Buck-Boost DC-AC Converters Suitable for Renewable Applications

The operational limitations of the voltage and current transfer ratios are inherent to conventional current source converters (CSCs) and voltage source converters (VSCs), which prompts the multiple-stage power conversion solution for applications that demand a wide voltage or current transfer ratio. In response to the undesired characteristics of the multiple-stage solution, such as augmented component count and the resulting higher cost and reduced reliability and efficiency, Z-source converters (ZSCs) have been proposed as a viable single-stage solution alternative to the solution of cascading multiple converters in series. In spite of the wide operating range featured by ZSCs, a fourth-order symmetrical lattice network constituting the DC link of existing ZSCs introduces additional design complexities, which hinders a broad adoption of the Z-source converter. This paper presents a unified framework for topological development of a family of power converters that are capable of operating over an expanded operating range that is comparable to the existing Z-source inverters. With a notable difference, the resultant topologies contrast existing ZSCs with significantly reduced complexity, in particular, the considerably reduced order of passive components. The reduced complexity renders the proposed topologies most suitable for applications that demand high efficiency, reliability and cost effectiveness. Renewable energy is one of the specifically targeted application areas. Index Words: dynamic stiffness, pulse width modulation, static stiffness, Z-source converter