Full Day Tutorial on Multilevel Converters:
Current Developments and Future Trends

Abstract:

Multilevel converters have emerged as a very important alternative in the area of high-power medium-voltage applications. Voltage operation above classic semiconductor limits, lower common mode voltages, near sinusoidal outputs together with small dv/dt's, are some of the characteristics that have made this power converters popular for industry and research. In this tutorial, most recent multilevel converter research from the proposers will be included, specifically in the areas of multilevel converters modeling, capacitor voltages balancing methods and operation under faulty conditions.

This tutorial presents the most important topologies: the Neutral Point Clamped, Flying Capacitor, and Cascaded H-bridge inverters. Emerging topologies like asymmetric hybrid cells and other hybrid topologies are also addressed. Special attention is devoted to the most relevant control and modulation methods developed for multilevel inverters: multilevel sinusoidal pulsewidth modulation (Phase Disposition or Level Shifted and Phase Shifted), Space Vector Modulation, Hybrid modulation, multilevel Selective Harmonic Elimination and multilevel Space Vector Control. Another objective is to introduce modulation algorithms that drastically simplify the computation of switching times and vector selection in complex multilevel systems; also practical problems as voltage unbalance are solved using control algorithms. In addition a special part of the tutorial is dedicated to rectifiers for multilevel inverters, covering both regenerative and non-regenerative topologies. Technical issues like fault detection and operation under faulty conditions are also included. Finally, a review of important applications is presented to highlight the practical impact of this converter family. Simulation and experimental results will be presented.

Tutorial Outline

1. Introduction to multilevel converters
• Inverter Topologies: Two level, NPC, Flying Capacitor, Cascade Inverters, Generalized P2.

2.  Multilevel power converters modelling
•  Modeling techniques applied to electronic power converters
•  Multilevel electronic power converter switching model
•  Averaged continuous model for three level DCC
•  Averaged continuous model for more than three-level converters
•  Example applications of the model

3. PWM algorithms for multilevel converters
•  Classification of modulation and control methods.
•  Introduction to Modulation: (PWM)
•  Phase Shifted (PS-PWM)
•  Level Shifted (LS-PWM)
•  Hybrid Modulation

4. Space vector modulation algorithms for multilevel converters
a. Algorithms for Balanced Systems
b. Algorithms for Unbalanced Systems
c. Algorithms for Single-Phase systems
d. Feed-forward space vector modulation

5. Other modulation and control algorithms for multilevel converters
•  Selective Harmonic Elimination (SHE)
•  Selective Harmonic Mitigation (SHM)
•  Space Vector Control (SVC)
•  Direct Torque Control (DTC)
•  Direct Power Control (DPC)
•  Predictive Control

6.  Rectifiers for multilevel inverters
•  Non regenerative
•  Regenerative

7. Operational and technological issues
•  Capacitor voltages balance
•  Operation under faulty conditions
           •  Fault detection
           •  Fault tolerant operation
           •  Reconfiguration and improved operation
•  DC-link unbalance in asymmetric cascaded inverters

8. Multilevel inverter applications
•  Adjustable speed drives
•  Mining applications
•  Energy conversion
•  Traction, propulsion and automotive applications
•  Other

Description of potential audience and any prerequisite knowledge expected from audience:

• Auditors for this tutorial are mainly:
- Undergraduate and postgraduate students in the field of power electronics.
- Practicing engineers and researchers that want to update or refresh their knowledge on multilevel converters.
- Experts in the field of multilevel converters.

