外文翻译--小型网络互联风力发电机功率器件可靠性分析(编辑修改稿)

外文翻译--小型网络互联风力发电机功率器件可靠性分析(编辑修改稿)内容摘要：

n the accessible data provided by the military handbook for reliability prediction of electronic equipment which is criticized for being obsolete and pessimistic [5,6]. A parative reliability analysis of different converter systems has been carried out based on the military handbook by Aten et al. [6]。 however, the absence of environmental and current stress factors can pose grim constraints on the calculated reliability value. Rohouma et al. [7] provided a reliability calculation for an entire PV unit which can be considered more useful, but the approach lacks valid justification as the data provided by the author is taken from the manufacturers’ published data which is somewhat questionable. Indeed, accurate reliability data of the rectifier, converter, or inverter are helpful to determine the total PCS reliability。 however, the calculated reliability could be uncertain once approaching to reliability calculation using purely statistical methods [8], from the manufacturers’ provided data [3,7] or using the military handbook data [9], which consider rectifier, converter and inverter as a total system and neglect their operating point that could vary from one user to other. Moreover, the total number of ponents could vary for a same system in order to meet a certain criteria of the overall system. Although higher ponents in the PCS will exhibit less reliability and vice versa, but the effects of the covariates could be different and consequently leading to a variation in the reliability [10]. Furthermore, a need of the reliability evaluation for the PCSof a grid connected small wind turbine is essential in order to optimize the system performances as well as system cost [11]. On the strength of the above analysis, this paper presents a ponent level reliability calculation by considering temperature as a covariate as usually used in highly accelerated lifetime testing (HALT) procedure [12] to achieve a substantial gain on the reliability prediction of a PCS. A change in operating point is also investigated, thus a clear understanding of the reliability of the system is acplished. The mean time between failures of the PCS is quantified, which can be considered the most widely used parameter in reliability studies [5]. The least reliable ponent of the PCS is also identified in order to optimize the design consideration of the power electronic interface of a grid connected small wind turbine prior to installation. The paper is organized as follows: The PCS required for the grid connection of a PMG based small wind turbine (SWT) is described in Section 2. This is followed by the identification of the most frequent failure subassembly of a SWT from published data in Section 3. Section 4 presents the mathematical analysis for conversion losses calculations followed by the reliability analysis of the power electronics. Finally, the results of the study are described in Section 5, and the important finding of the investigation is highlighted in the conclusions. 2. Grid connection of small wind turbine The power electronics for grid connection of small wind turbines (SWTs) has changed over the years from converters based on SCRs to optimized AC–DC–AC link. This change has led to less harmonic injection to the grid and has bee possible due to low cost digital signal processors and new power devices such as IGBTs and MOSFETs. The design concept of small wind turbine has progressed from induction generator based fixed speed, flapping/passive pitching controlled drive train with gearbox to PMG based variable speed, furling/soft stallcontrolled systems with or without gearbox. Fig. 1 shows the widely used configuration of a small grid connected PMG based wind turbine system. This arrangement employs a PCS which includes a 3phase bridge rectifier, a boost converter and a grid connected inverter. The boost converter boosts the 9 voltage of the dc link as required by the inverter. The boost converter or inverter is controlled so as to ensure optimum power extraction, high overall conversion efficiency and variable speed operation. A drawback of this configuration is the use of an inverter for grid connection. The inverter used by the wind turbine industry is primarily designed for PV applications [13]. Reliability of such grid connected inverters is ambiguous [13] and several key aspects to increase the reliability of such inverters have been identified by previous researchers [4,12,14]. The dominant factor that contributes low technical reliability is the heat generation caused by the power losses when the current flows through the semiconductor switches [2,12,15]. A reduction in heat generation can significantly increase the reliability. In addition, fans inside the inverter have a limited lifetime and deserve special attention [12]. Nevertheless, there are other aspects (. humidity, modularity, and packaging) that also require special attention beyond the technical improvement and are not a part of this present study. 3. Failure modes of small wind turbine systems The need for long term field data is of great importance to the evaluation of technical and economical performances. Long term failure and reliability data for wind turbine subsystems are readily available because of the significant (and growing) number of wind turbines of various age, type and location in existence across the world. This information facilitates the identification of the most probable failure subsystems in WECS, and allows optimization of the design features as well as system configuration. A review has been conducted for the failure distribution of SWT subsystems. Data published by The Scientific Monitoring and Evaluation Programme (WMEP) in Germany [16], Elsfork, Sweden [17], and Landwirtschaftskammer, SchleswingHolstein, Germany (LWK) [18] are presented in Fig. 2 along with the large wind turbine d。