Multi-level PV inverter with photovoltaic groups independent MPPT control

Partial shading or mismatching of series-connected photovoltaic (PV) arrays makes conventional maximum power point tracking (MPPT) techniques ineffective. Although improved MPPT algorithms are adopted, the power mismatching problem cannot be solved fundamentally. Because of this, significant solar energy is wasted, which raises the cost of solar power generation. In this paper, series-connected photovoltaic modules are divided into several groups, which become the multiple dc units of multi-level inverter. The benefit is that, the voltage of each DC unit in multi-level inverter can be adjusted independently, with no output AC voltage distortion caused by unbalanced dc unit voltage. Based on this principal, each PV group´s MPPT control can be done independently, and the overall generated electric energy is increased. The control strategy of a three level PV inverter of this kind is detailed analyzed. Simulation and prototype are made to verify the goodness of proposed strategy.