【導(dǎo)讀】式整流器，DC-DC變換器和并網(wǎng)逆變器組成。這就提出了可靠性分析，并且要確定這個網(wǎng)絡(luò)互聯(lián)的功?？煽啃苑治鍪窃谀骋惶囟L(fēng)速和最壞配置的條件下最高轉(zhuǎn)換損失。之內(nèi)降低到初始值的84%。通過對功率調(diào)節(jié)系統(tǒng)最不可靠組件的確定更證實了這一結(jié)論。出主要是逆變器決定著系統(tǒng)的可靠性，DC-DC變換器的影響最不顯著。確定小型風(fēng)力發(fā)電機(jī)變換系統(tǒng)的可靠的電力電子配置。任意一個子系統(tǒng)的失敗都會造成重大經(jīng)濟(jì)損失。將會使問題更加嚴(yán)重。幾乎所有的商用小型風(fēng)力發(fā)電機(jī)組是根據(jù)PMG系統(tǒng)。系統(tǒng)可靠性影響的調(diào)查是可取的。事實上，整流器，轉(zhuǎn)換器或逆變器可靠性的準(zhǔn)確數(shù)據(jù)對確定總的。一個變量，來獲得對一個PCS組件的可靠性預(yù)測。將平均故障間隔時間進(jìn)行量化是在可靠性研究中普遍使用。這些信息有助于確定WECS中最有可能失效的子系統(tǒng)，并能夠?qū)ζ浼捌渑渲眠M(jìn)行優(yōu)化設(shè)計。個部分，它不僅決定了性能，而且還承擔(dān)了小型WECS成本的主要部分。就整體而言，為了確保系統(tǒng)

　　

【正文】 ere the failure rate is constant over time in a bathtub curve [23]. In addition, the system is considered repairable. It is assumed that the system ponents are connected in series from the reliability standpoint. The lifetime of a power semiconductor is calculated by considering junction temperature as a covariate for the expected reliability model. The junction temperature for a semiconductor device can be calculated as [24]： JAlossAJ RPTT ?? （ 16） losP is the power loss (switching and conduction loss) generated within a semiconductor device and can be found by replacing the losP from the loss analysis described in Section for each ponent. The life 12 time, ? ?JTL of a semiconductor is then described as ? ? ???????? ??JJ TBLTL e xp0 （ 17） where L0 is the quantitative normal life measurement (h) assumed to be。 K is the Boltzman’s constant which has a value of eV/K, EA is the activation energy, which is assumed to be eV, a typical value for semiconductors, DTJ is the variation of junction temperature and can be expressed as ? ? ???????? ??JJ TBLTL e xp0 （ 18） The failure rate, is described by [26] ? ?JTL1?? （ 19） The global failure rate, ksystem is then obtained as the summation of the local failure rates, ki as: ???Ni isystem 1 ?? （ 20） The mean time between failures, MTBFsystem and reliability, Rsystem of the system are given, respectively by MTBFsystem 188。 systemsystemMT BF ?1? （ 21） tsystem systemeR ??? （ 22） . Reliability calculation for a PMG based SWT The reliability analysis for the PCS of the PMG based configuration is performed by the formulation described in Sections and . A Matlab program is developed which putes the ponent junction temperature using the conduction and switching loss formulations described in Section . After the determination of the failure rate for each ponent using (19), the program sums up the failure rates to evaluate the total system failure rates (20).The reliability of the system is obtainable once the system MTBF (21) is known. A brief schematic of the program and its operating procedure is given in Fig. 3. 5. Results The analytical calculations illustrated in the preceding section were carried out to determine the MTBF and consequently the reliability of a SWT configuration for a preassumed wind speed condition. The rated power for the wind turbine is assumed to be kW. The expected operating condition of the rated wind speed is considered as 13 m/s. It is assumed that the generator speed is proportional to the output voltage of the 3phase bridge rectifier which provides a rated 280 volt output at the rectifier terminal at the rated rotational speed. The switching frequency of the boost converter and inverter is considered as 20 kHz which is usual for 13 most of the practical applications [27]. In order to investigate the worst case scenario of the power loss in the numerical simulation study, the modulation index is assumed unity and the load current is assumed to be in phase with the output. A standard grid is considered which will reflect the optimum behavior as required by the optimum wind turbine operation. The analytical calculation is based on the data sheet on the EUPEC IGBT module FP15R12W1T4_B3 [28] and the parameters are provided in Appendix A (Table ). The results of the analysis following the procedure outlined in Section are presented in Table 1. It is well understood that small wind turbines and so as the PCSs need to be affordable, reliable and most importantly, almost maintenance free for the average person consider installing one. The calculation revealed that the PCS failure rate is 1:9009 10 5 and MTBF is 5:2607 104 h (6 years). As can be seen, the need of replacing the PCS corresponds to the MTBF value of 6 years leads to a more vulnerable system as pared to the life span of the wind turbine system, which is usually 15–20 years. Also from the financial standpoint, replacement of such a plex PCS is expensive and needs a highly skilled repair professional. Fig. 4 shows the reliability of the PCS for a period of 1 year (8760 h). The result reveals that the reliability of the PCS drops to 84% after 1 year and is less than 50% at 40,000 h ( years) as shown in Fig. 5, which is undesirable for a SWT turbine due to high maintenance and replacement costs. In addition, a reliable PCS is desirable by sacrificing a small percentage of the total system efficiency. The analysis thus helps to recognize that an optimum substitute PCS design is fundamental prior to operation of the small wind turbine system leading to a more robust system. The emphasis is then given to identify the most important subsystems in the PCS that is the least reliable. To achieve this objective, the MTBF of the bridge rectifier is decreased by 50% while the MTBFs of the boost converter and inverter are unchanged. In the same way, the effect of changes in the MTBFs for each of the boost converter and inverter on the systems reliability has been calculated and is presented in Fig. 6 along with the actual reliability of the system. It is observed from that the inverter is the dominating subsystem while, the boost converter has less significant effect than the bridge rectifier. It has been found in the literature that the inverter is the least reliable system [29]. Noheless, a higher reliability of the PCS is achievable by