ISSN: 2379-3686 International Journal of Science Research and Technology
V olume 1 Issue 2 p p 6-11 15th December 2015
6
A ZERO HARMONIC DISTORTION IMPROVEMENT OF
POWER QUALITY USING CASCADED H-BRIDGE
Radhey Shyam Meena Mukesh Kr. Lodha Jeetendra Singh Rathore Ritu Raj Soni
Member- The Institution of Engineering and Technology IET
1
Dept. Of Electrical Engineering
Sri Balaji College of Engineering Technology Jaipur Rajasthan
Rajasthan Technical University Kota
Abstract-
In reactive power compensation cascaded voltage
source converter with separated dc sources seems to
be the most feasible topology for many reasons. The
cascaded converter is constructed with a number of
identical H-Bridge inverters. This modular feature
makes the cascaded converter very attractive. The
cascaded converter topology not only specifies
hardware manufacture ability but also makes the
entire system flexible in term of power capability. In
Multilevel converter has become attractive in the
power industries and it can be applied in many
applications especially on improvement of the power
quality and distortion of zero harmonic components.
This paper also presents the generation of triggering
signals used to control the cascaded H-bridge
multilevel converter. As the number of levels
increases the synthesized output waveform adds
more steps producing a staircase which approaches
the sinusoidal wave with minimum harmonic
distortion. Ultimately a zero harmonic distortion of
the output wave can be obtained by an infinite
number of levels. One of the major limitations of the
multilevel converters is the voltage unbalance
between different levels. The techniques to balance
the voltage between different levels normally involve
voltage clamping or capacitor charge control. This
paper presents the cascaded multi nine and eleven
level converter to improving the voltage sharing
problems.
Keywords— Multilevel Converter Multilevel
Inverter Cascaded Multi nine and eleven Level
Converter Power Converter Matlab.
I. INTRODUCTION
Recently the ―multilevel converter‖ has drawn
tremendous interest in the power industry. The general
structure of the multilevel converter is to synthesize a
sinusoidal voltage from several levels of voltages
typically obtained from dc voltage sources. The
multilevel converters start from three levels. A three
level converter also known as a ―neutral-clamped‖
converter consists of two capacitor voltages in series
and uses the centre tap as the neutral. Each phase leg of
the three-level converter has two pairs of switching
devices in series. The center of each device pair is
clamped to the neutral through clamping diodes. The
waveform obtained from a three-level converter is a
quasi-square wave output.
The diode-clamped method can be applied to higher
level converters. As the number of levels increases the
synthesized output waveform adds more steps
producing a stair-case wave which approaches the
sinusoidal wave with minimum harmonic distortion.
Ultimately a zero harmonic distortion of the output
wave can be obtained by an infinite number of levels.
More levels also mean higher voltages can be spanned
by series devices without device voltage sharing
problems. Therefore we used the cascaded multilevel
converter to improving the voltage sharing problems. A
three phase CHB multilevel converter circuit is designed
and simulated using the MATLAB SimPowerSystems
software.
II. CONVERTER TOPOLOGY
A power converter is an electrical or
electro-mechanical device for converting electrical
energy. It may be converting AC to or from DC or the
voltage or frequency or some combination of these.
Amongst the many devices that are used for this
purpose are-
Switched-mode power supply
Rectifier
Inverter
Motor generator set
DC-DC converter
Transformer
But in this paper we considered a multilevel inverter. So
first of all define the single inverter and then also
explain the multilevel inverter. A device that converts dc
power into ac power at desired output voltage and
frequency is called an inverter. Some industrial
applications of inverters are for adjustable-speed ac
drives induction heating stand by air-craft power
supplies UPS uninterruptible power supplies for
computers HVDC transmission lines etc. Phase
controlled converters when operated in the inverter
mode are called line-commutated inverters. But
line-commutated inverters require at the output
terminals an existing ac supply which is used for their
commutation. This means that line-commutated
inverters can‘t function as isolated ac voltage sources or
as variable frequency generators with dc power at the

slide 2:

