DC-DC high-order converters for renewable applications

Abstract

This dissertation develops new theory and techniques for DC-DC power converters interfacing renewable energies, specifically for converters classified as high-order based on their mathematical model, and thus generally more complex and difficult to analyze. The thesis encompasses the development of a new circuit topology, a control design focused on high-order dynamic systems, and the study of conversion systems between renewables and the utility grid. The dynamics of high-order converters present challenges for the stability and synthesis of controllers. By studying the nonlinear model of fourth-order non-minimum phase converters through zero dynamics, it has been established that some of these can attain stability under direct voltage at high regulation, in contrast to second-order converters. Controllers have been designed to take advantage of these results in order to remove the current sensing stage while still achieving high bandwidth voltage regulation. Research has also been conducted into creating novel DC converters with a lower component size than similar circuits. From this, an improved super-boost converter has been developed that requires lower energy storage on its capacitors and inductors than the traditional boost and fourth-order boost converters, for a given specification of input current and output voltage ripples. Additionally, an inverter system for a fuel cell stack has been developed using double-dual converters in cascade to increase the voltage gain and power handling of the system. Results from tests at different power and voltage levels show that the proposed system also achieves reduced switch voltage stresses and reduced output current ripples. Simulation and experimental results were obtained in order to validate the theoretical analysis. Mathematical models, steady state values and stability conditions were calculated, and prototype designs were developed to corroborate the performance of the converters, control and efficiency.