Performance Comparison of 10 kV and Series-connected 3.3 kV SiC MOSFETs based VSCs for MV Grid Interfacing Applications

Abstract

The latest HV SiC devices can significantly improve the efficiency and power density of MV grid interfacing converters. A VSC (Voltage Source Converter) with 7.2 kV dc bus can directly interface with a 4160 V grid which can be realized in a 2-level configuration using a 10 kV blocking switch. HV SiC devices such as 6.5 kV and 10 kV SiC MOSFETs are still in their nascency and being used in research applications, whereas 3.3 kV SiC MOSFETs have already been qualified for commercial applications by multiple vendors. In this regard, an equivalent 10 kV switch formed by series connection of three 3.3 kV SiC MOSFETs has been proposed as a potential alternative, and it has been quantitatively compared to a single 10 kV SiC MOSFET. Normalized device parameters have been considered in both cases for a fair comparison. Two types of 10 kV <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$120\ \mathrm{m}\Omega$</tex> switching cells have been realized through series connected 3.3 kV <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$40\ \mathrm{m}\Omega$</tex> SiC MOSFETs and parallel connected 10 kV <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$350\ \mathrm{m}\Omega$</tex> SiC MOSFETs for effective power loss comparison. Experimentally determined device conduction and switching losses have been employed for further efficiency and loss modeling of 3-phase VSCs using both switching cells. The power loss and efficiency trends with load and switching frequency variation have been presented for both cases. The converter power processing capability dependence on the switching frequency has also been compared for both cases.