Single-stage grid-connected forward microinverter with constant off-time boundary mode control

This paper presents a micro-inverter to be integrated into a photovoltaic panel. The proposed single-stage solution combines a forward converter with a constant off-time boundary mode control, providing MPPT capability and unity power factor. The transformer structure of the power stage remains as in the classical DC-DC forward converter. Transformer primary windings are utilized for power transfer or demagnetization depending on the grid semi-cycle. Furthermore, bidirectional switches are used on the secondary side allowing direct connection of the inverter to the grid. Design considerations regarding the inductance value, transformer turns ratio and frequency variation during a line semi-cycle are provided. The decoupling of the twice the line frequency power pulsation is also discussed, as well as the maximum power point tracking (MPPT) capability. Simulation and experimental results for a 50W@110V prototype are enclosed.