Test Fixtures to Apply Variable 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 lifetime. Typically, the lifetime 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 specified in the datasheet, a test fixture is needed to apply both adjustable dc-bias voltage and ac ripple current at a specific frequency. In this paper, two portable test fixtures with low kVA requirements are proposed for electrolytic capacitor reliability testing for different dc-bias voltage. The test fixtures 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 fixtures and reliability test results are provided.