AC Filter Capacitors Reliability and Lifetime in Grid-Tied Inverters

Abstract:
The capacitor lifetime in the application is usually limited by a certain capacitance drop, or by the increase of loss factor or leakage current above a certain value. Depending on the application, one parameter may be more critical than others and may be directly linked to the failure of the inverter. One of the main challenges regarding capacitors is being able to predict their remaining lifetime to anticipate catastrophic failures, which may end in the capacitor melting or taking fire. In this paper, four different capacitor types from two manufacturers were tested using a “modified Temperature-Humidity-Bias (THB) test”. Detailed results of the loss factor (D) and capacitance (C) evolutions are presented and compared among the four candidates. After the test, the capacitors were opened and unwound to analyze their electrodes. Based on con-ventional end-of-life criteria, it is revealed that the capacitance drop (DeltaC/C0) is the dominant criterion for the test profile and samples under tests. Considering a maximum admissible loss of 10% of capacitance, the lifetime of the various capacitor types are then extrapolated. Based on the lifetime under these test conditions, an example of applying the test results into an inverter with different mission profiles is discussed.