Novel DC Ring Topology and Protection System – a Comprehensive Solution for mega city power grids

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Title: Novel DC Ring Topology and Protection System – a Comprehensive Solution for mega city power grids
Author: Haj-Maharsi, Mohamed Yassine
Advisors: Dr. Alex Q. Huang, Committee Chair
Dr. Subhashish Bhattacharya, Committee Member
Dr. Robert E. White, Committee Member
Dr. Mesut E. Baran, Committee Member
Abstract: The development of mega cities such as Tokyo, Mumbai, Beijing, Shanghai, Guangzhou, and Dhaka leads to increased load concentration and brings additional challenges to managing power on already strained networks while keeping power available for critical loads. Problems such as power factor regulation, power quality, voltage instability, increased short circuit levels and environmental impact are not easily solved by adding parallel lines, shunt capacitors, or building new substations. To ensure power availability and redundancy, mega cities are fed from multiple power sources using AC and DC links with AC terminal connections through transformers to city loads. This topology presents risk of cascading failures and total blackout should a problem happens anywhere in the AC network even when a sophisticated protection scheme is deployed. Therefore, techniques using FACTS devices are being applied in some areas to alleviate power management difficulties but the increased rate of cities expansions forces utilities to overrate these devices or increase their numbers. This approach may results in control and protection coordination problems, power oscillation, subsynchronous resonance, and torsional interaction with nearby generator units. Furthermore, any future load or supplied generation increase would require additional tuning of system controls or new installations of these device-based solutions. Consequently, the most effective solution is obtained when the individual AC subsystems representing sources and loads are decoupled so a fault in a given subsystem is not propagated to others. This solution can be achieved by a DC system where power sources and loads are connected to the DC bus through voltage source converters. For a mega city, this would be conceived as a DC ring feeding multiple loads and connected to remote and local power sources. Unfortunately, the lack of fast DC Circuit Breaker has been one of the key issues affecting extensive applications of DC systems with common DC buses. Because a DC fault would discharge all the capacitors causing delays in system recovery and possible wide system collapse. In this research, we provide a comprehensive solution by identifying the proper DC system topology, designing the required protection device, and implementing a fast control algorithm.
Date: 2010-02-03
Degree: PhD
Discipline: Electrical Engineering

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