ISSN: 2379-3686 International Journal of Science Research and Technology
V olume 1 Issue 2 p p 6-11 15th December 2015
7
input. Therefore voltage level frequency and waveform
on the ac side of line-commutated inverters cannot be
changed. On the other hand force commutated inverters
provide an independent ac output voltage of adjustable
voltage and adjustable frequency and have therefore
much wider applications.
Numerous industrial applications have begun to
require higher power apparatus in recent years. Some
medium voltage motor drives and utility applications
require medium voltage and megawatt power level. For
a medium voltage grid it is troublesome to connect only
one power semiconductor switch directly. As a result a
multilevel power converter structure has been
introduced as an alternative in high power and medium
voltage situations. A multilevel converter not only
achieves high power ratings but also enables the use of
renewable energy sources. Renewable energy sources
such as photovoltaic wind and fuel cells can be easily
interfaced to a multilevel converter system for a high
power application.
However the elementary concept of a
multilevel converter to achieve higher power is to use a
series of power semiconductor switches with several
lower voltage dc sources to perform the power
conversion by synthesizing a staircase voltage
waveform. Capacitors batteries and renewable energy
voltage sources can be used as the multiple dc voltage
sources. The commutation of the power switches
aggregate these multiple dc sources in order to achieve
high voltage at the output however the rated voltage of
the power semiconductor switches depends only upon
the rating of the dc voltage sources to which they are
connected.
A multilevel converter has several
advantages over a conventional two-level converter that
uses high switching frequency pulse width modulation
PWM. The attractive features of a multilevel converter
can be briefly summarized as follows.
● Staircase waveform quality: Multilevel converters not
only can generate the output voltages with very low
distortion but also can reduce the d v/dt stresses
therefore electromagnetic compatibility EMC
problems can be reduced.
● Common-mode CM voltage: Multilevel converters
produce smaller CM voltage therefore the stress in the
bearings of a motor connected to a multilevel motor
drive can be reduced. Furthermore CM voltage can be
eliminated by using advanced modulation strategies.
● Input current: Multilevel converters can draw input
current with low distortion.
● Switching frequency: Multilevel converters can
operate at both fundamental switching frequency and
high switching frequency PWM. It should be noted that
lower switching frequency usually means lower
switching loss and higher efficiency.
Unfortunately multilevel converters do have some
disadvantages. One particular disadvantage is the
greater number of power semiconductor switches
needed. Although lower voltage rated switches can be
utilized in a multilevel converter each switch requires a
related gate drive circuit. This may cause the overall
system to be more expensive and complex. To date the
MOSFET GTO/Diode semiconductor switches are used
to solve above problems. The cascade converter has
drawn more interest lately as research shows its
remarkable advantages over its counterparts. The simple
repetitive modular structure of the converter allows high
modification flexibility and greatly simplifies control
designs. The technology also permits easy
troubleshooting and packaging.
Fig.1 Schematic of a 1-phase cascaded-multilevel
converter
In this circuit a single-phase structure of an m-level
cascaded inverter with SDCSs is illustrated in Figure 1.
A relatively new converter structure cascaded-inverters
with separate dc sources SDCSs is introduces here.
This new converter can avoid extra clamping diodes or
voltage balancing capacitors. Each separate dc sources
SDCSs is connected to a single-phase full-bridge or
H-bridge inverter. The ac terminal voltages of different
level inverters are connected in series. Each inverter
level can generate three different voltage outputs +V
dc
0 and –V
dc
by connecting the dc source to the ac output
by different combinations of the four switches S
1
S
2
S
3
and S
4
. To obtain +V
dc
switches S
1
and S
4
are turned on
whereas –V
dc
can be obtained by turning on switches S
2
and S
3
. By turning on S
1
and S
2
or S
3
and S
4
the output
voltage is 0. The ac outputs of each of the different
full-bridge inverter levels are connected in series such
that the synthesized voltage waveform is the sum of the
inverter outputs. The number of output phase voltage
levels ‗m‘ in a cascade inverter is defined by m2s+1
where s is the number of separate dc sources. Each
single-phase full bridge inverter can generate three level
outputs +V
dc
0 and –V
dc
. This is made possible by
connecting the dc sources sequentially to the ac side via
the n gate-turn-off devices. Similarly the ac output

slide 3:

ISSN: 2379-3686 International Journal of Science Research and Technology
V olume 1 Issue 2 p p 6-11 15th December 2015
8
voltage at each level can be obtained by controlling the
conducting angles at different inverter levels.
The phase output voltage is synthesized by the sum of
individual inverter outputs i.e.
V
an
V
1
+V
2
+V
3
+………….V
n
Therefore the phase voltage for 11-level cascaded
inverter is
V
an
V
1
+V
2
+V
3
+V
4
+V
5
For a stepped waveform such as the one depicted in
Fig.5 with s steps the Fourier Transform for this
waveform-
Error Reference source not found.
The conducting anglesError Reference source not
found. Error Reference source not found.……..
Error Reference source not found. can be chosen
such that the voltage total harmonic distortion is a
minimum. Generally these angles are chosen so that
predominant lower frequency harmonics 5
th
7
th
11
th
and 13
th
harmonics2.For the 11-level case the 5
th
7
th
11
th
and 13
th
harmonics can be eliminated with the
appropriate choice of the conducting angles. One degree
of freedom is used so that the magnitude of the output
waveform corresponds to the reference amplitude
modulation index m
a
which is defined as V
L
/V
Lmax
where V
L
is the amplitude command of the
inverter
output voltage and V
Lmax
is the maximum attainable
amplitude of the converter i.e.
V
Lmax
s.V
dc
.
Let the equation from above Hn be as follows:
Error Reference source not found.
Error Reference source not found.
Error Reference source not found.
Error Reference source not found.
Error Reference source not found.
The set of nonlinear transcendental equations 5 to 9
can be solved by iterative method such as the
Newton-Raphson method. For example using a
conducting angles-
Therefore the modulation index m
a
0.73.
This means that if the inverter output is symmetrically
switched during the positive half cycle of the
fundamental voltage to +V
dc
at Error Reference
source not found. +2V
dc
at Error Reference source
not found. +3V
dc
at Error Reference source not
found.+4V
dc
at Error Reference source not found.
and +5V
dc
at Error Reference source not found. and
similarly in the negative half cycle to –V
dc
at Error
Reference source not found. -2V
dc
at Error
Reference source not found. -3V
dc
at Error
Reference source not found. -4V
dc
at Error
Reference source not found. and-5V
dc
at Error
Reference source not found. the output voltage of the
11-level inverter will not contain the 5
th
7
th
11
th
and 13
th
harmonic components. For a three-phase system the
output voltages of the three cascaded inverters can be
connected in either star- or –delta configuration. Fig.2
illustrates the connection diagram for a star-
configuration 11-level converter using
cascaded-inverters with five SDC sources.
Fig. 2 Three phase 11-level CHB Multilevel converter
Single phase and Three phase Eleven Levels
Cascaded H-bridge Multilevel Converter
This type of CHB cascaded multilevel converter has
been designed and simulated using MATLAB
SimPowerSystems. The multilevel circuits are
illustrated in Fig.
a
b
Fig 3 a Simulation model of 3-phase Cascaded Eleven

