Dual-mode flyback inverters in grid-connected photovoltaic systems

A dual-mode flyback inverter is proposed for photovoltaic power applications. The proposed dual-mode flyback inverter makes use of both discontinuous conduction mode (DCM) and continuous conduction mode (CCM) operations for more than 200 W power applications. However, it suffers from output current control problems such as low system gain during DCM and right-half-plain zero problem during CCM. To achieve accurate reference tracking, the authors propose to adopt the repetitive control scheme that increases the system gain at the fundamental and its harmonic frequencies of the grid. To reduce the burden from the conventional proportional-integral controller, the authors use the dual-mode nominal duty that helps the dual-mode flyback inverter generate the target output current while attenuating the effect of disturbances. To make the dual-mode flyback inverter operate at the maximum power point (MPP), the authors use the incremental conductance method that offers smooth transition to the MPP. The experimental results show that the proposed flyback system implemented for 200 W dual-mode flyback inverter prototype achieves high MPP tracking efficiency, low total harmonic distortion, high power conversion efficiency, and high power capacity.