Abb technical guide no.06 revc

ABB drives
Technical guide No. 6
Guide to harmonics with
AC drives

2 Guide to harmonics with AC drives | Technical guide No. 6

Technical guide No. 6 | Guide to harmonics with AC drives 3
© Copyright 2011 ABB. All rights reserved.
Specifications subject to change without notice.
3AFE64292714 REV C EN 11.5.2011
Technical guide No. 6
Guide to harmonics with AC drives

Contents
Chapter 1 - Introduction ............................................................................7
General..............................................................................................7
Chapter 2 - Basics of the harmonics phenomena......................................8
Chapter 3 - Harmonic distortion sources and effects..............................10
Chapter 4 - Harmonic distortion calculation by using DriveSize
software...................................................................................................11
4.1 Circuit diagram for the calculation example ..................................11
4.2 Input data for motor load ............................................................11
4.3 Motor selection...........................................................................12
4.4 Inverter selection ........................................................................12
4.5 Inverter supply unit data..............................................................12
4.6 Network and Transformer data input............................................13
4.7 Calculated harmonic current and voltage .....................................13
4.8 Calculated harmonic currents in graphical form ............................13
4.9 Part of the printed report.............................................................14
Chapter 5 - Standards for harmonic limits...............................................15
5.1 EN61800-3 (IEC1800-3) Adjustable speed electrical power drive
systems ...........................................................................................15
5.2 IEC1000-2-2, Electromagnetic compatibility (EMC) ......................16
5.3 IEC1000-2-4, Electromagnetic compatibility (EMC) ......................16
5.4 IEC1000-3-2, Electromagnetic compatibility (EMC).......................16
5.5 IEC1000-3-4, Electromagnetic compatibility (EMC).......................16
5.6 IEEE519, IEEE Recommended practices and requirements for
harmonic control in electrical power systems .....................................17
Chapter 6 - Evaluating harmonics ...........................................................19
Chapter 7 - How to reduce harmonics by structural modifications
in the AC drive system.............................................................................20
7.1 Factors in the AC drive having an effect on harmonics .................20
7.2 Table: List of the different factors and their effects........................21
7.3 Using 6-pulse diode rectifier........................................................21
7.4 Using 12-pulse or 24-pulse diode rectifier....................................22
7.5 Using phase controlled thyristor rectifier ......................................22
7.6 Using IGBT bridge ......................................................................23
7.7 Using a larger DC or AC inductor ................................................24

Chapter 8 - Other methods for harmonics reduction...............................27
8.1 Tuned single arm passive filter ....................................................27
8.2 Tuned multiple arm passive filter .................................................27
8.3 External active filter ....................................................................28
Chapter 9 - Summary of harmonics attenuation......................................30
9.1 6-pulse rectifier without inductor .................................................30
9.2 6-pulse rectifier with inductor ......................................................30
9.3 12-pulse rectifier with polycon transformer...................................30
9.4 12-pulse with double wound transformer .....................................30
9.5 24-pulse rectifier with 2 3-winding transformers ...........................31
9.6 Active IGBT rectifier ....................................................................31
Chapter 10 - Definitions...........................................................................32
Index .......................................................................................................34

Chapter 1 - Introduction
General
This guide continues ABB’s technical guide series, describing
harmonic distortion, its sources and effects, and also distortion
calculation and evaluation. Special attention has been given to
the methods for reducing harmonics with AC drives.

, where
the total RMS current and
direct current output from the rectifier.
(valid for ideal filtered DC current)
is(t) = i1(t) + Σ ih(t)
Converter
load
Other
loads
Point of Common
Coupling (PCC)
Mains transformer
Rs Ls
u(t)
Chapter 2 - Basics of the harmonics
phenomena
Harmonic currents and voltages are created by non-linear loads
connected on the power distribution system. Harmonic distortion
is a form of pollution in the electric plant that can cause problems
if the sum of the harmonic currents increases above certain limits.
All power electronic converters used in different types of elec-
tronic systems can increase harmonic disturbances by injecting
harmonic currents directly into the grid. Figure 2.1 shows how
the current harmonics (ih) in the input current (is) of a power
electronic converter affect the supply voltage (ut).
Figure 2.1 Plant with converter load, mains transformer and other loads.
The line current of a 3-phase, 6-pulse rectifier can be calculated
from the direct output current by using the following formula.
The fundamental current is then

Order of harmonic component
Harmonic-
Current
(%)
The rms values of the harmonic components are:
where
In a theoretical case where output current can be estimated as
clean DC current, the harmonic current frequencies of a 6-pulse
three phase rectifier are n times the fundamental frequency (50
or 60 Hz). The information given below is valid in the case when
the line inductance is insignificant compared to the DC reactor
inductance. The line current is then rectangular with 120° blocks.
The order numbers n are calculated from the formula below:
Basics of the harmonics phenomena
and the harmonic components are as shown in Figure 2.2.
Figure 2.2 The harmonic content in a theoretical rectangular current of a
6-pulse rectifier.
The principle of how the harmonic components are added to
the fundamental current is shown in figure 2.3, where only the
5th
harmonic is shown.
Figure 2.3 The total current as the sum of the fundamental and 5th
harmonic.

