Topology and control strategy for accelerated lifetime test setup of DC-link capacitor of wind turbine converter

Back-to-back converters for wind turbine systems (WTS) feature capacitors in the DC-link to maintain a stable DC-link voltage and to decouple the generator from the grid. Electrolytic and film capacitors can be chosen to this purpose. Long-term field experience and recorded failure data reveal that capacitor failures are one of the main reasons for the downtime of WTS. The ripple current accelerates the wear-out of the capacitors, which is strongly dependent on the mission profile of the system. Therefore, it becomes important to estimate the useful lifetime of a capacitor as a function of the ripple current. In this paper, aging characteristics of electrolytic capacitors are described, and a power converter topology and its control strategy are designed to perform accelerated lifetime tests. The voltage and ripple current of the capacitor under test (CUT) can be controlled with low THD to correlate wear-out with ripple.