【电力电子】【2014.02】多相多电平逆变器输出电流峰间纹波分析
本文對(duì)多相多電平逆變器的峰-峰輸出電流紋波幅度進(jìn)行了分析和討論。根據(jù)交流電壓分量計(jì)算電流紋波,并根據(jù)開(kāi)關(guān)周期內(nèi)電壓電平的電流斜率和應(yīng)用次數(shù)定義峰峰值。給出了基波周期內(nèi)峰-峰電流紋波分布隨調(diào)制指數(shù)變化的詳細(xì)解析表達(dá)式。在所有情況下,都參考了由基于載波或空間矢量PWM產(chǎn)生的中心對(duì)稱(chēng)開(kāi)關(guān)模式。通過(guò)這種PWM策略,以簡(jiǎn)單有效的方式使直流母線利用率最大化,并得到一個(gè)近似最優(yōu)的調(diào)制方式,使電流紋波均方根最小。從三相二電平逆變器輸出電流紋波的定義和分析入手,將理論擴(kuò)展到多相逆變器,重點(diǎn)研究了五相和七相逆變器。針對(duì)由串聯(lián)RL阻抗和交流反電勢(shì)組成的一般平衡多相負(fù)載,引入了瞬時(shí)電流紋波。定義了輸出電流紋波最大值的簡(jiǎn)化有效表達(dá)式。給出并討論了峰-峰電流紋波圖。通過(guò)仿真和實(shí)驗(yàn)驗(yàn)證了分析結(jié)果的正確性。輸出電流紋波的分析也擴(kuò)展到多電平逆變器,特別是三相三電平逆變器。如前所述,最佳調(diào)制是根據(jù)電流紋波均方根最小化來(lái)確定的。此外,在這種情況下,對(duì)由串聯(lián)RL阻抗和交流反電動(dòng)勢(shì)(RLE)組成的三相平衡系統(tǒng)進(jìn)行了電流紋波分析,該系統(tǒng)代表了電機(jī)負(fù)載和并網(wǎng)應(yīng)用。給出并討論了峰-峰電流紋波圖。此外,還進(jìn)行了仿真和實(shí)驗(yàn),驗(yàn)證了分析方法的有效性。對(duì)不同相數(shù)、不同電平的情況進(jìn)行了比較,得出了一些有益的結(jié)論。并給出了一些應(yīng)用實(shí)例。
Analysis of the peak-to-peak output currentripple amplitude for multiphase and multilevel inverters is presented anddiscussed in this PhD thesis. The current ripple is calculated on the basis ofthe alternating voltage component, and peak-to-peak value is defined by thecurrent slopes and application times of the voltage levels in a switchingperiod. Detailed analytical expressions of peak-to-peak current rippledistribution over a fundamental period are given as function of the modulationindex. For all the cases, reference is made to centered and symmetrical switchingpatterns, generated either by carrier-based or space vector PWM. By this PWMstrategy, the dc bus utilization is maximized in a simple and effective way,and a nearly-optimal modulation is obtained to minimize the current ripple RMS.Starting from the definition and the analysis of the output current ripple inthree-phase two-level inverters, the theoretical developments have beenextended to the case of multiphase inverters, with emphasis on the five- andseven-phase inverters. The instantaneous current ripple is introduced for ageneric balanced multiphase loads consisting of series RL impedance and ac backemf (RLE). Simplified and effective expressions to account for the maximum ofthe output current ripple have been defined. The peak-to-peak current ripplediagrams are presented and discussed. Both simulation and experimental resultsare carried out to prove the validity of the analytical developments. Theanalysis of the output current ripple has been extended also to multilevelinverters, specifically three-phase three-level inverters. The optimalmodulation has been identified with reference to current ripple RMS minimization,as in the previous cases. Also in this case, the current ripple analysis iscarried out for a balanced three-phase system consisting of series RL impedanceand ac back emf (RLE), representing both motor loads and gridconnectedapplications. The peak-to-peak current ripple diagrams are presented anddiscussed. In addition, simulation and experimental results are carried out toprove the validity of the analytical developments. The cases with differentphase numbers and with different number of levels are compared among them, andsome useful conclusions have been pointed out. Furthermore, some applicationexamples are given.
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