Design and implementation of a two-switch buck-boost typed inverter with universal and high-efficiency features

A typical photovoltaic (PV) grid-connection power system is usually consisted of multi-stage converters to perform multiple functions simultaneously. In order to simplify system configuration, reduce cost, and improve conversion efficiency, this paper proposes to adopt two-switch buck-boost (TSBB) dc-dc converters, and then develops families of buck-boost typed inverters via the connection with an H-bridge unfolding circuit with line-commuted operation. The proposed inverters have both step-up and step-down functions so that they are suitable for the applications with wide voltage-variation range. Depending on the conditions of dc input-voltage and ac output-voltage, the proposed circuits can work functionally as either buck-typed or boost-typed inverter. Due to operating with buck or boost principle, partial energy can be directly delivered to output to improve efficiency. Besides, since only one power switch operates with high-frequency, switching losses can be reduced significantly. Finally, one of the proposed TSBB inverters, named buck-cascaded buck-boost (BuCBB) inverter, is then implemented accordingly to generate 110 Vrms / 60 Hz output voltage. Experimental results have verified the validity of theoretical predictions and the feasibility of proposed inverters.