This paper investigates the losses of permanent magnet synchronous machines fed through a 2-level or 3-level-NPC (Neutral Point Clamped) converter. Fundamental and additional losses are calculated analytically from measured voltage and current harmonics. The theoretical results are verified by power measurements under rated conditions as well as under partial load and partial speed at different converter pulse frequencies. As a 3-level converter produces voltages with lower harmonic contents than a 2-level converter, the losses in the machine reduce significantly in a wide operation range when changing the converter topology from 2-level to 3-level.