Chapter 3 - Harmonic distortion sources
and effects
Common non-linear loads include motor starters, variable speed
drives, computers and other electronic devices, electronic light-
ing, welding supplies and uninterrupted power supplies.
The effects of harmonics can be overheating of transformers,
cables, motors, generators and capacitors connected to the
same power supply with the devices generating the harmonics.
Electronic displays and lighting may flicker, circuit breakers can
trip, computers may fail and metering can give false readings.
If the cause of the above mentioned symptoms is not known,
then there is cause to investigate the harmonic distortion of the
electricity distribution at the plant. The effects are likely to show
up in the customer’s plant before they show on the utility system.
This Technical guide has been published to help customers to
understand the possible harmonic problems and make sure the
harmonic distortion levels are not excessive.

Supply
Sk = 150 MVA
U = 22 kV
Transformer:
S = 400 kVA
U1
= 22 kV
U2
= 415 V
z = 4,5%
Cable:
Length = 60 m
R = 0,007 mΩ/m
Motor:
P = 100 kW
IN
= 200 A
S’k
Xk
Xt
X’k
I
Motor load
Load type
Overload type
Speed [rpm]
Power [kW]
Overload [%]
Const. torque/power
One overload
min base max
0
0
1450
100
100
100
100
1500
60 600Overload time [s] every [s]
Chapter 4 - Harmonic distortion calculation
by using DriveSize software
The harmonic currents cause a distortion of the line voltage. In
principle the voltage harmonics can be calculated at any point
of the network if the harmonic currents and the corresponding
source impedance are known. The circuit diagrams in figure
4.1. show the network supplying the converter and the other
essential parts of the installation. ABB DriveSize software is used
for the calculation.
4.1 Circuit diagram for the calculation example
Figure 4.1. Network supplying a frequency converter in the middle and
its equivalent diagram on the right. The data for this example is on the
left.
4.2 Input data for motor load
Figure 4.2. The most important motor load data for harmonics
calculation is the base power in kW.

Selected motor data
M2BA 315 SMC 6
Selection
Voltage [V]
Connection
Frequency [Hz]
Power [kW]
Poles
Speed [rpm]
Max mech.speed [rpm]
Current [A]
Torque [Nm]
T max/Tn
Power factor
Efﬁciency [%]
Insulation class
DriveSize
415
D
50
110
992
6
2300
197
1060
3,2
0,82
95,6
F
Selection
Selection method
Voltage [V]
Drive power [kVA]
Pn [kW]
Normal Icont [A]
Normal Imax [A]
Phd [kW]
Heavyduty Icont [A]
Heavyduty Imax [A]
Pulse
Frame type
P&F 12Nsq [A]
Selected inverter data
ACS607-0140-3
User
Current (normal)
400
140
110
238
216
90
178
267
6
R8
260
Supply unit data
Pulse #
Lv [μH]
Cdc [mF]
Udc [V]
Idc [A]
6
110
4,95
560
191
Figure 4.5. The supply unit data is defined by DriveSize according to the
inverter type selected.
4.3 Motor selection
Figure 4. 3. The software makes the motor selection for the defined
load. If required there is an option to select a different motor than that
selected by the DriveSize.
4.4 Inverter selection
Figure 4.4. The inverter selection is based on the previous motor
selection and here also the user has an option to select the inverter
manually.
4.5 Inverter supply unit data
Harmonic distortion calculation by using DriveSize software

Network and Transformer data
Primary voltage [V] Secondary voltage [V]
Frequency [Hz]
Network Sk [MVA]
Transformer Sn [kVA]
Transformer Pk [kW]
Transformer Zk [%]
Supply cable type Cable Busbar
Cable quantity
Cable lenght [m]
Impedance [μΩ]
unknow
22000
50
150
400
3,0
3,8
3
60
415
70
THD
Data
Show Mode
VoltageCurrent
Result
IEEE Calc
IEEE Limit
47,1% 0,2%
0,2%/ 0,2%/
15,0% 0,5%
Primary side
Secondary
Table
Graph
n
1
5
7
11
13
17
19
23
25
29
31
35
37
50
250
350
550
650
850
950
1150
1250
1450
1550
1750
1850
2,8
1,2
0,6
0,2
0,2
0,1
0,1
0,1
0,0
0,0
0,0
0,0
0,0
100,0%
0,6%
41,2%
19,5%
8,6%
5,6%
4,2%
2,7%
2,3%
1,4%
1,2%
0,8%
0,5%
21996,6
32,9
21,7
15,1
11,7
11,3
8,1
8,2
5,5
5,3
3,7
3,0
3,3
f [Hz] Current [A] In/I1 Voltage [V]
50
[%]
Frequency [Hz]
40
30
20
10
0
250
350
550
650
850
950
1150
1250
1450
1550
1750
1850
4.6 Network and Transformer data input
Figure 4.6. The network and transformer data input is given here.
For standard ABB transformers the data is shown automatically.
4.7 Calculated harmonic current and voltage
Figure 4.7. The harmonics are calculated by making discrete Fourier
transformation to the simulated phase current of the incoming unit.
Different kinds of circuit models are used, one for SingleDrive with AC
inductors and one for diode and thyristor supply with DC inductors.
There are also models for 6, 12 and 24 pulse connections.
4.8 Calculated harmonic currents in graphical form
Figure 4.8. The results of calculations can be shown in table form as
above or as a graph.

