Decoding and Synthesizing Transformerless PWM Converters

Pulse-width-modulated (PWM) converters have been widely applied for power processing, and they are typically the stems of other types of converters, such as quasi-resonant, Z-source, and switched-inductor hybrid converters. Development of PWM converters has been spanning over a century, starting from the buck converter. The well-known PWM converters include buck, boost, buck-boost, Ćuk, single ended primary inductive converter (SEPIC), zeta, Z-source, quasi-Z source, etc. Many attempts have been proposed to develop these converters based mostly on canonical cell concepts and by introducing extra LC filters to the cells. This paper presents an enhancement to the layer and graft schemes by introducing the ideas of dc voltage/current offsetting, capacitor/inductor component splitting, diode grafting, and inverse operation of PWM converters. The PWM converters, which can be operated in continuous conduction mode (CCM) or discontinuous conduction mode (DCM), therefore can be synthesized systematically according to decoded transfer gains. Decoding and synthesizing PWM converters uniquely bridge transfer gains to converter topologies and provide readers a comprehensive understanding of PWM-converter evolution from the original converter, the buck converter. Additionally, in this paper, the Ćuk, SEPIC, and zeta converters all with the same transfer gain of D/(1 - D) are proved to be equivalent to the buck-boost converter with an extra LC filter. For further illustrating the proposed approaches, various types of Z-source converters, switched-capacitor/switched-inductor hybrid converters, and a single-stage interleaved converter are reviewed, and new PWM converters are developed.