外文翻譯---一種新型使用永磁同步發(fā)電機和z源逆變器的變速風力發(fā)電系統(tǒng)

1、<p><b>　　畢 業(yè) 設 計</b></p><p>　　外 文 文 獻 譯 文 及 原 文</p><p>　　學 生： 曹 文 天 </p><p>　　學 號： 200806010211 </p><p>　　院 （系）： 電氣與信息工程學院

2、 </p><p>　　專 業(yè)： 電氣工程及其自動化 </p><p>　　指導教師： 陳 景 文 </p><p><b>　　2012年6月8日</b></p><p>　　一種新型使用永磁同步發(fā)電機和Z源逆變器的變速風力發(fā)電系統(tǒng)</p><p>&l

3、t;b>　　1 介紹</b></p><p>　　風機發(fā)出的電作為能源使用在世界上已經有了很顯著地增長。隨著風能變換系統(tǒng)（WECSs）應用的增加，各種各樣適合它們的技術正在發(fā)展。正因為有著眾多的優(yōu)勢，永磁同步發(fā)電機（PMSG）發(fā)電系統(tǒng)在風力發(fā)電技術發(fā)展中已成為一種主流趨勢。從風能中獲得最大能量以及在電網(wǎng)中得到高品質的電能是風能變換系統(tǒng)的兩個主要目標。對于這兩個目標，交-直-交變換器是風能變換系統(tǒng)

4、最好的拓撲結構之一。圖1展示了一種傳統(tǒng)的永磁同步發(fā)電機的交-直-交拓撲結構。這個結構包括二極管整流電路，升壓直流變換電路和三相逆變電路。在這種拓撲結構中，升壓變換電路被控制用來跟蹤最大功率點（MPPT），逆變電路用來給電網(wǎng)傳遞高品質的電能。</p><p>　　圖1 傳統(tǒng)的基于永磁同步電機并帶直流升壓斬波的風能變換系統(tǒng)</p><p>　　Z源逆變器目前被認為替代現(xiàn)有的逆變拓撲結構有著固有

5、的優(yōu)勢，例如電壓上升。這個逆變電路在相同的逆變相角（直通狀態(tài)）中，伴隨著兩個轉換開關的導通可以促進電壓的上升能力。</p><p>　　本篇論文提出了一種新型的有著Z源逆變電路并且基于永磁同步電機的風能變換系統(tǒng)。這種系統(tǒng)的拓撲結構如圖2所示。這種拓撲結構的升壓轉換電路沒有任何的改變。而且，系統(tǒng)的可靠性得到了很大的提升，因為短路通過逆變器中的任何相角都是被允許的。由于沒有相角死區(qū)時間，逆變輸出功率的失真很小。<

6、;/p><p>　　圖2 有著Z源逆變電路并且基于永磁同步電機的風能變換系統(tǒng)</p><p>　　這篇論文的第二部分介紹了Z源逆變電路并描述從整流電路到Z源逆變電路的操作過程。然后，介紹了功率傳遞和最大功率點跟蹤的系統(tǒng)。</p><p><b>　　2 Z源逆變電路</b></p><p>　　圖3展示了Z源逆變電路。在它的

7、直流側有阻抗網(wǎng)絡，連接著電壓源與逆變器。阻抗網(wǎng)絡由兩個電感和兩個電容組成。傳統(tǒng)的電壓源逆變電路有六個有效矢量和兩個零矢量。然而，Z源逆變電路僅有一個零矢量（狀態(tài)）。對于升壓來說，它被稱為直通矢量。在這種狀態(tài)下，負載端可以短路通過上下設備的任何一組橋臂，任何兩組橋臂，甚至所有的三組橋臂。</p><p>　　圖3 電壓型Z源逆變器</p><p>　　直流電壓可以表示成為</p>

8、<p><b>　?。?-1）</b></p><p>　　是電壓源，是升壓系數(shù)，它決定于</p><p><b>　?。?-2）</b></p><p>　　是間隔一個周期的導通時間。輸出的電壓峰值向量為</p><p><b>　?。?-3）</b></

9、p><p>　　是調制系數(shù)，電容電壓可以表示為</p><p><b>　?。?-4）</b></p><p><b>　　（2-5）</b></p><p><b>　　和之間的關系為</b></p><p><b>　?。?-6）</b&

10、gt;</p><p>　　電感的電流紋波可以這樣計算</p><p><b>　?。?-7）</b></p><p>　　圖4展示了Z源逆變器基本的PWM控制方法。這種方法需要和兩個額外的直線作為直通信號。當載波信號高于或低于，逆變電路會產生一個直通矢量。可表示為</p><p><b>　?。?-8）<

