International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 3 – Sep 2014
PV and Wind Energy Hybrid Integrated Full-BridgeDC–DC Converter for a Residential Application
G.Revan Sidda#1 Mohandas. Audirala *2 Mohammed Mustafa*3
#
M.Tech student (PE&ED), & EEE Department & JNTUH
Hyderabad, A.P, INDIA.
Abstract— Hybrid power system can be used to reduce energy
storage requirements. There is increasing demand for the use of
alternate or renewable energy sources to achieve clean and lowcost electricity for Residential Application The PV-wind hybrid
system returns the lowest unit cost values to maintain the same
level of DPSP as compared to standalone solar and wind systems.
For all load demands the levelised energy cost for PV-wind hybrid
system is always lower than that of standalone solar PV or wind
system. The PV-wind hybrid option is techno-economically viable
for rural electrification. This paper proposes a novel integrated
converter topology for interfacing between the energy storage
system and the dc bus for a residential microgrid application The
proposed integrated full-bridge dc–dc converter presents the
following features: low number of active devices compared to the
converters usually applied to similar applications, low input and
output current ripple, high voltage ratio, bidirectional power flow,
and galvanic isolation.
Keywords— DC bus interconnection, dc–dc converter, energy
storage system, microgrid, power converter integration.
I.
INTRODUCTION
ELECTRICAL energy consumption has been increasing in
recent years, and this fact has been essential to the increase of
electric power generation. Distributed generation (DG)
technologies have been gaining interest due to some benefits
such as high reliability, high power quality, modularity,
efficiency, reduced or absent emissions, security, and load
management [1], [2]. However, the uncontrolled use of
individual DG units can cause various problems thereby
compromising their benefits [3], [4]. Difficulties in connecting
these units directly to the bulky ac system due to their variable
and intermittent power generation, voltage oscillation in the line
to which the sources are connected, and protection issues are
some of these problems. As an alternative to reduce such
problems, the microgrid concept has been gaining more
notoriety each day [5], [6]. Some advantages of themicrogrids
are the possibility to generate electric power with lower
environmental impact and easier connection of these sources to
the utility, including the power management capability among
their elements. Regarding the connection methods of the
distributed energy sources, energy storage devices, and loads in
a microgrid, the dc bus is the simplest interconnection bus [2].
has low distribution and transmission losses, low cost, the
possibility to operate across long distances, and it does not use
transformers, in turn leading to volume and cost reduction [2].
II. PV SOURCE MODELLING
PV generator as input source has significant effect on the
converter dynamics. The nonlinear V −I characteristic
of a PV generator can be modeled using current source,
diode, and resistors. The single-diode model shown in Fig.
1 (a) is widely used for the PV source modeling. This
model provides a trade- off between accuracy and
complexity. Thevenin’s equivalent model with non
constant voltages and resistances has been proposed in
toclosely approximate the characteristic of PV generator.
The Thevenin’s based model provides simpler prediction
and computation for the maximum power point of PV
array under different operating conditions. Thevenin’s
theorem is not valid for a nonlinear model, but the
nonlinear model could be represented by a linear one with
non constant parameters. In for example, the piece- wise
linearization is used to linearize the diode. The parameters
in Fig. 1(a) can be estimated using the manufacturer’s
datasheet. As shown in Fig. 1(b), the actual diode
characteristic has been divided into three regions and the
characteristic in each region is approximated as a straight line.
Each line can be further represented by a set of voltage
source Vx,n and resistance one of the boundary points
such that the operation at this point has no approximation
error. The single-diode model of the PV generator with
linearize diode is shown in Fig. 1(c), where the diode is
approximated by the voltage source Vx,n and resistance
Rd . The values of Vx and Rd are dependent on the
operation region of the PV generator. The Thevenin’s
equivalent model of Fig. 2(c) is shown in Fig. 1(d). From
the derivation in, the Vpv_th,n and Rpv_ th,n can be
calculated by
This configuration results in high efficiency, high reliability,
and no frequency or phase control requirements, when
compared to the ac interconnection bus [7], [8]. Moreover, it
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International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 3 – Sep 2014
(2)
where, U is the kinetic energy in joule, A is the cross-sectional
area in m2, is the air density in kg/m3, and x is the thickness of
the parcel in m. If we visualize the parcel as in Fig. 2 with side,
x, moving at speed, vw (m/sec), and the opposite side fixed at
the origin, we see the kinetic energy increasing uniformly with
x, because the mass is increasing uniformly.
