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Title: Analysis and protection of multi-terminal HVDC system
Author: Gao, Yang
ISNI:       0000 0004 6058 3527
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2016
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The thesis is essentially concerned with the modeling and fault analysis of Modular Multilevel Converter (MMC) based High Voltage Direct Current (HVDC) systems with DC circuit breakers connected. A generalized MMC model is proposed and the system behaviour of MMCs subject to both DC line-to-line and line-to-ground faults is analyzed. Various stages of DC voltage / current transient processes are studied and analyzed. Simulation results are presented to illustrate the behaviour of the system under such faults. A hybrid multi-terminal HVDC transmission system model consisted of one MMC, one Full-Bridge Modular Multilevel Converter (FB-MMC) and one conventional two-level Voltage Source Converter (VSC) has been studied in this thesis. In the first part, the steady-state behaviors of these three converters are described, and the simulation results testing the normal performance of MMC, FB-MMC and VSC are given. Considering the necessity of analysis on the hybrid three-terminal DC grid under different DC fault conditions, five fault conditions have been tested, i.e. pole-to-pole DC fault near MMC, pole-to-pole DC fault near FB-MMC, pole-to-ground DC fault at FB-MMC, pole-to-ground DC fault at MMC and pole-to-ground DC fault at VSC. To isolate the DC fault, DC breakers are discussed and the hybrid DC breaker is adopted for the simulation. Because of the DC breaker, after the fault occurs, the three-terminal hybrid DC grid can be transformed a two-terminal hybrid HVDC with these healthy converters, so that the healthy HVDC can continue to operate. The simulation results demonstrate the behaviors of the three different converters under two different DC fault conditions. Finally two simplified models are proposed for studying DC fault behaviour of MMC based HVDC systems, one is an average model and the other is a diode model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available