Grid-connected boost inverter for small-wind urban integration: Analysis and design

Small grid-connected PV-systems are quite usual in domestic roofs, but urban integration is still an open issue for wind systems. Similarly to grid PV systems, direct grid injection in a wind system requires two stages, a PFC boost rectifier and a grid-tie inverter. Nevertheless, although a buck inverter is a common choice in many grid PV systems, this topology imposing a minimum DC-Link voltage complicates the boost stage design, because the voltage variation range of a wind alternator, greater than the variation margin of a PV-array, would be absorbed only by the first converter. Consequently, we propose to share the voltage gain between both processor stages, using step-up voltage inverter instead of a buck one. In this work, boost and buck-boost based inverters are analyzed, and finally, a sliding mode controlled boost inverter with bipolar operation is proposed. To demonstrate the feasibility of this proposal, some relevant experimental results from a 1kW inverter prototype are given.