11、;/b></p><p>　　圖4 Z源逆變器的PWM控制方法</p><p>　　在風能變換系統(tǒng)中，帶著輸入電容（、和）的二極管整流橋作為Z源逆變器的直流源部分。這個結構如圖5所示。當二極管整流與逆變器處于直通狀態(tài)時，輸入電容抑制浪涌電壓可能會產生線電感。</p><p>　　圖5 帶二極管整流橋的Z源逆變器</p><p>　　在任

12、何時刻，只用擁有最大電位差的兩相會導通，導通電流從永磁同步發(fā)電機側流向阻抗網(wǎng)絡側。圖6展示每個周期六種可能的狀態(tài)。在任何狀態(tài)下，一個上橋臂，一個下橋臂和一個與它們相連的電容是導通的。例如，當電位差在a相與b相達到最大，二極管和以及它們相連的電容導通，如圖7所示。</p><p>　　圖6 整流器的六種導通狀態(tài)</p><p>　　圖7 當電位差在a相與b相達到最大時的等效電路圖</p

13、><p>　　在每一個導通周期內，逆變電路有兩種工作模式。模式1，逆變電路工作于直通狀態(tài)。這種模式下，二極管（和）是關斷的，直流側與交流線路被分隔。圖8展示這種模式的等效電路。模式2，逆變電路工作于六個有效矢量或兩個零矢量當中，因此，可將帶二極管（和）的Z源逆變電路看成直流源。圖9展示這種模式的等效電路。負載電流在電路工作于零矢量時為零。</p><p>　　圖8 Z源逆變電路處于第一種模式的

14、等效電路圖</p><p>　　圖9 Z源逆變電路處于第一種模式的等效電路圖</p><p><b>　　3 控制系統(tǒng)</b></p><p>　　控制系統(tǒng)的結構如圖10所示?？刂葡到y(tǒng)由兩部分組成：1）電網(wǎng)功率的控制，2）最大功率點的跟蹤。</p><p>　　圖10 風能變換系統(tǒng)的控制方框圖</p>&l

15、t;p><b>　　1）電網(wǎng)功率的控制</b></p><p>　　在同步參考系中的功率方程為</p><p><b>　?。?-1）</b></p><p><b>　?。?-2）</b></p><p>　　P和Q分別是有功和無功功率，V是電網(wǎng)電壓，i是電網(wǎng)電流。下標

16、d和q分別代表著直軸和交軸分量。如果參考系按照電網(wǎng)電壓定向， 就等于零。那么，有功與無功功率就可以表示為</p><p><b>　　（3-3）</b></p><p><b>　?。?-4）</b></p><p>　　根據(jù)上式，分別控制直軸和交軸電流就可以實現(xiàn)控制有功和無功功率。</p><p>

17、;　　兩條控制路徑用來控制這些電流。在第一條路徑中，隨著無功功率的給定，q軸電流的參考值也給定了。為了獲得單位的功率因數(shù)，q軸電流的參考值應設為零。在第二條路徑中，為了控制有功功率，用一個外部的電容電壓控制回路來設定d軸電流的參考值。這使得所有來自整流器的功率被傳輸?shù)诫娋W(wǎng)。對于這種控制有兩種方法：1）電容電壓（）的控制 2)直流電壓（）的控制。</p><p>　　第一種控制方法（控制模型1如圖10所示），電容電

18、壓保持在參考值不變。在控制回路中，當直通時間改變，和將會改變。然而，另一種方法（控制模型2如圖10所示），直流電壓（）的參考量被設定。在這種方法中，當直通時間改變，和將會改變。在直通狀態(tài)下，逆變電路的輸入電壓為零，這使成為一個很難控制的變量。因此，如公式（2-6）所示，通過控制間接控制。</p><p><b>　　2）最大功率點跟蹤</b></p><p>　　風機

19、的機械功率傳遞公式為</p><p><b>　?。?-5）</b></p><p>　　是空氣密度；是風力機葉片迎風掃掠面積；是風速；是風能利用系數(shù)，定義為風力機輸出功率和風能功率的比例，取決于葉片的空氣動力學特性。圖11展示了風速變化時發(fā)電機的轉速與風力機輸出功率之間的聯(lián)系?？梢钥闯觯煌L速時最大功率所對應的發(fā)電機轉速不同。</p><p&g

20、t;　　圖11 風速變化時機械功率與轉子轉速的關系</p><p>　　永磁同步發(fā)電機的穩(wěn)態(tài)感應電壓與轉矩方程為</p><p><b>　?。?-6）</b></p><p><b>　?。?-7）</b></p><p>　　是轉子速度，是定子電流。同時，我們知道</p><

