Modified rainflow algorithm for temperature-time-dependent counting in lifetime estimation of power devices

Power electronic systems include many fragile elements, with power devices being the most prone to failure. Cycle counting algorithms are essential to evaluate power devices degradation and system reliability. Among the available options, the rainflow algorithm is the most widely used. Since the rainflow algorithm was originally designed for fatigue analysis, it faces challenges when applied to power devices. Specifically, the conventional rainflow algorithm cannot compute the effective heating time and the time-dependent equivalent mean temperature of the thermal cycles. Additionally, it counts cooling half-cycles, which contradicts the basis of lifetime models, as these models rely on data associated with heating temperature gradients. To address these limitations, this work introduces a modified rainflow algorithm for cycle counting in the lifetime estimation of power devices. This methodology enhances the conventional rainflow by enabling the calculation of effective heating time and mean temperature while also filtering out cooling half-cycles. The results demonstrate that the modified rainflow algorithm significantly affects the lifetime predictions for all critical joints in an IGBT module, regardless of the mission profile. Across all case studies, the utilization of the modified rainflow algorithm resulted in a damage reduction exceeding 53\%. %.