As greenhouse gases produced from the conventional power plant causes global climate change, using renewable energy sources (RESs) in the future power system is inevitable. To minimize greenhouse gases emission, the interest in renewable grid or micro-grid is growing nowadays. In the microgrid, especially in AC microgrids, converters play an important role in many areas, including microgrid integration, uninterrupted power supply, and flexible alternating current transmission systems. Inverter plays an essential role in grid integration because it serves the interface between the energy source and the power grid. The important aspect of the inverter is control. This thesis studies several control strategies for the microgrid in both islanded and grid-connected modes while considering the intermittency of demand power and RESs. Generally, there are two types of control strategies: centralized control, the other is decentralized control. Decentralize control schemes are robust compare to other control systems and require low bandwidth e.g., only the nearest neighbor information is required. Droop control, one of the conventional decentralized control, is a well-established technique used extensively in power systems ever since synchronous generators were utilized. Since the features between the synchronous generator and the inverter are different, e.g., the inertia of the inverter is low, the traditional droop control needs to be modified in controlling the inverter. In this thesis, to eliminate the traditional droop tradeoff between power-sharing and grid voltage, we introduce virtual droop control. In case of transmission impedance mismatch between DG inverter, we use a large virtual resistance in both inverters to match the transmission impedance. The virtual impedance control is implemented and validated in MATLAB/Simulink and experiment. In this thesis, a microgrid consists of several units are selected for testing In conventional droop control, we observe a phase shift between inverter current which causes the circulation current inside the grid. But by using virtual droop control, this circulation current is minimized as well as we obtain a proper power-sharing among DG’ inverter.
Date of Degree
Master of Science (MS)
Electrical and Computer Engineering and Technology
Science, Engineering and Technology
Mishan, R. (2020). Virtual impedance based decentralized control for a microgrid system [Master’s thesis, Minnesota State University, Mankato]. Cornerstone: A Collection of Scholarly and Creative Works for Minnesota State University, Mankato. https://cornerstone.lib.mnsu.edu/etds/1083
Final Presentation December 7, 2020
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Available for download on Wednesday, August 18, 2021