• The audience should have basic knowledge about:
- Power electronics.
- Modulation and converter control concepts

Presenters

Leopoldo Garcia Franquelo was born in Málaga , Spain . He received the M.Sc. and Ph.D. degrees in electrical engineering from the Universidad de Sevilla, Seville , Spain in 1977 and 1980 respectively. In 1978 he joined the Universidad de Sevilla as Research Assistant, being Associated Professor in 1982 and Professor since 1986. Since 1998 till 2005 has been Director of the Electronics Engineering Department. Currently is Responsible for the PhD Courses in the Department. His technical interests have started in 1978 with Microprocessor Industrial Electronics Applications, evolving to Electronics Power Applications and in the 90's to Application Specific ICs design for the control of Power Converters. His current research interest lies on modulation techniques for multilevel inverters and its application to power electronic systems for renewable energy systems. He is leading a large research and teaching team in Spain . In the last five years his group activity can be summarized as: 40 Publications in International Journals, 165 in International Conferences, 10 Patents, advisor for 10 PhD dissertations and 96 R&D projects. His research team has been awarded with the “Excellence Status” by the Regional Government. He is IEEE member since 1984, Senior Member since 1996 and Fellow since 2005. He has been Vice-president of the Industrial Electronics Society Spanish Chapter (2002-2003), Member at large of the Industrial Electronics Society AdCom (2002-2003), Vice-president for Conferences of the Industrial Electronics Society (2004-2007), and currently he is serving as President Elect of the IEEE Industrial Electronics Society since 2008. In addition he is Distinguished Lecturer of the same society since 2006 and Associated Editor of the IEEE Transactions on Industrial Electronics since 2007.

Jose Rodriguez Perez received the Engineer degree from the Universidad Técnica Federico Santa Maria, Valparaíso , Chile , in 1977, and the Dr.-Ing. degree from the University of Erlangen , Erlangen , Germany , in 1985, both in electrical engineering. Since 1977, he has been with the Department of Electronics Engineering, University Técnica Federico Santa María, where he is currently a Professor. From 2001 to 2004, he was the Director of the Department of Electronics Engineering. From 2004 to 2005, he served as Vice Rector of academic affairs, and since 2005, he has been the Rector of the university. During his sabbatical leave in 1996, he was responsible for the Mining Division, Siemens Corporation, Santiago , Chile . He has extensive consulting experience in the mining industry, particularly in the application of large drives such as cycloconverter-fed synchronous motors for SAG mills, high-power conveyors, and controlled ac drives for shovels and power quality issues. He has directed more than 40 R&D projects in the field of industrial electronics. He has coauthored more than 250 journal and conference proceeding papers and contributed one book chapter. His research group has been recognized as one of the two centers of excellence in engineering in Chile from 2005 to 2008. His main research interests include multilevel inverters, new converter topologies, and adjustable-speed drives. Prof. Rodríguez has been an active Associate Editor for the IEEE Power Electronics and IEEE Industrial Electronics Societies since 2002. He has served as Guest Editor for the IEEE Transactions on Industrial Electronics in five instances [Special Sections on Matrix Converters (2002), Multilevel Inverters (2002), Modern Rectifiers (2005), High Power Drives (2007) and Predictive Control of Power Converters and Drives (2008)].

Jose I. Leon (S'04, M'07) was born in Cádiz, Spain, in 1976. He received the B.S. and M.S. and PhD degrees in telecommunications engineering from the University of Seville (US), Seville, Spain, in 1999, 2001 and 2006 respectively. In 2002, he joined the Power Electronics Group, US, working in R&D projects. Currently, he is an Associate Professor with the Department of Electronic Engineering, US. His research interests include electronic power systems, modeling, modulation and control of power-electronics converters and industrial drives.

Samir Kouro (S'04 – M'08) was born in Valdivia , Chile , in 1978. He received the M.Sc. and Ph.D. degrees in electronics engineering from the Universidad Técnica Federico Santa María (UTFSM), Valparaíso , Chile , in 2004 and 2008 respectively. In 2004 he joined as Research Assistant the Electronics Engineering Department of UTFSM, where he is currently an Associate Researcher. In 2004 he was distinguished as the youngest researcher of Chile in being granted with a governmental funded research project (FONDECYT) as Principal Researcher. His research interests include power converters and adjustable speed drives.