Current-fed quadratic full-bridge converter for PV systems interfacing: Static operation

Interfacing a single photovoltaic (PV) module into either a single-phase or a three-phase inverter requires an interfacing converter with wide conversion range and sufficient dynamic headroom. In terms of avoiding issues with common-mode currents between the PV module and the inverter, a converter with galvanic isolation is preferred. This is especially important with the emerging thin-film modules that have larger cell-to-frame parasitic capacitances compared to traditional modules. This paper presents the current-fed quadratic full-bridge buck converter (CFQFB) for the first time and discusses its steady-state operation. The foundation for the proposed topology is based on the concept of true current-fed converters that differ fundamentally from the conventional voltage-fed converters as will be discussed. The relevant analytical steady-state equations and waveforms are presented first with the operational details of the proposed converter. The analytical claims are verified with extensive measurement results from a corresponding 190-W prototype. According to the measurements, the prototype reached an efficiency of 92% at the maximum power point (MPP) of the PV module.