High Performance Power Electronics with Wide Bandgap Power Semiconductors for Industrial, Marine, Renewable Energy & Smart Grid Applications

Consumption and production of electric energy most often requires the available power to be converted in size and shape. Consider for example solar cells which produce direct current. Since the electric power system is based on alternating current, the power from the solar cells must be converted before connection to the grid. Power electronics is the technology behind this conversion, but it is also essential in harvesting as much energy from the source as possible. The processing of power takes place through the use of semiconductor components such as transistors and diodes. In power electronics these are designed to handle high power, and they are controlled either on or off, resulting in minimal power loss. Until recently, the semiconductor components have been based on silicon, but lately research on new materials has resulted in breakthroughs such that components based on silicon carbide and gallium nitride are becoming available. The new components are characterized by material properties, hereunder wide band gap (the energy which is required to liberate an electron), which in principle make them very advantageous compared to traditional technology. The new components could lead to a paradigm shift, resulting in converters that are much more compact and cheaper, but at the same time with higher rating and lower loss. To get there, however, research in the application of the new components is necessary, and this is the purpose of this project. Such research will not only result in new power electronic systems, but will also influence the design of the components themselves, in an interaction with the component manufacturers. This project builds competence that will enable the industry to put the next generation power semiconductors with wide band gap into use, which in turn will result in new power electronics of high quality for the future, with applications in industry, marine sector, renewable energy and smart grid. The project employs 2 PhD-students, where one is working on devices made of gallium nitride (GaN), and the other is working on devices made of silicon carbide (SiC). In addition, SINTEF Energy Research has a work package on EMC and compact design. For the period 2015-2017, we refer to previous reports for results and activities in the project. For 2018, the main activities have been as follows. The PhD-student working on SiC has focused on the quality of intrinsic diodes in SiC field effect transistors, and techniqes to best utilize the fast switching potential of SiC devices. In addition, performance gains that SiC MOSFETs can bring over Si IGBTs (traditional technology) for wind power applications have been quantified from an efficiency point of view. 3 papers have been published in 2018. The PhD-student working on GaN technology has successfully completed the planned 3 month exchange stay abroad at G2Elab, Grenoble, France. This exchange has led to collaboration on two papers that are presently under preparation. The candidate passed his midterm evaluation of the PhD on the 27th September, where associate professor Pierre Lefranc from G2Elab was one of the evaluators. 1 paper has been published in 2018. SINTEF Energy Research has worked on the development of an advanced, active gate driver prototype, which is meant to lead to improved switching behavior of the components. The prototype is currently under testing and a conference paper on the topic has been submitted, and is presently under review. We have organized a workshop in cooperation between the project and IEEE Norway PELS/IAS/IES joint chapter, with the title "Seminar on Wide Band Gap Power Semiconductors". This was arranged in Trondheim on the 27th September 2018 with wide participation from industry, as well as PhD- and Masters-students from NTNU. In 2019, Subhadra Tiwari has finished her PhD-thesis, which is entitled "SiC MOSFETs and Diodes: Characterization, Applications and Low-Inductive Converter Design Considerations". The planned disputation date is 13th September 2019. SINTEF Energy Research has concluded their work package and documented the results in the report "Gate driving techniques for EMI mitigation". Ole Christian Spro continues his work on GaN technology; this part of the project will conclude in 2020 since Spro has had and extended contract at NTNU as well as paternal leave during the project period.

The project has made scientific contributions in: *Development of ancillary electronics needed for the efficient use of wide bandgap devices in power electronics converters. *The implementation of prototypes of new converters based on the new devices, both for SiC and GaN devices. *Modelling of the devices. *Low-inductive design. *EMI mitigation and driver design. The project has in addition: *Transferred the knowledge to Norwegian industry. *Educated 2 PhD-students. *Made an impact on research based education at NTNU. The project has also had an impact on product development in Norwegian power electronics industry: -EFD Induction has launched a 1.85 MW, 300 kHz welder, based on SiC. -Eltek has launched a compact, high efficiency power supply based on GaN.

Power Electronics, conversion of electric energy from one form to another by the use of power semiconductors such as transistors and diodes, is key technology for the efficient utilization of electricity in production, transmission, and end use. Power electronics is required for the integration of new renewable electricity from offshore wind and solar resources, for marine, and for many industrial applications. New power semiconductors based on silicon carbide and gallium nitride are expected to lead to a paradigm shift in power electronics, as they offer improved performance compared to their traditional counterparts based on silicon, leading to improved efficiency, smaller size, lower weight, and ultimately lower cost. Wide bandgap devices also enable high temperature operation of power electronics, for e.g. down-hole applications for the efficient utilization of offshore oil and gas resources. For the Norwegian power electronics industry, it is important to be in the forefront of the developments. With a fierce international competition in the field, it is hard for them to prioritize research where commercially competitive products cannot be expected in the nearest future. Therefore, a competence building project in co-operation with NTNU and SINTEF Energy is an ideal solution to the R&D efforts required to deal with challenges in design with wide bandgap devices. One challenge is related to the extremely fast switching speeds of the new components, which makes the design of driver circuits (the circuits that turn the semiconductor devices on and off) very challenging, and which leads to increased problems with electromagnetic interference (EMI), which must be handled appropriately. The present project will build competence for the Norwegian industry, which will enable the industry to utilize the improved characteristics of the new devices in new products, based on a thorough understanding of the devices and associated challenges such as driver design and EMI.