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No description available.

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No description available.

There is ever-increasing demand in telecommunication system, data server and computer equipment for low voltage, high current power supply. LLC resonant converter is a good topology on primary side of the converter because it has soft switching and resonant conversion. However, the passive rectifier in the secondary side has high power dissipation. Synchronous rectifier is a popular method to reduce this rectification loss. Although there are many types of synchronous rectifier for PWM converter, most of them do not function well in LLC resonant converters. It is because the wave form of LLC resonant converter is different from PWM. The objective of this research is to reduce the power dissipation and physical size at the same time. In this thesis, a novel current driven synchronous rectifier with saturable current transformer and dynamic gate voltage control for LLC resonant Converter is presented. This novel circuit reduces the rectification loss and size of the current transformer in the synchronous rectifier. This synchronous rectifier has several outstanding characteristics compared with generic voltage driven and current driven synchronous rectifier. The saturable feature reduces the current transformer turns. Inherent dynamic gate voltage controlled by saturable current transformer reduces gate loss in the MOSFET. A novel driving circuit is proposed for accurate turn off time. It reduces loss significantly. This synchronous rectifier is completely self-contained which can replace the rectifier diode as a drop in replacement. It is insensitive to parasitic inductance. In order to explain the current transformer saturable, a model of saturable current transformer is proposed. A prototype demonstrates the advantages of the proposed current driven synchronous rectifier. Furthermore, a novel integrated synchronous rectifier is presented which provides a more compact system. The synchronous rectifier current transformer is integrated with the main transformer which reduces the number of circuit joints in power path. Each soldering joint generates significance loss in power converter. A pair of 0.5mΩ soldering joint in 25A current path produces 0.62W loss. The placement of the integrated current transformer is important. A criterion for the placement of the current transformer within the main transformer is to avoid interference to the current transformer from the magnetic flux of the main transformer. Thus, a placement method to integrate the current transformer into the main transformer is proposed. An integrated current transformer model is suggested to explain the operation of the integrated synchronous rectifier. A prototype demonstrates the advantages of the integrated synchronous rectifier. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 12, 2008) Includes bibliographical references (p. 102-107).

Thesis (Ph.D.) - University of Queensland, 2006. / Includes graphs in back pocket. Includes bibliography.

The integrated high-quality rectifier-regulators [1] are not practical for universal input voltage and wide load range applications because of high bulk-capacitor voltage stress at lighter loads. This load-dependent characteristic of the bulk-capacitor voltage is due to the integration of a discontinuous conduction mode boost converter and a continuous conduction mode dc-dc converter. In addition, this power factor correction technique suffers from a high-voltage spike on the switch at turn-off. In this thesis, variable frequency control, swinging choke, and low loss LC snubber techniques are proposed to alleviate these problems. Finally, several experimental converters with different specifications are evaluated with respect to efficiency and ability to meet the IEC555-2 standards. / Master of Science

Approved for public release; distribution is unlimited / The main focus in the design of the next generation combatant, DD(X), is the US Navy's proposed Integrated Power System (IPS) which includes an all-electric propulsion drive system. The reduction of current waveform harmonics is critical in combatant propulsion systems such as the IPS. One method of reducing the current harmonics is to utilize a multilevel converter topology. The multi-level converter, as compared to a standard converter, features low dv/dt losses and low switching losses. This thesis examines the design, construction and testing of two multi-level converters operated in tandem, called a Cascaded Multi-Level Converter (CMLC). A digital logic switching circuit is designed and constructed to control the CMLC during the operational testing phase. The CMLC is demonstrated in a three-phase high-voltage configuration with 178.5 V zero-to-peak voltage, 2.10 A zero-to-peak current achieved using an R-L load. / Lieutenant Commander, United States Navy

M.Phil. (Electrical and Electronic Engineering) / There are two methods that can be used when power is converted from one frequency to another. One way uses a DC link as an intermediate stage and the other uses no intermediate stage. When no DC link exists, the conversion process is referred to as AC-AC conversion, (Cha, Enjeti & Ratanapanachote, 2004:2237). This method essentially chops the AC signal in a specific manner which yields an AC signal with a different frequency directly. Depending on how the AC signal is chopped, it would result in a varied number of wave shapes are constructed. The construction of these various wave shapes results in devices that can accomplish different tasks. One such device is called a unity displacement factor frequency converter (UDFFC). This research attempts to develop a model, to simulate and design a unity displacement factor frequency converter. The primary idea about this device is that the power factor or displacement factor is unity regardless of the load. There are three parts in the development of the UDFFC. The power circuit is an array or matrix of switches that link the three phase supply to the three phase load. The power circuit is interfaced to the control circuit which generates pulses that control the matrix of switches. The control circuit utilizes embedded control software that performs the control logic in a microcontroller. The development of the UDFFC has a potential to solve real power engineering problems, such as eliminating the DC link in a converter. This achieves the conversion of AC directly to AC in the absence of a DC link. The other major advantage is the variation of the output frequency to a desired value. The most important is that the displacement factor can be controlled as well.