Reliability Modeling for Metallized Film Capacitors Based on Time-Varying Stress Mission Profile and Aging of ESR

Metallized film capacitor (MFC) is one of the key components in power electronic converters, accounting for a large proportion of failures. However, the time-varying external stress in long-term mission profile and time-varying internal stress due to the degradation of MFC are not well described by the conventional reliability evaluation method, which leads to a large deviation between the evaluation results and the engineering practices. Therefore, an improved reliability evaluation method considering time-varying stress mission profile and aging process for MFC is proposed. First, this article analyzes the influence of harmonics and provides a more accurate lifetime model under constant stress condition, compared with the conventional method. Second, the subsection integral accumulated damage model is proposed to transform the long-term time-varying stress mission profile to the short-term ideal constant stress condition, solving the reliability evaluation under time-varying external stress condition. And then, an improved aging model is proposed to describe the nonlinear variation of equivalent series resistance (ESR) and internal temperature rise due to the degradation process of MFC. Furthermore, Monte Carlo simulation is applied to analyze the difference of individual capacitor, obtaining lifetime distribution. Finally, a practical application example of modular multilevel converter (MMC) system is implemented to verify the superiority of the improved method.