The power in the wind, Pw, is the time derivative of the kinetic
energy:
(3)
Fig. 2 Packet of air moving at speed, vw
The mechanical power extracted is then the difference between
the input and output power in the wind:
Fig. 1. Thevenin’s equivalent circuit derived from the single-diode model.(a)
Single-diode model of a PV generator.(b) V −I characteristic of diode: actual
and linear approximation . (c) Single-diode model with linearize diode.(d)
Thevenin’s equivalent circuit for a single-diode model with linearized diode.
III. WIND ENERGY MODELING
A. Power Output from an Ideal Turbine:
The kinetic energy in a parcel of air of mass, m, flowing at
speed, vw in the x direction
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(4)
This states that 8/9 of the power in the original tube of air is
extracted by an ideal turbine. This tube is smaller than the
turbine, however, and this can lead to confusing results. The
normal method of expressing this extracted power is in terms of
the undisturbed wind speed, vw1, and the turbine area, A2. This
method yields
(5)
The factor 16/27 = 0.593 is called the Betz coefficient. It shows
that an actual turbine cannot extract more than 59.3 percent of
the power in an undisturbed tube of air of the same area. In
practice, the fraction of power extracted will always be less
because of mechanical imperfections. A good fraction is 35 –
40 % of the power in the wind under optimum conditions,
although fractions as high as 50 % have been claimed. A
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International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 3 – Sep 2014
turbine extracts 40 % of the power in the wind, is extracting The microgrid has two buses: one main dc bus in which the DG
about two-thirds of the amount that would be extracted by an sources, storage devices, and dc loads are connected, and one
ideal turbine. This is rather good, considering the aerodynamic ac bus in which the ac loads are connected and the point of
problems of constantly changing wind speed and direction as common coupling (PCC) with the utility grid is located. The
well as the frictional loss due to blade surface roughness.
arrows beside each converter indicate the possible power flow
directions. The investigated power converter in this paper is
B. Power Output from Practical Turbines:
also indicated. Table I presents the microgrid sources and
converter power levels. Further information can be found in
The fraction of power extracted from the power in the wind by [9].
a practical wind turbine is usually given by the symbol Cp,
TABLE - I
standing for the coefficient of performance or power
MICROGRID POWER L EVELS
coefficient. Using this notation and dropping the subscripts of
Eq. 6 the actual mechanical power output can be written as
(6)
(7)
(8)
IV. PROPOSED RESIDENTIAL MICROGRID SYSTEM
UNDER STUDY.
Considering the local generation of distributed sources,
residential microgrids are being proposed as an interesting
solution for increasing renewable energy production and system
reliabil- ity for household appliances. The residential microgrid
under study here, as shown in Fig. 2 [9], comprises two DG
sources (photovoltaic panels and biofuel generator), an energy
storage system (one battery and one supercapacitor bank), and a
plug-in hybrid electric vehicle (PHEV). Moreover, it is able to
supply both ac and dc loads.
Fig. 4 Residential microgrid system under study.
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In the microgrid systems, the energy storage system is of great
importance. It is responsible for supplying energy to the loads
when the main sources are not capable during short periods
of time and steady-state operation. The proposed residential
microgrid energy storage system composed of a battery bank
and a supercapacitor bank has two main functions. The battery
bank acts as a backup device due to its high energy density
[10], providing energy under the steady-state condition when
the other sources are not capable. The supercapacitor bank acts
as a quick discharge device due to its high power density [11],
providing energy to the microgrid during transitory periods,
mainly during the biofuel generator start-up time. Consequently,
due to the importance of the energy storage system, this paper
focuses specifically on the dc power module of the microgrid
energy storage system.
A dc–dc converter is necessary to connect the energy storage
system to the microgrid dc bus. Once the supercapacitor bank
voltage is low and not controlled, the dc–dc converter must have
a high voltage ratio between the input and output stages.
Moreover, it must be able to operate under a wide output power
range. Since the supercapacitor and battery banks are not
demanded at the same time according to the microgrid
operation, the same converter is used for both, including a
selector switch to choose the appropriate storage device for
each situation.
