Test fixture to apply DC bias and AC ripple current for reliability testing of electrolytic capacitors

Electrolytic capacitors are widely used in the DC link of variable frequency drives (VFDs). Their reliability has a significant impact on VFD performance and life time. Typically, the life time of electrolytic capacitors is specified in vendors' datasheets at the rated continuous DC voltage and at the rated ripple current at one fixed frequency, under rated temperature and humidity conditions. In order to analyze and verify their life time, a test fixture is needed to apply both adjustable DC bias voltage and AC ripple current at a specific frequency. In this paper, a portable test fixture with low kVA requirements is proposed for electrolytic capacitor reliability testing. The test fixture can easily be scaled to test large capacitors with high ripple current rating. Multiple capacitor samples or entire capacitor bank assemblies used in VFDs can be tested. Design details of the test fixture and reliability test results are provided.