Authors: SARA NOUROLLAH, ABOLFAZL PIRAYESH, MATTHIAS FRIPP
Abstract: The use of renewable energies, such as wind and solar, is rising in microgrids. However, because of their intermittent nature, achieving a stable system in spite of the fluctuations of generation and demand is very difficult. Aiming to increase the stability margin of AC islanded microgrids comprising nondeterministic resources, properly share real power (P), and keep the network frequency ($f)$ at nominal value, this study exploits the presence of energy storage units (ESUs) along with a load-shedding scheme. To this end, this study proposes a multitier decentralized control strategy that is based on frequency and includes three control schemes, distributed generation unit (DGU) control, ESU control, and local loads control (LLC). These controllers operate simultaneously. The DGU controller shares the loads among DGUs in accordance with the frequency droop method. On the other hand, the ESU controller controls the production of ESUs and also the LLCs manage the loads and dump-load of the microgrid. This method ensures the proper operation of AC microgrids that comprise intermittent resources under stand-alone conditions and despite numerous events. The time responses of P and $f$ prove the high performance of the method. The simulations are performed and coded in m-file of MATLAB.
Keywords: Energy storage unit, inverter-based microgrid, load management, multitier control scheme, nondeterministic resource
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