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Concepts for Achieving 99% Efficiency in Back-to-Back Converters for Regenerative Variable Speed Drives

Date: 13/11/2025
Time: 9:00 am
Presenter: Marcelo L. Heldwein
Abstract: (Sponsored by PELS TC 3) (Please note: This webinar will be in Portuguese.) Electric motors account for nearly 45% of electricity consumption. Variable speed drives (VSDs) replace motors, improving efficiency and costs, also in wind power generation. Electrification is crucial in decarbonizing, but requires integrating renewable energy and increasing power conversion efficiency. The latter is cost-effective in increasing energy availability. Improving VSD efficiency is a priority, but long motor cables pose challenges due to transmission line effects. Wide bandgap semiconductors enable higher frequencies but also increase insulation stresses. Concepts that limit voltage efforts at the machine terminals are welcome. Integrated Motor Drives, in which the power electronics are placed inside the machine housing, are promising for the next VSD generations. There, not only efficiency but also power density are paramount. This presentation will discuss the state-of-the-art converters for bidirectional VSDs and present two new concepts capable of meeting the demands through the use of the multiple degrees of freedom of the conversion stages, allowing reduced losses to be achieved, even with the use of higher switching frequencies than those used in conventional solutions. A holistic view of the conversion stages as a single entity is the main factor driving the concepts. Pareto fronts in the efficiency-power density space are discussed, and the limits of the new concepts are explored. A comparison with the conventional voltage source back-to-back converter shows that the proposed ideas are advantageous concerning efficiency and power density. Possible practical realizations are discussed, which lead to close to 98.8% efficiency and between 5 and 8 kW/dm3 power density.

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Marcelo Lobo Heldwein received the bachelor and master degrees in electrical engineering from the Federal University of Santa Catarina (UFSC), Brazil, in 1997 and 1999, respectively, and his doctoral degree from the Swiss Federal Institute of Technology (ETH Zurich), Switzerland, in 2007. He is a Professor at the Technical University of Munich, Germany, leading the research group at the Chair of High-Power Converter Systems. From 1999 to 2003, he worked with industry, including R&D activities at the Power Electronics Institute in Brazil and Emerson network Power in Brazil and Sweden. He was a Postdoctoral Fellow at the ETH Zurich and the UFSC from 2007 to 2009. He was an Associate Professor with the Department of Electronics and Electrical Engineering at the UFSC from 2010 to 2022. Dr. Heldwein is a senior member of the IEEE, a member of the Brazilian Power Electronics Society (SOBRAEP), and a member of the Advisory Board of PCIM Europe. His research focuses on power converters and motor drives, including their topologies, modeling, design, and control. The research is motivated to develop sustainable and intelligent solutions to the challenges posed by the energy transition. The focus topics involve an in-depth systemic and multidisciplinary knowledge of power converters and their components and applications.