0 0
- 5th harmonic 32.0%
- 7th harmonic 9.5%
-11th harmonic 6.4%
-13th harmonic 3.3%
Variable speed drive or some
other harmonic source
Active filter
-17th harmonic 2.4%
-19th harmonic 1.8%
Figure 5. The effect of the connection of an active filter parallel to the harmonic
producing load.
It should be noted that the output current of an active filter has a continuous
spectrum of all harmonics due to the accuracy of the control system. Therefore
in the network current there are still some harmonic currents.
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
0. 2000
EN-TH05-11/2004
Martti Tuomainen
4 (9)
Connection of Shunt Active Filters
In case of 3-phase 3-wire system current of the load is measured from two
phases and the current of the third phase is derived from two others.
Measured currents are used to control the output of the active filter. In Figure 6
there is the connection of an active filter in 3-phase 3-wire supply system.
L1
L2
L3
N
PE
950
850
750
650
550
450
1.500
350
250
1.000
150
50
0.500
-50
0 .4 8 0 0
-150
0.000
0
50
100
150
200
250
300
0 .4 8 5 0
0 .4 9 00
0 .4 9 5 0
0 .50 0 0
CT L1
-250
350
-350
-0.500
-450
-550
-1.000
-650
-750
-1.500
-850
-950
1.500
1.000
950
0.500
850
750
0.000
0
50
100
150
200
250
300
650
350
550
-0.500
450
350
-1.000
250
150
-1.500
50
-50
0 .4 8 0 0
-150
0 .4 8 5 0
0.4 9 0 0
0 .4 9 5 0
0 .5 0 0 0
CT L2
-250
1. 500
-350
-450
1. 000
-550
0. 500
-650
-750
0. 000
-850
0
50
100
150
200
250
300
350
-950
-0. 500
-1. 000
-1. 500
Network currents
1.500
PE L1 L2 L3
1.000
1 2 3 4 1 2 3 4
0.500
0.000
0
50
100
150
200
250
300
350
-0.500
-1.000
-1.500
Source of
harmonics
Active filter
1.500
1.000
0.500
0.000
0
50
100
150
200
250
300
350
-0.500
-1.000
-1.500
Figure 6. Connection of the active filter to 3-phase 3-wire supply system.
In Figure 7 there is the connection of the active filter to 3-phase 4-wire supply
system. In this case current is measured from each phase to allow also
unsymmetrical operation of the active filter. This version of the active filter can
compensate zero sequence harmonics too.
L1
L2
L3
N
PE
95 0
85 0
75 0
65 0
55 0
45 0
1. 500
35 0
25 0
1. 000
15 0
50
0. 500
- 50
0 .4 8 0 0
- 1 50
0. 000
0
50
100
150
200
250
300
0.4 8 5 0
0 .4 90 0
0 .4 9 50
0.5 0 0 0
CT L1
- 2 50
350
- 3 50
-0. 500
- 4 50
- 5 50
-1. 000
- 6 50
- 7 50
-1. 500
- 8 50
- 9 50
1.500
1.000
950
0.500
850
750
650
0.000
0
50
100
150
200
250
300
350
550
-0.500
450
350
-1.000
250
150
-1.500
50
-50
0.4 8 0 0
-150
0 .4 85 0
0 .4 9 00
0 .4 9 5 0
0 .50 0 0
CT L2
-250
1.500
-350
-450
1.000
-550
-650
0.500
-750
-850
0.000
0
50
100
150
200
250
300
-950
350
-0.500
-1.000
950
-1.500
850
750
650
550
1. 500
450
350
1. 000
250
150
0. 500
50
-50
0 .4 80 0
-150
0. 000
0
50
100
150
200
250
300
350
-0. 500
0 .4 8 50
-250
-350
-1. 000
-450
-550
-1. 500
-650
-750
-850
Network currents
-950
0 .4 9 0 0
0 .4 9 5 0
0 .5 00 0
CT L3
1.500
PE L1 L2 L3 N
1 2 3 4 1 2 3 4 1 2 3 4
Active filter
1.000
0.500
0.000
0
50
100
150
200
250
300
350
-0.500
-1.000
-1.500
Source of
harmonics
1.500
1.000
0.500
0.000
0
50
100
150
200
250
300
350
-0.500
-1.000
-1.500
Figure 7. Connection of the active filter to 3-phase 4-wire supply system.
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
EN-TH05-11/2004
Martti Tuomainen
5 (9)
Figure 8 shows the block diagram of the active filters with its main
components.
L1
L2
L3
EMC filter
EMC
IGBT bridge
Output
reactor
1.50 0
Men
machine
interface
Inverter control
IGBT-Drivers
Current
Transducers
1.00 0
0.50 0
0.00 0
0
50
10 0
15 0
20 0
25 0
30 0
35 0
-0.50 0
-1.00 0
-1.50 0
Source of
harmonics
1 .500
1 .000
Inverter
+
0 .500
0 .000
0
50
10 0
150
200
250
300
3 50
-0 .500
-1 .000
-1 .500
Figure 8. Connection of the active filter to 3-phase 4-wire supply system.
Experiences with shunt active filter
To demonstrate the operation of shunt active filter measurement was made at
a DC-drive without and with shunt active filter Figure 9. As can be seen the
curve form of the supply current is almost fundamental current only when
active filter is on. It should also be noted that the fast changes of the supply
current can be followed easily.
Figure 9. Network current of a DC-drive without active filter (a) and with shunt
active filter (b).