Network check
Network and Transformer data
ACS607-0140-3
Supply unit data
Normal voltage [V]
Frequency [Hz]
Network Sk [MVA]
Transformer Sn [kVA]
Transformer Pk [kW]
Transformer Zk [%]
Supply cable type
Cable quantity
Cable lenght
22000 (primary side)
50
150
400
3,0
3,8
Cable
3
60
Pulse #
Lv [μH]
Cdc [mF]
Udc [V]
Idc [A]
6
110
4,95
560
191
Result
Cosﬁi
Tot. power factor
Unmax mot.
0,999
0,90
98%
THD Current
THD Voltage
47,1%
0,2%
THD Current
THD Voltage
IEEE 519 limits calc/limit
0,2%/15,0%
0,2%/5,0%
Figure 4.9. The input data and calculated results can be printed out as a
report, which is partly shown here.
4.9 Part of the printed report

Chapter 5 - Standards for harmonic limits
The most common international and national standards setting
limits on harmonics are described below. Figure 5.1 is shown
as an example for harmonic distortion limits.
5.1 EN61800-3 (IEC1800-3) Adjustable speed electrical power
drive systems
Part 3: EMC product standard including specific test meth-
ods
The countries of the European Economic Area (EEA) have agreed
on common minimum regulatory requirements in order to ensure
the free movement of products within the EEA. The CE marking
indicates that the product works in conformity with the directives
that are valid for the product. The directives state the principles
that must be followed. Standards specify the requirements that
must be met. EN61800-3 is the EMC product standard of adjust-
able speed electrical power drive systems (PDS). Meeting the
requirements of this standard, is the minimum condition for free
trade of power electronics converters inside the EEA.
EN61800-3 states, that the manufacturer shall provide in the
documentation of the PDS, or on request, the current harmonic
level, under rated conditions, as a percentage of the rated fun-
damental current on the power port. The referenced values shall
be calculated for each order at least up to the 25th
. The current
THD (orders up to and including 40), and its high-frequency
component PHD (orders from 14 to 40 inclusive) shall be evalu-
ated. For these standard calculations, the PDS shall be assumed
to be connected to a PC with Rsc = 250 and with initial voltage
distortion less than 1%. The internal impedance of the network
shall be assumed to be a pure reactance.
In a low voltage public supply network, the limits and require-
ments of IEC1000-3-2 apply for equipment with rated current
≤ 16 A. The use of the future IEC1000-3-4 is recommended
for equipment with rated current > 16 A. If PDS is used in an
industrial installation, a reasonable economical approach, which
considers the total installation, shall be used. This approach is
based on the agreed power, which the supply can deliver at
any time. The method for calculating the harmonics of the total
installation is agreed and the limits for either the voltage distor-
tion or the total harmonic current emission are agreed on. The
compatibility limits given in IEC1000-2-4 may be used as the
limits of voltage distortion.

5.2 IEC1000-2-2,
Electromagnetic compatibility (EMC)
Part 2: Environment - Section 2: Compatibility levels for low
frequency conducted disturbances and signalling in public
low voltage power supply systems
This standard sets the compatibility limits for low frequency
conducted disturbances and signalling in public low voltage
power supply systems. The disturbance phenomena include
harmonics, inter-harmonics, voltage fluctuations, voltage dips
and short interruptions voltage inbalance and so on. Basically
this standard sets the design criteria for the equipment manu-
facturer, and amounts to the minimum immunity requirements
of the equipment. IEC1000-2-2 is in line with the limits set in
EN50160 for the quality of the voltage the utility owner must
provide at the customer’s supply-terminals.
5.3 IEC1000-2-4,
Part 2: Environment - Section 4: Compatibility levels in indus-
trial plants for low frequency conducted disturbances
IEC1000-2-4 is similar to IEC1000-2-2, but it gives compatibility
levels for industrial and non-public networks. It covers low-
voltage networks as well as medium voltage supplies excluding
the networks for ships, aircraft, offshore platforms and railways.
5.4 IEC1000-3-2,
Part 3: Limits - Section 2: Limits for harmonic current emis-
sions (equipment current < 16 A per phase)
This standard deals with the harmonic current emission limits of
individual equipment connected to public networks. The date
of implementation of this standard is January 1, 2001, but there
is extensive work going on at the moment to revise the standard
before this date. The two main reasons for the revision are the
need for the standard to cover also the voltage below 230 V and
the difficulties and contradictions in applying the categorisation
of the equipment given in the standard.
5.5 IEC1000-3-4,
This standard has been published as a Type II Technical report.
Work is going on to convert it into a standard. It gives the har-
monic current emission limits for individual equipment having a
rated current of more than 16 A up to 75 A. It applies to public
networks having nominal voltages from 230 V single phase to
600 V three phase.
Standards for harmonic limits

