International Journal of Research and Engineering
Volume 2, Issue 12
PERFORMANCE ANALYSIS OF MULTILEVEL INVERTER UPTO XI LEVEL
WITH PEM FUEL CELL BASED ENERGY SYSTEM
Author(S): Kishwar Jhan Ali1, Prof. Rajesh Sahu2
Research scholar1, Professor2
Department of Electrical engineering,
TIT Bhopal
Abstract— Nowadays Renewable energy sources play a
prominent role in the areas of research, due to exhaustion of
conventional energy sources. The major available renewable
energy sources are sunlight, wind energy and Fuel Cells. In
this work Fuel cells were used as a source of energy for
multilevel inverters instead of DC sources. Multilevel
converters are very interesting solution for medium and high
voltage applications, due to its characteristic to synthesize a
sinusoidal voltage from several DC levels. The better
topology for power quality and transmission system
applications is the cascaded multilevel inverters. However,
this topology presents a problem that consists of use of
several DC sources or Fuel cell energy system. Nowadays
multilevel inverters have a great relevance in transmission
and distribution systems, due to its general structure which
synthesizes a sinusoidal voltage in many voltages levels.
Multilevel inverters generates an output signal with low
THD, because of this the size of the output filter reduces,
whose cut-off frequency depends on the modulation
technique and the switching frequency used. In addition it
can be possible to use PWM modulation over each step
staircase voltage, generating a high PWM frequency output.
The Topology-I of cascaded H-Bridge multilevel inverter is
general type of 11 levels Multi Level Inverter (MLI).
Keywords —Fuel Cell, Multilevel Inverter, Synthesize,
THD,PWM Modulation.
INTRODUCTION
Fuel Cell : Fuel Cells are a promising technology in
distributed generation. Some analysts even suggest that if
aspects like cell durability and manufacturing cost are
improved, fuel cells can displace some of the traditional
generation sources.
A fuel cell by definition is an electrical cell which unlike
storage cells can be continuously fed with a fuel so that the
electrical power output is sustained indefinitely. It converts
hydrogen, or hydrogen containing fuels, directly into the
electrical energy plus heat through the electrochemical
reaction of hydrogen and oxygen into water.
Figure 1: Fuel cell principle
The process is that of electrolysis in reverse. Over all
reaction:
10
ISSN 2348-7852 (Print) | ISSN 2348-7860 (Online)
2H2 (gas) +O2 (gas) --> 2H2O+energy
A fuel cell consists of two electrodes sandwiched around an
electrolyte. Oxygen passes over one electrode and hydrogen
over the other, generating electricity, water and heat.
Hydrogen fuel is fed into the "anode" of the fuel cell. Oxygen
(or air) enters the fuel cell through the cathode. Encouraged
by a catalyst, the hydrogen atom splits into a proton and an
electron, which take different paths to the cathode. The
proton passes through the electrolyte. The electrons create a
separate current that can be utilized before they return to the
cathode, to be reunited with the hydrogen and oxygen in a
molecule of water. A fuel cell system which includes a "fuel
reformer" can utilize the hydrogen from any hydrocarbon
fuel - from natural gas to methanol, and even gasoline. Since
the fuel cell relies on chemistry and not combustion,
emissions from this type of a system would still be much
smaller than emissions from the cleanest fuel combustion
processes.
II. CALCULATION OF THE STACK VOLTAGE
Applying Nernst’s equation and Ohm’s law _to
consider ohmic losses. The stack output voltage is
represented by the following expression:
where E is the voltage associated with the reaction free
energy V; R is the same gas constant as previous, but care
should be taken with the system unit J / kmolK; r describes
the ohmic losses of the stack Ω.
III. DC TO DC CONVERTER (CHOPPER)
DC-DC power converters are employed in a variety of
applications, including power supplies for personal
computers, office equipment, spacecraft power systems,
laptop computers, and telecommunications equipment, as
well as dc motor drives. The input to a dc- dc converter is an
unregulated dc voltage Vg. The converter produces a
regulated output voltage V, having a magnitude (and possibly
polarity) that differs from Vg. The ideal dc-dc converter
exhibits 100% efficiency; in practice, efficiencies of 70% to
95%this is achieved using switched-mode, or chopper,
circuits whose elements dissipate negligible power.
Pulse-width modulation (PWM) allows control and
regulation of the total output voltage. This approach is also
employed in applications involving alternating current,
including high-efficiency dc-ac power converters (inverters
and power amplifiers), ac-ac power converters, and some
ac-dc power converters (low-harmonic rectifiers).
