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Title:High-density multilevel power converters for use in renewable and transportation applications
Author(s):Barth, Christopher Brandon
Director of Research:Pilawa-Podgurski, Robert C. N.
Doctoral Committee Chair(s):Pilawa-Podgurski, Robert C. N.
Doctoral Committee Member(s):Alleyne, Andrew G.; Haran, Kiruba S.; Banerjee, Arijit; Sridharan, Srikanthan
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Multilevel inverter
Power electronics
Electric Aircraft
Flying Capacitor
Multilevel Inverter
Gallium Nitride
Multilayer Ceramic Capacitors
motor drive
synchronous Machine
liquefied natural gas
power density
specific power
specific power density
permanent magnet
Silicon carbide
motor control
high speed motor
low inductance
Abstract:Electrification of transportation and the development of renewable resources promise to offer both environmental and economic benefits. In each instance, the size and weight of the power electronics play a role in the overall system efficiency and installation cost. This dissertation demonstrates opportunities for increasing the power density and efficiency of inverter systems through the use of high-density capacitive energy storage and flying capacitor multilevel (FCML) power converters. While historically limited to energy-dense electrolytic or low-loss film-based capacitors, designers now have an increasing array of high-energy-density ceramic capacitors available to them. In addition to the small signal characteristics of these devices which are typically provided by the manufacturer, designers need to understand the characteristics of these devices under large voltage swing. This dissertation addresses this need by developing and demonstrating a method of characterizing capacitors under large voltage swing. The significance of a proper understanding of the large-signal characteristics of these devices has been demonstrated through the a wide survey of available devices and the development of a design process for maximizing the power density of active energy buffers based on capacitor technology. Building on an understanding of the potential benefits of capacitor technology, this dissertation next explores the application of ceramic capacitors as the primary energy storage mechanism in DC-AC inverters. The flying capacitor multilevel topology (FCML) has been shown to exhibit high efficiency and high power density. This is especially true in applications requiring low harmonic distortion such as inverters driving low-inductance high-density electric machines. Much of the prior work on the FCML converter has focused on various aspects of converter control. However, the demonstration of the power density and efficiency benefits of the topology have often been masked by the use of general-purpose lab hardware and low switching frequency. This work seeks to demonstrate the applicability and advantages of the FCML architecture for a range of applications. Through the design and implementation of a 13-level flying capacitor converter, the passive balancing characteristics of the FCML converter previously demonstrated at level counts of four to seven can be extended to higher level counts and voltage using high-speed, wide bandgap gallium nitride (GaN) devices. The FCML topology holds special potential in applications where high specific power density (kW/kg) has significant value such as three-phase motor drives for hybrid electric aircraft. These designs incorporate turbine-driven electric generation with distributed electric propulsion to achieve system-level aerodynamic benefits. While conventional Jet-A fuel may be used, low-temperature fuels such as liquefied natural gas (LNG) offer additional system-level benefits through the use of low-temperature fuel to cool the power electronics. This can not only improve the efficiency of the power conversion, but also reduce the energy expended to heat the fuel before combustion. This dissertation demonstrates that GaN-based FCML converters can be advantageous at low temperature through the design and detailed evaluation of a 3-level flying capacitor converter operating near cryogenic temperatures. Having demonstrated the benefits of the FCML architecture on a single-phase basis, the dissertation commences with the design of a complete FCML-based motor drive tailored for high-density, low-inductance permanent magnet machines. The drive system incorporates a scalable architecture allowing a wide variety of applications to be met using an optimized single-phase FCML module. Even current sharing and vector control of a low-inductance permanent magnet machine were achieved.
Issue Date:2019-12-05
Rights Information:Copyright 2019 Christopher Brandon Barth
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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