Medium-Voltage DC Solid-State Transformer Enabled by 10 kV SiC MOSFETs with Digital Design

Abstract:
To meet the carbon-neutral target for global temperature control, renewable energy is quickly growing all over the world. One of the major renewable energy sources is wind power, which is estimated to provide 24.4 % of the European Union electricity demand. The MVolt project in Aalborg University is proposed to meet this societal need for sustainable electricity by lowering the cost of wind power. Its goal is to design medium voltage (MV) converters based on 10kV Silicon Carbide (SiC) MOSFET. The objective is to build an MV power stack based on an MV power module that adheres to industry standards, adapting it to comply with wind power requirements and show its outstanding performance.
Generally, these converters interfacing between MV side and LV side are also called solid-state transformers (SSTs). One of the most challenging stages in SST is the MV-DC to LV-DC stage, which is referred to as DC-SST. It has many challenges, such as high input voltage, high output current, and high-frequency isolation. Compared to cascaded multi-cell DC-SSTs, single-cell DC-SSTs, which is built by 10 kV SiC MOSFETs, can directly interface MV-DC bus, resulting in a reduction of the complexity. However, faster switching speeds of wide bandgap semiconductors (up to 250 V/ns) result in a higher switching frequency. The parasitic parameters in DC-SST system could lead to some resonance or potential risks, therefore, the influences of parasitic parameters cannot be neglected. But reduced parasitic parameter generally requires that the components are highly compact, which causes difficulty in measuring voltage, current, and temperature. In these cases, one of the most effective solutions to obtain such information might be the use of digital design. The internal states of the system can be obtained to help identify and solve problems by digital design. Hence, using digital design framework to study has become even more valuable for designers.
Based on the above, in this Ph.D. project, the accurate high-frequency model of different components (including bipolar MV DC chopper, MV inductor, MV transformer) in MV DC-SST should be built by digital design tools, followed by the experimental verification of the high-frequency model. Next, the accurate high-frequency system-level modeling of MV DC-SST will be established to identify interactions among different components and overcome the negative issues. Finally, the whole DC-SST experimental prototype will be built to verify the design. The experiment will be conducted in power electronics laboratory and medium-voltage laboratory at Aalborg University. The main research outcome of this Ph.D. project is expected to contribute efforts to overcoming some engineering challenges in MV converter, which can give some basic references to the future MV converters with 10kV SiC MOSFETs.

Funding: AAU Energy Scholarship