Several dc–dc converter topologies employing a
supercapacitor bank to complement the energy supplied by
other sources, such as fuel cells, batteries, or generators, have
been proposed in the literature [12]–[27]. These topologies are
applied to hybrid vehicles, uninterruptable power supply (UPS)
systems, buses in general, and critical loads, among other
applications.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 3 – Sep 2014
The dual active bridge (DAB) or modified DAB converters are discharge, making it reach lower voltage levels (requiring high
approached in [12]–[20]. Papers [12] and [13] propose voltage ratio). A long battery lifetime is achieved by draining
modulation schemes different from the conventional phase-shift from and providing to the battery a low ripple dc current.
modulation. In [12], a new hybrid modulation technique to expand
the converter power range is proposed, while paper [13]
proposes an optimal modulation scheme that enables minimum
TABLE III
conduction and copper losses for a DAB converter. In [14], an
input stage composed of a qZSI converter is proposed, which
guarantees the voltage boost during the supercapacitor
discharge, but increases the number of active switches. In [15],
a DAB con- verter including unified soft-switching scheme
(voltage clamp branch on the current-fed bridge) is proposed.
Paper [16] discusses the steady-state operation of a phase-shift
modulated dual-bridge series resonant converter. In [17],
design issues of the DAB converter such as leakage
inductance, switching
frequency, and turns ratio are approached aiming for higher
efficiency. Paper [18] describes the design and performance of
the converter and analyzes the effect of unavoidable dc-bias
cur- rents on the magnetic-flux saturation of the transformer.
These topologies present high number of active devices and
most of them present high input and output current ripple. A
common feature of these topologies is that a transformer is used
to aid voltage boosting due to the low-voltage level of the
supercapacitor bank, besides providing galvanic isolation. The
exception is a nonisolated converter presented in [27]. However,
in this case the supercapacitor bank voltage level is much higher
than in the other topologies.
Consequently, the desired converter must present the
following features: bidirectional power flow, high power
operation, galvanic isolation, high usage of the supercapacitor
stored en- ergy, and long battery lifetime. High usage of the
supercapacitor stored energy is achieved through a deeper
Fig. 14. Main waveforms of the proposed converter with passive Clamping
circuit
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International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 3 – Sep 2014
VII. CONCLUSION
This paper proposes an integrated full-bridge-forward dc–dc
converter to connect the energy storage system to the dc
bus of a residential micro grid. The converter major
advantages are reduced active switches compared to the DAB
converter and individual topologies, high usage of the super
capacitor bank stored energy, and a long battery bank
lifetime. The proposed topology presents low input and output
current ripple, high volt- age ratio, high power operation on
the discharging process, galvanic isolation, and bidirectional
power flow, as requested by the application.
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REFERENCES
[1] K. Sun, L. Zhang, Y. Xing, and J. M. Guerrero, “A distributed control
strategy based on DC bus signaling for modular photovoltaic generation systems
with battery energy storage,” IEEE Trans. Power Electron., vol. 26, no. 10, pp.
3032–3045, Oct. 2011.
[2] F. A. Farret and M. G. Sim˜oes, Integration of Alternative Sources of Energy,
1st ed. New Jersey: Wiley, 2006.
[3] Y. A.-R. I. Mohamed, “Mitigation of converter-grid resonance, gridinduced
distortion, and parametric instabilities in converter-based distributed generation,”
IEEE Trans. Power Electron., vol. 26, no. 3, pp. 983– 996, Mar. 2011.
[4] R. H. Lasseter and P. Paigi, “Microgrid: A conceptual solution,” in Proc.
IEEE Power Electron. Spec. Conf., Jun. 2004, vol. 6, pp. 4285–4290.
[5] H. Zhou, T. Bhattacharya, D. Tran, T. S. T. Siew, and A. M. Khambadkone,
“Composite energy storage system involving battery and ultracapacitor with
dynamic energy management in microgrid applications,” IEEE Trans. Power
Electron., vol. 26, no. 3, pp. 923–930, Mar. 2011.
[6] J.-Y. Kim, J.-H. Jeon, S.-K. Kim, C. Cho, J. H. Park, H.-M. Kim, and K.-Y.
