A novel control method for photovoltaic grid-connected micro-inverters to achieve high efficiency in light load

Boundary Conduction Mode (BCM) and Discontinuous Conduction Mode (DCM) control strategies are widely used for the photovoltaic micro-inverter. For the interleaved flyback micro-inverter, BCM and DCM control strategies are investigated concentrating on the loss analysis under different load condition. The dominant losses with heavy load include the conduction loss of the MOSFETs and diodes, and the core loss and copper loss of the transformer, while the dominant losses with light load include the driving loss, turn-off loss of the MOSFETs and the transformer core loss. Based on the loss analysis, a new Multi-mode control strategy combing the two-phase DCM, one-phase DCM and phase skipping mode control is proposed to improve the efficiency in wide load range without increasing the cost or complexity of the design by reducing the dominant losses depending on the load current. A distributed system prototype with two micro-inverters in parallel has been built and tested. The experimental results verified the effectiveness of the proposed method.