Power density investigations for the large wind turbines´ grid-side press-pack IGBT 3L-NPC-VSCs

Power density is the important design criterion in wind turbine converter design provided that satisfactory converter performance is guaranteed. In order to assess a converter in terms of power density, which is dependent on converter electrical and thermal behaviors, converter electro-thermal models are required to be derived, implemented, and utilized. In this study, employed as a grid-side medium voltage full-scale voltage source converters (VSCs) in a multi-MW wind turbine, press-pack IGBT three-level neutral-point-clamped VSC (3L-NPC-VSC), 3L active NPC-VSC (3L-ANPC-VSC), and 3L neutral-point-piloted VSC (3L-NPP-VSC) are characterized in terms of converter operating principles, physical structure, power loss, and DC bus capacitor size for establishing the basis for converter electro-thermal modeling. Via the practical implementations of the converter electro-thermal models in a computation platform (e.g. MATLAB), these VSCs are investigated with respect to power capability and DC bus capacitor size. Based on these investigations, the VSCs´ power densities are quantified and compared. It is shown that the converter power density can be improved by 13% for 3L-ANPC-VSC and by 22% for 3L-NPP-VSC compared to 3L-NPC-VSC under the given conditions for this study.