Novel Bidirectional Three-Switch Single-Stage Single-Phase AC–DC Buck-Boost Converter With Ground-Referenced Output

DC loads or sources like motor drives, batteries, and strings of photovoltaic (PV) panels with power levels up to the lower single-digit kilowatt range are typically connected to the single-phase mains using bidirectional ac-dc converters providing power factor correction (PFC) functionality. Often, a dc output voltage range spanning from values lower than to values greater than the grid voltage amplitude is required, and hence, the ac-dc converter must provide buck-boost capability. As an alternative to conventionally used two-stage systems, single-stage converters promise lower realization effort and, in particular, fewer active components like power transistors. This article, therefore, analyzes a new bidirectional single-stage single-phase ac-dc buck-boost converter with only three power transistors, whose topology is identified using a systematic approach that is briefly summarized. Advantageously, the new ac-dc converter’s negative dc output terminal is connected to the mains neutral, i.e., there is no common-mode (CM) voltage at the dc output. The operating principle is explained in detail, and a new advanced modulation method is proposed, which reduces the switching losses by more than 33% and lowers the component stresses. A 3.3-kW proof-of-concept (non-optimized) demonstrator is developed, which connects to the single-phase European ac mains (230 V rms, line-to-neutral) and provides a wide dc output voltage range of 300–450 V. Both the conventional and the proposed advanced modulation method are experimentally verified, confirming an improvement of the peak efficiency from 95.9% to 96.7% (300 V dc output, 2.5 kW output power) for the advanced modulation method.