Dual Switching Mode Scheme for Hybrid Boost‐Flyback/Flyback Photovoltaic Microinverter Applications

ABSTRACT Due to a significantly increase of switching frequency in F mode of boundary conduction mode (BCM) hybrid boost‐flyback/flyback (BF/F) microinverter, simply applying discontinuous conduction mode (DCM) to F mode could be an intuitive method to solve this issue but brings a serious distortion in the fixed operation mode transition point, which would deteriorate the power quality. Hence, based on a transition mechanism of a variable transition point and a small modification of the topology, this paper proposed a novel dual switching mode scheme, BCM‐BF/DCM‐F, in which the microinverter is in BCM when operated at BF mode, while in DCM when in F mode. This new scheme smoothly limits the switching frequency of DCM‐F mode to a specified value, thereby minimising the switching losses and guaranteeing a satisfactory power quality. Furthermore, it maintains the natural soft‐switching features of BCM‐BF mode: the zero‐voltage switching (ZVS) and the zero‐current switching (ZCS), as well as the intrinsic snubber. To reduce the cost and signal to noise ratio, an ON‐time control strategy without high‐frequency sensors is employed in this scheme. The characteristics of the proposed BCM‐BF/DCM‐F scheme, including primary side peak current, switching frequency and voltage stress, are also analysed and discussed in detail. Finally, numerous experimental results are presented to verify the theoretical analyses and the performance of the proposed dual switching mode.