Date of Graduation

12-2018

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Degree Level

Graduate

Department

Electrical Engineering

Advisor

Juan C. Balda

Committee Member

Roy A. McCann

Second Committee Member

Simon Ang

Keywords

Distributed Energy Resources, Grid-connected Converters, High Power, Microgrids, Scaled-down Prototype, Stability Analysis

Abstract

The objective of this thesis is to perform the modeling and stability analysis of a high-power microgrid with multiple parallel-and grid connected voltage source converters using the system parameters from the high-power microgrid testbed at the National Center for Reliable Electric Power Transmission (NCREPT) at the University of Arkansas in order to identify, minimize, if not eliminate, the potential instabilities that can affect the proper operation of the microgrid testbed. To achieve this objective, the mathematical modeling of the high-power microgrid considering the adverse effects of resonances due to interactions among the converter LCL output filters is presented and analyzed. Moreover, the stability range of the high-power microgrid under different conditions is examined using the root locus analysis technique and the theoretical analysis is validated through MATLAB/SimulinkTM simulations. The results from this analysis are then used to develop general guidelines to avoid resonance and stability issues when connecting power converters into a microgrid.

In addition, a scaled-down prototype of the high-power microgrid testbed at NCREPT, the so-called “mini-NCREPT”, is designed and constructed to reproduce some of the issues already encounter in the high-power tested and to developed countermeasures in a laboratory environment without the safety restrictions typical of high-power applications. Furthermore, this scaled-down prototype can be used in future applications to test advanced microgrid control algorithms before deploying them at the high-power microgrid testbed. Finally, an in-depth analysis of the experimental results of the scaled-down prototype is presented and solutions to improve the power quality of the system are suggested.

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