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Access Type

WSU Access

Date of Award

January 2019

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Electrical and Computer Engineering

First Advisor

Le Y. Wang

Abstract

The work developed new control strategies to address fundamental issues of power balance, line loss reduction, and voltage profile management in DC microgrids. In microgrids of distributed renewable generations and controllable loads, load allocation to different distributed generators, line losses, voltage stability and quality are intimately coupled, departing significantly from traditional power grids in which economic dispatch and voltage stability are typically separate control tasks.

In this work, a multi-objective optimization strategy is introduced to address the challenges imposed by these coupled issues. Global optimal solutions are derived. Recursive optimization algorithms for distributed control strategies are introduced and shown to converge to the global optima. Case studies using DC-powered trolleybus systems are conducted to evaluate the algorithms, showcasing their convergence, ability to function under scalable networks, and robustness to load perturbations.

Finally, the work develops optimal control strategies for the management of DC microgrids including subsystem dynamics. The inclusion of subsystem dynamics accounts for many real systems, especially converter dynamics, impacts performance significantly, and complicates system analysis. A comparison to the trolley bus system without the inclusion of subsystem dynamics was part of the case studies. Additionally, case studies covering the effect of controllers and dynamics of the DC-DC converter are conducted to evaluate the modified algorithm. Sampling interval and step size effects on the system's behavior were also discussed.

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