IV. Cascaded H-bridge Converter
A cascaded H-bridge converter is several H- bridges in
series configuration [2], [7], [8], [12]. A single H-bridge is
shown in Figure 2. A single H-bridge is a three-level
converter. The four switches Sh S2, S3 and S4 are controlled to
generate three discrete outputs Vout with levels Vdc, 0 and
-Vdc. When S3 and S4 are on, the output is Vdc; when S2 and S3
are on, the output is -Vdc; when either pair S3 and S2 or S3 and
http://www.ijre.org
International Journal of Research and Engineering
S4 are on, the output is 0.
A H-bridge cascaded multilevel converter with s separate DC
sources is shown in Figure 3. A staircase sinusoidal
waveform can be generated by combining specified output
levels. The number of output phase voltage levels m in a
cascade converter with S separate DC sources is M = 2S+1.
Load balance control for each H-bridge and each DC source
can be acquired by rotating the switching angles to the
H-bridges [2].
The advantages for cascaded multilevel H-bridge converter
are the following:
(1)The series structure allows a scalable, modularized
circuit layout and packaging due to the identical structure of
each H-bridge.
(2)No extra clamping diodes or voltage balancing
capacitors is necessary.
(3)Switching for inner voltage levels is possible because the
phase voltage is the sum of each bridge’s output.
Volume 2, Issue 12
with s separate DC sources
Another kind of cascaded multilevel converters with
transformers using standard three-phase bi-level converters
has recently been proposed [8]. The converter uses output
transformers to add different voltages. In order for the
converter output voltages to be added up, the outputs of
the three converters need to be synchronized with a
separation of 120° between each phase. For example,
obtaining a threelevel voltage
The disadvantage for cascaded multilevel H-bridge converter
is the following:
(1) Needs separate DC sources.
Figure 4: Staircase sinusoidal waveform generated by
H-bridge cascaded multilevel converter
between outputs a and b, the output voltage can be
synthesized by Vab = Va1-b1+Vb1-a2+Va2-b2. An isolated
transformer is used to provide voltage boost. With three
converters synchronized, the voltages Va1-b1, Vb1-a2,
Va2b2, are all in phase; thus, the output level can be tripled
[13].
Figure 2 : Single H-bridge topology
Figure3: H-bridge cascaded multilevel converter
11
ISSN 2348-7852 (Print) | ISSN 2348-7860 (Online)
Figure 5: MATLAB/SIMULIK model of 2 level inverter with
connected fuel cell energy system
For a three-phase system, the output of three identical
structure of single-phase CHMI can be connected in
either wye or delta configuration. Fig. 3 illustrates the
schematic diagram of a wye-connected m-level CHMI
with separate DC sources. For a three-phase
11-levelCHMI, two H-bridge cells with eight switches are
needed per phase. Thus a total of six Hbridge cells
involving 24 power switches are required for this circuit
configuration. This means that twelve pairs of gating
signals have to be generated to be fed to the switches.
For each H-bridge cell, the switchings are designed in
such a way that only one pair of switches operate at the
carrier frequency while, the other pair operates at the
reference frequency, thus having two high- frequency
http://www.ijre.org
International Journal of Research and Engineering
Volume 2, Issue 12
switches and two low-frequency switches. of two phase
voltages. For example, the potential between phase A and
B is VAB, which can be computed from:
VAB = VAN -VBN where is the line
voltage VAN is the voltage of phase A with respect to
neutral point N VBN is the voltage of phase B with
respect to neutral point N.
The principle of MSPWM is to use several triangular carrier
signals with only one modulation signal per phase. For an
m-level inverter, (m-1) triangular carriers of the same
frequency fc and amplitude Ac, are disposed so that the bands
they occupy are contiguous. The zero reference is placed in
the middle of the carrier set. The modulation signal is a
sinusoidal of frequency fm and amplitude Am. At every
instant each carrier signal is compared with the reference
modulation signal. Each comparison switches the device on if
the reference signal is greater than the triangular carrier
assigned to that level. Otherwise, the device switches off [1].
For a three-phase 11-levelCHMI, four carrier waveforms are
needed and compared at every one time to a set of three
reference waveforms, each 1200 phase shifted apart [5].
Figure 6: MATLAB/SIMULIK model of 11 level inverter with
connected fuel cell energy system
V. RESULTS & DISCUSSION
The three-phase 11-level multilevel inverter and 2-level
multilevel inverter are simulated using MATLAB/Simulink.
In the simulation study, it is assumed that the DC voltage
output form PEM Fuel cell to each module is E = 48V, the
output voltage fundamental frequency is fm = 50 Hz, the
three-phase CHMI in terms of output voltage waveforms,
output voltage harmonic spectrums, fundamental voltage and
Total Harmonic Distortion (THD).
