This work presents the modeling and analyses of multiple-output forward converters with weighted voltage control. Based upon the analyses, the systematic design methodologies and design tools are provided. A power stage de model including all the major parasitics, which are detrimental to the output voltages, is derived. A nonlinear programming based design tool is developed to search for the weighting factors. Five methods of stacking secondaries to improve cross-regulation are presented, and the improvement of cross-regulation is quantified. A small-signal model of the multiple-output converters with coupled output filter inductors and weighted voltage control is established. The small-signal characteristics are studied, and the model shows that the system behavior is very sensitive to the coupling coefficient, which has been reported, but never been quantified. The pole-zero interlaced condition is derived. A current-mode control small-signal model is also presented, which can predict all the observed phenomena of current-mode control. Compensator design is discussed for different types of power stage transfer functions for both voltage-mode and current-mode control. / Ph. D.

This dissertation addresses several key issues related to high-frequency soft-switching PWM three-phase power converters. These are: 1. Analysis, synthesis, and design of three-phase soft-switching PWM power converter topologies 2. Design of input EMI filters for three-phase converters 3. Design of microprocessor controllers for three-phase converters. An analysis of existing soft-switching PWM techniques is performed, and two generalized soft-switching PWM converter circuit representations are derived. Based on these representations and common topological properties of three-phase and dc-dc PWM converters, two new procedures for synthesis of three-phase soft-switching PWM converters are derived. The two procedures are used to synthesize five new three-phase soft-switching PWM converter topologies suitable for wide range of applications. A digital signal processor-based controller implementation example is presented. It demonstrates the feasibility of producing versatile, high performance, reliable, low-cost digital controllers for soft-switching PWM three-phase power converters operating at high switching frequencies. A new approach to the design of input filters for ac power electronic circuits is presented here. This approach is based on the application of a vast body of knowledge about passive L-C filters that has existed for many years, but has not been used in power electronics. New passive and active filter pole damping schemes are applied to high-order elliptic filters, resulting in significant filter size reduction compared to the standard filter designs. / Ph. D.

A software program was developed to facilitate the design and analysis of a series resonant converter. Using the program, the values of the inductor and capacitor of the resonant tank can be easily determined to meet design specifications. Following the design, a dc analysis is performed to determine such salient parameters as peak inductor current and peak capacitor voltage. The program is user-friendly with graphic capabilities and is written for the IBM-PC. / Master of Science

The specific circuit effects in the phase-shifted, zero-voltage switched, pulse width modulated (PS-ZVS-PWM) converter and their impact on the converter dynamics are analyzed. The small-signal model is derived incorporating the effects of phase-shift control and the utilization of transformer leakage inductance and power FETs junction capacitances to achieve zero-voltage resonant switching. The thesis explains the differences in the dynamic characteristics of the PS-ZVS-PWM converter and its PWM counterpart. Model predictions are confirmed by experimental measurements. / Master of Science

Two issues pertinent to magamp post regulator are treated in this thesis. One of the issues considered is the operation of a magamp under extreme loading conditions. Practical design equations are derived to allow magamp operation under extreme load conditions such as shutdown of output, foldback of output current and very light load (discontinuous operation). The other issue considered concerns with magamp post regulation for a quasi-resonant converter. A magamp circuit is proposed, designed and tested for a zero current switching quasi-resonant forward converter. It demonstrates that output regulation in a quasi-resonant converter can be achieved with a fixed switching frequency operation. It also demonstrates the feasibility of multiple regulated output application of a quasi-resonant converter. / Master of Science

A novel, zero-current-transition (ZCT) topology of the single-switch three-phase boost PFC rectifier is proposed. The soft transition is achieved with a low-power auxiliary circuit employing an additional switch. The circuit can be used with an IGBT at switching frequencies up to 50. Its operation is analyzed in detail, and design guidelines are provided. The small signal model of the circuit is developed, and voltage mode control is designed. The results are verified on a 4 kW, 50 kHz, experimental ZCT rectifier with an IGBT; total harmonic distortion below 9% and efficiency above 95% were obtained. / Master of Science

The performance of the clamped-mode series resonant converter operating at a fixed frequency is studied for off line applications. A new set of characteristics for the converter operating above and below resonant frequency has been developed by including the effect of losses in the analysis. Based on the analytical results, design guidelines are established and two prototypes were built to operate below and above resonant frequency respectively. The advantages and limitations of the two breadboards are assessed and their major sources of loss identified. / Master of Science

State-plane technique was adopted for analysis of a class of resonant de to de power converters. A comprehensive method was developed to understand the complex operation of a resonant converter, identify its operating modes along with their regions of occurrence and determine the de characteristics of the converter in each mode. The method was shown by application to a series resonant converter (SRC), a parallel resonant converter (PRC) and the family of quasi resonant converters (QRCs). Several major conclusions were experimentally verified. By suitably modifying the method, the effect of parasitic losses on the performance of a SRC was also studied. The operating regions where significant deviations in de characteristics occurred due to losses were also identified. In addition, from the mode and de analysis of a PRC, a novel resonant buck converter with de gain almost insensitive to load variations was proposed. Generalized mode and de analysis applicable to all QRC topological variations were performed using state-plane diagrams. Four sets of mode and de analyses were shown to be adequate to characterize the steady-state operation of nearly a hundred QRC variations. This simplified the understanding and analysis of these converters. Also, two simple circuit rules were introduced using which several QRC topological variations were generated and evaluated based on relative component stresses. The state-plane technique was also used to understand and evaluate different control methods of a SRC. The occurrence of large, undesirable tank energy surges with analog-signal-to-discrete-time-interval-converter (ASDTIC) control was investigated and explained using state-plane trajectories. A new control method called #optimal trajectory control*, which attempts to achieve the fastest response possible was proposed. By exploiting the structure of SRC state portrait, the tank energy is always kept within bounds with this control. Experimental implementation was discussed in detail along with experimental oscillograms which confirm the predicted fast response. / Ph. D.

Master of Science

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.