Microgrid Expansion Planning

Among different categories of microgrids, i.e. AC, DC, and hybrid, extensive research has been conducted on operations and control of AC microgrids. DC microgrids could, however, offer several advantages compared to AC microgrids by providing a more efficient supply of DC loads, reducing losses due to the reduction of multiple converters used for DC loads, allowing easier integration of DC DERs, and eliminating the need for synchronizing generators. In this chapter, different components of AC, DC, and hybrid AC/DC microgrids were explained, followed by developing a microgrid planning model for determining the optimal size and the generation mix of distributed energy resources (DERs) as well as the microgrid type, i.e. AC or DC. Considering the growing ratio of DC loads and DERs, DC microgrids can be potentially more beneficial than AC microgrids by avoiding the need to synchronize generators, reducing the use of converters, facilitating the connection of various types of DERs and loads to the microgrid common bus with simplified interfaces, and reducing losses associated with the AC–DC energy conversion. The problem objective was to minimize the total planning cost subject to prevailing planning and operational constraints and was formulated using mixed‐integer programming (MIP). The microgrid type is selected based on economic considerations, where the planning objective includes the investment and operations costs of DERs, cost of energy purchase from the main grid, and the reliability cost. It was shown that the proposed model can effectively identify threshold ratios of DC loads, which made the DC microgrid a more economically viable solution than the AC microgrid. In other words, for ratios smaller than the threshold ratio, AC microgrid would be more economical, and for ratios larger than that, DC microgrid would be more economical. A set of case studies was presented to analyze the impact of the ratio of DC loads, the ratio of critical loads, converters' efficiency, and market price on microgrid planning solutions. It was verified that the decisive factor in determining the type of microgrid would be the ratio of DC loads. In other words, if other parameters changed except for the ratio of DC loads, the type of the microgrid would not change. It was also shown that increasing the ratio of critical loads would increase the total installed dispatchable generation capacity. Finally, it was demonstrated that changing critical loads, converters’ efficiency, or the market price would significantly affect the operations and reliability costs. Our case studies demonstrate the effectiveness of the proposed model and investigate in detail the impact of a variety of factors on planning results, including the ratio of critical loads, the ratio of DC loads, and the efficiency of inverters and converters.