Hybrid Discontinuous/Boundary Conduction Mode of Flyback Microinverter for AC-PV Modules

The current-source flyback inverter has been proven an excellent solution for ac-PV modules. The two principal modes of operation of this converter are the discontinuous conduction mode (DCM) and the boundary conduction mode (BCM). Although BCM offers higher power density, it suffers at lower power levels, because of the significantly increased switching frequency that consequently leads to higher switching losses and lower overall converter efficiency. In this paper, a hybrid operating mode is presented, that combines both DCM and BCM during a utility grid period, so as to improve the converter performance as well as the efficiency and the power density on a wider power range. The mathematical analysis that describes the control specifics especially for a smooth transition between the two modes of operation is presented and demonstrated through computer simulations and experimental results on a laboratory prototype.