FlexiCoil - Development of an Economical Series Production Process for Preformed Coils in Electrical Drives

15/04/2021

According to the state of the art, stator coils of an electric machine are wound from conventional enameled copper wire with a round conductor cross-section. This process limits the maximum achievable copper fill factor and thus the efficiency of electrical machines. The aim of the research project FlexiCoil was therefore to develop a process and tool technology for the economical production of electric motors with a high copper fill factor. To this end, coils with variable conductor cross-sections produced using forming technology were investigated and manufactured.

  Cross-section Flexicoil Copyright: IEM Cross-section of a stator segment with the FlexiCoil winding.

The target geometry of the coil was determined at the start of the project. Preliminary tests showed that multi-stage forming achieves the best compromise between manufacturability of the coil and near-series, economical production. The target geometry could be realized with five forming stages. The formed coils were insulated with an epoxy-based varnish and installed in the prototype. To enable assembly, the stator was designed without tooth tips. Additionally, a segmented stator was used. The efficiency and thermal behavior of the test carrier were determined by measurement and compared with the behavior of a reference machine with round wire winding.

The copper fill factor achieved by FlexiCoil coils exceeds that of a conventional winding by 33%. At high torque, this results in a reduction of copper losses of up to 17%. The innovative production of the coil leads to an increase in the production costs of the complete drive of 10 to 15%. The molded coils are still in the early stages of development. Future research is expected to further reduce the cost of the coils. Already, the FlexiCoil project shows a way to increase the copper fill factor of an e-machine and thus the power and torque density as well as the efficiency.