Reliability analysis of two frequency converter generations using system-level stress testing

Acceleration of reliability testing is required especially with products having high-reliability requirements and long-service lives. Reduction of test time can be achieved by increasing the stress level. However, this increase is restricted by the operational limits of the product, which must not be exceeded. Acceleration of test time may also be realised by using simultaneous stresses. Although the interpretation of failures in such testing can be more complicated due to concurrent failure mechanisms, it may provide important information about the interaction effects of the used stresses. In this study, the application of system-level reliability testing incorporating simultaneous environmental stresses was studied with two frequency converter models. The test method was developed using a device model with field failure data available from use conditions. This test method was then applied to a newer device model and the failure times and the failure modes were compared. The results show that by using concurrent stresses the testing time could be markedly reduced and similar failure modes were discovered in both device models that are comparable with normal use conditions. However, when a same test method is applied to two different device models, limitations such as material properties and component ratings must be taken into account.