Single-Stage Grid-Connected Forward Micro-inverter with Constant Off-time Boundary Mode Control

1. Single-Stage Grid-Connected Forward Micro-inverter with Constant Off-time Boundary Mode Control D. Meneses This work 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. Forward Micro-inverter with Constant Off-time Boundary Mode Control AC-Module technology • Integration of a PV panel and a grid-connectedinverter (micro-inverter) • Input capacitor power decoupling • Simple /single-stage • Integrated unfolding stage: MA-MD line frequency switched • DC/DC forward magnetic structure 110V@60Hz 230V@50Hz AC-Module Designconsiderations Frequencyvariation • High voltage boost required  transformer • MPPT capability • Unity Power Factor • Commercial PFC controller • Single panel MPPT • Modular / expandable solution • Simple and safe installation (lower cost) Control stage implementation Experimental results DC behaviour • 150Vo • -120Vo Variable frequencyoperation Transformerdemagnetization • PFC commercialcontroller (UCC38050) • Rectification circuitry necessary • ZCD using inductor voltage • MPPT compatible AC behaviour • 110V@60Hz • RM12; 1-14 • 81% efficiency (50W) • Zero crossdistortion • Controllerinternal offset • Controller ZCD threshold Other topological options Primaryside • Forward/push-pull • Half-bridge Secondaryside • Currentdoubler • Full-bridge • Center tapped Conclusions • Simple and low-cost forward micro-inverter based on the boundary mode control • Single-stage converter • Unity power factor current • Integrates MPPT function capability • Transformer configuration remains as in the classical forward converter • Integrated unfolding stage Zero cross distortion • PFC commercial controller