A high efficiency flyback micro inverter with a new adaptive snubber for photovoltaic applications

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IEEE SOFTWARE | EMBEDDED | MECHANICAL | ROBOTICS PROJECTS DEVELOPMENT
A HIGH EFFICIENCY FLYBACK MICRO-INVERTER WITH A NEW ADAPTIVE
SNUBBER FOR PHOTOVOLTAIC APPLICATIONS
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 “A HIGH EFFICIENCY FLYBACK MICRO-
INVERTER WITH A NEW ADAPTIVE SNUBBER FOR PHOTOVOLTAIC
APPLICATIONS” 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 “A HIGH EFFICIENCY FLYBACK MICRO-
APPLICATIONS” 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 “A HIGH EFFICIENCY FLYBACK MICRO-
APPLICATIONS” 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:
Based on the hybrid operation of interleaved flyback micro-inverter in Discontinuous and
Boundary Conduction Modes (DCM and BCM), a novel adaptive snubber is proposed in this
paper. The proposed snubber limits the drain-to-source voltage overshoot of the flyback’s main
switch during the turn-off process, enabling the use of lower voltage MOSFETs.
It also recovers the stored energy in the leakage inductance of the flyback transformer
and provides soft switching for the main flyback switch by limiting the rising slope of the
MOSFET voltage during the turn off process resulting in higher efficiency.
Exploiting the natural resonant of the flyback converter in BCM the adopted controller
provides ZVS and ZCS for the main switch during the BCM operation. The operation of the
flyback micro-inverter with associated controllers is analytically studied, and considerations for
an optimum design aiming to higher efficiency are presented.
Performance of the flyback micro-inverter with the proposed adaptive snubber and the
corresponding controllers are experimentally verified based on a 250W interleaved flyback
micro-inverter hardware setup

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INTRODUCTION:
The flyback based microinverter is one of the most attractive solutions due to its simple
structure and control and also inherent galvanic isolation. The flyback micro-inverter, which
consists of decoupling capacitor, interleaved flyback converter, unfolding bridge, and CL filter,
is proposed.
The unfolding bridge is switched at line frequency by a simple square-wave control,
generating a rectified sinusoidal waveform at the dc-link between the interleaved flyback
converter and unfolding bridge.
The decoupling capacitor, which consists of several parallel connected electrolytic
capacitors, maintains the power balance between the constant input power and variable output
power oscillating at double-line-frequency. All the other functionalities required in PV micro-
inverter are performed by the flyback converter.
Therefore, the flyback converter has been widely scrutinized to improve its performance
in terms of efficiency, reliability, and cost. In order to improve efficiency and power density,
both the discontinuous conduction mode (DCM) and the boundary conduction mode (BCM)
operations have been comprehensively analyzed and a hybrid switching strategy has been
adopted.
To further improve the weighted efficiency of the micro-inverter system, synchronous
rectification at the high voltage side of the flyback inverter is employed, which leads to slight
improvement in the overall efficiency of the flyback micro-inverter system

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illustrates the conventional flyback micro-inverter, which consists of decoupling
capacitor(s), interleaved flyback converter, unfolding bridge, and CL filter. The unfolding bridge
is switched at line frequency by a simple square-wave control, generating a rectified sinusoidal
waveform at the dc-link between the interleaved flyback converter and unfolding bridge.
The decoupling capacitor, which consists of several parallel connected electrolytic
capacitors, maintains the power balance between the constant input power and variable output
power oscillating at double-line-frequency. All the other functionalities required in PV micro-
inverter are performed by the flyback converter.
Therefore, the flyback converter has been widely scrutinized to improve its performance
in terms of efficiency, reliability, and cost. In order to improve efficiency and power density,
both the discontinuous conduction mode (DCM) and the boundary conduction mode (BCM)
operations have been comprehensively analyzed and a hybrid switching strategy has been
adopted. To further improve the weighted efficiency of the micro-inverter system, synchronous
rectification at the high voltage side of the flyback inverter is employed in which leads to slight
improvement in the overall efficiency of the flyback micro-inverter system.
A non-complementary active clamp control method is proposed to achieve high
efficiency both for full-load and light-load condition by reducing a circulating energy
Furthermore, appropriate design parameters under DCM operation have been specified to obtain
maximum weighted efficiency through analytical loss calculation and adaptive active clamping
and phase control method and hybrid control strategy combing two-phase and onephase DCM
control have been proposed to improve weighted efficiency according to the output power of a
PV module. Using a center-tapped transformer and bidirectional switched on the grid-side, a
turn-on ZVS approach is proposed in which utilizes snubber to maintain the voltage spike within
limits.

