Grid connected forward microinverter with primary-parallel secondary-series transformer

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IEEE SOFTWARE | EMBEDDED | MECHANICAL | ROBOTICS PROJECTS DEVELOPMENT
GRID-CONNECTED FORWARD MICROINVERTER WITH PRIMARY-PARALLEL
SECONDARY-SERIES TRANSFORMER
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 “GRID-CONNECTED FORWARD
MICROINVERTER WITH PRIMARY-PARALLEL SECONDARY-SERIES
TRANSFORMER” 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 “GRID-CONNECTED FORWARD
TRANSFORMER” 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:

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ACKNOWLEDGEMENT
I am extremely glad to present my project “GRID-CONNECTED FORWARD
TRANSFORMER” 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:
This paper presents a primary-parallel secondaryseries multicore forward microinverter
for photovoltaic ac-module application. The presented microinverter operates with a constant
off-time boundary mode control, providing MPPT capability and unity power factor. The
proposed multitransformer solution allows using low-profile unitary turns ratio transformers.
Therefore, the transformers are better coupled and the overall performance of the microinverter
is improved. Due to the multiphase solution, the number of devices increases but the current
stress and losses per device are reduced contributing to an easier thermal management.
Furthermore, the decoupling capacitor is split among the phases, contributing to a low-profile
solution without electrolytic capacitors suitable to be mounted in the frame of a PV module. The
proposed solution is compared to the classical parallel-interleaved approach, showing better
efficiency in a wide power range and improving the weighted efficiency

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INTRODUCTION:
Traditionally, central inverter technology is used to overcome the low voltage generated
by photovoltaic (PV) arrays. However, in residential applications, the energy yield is jeopardized
due to mismatches and partial-shading. Distributed maximum power point tracking (DMPPT)
architectures, in both dc–dc and dc–ac systems, improve the energy harvesting capability by
means of a module-integrated converter.
Despite nonisolated solutions have been presented for dc–dc optimizers and ac-module
applications, the use of a transformer is widespread providing flexibility, an adequate voltage
boost and compliance with safety standards. Current-fed-isolated converters are widely used in
DMPPT architectures due to their inherent boosting capabilities. Single-stage flyback inverter is
a commonly used topology in ac-module applications due to its simple structure. Buck derived
topologies are mainly used as step-up dc–dc converters in two-stage inverters.
The use of parallel-interleaved converters is common in lowvoltage high-current
applications to reduce the current stress and magnetic components size. In addition, light load
efficiency is improved by connecting or disconnecting phases an isolated boost converter with
parallel-interleaved primary and series-connected secondary is presented, thus reducing current
stress in the primary side and improving voltage gain.
Similar configurations are also presented using planar magnetics. The interleaved
operation of forward converters is well known and the secondary side series connection has also
been presented with different configurations for dc–dc applications.

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This paper presents a primary-parallel secondary-series forward inverter for ac-module
application. In Section II, the single-transformer approach is presented, analyzing the operation
mode to achieve unitary power factor. Section III introduces the multitransformer topology as
well as the operation principle and the main design considerations.
The light load operation of the inverter is analyzed in Section IV and the estimated
weighted efficiency for the analyzed configurations is compared. In Section V, the transformers
design and size are compared for configurations with different number of transformers.

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EXISTING SYSTEM:
The topology structure is constituted of high frequency pulse DC link circuit and DC/AC
inverter. The high frequency pulse DC link circuit has the functions such as high frequency
electrical isolation, power conversion, producing high frequency pulse DC voltage, and
absorbing reactive energy from AC side of DC/AC inverter bridge. The power devices of the
DC/AC inverter turn on/off when the high frequency pulse DC voltage gets to zero and make
zero-voltage switching possible.

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PROPOSED SYSTEM:
In the configuration presented, the necessary primary to secondary turns ratio to achieve a
proper interfacing between the low PV module voltage and the grid is large, thus the
performance of the converter can be worsened. The proposed method, which consists of several
highly coupled transformers which are parallel connected in the primary side and series
connected in the secondary side. The parallelization in the primary side reduces the current stress
in both switches and primary windings of the transformer. The current sharing is guaranteed
because of the secondary series connection, although affected by the coupling of the individual
transformers. The current stress is also decreased in the secondary side diodes due to the
common cathode configuration and the synchronized driving of the primary switches. As a
result, SMD devices can be used, a low-profile implementation is feasible and the thermal
management is improved, although more devices are needed. The secondary series connection
allows achieving the grid voltage using transformers of lower turns ratio.

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ADVANTAGES:
 Leakage inductance can be reduced.

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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:
 Photovoltaic (PV) arrays.

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CONCLUSION:
This paper introduces a multiphase primary-parallel secondary-series forward
microinverter operated in boundary and DCM, suitable for PV ac-module application. The key
parameter is the number of transformers and its influence in terms of size, losses, leakage
inductance, series resistance and resonance frequency of the transformers is explored. An
increase in the number of transformers allows the utilization of better coupled transformers,
improving the inverter performance. The total surface of the proposed solution increases with the
number of transformers, however the height decreases making the solution suitable for PV ac-
module application. DCM operation is introduced to overcome the performance degradation due
to the increase in the operation frequency of BCM at light load. Based on the analysis, single
transformer prototype as well as prototypes of 2 and 8 transformers were built. Both
multitransformer inverters present the same weighted efficiency of 92.4%, improving the single-
transformer inverter performance in around 2%.

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REFERENCES:
[1] N. Femia, G. Lisi, G. Petrone, G. Spagnuolo, and M. Vitelli, “Distributed maximum power
point tracking of photovoltaic arrays: Novel approach and system analysis,” IEEE Trans. Ind.
Electron., vol. 55, no. 7, pp. 2610–2621, Jul. 2008.
[2] L. Quan and P. Wolfs, “A review of the single phase photovoltaic module integrated
converter topologies with three different DC link configurations,” IEEE Trans. Power Electron.,
vol. 23, no. 3, pp. 1320–1333, May 2008.
[3] L.Wuhua andH.Xiangning, “Reviewof nonisolated high-step-upDC/DC converters in
photovoltaic grid-connected applications,” IEEE Trans. Ind. Electron., vol. 58, no. 4, pp. 1239–
1250, Apr. 2011.
[4] D. Meneses, F. Blaabjerg, O. Garca, and J. A. Cobos, “Review and comparison of step-up
transformerless topologies for photovoltaic AC-module application,” IEEE Trans. Power
Electron., vol. 28, no. 6, pp. 2649–2663, Jun. 2013.
[5] Z. Yi, L.Wuhua, D. Yan, and H. Xiangning, “Analysis, design, and experimentation of an
isolated ZVT boost converter with coupled inductors,” IEEE Trans. Power Electron., vol. 26, no.
2, pp. 541–550, Feb. 2011

Grid connected forward microinverter with primary-parallel secondary-series transformer

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Grid connected forward microinverter with primary-parallel secondary-series transformer