Two-stage interleaved three-level DC/AC converter with neutral point voltage balancing

This paper proposes a two-stage three-level DC/AC converter, which consists a three-level inter-leaved dc/dc boost converter in the first stage, and a three-level neutral-point-clamped (NPC) inverter in the second stage. The boost converter regulates variable and/or wide-range dc source, then provides suitable and stable dc voltage to the NPC inverter. The NPC inverter generates variable frequency and variable voltage source to drive an AC motor load. The well-known drawback of NPC inverter, unbalanced neutral point voltage caused by the zero-sequence components, is investigated and compensated by the first stage. Both lower output frequency and poor power factor load of NPC inverter may drive the unbalance to severe situation. In this paper, the current in the neutral point path is used as a forward compensation factor to mitigate the voltage ripple at the neutral point. A 2-kW prototype was built to evaluate the performance of the proposed system. Both simulation and measured results demonstrate the validity of the proposed method.