Improved Aging Enhancement Factor for Reliability Assessment of Motor Windings in Electric Vehicle Applications

Abstract

Inverter-fed electrical machines used in electric vehicle applications are increasingly prone to experiencing partial discharge (PD), particularly in 800 V powertrains. Therefore, a precise assessment of PD risk is crucial for ensuring a PD-free design and guaranteeing reliability. Several enhancement factors are introduced in IEC 60034-18-41 accounting for the effect of influencing factors on PD activities. However, an accurate determination of the thermal aging enhancement factor remains a challenging issue. In this paper, PDIV variations are measured under three accelerated aging temperature levels with more than 10 aging sub-cycles. The data are then used to deduce the changing rate of PDIV at generic temperature conditions and finally, the thermal aging enhancement factor considering lifetime constraints and temperature is derived based on the rate theory and Arrhenius law. With this factor, PD risk could be easily and accurately determined considering thermal lifetime constraints during the design stage, and an automotive study case is presented to effectively illustrate the application of the derived enhancement factor.