A new stacked NPC converter: 3L-topology and control

In this paper a new three-level (3L) voltage source converter is presented. This new topology called Stacked Neutral Point Clamped (3L-SNPC) increases the apparent switching frequency compared with other 3L structures (3L-Stacked Cells, 3L-Neutral Point Clamped and 3L-Active NPC). This advantage leads to a better balancing of total losses in power switches under all specified operating conditions (low or high modulation index). The topology has more degrees of freedom and allows a parallel conversion. The load current passes simultaneously or alternatively through two parallel paths, depending on PWM strategy. In the paper three PWM strategies are proposed and their switching states and commutations are analyzed. The total losses in power switches are calculated and compared to the most popular 3L structures. Experimental and simulation results are illustrated in the paper to confirm the operation of the proposed topology.