Adaptive Silicon Carbide Electrical Energy Conversion Technologies for Medium Voltage Direct Current Grids

The urgent societal challenge of decarbonization of the existing electric power grid infrastructure necessitates the integration of more renewable energy sources, which imposes the entire transformation of the existing grid infrastructure towards the future smart grid. The medium-voltage direct current (MVDC) grids are the key technology that will fulfill several design and operating constraints of the future smart grid, such as flexible power control and a more liberal energy market. Power electronics converters (PECs), which are semiconductor-based electrical energy conversion apparatus, will be one of the most vital components of the future MVDC grids. However, the current Silicon-based semiconductor technology has reached its theoretical limits. Exploiting the advantageous characteristics of Silicon Carbide (SiC) technology will enhance the performance of PECs in terms of efficiency, operating temperature and power density. High-voltage SiC is the ideal semiconductor replacement of Silicon in MVDC PECs. Today, PECs have fixed designs and exhibit their maximum performance for a narrow operating range. The key objective of ASiCC is to deliver digitally adaptive PECs designs and operating methodologies by incorporating digital information from load and source variability and semiconductors temperature variations. The novel digitally adaptive PECs designs will dynamically alter their overall electrical, thermal and reliability performance by shaping the switching and conducting behavior of the high-voltage SiC semiconductors. The research activities within ASiCC will be implemented by conducting theoretical and simulation studies, as well as, by experimentally validating various digitally-adaptive PECs concepts. During the initial phase of the ASiCC project, the design and performance of SiC-based and medium-voltage PECs interfaces for utility scale photovoltaic installations and utility-scale battery storage systems with MVDC grids were investigated. The focus of these investigations was on assessing the thermal performance and reliability of SiC metal oxide semiconductor field-effect transistors (MOSFETs) employed in the PEC. To perform advanced electrical designs of SiC-based PECs the static and dynamic characterization of SiC MOSFETs, as well as their modeling are needed. A flexible experimental setup was designed and built for assessing the dynamic characteristics of various types of SiC MOSFETs. Using experimental data from this setup, accurate static and dynamic models for low- and high-voltage SiC MOSFETs have been developed. In addition, challenges on utilization of high-voltage SiC MOSFETs in high-power DC/DC converters have been analyzed with a focus on optimal choice of deadtimes and switching frequency. Besides, the electrothermal modelling and the optimal design of PEC’s components for minimized thermal stress have been studied. It has been shown that a proper design of magnetic components combined with the choice of operating region minimizes the thermal stress of SiC MOSFETs under load variations. An adaptive modulation scheme enabling optimal operation of high-power DC/DC PECs that operate with variable load profiles was developed. The focus is on maximizing efficiency, as well as on minimizing temperature stress and, hence enhancing reliability of the SiC MOSFETs. The proposed adaptive modulation scheme was validated in terms of simulations. Currently, we are developing a 100-kW laboratory prototype of an isolated DC/DC PEC for validating the performance of this modulation scheme experimentally. Moreover, we have developed a digitally adaptive gate driver for SiC MOSFETs that enables adjustment of their electrical and thermal performance under extensive load variations. This gate driver has been simulated extensively and tested experimentally in the laboratory. At present, we are assessing the performance of this gate driver in high-power SiC MOSFET modules and developing a wireless communication interface for controlling the operation of the gate driver. The project team consists of the project manager and two PhD students who will be employed at the Department of Electric Power Engineering at NTNU. Through the ASiCC project, six master projects have been assigned to students. Dissemination activities and communication of the research findings with Academia and industry are planned to ensure the highest impact of the proposed research. The first scientific tutorial will be delivered at the Applied Power Electronics Conference in March 2023.

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Decarbonization of the existing electricity grid infrastructure remains an urgent societal challenge that presently hinders the supply of clean and sustainable electric power. This challenge requires the urgent transformation of the electricity grid by enabling decentralization of electric power generation through integrating more renewable energy sources and by electrifying transport and heating sectors. The medium-voltage direct current (MVDC) is the key technology that will fulfill several design and operating constraints of the future smart grid, such as flexible power control, grid stability, bidirectional power flow and a more liberal energy market. Power electronics converters are vital MVDC grid apparatus that perform electrical energy conversion by using semiconductor switches. However, the current Silicon technology of semiconductor switches has reached its theoretical limits. Exploiting the advantageous characteristics of wide bandgap semiconductors and in particular, Silicon Carbide (SiC) based switches to build power electronics converters for MVDC applications is crucial. High-voltage SiC is the ideal semiconductor replacement of Silicon in MVDC converters. The reason being that SiC switches will advance the performance of power electronics in terms of efficiency, operating temperature and power density. Research on adaptive designs for driving SiC semiconductors incorporating information from load and source variability and semiconductor switch temperature is the key objective of the ASiCC project. The novel digital-based, adaptive gate driving technologies will shape the switching behavior of the high-voltage SiC semiconductor switches and dynamically alter the overall performance of the converter in a coordinated way. Dedicated dissemination activities and communication of the research findings with academic and industrial users are planned to ensure the highest impact of the proposed research.