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The growing awareness for a pollution-free environment coupled with the concern of the limited amount of fossil fuels has triggered an increase in the deployment of renewable energy sources (RES) throughout the globe. Particularly, the share of power converter-based RES such as wind and solar-based power sources has been exponentially increasing in the existing power system. The converter-based RESs are often integrated into the existing grid in the form of a microgrid which may be required to operate autonomously/islanded mode. The inertia of the islanded microgrid is very low and they are more vulnerable to frequency instability in the event of a sudden and large power mismatch. To address this issue, a battery energy storage system (BESS) is considered a suitable option due to various factors such as better reliability, fast response, continuous improvement in battery technology, etc. The presented works in this thesis are dedicated to the development of control methods for efficient operation of BESS, particularly for frequency control in an islanded microgrid. In this direction, this thesis presents two novel control methods for a battery-based modular multi-level converter (MMC), ensuring the required amount of power flow with the grid/microgrid as well as performing SoC balancing among its battery packs (BPs). The proposed methods are verified by experiments on a laboratory prototype of 1kW. Further, to improve the quality of power being drawn from the battery, a novel ripple energy balancing control of a buck-type active power filter is proposed. For fast regulation of frequency in an islanded microgrid, a model-based disturbance controller is proposed which controls the active power of the BESS for power imbalance compensation in the microgrid. For the implementation of this method, a model of frequency dynamics in an islanded microgrid is proposed assuming both synchronous and asynchronous variation of frequency among the synchronous generators. The proposed method is further extended and implemented to a low inertia system with multiple small-scale BESS. The proposed model and the fast frequency control methods are validated using Typhoon real-time simulator.



Battery Energy Storage, Frequency Control, Mixed Microgrids, Sta


Portions of this document appear in: A. Hussain, K. Raj, K. Rajashekara, H. Krishnamoorthy and S. Atcitty, “A Voltage Droop-Based State of Charge Control among Split Batteries in Modular Multilevel Converter for Grid Energy Storage Interface," 2019 IEEE Industry Applications Society Annual Meeting, Baltimore, MD, USA, 2019, pp. 1-14; and in: A. Hussain, K. Raj, K. Rajashekara, H. Krishnamoorthy and S. Atcitty, “Current Controlled Operation of Cascaded H-Bridge Converter for Fast SoC Balancing in Grid Energy Storage," 2019 IEEE Energy Conversion Congress and Exposition (ECCE), Baltimore, MD, USA, 2019, pp. 5373-5379; and in: A. Hussain and W. Shireen, “Instantaneous Ripple Energy Balancing Control to reduce Input Ripple Current in Grid connected BESS," 2021 IEEE Power & Energy Society General Meeting (PESGM), 2021, pp. 01-05; and in: A. Hussain and W. Shireen, “Model for Frequency Dynamics in an Islanded Microgrid and Primary Frequency Control Based on Disturbance Compensation," in IEEE Access, vol. 9, pp. 52784-52795, 2021; and in: A. Hussain, S. Hasan, S. Patil and W. Shireen, “Fast Frequency Regulation in Islanded Microgrid Using Model-Based Load Estimation," in IEEE Transactions on Energy Conversion, vol. 36, no. 4, pp. 3188-3198, Dec. 2021; and in: Hussain, Amir, and Wajiha Shireen. “Grid-Following Mode Operation of Small-Scale Distributed Battery Energy Storages for Fast Frequency Regulation in a Mixed-Source Microgrid." Energies 14.22 (2021): 7710.