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Date of Award


Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Gordon G. Parker

Advisor 2

Rush D. Robinett III

Committee Member 1

Wayne W. Weaver

Committee Member 2

Steven Y. Goldsmith


The primary goal of the research presented in this dissertation is the development of a decentralized control method for both dc and ac inverter islanded microgrids with high penetration of stochastic renewable sources that is an effective alternative to a centralized, optimal solution. One of the contributions of this work is the development of the Decentralized Mode Adaptive (DMA) guidance law for a Hamiltonian-based controller of an islanded, N-source, dc microgrid. The DMA guidance law reduces the gap between droop control and centralized control by providing a method that can operate autonomously in the event of source and bus load fluctuations as well as reduce communication requirements of centralized controllers, and thus increase resiliency and scalability. This is a significant trait, as stochastic renewable sources are prone to sizable fluctuations or even suddenly dropping offline. The high penetration of stochastic renewable sources mandates controls that can handle such swings. The proposed DMA guidance law is compared to the centrally-controlled optimal exergy destruction (OXD) power apportionment strategy, as well as a Hamiltonian-based droop control strategy. After adding a guidance law to the Hamiltonian-based droop controller to allow it to handle the removal of a source, both the DMA and droop controller can maintain a constant bus voltage. The DMA guidance law makes an improvement over droop control in that it is able to track OXD steady state performance when droop control cannot. Finally, it is shown that for a sufficiently large number of converters supplying a microgrid, the presented decentralized, mode-adaptive strategy provides an efficient and practical alternative to both droop control and centralized control schemes.

Another contribution of this work is development of the Optimal Exergy Destruction (OXD) and Decentralized Power Apportionment (DPA) feedforward control law for a Hamiltonian-based controller for islanded, N-source ac inverter microgrids. The importance of the OXD guidance law is that it is an analytical, closed-loop optimal feedforward controller that was developed utilizing exergy analysis to minimize the exergy destruction in the microgrid. As in the dc microgrid case, the OXD outer loop controller requires a star or fully connected topology whereas the DPA operates with no communication among the inverters. The decentralized power apportionment feedforward controller eliminates some critical drawbacks to conventional P-ω/Q-V droop control. Unlike conventional P-ω/Q-V droop control, the DPA control scheme holds the bus frequency constant and is able to return the bus voltage to the reference value after large load or source swings. Additionally, the proposed decentralized power apportionment control method takes advantage of distributed storage assets necessary for the material integration of stochastic renewable sources. Furthermore, the DPA control scheme can track near OXD performance without communication among the inverters, making it an efficient and practical alternative to both conventional P-ω/Q-V droop control and centralized control schemes.