Figure 7: MATLAB/SIMULINK model of fuel cell energy
system
Figure 10: Three phase Load Voltage waveform for fuel cell
system
12
ISSN 2348-7852 (Print) | ISSN 2348-7860 (Online)
http://www.ijre.org
International Journal of Research and Engineering
Volume 2, Issue 12
30.90%
VI. CONCLUSION
The aim of this paper was to demonstrate the successful
implementation of the multilevel inverter with fuel cell
energy system. After a brief overview of the background
information, design considerations presented multilevel
voltage source converters that synthesize the converter
voltage by equally divided capacitor voltages. All these
converters have been completely analyzed and simulated.
The current trend of modulation control for multilevel
converters is to output high quality power with high
efficiency. For this reason, popular traditional PWM methods
and space vector PWM methods are not the best methods for
multilevel converter control due to their high switching
frequency. The selective harmonic elimination method has
emerged as a promising modulation control method for
multilevel converters. But the major difficulty for the
selective harmonic elimination method is to solve
transcendental equations characterizing harmonics,
TABLE 1: THD COMPARISON
THD(2level)
THD(lllevel)
Difference
13
ISSN 2348-7852 (Print) | ISSN 2348-7860 (Online)
12.17%
18.73
REFERENCES
[1] J.M. Correa, F.A. Farret, L.N. Canha, M.G. Simoes, “An
Electrochemical-Based Fuel Cell ModelSuitable for
Electrical Engineering Automation Approach,” IEEE Trans.
Industrial Engineering,vol. 51, no. 5, pp. 1103-1112, Oct.
2000. [2]R.F. Mann, J.C. Amphlett, M.A.I. Hooper, H.M.
Jensen, B.A. Peppley, P.R. Roberge, Development and
Application of a generalized Steady-State Electrochemical
Model for a PEM uel Cell,” J. of Power Sources, vol. 86, pp.
173-180, 2000. [3]E. Hernandez, B. Diong, “A Small-Signal
Equivalent Circuit Model for PEM Fuel Cells,”
IEEE,Applied Power Electronics Conference and Exposition,
vol. 1, no. 1, pp. 121-126, 6-10 March 2005. [4]P. Famouri,
R. S. Gemmen, “Electrochemical Model of a PEM Fuel
Cell,” IEEE Power Engineering Society General Meeting,
vol. 3, pp. 1436-1440, Jul. 2003. [5] R.F. Mann, J.C.
Amphlett, T.J. Haris, B.A. Peppley, P.R. Roberge, R.M.
Baumert, “Performance Modeling of the Ballard Mark IV
Solid Polymer Electrolyte Fuel Cell,” J. of Electrochemical
Society, vol.142, no.1, pp. 9-15, Jan. 1995.
[6]M. Uzunoglu, M. S. Alam, “Dynamic Modeling, Design,
and Simulation of a Combined PEM Fuel Cell and
Ultracapacitor System for Stand-Alone Residential
Applications,” IEEE Trans. Energy Conversion, vol. 21, no.
3, pp. 767-775, Sept. 2006. [7]J. Padulles, G. W. Ault, and J.
R. McDonald, “An Integrated SOFC Plant Dynamic Model
for Power System Simulation,” J. Power Sources, vol. 86, no.
1-2, pp. 495500, Mar. 2000. [8]K. Xing, and A. M.
Khambadkone, “Dynamic Modeling of Fuel Cell with Power
Electronic Current and performance analysis,” IEEE
International Conference on Power Electronics and Drive
Systems, vol. 1, pp. 607-612, 17-20, Nov. 2003. [9]P. T.
Krein, S. Balog, Xin Geng, “High-Frequency Link Inverter
for Fuel Cells Based on Multiple- Carrier PWM,” IEEE
Trans. Power Electronics, vol. 19, no. 5, pp. 12791288, Sept.
2005. [10]J. N. Chiasson, L. M. Tolbert, K. McKenzie, Z. Du,
“Harmonic Elimination in Multilevel Converters,” IASTED
International Conference on Power and Energy Systems
(PES 2003), February 24-26, 2003, Palm Springs, California,
pp. 284-289. [11]J. S. Lai, F. Z. Peng, “Multilevel
Converters - A New Breed of Power Converters,” IEEE
Transactions on Industry Applications, vol. 32, no. 3, May
1996, pp. 509-517. [12] F. Z. Peng, J. W. McKeever, D. J.
Adams, “A Power Line Conditioner Using Cascade
Multilevel Inverters for Distribution Systems,” IEEE
Transactions on Industry Applications, vol. 34, no. 6, Nov.
1998, pp. 1293-1298. [13] L. M. Tolbert, F. Z. Peng, T. G.
Habetler, “A Multilevel Converter-Based Universal Power
Conditioner,” IEEE Transactions on Industry Applications,
vol. 36, no. 2, Mar./Apr. 2000, pp. 596-603.
http://www.ijre.org