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EXISTING SYSTEM:
The conventional flyback micro-inverter with the active clamping circuit to improve the
weighted efficiency is proposed. It should be noted that output unfolding stage is replaced with
the equivalent rectified sinusoidal voltage source in order to simplify the analysis of the
operational modes.
This flyback converter is normally operated in CCM or DCM and uses the active
clamping circuit to clamp the voltage across the main switch and prevent voltage overshoot at
turn-off and achieve ZVS turn-on of the main switch. This enables the operation of the converter
with higher efficiency through soft-switching and also the use of MOSFET with lower Rds(on).
Furthermore, the non complementary gate driving signal for the active clamp switch
presented can reduce the circulating energy compared to the conventional complementary
control signal, and the hybrid control method that disables the active clamp circuit at the low grid
voltage improves the weighted efficiency by reducing the switching, conduction, and gate
driving loss of the active clamp switch

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PROPOSED SYSTEM:
The BCM operation of the flyback converter has several advantages compared to DCM
operation in terms of power density and conversion efficiency. Since the BCM operation
provides a natural ZVS turn-on for the main switch, the reduced switching loss allows higher
switching frequency and compact design. However, it still has the turn-off switching loss that
limits the maximum allowable switching frequency.
Also, during the BCM operation of the converter and near the peak grid voltage where
the instantaneous transferred power is high, the leakage inductance in flyback converter causes
voltage overshoot across the main switch at turn-off and the turn-off switching loss becomes
more severe. The proposed snubber solves these problems by adding additional capacitor in
parallel with the main switch. This capacitor reduces the voltage overshoot and also lowers the
rising slope of the turn-off voltage.
These effects allow low conduction loss from the usage of lower voltage rating device
and also reduce the turn-off switching lossof the main switch. This additional capacitor does not
affect the soft-switching of the main switch at turn-on if enough time delay is applied between
zero crossing of magnetizing current and the next turn-on switching signal.
Since natural turn on ZVS is not provided during the DCM operation of the flyback
micro inverter, the turn-on switching loss associated with the additional capacitor becomes
dominant and the reduction of turn-off switching loss becomes marginal.

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ADVANTAGES:
 Reduce the cost and complexity and also increase the overall efficiency.
 Zero voltage switching and also limiting the voltage across the main switch.

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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) micro-inverters.

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CONCLUSION:
This work presented a new adaptive snubber for the hybrid (DCM-BCM) operation of
flyback micro-inverter. The proposed adaptive snubber consists of the minimum number of
components, namely, a small auxiliary switch and a small capacitor. It also exploits the parasitic
capacitors of the flyback circuit (the main switch Coss, transformer winding capacitor and
secondary rectifier capacitor) to further reduce the required value of the snubber capacitor.
Furthermore, the auxiliary MOSFET switches at only double-line frequency and shares the same
source terminal with the main switch of the flyback, which reduces the cost and complexity
controller and the gate drive circuit

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REFERENCES:
[1] Q. Li 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.
[2] H. Hu, S. Harb, N. Kutkut, I. Batarseh, and Z. J. Shen, “A review of power decoupling
techniques for micro-inverters with three different decoupling capacitor locations in PV
systems,” IEEE Trans. Power Electron., vol. 28, no. 6, pp. 2711–2726, Jun. 2013.
[3] D. Meneses, F. Blaabjerg, Ó. García, 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.
[4] M. Gao, M. Chen, C. Zhang, and Z. Qian, "Analysis and implementation of an improved
flyback inverter for photovoltaic AC module applications," IEEE Trans. Power Electron, vol.29,
no.7, pp. 3428-3444, July 2014.
[5] A. C. Kyritsis, E. C. Tatakis, and N. P. Papanikolaou, “Optimum design of the current-source
flyback inverter for decentralized grid-connected photovoltaic systems,” IEEE Trans. Energy
Convers., vol. 23, no. 1, pp. 281–293, Mar. 2008.

A high efficiency flyback micro inverter with a new adaptive snubber for photovoltaic applications

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A high efficiency flyback micro inverter with a new adaptive snubber for photovoltaic applications