Title page for ETD etd-01052006-105209

Type of Document Master's Thesis
Author Thacker, Timothy Neil
Author's Email Address tthacker@vt.edu
URN etd-01052006-105209
Title Control of Power Conversion Systems for the Intentional Islanding of Distributed Generation Units
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Boroyevich, Dushan Committee Chair
De La Ree Lopez, Jaime Committee Member
Wang, Fei Fred Committee Member
  • voltage control
  • Voltage Source Inverter (VSI)
  • Power Conversion System (PCS)
  • current control
  • Islanding Detection
  • Intentional Islanding
  • Distributed Generation (DG)
Date of Defense 2005-09-26
Availability unrestricted
Within the past decade, talk has arisen of shifting the utility grid from centralized, radial sources to a distributed network of sources, also known as distributed generation (DG); in the wake of deregulation, the California energy crisis, and northeastern blackouts.

Existing control techniques for DG systems are designed to operate a system either in the connected or disconnected (islanding) mode to the utility; thus not allowing for both modes to be implemented and transitioned between. Existing detection and re-closure algorithms can also be improved upon. Dependent upon the method implemented, detection algorithms can either cause distortions in the output or completely miss a disturbance. The present re-closure process to reconnect to the utility is to completely shutdown and wait five minutes. The proposed methods of this study improve upon existing methods, via simulation and hardware experimentation, for DG systems that can intentionally islanding themselves.

The proposed, “switched-mode”, control allows for continuous operation of the system during disturbances by transitioning the mode of control to reflect the change in the system mode (grid-connected or islanding). This allows for zero downtimes without detrimental transients.

The proposed detection method can sense disturbances that other methods cannot; and within 25 ms (approximately 1.5 line-cycles at 60 Hz). This method is an improvement over other methods because it eliminates the need to purposely distort the outputs to sense a disturbance.

The proposed re-closure method is an improvement over the existing method due to the fact that it does not require the system to de-energize before re-synchronizing and reconnecting to the utility. This allows for DGs to continuously supply power to the system without having to shut down. Results show that the system is generally ready to reconnect after 2 to 5 line cycles.

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