A novel thermal performance evaluation method for inverter passive components

Improvement in the reliability of grid-connected inverters is desirable with their increasing use. Inverter reliability tests usually focus on thermal testing of semiconductor devices. Regenerative methods are adopted to minimize the energy consumed during these tests. Regeneration requires additional systems - converters or passive components. In this paper, a novel method for thermal testing of the passive components associated with a grid-connected inverter is proposed. The method can be used to test the output filter inductors, output ac filter capacitors and input dc electrolytic capacitors. Thermal stress affects the working life of capacitors and can cause insulation failure in inductors. Thermal testing of these passive components, besides the semiconductor device thermal testing, contributes to improved reliabilty of the grid-connected inverter system. Unlike regenerative methods that require additional systems of high-power rating, the proposed method circulates rated current within the three legs of the inverter under test. The only additional system required is a low power dc supply with variable output voltage. The variable dc input supplies the losses in the system under test. The applicability of the proposed test for both three-wire and four-wire grid-connected inverter systems is discussed.