Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Department

Electrical Engineering

First Advisor

David A Jr Wetz

Abstract

Microgrids have proliferated the landscape of the world’s power systems as distributed energy generation, energy storage, and evolving electrical loads become more abundant. Microgrids offer many advantages to the end user of electrical power over traditional power distribution networks that rely on exceedingly large rotating machines producing power for a large group of electrical loads over long physical distances. Microgrids provide a unique benefit to smaller electrical networks that may be isolated, may have unique electrical loads, or may have a network of energy storage devices that can be utilized to serve the microgrid in particular operational scenarios. With the continual improvement and development of power electronic converters at the electrical grid level, new distribution topologies, such as medium voltage DC distribution, have been proposed for isolated microgrids that provide advantages to reliability, redundancy, and integrability. Since rotating machines are essential as reliable sources of power generation for isolated microgrids, it is necessary to convert the AC power they produce into DC power for distribution across the DC microgrid. While rectifier circuits that convert AC power into DC power are well understood for individual converter and steady-state industrial applications, the DC microgrid provides a unique set of circumstances that needs to be better understood before designing converters for DC microgrid applications. While traditional modeling and simulation can provide a good check on theoretical design, power hardware-in-the-loop emulation can extend these advantages by interfacing the rectifier models with hardware loads. While power hardware-in-the-loop has been verified as a legitimate tool, there is a lack of concrete data on the efficacy of power hardware-in-the-loop at medium voltage and medium power levels. Initially, rectifier models are developed for a real-time simulator for use in power hardware-in-the-loop applications. It is shown that at standard rotating machine frequencies the limiting factor in terms of developing valid models is modeling imbalances in the magnetic elements inherent to multi-pulse rectifier circuits. A novel, data-based approach is used to approximate unbalanced transformer saturation, circumventing an inherent limitation of the real-time simulator. These more accurate models are validated against hardware over a wide range of rectifier operation. The validated rectifier models are used to emulate a real rectifier system by utilizing the real-time simulator and a high slew-rate power supply, and then are then compared to data from the low-voltage and low-power hardware testbed. It is then quantifiably shown that the power hardware-in-the-loop system is a valid representation of the low voltage hardware testbed. Finally, a medium voltage rectifier system is modeled and implemented in power hardware-in-the-loop with a state-of-the-art medium voltage power supply. The results of the medium voltage rectifier emulation are presented and quantifiably validated. This work concludes by commenting on difficulties encountered in real-time simulation as well as the viability of particular power hardware-in-the-loop applications once voltage and power are scaled up to unprecedented levels.

Keywords

Multi-pulse rectifiers, Real-time simulation, Power hardware-in-the-loop, Medium-voltage, Power quality, Power electronics

Disciplines

Electrical and Computer Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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