Dissertation/Thesis Abstract

High Power DC-AC and AC-DC Multilevel Converter Based on H-Bridge Topology Using Improved Control Strategies
by Almahmoodi, Haider Neamah Hashim, Ph.D., Western Michigan University, 2018, 192; 13877012
Abstract (Summary)

Rising worldwide demand for energy, pressing economic constraints, and substantial environmental concerns have led to the harvesting of clean, renewable energy sources such as solar PV and wind energy. To integrate these new resources into the power grid, power electronic converters play a crucial role and have become indispensable devices.

Multilevel converters are considered to be state-of-the-art, efficient solutions for mediumand high-voltage industrial applications, due to the difficulty of connecting traditional two-level converters to high- and medium-voltage grids, since a single power switch cannot stand such high voltage. The standard multilevel converter topologies, such as the neutral point clamped (NPC), flying-capacitor multilevel (FCM), and cascaded H-bridge (CHB), are currently used; however, the need for higher efficiency multilevel topologies that require the lowest number of components These benefits make the proposed. The cascaded H-bridge multilevel converter topology has been the preferred solution over other standard multilevel converter topologies because each level has the same structure, with no extra clamping diodes or capacitors. Therefore, this study proposes a CHB converter with a new structure that requires fewer number of the insulated-gate bipolar transistors (IGBTs) for generating AC voltage at the output stage of the converter, using a modified phase shift pulse width modulation (PWM) control system. The reduction in the number of required IGBTs will decrease the converter cost, size, and installation area, while also improving its reliability. These benefits make the proposed topology a good candidate for renewable energy applications, especially for photovoltaic integration. The ability of the proposed inverter to generate the desired output voltage waveform has been validated through a laboratory low-power prototype. A comparative analysis with other topologies is provided, which supports the capability of the proposed topology for reducing the number of high-frequency IGBTs and isolated DC-link.

Since one of the most commonly and extensively used converter topologies in power electronics are rectifiers, a grid-connected, active front-end (AFE) rectifier based on the suggested reduced-switch-count CHB converter family is also proposed. The bidirectional capabilities of the proposed multilevel converter are verified through simulation and operation in the inverting and rectifying modes. It was shown that the proposed topology is able to inject the commanded active and reactive power into the grid in addition to the abilities to absorb power from the grid. The voltage-oriented control (VOC) method has been implemented on the grid-tied bidirectional multilevel converter, and simulation results verify the benefits of the new topology.

The proposed converter, modulated with the selective harmonic elimination method (SHEM), has inherited complexity due to the set of nonlinear equations derived to determine the switching angles for the CHB converter with different modulation indices, voltage levels, and various harmonics selected for elimination. Therefore, a generalized solution to address total harmonic distortion (THD) is also proposed.

Indexing (document details)
Advisor: Abdel Qader, Ikhlas
Commitee: Abdel-Qader, Ikhlas, Gomez, Pablo, Houshyar, Azim
School: Western Michigan University
Department: Electrical and Computer Engineering
School Location: United States -- Michigan
Source: DAI-B 80/08(E), Dissertation Abstracts International
Subjects: Computer Engineering, Electrical engineering
Keywords: Multilevel converter, Multilevel inverter
Publication Number: 13877012
ISBN: 978-1-392-05452-9
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