Fundamentals for reliability and early diagnosis for inverter power drives

Fundamentals for reliability and early diagnosis for inverter power drives

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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.

Chapter Contents:

  • 1.1 Introduction
  • 1.1.1 Manufacture defects (early failure)
  • 1.1.2 Random failure
  • 1.1.3 Wear-out failure
  • 1.2 Statistical life estimation and failure rate: the bathtub curve
  • 1.2.1 Reliability R(t) and unreliability F(t) functions
  • 1.2.2 Probability density function and medium time before failure
  • 1.2.3 Failure rate function
  • 1.2.4 Exponential distribution
  • 1.2.5 Weibull distribution
  • 1.3 Degradation, failure mechanisms,and life model estimation
  • 1.3.1 Solid-stare materials
  • Insulator
  • Conductors
  • Semiconductors
  • 1.3.2 Failure modes and physics-based life model calculation
  • Physics-based life models
  • The Arrhenius model
  • Power model
  • Eyring model
  • Thermal cycling
  • 1.4 Inverters failure and power drives
  • 1.5 Circuit with ideal switches: power switches fundamentals
  • 1.6 PWM, the enabler of power electronics
  • 1.7 Switching under RL circuit load
  • 1.8 RLC circuit1
  • 1.8.1 Series RLC model
  • 1.8.2 Shunt RLC model
  • 1.9 PWM in inverters
  • 1.10 Inverter basic operation
  • 1.11 Three-phase and multilevel inverters
  • 1.12 Operation principle of multilevel inverters
  • 1.13 Dominant topology
  • 1.14 Resonant converters
  • 1.15 Real switches: power losses in hard switching
  • 1.15.1 Conduction losses
  • 1.15.2 Switching losses
  • 1.16 Thermal consideration
  • 1.16.1 State modeling of the thermal system
  • 1.16.2 Thermal runaway
  • References

Inspec keywords: reliability; fault diagnosis; invertors; electric drives

Other keywords: three-phase inverters; RL circuit load; failure rate; aging; early diagnosis; impurities; RLC circuit; hard switching power losses; losses; statistical life estimation; topology; reliability; PWM; elasticity; degradation process; power switches; electromagnetic energy conversion; multilevel inverters; energy transfer; bathtub curve; resonant converters; thermal considerations; inverter power drives

Subjects: Power electronics, supply and supervisory circuits; Reliability; Drives

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