【正文】 id or offgrid applications. WECS are considered as plex systems prising mechanical subsystems (rotor, hub, and gearbox) and electrical subsystems (converter/inverter, rectifier, and control) and loads. Failures in any of the subsystems can cause substantial financial loss. The problem bees more severe if the system is offgrid leading to unavailability of power. In light of this, there is a need for reliability evaluation of small WECS in order to determine a configuration that is efficient and reliable. Almost all mercially available small wind turbines are based on PMGs. The power conditioning systems (PCSs) for grid connection of the PMG based configuration requires a rectifier,boost converter, and a gridtie inverter. The reliability analysis of such PCS is greatly influenced by the operating conditions, ., covariates and therefore it is desirable to investigate the magnitude of their effects on the system reliability. Reliability calculation consider the voltage or current as a covariate for an electromechanical system [1], while the reliability of power electronic ponents is strongly influenced by the ponent temperature and variations [2]. Knowledge of the reliability of power electronic ponents is a key concern when differentiating between topologies. However, recent research intermittently endeavors to determine the reliability and advancement of the inverter rather than the PCS [2–4]. Most of the reliability calculations are 8 based on 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]。因而更可靠，成本更低。 重點是確定最重要子系統(tǒng)的 PCS 是否可靠，為了實現這一目標，在平均無故障時間 MTBF 的橋式整流減少了 50%，而升壓變換器和逆變器是不變的。簡單示意圖程序和作業(yè)程序是在圖 3中。對于升壓裝置， IGBT被打開時間 d,而二極管導通時間為（ 1d）。由于世界各地顯著的（和日益增長的）一些不同年限，類型和位置的風力渦輪機的存在，這些長期記錄得來的實效數據和可靠性數據都是現成可用的。一個操作點的改變也可以在這種方法中被體現，所以對于系統(tǒng)可靠性可以有一個清晰的認識。 幾乎所有的商用小型風力發(fā)電機組是根據 PMG系統(tǒng) 。分析表明，這些基于風力渦輪機的永磁發(fā)電機（ PMG）的功率調節(jié)系統(tǒng)的可靠性是相當低的，它在一年之內降低到 初始值的 84%。一個可比較的轉換器的可靠性分析就是基于 Aten等編寫的軍事手冊 [6]。圖 1常用的小型并網永磁風力發(fā)電機組的電路結構。就整體而言，為了確保系統(tǒng)的高可靠性，應該將注意力集中在簡單可靠設計的小型 WECS，確保零件容易保養(yǎng)和維修，以及控制結構的低復雜度一遍達到最佳效果。本文計算出來的平均無故障時間 MTBF是在組件級別進行的。 這些分析計算是基于 EUPEC IGBT模塊 FP15R12W1T4_B3[28]的數據和表 。所以應該要權衡開關頻率和系統(tǒng)系能。 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。作為一個整體，研究的范圍應著眼于優(yōu)化配置，降低功率損耗 提高效率，并且結構不復雜。這有助于幫助找到一個更佳的替代設計使系統(tǒng)更加強大。一旦系統(tǒng)的 MTBF（ 21） 知道就可以得到系統(tǒng)的可靠度。二極管的開通損耗用 DBdcdP, 表達為： dfoDBdcd IVP ?, （ 1） 在一個二極管線性損耗模型中，每個二極管的開關損耗可以表達為： drefdcdrefdcSRWTDB dcd IIVVEfP,1,1, ??? （ 2） 三相二極管整流橋中用 DBdtP, 表示 6個 二極管的總損耗 [20] DB DBsw tDB dc d tDB dswDB dcdDBdt PPPPP , 66 ???? （ 3） 升壓變換器的開通損耗和開關損耗的計算是假定一個理想電感輸入來計算的。 長期的野外數據對于技術和經濟性能的評價是很重要的。這種方法就像通常使用的高加速壽命測試程序 [5]一樣將溫度看作是一個變量，來獲得對一個 PCS組件的可靠性預測。有鑒于此，有必要對小型風能變換系統(tǒng)進行可靠性評估，一遍確定這種配置的有效性和可靠性。通過對功率調節(jié)系統(tǒng)最不可靠組件的確定更證實了這一結論。然而由于缺乏環(huán)境和當前的緊張因素的考慮使得計算的可靠性價值有了很大限制。這種電路結構需要 3相整流橋，升壓轉換器和一個并網逆變器。 3 為了完成一個設備的可靠性分析，對于風力發(fā)電機的電力電 子元件即半導體（二極管， IGBT等）的功率損耗進行數學分析是必不可少的。系統(tǒng)組件根據環(huán)境的變化，其失效率隨時間的推移呈現出浴缸曲線，此外，系統(tǒng)可以被看作是可修復的。程序之后的分析結果在 節(jié)的表 1中。為了觀察平均無故障時間 MTBF的開關頻率已經經行了調查。 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 s