Design of a permanent magnet synchronous machine for hybrid electric vehicles with twin electric machines and a range extender

In this work, design processes of an electric machine with a high power to weight and volume ratios via an intensified water jacket cooling for the DE-REX powertrain are presented. For a high-power density, a 6-pole interior permanent magnet synchronous machine with a continuous power of 24 kW and a short-term power of 48 kW (30 s, overload) at rated speed of 4167 /min was designed. The electric machine rotates up to a maximum speed of 10000 /min with field weakening control to achieve the demanded maximum speed of 180 km/h at hybrid driving mode. A prototype electric machine and four further electric machines for the DE-REX powertrain (two for the powertrain test bench and two for the prototype vehicle) were constructed and tested in the Institute of Electrical Energy Conversion at TU Darmstadt. Based on the measurement results, the electromagnetic design of the machines was validated and the analytically and numerically calculated losses were verified. In addition, measured efficiency maps of the prototype machine with the corresponding inverter were created over the entire torque-speed range. The functionality test of the DE-REX powertrain was performed at the individual electric machine test bench with two driving cycles, the NEDC and the WLTC. The effectiveness of the chosen cooling system was verified by temperature measurements. The measured temperatures showed that the machine has certain thermal reserve for the used Thermal Class H. Thus, the machine could produce more power to avoid high thermal reserve and to increase thermal utilization. Also, it is possible to downsize the machine to avoid big thermal reserve. In this work, two possible downsizing methods are presented; increasing electromagnetic and thermal utilization by reducing active volume of electric machine and using hair wave winding which has higher slot fill factor. The redesigned machine with round wire lap winding reduced an active volume by 23 %. Using a hairpin lap winding, the rede-signed machine had an active volume reduction of 32 %, compared to the prototype machine