【正文】 = ILf(t1) ILf(t0) =(VinVo)(t1t0)/Lf =(VinVo)/Lf *(TonToff)/2 =(VinVo)(2D1)Ts/2Lf (14)Io=1/2(ILfmax_H+ILfmin_H) (15) 其中，fs是開關(guān)頻率，Ts＝1/fs是開關(guān)周期；Ton為開關(guān)管的導(dǎo)通時(shí)間，Toff為開關(guān)管的截止時(shí)間。定義 D＝Ton/Ts為占空比；ΔILf_H、ILfmin_H和 ILfmax_H分別為 D 的電感電流脈動(dòng)值、電感電流最小值和最大值。D 的工作模式當(dāng)開關(guān)管的占空比小于 時(shí)，變換器的主要波形如圖 4 所示,一個(gè)開關(guān)周期內(nèi)包括 4 個(gè)開關(guān)模態(tài)。圖14 D（1） 開關(guān)模態(tài) 1 [t0，t1] （如圖 2 (c)）Q1導(dǎo)通，D2導(dǎo)通，vAB=Vin/2，Q2和 D1上的電壓為 Vin/2。iLf（t）=ILf(t0)+(Vin/2Vo)(tt0)/Lf （16）（2） 開關(guān)模態(tài) 2 [t1，t2] （如圖 2 (d)）t1時(shí)刻關(guān)斷 Q1，D1和 D2導(dǎo)通。vAB=0，QQ2兩端電壓均為 Vin/2。 iLf（t）=ILf(t1)+Vo(tt1)/Lf （17）t2時(shí)刻開通 Q2，電路進(jìn)入開關(guān)模態(tài) 3。開關(guān)模態(tài) 3 與開關(guān)模態(tài) 1 相類似，此時(shí) Q2導(dǎo)通，D1導(dǎo)通，如圖2 (b)所示。t3時(shí)刻關(guān)斷 Q2，電路進(jìn)入開關(guān)模態(tài)4，同開關(guān)模態(tài) 2 工作情況相同，如圖2 (d)所示，此處不贅述。由圖 4可知：Vo =1/Ts*∫t0t4vABdt =D*Vin (18) ΔILf_L=ILfmax_LILfmin_L =(VinVo)*Ton/Lf =(Vin2Vo)D*Ts/2Lf (19) Io=1/2(ILfmax_L+ILfmin_L) (110) 其中ΔILf_L、ILfmin_L和 ILfmax_L分別為 D 時(shí)的電感電流脈動(dòng)、電感電流最小值和最大值。 直流三電平Buck變換器的Matlab仿真分析 為驗(yàn)證上述理論分析的正確性，應(yīng)用Matlab2012搭建了直流三電平Buck變換器的仿真模式，其參數(shù)設(shè)置如下：輸入直流電壓： Vin=220V；輸出直流電壓： Vo=100V；輸出直流電流： Io=1A；輸出濾波電感： Lf=；輸出濾波電容； Cf=；開關(guān)管（Q1Q2）:IRF644。續(xù)流二極管： DSEI802。開關(guān)頻率： fs=20kHz； 系統(tǒng)控制框圖直流三電平Buck變換器系統(tǒng)的控制框圖如下：圖15 直流三電平Buck變換器系統(tǒng)的控制框圖 MATLAB仿真圖圖16 MATLAB 仿真圖 仿真結(jié)果開環(huán)仿真電壓輸出波形：圖52 開環(huán)仿真電壓輸出波形開關(guān)管驅(qū)動(dòng)波形：圖53 開關(guān)管驅(qū)動(dòng)波形三、遇到的問題及解決措施1. 如何保持輸出電壓穩(wěn)定？引入輸出電壓負(fù)反饋可以有效的實(shí)現(xiàn)輸出電壓穩(wěn)定，PI調(diào)節(jié)器作為最常用的調(diào)節(jié)器，可以有效的實(shí)現(xiàn)這一功能，其所包含的積分環(huán)節(jié)能夠使系統(tǒng)的輸出無差別的跟蹤給定信號，使系統(tǒng)輸出穩(wěn)態(tài)誤差，從而達(dá)到輸出電壓穩(wěn)定的目的。2. 如何解決開關(guān)管和續(xù)流二極管的電壓應(yīng)力過高問題？ 此次設(shè)計(jì)采用的直流三電平Buck變換器采用兩個(gè)電壓分壓，雙二極管串聯(lián)的電路，使開關(guān)管和續(xù)流二極管的電壓應(yīng)力為輸入電壓的一半，大大改善開關(guān)管工作環(huán)境，有利于選擇合適的開關(guān)管。收獲：首先，最直觀的便是對Matlab仿真軟件有了較深入的了解，能夠比較熟練的使用Matlab仿真軟件，熟悉了各模塊的作用以及其參數(shù)設(shè)置，以及如何設(shè)置仿真參數(shù)以得到合適的波形。在不斷解決直流三電平Buck變換器問題的同時(shí)，也對PWM調(diào)制有了更深一步的了解；其次，在與同學(xué)們的討論中，能夠以更全面的眼光來看待問題，同時(shí)也讓我意識到，閉門造車是不可取的，一定要懂得團(tuán)隊(duì)的重要性四、工作安排第11周：完成直流三電平Buck變換器的驅(qū)動(dòng)電路設(shè)計(jì)：第12周：完成驅(qū)動(dòng)電路設(shè)計(jì)：第13周：完成保護(hù)電路設(shè)計(jì)：第14周：繪制畢業(yè)論文插圖及畢業(yè)論文大圖；第15周：撰寫畢業(yè)設(shè)計(jì)論文；第16周：整理論文，準(zhǔn)備答辯；第17周；畢業(yè)答辯。五．畢業(yè)論文進(jìn)度安排1. 對整個(gè)前期設(shè)計(jì)結(jié)果進(jìn)行整理；2. 確定畢業(yè)論文提綱；3. 撰寫畢業(yè)論文正文；4. 外文文獻(xiàn)翻譯六、參考文獻(xiàn)[1] 薛稚麗,李斌,阮新波. Buck三電平變換器[C],第十五屆全國電源技術(shù)年會(huì)論文集,南京航空航天大學(xué)(南210016):153~158。[2] 劉學(xué)超,潘虹,[J],(3):37~38,94。[3] 董鋒斌,皇金鋒. 改進(jìn)型三電平Buck直流變換器的建模研究[J],(2):24~26。[4] 李柯平,周繼華,[J],40(06):115~117。[5] 阮新波,危健,[J].中國電機(jī)工程學(xué)報(bào),(11):18~20。[6] 阮新波,[J].科學(xué)出版社, 2000:301~303。[7] 阮新波, DC/DC 全橋變換器的軟開關(guān)技術(shù)[J]. 科學(xué)出版社, 1999:15~16。[8] 劉樹林,劉健,鐘久明. BuckBoost變換器的能量傳輸模式及輸出紋波電壓分析[J].:838~843。[9] 肖國慶. 基于降壓斬波電路的可變電流源設(shè)計(jì)[J].~22。[10] 徐洪哲. 降壓式三電平直流變換器的研究[D]. 哈爾濱工業(yè)大學(xué),2008。[11] 朱德明,秦海鴻,嚴(yán)仰光. 三電平BuckBoost雙向變換器的仿真研究[J]. :19~23。[12] 石勇,楊旭,[N]. (12):1276~1279。[13] 金科,楊孟雄,[J].