Step up PWM DC - DC converters based on quasi Z-source and quadratic boost converter

Abstract

Step-up DC-DC converters are having increasing demand because of its applications in photovoltaic (PV) power generation, fuel cell based energy conversion, uninterrupted power supplies (UPS) and battery powered equipment. In general, a conventional boost converter can be adopted to provide a high step-up voltage gain with a large duty ratio. However, the conversion efficiency and the step-up voltage gain are limited due to the constraints of the losses of power switches and diodes, the equivalent series resistance of inductors and capacitors, and the reverse-recovery problem of diodes. Therefore, a step-up converter with a low duty ratio to achieve high efficiency and high voltage gain is very important for these applications. In order to improve the conversion efficiency at low power, non-isolated converters are preferred for these high step-up applications. Among non-isolated topologies reported in literature for step up applications, Z-source converter and Quasi Z-source converter topologies are comparatively new with many desirable features.The work in the thesis focuses on study and development of new configurations based on Quasi Z-source DC-DC converters and quadratic boost converter for high step-up applications. Fourth order step up converter based on quasi Z-source converter is presented with its small signal mode and controller design in second chapter of thesis. The fourth-order converter poses many desirable features. Proposed converter’s design equations are established and same are validated through laboratory prototypes. The work also focuses on control of these converters, One Cycle Control technique is used for controlling output voltage of Z-source and quasi Z-source based converters. Further, tapped-inductor and coupled-inductor variations of QZS based fourth order DC-DC converter are proposed. Tapped-inductor is utilized for voltage gain enhancement of fourth-order converter. In tapped-inductor based configuration voltage gain of the converter is depend upon duty ratio and turns ratio. Voltage gain expressions for ideal and non-ideal tapped-inductor based converter is derived and experimentally verified. The main aim of coupled-inductor based converter is to reduce input current ripple offourth order quasi z-source converter. Theoretical analysis of current ripple in coupled inductor is presented and also verified using simulation and hardware results. A high step up converter based on fourth order quasi Z-source converter and boost converter is derived. Performance of non-ideal converter is theoretically analyze and demonstrated. Small signal model of the converter is utilized for controller design of high step up converter. Two converter configurations based on quadratic boost converter and tapped-inductor are introduced in sixth chapter of thesis. Performance of both converters for different load resistance and for different combination of turns ratio is studied.