Enhanced power device configuration and operation of a grid-connected active-neutralpoint- clamped inverter for wind energy conversion systems

The power ratings of wind energy conversion systems (WECS) are increasing considerably due to high demand on wind power. Thus, multilevel power converters are becoming an interesting solution in the largest WECS, especially the three-level neutral-point-clamped (3L-NPC) thanks to its simple implementation and proper performance compared to other topologies. However, the main drawback of the 3L-NPC is that the power losses are unevenly distributed among the switching devices, limiting its output power capability. Current literature focuses on the threelevel active neutral-point-clamped (3L-ANPC) as an evolution of the 3L-NPC, enabling a more even power loss distribution. However, in the 3L-ANPC there are still some devices suffering from both large switching and conduction power losses. Thus, this paper proposes new design guidelines for a 3L-ANPC inverter to force that each device mainly withstands either switching or conduction power losses. Then, the most suitable device is selected for each position, enabling a significant improvement in power loss distribution, thermal performance, converter 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 25% in power losses, a reduction of 50% in maximum junction temperature increase above ambient temperature, a reduction of 75% in maximum junction temperature variation, and an increase of around 85% in converter output power rating, compared to the conventional 3L-NPC and the 3L-ANPC