Multilevel Inverter for Grid Interconnection with Square Wave Voltage Sources and Series Connected Active Filter

This paper proposes a photovoltaic module integrated microinverter using a gradationally controlled voltage source and a series connected active filter. Recently, a microinverter based on an isolated resonant DC-DC converter is widely used. A typical microinverter can achieve high efficiency around 97%. In addition, a microinverter system can achieve high Maximum Power Point Tracking (MPPT) efficiency by its small photovoltaic area. The proposed circuit is a combination of a gradationally controlled voltage source, an active filter connected in series and an unfolding circuit. This circuit reduces the power to be converted to 1/8 as compared with a conventional inverter. The control strategy for the proposed circuit is also discussed in this paper. Finally, the grid connected operation is verified by circuit simulation.