132 kV Net
33 kV Net
11 kV Net
400 kV Net
Typical values
Min’m
Rsce
66
120
175
250
350
450
>600
12
15
20
30
40
50
60
10
12
14
18
25
35
40
9
12
12
13
15
20
25
6
8
8
8
10
15
18
2.36
1.69
1.25
1.06
0.97
1.02
<=0.91
I5 I7 I11 I13
VOLTAGE
%THD
STAGE 2 LIMITS
% I1
MAXIMUM LOAD
12p 6p
# 6.66 MW
(5.0 MW)
# 2.50 MW
(5.0 MW)
#
# 4.40 MW
(3.3 MW)
# 1.65 MW
(3.3 MW)
# 1.11 MW
(830 kW)
# 415 kW
(830 kW)
# 760 kW
(215 kW)
# 108 kW
(215 kW)
PCC
**Contribution to existing
THD level at selected
PCC
(26 MVA assumed)
(100 MVA assumed)
(400 MVA assumed)
(600 MVA assumed)
**
The standard gives three different stages for connection proce-
dures of the equipment. Meeting the individual harmonic limits
of stage 1 allows the connection of the equipment at any point
in the supply system. Stage 2 gives individual harmonic current
limits as well as THD and its weighted high frequency counterpart
PWHD. The limits are classified and tabulated by the short circuit
ratio. The third stage of connection is based on an agreement
between the user and the supply authority, based on the agreed
active power of the consumer’s installation. If the rated current
is above 75 A, stage 3 applies in any case.
The structure of this standard is generally seen to be good, but it
may justly be questioned whether single and three-phase equip-
ment should have different limits in stage 2. It is very probable that
the structure of the standard will remain as it is, but the version
having the status of actual standard, will contain different limits
for single and three-phase equipment.
Figure 5.1 Limits on harmonics in the proposed EN61000-3-4.
5.6 IEEE519, IEEE Recommended practices and requirements for
harmonic control in electrical power systems
The philosophy of developing harmonic limits in this recom-
mended practice is to limit the harmonic injection from individual
customers so that they will not cause unacceptable voltage
distortion levels for normal system characteristics and to limit
overall harmonic distortion of the system voltage supplied by
the utility. This standard is also recognised as American National
Standard and it is widely used in the USA, especially in the mu-
nicipal public works market.

The standard does not give limits for individual equipment, but
for individual customers. The customers are categorised by the
ratio of available short circuit current (Isc) to their maximum
demand load current (IL) at the point of common coupling. The
total demand load current is the sum of both linear and non-linear
loads. Within an industrial plant, the PCC is clearly defined as
the point between the non-linear load and other loads.
The allowed individual harmonic currents and total harmonic dis-
tortion are tabulated by the ratio of available short circuit current
to the total demand load current (Isc/IL) at the point of common
coupling. The limits are as a percentage of IL for all odd and even
harmonics from 2 to infinity. Total harmonic distortion is called
total demand distortion and also it should be calculated up to
infinity. Many authors limit the calculation of both the individual
components and TDD to 50.
The table 10.3 of the standard is sometimes misinterpreted to
give limits for the harmonic emissions of a single apparatus by
using Rsc of the equipment instead of Isc/IL of the whole instal-
lation. The limits of the table should not be used this way, since
the ratio of the short circuit current to the total demand load
current of an installation should always be used.

Verification measurements
and calculations (if necessary)
UTILITY
Calculate average maximum
demand load current (IL)
Choose PCC
Calculate short circuit
capacity (SSC, ISC)
Calculate short circuit ratio
(SCR=(ISC /IL)
Yes
Yes
No
Yes
No
Is power
factor correction existing
or planned?
Stage 1:
Is detailed evaluation
necessary?
No
Estimate weighted disturbing
power (SDW) or% non-linear load
Stage 2:
Does facility meet
harmonic limits?
Characterise harmonic levels
(measurements, analysis)
Design power factor correction
and/or harmonic control
equipment
(include resonance concerns)
CUSTOMER
Chapter 6 - Evaluating harmonics
The “Guide for Applying Harmonic Limits on Power Systems”
P519A/D6 Jan 1999 introduces some general rules for evaluating
harmonic limits at an industrial facility. The procedure is shown
in the flowchart in figure 6.1.
Figure 6.1 Evaluation of harmonic distortion.

