Three port dc–dc converter for stand-alone photovoltaic systems

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IEEE SOFTWARE | EMBEDDED | MECHANICAL | ROBOTICS PROJECTS DEVELOPMENT
THREE-PORT DC–DC CONVERTER FOR STAND-ALONE PHOTOVOLTAIC
SYSTEMS
By
A
PROJECT REPORT
Submitted to the Department of electronics & communication Engineering in the
FACULTY OF ENGINEERING & TECHNOLOGY
In partial fulfillment of the requirements for the award of the degree
Of
MASTER OF TECHNOLOGY
IN
ELECTRONICS & COMMUNICATION ENGINEERING
APRIL 2016

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CERTIFICATE
Certified that this project report titled “THREE-PORT DC–DC CONVERTER FOR STAND-
ALONE PHOTOVOLTAIC SYSTEMS” is the bonafide work of Mr. _____________Who
carried out the research under my supervision Certified further, that to the best of my knowledge
the work reported herein does not form part of any other project report or dissertation on the
basis of which a degree or award was conferred on an earlier occasion on this or any other
candidate.
Signature of the Guide Signature of the H.O.D
Name Name

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DECLARATION
I hereby declare that the project work entitled “THREE-PORT DC–DC CONVERTER FOR
STAND-ALONE PHOTOVOLTAIC SYSTEMS” Submitted to BHARATHIDASAN
UNIVERSITY in partial fulfillment of the requirement for the award of the Degree of MASTER
OF APPLIED ELECTRONICS is a record of original work done by me the guidance of
Prof.A.Vinayagam M.Sc., M.Phil., M.E., to the best of my knowledge, the work reported here
is not a part of any other thesis or work on the basis of which a degree or award was conferred on
an earlier occasion to me or any other candidate.
(Student Name)
(Reg.No)
Place:
Date:
ACKNOWLEDGEMENT

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I am extremely glad to present my project “THREE-PORT DC–DC CONVERTER FOR
STAND-ALONE PHOTOVOLTAIC SYSTEMS” which is a part of my curriculum of third
semester Master of Science in Computer science. I take this opportunity to express my sincere
gratitude to those who helped me in bringing out this project work.
I would like to express my Director, Dr. K. ANANDAN, M.A.(Eco.), M.Ed., M.Phil.,(Edn.),
PGDCA., CGT., M.A.(Psy.) of who had given me an opportunity to undertake this project.
I am highly indebted to Co-Ordinator Prof. Muniappan Department of Physics and thank from
my deep heart for her valuable comments I received through my project.
I wish to express my deep sense of gratitude to my guide
Prof. A.Vinayagam M.Sc., M.Phil., M.E., for her immense help and encouragement for
successful completion of this project.
I also express my sincere thanks to the all the staff members of Computer science for their kind
advice.
And last, but not the least, I express my deep gratitude to my parents and friends for their
encouragement and support throughout the project.

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ABSTRACT:
System efficiency and cost effectiveness are of critical importance for photovoltaic (PV)
systems. This paper addresses the two issues by developing a novel three-port dc–dc converter
for stand-alone PV systems, based on an improved Flyback- Forward topology. It provides a
compact single-unit solution with a combined feature of optimize maximum power point
tracking (MPPT), high step-up ratio, galvanic isolation, and multiple operating modes for
domestic and aerospace applications. A theoretical analysis is conducted to analyze the operating
modes followed by simulation and experimental work. This paper is focused on a comprehensive
modulation strategy utilizing both PWM and phase-shifted control that satisfies the requirement
of PV power systems to achieve MPPT and output voltage regulation. A 250- W converter was
designed and prototyped to provide experimental verification in term of system integration and
high conversion efficiency.

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INTRODUCTION:
Traditionally, the two-port topology utilizes the dual active bridges and the half or full
bridges can support the multiport structure to some extent. A combination of Flyback-Forward
converter with full bridge has shown some advantages in zero voltage switching (ZVS) and high
conversion ratio for fuel cell applications.
A modified half-bridge converter, which consists of one PV input port, one bidirectional
battery port, and an isolated output for satellite applications. However, in these converters, a
multi-input-multi-output solution is generally difficult to achieve for power electronic
applications.
In theory, multiple-input converters (e.g., three-port converters) can provide a single-unit
solution interfacing multiple energy sources and common loads. They perform better than
traditional two-port converters due to their lower part count and smaller converter size.
In particular, the isolated three-port converter (ITPC) has become an attractive topology
for various applications owing to their multiple energy source connection, compact structure. In
this topology, a simple power-flow management scheme can be used since the control function is
centralized.
A high-frequency transformer can provide galvanic isolation and flexible voltage
conversion ratio. The ITPC is usually integrated into an individual converter such as forward,
push–pull, full-bridge, and Flyback converters.