Nam, “Cooperative control strategy of energy storage system and microsources
for stabilizing the microgrid during islanded operation,”IEEE Trans. Power
Electron., vol. 25, no. 12, pp. 3037–3048, Dec. 2010.
[7] R. S. Balog and P. T. Krein, “Bus selection in multibus DC microgrids,”IEEE
Trans. Power Electron., vol. 26, no. 3, pp. 860–867, Mar. 2011.
[8] J. Chen, J. Chen, R. Chen, X. Zhang, and C. Gong, “Decoupling control of
the non-grid-connected wind power system with the droop strategy based on a
DC micro-grid,” in Proc. World Non-Grid-Connected Wind Power Energy Conf.,
2009, pp. 1–6.
[9] L. Roggia, C. Rech, L. Schuch, J. E. Baggio, H. L. Hey, and J. R. Pinheiro,
“Design of a sustainable residential microgrid system including PHEV and
energy storage device,” in Proc. Eur. Conf. Power Electron. Appl., 2011, pp. 1–9.
[10] F. Ongaro, S. Saggini, and P. Mattavelli, “Li-ion battery-supercapacitor
hybrid storage system for a long lifetime, photovoltaic-based wireless sensor
network,” IEEE Trans. Power Electron., vol. 27, no. 9, pp. 3944–3952, Sep.
2012.
[11] J. Cao and A. Emadi, “A new battery/ultracapacitor hybrid energy storage
system for electric, hybrid, and plug-in hybrid electric vehicles,” IEEE Trans.
Power Electron., vol. 27, no. 1, pp. 122–132, Jan. 2012.
[12] H. Zhou and A. M. Khambadkone, “Hybrid modulation for dualactivebridge bidirectional converter with extended power range for ultracapacitor
application,” IEEE Trans. Ind. Appl., vol. 45, no. 4, pp. 1434–1442, Jul. 2009.
[13] F. Krismer and J. W. Kolar, “Closed form solution for minimum conduction
loss modulation of DAB converters,” IEEE Trans. Power Electron., vol. 27, no.
1, pp. 174–188, Jan. 2012.
[14] D.Vinnikov, I. Roasto, and J. Zakis, “Newbi-directionalDC/DC converter
for supercapacitor interfacing in high-power applications,” in Proc. Int. Power
Electron. Motion Control Conf., 2010, pp. T11-38–T11-43.
[15] K. Wang, F. C. Lee, and J. Lai, “Operation principles of bi-directional fullbridge DC/DC converter with unified soft-switching scheme and softstarting
capability,” in Proc. IEEE Appl. Power Electron. Conf., 2000, vol. 1, pp. 111–
118.
[16] L. Corradini, D. Seltzer, D. Bloomquist, R. Zane, D. Maksimovic, and B.
Jacobson, “Minimum current operation of bidirectional dual-bridge series
resonant DC/DC converters,” IEEE Trans. Power Electron., vol. 27, no. 7, pp.
3266–3276, Jul. 2012.
http://www.ijettjournal.org
Page 128
International Journal of Engineering Trends and Technology (IJETT) – Volume X Issue Y- Month 2013
[17] Z. Zhang, Z. Ouyang, O. C. Thomsen, and M. A. E. Andersen, “Analysis
and design of a bidirectional isolated DC–DC converter for fuel cells and
supercapacitors hybrid system,” IEEE Trans. Power Electron., vol. 27, no. 2,
pp. 848–859, Feb. 2012.
[18] N. M. L. Tan, T. Abe, and H. Akagi, “Design and performance of a
bidirectional isolated DC–DC converter for a battery energy storage system,”
IEEE Trans. Power Electron., vol. 27, no. 3, pp. 1237–1248, Mar. 2012.
[19] M. N. Gitau, G. Ebersohn, and J. G. Kettleborough, “Power processor for
interfacing battery storage system to 725 V DC bus,” Energy Convers.
Manage., vol. 48, no. 3, pp. 871–881, Mar. 2007.
[20] M. Nowak, J. Hildebrandt, and P. Luniewski, “Converters with AC
transformer intermediate link suitable as interfaces for supercapacitor energy
storage,” in Proc. IEEE Power Electron. Spec. Conf., Jun. 2004, vol. 5, pp.
