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Capacitor Voltage Control in NPC and Hybrid Multilevel Converters: Where are we now?

Xibo Yuan and Sergio Busquets-Monge

Brief Introduction:

    The controllability of capacitor voltages in multilevel converters is essential to enable their use in practice. This includes the voltage balancing of the dc-link capacitors and the flying capacitor (FC) voltage control. When the number of voltage levels of neutral-point-clamped (NPC) converters is four or higher, the capacitor voltage control becomes particularly challenging. To address this issue, various new hybrid multilevel topologies and new modulation and control strategies have been proposed with many recent developments. In particular, the virtual vector/zero modulation, combined with optimal zero-sequence injection, has shown superior capability to balance the dc-link capacitor voltages through software, without the need of additional hardware. This enables conventional NPC converters with four or higher number of levels to operate independently as a single rectifier or inverter (or with a passive front end) over the full power factor and modulation index range. This education seminar will answer questions such as: How can we derive various multilevel topologies integrating semiconductor devices, dc-link capacitors, and flying capacitors? How do we enable their capacitor voltage balance through modulation and control? This tutorial will cover the basic multilevel converter topologies, their control, and their applications as well as advanced modulation/control strategies and their latest development. It is suitable for researchers interested in multilevel converters at various levels.

image.pngXibo Yuan (S’09-M’11-SM’15) received the B.S. degree from China University of Mining and Technology, Xuzhou, China, and the Ph.D. degree from Tsinghua University, Beijing, China, in 2005 and 2010, respectively, both in electrical engineering.

He has been a Professor since 2017 in the Electrical Energy Management Group, Department of Electrical and Electronic Engineering, University of Bristol, Bristol, U.K, where he became a Lecturer, Senior Lecturer and Reader in 2011, 2015 and 2016, respectively. He also holds the Royal Academy of Engineering/Safran Chair in Advanced Aircraft Power Generation Systems. He is an executive committee member of the UK National Centre for Power Electronics and the IET Power Electronics, Machines and Drives (PEMD) network. He was a Visiting Scholar at the Center for Power Electronics Systems, Virginia Tech, Blacksburg, VA, USA, and the Institute of Energy Technology, Aalborg University, Denmark. He was a Postdoctoral Research Associate in the Electrical Machines and Drives Research Group, University of Sheffield, Sheffield, U.K.

His research interests include power electronics and motor drives, multilevel converters, wind power generation, application of wide-bandgap devices and electric vehicles. Professor Yuan is an Associate Editor of IEEE Transactions on Industry Applications and IEEE Journal of Emerging and Selected Topics in Power Electronics. He is a Fellow of IET and received The Isao Takahashi Power Electronics Award in 2018.

He has proposed several new multilevel converter topologies, simplified modulation and control methods, and fault detection and protection for multilevel converters. Working with industry partners, he has successfully delivered several multilevel converter prototypes for wind power generation and more electric aircraft systems, which have been further turned into products by industry.

image.pngSergio Busquets-Monge (S’99-M’06-SM’11) was born in Barcelona, Spain. He received the M.S. degree in electrical engineering and the Ph.D. degree in electronic engineering from the Universitat Politècnica de Catalunya (UPC), Barcelona, in 1999 and 2006, respectively, and the M.S. degree in electrical engineering from Virginia Polytechnic Institute and State University (VPI↦SU), Blacksburg, VA, USA, in 2001.

From 2001 to 2002, he was with Crown Audio, Inc. Since 2007, he has been an Associate Professor with the Electronic Engineering Department, UPC. In 2009, he was a Visiting Scholar at the Center for Power Electronics Systems, VPI↦SU, VA, USA, and the Institute of Energy Technology, Aalborg University, Denmark.

His current research interests include standardized/modular power converter design based on neutral-point-clamped (NPC) topologies and electric vehicles.

His contributions to the field of Power/Industrial Electronics have mainly focused on power converter design optimization and multilevel conversion. Within the area of multilevel conversion, he has proposed novel topologies, modulations, and controls of NPC converters. In particular, through the introduction of novel modulations and controls, he has demonstrated that NPC converters with an arbitrary number of levels can be operated with dc-link capacitor voltage balance in every switching cycle over the full operating range in all types of power conversion configurations (dc-dc, dc-ac, ac-dc, and ac-ac).