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EXISTING SYSTEM:
The dc–dc full-bridge converter uses resonant techniques in which resonant elements
such as capacitors and inductors are used to shape the current through a converter switch so that
it can fall to zero to allow the switch to turn off with ZCS. The resonant elements, however, are
large and bulky, which makes their use impractical for many applications, and the converter is
operated with variable frequency control, which makes the design of the converter more difficult
and also increases the size of the converter as it must operate with low switching frequencies at
lighter loads.

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PROPOSED SYSTEM:
The ITPC utilizes the triple active bridges (TAB) with inherent features of power
controllability and ZVS. Their softswitching performance can be improved if two series-resonant
tanks are implemented. An advanced modulation strategy is reported, which incorporates a phase
shift (PS) and a PWM to extend the operating range of ZVS.
Nonetheless, the TAB topology suffers from the circuit complexity using three active full
bridges or half bridges and the power loss caused by reactive power circulation. Therefore, a
Buck-Boost converter is proposed to integrate a three-port topology in the half bridge and to
decompose the multivariable control problem into a series of independent single-loop
subsystems. By doing so, the power flow in each loop can be independently controlled. The
system with one converter interfaces with the three components of the PV array, battery, and
loads.
However, in each energy transfer state, current passes through at least five inductor
windings, especially under high-switching frequency conditions, giving rise to power loss; its
peak efficiency is less than 90% and its power capability is limited by the transformer size. The
main switches S1 and S2 transfer the energy from the PV to the battery or load, and can work in
either interleaved or synchronous mode.
The switches S3 and S4 are operated in the interleaved mode to transfer energy from
source to load. L1 and L2 are two coupled inductors whose primary winding (n1) is employed as
a filter and the secondary windings (n2 ) are connected in series to achieve a high-output voltage
gain. LLK is the leakage inductance of the two coupled inductors and N is the turns ratio from
n2/n1 . CS1 , CS2 , CS3 , and CS4 are the parasitic capacitors of the main switches S1 , S2 , S3 ,
and S4 , respectively.

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ADVANTAGES:
 Power controllability.
 Low cost

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BLOCK DIAGRAM:

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TOOLS AND SOFTWARE USED:
 MPLAB – microcontroller programming.
 ORCAD – circuit layout.
 MATLAB/Simulink – Simulation

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APPLICATIONS:
 PV systems.
 Renewable applications

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CONCLUSION:
This paper has presented an isolated three-port dc–dc converter for stand-alone PV
systems, based on an improved Flyback-Forward topology. The converter can provide a high
step-up capability for power conversion systems including the PV array, the battery storage, and
the isolated load consumption. Three operating modes are analyzed and have shown the effective
operation of the proposed topology for PV applications. From simulation and experimental tests,
it can be seen that the output voltage and PV voltage can be controlled independently by the
phase angle shift and PWM, respectively. The decoupled control approach is a simple but
effective way to achieve the regulation of output voltage and PV voltage, which is important for
MPPT of stand-alone PV systems. In addition, a 250-W converter is prototyped and tested to
verify the effectiveness of the proposed converter topology and control scheme

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REFERENCES:
[1] K. Basu and N. Mohan, “A high-frequency link single-stage PWMinverter with common-
mode voltage suppression and source-based commutation of leakage energy,” IEEE Trans.
Power Electron., vol. 28, no. 8, pp. 3907– 3918, Oct. 2014.
[2] C. Konstantopoulos and E. Koutroulis, “Global maximum power point tracking of flexible
photovoltaic modules,” IEEE Trans. Power Electron., vol. 29, no. 6, pp. 2817–2828, Oct. 2014.
[3] W. Li, W. Li, X. Xiang, Y. Hu, and X. He, “High step-up interleaved converter with built-in
transformer voltage multiplier cells for sustainable energy applications,” IEEE Trans. Power
Electron., vol. 29, no. 6, pp. 2829–2836, Jun. 2014.
[4] Y.Hu,Y. Deng, Q. Liu, andX.He, “Asymmetry three-level grid-connected current hysteresis
controlwith varying bus voltage and virtual over-sample method,” IEEE Trans. Power Electron.,
vol. 29, no. 6, pp. 3214–3222, Jun. 2014.
[5] F. Nejabatkhah, S. Danyali, S. H. Hosseini, M. Sabahi, and S. M. Niapour, “Modeling and
control of a new three-input DC-DC boost converter for hybrid PV/FC/battery power system,”
IEEE Trans. Power Electron., vol. 28, no. 10, pp. 4612–4624, Oct. 2013.

Three port dc–dc converter for stand-alone photovoltaic systems

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Three port dc–dc converter for stand-alone photovoltaic systems