Power Electronic Converters for Solar Photovoltaic Systems

By L. Ashok Kumar, S.Albert Alexander and Madhuvanthani Rajendran

Power Electronic Converters for Solar Photovoltaic Systems provides design and implementation procedures for power electronic converters and advanced controllers to improve standalone and grid environment solar photovoltaics performance. Sections cover performance and improvement of solar photovoltaics under various conditions with the aid of intelligent controllers, allowing readers to better understand the nuances of power electronic converters for renewable energy systems. With algorithm development and real-time implementation procedures, this reference is useful for those interested in power electronics for performance improvement in distributed energy resources, design of advanced controllers, and measurement of critical parameters surrounding renewable energy systems. 

By providing a complete solution for performance improvement in solar PV with novel control techniques, this book will appeal to researchers and engineers working in power electronic converters, renewable energy, and power quality. 

• Includes simulation studies and photovoltaic performance analysis
• Uses case studies as a reference for design and research
• Covers different varieties of power converters, from fundamentals to implementation

• Language: English
• Publisher: Academic Press
• Release date: Nov 1, 2020
• ISBN: 9780128227503

L. Ashok Kumar

Professor Ashok Kumar is at the Department of Electrical & Electronics Eng., PSG College of Technology. He is Associate Head of Department and his is current research focuses are Integration of Renewable Energy Systems in the Smart Grid and Wearable Electronics. He has 3 years of industrial experience and 17 years of academic and research experiences. He has authored 9 books, published 110 technical papers in International and National Journals and presented 107 papers in National and International Conferences.