Line
Transformer
AC drive
Load
Short circuit power
Rated power and
impedance
Type of rectiﬁer
DIODE, THYRISTOR; INVERTER:
MVA
MVA
%
mH
PWM;CSI
kW
%
6-p, 12-p, 24-p
Reactor inductance
Type of inverter
Rated power and
load
Inverter
Motor
Alternative
7.1 Factors in the AC drive having an effect on harmonics
Harmonics reduction can be done either by structural modifi-
cations in the drive system or by using external filtering. The
structural modifications can be to strengthen the supply, to use
12 or more pulse drive, to use a controlled rectifier or to improve
the internal filtering in the drive.
Figure 7.1 shows the factors in the AC drive system which have
some influence on harmonics. The current harmonics depend on
the drive construction and the voltage harmonics are the current
harmonics multiplied by the supply impedances.
Chapter 7 - How to reduce harmonics by
structural modifications in the AC drive
system
Figure 7.1 Drive system features affecting harmonics.

The cause The effect
The larger the motor… the higher the current harmonics
The higher the motor load… the higher the current harmonics
The larger the DC or AC inductance… the lower the current harmonics
The higher the number of pulses in the rectifier… the lower the current harmonics
The larger the transformer… the lower the voltage harmonics
The lower the transformer impedance… the lower the voltage harmonics
The higher the short circuit capacity of supply… the lower the voltage harmonics
6-pulse rectifier 12-pulse rectifier 24-pulse rectifier
Current waveform Current waveform Current waveform
7.2 Table: List of the different factors and their effects
7.3 Using 6-pulse diode rectifier
The connections for different rectifier solutions are shown in figure
7.2. The most common rectifier circuit in 3-phase AC drives is a
6-pulse diode bridge. It consists of six uncontrollable rectifiers
or diodes and an inductor, which together with a DC-capacitor
forms a low-pass filter for smoothing the DC-current. The induc-
tor can be on the DC- or AC-side or it can be left totally out.
The 6-pulse rectifier is simple and cheap but it generates a high
amount of low order harmonics 5th
, 7th
, 11th
especially with small
smoothing inductance.
The current form is shown in figure 7.2. If the major part of the
load consists of converters with a 6-pulse rectifier, the supply
transformer needs to be oversized and meeting the requirements
in standards may be difficult. Often some harmonics filtering is
needed.
Figure 7.2 Harmonics in line current with different rectifier constructions.
How to reduce harmonics by structural modifications in the AC drive system

6-pulse rectifier 12-pulse rectifier 24-pulse rectifier
Harmonic order
In
I1
7.4 Using 12-pulse or 24-pulse diode rectifier
The 12-pulse rectifier is formed by connecting two 6-pulse
rectifiers in parallel to feed a common DC-bus. The input to the
rectifiers is provided with one three-winding transformer. The
transformer secondaries are in 30° phase shift. The benefit with
this arrangement is that in the supply side some of the harmonics
are in opposite phase and thus eliminated. In theory the harmonic
component with the lowest frequency seen at the primary of the
transformer is the 11th
.
The major drawbacks are special transformers and a higher cost
than with the 6-pulse rectifier.
The principle of the 24-pulse rectifier is also shown in figure 7.2.
It has two 12-pulse rectifiers in parallel with two three- winding
transformers having 15° phase shift. The benefit is that practically
all low frequency harmonics are eliminated but the drawback is
the high cost. In the case of a high power single drive or large
multidrive installation a 24-pulse system may be the most eco-
nomical solution with lowest harmonic distortion.
Figure 7.3 Harmonic components with different rectifiers.
7.5 Using phase controlled thyristor rectifier
A phase controlled rectifier is accomplished by replacing the
diodes in a 6-pulse rectifier with thyristors. Since a thyristor
needs a triggering pulse for transition from nonconducting to
conducting state, the phase angle at which the thyristor starts
to conduct can be delayed. By delaying the firing angle over 90o
,
the DC-bus voltage goes negative. This allows regenerative flow
of power from the DC-bus back to the power supply.