(18):41~46。[14] 王鴻雁,[J].(6):241~244。[15] Lisheng Shi,Mehdi Ferdowsi, Mariesa Crow. Dynamic Response Improvement in a ThreeLevel Buck Type Converter[J]. Missouri University of Science and Technology, Rolla, MO, 65401,1952~1958。[16] Pinheiro, Ivo Barbi. The threelevel ZVS PWM Converter A new concept in highvoltage dcdc conversion[J]. IEEE IECON, 2003:173~178。[17] Xinbo Ruan, Bin Li, Qianhong Chen. Three Level Converters A New Concept in High Voltage DCtoDC Conversion[J]. IEEE PESC, 2002: 663~668。[18] Pinheiro, Ivo Barbi. Wide load range the threelevel zvs pwm dctodc converter[J]. IEEE PESC, 2003:171~177。[19] Xinbo Ruan, Dayu Xu, Yangguang Yan. A simplified zerovoltageswitching pwm threelevel converter with two clamp diodes[J]. IEEE APEC, 2002:117~119。[20] ,. K Jain. A bidirectional DCDC converter topology for low power application[J]. IEEE Transaction on Power Electronics, 2005, 15(4):595~606。[21] Pinherio J Renes, Barbi Three level ZVS PWM DC to DC Converter[J].IEEE Transactions on power electronics, 2003,8(4):486~492.指導(dǎo)教師意見 指導(dǎo)教師簽字： 年 月 日81附錄 附錄3 英文原文Dynamic Response Improvement in a ThreeLevel Buck Type ConverterAbstracts—Compared to the conventional Buck converter,the equivalent switching frequency in the threelevel Buck converter (TLBuck) is doubled. This leads to a smaller output inductance required for the same inductor current ripple. Therefore, the dynamic response will be faster than that of the conventional Buck converter. In this paper, to further improve the dynamic performance, the current feedforward control scheme is applied to the TLBuck converter. To validate the effectiveness of the proposed topology and controller, both Matlab/Simulink based simulation and experimental results are presented. The main advantages of the proposed approach include faster dynamic response, simple topology configuration, and simple controller implementation.Index Terms—dcdc converter。 dynamic response。overshoot/undershoot voltage。 recovery timeI. INTRODUCTIONIn lowvoltage and highcurrent digital signal processor (DSP) and pointofload (PoL) applications, the dynamic response requirements are usually very stringent [14]. Another important issue is the high power density requirement due to circuit space limitations. To meet these tight requirements, several strategies have been reported which include control loop optimization [57], Buck topology variation [89], and assistant energy transition circuitry [10 11]. The threelevel Buck (TLBuck) converter has the merits of doubled equivalent switching frequency and half the switch voltage stress when pared with the conventional Buck converter [12]. This would make the TLBuck converter a good choice for these applications. In order to further improve the dynamic response, based on the TLBuck converter, a novel topology is proposed in this paper. By bining the proposed topology with the proposed control scheme, the system dynamic response has significantly improved.In section II, the principle of operation of the proposed topology is analyzed, which includes the propose