Reliability of Power Converters in Wind Turbines: Exploratory Analysis of Failure and Operating Data From a Worldwide Turbine Fleet

Abstract

In view of the frequent and costly failures of power converters in wind turbines, a large consortium of research institutes and companies has joined forces to investigate the underlying causes and key driving factors of the failures. This paper presents an exploratory statistical analysis of the comprehensive field data provided by the project partners. The evaluated dataset covers converter failures recorded from 2003-2017 during almost 7400 operating years of variable-speed wind turbines of different manufacturers and types, operating at onshore and offshore sites in 23 countries. The results include the distribution of failures within the converter system and the comparison of converter failure rates among turbines with different generator-converter concepts, from different manufacturers as well as from different turbine generations. By means of combined analyses of converter-failure data with operating and climate data, conditions promoting failure are identified. In line with the results of a previous, much smaller study of the authors, the present analysis provides further indications against the wide-spread assumption that thermalcycling induced fatigue is the lifetime-limiting mechanism in the power converters of wind turbines. Instead, the results suggest that humidity and condensation play an important role in the emergence of converter failures in this application.

Exploring the Causes of Power-Converter Failure in Wind Turbines based on Comprehensive Field-Data and Damage Analysis

“…Previous publications of the authors based on this data collection are [32][33][34][35][36]. The most relevant findings, which constitute important background information for the present paper, are summarized in the following.…”

“…On average, 0.48 a −1 failures of the main power-converter system occurred per WT in the considered worldwide turbine fleet. With a mean failure rate of 0.16 a −1 failures per WT, the largest share of this is accounted for by the core components of the converters denoted "phase module" [35]. This phase-module component category includes the power semiconductor modules with their gate-driver boards, the DC-link capacitors and busbars.…”

“…A failure-rate comparison between WTs commissioned from 1997 to 2015 has revealed that their average phase-module failure rates have not decreased over successive WT generations [35]. This has made clear that the high power-converter unreliability is a problem not limited to old turbine fleets but is also a critical issue in contemporary WTs.…”

“…The group of WTs with electrically excited synchronous generator (EESG) and full power converter was found to have the on average lowest failure rate, while that of WTs with squirrel-cage induction generator and full power converter (IG + FPC) showed the highest. The group of WTs with doubly-fed induction generator (DFIG) and partially rated converter, which is particularly well represented in the evaluated database, ranked between the other two groups [35]. However, it is important to note that this comparison has not taken into consideration the diverse wind regimes (and with that the load conditions) the WTs in the different groups have been operating in.…”

“…In Scandinavia, this pattern was found in WT fleets of three different manufacturers. The observation that periods with increased phase-module failure rates coincided with periods of high ambient absolute humidity suggested that moisture and condensation are factors with a relevant influence on converter failure in wind turbines [35].…”