Effects of current displacement in a PMSM traction drive with single turn coils

The current research concerning hybrid and electric vehicles brings forward several new ideas and concepts for electric traction drives that are explicitly tailored to the requirements of the automotive sector. An alternative approach for winding design is the use of a concentrated bar winding with only one turn per coil, which reduces the effort and volume for insulation material and increases the slot fill ratio up to 80 %. Consequently, traction drives with higher power density, reduced mass and improved efficiency are feasible. The major challenge of this design approach lies in the massive winding bars that can cause effects of current displacement especially for high speeds and a high number of pole pairs. The present paper focuses on the primary reasons for the current displacement (like skin effect, proximity effect and the magnetic stray field) and introduces three possibilities to reduce these effects: conductor splitting, conductor rearrangement and different conductor wiring. Related consequences for winding and stator design are highlighted in aspects of motor losses, efficiency and operating performance.