Development and Applications of Periodic Variable Temperature Lifetime Model for Low-Voltage Electric Machine

For electrified transportation applications, the winding insulation of an electric machine (EM) is often thermally aged by variable temperature profiles (TPs). Considering the high-reliability requirement, the overengineering approach is commonly adopted, although it conflicts with the high-power-density demand. Therefore, a reliability-oriented design (RoD) methodology is preferred to find a balance between reliability and performance. In order to apply the RoD, the physics of the failure mechanism of EM windings has to be investigated by performing accelerated lifetime tests (ALTs) on the electrical insulation system (EIS). Life prediction of winding is often based on constant temperature ALTs, which would lead to some inaccuracy for the EM working under variable temperature conditions. Thus, a lifetime model that accounts for aging effects caused by variable TPs is needed. In this article, the ALTs are performed at both constant and variable temperature conditions. Then, a newly developed lifetime model taking into account the thermomechanical stress is introduced based on experiment results and simulations. In this way, the EM life prediction could be obtained and more accurate in any temperature range and period. Meanwhile, the practical application of the lifetime is illustrated through a case study of an aerospace motor. Then, the application paradigm of irregular temperature situations is also illustrated with a counting algorithm. To conclude, this article developed a more comprehensive life model for the variable temperature conditions, which is able to cope with real-world scenarios and improve the EM design.