Doctor of Philosophy

dissertationMicroelectromechanical systems (MEMS) resonators on Si have the potential to replace the discrete passive components in a power converter. The main intention of this dissertation is to present a ring-shaped aluminum nitride (AlN) piezoelectric microreson

Design of Piezoelectric Transformers for Power Converters by Means of Analytical and Numerical Methods

Piezoelectric transformers (PTs) provide several advantages compared to magnetic components, which are higher power density, lower radiated noise, and higher voltage isolation capability. PT must be properly designed to benefit the power converter with the aforementioned advantages. Analytical models are widely used for PT design in order to validate it before constructing the prototype. In this paper, the additional usefulness of finite element analysis (FEA) for PT design is shown. With FEA, it is possible to optimize the PT design not only by maximizing the energy transference but also by cleaning the working frequency range of spurious modes (geometrical 2D/3D effects). Moreover, FEA tools allow the study of other main aspects of the PT design such as manufacturing tolerances or the influence of the fixing layer on PT performance (which is a critical design point). A method for modeling and designing PTs is proposed, combining analytical 1D models and FEA results. The proposed method is validated with measurements of a PT design for a 10-W ac/dc converter prototype for mobile phone battery charger

Piezoelectric Transformer Integration Possibility in High Power Density Applications

The contents of this work investigate the capability of integrating the PT in applications by invoking the ratio of the throughput power to volume represented by the term: power density. The fundamentals of the PT are introduced in chapter two. In chapter three, the fundamental limitations of the PT's capability of transferring power to the load are studied. There are three major limitations: temperature rise due to losses during operation, electromechanical limits of material, and interactions with output rectifier. The analysis and estimation are then verified by experiments and calculations implemented on three different PT samples fabricated from three different manufacturers. The subject of chapter four is the behavior of the PT's power amplifier. This chapter concentrates on two main amplifier topologies, optimized based on the simplicity of structure and minimization of components (passive and active): class D and class E amplifiers. The operational characteristics of these amplifiers with the PT are then comparison. Methods to track the optimum frequency and discontinuous working mode of the PT are proposed as the approaches to improve the energy transfer of the PT. In chapter five, prototypes of four devices using a PT are developed and introduced as illustrations of the integration of PTs into practical applications: an igniter for high intensity discharge (HID) lamps, high DC voltage power supplies, and electronic ballasts for LEDs, and stand-alone ionizers for food sterilizers. Some concluding statements and ideas for future works are located in the last chapter - chapter six

Self-Excited Single-Stage Power Factor Correction Driving Circuit for LED Lighting

This pa per proposes a self-excited single-stage high power factor LED lighting driving circuit. Being featured with power factor correction capability without needing any control devices, the proposed circuit structure is with low cost and suitable for commercial production. The power factor correction function is accomplished by using inductor in combination with a half-bridge quasi resonant converter to achieve active switching and yield out voltage regulation according to load requirement. Furthermore, the zero-voltage switching in the half-bridge converter can be attained to promote the overall performance efficiency of the proposed circuit. Finally, the validity and production availability of the proposed circuit will be verified as well

Critical Design Criterion for Achieving Zero Voltage Switching in Inductorless Half-Bridge-Driven Piezoelectric-Transformer-Based Power Supplies

A methodology for predicting the ability of inductor-less driven piezoelectric transformer (PT) based power supplies to achieve zero voltage switching (ZVS) is presented. A describing function approach is used to derive an equivalent circuit model of the PT operating in the vicinity of ZVS and the subsequent application of the model provides a quantitative measure of a PT's ability to achieve ZVS when driven by an inductor-less half-bridge inverter. Through detailed analysis of the analytical model, the limitations of the inductor-less half-bridge driven PT are exposed from which guidelines for designing both the PT and inverter are derived