A Novel commutation sequence for the three-level active neutral-point-clamped inverter to aid in splitting switching and conduction losses among the semiconductor devices

Abstract

The three-level neutral-point-clamped (3L-NPC) topology is competitive in the large wind energy conversion systems (WECS) thanks to its simple implementation and proper performance compared to other topologies. However, the 3L-NPC topology does not allow distributing power losses evenly among the switching devices, which limits its output power capability. Current literature focuses on the three-level active neutral-point-clamped (3L-ANPC) as an evolution of the 3L-NPC, enabling a more even power loss distribution. However, some devices still suffer from significant switching and conduction power losses with typical commutation sequences. This paper proposes a novel commutation sequence for a 3L-ANPC inverter leg to force that each device mainly withstands either switching or conduction losses. This enables the selection of optimum devices for each position, resulting in an improved converter loss distribution, thermal performance, efficiency, and output power capability. A 2 MW low-voltage WECS is simulated with an electro-thermal model developed in PLECS, reaching a reduction of around 16% in total switching losses. In addition, an enhanced thermal performance is achieved, reducing the maximum junction temperature increase above ambient temperature, on average for all devices, around 4%. The thermal advantages are considerably higher in certain devices, reaching maximum reductions of around 17% in the maximum junction temperature increase above ambient temperature and about 40% in the maximum device junction temperature variation. All reductions are with reference to the conventional commutation sequence.