Power electronics technology has been widely used in electric power system to achieve high energy efficiency and high renewable energy
penetration. Small signal instability phenomena could easily occur in systems with abundant power electronics because of high order passive
elements and controller interactions among power converters. These instability issues degrade power quality or even cause system failure.
Therefore it is necessary to build accurate small signal models for stability analysis and develop effective resonance mitigation techniques
for stability improvement. The general stability analysis methods including eigenvalues-based method, component connection method,
passivity-based method and impedance-based method have been evaluated and summarized. The impedance-based method is selected as the stability
analysis tool for this research due to its advantages compared to other methods. Besides, three popular resonance suppression techniques,
i.e. passive damper, active damper and virtual impedance control, are also studied and evaluated. The virtual impedance control is of
interest because it does not reduce system efficiency or reliability compared to both the passive and active damper. A unified
impedance-based stability criterion (UIBSC) has been proposed for paralleled grid-tied inverters. Compared to the traditional IBSC which
evaluates all minor loop gains (MLGs) of individual inverter, the UIBSC assesses the derived global minor loop gain (GMLG) only once to
determine system stability. As a result, the computation efforts can be significantly reduced when system contains a large number of
inverters. In addition, a stability-oriented design guideline has been derived for the paralleled grid-tied inverters based on the GMLG. By
using the guideline, the grid impedance, inverter filter parameters, time delays of digital control and control parameters can be analyzed or
designed to meet the system stability requirement. The small signal stability of the FREEDM system is a critical issue due to the abundant
power electronics devices and flexible control strategies. The impedance modeling methods for current controlled inverters, inverter stage of
the SST, DAB converters are developed. The influences of control schemes on power converter terminal behaviors are analyzed as well.
Stability criteria for several types of grid enabled by the SST are derived. The bidirectional power flow effect is also considered. These
instability phenomena are demonstrated in ac, dc, and hybrid ac/dc grids of FREEDM system using HIL test bed. Finally, the conclusions are
given and the scope of future work is discussed. / A Dissertation submitted to the Department of Electrical and Computer Engineering in partial fulfillment of
the requirements for the degree of Doctor of Philosophy. / Fall Semester 2017. / September 7, 2017. / FREEDM system, harmonics, instability mitigation, paralleled inverters, power converter interraction, stability
criterion / Includes bibliographical references. / Hui Li, Professor Directing Dissertation; Emmanuel G. Collins, University Representative; Mischa
Steurer, Committee Member; Ming Yu, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_605039 |
| Contributors | Ye, Qing (author), Li, Hui, 1970- (professor directing dissertation), Collins, E. (Emmanuel) (university representative), Steurer, Mischa (committee member), Yu, Ming (committee member), Florida State University (degree granting institution), College of Engineering (degree granting college), Department of Electrical and Computer Engineering (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (137 pages), computer, application/pdf |
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