Details

Autor(en) / Beteiligte

• Hu, Boxue

Titel

Challenges and Solutions of Applying Medium-Voltage Silicon Carbide Devices in Medium and High-Voltage Systems

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2019

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• After 60 years’ development, Silicon (Si) devices are approaching their performance limitations set by their own material properties. They have difficulties meeting requirements of future medium and high-voltage applications. Medium-voltage Silicon Carbide (SiC) devices break the constraints of Si devices and are projected to be their successors. However, the research of medium-voltage SiC devices is still at an early stage. Technical challenges hinder their applications. This dissertation aims to study and/or provide solutions to key challenges of applying medium-voltage SiC devices. This work first summarizes the major technical challenges and associated research efforts of applying medium-voltage SiC devices. The summary is based on a survey of recent developments of medium-voltage SiC devices and evaluation results of three device examples. Then this dissertation addresses four technical challenges: gate drive design for medium-voltage SiC devices, auxiliary power supply design for gate drives, partial discharges in motor windings, and reflected waves in motor drives. Designs of gate drives and its auxiliary power supplies are challenging. It is because of the fast switching speed of medium-voltage SiC devices and high insulation requirements in high-voltage systems. This work presents a gate drive and its auxiliary power supply targeting 10 kV SiC MOSFETs. The gate drive features a common-mode transient immunity (CMTI) over 200 kV/µs and an overcurrent protection time within 700 ns. Its power supply has an input voltage of 7 kV and an insulation capability over 10 kV. The gate drive and auxiliary power supply further enable the development of a self-sustained circuit building block, which can serve as one of the sub-modules in high-voltage multilevel converters. The high voltage rating and fast switching speed of medium-voltage SiC devices cause concerns of partial discharges. This work studies the partial discharge in a medium-voltage motor winding. A test platform based on 10 kV SiC devices is developed. A three-step test approach is employed to systematically investigate the effects of various voltage parameters. These include voltage rise/fall time, voltage pulse length, voltage polarity, pulse repetitive rate, duty ratio, fundamental frequency, and modulation index of the sine-PWM voltage. Test results show that voltage rise/fall time is one major parameter affecting the partial discharge inception voltages (PDIVs). Explanations are provided regarding the effects of voltage rise/fall time on the partial discharge processes. An empirical equation is proposed to estimate PDIVs under various conditions. The reflected wave phenomenon is common in motor drive systems with long connection cables. It causes voltage overshoot at motor terminals and has a negative impact on the motor insulation. In this work, the reflected wave phenomenon is studied in two medium-voltage motor drives. They are a two-level inverter based on 10 kV SiC devices and a seven-level modular multilevel converter (MMC) based on 1.7 kV SiC devices. Simulations and experiments are performed to compare the reflected waves in these two inverter setups with various cable lengths. The last part of this dissertation provides conclusions and outlooks for future research.