Soft-Switching Cells
研 究 生：洪金泉 Student: Jin-Chyuan Hung
指導教授：吳財福 博士 Advisor: Tsai-Fu Wu, Ph. D.
國立中正大學工學院 電機工程研究所
博士論文
A Dissertation Submitted to Institute of Electrical Engineering
College of Engineering National Chung Cheng University
in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy in Electrical Engineering
January 2005
Chiayi, Taiwan, Republic of China
ABSTRACT
Due to their simplicity and low steady-state component stress, pulse width modulated
(PWM) converters are broadly used in various power-conversion applications. However, they
have some drawbacks, such as high stress and high loss at switching transition, which will
limit their operation at high frequency. Soft-switching methods are thus used to reduce the
stress and loss.
A family of soft-switching cells (SSCs) for non-isolated and isolated PWM converters is introduced. These cells are derived from the quasi-square-wave converters (QSWCs), in which zero-voltage switching is an inherent feature. A selected SSC and a hard-switching PWM converter are combined by the synthesis process achieving that the PWM converter maintains the power process while the SSC performs the active-clamp function. The PWM converter with the SSC, clamping action and soft-switching feature in both main and auxiliary switches can be achieved. In this dissertation, synthesis process is proposed to unify some of the published soft-switching PWM converters. Based on the proposed synthesis process, families of new converter topologies can be systematically generated.
By introducing SSCs to the conventional single-stage power factor corrector (PFCs), the soft-switching features can be achieved and the energy trapped in the leakage inductor can be also recovered. For reducing input current ripple, two interleaving methods are proposed. Additionally, input power factor and total harmonics distortion of the PFCs with SSCs can be further improved by using an asymmetrical PWM manner.
By introducing SSCs to the coupled-inductor converters and push-pull converters, the
soft-switching features can be achieved and the energy trapped in leakage inductor can be also
recovered. Experimental results have shown that surge voltage can be suppressed effectively.
With the coupled inductors, active switches in the converters can sustain proper duty cycles
while operated with high step-up and/or high step-down voltage ratio, reducing component
stress significantly. Thus, the conversion efficiency of the converters is improved significantly.
In the push-pull converter, SSCs are used to eliminate potential flux imbalance existing in the
conventional push-pull converter which makes the converter more viable. In addition, all of
the proposed converters can be regulated with an asymmetrical PWM control, reducing cost and complexity.
Finally, based on the operational principles, detailed analysis, design procedures,
implementations and discussions of soft-switching PWM converters are presented. The
measured results have verified the feasibility of the discussed soft-switching converters.
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