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