Date of Award

May 2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Adel AN Nasiri

Committee Members

Brian BA Armstrong, Jun JZ Zhang, Tian TZ Zhao, Robert RC Cuzner, Necmi NA Altin

Abstract

Inverters play a vital part in microgrid operations and control, boosting system flexibility and efficiency. However, their limited physical inertia makes them vulnerable to network-induced oscillations. Research is primarily focused on addressing this by adding inertia to the inverter side. Earlier analysis of stand-alone microgrids utilized pure inverter-based systems with droop control for power sharing among units, and generators were responsible for voltage and frequency control. Inverter-based systems without communication latency have been studied. However, these studies don't provide a complete dynamic model of microgrids, especially for hybrid microgrids. In this study, a systematic approach is presented to model a hybrid microgrid consisting of one synchronous generator and two inverters operating in two modes. The master inverter is responsible for voltage and frequency control during islanded mode, and setting power values for the generator and slave inverter. It also supports the grid as a voltage source in grid-connected mode. The proposed MG differs from previous studies in its control approach, dynamics, and role of the master inverter for supporting pulse load and communication delay compensation. Power sharing is done via communication, not by droop control, so there's no need to add inertia to the inverter side. The synchronous generator will use an outer droop loop to adjust power based on values from the master inverter, while the slave inverter contributes power based on values received from the master inverter. The dissertation presents a state-space model for analyzing hybrid microgrids (MG) with various dynamic components, including a detailed model of generator, two inverters. The model captures the details of the control loops of the generator and inverters, but not the switching action. The energy storage-based inverter controls voltage and frequency, while the generator and slave inverter receive active and reactive power commands from the master inverter. The model also takes into account the effect of communication delay on the control of the hybrid MG. Each sub model is linearized around an operating point and the resulting system matrix is used to derive the eigenvalues. This dissertation focuses on the study of the transient response of a hybrid MG using eigenvalues to indicate the frequency and damping of oscillatory components in both islanded and grid-connected modes Electrical vehicle charger can serve as an example of a hybrid system based on the mentioned topology. This study can generate a platform to analyze such applications and increase the stability and resilience of the system

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