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Yoo, Paul

University of British Columbia

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, 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 aim of this thesis is to provide a method that will optimize the H3LC operation during the event of a grid voltage imbalance. The research challenge undertaken is to integrate a sequence analyzer and controller technology that was proven to have worked for other converter topologies with an emerging hybrid multilevel converter, i.e., H3LC. This thesis presents an unbalanced PCC current regulation control method with positive and negative-sequence component analyzers and an auxiliary controller for the H3LC. A sequence component analyzer is first used to separate the signals measured from the grid at the PCC into its positive and negative sequence components. With the extracted sequence components, the negative sequence current can be found and controlled. The main controller is used to regulate the positive-sequence current at the PCC with respect to the reference current while the proposed auxiliary controller is used to suppress any negative-sequence currents at the PCC. The integration of the developed technology and the H3LC is implemented and, a simulation imitating an unbalanced grid voltage case is performed for proof of concept. This thesis explores the unbalanced current regulation scheme by outlining the underlying principles and simulating case studies for operations under different modes with a detailed equivalent model of the H3LC in a MATLAB® Simulink environment.

Text

2023-01-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83762

Electrical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/