Novel single phase pwm ac–ac converters solving commutation problem using switching cell structure and coupled inductor

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IEEE SOFTWARE | EMBEDDED | MECHANICAL | ROBOTICS PROJECTS DEVELOPMENT
NOVEL SINGLE-PHASE PWM AC–AC CONVERTERS SOLVING COMMUTATION
PROBLEM USING SWITCHING CELL STRUCTURE AND COUPLED INDUCTOR
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 “NOVEL SINGLE-PHASE PWM AC–AC
CONVERTERS SOLVING COMMUTATION PROBLEM USING SWITCHING CELL
STRUCTURE AND COUPLED INDUCTOR” 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 “NOVEL SINGLE-PHASE PWM AC–AC
STRUCTURE AND COUPLED INDUCTOR” 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 “NOVEL SINGLE-PHASE PWM AC–AC
STRUCTURE AND COUPLED INDUCTOR” 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 novel single-phase pulse width modulation (PWM) ac–ac converters
that can solve the commutation problem in single-phase directPWMac–ac converters without
sensing the input voltage polarity. By using a basic switching cell structure and coupled
inductors, the proposed ac–ac converters can be short- and open-circuited without damaging the
switching devices. Neither lossy RC snubber nor dedicated soft commutation strategy is required
in the proposed converter. By replacing the conventional phase-leg of the PWM ac–ac converters
with the switching cell structure and the coupled inductor, three novel buck, boost, and buck-
boost type PWM ac–ac converters are developed. Although two coupled inductors are required
for the proposed converter, the input inductor of the proposed converter can be much smaller
than that of the conventional PWM ac–ac converters. The volume of the magnetic components
can be further reduced by increasing switching frequency of the converter because very fast
recovery diodes can be selected externally. In order to verify performance and robustness of the
proposed converter, a 200-W boost type prototype converter was built and tested with both
mismatched gate signals and highly distorted input voltage

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INTRODUCTION:
For AC–AC power conversion, the conventional approach is to use a diode or PWM
rectifier followed by a PWM voltage-source inverter with a DC link. Other approaches include
phase-controlled ac–ac converters employing thyristors, matrix converters, and so on. The output
voltage and frequency can be varied with these structures.
However, for applications where only voltage regulation is required, direct PWM ac–ac
converters are a more practical choice in terms of cost and size.
The ac–ac circuits shown in Fig. 1 have a common commutation problem. For example,
for the buck-type converter, the switches S2 and S3 are both turned ON and OFF simultaneously,
and they are complementary to the switches S1 and S4 in an ideal case.
However, due to the different time delays and limited switching speed of the switching
devices, there inherently exists a short dead-time or an overlap-time between switches. During
the dead-time, there is no current path for the output filter inductor (Lo ), so the switches may be
damaged by excessive voltage.
Similarly, the switches may be damaged by excessive current when there is an overlap-
time between switches S1 and S2 (or S3 and S4 ), because the input voltage will be short-
circuited. Fig. 2 illustrates this problem.
In order to solve this, bulky and lossy RC snubber circuits are required to protect the
switches. A better way is to implement safe commutation strategies that provide smooth current
transition. Several soft commutation strategies have been introduced and employed successfully
in the circuits

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However, most of them solve the commutation problem by sensing the voltage or current
polarity of the converter. When the voltage or current is distorted significantly, especially around
the zero crossing point, the conventional methods still cannot provide completely safe and
reliable commutation.

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EXISTING SYSTEM:
The switches S2 and S3 are both turned ON and OFF simultaneously, and they are
complementary to the switches S1 and S4 in an ideal case. However, due to the different time
delays and limited switching speed of the switching devices, there inherently exists a short dead-
time or an overlap-time between switches. During the dead-time, there is no current path for the
output filter inductor (Lo), so the switches may be damaged by excessive voltage. Similarly, the
switches may be damaged by excessive current when there is an overlap-time between switches
S1 and S2 (or S3 and S4), because the input voltage will be short-circuited.

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PROPOSED SYSTEM:
In this paper, very robust single-phase PWM ac–ac converters without the commutation
problem are introduced. The proposed converters use basic switching cell structure and coupled
inductors to implement phase legs of the converter. With this structure, the proposed converters
can tolerate both dead-time and overlap-time without damaging switching devices. In addition,
the proposed converters do not need to sense the voltage or current polarity for commutation.
Therefore, highly robust and reliable PWM ac–ac converters can be developed.

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ADVANTAGES:
 Stable operation even when the input voltage is highly distorted

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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:
 AC drives
 Wind power applications

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CONCLUSION:
In this paper, very robust single-phase buck, boost, and buckboost type PWM ac–ac
converters have been proposed. Unlike the existing PWMac–ac converters, the proposed
converters do not need to sense the input voltage polarity for safe commutation and the proposed
converter can guarantee stable operation even when the input voltage is highly distorted, which
is impossible with the conventional approach. Although two extra coupled inductors are
required, the input inductor can be designed to be much smaller than that of the conventional ac–
ac converter. The performance of the proposed converterwas successfully verified with the 200-
W boost type ac–ac converter.

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REFERENCES:
[1] F. Z. Peng, C. Lihua, and Z. Fan, “Simple topologies of PWM ac– ac converters,” IEEE
Power Electron. Lett., vol. 1, no. 1, pp. 10–13, Mar. 2003.
[2] B.H.Kwon, B. D. Min, and J.H.Kim, “Novel topologies ofACchoppers,” IEE Proc. Electr.
Power Appl., vol. 143, no. 4, pp. 323–330, Jul. 1996.
[3] F. Z. Peng, “Revisit power conversion circuit topologies-recent advances and applications,”in
Proc. IEEE Int. Power Electr. Motion Conf., May 2009, pp. 188–192.
[4] L. M. Tolbert, F. Z. Peng, F. H. Khan, and S. Li, “Switching cells and their implications for
power electronic circuits,” in Proc. IEEE Int. Power Electr. Motion Conf., 2009, pp. 773–779.
[5] F. H. Khan, L. M. Tolbert, and F. Z. Peng, “Deriving new topologies of DC–DC converters
featuring basic switching cells,” Proc. IEEEWorkshop Comput. Power Electron., 2006, pp. 328–
332.

Novel single phase pwm ac–ac converters solving commutation problem using switching cell structure and coupled inductor

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Novel single phase pwm ac–ac converters solving commutation problem using switching cell structure and coupled inductor