Systematic Topology Derivation and PWM Design of Multilevel Converters

  • Author / Creator
    Li, Yuzhuo
  • Multilevel converters (MLCs) have been widely accepted for decades in various applications, e.g. high-voltage transmission systems, medium-voltage drive systems, distributed generation integrations, low voltage power supply, etc. During the evolution of power electronics equip-ment, a large number of MLC topologies and pulse-width modulation (PWM) schemes are proposed. Due to the sophisticated topology structure of MLCs, the topology derivation and PWM design methods are normally case-by-case and lack generality. While the concrete meth-ods that emerged during the development of MLCs are still ambiguous and lack systematic methodology.
    At present, more new topologies keep emerging, resulting in a large number of circuits with resembling structures and similar features which require systematic analysis and optimal de-sign. To better understand the relationship of various MLC topologies, the general relation-ships of power converters are systematically discussed in this work, and new relationships are discovered and elaborated, especially for the voltage-source converters (VSCs) and current-source converters (CSCs). In addition to the famous duality principles, the novel isomorphic relationships of VSCs and CSCs are firstly revealed in the power converter field with thorough theoretical discussions and simulation/experimental verifications. To facilitate the derivation process of MLCs, the stage-based uniform structures are also derived from the structure-level duality and the equivalence and implemented for systematic topology synthesis and derivation for not only multilevel VSCs and CSC, but also matrix converters. Several newly proposed to-pologies are demonstrated as examples with practical considerations and experiments on a special 5-level case.
    To facilitate the PWM design process, a universal carrier-based PWM design method through hierarchical method is proposed. It iteratively utilizes the identical circuits in convert-ers and can provide an exhaustive list of carrier-based PWM schemes for the non-modular MLCs, e.g. active-neutral-point-clamped (ANPC) based converter. Based on this methodology, the novel phase shift PWM for improvement of loss distribution, the systematic simplification of ANPC converters and systematic fault tolerant operation under multiple fault switches are also investigated, which also has potentials for other ANPC-based derivatives. Various 4-level and 5-level PWM design cases are elaborated with both theoretical investigations and experi-mental verifications in this work.
    With the systematic knowledge of theory/circuit/structure/modulation level of MLCs, this work will simplify the topology derivation and PWM design process over conventional case-by-case methods and provide different innovation perspectives for MLC research.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.