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
EN-TH05-11/2004
Martti Tuomainen
6 (9)
Another example shows the high dynamics of the shunt active filter when
compensating fast changing harmonic producing loads. In Figure 10 there is
the current of a lift drive while accelerating without shunt active filter with the
typical 6-pulse rectifier current curve form. In Figure 11 there is the same
current when active filter is on. Comparison of the Figures 10 and 11 reveals
that harmonics are effectively compensated and the system being loaded with
fundamental current only.
Figure 10. Supply current of a lift drive while accelerating without active filter.
Figure 11. Supply current of a lift drive while accelerating with active filter.
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
EN-TH05-11/2004
Martti Tuomainen
7 (9)
Comparison of shunt active and passive filters.
When there is a need to compensate significant fundamental reactive power of
relatively stabile harmonic producing loads the passive filters have turned out
to be economically justified. With passive filters both reactive power
compensation and harmonic filtering can be made at the same time.
When there is a need to compensate fast changing harmonic currents and
fundamental reactive power active filters are the right solution. Very short
response time of the active filters allows the better utilization of the supply
system in respect of the voltage fluctuations.
The range of available shunt active filters
Current
IRMS:
25 A
30 A
35 A
40 A
50 A
60 A
70 A
85 A
100 A
140 A
200 A
260 A
3-phase 3-wire systems
3-phase 4-wire systems
400V, 50/60Hz
3L/17 kVA (40 A)
3L/20 kVA (45 A)
3L/25 kVA (50 A)
3L/28 kVA (60 A)
3L/35 kVA (75 A)
3L/42 kVA (100 A)
3L/50 kVA (110 A)
3L/60 kVA (130 A)
3L/70 kVA (150 A)
3L/100 kVA (200 A)
3L/140 kVA (300 A)
3L/180 kVA (400 A)
3x230V, 50/60Hz
4L/17 kVA (40 A)
4L/20 kVA (45 A)
4L/25 kVA (50 A)
4L/28 kVA (60 A)
4L/35 kVA (75 A)
4L/42 kVA (100 A)
4L/50 kVA (110 A)
4L/60 kVA (130 A)
4L/70 kVA (150 A)
4L/100 kVA (200 A)
4L/140 kVA (300 A)
4L/180 kVA (400 A)
Legend:
3L: for 3-phase 3-wire systems
4L: for 3-phase 4-wire systems with zero sequence harmonics
and asymmetrical loads
In brackets: the peak value of the current to be compensated
Please note that in case one active filter is not big enough it is possible to
connect several active filters parallel to reach required rated current.
The four wire active filters are available in three different variations:
Neutral current can be 1-time, 2-times or 3-times line current.
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
EN-TH05-11/2004
Martti Tuomainen
8 (9)
Application of shunt active filters
It should be noted that active filters can be designed to compensate both
harmonic currents and fundamental reactive power.
Additionally to the system voltage UL the following parameters of the current to
be compensated have to be determined to be able to design the capacity of
the shunt active filter:
1. The root-mean-square of the current to be compensated IRMS
2. The amplitude IS
3. The rate of rise of the current
di
dt
4. The harmonic coefficient ki
5. For the 4-wire shunt active filter: The geometric sum of all harmonics
divisible by 3.
Rated output of the shunt active filter for 3-wire and 4-wire application for the
compensation of the harmonic currents:
DMAX = 3 × UL × IRMS × k i
Rated output capacity of the shunt active filter for single phase application for
the compensation of the harmonic currents:
DMAX = U × IRMS × k i
Rated output of the shunt active filter for 3-wire and 4-wire application for the
compensation of the harmonic currents and reactive power:
2
2
2
QMAX = DMAX
+ Q1MAX
= ( 3 × UL × IRMS × k i )2 + Q1MAX
Rated output of the shunt active filter for single phase application for the
compensation of the harmonic currents and reactive power:
2
2
2
QMAX = DMAX
+ Q1MAX
= (U × IRMS × k i )2 + Q1MAX
Please note that the standard crest factor of the current of the shunt active
filter is 2 .
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360
EN-TH05-11/2004
Martti Tuomainen
9 (9)
Definitions:
Active power P:
P = U × I1 × cosϕ1 , where I1 is fundamental current and ϕ1 is
the angle between voltage and fundamental current
Apparent power S1: Fundamental apparent power S1 = U × I1
Reactive power Q1: Fundamental reactive power Q1 = U × I1 × sinϕ1
Displacement factor cosϕ1 : cosϕ1 =
P
S1
Total apparent power S:
S = U × I = U × I12 + I22 + I32 + .....
Total reactive power Q:
Q = S2 - P2
Q = (U × I1 × sinϕ1 )2 + U2 × (I22 + I32 + .... )
The reactive power consists of fundamental reactive power Q1 and distortion
reactive power D.
2
2
2
3
oo
ΣI
2
4
Distortion reactive power D: D = U I + I + I .... = U
Content of the fundamental frequency gi: gi =
Harmonic coefficient ki:
h>1
2
h
I1
I
I22 + I32 + I24 ....
ki =
I
I2 - I12
ki =
I
k i = 1 - g2i
k i2 + g2 = 1
i
Power factor λ :
λ=
P
= gi × cosϕ 1
S
Current harmonic total distortion THDi:
∞
THDi =
ΣI
2
n>1 n
I
Nokian Capacitors Ltd. P.O. Box 4 Tampere Finland Tel: +358-3-388311 Fax: +358-3-3883360