Book preview

Power Electronic Converters for Solar Photovoltaic Systems

L. Ashok Kumar

PSG College of Technology, Coimbatore, India

S. Albert Alexander

Kongu Engineering College, Perundurai, India

Madhuvanthani Rajendran

Sri Shakthi Institute of Engineering and Technology, Coimbatore, India

Table of Contents

Cover image

Title page

Copyright

Authors biography

Preface

Acknowledgments

Introduction

Chapter 1. Inverter topologies for solar PV

1.1. Introduction

1.2. Single-stage DC–AC converter

1.3. Line-commutated photovoltaic inverter

1.4. Self-commutated photovoltaic inverter with line frequency transformer

1.5. Grid-tie inverters

1.6. Inverter with high-frequency core-based transformer

1.7. Half-bridge zero-voltage state converters

1.8. H-bridge inverter

1.9. Summary

Chapter 2. Multilevel inverter topologies for solar PV

2.1. Introduction

2.2. Comparison of multilevel inverters

2.3. Reduced-order multilevel inverter

2.4. Summary

Chapter 3. Advanced multilevel inverter topologies

3.1. Switched battery boost multilevel inverter

3.2. Quasi Z-source cascaded H-bridge multilevel inverter

3.3. Switched capacitor multilevel inverter

3.4. String inverter

3.5. Multistring inverter

Chapter 4. Emerging inverter topologies

4.1. Introduction

4.2. Types of inverter

4.3. Classification of transformerless inverter topologies

4.4. Low-frequency inverter

4.5. Transformerless self-commutated photovoltaic inverter

4.6. Transformerless inverter topologies

4.7. Bidirectional DC–AC converter

4.8. High-frequency DC–AC converter

4.9. HERIC inverter

Chapter 5. DC–DC converter topologies for solar PV

5.1. Introduction

5.2. Topologies of DC–DC converters

5.3. Unidirectional DC–DC converter

5.4. Bidirectional DC–DC converter

5.5. Double-input pulse width modulation DC–DC converter

5.6. Single-input multiple-output DC–DC converter

Chapter 6. Control of DC–DC converters

6.1. Multiple-input buck–boost converter

6.2. Closed-loop buck–boost converter

6.3. Closed-loop boost converter

6.4. Closed-loop buck converter

6.5. Interleaved boost converter

6.6. Soft-switching converter

6.7. Half-bridge LLC resonant converter

6.8. Forward converter

Chapter 7. Emerging DC–DC converter topologies

7.1. SEPIC converter

7.2. Luo converter

7.3. Integrated SEPIC–Cuk converter

7.4. Flyback converter

7.5. ZETA converter

7.6. Self-lift Cuk converter

7.7. Push–pull converter

7.8. Advantages and disadvantages of push–pull converter

Chapter 8. Charge controls and maximum power point tracking

8.1. Introduction

Appendix 1. Selection of components from Simulink Library Browser

Nomenclature

Glossary

Index

Copyright

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Authors biography

Dr. L. Ashok Kumar was a Postdoctoral Research Fellow from San Diego State University, California. He is a recipient of the BHAVAN fellowship from the Indo-US Science and Technology Forum and SYST Fellowship from DST, Government of India. His current research focuses on integration of renewable energy systems in the smart grid and wearable electronics. He has 3  years of industrial experience and 19  years of academic and research experience. He has published 167 technical papers in international and national journals and presented 157 papers in national and international conferences. He has completed 26 Government of India–funded projects, and currently, 7 projects are in progress. His PhD work on wearable electronics earned him a National Award from ISTE, and he has received 24 awards on the national level. Ashok Kumar has seven patents to his credit. He has guided 127 graduate and postgraduate projects, and also he has produced 4 PhD scholars, and 12 scholars are pursuing their PhD work. He is a member and in prestigious positions in various national forums. He has visited many countries for institute industry collaboration and as a keynote speaker. He has been an invited speaker in 178 programs. Also he has organized 72 events, including conferences, workshops, and seminars. He completed his graduate program in Electrical and Electronics Engineering from the University of Madras and his postgraduate from PSG College of Technology, India, and Masters in Business Administration from IGNOU, New Delhi. After completion of his graduate degree, he joined as a project engineer for Serval Paper Boards Ltd., Coimbatore (now ITC Unit, Kovai). Presently, he is working as a Professor and Associate HoD in the Department of EEE, PSG College of Technology and also doing research work in wearable electronics, smart grid, solar PV, and wind energy systems. He is also a certified charted engineer and BSI-certified ISO 500001 2008 lead auditor. He has authored the following books in his areas of interest: (1) Computational Intelligence Paradigms for Optimization Problems Using MATLAB®/SIMULINK®, CRC Press, (2) Solar PV and Wind Energy Conversion Systems—An Introduction to Theory, Modeling with MATLAB/SIMULINK, and the Role of Soft Computing Techniques—Green Energy and Technology, Springer, United States, (3) Electronics in Textiles and Clothing: Design, Products and Applications, CRC Press, (4) Power Electronics with MATLAB, Cambridge University Press, London, (5) Automation In Textile Machinery: Instrumentation And Control System Design Principles—CRC Press, Taylor & Francis Group, United States, ISBN 9781498781930, April 2018, (6) Proceedings of International Conference on Artificial Intelligence, Smart Grid and Smart City Applications, Springer International Publishing, Springer, (7) Deep Learning Using Python, Wiley India Publications, India, (8) Monograph on Smart Textiles, (9) Monograph on Information Technology for Textiles, and (10) Monograph on Instrumentation & Textile Control Engineering. He is a senior member in IEEE and Fellow Member in IE (India), IETE, and IET (UK).

Dr. S. Albert Alexander was a Postdoctoral Research Fellow from Northeastern University, Boston, Massachusetts, United States. He is the recipient of prestigious Raman Research Fellowship from the University Grants Commission (Government of India). His current research focuses on fault diagnostic systems for solar energy conversion systems and smart grids. He has 13  years of academic and research experience. He has published 23 technical papers in international and national journals (including IEEE transactions, IET, Elsevier, Taylor & Francis, Wiley, etc.) and presented 23 papers at national and international conferences. He has completed four Government of India–funded projects, and one multilateral project is under progress with the overall grant amount of Rs.86 lakhs. His PhD work on power quality earned him a National Award from ISTE, and he has received 23 awards for his meritorious academic and research career (such as Young Engineers Award from IE(I), Young Scientist Award from SPRERI, Gujarat, etc.). He has also received the National Teaching Innovator Award from MHRD (Government of India). He is an approved Margadarshak from AICTE (Government of India). He is the approved Mentor for Change under Atal Innovation Mission. He has guided 31 graduate and postgraduate projects. He is presently guiding eight research scholars. He is a member and in prestigious positions in various national and international forums (such as senior member, IEEE, and Vice President for Energy Conservation Society, India, etc.). He has been an invited speaker in 210 programs covering nine Indian states and also at the United States. He has organized 11 events, including faculty development programs, workshops, and seminars. He completed his graduate program in Electrical and Electronics Engineering from Bharathiar University and his postgraduate program from Anna University, India. Presently, he is working as an Associate Professor in the Department of Electrical and Electronics Engineering, Kongu Engineering College, and also doing research work in smart grids, solar PV, and power quality improvement techniques. He has authored the following books in his areas of interest: (1) Computational Paradigm Techniques for Enhancing Electric Power Quality, CRC Press, (2) Basic Electrical, Electronics and Measurement Engineering, Anuradha Publishers, and (3) Special Electrical Machines, Anuradha Publishers.

