UBC Theses and Dissertations

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UBC Theses and Dissertations

Intelligent load shedding scheme for frequency control in communities with local alternative generation and limited main grid support Rostamirad, Shahrzad


The number of microgrids in the electric power system is increasing rapidly to meet the increased electrical demand at the distribution level instead of delivering the additional power from centralized generation stations. Due to the above-mentioned transformation and a number of other factors, the utilities find themselves less attracted to investing in the supply lines. As a consequence, the connection points of these, rather self-supplied, microgrids become more vulnerable to any major disturbances in the downstream network. Because microgrids with renewable energy resources do not have a generation reserve, an intelligent load shedding algorithm (based on a smart grid) is proposed, that balances the power demand and generation, and prevents the upstream supply lines from exceeding their capacity at any time. Although the algorithm is accurate, it may not be fast enough to prevent a cascading power outage in the isolated microgrid due to very fast frequency decline. To help maintain the frequency of the microgrid close to the normal level, a supplementary controller is added to the doubly fed induction generator wind turbine. The studied microgrid corresponds to a case study in the University of British Columbia (UBC). A scenario of demand and distributed generation of the campus in the year 2030 are modeled. The proposed algorithm, which combines intelligent load shedding with wind turbine controller, succeeds in managing the power requirements for both grid connected and isolated microgrids. However, the algorithm has a weakness which is its operation delay; for longer delays in deactivating the controller and load shedding, the frequency might drop below the threshold. A number of suggestions are made to overcome this problem.

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