Fundamentals for reliability and early diagnosis for inverter power drives

Several decades ago, the prevalent concept of the community was that there were fundamentally different approaches to diagnosing and maintaining mechanical versus electrical/electronic devices. For mechanical devices, the approaches were more concentrated on wear and tear, based on life-based model estimation; for electrical/electronic devices, the approaches were concentrated only on probabilistic and random phenomena. In other words, electronic approaches were mainly confined to statistics, assigning a probabilistic value of failure to each of the components to determine the overall reliability of the equipment. With some few exceptions, while the statistical approach is extremely valuable, we can do more in understanding reliability because the process of electromagnetic energy conversion of a device requires matter. More specifically, matter is the enabler of the process, channeling and regulating the conversion of one form of energy to another, usually from electric to magnetic or vice versa. The fact that the converters require matter as “the enabler” exposes the fundamental principle: that aging governs electrical elements in the same fashion as do the mechanical parts. Consequently, solid-state materials such as conductors, insulators, or semiconductors transfer energy from molecule to molecule, atom to atom, degrading during the process, which is modified by the level of temperature, electromagnetic fields, humidity, and other factors. Therefore, small cracks that appear due to impurities or “hot collisions” progress over time and are manifested as aging in the material, which usually shows as a loss of elasticity or an increase in the losses associated with energy transfer. This process creates a degradation “marker” that can be identified in many cases at the early stages of the degradation process. The understanding, identification, and progression of these degradation markers are the focal point of this chapter.