Supply
type
6-pulse
rectifier
12-pulse
rectifier
IGBT supply
unit
Current
TDH (%)
30
10
4
Voltage
TDH (%)
RSC=20
10
6
8
Voltage
TDH (%)
RSC=100
2
1.2
1.8
Current waveform
Distortion is in% of RMS values
Standard DC-bus and inverter configurations do not allow polar-
ity change of the DC-voltage and it is more common to connect
another thyristor bridge anti-parallel with the first one to allow
the current polarity reversal. In this configuration the first bridge
conducts in rectifying mode and the other in regenerating mode.
The current waveforms of phase controlled rectifiers are similar
to those of the 6-pulse diode rectifier, but since they draw power
with an alternating displacement power factor, the total power
factor with partial load is quite poor. The poor power factor
causes high apparent current and the absolute harmonic cur-
rents are higher than those with a diode rectifier.
In addition to these problems, phase-controlled converters cause
commutation notches in the utility voltage waveform. The angular
position of the notches varies along with the firing angle.
Figure 7.4 Distortion of different supply unit types. Values may vary
case by case.
7.6 Using IGBT bridge
Introducing a rectifier bridge, made of self commutated com-
ponents, brings several benefits and opportunities compared to
phase commutated ones. Like a phase commutated rectifier, this
hardware allows both rectification and regeneration, but it makes
it possible to control the DC-voltage level and displacement
power factor separately regardless of the power flow direction.
The main benefits are:
– Safe function in case of mains supply disappearance.
– High dynamics of the drive control even in the field weaken-
ing range.
– Possibility to generate reactive power.

Line generating unit
3~
Line generating unit
Harmonic order
In
I1
Current without
inductor
Current with
inductor
– Nearly sinusoidal supply current with low harmonic content.
Measured results for one drive is shown in figure 7.5. When
comparing with figure 7.3 we can see a clear difference. IGBT
has very low harmonics at lower frequencies, but somewhat
higher at higher frequencies.
– Voltage boost capability. In case of low supply voltage the
DC voltage can be boosted to keep motor voltage higher
than supply voltage.
The main drawback is the high cost coming from the IGBT bridge
and extra filtering needed.
Figure 7.5 Harmonics in line current IGBT line generating unit.
7.7 Using a larger DC or AC inductor
The harmonics of a voltage source AC drive can be significantly
reduced by connecting a large enough inductor in its AC input
or DC bus. The trend has been to reduce the size of converter
while the inductor size has been also reduced, or in several cases
it has been omitted totally. The effect of this can be seen from
the curve forms in figure 7.6.
Figure 7.6 The effect of the inductor on the line current.

415 V, 50 Hz
5th
7th
11th
13th
17th
19th
23rd
25th
THD
DC Inductance/mH = this ﬁgure/motor kW
Harmoniccurrent(pu)
Load 60 A, Transformer power 50 to 315 kVA, line fault level 150 MVA
THDofvoltage(%)
Short Circuit Ratio
No inductor, 6-pulse
Small inductor,
6-pulse
Large inductor,
6-pulse
Large inductor,
12-pulse
The chart in figure 7.7 shows the effect of the size of the DC
inductor on the harmonics. For the first 25 harmonic components
the theoretical THD minimum is 29%. That value is practically
reached when the inductance is 100 mH divided by the motor
kW or 1 mH for a 100 kW motor (415 V, 50 Hz). Practically sen-
sible is about 25 mH divided by motor kW, which gives a THD
of about 45%. This is 0.25 mH for a 100 kW motor.
Figure 7.7 Harmonic current as function of DC inductance.
The voltage distortion with certain current distortion depends
on the short circuit ratio Rsc of the supply. The higher the ratio,
the lower the voltage distortion. This can be seen in Figure 7.8.
Figure 7.8 THD voltage vs type of AC drive and transformer size.

A = Large DC-inductance
B, C = Small DC-inductance
D, E = Without DC-inductance
Example: 45 kW Motor is connected to ”a
200 kVA transformer. ”THD = ca. 3% with a
“Large Inductor Drive” and ca. 11% with a
“No Inductor Drive”
TotalHarminicVoltageDistortion
Input data to calculations:
- Rated motor for the dfrive
- Constant torque load
- Voltage 415 V
- Drive efficiency = 97%
- Supply Impedance = 10%
of transformer impedance
Supply
transformer
(kVA)
STOP TURN LEFT
START
TURN LEFT
TURN UP
Motor kW
No DC-Inductor,
6-pulse
Small DC-
Inductor,6-pulse
Large DC-
Inductor, 6-pulse
Large DC-
Inductor, 12-pulse
Figure 7.9 introduces a simple nomogram for estimation of har-
monic voltages. On the graph below right select first the motor
kilowatt, then the transformer kVA and then move horizontally
to the diagonal line where you move upwards and stop at the
curve valid for your application. Then turn left to the y-axis and
read the total harmonic voltage distortion.
Figure 7.9 Total harmonic distortion nomogram.
Results from laboratory tests with drive units from different
manufacturers are shown in figure 7.10. Drive A with large DC
inductor has the lowest harmonic current distortion, drives with
no inductor installed have the highest distortion.
Figure 7.10 Harmonic current with different DC-inductances.