Madhuvanthani Rajendran is a full-time doctoral scholar currently enrolled in Anna University, Chennai. Her current research focuses on Transient Power Management under different Load/Grid conditions of Hybrid AC/DC Microgrids. She previously worked as a curriculum facilitator at African Leadership University, Mauritius, where her primary role was to design Electrical Engineering courses using the flipped classroom approach. She has obtained her Master of Science degree in Electrical Engineering from Arizona State University, United States, with a focus in power and energy systems. During her master's degree, she had worked on several projects, some of which are Transmission Expansion Planning in Arizona, Design of Grid Connected Photovoltaic String Inverter, Project on Reactive Power Markets, Protection Design Project, Detailed Design of a Computer Power Supply, Multi-machine Transient Stability Analysis, and Design of a DFIG-Based Wind Energy System. She has published seven papers in national and international journals and presented four papers in national and international conferences. She has also previously worked as an Assistant Professor at Sri Shakthi Institute of Engineering and Technology, Coimbatore. She obtained her Bachelor of Engineering degree from Anna University (SSN College of Engineering), Chennai, in Electrical and Electronics Engineering where she worked on the Design of Soft Switched Interleaved Flyback Converters for Fuel Cells.

Preface

To meet the growing demand for electrical energy, renewable energy sources, especially solar photovoltaics (PVs), have become widely accepted alternatives to conventional power generation systems. It has been forecasted that the power produced by the nonconventional energy sources will satisfy 50% of the total power needs in near future. A common problem with the solar PV is the reduction of its delivered power, which can be caused by certain abnormal conditions such as faults, partial shading, maximum power point tracking failure, and inappropriate choice of converters. To alleviate the problems, a power electronic interface with harmonic reduction capability needs to be connected between the source and load. Hence, this book provides a complete overview on power electronic converters with improved performed parameters exclusively used for the solar PVs. It is well supported by the extensive literature survey, software simulations, and experimental investigation. The book will certainly be considered as a tool for making an appropriate choice of power converters for solar energy conversion system.

L. Ashok Kumar

S. Albert Alexander

Madhuvanthani Rajendran

Acknowledgments

The authors are always thankful to the almighty for their perseverance and achievements. The authors owe their gratitude to Shri L. Gopalakrishnan, Managing Trustee, PSG Institutions, and all the trustees of Kongu Vellalar Institute of Technology Trust, Perundurai. The authors also owe their gratitude to Dr K Prakasan, Principal in Charge, PSG College of Technology, Coimbatore, India, and Prof.V.Balusamy, Principal, Kongu Engineering College, Perundurai, India, for their wholehearted cooperation and great encouragement in this successful endeavor.

Dr. L. Ashok Kumar would like to take this opportunity to acknowledge those people who helped me in completing this book. I am thankful to all my research scholars and students who are doing their project and research work with me. But the writing of this book is possible mainly because of the support of my family members, parents, and sisters. Most importantly, I am very grateful to my wife, Y. Uma Maheswari, for her constant support during writing. Without her, all these things would not be possible. I would like to express my special gratitude to my daughter, A. K. Sangamithra, for her smiling face and support; it helped a lot in completing this work. I would like to dedicate this work to her.

Dr. S. Albert Alexander would like to take this opportunity to acknowledge those people who helped me in completing this book. I am thankful to all my research scholars and students who are doing their project and research work with me. But the writing of this book is possible mainly because of the support of my family members, parents, and brothers. Most importantly, I am very grateful to my wife, A. Lincy Annet, for her constant support during writing. Without her, all these things would not be possible. I would like to express my special gratitude to my son, A. Albin Emmanuel, for his smiling face and support; it helped a lot in completing this work.

Madhuvanthani Rajendran would like to take this opportunity to acknowledge all the people who have helped and supported me in completing this book. Firstly, I would like to thank Dr. S. Thangavelu, Chairman, Sri Shakthi Institute of Engineering and Technology, Coimbatore, whom I can also proudly call my father-in-law for providing me with all the opportunities and the resources needed for me to excel in my career. Secondly, I would like to express my immense gratitude to my husband, T. Dheepan, Vice Chairman, Sri Shakthi International School, Coimbatore, for always supporting me and encouraging me to break boundaries. I would also like to extensively thank my parents, mother-in-law, and my brother without whose support this book would not have been possible. I would like to express my special gratitude to my daughter Adheera who has been my main source of motivation for completing this book.

