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Advanced Gate Driving Techniques and Inverter Design Considerations of Wide-Band-Gap Devices

Description

The continuous demand for higher power density and better efficiency to reduce the global energy consumption, is the driving force to introduce new semiconductor technologies. Wide-band-gap (WBG) material based devices such as gallium nitride high electron mobility transistors (GaN HEMTs) and silicon carbide metal-oxide-semiconductor field-effect transistors (SiC MOSFETs) are considered promising candidates for replacing conventional silicon MOSFETs, mainly because of their capabilities of higher switching frequencies with less switching and conduction losses. Although WBG devices can largely improve the conversion efficiency, the implementation of WBG devices brings in some challenges in power converter design. Firstly, the high voltage changing slew rate of WBG devices introduces a distortion current to the gate through the coupling capacitance of the device. The distortion current may cause mis-trigger or overvoltage breakdown of the device gate. This issue is so-called crosstalk effect. This dissertation proposes a multilevel gate driving profile to address this issue. Secondly, due to the gate-to-substrate voltage bias, the integration of multiple GaN devices suffers from the high on-state resistance. This issue is so-called current collapse or electron trap. This dissertation proposes a gate current injection method to address this issue. By injecting relatively large gate current at specific time period, the on-state resistance is largely improved at both hard-switching and soft-switching scenarios. Thirdly, series connection of switches is an effective way to achieve higher blocking voltage of the device. The serial connection of WBG devices suffers from the dynamic voltage unbalance and short-circuit protection issues. The additional short-circuit scenarios are found in the series-connected devices, which are not covered by the traditional short-circuit protection scheme. Dynamic voltage sharing problem is addressed using porposed current source gate driver. Besides, the short-circuit protection circuit is integrated in the proposed gate driver to cover all the short-circuit scenarios of series-connected devices. Finally, this dissertation uses a practical converter design example to comprehensively elaborate the design considerations of WBG based converters. A 1.5 MHz/ 2 kV/ 80 A commercial burst-mode inverter using SiC MOSFETs is designed for electromagnetic acoustic transducer. This inverter design includes comprehensive fault protection, hardware and controller design.

ContributorsLiu, Chunhui (Author) / Lei, Qin QL (Thesis advisor) / Ayyanar, Raja RA (Committee member) / Ranjram, Mike MR (Committee member) / Mallik, Ayan AM (Committee member) / Arizona State University (Publisher)

Created2022

Unsuccessful Urban Governance of Brownfield Land Redevelopment: A Lesson From the Toxic Soil Event in Changzhou, China

Description

A public health crisis in the process of brownfield land redevelopment (BLR) has frequently appeared in the context of promoting industrial upgrading and de-industrialization in China. Recent discussions on the reasons for this problem centered on the lack of laws, standards, and policies needed to secure the process of BLR. However, we argue that an urban governance approach to BLR can identify the sources of the problem. This paper discusses a case study of a toxic soil event in Changzhou, China, based on the theoretical framework - the Institutional Industry Complex (IIC). Under the pressure of fiscal distress as well as the requirements of economic growth and urbanization, local governments in China are bound with fiscal revenue from land development and land urbanization and have formed a pro-growth alliance with enterprises, property developers, and even the public. The alliance is defined as the pro-growth IIC of land finance regime in this paper. Due to the path-dependence of the IIC, the conventional pro-growth IIC of land finance regime in China has been circulated, and then transformed into a pro-growth IIC of BLR. As a result, the goal of the pro-growth IIC of BLR is maximizing profit in the process of land development, a goal that is the same as the pro-growth IIC of land finance regime Thus, as the pivotal stockholders of the pro-growth IIC of BLR, local governments, enterprises, and property developers hesitate to pursue a prudent and secure BLR process, which effectively attenuates a series of serious environmental issues and public health crises. That is the root cause of the problem. This study suggests a positive interaction between central and local government, as well as between enterprise and the public to create a sustainable IIC of BLR in future.

ContributorsLiu, Chunhui (Author) / Song, Weixuan (Author) / Zhou, Chen (Author) / Biodesign Institute (Contributor)

Created2017-05-15