slide 4:

ISSN: 2379-3686 International Journal of Science Research and Technology
V olume 1 Issue 2 p p 6-11 15th December 2015
9
level converter b Simulation model of 3-phase
Cascaded Thirteen level converter.
III. MERITS AND DEMERITS OF MULTILEVEL
CONVERTER
The multilevel inverter approach allows the use of
high power and high voltage electric motor drive
systems.
Advantages/ Merits:
The number of possible output voltage levels is more
than twice the number of dc sources m 2s+1.The
series of H-bridges makes for modularized layout and
packaging. This will enable the manufacturing process
to be done more quickly and cheaply.
Disadvantages/Demerits:
Separate dc sources are required for each of the
H-bridges. This will limit its application to products that
already have multiple SDCSs readily available.
IV. SIMULATION RESULTS
The simulation results of the cascaded multilevel
converter are taken on eleven level converters. And the
nine level cascaded multilevel converter is used for the
studied purpose.
Fig.4 Out put results of Eleven and Thirteen Level
Fig.5 Individual waveform of inverter when delays are
o
0
18
0
36
0
54
0
72
0
respectively

slide 5:

ISSN: 2379-3686 International Journal of Science Research and Technology
V olume 1 Issue 2 p p 6-11 15th December 2015
10
a
b
Fig.6 aSingle-phase cascaded 11-level inverter
waveform. b Three-phase cascaded 11-level inverter
waveform. c line-to-line voltage
a
b
c
d
Fig. 7 a Bode Diagram and Response For Converter b
Impulse Response for Converter c Response in initial
conditions d Step response for converter
V. CONCLUSON
Among recently developed power converter topologies
multilevel converters have become an important
technology and have been utilized in higher-power
applications especially for FACTS controllers. Several
multilevel converter topologies have been developed to
demonstrate their superiority in such applications. With
converter modules in series and with balanced voltage
sharing among them the lower-voltage switches can
possibly be used in high-voltage systems. Thus the
low-voltage-oriented insulated gate bipolar transistor
IGBT devices can be stacked for medium-voltage
systems. For higher-voltage applications however
efforts were made to use GTO-based devices for
multilevel converters.

slide 6:

ISSN: 2379-3686 International Journal of Science Research and Technology
V olume 1 Issue 2 p p 6-11 15th December 2015
11
VI. REFERENCES
1. M. H. J. Bollen ―Understanding Power Quality
Problems V oltage Sags and Interruptions‖ IEEE Press New
York 2000.
2. J. Schlabbach D. Blume and T. Stephanblome ―V oltage
Quality in Electrical Power Systems‖ The Institution of
Engineering and Technology Stevenage 2000.
3. R. C. Dugan M. F. McGranaghan and H. W. Beaty
―Electric Power Systems Quality‖ 2nd Edition McGraw
Hill New York 2006.
4. A. Baggini ―Handbook on Power Quality‖ John Wiley
Sons Hoboken 2008.
5. IEEE Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems IEEE Std.
519-1992 Apr. 12 1993.
6. Pedro Roncero –Sanchez Jose Enrique Orgeta-
CalderonAurelio Garcia-Cervada ―A Versatile Control
scheme for a Dynamic V oltage Restorer For Power Quality
Improvement‖ IEEE Transaction On Power Delivery
V ol.24No.1 Jan 2009PP.277-284.
7. K. Surin and M.T. Leon ―Multilevel power
converters‖ Journal in the University of Tennessee 2000
V ol.31pp 150.
8. Jingsheng Liao Keith Corzine and Mehdi Ferdowsi
―A new control Method for Single-DC-Source Cascaded
H-Bridge Multilevel Converters using Phase-Shift
Modulation‖.

You do not have the permission to view this presentation. In order to view it, please
contact the author of the presentation.

Send to Blogs and Networks

Processing ....

Premium member

Use HTTPs

HTTPS (Hypertext Transfer Protocol Secure) is a protocol used by Web servers to transfer and display Web content securely. Most web browsers block content or generate a “mixed content” warning when users access web pages via HTTPS that contain embedded content loaded via HTTP. To prevent users from facing this, Use HTTPS option.