Event
Ph.D. Dissertation Defense: Daniel Zakzewski
Wednesday, March 26, 2025
9:00 a.m.
AVW Room 1146
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: Ph.D. Dissertation Defense
Name: Daniel Zakzewski
Committee:
Professor Alireza Khaligh (Chair)
Professor Francis Patrick McCluskey (Dean's Representative)
Professor Xin Zan
Professor Sahil Shah
Professor Timothy Horiuchi
Professor Francis Patrick McCluskey (Dean's Representative)
Professor Xin Zan
Professor Sahil Shah
Professor Timothy Horiuchi
Date/Time: Wednesday, March 26, 2025 at 9:00 a.m.
Location: AVW Room 1146
Location: AVW Room 1146
Meeting Link: https://umd.zoom.us/j/
Title: Advancements in Hybrid Multilevel Circuits: Leveraging Joint-Phase Redundancy for Enhanced Performance Metrics
Abstract:
Efficiency, size, and cost are crucial performance metrics in high-powered electrical systems required for transportation electrification, renewable energy integration, and grid modernization. Improvements in these metrics facilitate further adoption of green technologies over combustion-based alternatives.
The power converter is central to these electrified systems, thus the research and optimization of power electronics converter circuits are essential for overall performance improvements. Multilevel converters are the preferred choice for applications exceeding a kilovolt because of their ability to achieve high efficiency and high-quality waveforms while withstanding the voltage stresses required for medium voltage applications. However, traditional multilevel converter topologies rely on many bulky circuit components, leading to high converter cost, size, and weight. Despite this, traditional multilevel circuit configurations remain widely used in contemporary power systems because alternatives often increase complexity without delivering clear performance benefits.
This dissertation focuses on one alternative, the hybrid neutral point clamped (NPC) converter, a less commonly used class of power electronic circuits. This topology integrates features from well-established and traditional topologies, namely the neutral point clamped converter, flying capacitor converter, and cascaded H-bridge converter. However, as with other alternative multilevel converter designs, performance benefits are unclear in existing literature. This work demonstrates through comprehensive analysis, simulation, and experimentation that the hybrid NPC outperforms the traditional multilevel designs across the key performance metrics, thus establishing the hybrid NPC as a viable solution for future high-powered electrical systems.
This work also proposes several innovations to the hybrid NPC topology that further improve the topology's performance. The key to these innovations is the introduction of `joint-phase redundancy,' which uses common mode voltages to reveal additional system states using are leveraged to increase overall converter performance. Joint phase redundancy can both enhance the cost, size, and efficiency of existing hybrid multilevel designs, and enable novel configurations that are otherwise not possible with traditional per-phase redundancy. This joint-phase redundancy specifically allows the use of lower voltage devices, which results in lower converter cost and size while increasing output waveform quality and efficiency. The proper application of joint-phase redundancy also enables operations in an extended voltage range, thereby increasing the power rating of the converter without hardware design modifications.
Additionally, this work addresses the complexity often associated with these multilevel topologies involving floating capacitors. These circuits are often cited for their increased control complexity and the need for large capacitances. The work addresses these challenges with a novel model predictive control strategy designed to minimize switching losses while ensuring high-frequency regulation of the capacitors, thus maintaining low capacitance requirements. Experimental results validate the practicality of this approach, showing its potential for use in industrial applications while offering substantial improvements in efficiency and control over previous designs. The extensibility of this analysis and control framework is used to compare the hybrid NPC class of circuits against competing designs.
This dissertation demonstrates that the hybrid NPC converter is a promising alternative to traditional multilevel converter topologies for high-powered electrical systems. The introduction of joint-phase redundancy and the associated analysis and control methodologies further the value of the hybrid NPC converter. The findings from this work provide valuable insights and practical guidance for future designers to adequately consider hybrid NPC circuits, offering an effective path toward optimizing power converter designs for next-generation, high-performance electrical systems
The power converter is central to these electrified systems, thus the research and optimization of power electronics converter circuits are essential for overall performance improvements. Multilevel converters are the preferred choice for applications exceeding a kilovolt because of their ability to achieve high efficiency and high-quality waveforms while withstanding the voltage stresses required for medium voltage applications. However, traditional multilevel converter topologies rely on many bulky circuit components, leading to high converter cost, size, and weight. Despite this, traditional multilevel circuit configurations remain widely used in contemporary power systems because alternatives often increase complexity without delivering clear performance benefits.
This dissertation focuses on one alternative, the hybrid neutral point clamped (NPC) converter, a less commonly used class of power electronic circuits. This topology integrates features from well-established and traditional topologies, namely the neutral point clamped converter, flying capacitor converter, and cascaded H-bridge converter. However, as with other alternative multilevel converter designs, performance benefits are unclear in existing literature. This work demonstrates through comprehensive analysis, simulation, and experimentation that the hybrid NPC outperforms the traditional multilevel designs across the key performance metrics, thus establishing the hybrid NPC as a viable solution for future high-powered electrical systems.
This work also proposes several innovations to the hybrid NPC topology that further improve the topology's performance. The key to these innovations is the introduction of `joint-phase redundancy,' which uses common mode voltages to reveal additional system states using are leveraged to increase overall converter performance. Joint phase redundancy can both enhance the cost, size, and efficiency of existing hybrid multilevel designs, and enable novel configurations that are otherwise not possible with traditional per-phase redundancy. This joint-phase redundancy specifically allows the use of lower voltage devices, which results in lower converter cost and size while increasing output waveform quality and efficiency. The proper application of joint-phase redundancy also enables operations in an extended voltage range, thereby increasing the power rating of the converter without hardware design modifications.
Additionally, this work addresses the complexity often associated with these multilevel topologies involving floating capacitors. These circuits are often cited for their increased control complexity and the need for large capacitances. The work addresses these challenges with a novel model predictive control strategy designed to minimize switching losses while ensuring high-frequency regulation of the capacitors, thus maintaining low capacitance requirements. Experimental results validate the practicality of this approach, showing its potential for use in industrial applications while offering substantial improvements in efficiency and control over previous designs. The extensibility of this analysis and control framework is used to compare the hybrid NPC class of circuits against competing designs.
This dissertation demonstrates that the hybrid NPC converter is a promising alternative to traditional multilevel converter topologies for high-powered electrical systems. The introduction of joint-phase redundancy and the associated analysis and control methodologies further the value of the hybrid NPC converter. The findings from this work provide valuable insights and practical guidance for future designers to adequately consider hybrid NPC circuits, offering an effective path toward optimizing power converter designs for next-generation, high-performance electrical systems
