The Lifetime/Volume ratio as an index to assess the reliability of power converters

The Lifetime/Volume ratio, expressed in hours of operational life per cubic centimeters, and denoted herein as LV, is proposed as a suitable metric to asses the reliability performance of power converters. It is a more sensible index than operational lifetime alone. Two examples are included to exemplify the usefulness of the index. The first one is a power diode in an extruded heatsink. The life time is calculated using the procedure outlined in the Mil Hdbk 217F, and it is shown that the index can be improved in a simple manner. Electrolytic capacitors have long been blamed as highly failure-prone components, and they occupy a large volume. Thus, the second example corresponds to the electrolytic capacitor in the DC-link filter in an adjustable speed drive. The procedure to optimize the index is much more complicated, and the Design-of-Experiments technique is applied to explore the relationship between the index and the design parameters.