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Issues in dynamic analysis and design of interconnected DC-DC power supply systems

Research output: Collection of articlesDoctoral Thesis

Details

Original languageEnglish
Place of PublicationTampere
PublisherTampere University of Technology
Number of pages174
ISBN (Electronic)978-952-15-2096-9
ISBN (Print)978-952-15-2056-3
StatePublished - 21 Nov 2008
Publication typeG5 Doctoral dissertation (article)

Publication series

NameTampere University of Technology. Publication
PublisherTampere University of Technology
Volume764
ISSN (Print)1459-2045

Abstract

This thesis studies issues in dynamic analysis and design of interconnected DC-DC power supply systems. The history of the dynamic analysis dates back to the 1970s, when the modeling method for an individual switched-mode converter was introduced. Later on, the methods to analyze stability and performance of interconnected systems have been widely discussed in literature. However, a full understanding of many issues regarding the impedance interactions within the systems still seems to be missing. Therefore, the main objective of the thesis is to show that the minor-loop gain, which is commonly used in the interaction analysis, contains perfect information on the stability of the interconnected system but not necessarily much information on the robustness of the stability and the interactions taken place inside the converters. As a consequence of this, the second objective is to introduce techniques with which the interactions can be reduced or totally removed, thus making the dynamic analysis and design of the systems deterministic. The thesis utilizes two-port networks and the concept of dynamic profile introduced recently in the analyses of converters. Comprehensive formalism is derived to analyze also the effect of output-voltage remote sensing on converter dynamics. Such formalism is not found in literature, although remote sensing is widely used to improve voltage regulation of a converter. The effect of source and load interactions on the converter dynamics are discussed by the general interaction formalisms and the minor-loop gains defined at the input and output of the converter. Peak-current-mode, input-voltage feedforward and output-current feedforward controls are treated in the thesis as an example of the methods with which the interactions can be reduced. It is shown that a converter under peak-current-mode or input-voltage feedforward control can have ideal input-voltage noise attenuation. Dynamically, this means that the converter would be invariant to source interaction and the converter would act as a buffer within a system preventing the interactions from propagating through the converter. It is shown that the output-current feedforward control can improve the load-transient response of the converter. However, the converter can be more prone to source interaction if the implementation of the feedforward is not made for a converter which has high invariance to source interactions. In addition, the ideal reverse current transfer function is introduced to be an important parameter of the dynamic profile defining the ideality of output-voltage feedback or output-current feedforward control. Extensive experimental measurements are provided to support the theoretical findings with conventional buck converters under different control methods and a fourth-order step-down converter known as superbuck under peak-current-mode control.

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