ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: Modular Multilevel Converter
- Creators: Ayyanar, Raja
Description
Wide-BandGap (WBG) material-based switching devices such as gallium nitride (GaN) High Electron Mobility Transistors (HEMTs) and Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) are considered very promising and valuable candidates for replacing conventional Silicon (Si) MOSFETs in various industrial high-frequency high-power applications, mainly because of their capabilities of higher switching frequencies with less switching and conduction losses. However, to make the most of their advantages, it is crucial to understand the intrinsic differences between WBG-based and Si-based switching devices and investigate effective means to safely, efficiently, and reliably utilize the WBG devices. Firstly, a comprehensive understanding of traditional Modular Multilevel Converter (MMC) topology is presented. Different novel SubModule (SM) topologies are described in detail. The low frequency SM voltage fluctuation problem is also discussed. Based on the analysis, some novel topologies which manage to damp or eliminate the voltage ripple are illustrated in detail. As demonstrated, simulation results of these proposed topologies verify the theory. Moreover, the hardware design considerations of traditional MMC platform are discussed. Based on these, a 6 kW smart Modular Isolated Multilevel Converter (MIMC) with symmetrical resonant converter based Ripple current elimination channels is delivered and related experimental results further verify the effectiveness of proposed topology. Secondly, the evolution of GaN transistor structure, from classical normally-on device to normally-off GaN, is well-described. As the benefits, channel current capability and drain-source voltage are significantly boosted. However, accompanying the evolution of GaN devices, the dynamic on-resistance issue is one of the urgent problems to be solved since it strongly affects the GaN device current and voltage limit. Unlike traditional methods from the perspective of transistor structure, this report proposes a novel Multi-Level-Voltage-Output gate drive circuit (MVO-GD) aimed at alleviating the dynamic on-resistance issue from engineering point of view. The comparative tests of proposed MVO-GD and the standard 2-level gate driver (STD-GD) are conducted under variable test conditions which may affect dynamic on-resistance, such as drain-source voltage, gate current width, device package temperature and so on. The experimental waveforms and data have been demonstrated and analyzed.
ContributorsLIU, YIFU (Author) / Lei, Qin (Thesis advisor) / Ayyanar, Raja (Committee member) / Ranjram, Mike (Committee member) / Mallik, Ayan (Committee member) / Arizona State University (Publisher)
Created2022
Description
Modular multilevel converters (MMCs) have become an attractive technology for high power applications. One of the main challenges associated with control and operation of the MMC-based systems is to smoothly precharge submodule (SM) capacitors to the nominal voltage during the startup process. The existing closed-loop methods require additional effort to analyze the small-signal model of MMC and tune control parameters. The existing open-loop methods require auxiliary voltage sources to charge SM capacitors, which add to the system complexity and cost. A generalized precharging strategy is proposed in this thesis.
For large-scale MMC-embedded power systems, it is required to investigate dynamic performance, fault characteristics, and stability. Modeling of the MMC is one of the challenges associated with the study of large-scale MMC-based power systems. The existing models of MMC did not consider the various configurations of SMs and different operating conditions. An improved equivalent circuit model is proposed in this thesis.
The solid state transformer (SST) has been investigated for the distribution systems to reduce the volume and weight of power transformer. Recently, the MMC is employed into the SST due to its salient features. For design and control of the MMC-based SST, its operational principles are comprehensively analyzed. Based on the analysis, its mathematical model is developed for evaluating steady-state performances. For optimal design of the MMC-based SST, the mathematical model is modified by considering circuit parameters.
One of the challenges of the MMC-based SST is the balancing of capacitor voltages. The performances of various voltage balancing algorithms and different modulation methods have not been comprehensively evaluated. In this thesis, the performances of different voltage-balancing algorithms and modulation methods are analyzed and evaluated. Based on the analysis, two improved voltage-balancing algorithms are proposed in this thesis.
For design of the MMC-based SST, existing references only focus on optimal design of medium-frequency transformer (MFT). In this thesis, an optimal design procedure is developed for the MMC under medium-frequency operation based on the mathematical model of the MMC-based SST. The design performance of MMC is comprehensively evaluated based on free system parameters.
For large-scale MMC-embedded power systems, it is required to investigate dynamic performance, fault characteristics, and stability. Modeling of the MMC is one of the challenges associated with the study of large-scale MMC-based power systems. The existing models of MMC did not consider the various configurations of SMs and different operating conditions. An improved equivalent circuit model is proposed in this thesis.
The solid state transformer (SST) has been investigated for the distribution systems to reduce the volume and weight of power transformer. Recently, the MMC is employed into the SST due to its salient features. For design and control of the MMC-based SST, its operational principles are comprehensively analyzed. Based on the analysis, its mathematical model is developed for evaluating steady-state performances. For optimal design of the MMC-based SST, the mathematical model is modified by considering circuit parameters.
One of the challenges of the MMC-based SST is the balancing of capacitor voltages. The performances of various voltage balancing algorithms and different modulation methods have not been comprehensively evaluated. In this thesis, the performances of different voltage-balancing algorithms and modulation methods are analyzed and evaluated. Based on the analysis, two improved voltage-balancing algorithms are proposed in this thesis.
For design of the MMC-based SST, existing references only focus on optimal design of medium-frequency transformer (MFT). In this thesis, an optimal design procedure is developed for the MMC under medium-frequency operation based on the mathematical model of the MMC-based SST. The design performance of MMC is comprehensively evaluated based on free system parameters.
ContributorsZhang, Lei (Author) / Qin, Jiangchao (Thesis advisor) / Ayyanar, Raja (Committee member) / Weng, Yang (Committee member) / Wu, Meng (Committee member) / Arizona State University (Publisher)
Created2020