4067–4073.
[21] H. Tao, A. Kotsopoulos, J. L. Duarte, and M. A. M. Hendrix, “Multiinput
bidirectional DC–DC converter combining DC-link and magneticcoupling for
fuel cell systems,” in Proc. IEEE Ind. Appl. Conf., Oct. 2005, vol. 3, pp.
2021–2028.
[22] H. Tao, J. L. Duarte, andM. A.M. Hendrix, “Three-port triple-half-bridge
bidirectional converter with zero-voltage switching,” IEEE Trans. Power
Electron., vol. 23, no. 2, pp. 782–792, Mar. 2008.
[23] G. Chen, Y.-S. Lee, D. Xu, and Y. Wang, “A novel soft-switching and
low-conduction-loss bidirectional DC–DC converter,” in Proc. Int. Power
Electron. Motion Control Conf., 2000, vol. 3, pp. 1166–1171.
[24] F. G. Capponi, P. Santoro, and E. Crescenzi, “HBCS converter: A
bidirectional DC/DC converter for optimal power flow regulation in
supercapacitor applications,” in Proc. IEEE Ind. Appl. Conf., Sep. 2007, pp.
2009– 2015.
[25] M. H. Todorovic, L. Palma, and P. N. Enjeti, “Design of a wide input
range DC–DC converter with a robust power control scheme suitable for fuel
cell power conversion,” IEEE Trans. Ind. Electron., vol. 55, no. 3, pp. 1247–
1255, Mar. 2008.
[26] S.-J. Jang, T.-W. Lee, W.-C. Lee, and C.-Y. Won, “Bi-directional dc–dc
converter for fuel cell generation system,” in Proc. IEEE Power Electron.
Spec. Conf., Jun. 2004, vol. 6, pp. 4722–4728.
[27] M. B. Camara, H. Gualous, F. Gustin, and A. Berthon, “Design and new
control of DC/DC converters to share energy between supercapacitors and
batteries in hybrid vehicles,” IEEE Trans. Veh. Technol., vol. 57, no. 5, pp.
2721–2735, Sep. 2008.
[28] Y.-S. Lee andB.-T. Lin, “Modeling, analysis, and design criteria of
actively clamped double-ended converters,” IEEE Trans. Circuits Syst. I,
Fundam. Theory Appl., vol. 47, no. 3, pp. 312–323, Mar. 2000.
[29] R. W. Erickson and D. Maksimovic, Fundamentals of Power Electronics.
New York: Kluwer, 2004.
[30] A. I. Pressman, Switching Power Supply Design. New York: McGrawHill, 1998.
Mr. Mohandas. Audirala, at present is a
Associate Professor in the department of EEE in Arjun
College of Technology& Sciences Hyderabad Andhra
Pradesh, India. He received B.E degree in EEE from A.U.
Vishakhapatnam in 2005. He received M.Tech degree in
Power Electronics & Drives from NIT Warangal in 2008.
He is currently pursuing Ph.D from JNTU Hyderabad. His
research interests accumulate in the area of Power
Electronics, Drives, Multilevel inverters DC-DC Converters,
AC-DC Converters and Renewable energy sources and
Electrical Machines.
Mr. Mohammed Mustafa , at present is a
Assistant Professor department of Electrical & Electronics
Engineering, Aurora’s Scientific, Technological & Research
academy Hyderabad Andhra Pradesh, India. He received
B.Tech. Degree in Electrical and Electronics Engineering
from J.N.T.U Hyderabad in 2010, He is currently pursuing
M.Tech (Electrical Power System) from J.N.T.U, Hyderabad
India. His research interests accumulate in the area of power
systems, Power Electronics, Drives, DC-DC Converters,
AC-DC Converters and Renewable energy sources and
Electrical Machines
Mr. G. Revan Sidda received B.Tech.
Degree in Electrical and Electronics Engineering from
J.N.T.U Hyderabad in2010, He is currently pursuing
M.Tech (Power Electronics and Electrical Drives) from
J.N.T.U, Hyderabad India. His research interests
accumulate in the area of Power Electronics, Drives, DCDC Converters, AC-DC Converters and Renewable
energy sources and Electrical Machines.
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