- Detuned - Single tuning frequency
- Above tuned frequency harmonics absorbed
- Below tuned frequency harmonics may be amplified
- Harmonic reduction limited by possible over compensation
at the supply frequency and network itself
Chapter 8 - Other methods for
harmonics reduction
Filtering is a method to reduce harmonics in an industrial plant
when the harmonic distortion has been gradually increased or
as a total solution in a new plant. There are two basic methods:
passive and active filters.
8.1 Tuned single arm passive filter
The principle of a tuned arm passive filter is shown in figure 8.1.
A tuned arm passive filter should be applied at the single lowest
harmonic component where there is significant harmonic genera-
tion in the system. For systems that mostly supply an industrial
load this would probably be the fifth harmonic. Above the tuned
frequency the harmonics are absorbed but below that frequency
they may be amplified.
Figure 8.1 Tuned singel arm passive filter.
8.2 Tuned multiple arm passive filter
This kind of filter consists of an inductor in series with a capacitor
bank and the best location for the passive filter is close to the
harmonic generating loads. This solution is not normally used
for new installations.
The principle of this filter is shown in figure 8.2. This filter has
several arms tuned to two or more of the harmonic components
which should be the lowest significant harmonic frequencies in
the system. The multiple filter has better harmonic absorption
than the one arm system.

Fundamental only idistortion
icompensation
Load
Active
filter
Current waveforms
Supply
- Capacitive below tuned frequency/Inductive above
- Better harmonic absorption
- Design consideration to amplification harmonics by filter
- Limited by KVAr and network
Figure 8.2 Tuned multiple arm passive filter.
The multiple arm passive filters are often used for large DC
drive installations where a dedicated transformer is supplying
the whole installation.
8.3 External active filter
A passive tuned filter introduces new resonances that can cause
additional harmonic problems. New power electronics technolo-
gies are resulting in products that can control harmonic distortion
with active control. These active filters, see figure 8.3, provide
compensation for harmonic components on the utility system
based on existing harmonic generation at any given moment in
time.
Figure 8.3 External active filter principle diagram.
The active filter compensates the harmonics generated by non-
linear loads by generating the same harmonic components in
opposite phase as shown in figure 8.4. External active filters are
most suited to multiple small drives. They are relatively expensive
compared to other methods.
Other methods for harmonics reduction

Clean
feeder
current
Load
current
Active filter
current
HarmonicsWaveforms
Figure 8.4 External active filter waveforms and harmonics.
Other methods for harmonics reduction

There are many options to attenuate harmonics either inside
the drive system or externally. They all have advantages and
disadvantages and all of them show cost implications. The best
solution will depend on the total loading, the supply to the site
and the standing distortion.
In the following tables different internal actions are compared
to the basic system without inductor. The harmonic content is
given with 100% load. The costs are valid for small drives. For
multidrive the 12-pulse solution is quite a lot cheaper.
9.1 6-pulse rectifier without inductor
Manufacturing cost 100%
Typical harmonic current components.
Fundamental 5th
7th
11th
13th
17th
19th
100% 63% 54% 10% 6,1% 6,7% 4,8%
9.2 6-pulse rectifier with inductor
Manufacturing cost 120%. AC or DC choke added
Fundamental 5th
7th
11th
13th
17th
19th
100% 30% 12% 8,9% 5,6% 4,4% 4,1%
9.3 12-pulse rectifier with polycon transformer
Fundamental 5th
7th
11th
13th
17th
19th
100% 11% 5,8% 6,2% 4,7% 1,7% 1,4%
9.4 12-pulse with double wound transformer
Fundamental 5th
7th
11th
13th
17th
19th
100% 3,6% 2,6% 7,5% 5,2% 1,2% 1,3%
Chapter 9 - Summary of harmonics
attenuation

9.5 24-pulse rectifier with 2 3-winding transformers
Fundamental 5th
7th
11th
13th
17th
19th
100% 4,0% 2,7% 1,0% 0,7% 1,4% 1,4%
9.6 Active IGBT rectifier
Manufacturing cost 250%. Not significant if electrical braking is
anyway needed.
Fundamental 5th
7th
11th
13th
17th
19th
100% 2,6% 3,4% 3,0% 0,1% 2,1% 2,2%
Summary of harmonics attenuation

Chapter 10 - Definitions
S: Apparent power
P: Active power
Q: Reactive power
Rsc: Short circuit ratio is defined as the short circuit power of
the supply at PCC to the nominal apparent power of the
equipment under consideration. Rsc = Ss / Sn.
ω1: Angular frequency of fundamental component ω1 = 2*π*f1,
where f1 is fundamental frequency (eg. 50 Hz or 60 Hz).
n: Integer n = 2, 3, ... ∞. Harmonic frequencies are defined
as wn = n*ω1.
In: RMS-value of n:th harmonic component of line current.
Zn: Impedance at frequency n*ω1.
%Un: Harmonic voltage component as a percentage of
fundamental (line) voltage.
THD: Total Harmonic Distortion in the input current is defined
as:
where I1
is the rms value of the fundamental frequency current.
The THD in voltage may be calculated in a similar way. Here is
an example for the 25 lowest harmonic components with the
theoretical values:
PWHD: Partial weighted harmonic distortion is defined as:

