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Thesis Defence: Negative Sequence Current Control of Hybrid Cascaded Three-Level and Multilevel Power Converter for High Voltage Direct Current (HVDC) Transmission

January 5, 2023 at 9:00 am - 2:00 pm

Paul Yoo, supervised by Dr. Liwei Wang, will defend their dissertation titled “Negative Sequence Current Control of Hybrid Cascaded Three-Level and Multilevel Power Converter for High Voltage Direct Current (HVDC) Transmission” in partial fulfillment of the requirements for the degree of Master of Applied Science in Electrical Engineering.

An abstract for Paul Yoo’s thesis is included below.

Examinations are open to all members of the campus community as well as the general public.

To access a zoom link to attend this defence please contact the supervisor at liwei.wang@ubc.ca.


High voltage direct current transmission (HVDC) is used for massive transmission of electricity over long distances in the form of direct current (DC). HVDC power systems enable utilities to transfer bulk power, to efficiently integrate clean renewable energies, to interconnect grids, and to improve overall network performance with low losses. The latest generation of HVDC systems make use of modular multilevel converter (MMC) topologies to convert high voltage efficiently. Hybrid converter topologies combine the basic two- or three-level converter topologies with MMC topologies to reduce the number of semiconductor switches in the current-conducting path and consequently, reducing semiconductor losses. The hybrid converter investigated in this thesis is a hybrid 3-level converter (H3LC) which has been shown to have DC-fault blocking capabilities and remains compact while having less semiconductor losses than the conventional hybrid 2-level converter. The H3LC operates by using director switches (DS), composed of series connected IGBTs to generate 3-level voltage waveforms which are then passed through cascaded full bridge submodules (FBSMs) converting the 3-level voltage waveforms into multilevel sinusoidal voltage waveforms at the point of common coupling (PCC). However, in various industrial power system applications where individual phase voltage magnitude fluctuation and three-phase voltage unbalance at the PCC may occur, the H3LC would cause power quality problems during such events.
This thesis presents an unbalanced PCC voltage regulation control method with positive and negative-sequence component analyzers and controllers for the H3LC. The main controller is used to regulate the positive-sequence voltage at the PCC to the reference voltage while the purposed auxiliary controller is used to suppress any negative-sequence currents at the PCC. This thesis explores the unbalanced voltage regulation scheme by outlining the underlying principles and simulating case studies with a H3LC model in a MATLAB® Simulink environment.


January 5, 2023
9:00 am - 2:00 pm

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Event Type
Thesis Defence
Research and Innovation, Science, Technology and Engineering
Alumni, Community, Faculty, Staff, Families, Partners and Industry, Students, Postdoctoral Fellows and Research Associates