Asymmetrical multilevel inverters for partially shaded PV systems

This paper proposes an economic way to address partial shading condition in photovoltaic (PV) array. When series connected PV panels are not uniformly illuminated, local hot spots develop due to the increased stress on low illuminated PV panels. This may eventually cause permanent damage to the low illuminated cells/ panels. Anti-parallel diodes are normally connected to protect the panels from this kind of damage and this introduces multiple peaks in the power characteristics. This increases the burden on maximum power point algorithm and tracker as it has to track the global peak among the multiple peaks. Grouping of PV panels based on insolation is proposed in this work. Panels with same insolation are grouped together to form a string and these strings are then interfaced with an asymmetrical multilevel inverter for further power conversion. This paper further analyses the performance of the asymmetrical multilevel inverter controlled by different pulse width modulation (PWM) schemes under partial shaded conditions.