Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 240-251). Also available via the Internet.

Graduate

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on July 2, 2009. "June 2009." "In partial fulfillment of the requirements for the degree [of] Master of Science in Electrical Engineering." "Presented to the faculty of California Polytechnic State University, San Luis Obispo." Major professor: Taufik, Ph.D. Includes bibliographical references (p. 97-98).

High performance ac-to-dc converters are required to meet the regulation standards to suit wide variety of applications. This thesis presents the steady state analysis, design and operation of high frequency (HF) transformer isolated resonant converters on the single phase utility line as a low harmonic controlled rectifier. Two resonant converter configurations of third order have been studied namely the LCC-type parallel resonant converter also popularly known as series-parallel resonant converter (SPRC) and the hybrid parallel-series resonant converter bridge (HPSRCB). These converters are operated at HF using variable frequency as well as fixed frequency control and they operate in different modes depending on the choice of switching frequency and load. The variable frequency SPRC is operated in discontinuous current mode (DCM), to obtain low line current total harmonic distortion (T.H.D.) and high power factor (pf), without using active control. State space analysis has been presented for one of the predominant circuit modes encountered during its operation in DCM. The various design constraints for operating the resonant converter on the utility line for high pf operation have been stated for different control schemes. In addition, steady state analysis, design optimization carried out for dc-dc converter have been presented. The effect of resonant capacitor ratio on the converter performance characteristics have been studied. SPICE3 simulations and experimental results obtained from a 150 W converter are presented to verify the theory. Continuous current mode (CCM) operation of the SPRC, and its effect on the line current T.H.D. and pf are studied. Both fixed and variable frequency control schemes have been used to control the SPRC. Complex ac circuit analysis method has been considered as the design tool to get the design curves and design of the SPRC operating on the utility line. SPICE3 simulation results for open loop operation and experimental results for both open as well as closed loop operations (active control), for two capacitance ratio's have been presented to verify the converter performance. It is shown that nearly sinusoidal line current operation at unity pf can be obtained with closed loop operation. A HPSRCB has been proposed and operated at very high pf on the utility line as a controlled rectifier. Some of the predominant operating modes of the fixed and variable frequency HPSRCB have been identified. The steady state analysis using state space modeling presented for a dc-to-dc converter has been extended to analyze the ac-to-dc converter. Using the large signal discrete time domain model, the time variation of line current and line pf have been predicted using PROMATLAB for both fixed and variable frequency operations of HPSRCB on the utility line. SPICE3 simulation results without active control and experimental results obtained from the bread board model for both open as well as closed loop fixed and variable frequency operations have been presented to verify the theory and design performance. / Graduate

Two new power conversion techniques, the constant-frequency zero-voltage-switching multiresonant-converter (CF ZVS-MRC) technique and the zero-voltage-switching technique that uses the magnetizing inductance of the power transformer as a resonant element {ZVS {L_M)) are proposed. analyzed, and evaluated for high-frequency applications. In addition, a novel design optimization approach for resonant type converters is introduced. Complete dc analysis of CF forward and half-bridge {HB) ZVS-MRCs are given, and the dc voltage-conversion-ratio characteristics for each of these two converters are derived. Graphic design procedures that maximize the efficiency and minimize current and voltage stresses are established. The design guidelines are verified on a 50 W CF forward ZVS-MRC operating with a switching frequency above 2 MHz, and on a 100 W HB ZVS-MRc operating with a switching frequency of 750 kHz. The ZVS (LM) technique is developed to eliminate the need for a large, inefficient external resonant inductor in ZVS resonant converters. This new family of isolated converters can operate with zero-voltage-switching of the primary active switches only (quasi-resonant (QR) operation) or with soft-switching of all semiconductor devices (multi-resonant (MR) operation). Furthermore, variable and constant frequency operation of all topologies in this new family of dc/dc converters are possible. A complete dc analysis of the HB ZVS-MRC (L_M) is given, and the dc voltage-conversion-ratio characteristics are derived. Design guidelines are defined using the same graphic method employed in the design of CF ZVS-MRCs. Constant frequency implementation of the HB ZVS-MRC (L_M) using controllable saturable inductors is also proposed. Finally, a novel approach to evaluate and design resonant converters based on the minimization of reactive power is developed. / Ph. D.

A steady-state analysis of a Constant-Frequency Parallel-Resonant Converter operating in the Clamped-Mode is performed for the continuous-conduction mode of operation (CCM). Unified closed-form expressions are derived for such circuit characteristics as the control to output, boundary conditions for natural commutation and forced commutation, and stresses on power devices. These characteristics are experimentally verified and simulated by using IO-SPICE. Considerations for practical design are discussed based on hardware operating at 300KHz, with a 300V input, 5V and 300W output. / M.S.

Two constant-frequency resonant power processors are discussed. The parallel resonant converter(PRC) with a controlled output rectifier can provide both forward and reverse power flow. A new control parameter — "θ-angle" is proposed for achieving output regulation and bidirectional power flow of the PRC. The θ-angle, measured as the displacement angle between the firing of the inverter switches and the firing of their corresponding output rectifier switches, provides a control-to-output characteristic independent of load variations and is very easy to implement. Unified closed-form expressions for the steady-state operating conditions are derived. Circuit performances are analyzed through closed-form solutions. Similar analyses are performed for a phase-controlled dual-inverter resonant converter. The feasibility of generating a regulated high-frequency AC bus employing this circuit is investigated. A controlled rectifier and LC filter type of load is used for the circuit to demonstrate the complex interactions between the inverters and the load and the effect of load power factor on the quality of the ac bus voltage. Desired operating regions for input, output, and various control parameters are analytically defined through closed-form solutions such that good quality ac bus voltage can be achieved. / M.S.

The management of parallel and series resonance conditions is important for ensuring that harmonic levels are managed on utility networks, and that shunt compensators are able to operate without constraints for various network conditions (states). For these and similar problems, harmonic impedance assessment of the ac network is required for the design of ac filter or shunt capacitor bank installations. This is particularly important for large installations connected to HV or EHV systems, because resonances at these voltage levels tend to be highly un-damped resulting in potentially damaging voltage and current amplification. The objective of this dissertation was to develop and demonstrate a design methodology which makes use of network impedance assessment methods to provide robust harmonic integration of large shunt compensators into a transmission and HVDC systems. The design methodology has two aspects. The first part considers network modeling, evaluation of different models and simulation of harmonic impedance. In the second part, methods of analyzing and assessing the simulated harmonic impedance are developed. A detailed step-by-step approach was taken in the development of the design methodology. The methodology was documented as a guideline and accompanied by the development of an Excel tool that can be used to assess the simulated harmonic impedance. The Excel tool permits a systematic assessment of the simulated network impedance where shunt compensators are integrated into transmission systems. The tool also ensures that the design of transmission and HVDC ac shunt compensation is optimally robust in terms of harmonic resonances. The theoretical and computational review has been tested and demonstrated on the existing Eskom Transmission system through several case studies. The results have shown the merits of the design methodology. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.