An Improved SI-ANPC Grid-Connected Inverter Without Short-Circuit and Circulating-Current Issues

To mitigate the risk of DC-link capacitors short-circuit occurred in neutral-point-clamped (NPC) and active neutral-point-clamped (A-NPC) inverters, various topologies have incorporated the split-inductor structures to suppress the short-circuit current. However, circulating current between the split inductors may arises and the risk of capacitors short-circuit may not be eliminated completely. Besides, large inductors are often required as the split inductors and filter inductors. To address these issues, this paper proposes an improved split-inductor A-NPC inverter (SI-ANPC). The detailed description of the improvement process is provided in the paper. By separating the connection point of the freewheeling switches and the phase leg switches, the two types of risk of DC-link capacitors short-circuit in the A-NPC circuit is solved, and the circulating current in the split inductors is also eliminated. By improving the function of split inductors, the value of the split inductors is reduced in the proposed topology. The proposed inverter maintains the advantages of low voltage stress in the neutral-point-clamped type inverters and the multiple freewheeling current paths of A-NPC type inverters. The operating principles during normal operation and short-circuit are analyzed in detail. The effectiveness of the proposed topology is verified through simulations and experiments.