Brad Bryant (Committee Member), Ronald Coutu (Committee Member), Marian Kazimierczuk (Committee Chair), Saiyu Ren (Committee Member), Ray Siferd (Committee Member)
Doctor of Philosophy (PhD)
Pulse-width modulated (PWM) buck-boost converters have a significant role in power electronic systems for renewable energy applications. A new hybrid, the switched-inductor buck-boost converter, is superior to the conventional buck-boost because it uses less energy in the magnetic field, has smaller component size of inductors, and produces less current stresses in the switching elements. Steady-state and dynamic modeling of the switched-inductor buck-boost converter is essential to design and implement of a feed-back network. The objective of this work is to present the steady-state analysis of a PWM switched-inductor buck-boost dc-dc converter operating in continuous conduction mode (CCM). The idealized voltage and current waveforms, and expressions for steady-state operations of the converter are presented. The minimum values to ensure CCM operation for for inductance and capacitance are derived. The filter capacitor and its ESR with the ripple voltage effects are derived. Expressions for power losses and the overall efficiency of the PWM switched-inductor dc-dc buck-boost converter are given. A PWM switched-inductor buck-boost is designed, and a laboratory prototype is built and tested per given specifications. The theoretical and simulated analysis was in accordance with the experimental results. Small-signal modeling of PWM switched-inductor dc-dc buck-boost converter operating in CCM is presented. The averaged large-signal, dc, and time-invariant linear small-signal circuit models of a PWM switched-inductor dc-dc buck-boost converter power stage operating in CCM are presented. The small-signal modeling focuses on the dynamics introduced by the switched-inductor dc-dc buck-boost converter. Using the small-signal model to derive the open-loop power stage transfer functions: the input-to-output voltage, inductor current-to-input voltage, control-to-output voltage, input impedance and output impedance are derived. These transfer functions and their associated theoretical Bode plots are illustrated using MatLab. Using discrete point method, the transfer functions are also verified by circuit simulation. The laboratory prototype experimental validates the small-signal models. The theoretical, simulated and experimental results were in excellent accordance. The effects of the PWM frequency and its effects on the switching elements of the switched-inductor buck-boost converter, the size of inductor and capacitor, and switching losses are presented. Also, studied were the effects of raising the frequency of the PWM to determine the impact on the current and voltage waveforms for the switching elements using saber sketch circuit simulator. The prototype was used to validate the simulated current and voltage waveforms. Another expansion for a PWM switched-inductor buck-boost converter, is explored by deriving the digital open-loop transfer functions: control-to-output voltage, input-to-output voltage, input voltage-to-inductor current, input impedance, and output impedance. The theoretically predicted transfer functions with a step input are theoretically plotted in MatLab, and are in accordance with the experimental step responses.
Department or Program
Ph.D. in Engineering
Year Degree Awarded
Copyright 2012, all rights reserved. This open access ETD is published by Wright State University and OhioLINK.