Stable DC bus voltage balancing in a renewable source grid connected neutral point clamped inverter

Multilevel inverters supplied by independent sources are increasingly studied to connect these sources to grid. One of the challenges is voltage balancing. Indeed, when supplying powers coming from renewable sources are different, the inverter input voltages are unbalanced. In this paper, a stable DC bus voltage balancing technique without modifying MPPT algorithm is presented. This allows an MPPT operating independently on each renewable source maximizing total absorbed power. In this work, the power topology includes two boost converters (one for each single source) and a 3-level Neutral Point Clamped (NPC) inverter. The boost converters are used to implement independent MPPT for each renewable source while the proposed voltage balancing is realized by modifying the inverter control. The main objective of this paper is to demonstrate the stability of the proposed technique. Simulation and experimental results confirm the effectiveness and the stability of the voltage balancing technique.