Introduction

The ever-rising demand for electrical energy and depleting fossil fuel reserves are compelling reasons to use existing resources more efficiently. Highly efficient power electronic technologies and proper control strategies are therefore needed to reduce energy waste and to improve their performance parameters. The increasing demand for energy has stimulated the development of alternative power sources such as photovoltaic (PV) modules, fuel cells, and wind turbines. The PV modules are particularly attractive as renewable sources due to their relative small size, noiseless operation, simple installation, and the possibility of installing them closer to the user. PV power generators convert the energy of solar radiation directly to electrical energy without any moving parts. PV power generators can be classified into stand-alone and grid-connected systems. In a stand-alone system, the energy storage has a big influence on the design of the systems. In grid-connected system, the grid acts as an energy storage into which the PV power generator can inject power whenever power is available.

In PV modules, the output voltage has low DC amplitude. To be connected to the grid, the PV modules output voltage should be boosted and converted into an AC voltage. This task can be performed using one or more conversion stages (multistage). Most of the topologies for PV systems are multistage, having a DC-to-DC converter with a high-frequency transformer that adjusts the inverter DC voltage and isolates the PV modules from the grid.

In PV systems where series modules are connected to a conventional two-level inverter, the occurrence of partial shades and the mismatching of the modules lead to a reduction of the generated power. In addition, the conventional two-level voltage source converters will not be able to deliver the performance parameters such as improved power quality, maximum allowed switching frequency, higher-voltage operation, and reduction in filter size. To overcome these problems, advanced power converter topologies are highly solicited.

Grid connection of PV systems has been traditionally performed by three different types of configurations: centralized conversion topology (large three-phase system), string topology (medium single-phase system), and the AC module topology (small single-phase system). More recently, a hybrid between the centralized and the string configuration, called multistring topology (for medium to large, single- or three-phase system), has gained more attention. The centralized topology uses a single three-phase inverter to connect to the grid. The advantages are its simple structure and control which come at the expense of reduced power generation due to module mismatch and partial shading. This topology is considered nowadays obsolete.

The string topology uses one inverter per string, improving the total generated power. It also increases modularity, since additional strings can be added to the system without the need of changing the inverter dimensions. Depending on the size of the string, a boost DC-to-DC converter or a step-up transformer is necessary to reach the grid voltage. The string topology is the most widely installed solution for PV grid-connected systems today.

The AC module topology or converter-integrated module is the most modular and has the best maximum power tracking capability, since one converter is dedicated per module. This is intended for smaller systems and more domestic use. The main disadvantage is that a DC–DC boost stage or step-up transformer is a must, which increases the cost if an AC module system of the same power of a string system is compared.

The CMLI has attracted attention for the PV integration as each H-bridge (or power cell) needs isolated DC sources, which can be easily given by PV modules or strings. Furthermore, it adds interesting benefits such as higher-voltage operation by interconnecting enough modules or strings in series to reach grid voltage, eliminating the need of step-up transformer or boost DC–DC converters. In addition the inherent improved power quality of multilevel converters reduces filter size and switching frequency, improving the system efficiency.

L. Ashok Kumar

S. Albert Alexander

Madhuvanthani Rajendran

Chapter 1: Inverter topologies for solar PV

Abstract

In general, the converter devices that transform DC power into AC power is denoted as inverters at a desired output frequency and voltage, where the output voltage could be established at an alternative or variable frequency. They are low contorted sine wave devices. The output voltage can be controlled with the assistance of drives of the switches. The pulse width modulation (PWM) strategies are most normally used to control the output voltage of inverters. Such inverters are called as PWM inverters. The output voltage of the inverters contains harmonics at whatever point it is nonsinusoidal. These harmonics can be lessened by utilizing legitimate control plans. This chapter focuses on single--stage inverter, line-commutated inverter, self-commutated, and grid tie inverters exclusively used for the solar photovoltaic systems.

