US Patent 7978488 Three-level power converting apparatus

Each phase of a three-level power converting apparatus is configured by a single unit, and four switching devices (1u-4u) and two diodes (9u, 10u) provided in each unit are arranged along a flow direction of cooling air on a heat sink (15) of a cooling device with long sides of the switching devices (1u-4u) and the diodes (9u, 10u) oriented perpendicular to the flow direction of the cooling air. The first and second diodes (9u, 10u) are arranged in a central area of the heat sink (15), whereas the second switching device (2u) and the third switching device (3u) with high heat generation loss are arranged in a distributed fashion to sandwich a group of diodes in the central area in between.