Technological Study of mechanical, electrical, and thermal Characteristics for Profiled High Frequency Litz Wires for Traction Motor Applications

With the increasing demand for high-performance electric traction motors across various industries, such as automotive and transportation, the requirements for electric traction motors are becoming increasingly diverse. As a result of technological innovations in the electric drivetrain (e.g., modern semiconductor technologies), switching frequencies are increasing. Since these have a negative impact on the AC losses of the electric motor, the use of high frequency (HF) litz wire for the stator winding comes to the fore. HF litz wires promise to reduce the skin effect during motor operation, thereby increasing the overall efficiency of the drivetrain. Compared to solid rectangular copper wires used in the established hairpin winding technology, a wide variety of different HF litz wire configurations are available. These variations are determined by, among other things, the diameter of the individual strands, the lay length, the aspect ratio, chemical resistivity and insulation material. For the further industrialization of HF litz wire windings, understanding the behaviour of these wide variety of specialized wires is crucial. Given different backgrounds in aviation applications or for contactless charging a variety of investigation in regards of mechanical, electrical, and thermal properties have been published. This paper aims to summarize the relevant characteristics for applications in automotive powertrains using litz wire hairpin and continuous hairpin designs.