Power density investigation on the press-pack IGBT 3L-HB-VSCs applied to large wind turbines

With three different DC-side and AC-side connections, the three-level H-bridge voltage source converters (3L-HB-VSCs) are alternatives to 3L neutral-point-clamped VSCs (3L-NPC-VSCs) for interfacing large wind turbines with electricity grids. In order to assess their feasibility for large wind turbines, they should be investigated in terms of power density, which is one of the most important design criteria for wind turbine converters due to turbine nacelle space limitation. In this study, by means of the converter electro-thermal models based on the converter characteristics, the power capabilities, DC capacitor sizes, converter cabinet volumes of the three 3LHB- VSCs utilizing press-pack IGBTs are investigated in order to quantify and compare the power densities of the 3L-HB-VSCs employed as grid-side converters. Also, the suitable transformer types for the 3L-HB-VSCs are determined and comparatively studied in terms of volume and weight in order to estimate the size effects of the 3L-HB-VSC topology on the whole wind turbine connection system. Finally, based on the power density and transformer-size investigations, the feasibility of each 3LHB- VSC is discussed.