The frequent power-converter failure experienced in wind turbines has a strong economic impact through both the related turbine unavailability and the maintenance cost. Up to now, the prevailing mechanisms and causes underlying the converter failure in wind turbines are mostly unknown. Their identification is, however, a prerequisite for the development of effective solutions. This paper describes a multi-track empirical approach to failure analysis including systematic field-data evaluation, exploration of the real converter operating environment, and post-operational laboratory investigation of converter hardware. The analysis is carried out for two widelyused multi-MW wind turbines with low-voltage, IGBT-based converters (topology 1: doubly-fed induction generator with partially rated converter, topology 2: induction generator with fully-rated converter). The findings suggest that the principle failure mechanisms of power electronics found in other applications, namely solder degradation and bond-wire damage, play a minor role in the investigated types of wind turbines. Instead, the analysis reveals indications of insufficient protection of the converter hardware against the environment (salt, condensation, and insects) as well as indications of electrical overstress.Index Terms-wind turbine, converter, reliability, failure, root-cause analysis, power electronics I. INTRODUCTIONOWER converters are a frequent source of failure in modern wind turbines. In a reliability field-study on pitchcontrolled, variable-speed onshore wind turbines with rated capacity ≥850 kW, in which more than 31000 downtime events were evaluated, the frequency converters were found to Manuscript

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