Analytical methods for modulation of cascaded H-bridge multilevel converters
Abstract: Multilevel Converters (MLC) are gaining popularity in many areas of energy conversion including Renewable Energy Systems, Distributed Generation, Smart Grids, E-Transportation, Electrical Drives for Industry. Distinctive features of multilevel converters are their capability to overcome the voltage limits imposed by the adopted power devices (SCR, IGBT, MOSFET) and to reduce voltage and current harmonics content, thus reducing power losses, heat, noise and increasing efficiency and reliability. Many of their characteristics depend on the adopted modulation algorithm, that imposes conduction states to output devices. The numerous modulation methods can be classified in high frequency, pulse width modulation methods, and in fundamental frequency modulation methods. Among them, Selective Harmonic Modulation techniques (SHE) usually operate at fundamental frequency and are capable to cancel or mitigate one or more frequencies from the outputs. The better the voltage and current waveforms, the higher the efficiency of the conversion process. In conventional SHE methods, a set of switching angles is computed off-line (e.g. using Simulink) and stored within a look-up table (LUT), which is implemented within the memory of the digital control system. Then, LUT is scanned at the beginning of each sampling time to select the most appropriate pre-calculated set of conduction intervals/angles. The determination of the sets of angles is not trivial and is time consuming. It is often accomplished by using artificial intelligence methods, which cannot be performed in real-time and require a large memory. A reduction of the number of pre-computer sets of angles brings to low resolution commutation angles and poor THD, moreover it is still not exible for closed-loop operations. Analytical methods, instead, lead to an exact mathematical problem formulation and bring to simple equations, which can be computed in real-time using conventional hardware, moreover, they do not need large memory spaces and can be easily implemented in closed loop control algorithms. After a theoretical discussion on the fundamentals of modulation algorithms with analytical methods, the speech will introduce and discuss in detail some of the methods developed for modulation for cascaded H-Bridge multilevel converters and will present some experimental results obtained using multilevel converters produced by DigiPower Ltd, an innovative SME based in L'Aquila.
Biography: Carlo Cecati (IEEE Fellow), received the Dr. Ing. Degree in Electrotechnical Engineering from the University of L'Aquila, L'Aquila, Italy,in 1983. Since then he has been with the same university becoming full professor in 2006. From 2014-2017 he has been with Harbin Institute of Technology, Harbin, China, being invited professor, international academic advisor, and, from 2015 till 2017, Qianren Talents Professor (1000 Talents Program distinguished professor). In 2007 he has been a co-founder and the CEO of DigiPower srl., an University of L'Aquila spin-off, now Innovative SME. Since 2012, is has been the Chief Technical Officer of the company. Prof. Cecati's main research interests include power electronics, distributed generation, smart grids and e-transportation. In these fields he authored more than 200 journal and conference papers. From 2010 until 2012 he has been a Co-Editor-in-Chief and from 2013 to 2015 the Editor-in-Chief of the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS. Prof. Cecati has been a corecipient of the 2012 and the 2013 Best Paper Award of the IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, of the 2012 Best Paper Award of the IEEE Industrial Electronics Magazine and of the 2019 Outstanding Paper Award of the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS. In 2017 he received the Antony J. Hornfeck Award for his contributions to the IEEE Indutrial Electronics Society. In 2019 he was appointed "Commendatore dell'Ordine al merito della Repubblica Italiana", by the President of Republic of Italy. Carlo Cecati has been included in the Highly Cited Researchers 2018 list by Clarivate Analytics.
Recent Advances in Grid-connected Photovoltaic Inverters, a Survey of Academic and Industrial Trends
Abstract: Today, evolution of the photovoltaic grid connected inverters continues in both academia and industries after more than two decades of progress. In recent years, new applications emerged for such inverters. The Energy Storage System (ESS) integrates the energy storage solutions with PV generation. The micro inverters and power optimizers enable new solutions for PV applications where a complicated roof or extreme shading conditions exist. By introducing the 1500 V solar panels into the market, the operating voltage of the utility-scale string inverters have been raised to fulfill this demand. The novel power converter design techniques have enhanced the PV system’s efficiency and the presence of the new manufacturers and markets have impacted the cost of the PV systems. The PV Inverters can engage into grid compensation and smart grid functions by extending their functionalities. Reactive power generation, distributed protection, and innovative commutation protocols are among the new operating modes demanded by modern grids. This presentation evaluates the recent advances on the PV grid connected inverters. The novel applications, requirements, and the achievements will be presented. Additionally, an insightful vision will be provided for investors and researchers by concluding the futuristic trends in the grid connected PV system development.
Biography: Shahrokh Farhangi ( IEEE M94, SM19 ) obtained the B.Sc., M.Sc. and Ph.D. degrees in electrical engineering from University of Tehran, Tehran, Iran, with honors. He is currently a professor at the School of Electrical and Computer Engineering, University of Tehran. His research interests include design and modeling of Power Electronic Converters, and application of power electronics in Electrical Drives, Photovoltaics and Renewable Energy Systems. He has managed several research and industrial projects, which some of them have won national and international awards. He has been selected as the distinguished engineer in electrical engineering by Iran Academy of Sciences, in 2008.