Aging Methodologies and Prognostic Health Management for Electrolytic Capacitors

Kai Goebel, Gautam Biswas, Xenofon Koutsoukos, Jose Celaya, and Chetan Kulkarni
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Full Paper
phmc_10_030.pdf324.17 KBSeptember 1, 2010 - 11:16am

Understanding the aging mechanisms of electronic components in an avionics system is extremely important as they are part of the critical sub-systems avionics which includes the GPS and INAV systems. Electrolytic capacitors and MOSFET’s have higher failure rates than the other components in DC-DC power converter systems. With increased use of electronics in avionics system, it becomes very much important to understand these components degradation mechanisms and their effects on the rest of the system. Our current work focuses on analyzing and modeling degradation phenomena in electrolytic capacitors and its effects on the output of DC-DC converter systems. The output degradation is typically measured by the increase in ripple current and the drop in output voltage at the load. Typically the ripple current effects dominate, and they can have adverse effects on downstream components. For example, in avionics systems where the power supply drives a GPS unit, ripple currents can cause glitches in the GPS position and velocity output, and this may cause errors in the Inertial Navigation (INAV) system causing the aircraft to fly off course.

Literature reports a number of operating conditions that may cause capacitor degradation. These include High Voltage conditions, Transients, Reverse Bias, Strong Vibrations and high ripple current. In our work, we have studied the effects of capacitor degradation on DC-DC converter performance by developing a combination of converter system model and a physics of failure model of electrolytic capacitor degradation when subjected to thermal and electrical stresses. Thermal stress occurs when the capacitors operate in high temperature environments, while electrical stress conditions occur due to high operating voltages and even ripple currents above the rated values. In our work we are developing models to capture the failure phenomenon in these components.

In this paper, we discuss two experiments to observe degradation in electrolytic capacitors. In the first ageing experiment study, the capacitor was subjected to degradation for over 1000 hours of capacitor operation time under nominal room temperature conditions, and the degradation was monitored at regular intervals. In the accelerated ageing methodology study, the capacitors were subjected to high electrical stress. During the accelerated testing we observed a faster degradation in the capacitors where we measured the ESR (Equivalent Series Resistance) which increased over the period of time.

We also discuss the future accelerated ageing method and tests for capacitor degradation. In this paper we present the details of our aging methodology along with details of experiments and analysis of the results.

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Submission Keywords: 
Electrolytic Capacitors
Ageing Methods
Avionics Systems
electronics PHM
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