Keywords

Grid tie inverters; Line-commutated inverter; Self-commutated inverter; Single-stage inverter; Solar PV systems

1.1 Introduction

1.2 Single-stage DC–AC converter

1.2.1 Inverter and its classifications

1.2.2 Voltage source inverter

1.2.3 Single-phase full-bridge inverter with R load

1.2.4 Pulse width modulation

1.2.5 Unipolar pulse width modulation inverter

1.2.6 Performance parameters

1.3 Line-commutated photovoltaic inverter

1.3.1 Types of commutated inverters

1.3.2 Filters and reactive power compensation

1.3.3 Input voltage clamping of inverter

1.3.4 Advantages of line-commutated inverter

1.3.5 Analysis of line-commutated inverter

1.3.6 Inverter control

1.4 Self-commutated photovoltaic inverter with line frequency transformer

1.4.1 Selection of snubber capacitor

1.5 Grid-tie inverters

1.5.1 Types of grid-tie inverters

1.6 Inverter with high-frequency core-based transformer

1.7 Half-bridge zero-voltage state converters

1.7.1 Simulation

1.8 H-bridge inverter

1.9 Summary

Suggested reading

1.1. Introduction

Energy demand is increasing day by day due to increase in population, urbanization, and industrialization. The world's fossil fuel resources will thus be depleted in a few hundred years, which has necessitated an urgent search for an alternative energy source to meet the present-day demand and to accelerate the development of advanced clean energy technologies to address the global challenges of energy security, climate change and sustainable development.

Renewable energy source is a practical solution to address the persistent demand supply gap in the power industry. Solar energy is clean, inexhaustible and environmentally friendly potential resource among renewable energy options. Solar photovoltaic (PV) is a technology that offers a solution for a number of problems associated with fossil fuels. On the top of that, India has among the highest solar irradiance in the world, which makes solar PV all the more attractive for India. Production costs make solar expensive for generating electricity, but costs are reducing as solar technology is developed and commercialized. The demand of PV generation systems seems to be increased for both stand-alone and grid-connected modes of PV systems.

In solar systems, PV principle is applied to produce electricity. The light energy from the sun is converted into electrical energy by the solar power conditioning systems. The components included in solar PV system includes solar panels which collects the light rays from the sun, charge controller, battery and inverter for DC to AC power conversion. A charge controller, or charge regulator, is basically a voltage and/or current regulator to keep batteries from overcharging. It regulates the voltage and current coming from the solar panels going to the battery. All PV panel voltages on grid tie panels vary usually from 21 to 60  V. Some are standard 24  V panels, but most are not, so there is the need for charge controllers. The most common controls used for all battery-based systems are in the 4–60  amp range. The battery arrangements are used to store the power obtained from the solar panels. The block diagram for solar energy conversion is shown in Fig. 1.1.

PV inverters become more and more widespread within both private and commercial circles. The utilization of PV inverters classifies the solar energy conversion systems into three types, such as stand-alone (off-grid), grid-connected (on-grid), and bimodal systems (combination of on-grid and off-grid configurations). The stand-alone systems are finding their maximum application in the areas which has the absence of grid.

The grid-connected inverters convert the available direct current supplied by the PV panels and feed it into the utility grid. There are two main topology groups used in the case of grid-connected PV systems, namely, with and without galvanic isolation. Galvanic isolation can be on the DC side in the form of a high-frequency transformer or on the grid side in the form of a big bulky AC transformer. Both of these solutions offer the safety and advantage of galvanic isolation, but the efficiency of the whole system is decreased due to power losses in these extra components.

Figure 1.1  Solar energy conversion system.

In case the transformer is omitted, the efficiency of the whole PV system can be increased with an extra 1%–2%. The most important advantages of transformerless PV systems can be observed in Fig. 1.2, such as higher efficiency and smaller size and weight compared with the PV systems that have galvanic isolation (either on the DC or AC side).

Fig. 1.2 has been made from the database of more than 400 commercially available PV inverters. Transformerless inverters are represented by the dots (transformerless), the triangles represent the inverters that have a low-frequency transformer on the grid side (LF transformer), and last, the stars represent the topologies, including a high-frequency transformer (HF transformer), adding a galvanic isolation between the PV and grid.

The inference arrived from these graphs is that transformerless inverter has higher efficiency, smaller weight, and size than their counterparts with galvanic separation. Transformerless PV inverters use different solutions to minimize the leakage ground current and improve the efficiency of the whole system.

1.2. Single-stage DC–AC converter

A single-stage DC–AC converter comprises of four semiconductor switches as in the case of single phase and six switches for three-phase configurations. Any increase or