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, low-inductive 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. Real-time models of SiC MOFETs and SiC-based DC/DC PECs have been developed for shortening the simulation times and minimizing possible numerical convergence issues. 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 in fuel-cell applications. 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 thermal stress and, hence enhancing reliability of the SiC MOSFETs. The proposed adaptive modulation scheme was validated in terms of simulations, as well as on the real-time SiC-based DC/DC converter model. In the last phase of ASiCC, a 100-kW laboratory prototype of an isolated DC/DC PEC for validating the performance of this modulation scheme experimentally has been built. 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. Moreover, a wireless communication interface for controlling the operation of this adaptive gate driver in high-power SiC MOSFET modules has been developed. The project team consisted of the project manager and two PhD students who were funded by ASiCC and employed at the Department of Electric Energy at NTNU. During ASiCC, 7 master projects have been assigned to students. Dissemination activities and communication of the research findings with Academia and industry have been conducted and ensured the highest impact of the proposed research. A scientific tutorial was presented at the Applied Power Electronics Conference in March 2023 and several invited talks have been delivered to international conferences and workshops. Finally, the 1st PhD thesis was successfully defended in November 2023 and the defence of the 2nd PhD thesis is planned for autumn 2024.

The ASiCC project aimed at delivering adaptive power electronic technologies that utilize Silicon Carbide (SiC) power semiconductors, which can continuously optimize their efficiency and reliability under source and load variations. ASiCC has two key outcomes. The first outcome (component-level) is the development of adaptive technologies enabling a fine-tuned electrothermal performance optimization of SiC power semiconductor devices employed in low-voltage and medium-voltage power electronic systems. The second outcome (system-level) is the development of adaptive operating schemes for continuous reliability enhancement of SiC-based power electronic systems under stochastic operating modes. ASiCC created the necessary expertise in the area of high-performance power electronics for DC grids, which, in the near future, will facilitate the penetration of more solar and offshore wind energy generation and enable a smoother integration of storage systems with the electric grid at higher efficiencies and improved reliabilities. The project’s outcome will be exploited by various sectors of industry. Power electronic manufacturers will enhance their technology and products portfolio by integrating the new adaptive power converter designs, allowing them to be more competitive and penetrate into new markets. Renewable electrical energy operators will maximize the harvested electricity due to the increased power electronics efficiencies and minimize the maintenance costs due to the improved reliability; thus, decreasing operating costs and increasing revenue. Electric vehicle manufacturers will be able to offer vehicles with longer driving ranges, making them a more attractive alternative for drivers. ASiCC’s outcomes will also be exploited by the scientific and academic communities by setting the foundation for a new era in the development of high-efficiency and high-reliability power electronics. Finally, the outcomes are expected to be used by policy makers developing new regulatory frameworks for electricity generation and utilization. ASiCC has a strong environmental and societal impact. The new adaptive power electronic technologies will accelerate the integration of more distributed renewables that will also have an impact on the further reduction of green-house emissions. This is in line with EU target on 27% renewables integration to 2030 that sets targets on CO2 and NOx emissions reductions by 25%. The Norwegian Government has also set an ambitious goal to make Norway carbon neutral by 2050. Increasing renewables in the grid will pave the way for extensive freedom in the energy market allowing the reduction of the electricity cost. The higher degree of electrification in marine vessels enabled by ASiCC’s developments results in higher operating efficiencies which will lower their operating cost and reduce logistic and transportation costs. A further impact is the generation of more jobs in the Norwegian and global industry.

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.