Towards reliable power converters for wind turbines: Field-data based identification of weak points and cost drivers

The power-converter system in variable-speed wind turbines is a frequent source of failure, which causes considerable maintenance cost and downtime. As a basis for the development of effective measures for enhancing the converter reliability, it is crucial to understand the prevailing causes and mechanisms leading to these failures within the wind-power application. This is the subject of a research project carried out in a large consortium including wind-turbine and component manufacturers, operators and maintenance service providers, Fraunhofer institutes and academia. This paper presents first results of the statistical analysis of field-failure and cost data collected during 2003-2014, which covers 1269 operating years of onshore wind turbines with doubly-fed induction generator (DFIG) and electrically-excited synchronous generators (EESG). Stepping from subsystem to component-level reliability analysis, the investigation aims at identifying the weak points and main cost drivers within the converter system. For both DFIG- and EESG-based wind turbines, the phase-module category, which includes the power-electronic components, their driver boards as well as DC-link capacitors and busbars, stands out with respect to failure rates, related downtime and repair cost. A comparison of repair cost and revenue losses resulting from downtime shows that the economic impact of converter failure is dominated by the repair cost. Based on the analysed dataset, the reliability of the fully-rated power converters in the turbines with EESG is found to be higher than that of the partially- rated converters in the turbines with DFIG.