An optimal control method for grid-connected photovoltaic micro-inverter to improve the efficiency at light-load condition

Abstract-Micro-inverters convert direct current (DC) from a single solar panel to alternating current (AC). They have several advantages over conventional string inverters like higher maximum power point tracking efficiency, easier installation and longer lifetime. For the control of micro inverter, boundary current mode (BCM) is chose to improve the efficiency while discontinuous current mode (DCM) is used to limit the switching frequency. If the switching frequency in DCM is constant, the switching loss will play a more significant role in the overall power loss at light load condition. In this paper, the effect of the DCM/BCM control and frequency limitation to the efficiency and output performance is analyzed first. Then a variable switching control method is proposed to reduce the switching loss under different PV panel´s output power level and input/output voltage changes. Simulation and a 120W prototype´s experimental results validated the proposed control method.