Ultrahigh-Voltage Silicon Carbide Device Performance, Requirements, and Limitations in High-Power Applications
Time: Tue 2021-06-08 08.00
Location: Sten Velander Seminarroom, Teknikringen 33, Stockholm (English)
Subject area: Electrical Engineering
Doctoral student: Daniel Johannesson , Elkraftteknik, Power Electronics
Opponent: Professor Alberto Castellazzi, Kyoto University of Advanced Science
Supervisor: Hans-Peter Nee, Elektrotekniska system, Elkraftteknik; Staffan Norrga, Elektrotekniska system, Elkraftteknik; Muhammad Nawaz, Hitachi ABB Power Grids
The increased awareness of the on-going climate change accelerates the electric energy system transformation from fossil-fueled power sources towards systems with larger portions of renewable energy sources. Moreover, the grid infrastructure requires reinforcements to cope with increasing electrical energy demand. Flexible AC transmission systems (FACTS) and high-voltage DC (HVDC) transmission systems allow higher grid capacity, efficient transmission over long distances and sub-sea electrical energy transfer. Efficient sub-sea transmission is required for off-shore wind- and intercontinental grid connections. It is predicted that basic power electronic building blocks (PEBB) utilizing SiC-based semiconductor devices will provide converter system benefits (e.g., reduced number of series connected devices, less complex system, lower energy losses, lower cooling requirements and smaller station footprint), in comparison to systems employing Si-based semiconductor devices. The main objective of this thesis is to design, evaluate and identify the performance, requirements, and limitations of high-voltage SiC devices suitable for high-power applications. The SiC semiconductor device characteristics have been investigated by two-dimensional numerical simulations and experiments to assess the suitability in high-power applications. A calibrated set of technology computer-aided design (TCAD) simulation models are used as foundation for estimating the performance of SiC PiN diodes, SiC insulated-gate bipolar transistors (IGBTs) and SiC gate turn-off (GTO) thyristors with blocking voltage capabilities in the range of 20–50 kV. The static and dynamic device performances are assessed along with related gate driver requirements and snubber design requirements. The devices characteristic are studied using physical parameters of device layer structures, device processing parameters, and varying circuit parameters using mixed-mode simulations that results in a wide range of data for device performance predictability. Moreover, the experimental characterization of 10 kV, 100 A SiC metal-oxide semiconductorfield-effect transistor (MOSFET) power modules are demonstrated and compared to Si counterparts. The junction termination extension (JTE) design aspects for 20, 30, 40, and 50 kV devices are investigated where the results are used to predict the active area ratio for each blocking voltage class. In addition, the limit of critical operating conditions such as dynamic avalanche and current filamentation are derived by TCAD simulations, which indicates that the critical operation points are significantly higher than that of Si-based counterparts. The wide-range simulation data have been used in benchmarking SiC-based devices with Si counterparts in an application case of a 1 GW, 640 kV, modular multilevel converter (MMC)-based HVDC system. The analytical benchmark model indicates an energy loss reduction to approximately half by employing SiC device configurations compared to state-of-the-art Si bi-mode insulated gate transistors (BiGTs). The low energy losses along with the benefits by reduction of system complexity, control hardware, cables, and fibers (due to a lower amount of PEBBs), the SiC converter design presents a promising alternative to existing Si-based high-power modular multilevel converters.