| Summary: | 碩士 === 國立臺灣大學 === 工業工程學研究所 === 103 === In recent years, microgrids developed as an integral to improve power systems and provide an affordable, reliable, and sustainable supply of electricity. Each microgrid is managed as a single controllable entity with respect to the existing power system but demands for joint operation and sharing the benefits between a microgrid and its hosting utility. This thesis focuses on the joint operation of a microgrid and its hosting utility which cooperatively minimizes daily generation costs through energy exchange, and proposes a payment calculation scheme that compensates for power transactions based on a fair allocation of reduced generation costs.
This research assumes that although the utility and the microgrid are operating as interconnected power systems, they have their own generation and loads and are still able to undergo standalone operations. To incentivize generation cost savings that can be realized by a power exchange coalition, we adopt the cooperative game theoretic solution concept of Shapley value and suggest a fair payment calculation scheme for power transactions which requires the evaluation of standalone and joint generation costs.
Our approach first calculates the “as-if” standalone generation cost for both the micro- and the utility grids based on the minimized cost of their individually owned generation units with no power exchange. To calculate the microgrid’s daily generation costs, we formulate its unit commitment (UC) and economic dispatch (ED) as a mixed integer programming problem given a fixed configuration of distributed generation, a renewable energy source and an energy storage and apply a commercial solution package. As for the utility grid’s generation cost, we model it as an aggregated unit, of which the hourly generation cost function for the available generation units over different load levels has been given.
To minimize the generation costs with power exchange between the grids, we then propose an ideally centralized decision model where the generation of the microgrid and its hosting utility are jointly dispatched. By exploiting the standalone and joint generation costs, we calculate joint savings and apply the model of Shapley value to distribute reduced system generation cost between the micro- and utility grids based on their individual marginal cost contributions to the power exchange coalition. To fairly compensate for energy exchange, we calculate the payments for mutual power transactions as the difference of the Shapley values and the actual generation cost of each grid under joint generation.
We design a fictitious interconnection model between the Mueller microgrid in Austin, Texas and the utility grid in Taiwan for case study to share the savings from their coalition through fair payments for energy exchange. Our case study shows that compared to standalone generation, both the micro- and utility grids are better-off when they collaborate in power exchange regardless of their individual contributions to the power exchange coalition. Fair payments for both a summer and winter generation scenario, however, show that joint savings through energy exchange depend on variations in load profiles and ask for different cost reimbursement schemes during summer and winter. To incentivize sharing the savings from energy exchange, we compensate microgrid saving contributions from solar power and distributed generation during summer by utility to microgrid payments, and mutually beneficial energy exports from the utility to the microgrid during winter by microgrid to utility payments.
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