PCC: Point of Common Coupling is defined in this text as such
a point of utility supply which may be common to the
equipment in question and other equipment. There are
several definitions of PCC in different standards and even
more interpretations of these definitions in literature. The
definition chosen here is seen as technically most
sound.
PF: Power Factor defined as PF = P/S (power / volt-ampere)
= I1
/ Is * DPF (With sinusoidal current PF equals to
DPF).
DPF: Displacement Power Factor defined as cosφ1, where φ1 is
the phase angle between the fundamental frequency
current drawn by the equipment and the supply voltage
fundamental frequency component.
Definitions

Index
Symbols
12-pulse rectifier 21, 22, 23, 30
24-pulse rectifier 21, 22, 31
3-winding 31
5th harmonic 9
6-pulse rectifier 8, 9, 21, 22, 23, 30
6-pulse three phase rectifier 9
A
ABB 7, 11, 13
AC inductor 13, 24
active filter 27, 28, 29
active power 17, 32
American National Standard 17
anti-parallel 23
apparent power 32
attenuation 30, 31
C
calculation 7, 11, 12, 13, 14, 15,
18, 19
CE marking 15
circuit breaker 10
common DC-bus 22
commutation notch 23
compatibility limit 15, 16
computer 10
consumer’s installation 17
converter 8, 11, 15, 21, 23, 24
converter load 8
D
DC-capacitor 21
DC-current 21
displacement power factor 23, 33
distortion calculation 7, 11, 12, 13,
14
distortion nomogram 26
DriveSize 11, 12, 13, 14
E
effect 7, 10, 20, 21, 24, 25
Electromagnetic compatibility 16
electronic device 10
Electronic display 10
electronic lighting 10
EMC product standard 15
European Economic Area 15
external filtering 20
F
filtering 20, 21, 24, 27
frequency 9, 11, 12, 13, 14, 15, 16,
17, 22, 27, 28, 32, 33
fundamental frequency 9, 32, 33
H
harmonic component 9, 22, 25,
27, 28, 32
harmonic currents 8, 11, 13, 18,
23
harmonic distortion 7, 8, 10, 11,
12, 13, 14, 15, 17, 18, 19, 22, 26,
27, 28, 32
harmonic limit 16, 17, 18, 19
harmonics phenomena 8, 9
harmonics reduction 20, 27, 28,
29
harmonic voltage 26, 32
I
IGBT bridge 23, 24
inductance 9, 20, 21, 25, 26
inductor 13, 21, 24, 25, 26, 27, 30
industrial installation 15
installation 11, 15, 17, 18, 22, 27,
28
inverter selection 12
Inverter supply unit data 12
L
laboratory test 26
line current 8, 9, 21, 24, 32
low-pass filter 21
M
mains transformer 8
manufacturing cost 30, 31
metering 10
motor load 11, 21
motor selection 12
motor starter 10
multiple arm passive filter 27, 28
N
network 11, 13, 14, 15, 16, 17,
27, 28
non-linear load 8, 10, 18, 19
O
overheating 10
P
passive filter 27, 28
phase commutated rectifier 23
point of common coupling 18, 33
power distribution 8
power drive system 15
power factor 12, 14, 19, 23, 33
power port 15
public supply 15
PWHD 17, 32

R
reactive power 23, 32
rectifier 8, 9, 20, 21, 22, 23, 30, 31
rectifying mode 23
regenerating mode 23
report 14, 16
S
short circuit power 20, 32
short circuit ratio 17, 19, 25, 32
source 7, 10, 11, 24
source impedance 11
standard 13, 15, 16, 17, 18, 21, 23,
33
structural modification 20, 21, 22,
23, 24, 25, 26
supply authority 17
supply cable 13, 14
supply transformer 21
supply voltage 8, 24, 33
T
TDD 18
THD 13, 14, 15, 17, 25, 32
three-winding transformer 22
thyristor 13, 20, 22, 23
total demand distortion 18
total harmonic distortion 18, 26, 32
transformer 8, 10, 11, 13, 14, 20,
21, 22, 25, 26, 28, 30, 31
tuned arm passive filter 27
V
variable speed drives 10
voltage 8, 11, 12, 13, 14, 15, 16,
17, 20, 21, 22, 23, 24, 25, 26, 32, 33
voltage boost 23, 24
Index

3AFE64292714REVCEN11.5.2011#15567
Contact us
© Copyright 2011 ABB. All rights reserved.
Specifications subject to change without notice.
For more information contact
your local ABB representative or visit:
www.abb.com/drives
www.abb.com/drivespartners

Abb technical guide no.06 revc

More Related Content

Similar to Abb technical guide no.06 revc (20)

More from Cesar Enrique Gutierrez Candia (20)

Recently uploaded (20)

Abb technical guide no.06 revc