21、p><b>　?。?-8）</b></p><p>　　是永磁同步發(fā)電機的端電壓，是其電感。整流后的直流電壓為</p><p><b>　?。?-9）</b></p><p>　　根據(jù)式（3-7）、（3-8）、（3-9）可得</p><p><b>　?。?-10）</b>

22、;</p><p>　　轉矩決定于發(fā)電機轉速和風速。因此根據(jù)式（3-10），對于直流電壓會得到一個關于轉速和風速的函數(shù)式。最后，通過設置直流電壓就可以調節(jié)發(fā)電機轉速。</p><p>　　A New Variable-Speed Wind Energy Conversion System Using Permanent-Magnet Synchronous Generator and Z-

23、Source Inverter</p><p>　　1 INTRODUCTION</p><p>　　Wind turbines usages as sources of energy has increased significantly in the world.. With growing application of wind energy conversion system(WE

24、CSs), various technologies are developed for them. With numerous advantages , permanent-magnet synchronous generator(PMSG) generation system represents an important trend in development of wind power applications. Extrac

25、ting maximum power from wind and feeding the grid with high-quality electricity are two main objectives for WECSs. To realize these obj</p><p>　　Fig.1. Conventional PMSG-based WECS with dc boost chopper <

26、/p><p>　　The Z-source inverters have been reported recently as a competitive alternative to existing inverter topologies with many inherent advantages such as voltage boost. This inverter facilitates voltage bo

27、ost capability with the turning ON of both switches in the same inverter phase leg (shoot-through state).</p><p>　　In this paper, a new PMSG-based WECS with Z-source inverter is proposed. The proposed topolo

28、gy is shown in Fig. 2. With this topology, boost converter is omitted without any change in the objectives of WECS. Moreover, reliability of the system is greatly improved, because the short circuit across any phase leg

29、of inverter is allowed. Also, in this configuration, inverter output power distortion is reduced, since there is no need to phase leg dead time.</p><p>　　Fig.2. Proposed PMSG-based WECS with Z-source inverte

30、r</p><p>　　Section II of this paper introduces Z-source inverter and describes operation of rectifier feeding the Z-source inverter. Then, power delivery and MPPT control of system are explained.</p>

31、<p>　　2 Z-Source Inverter</p><p>　　The Z-source inverter is shown in Fig. 3. This inverter has an impedance network on its dc side, which connects the source to the inverter. The impedance network is co

32、mposed of two inductors and two capacitors. The conventional voltage source inverters have six active vectors and two zero vectors. However, the Z-source inverter has one extra zero vector (state) for boosting voltage th

33、at is called shoot-through vector. In this state, load terminals are shorted through both the upper and lower dev</p><p>　　Fig.3. Voltage-type Z-source inverter</p><p>　　The voltage of dc link c

34、an be expressed as</p><p><b>　?。?-1）</b></p><p>　　Where is the source voltage and B is the boost factor that is determined by</p><p><b>　　（2-2）</b></p>

35、;<p>　　Where is the shoot-through time interval over a switching cycle T. The output peak phase voltage is</p><p><b>　　（2-3）</b></p><p>　　Where M is the modulation index. Th

36、e capacitors voltage can expressed as</p><p><b>　　（2-4）</b></p><p><b>　　Where</b></p><p><b>　?。?-5）</b></p><p>　　Relation between a

37、nd can be written as</p><p><b>　?。?-6）</b></p><p>　　And current ripple of inductors can be calculated by</p><p><b>　　（2-7）</b></p><p>　　Fig. 4

38、illustrates the simple PWM control method for Z-source inverter. This method employs two extra straight lines as shoot-through signals, and . When the career signal is greater than or it is smaller than , a shoot-throu

39、gh vector is created by inverter. The value of is calculated by</p><p><b>　　（2-8）</b></p><p>　　Fig.4. PWM control method for Z-source inverter</p><p>　　In the proposed

40、WECS, a diode rectifier bridge with input capacitors (,and ) serves as the dc source feeding the Z-source inverter. This configuration is shown in Fig. 5. The input capacitors suppress voltage surge that may occur due to

41、 the line inductance during diode commutation and shoot-through mode of the inverter.</p><p>　　Fig.5. Z-source inverter fed with a diode rectifier bridge</p><p>　　At any instant of time, only tw

42、o phases that have the largest potential difference may conduct, carrying current from the PMSG side to the impedance network side. Fig. 6 shows six possible states during each cycle. In any state, one of upper diodes, o

43、ne of lower diodes, and the corresponding capacitor are active. For example, when the potential difference between phases “a” and “b” is the largest, diodes and conduct in series with capacitor , as shown in Fig. 7.<

44、;/p><p>　　Fig.6. Six possible conduction intervals for the rectifier</p><p>　　Fig.7. Equivalent circuit when the potential difference between phases “a” and “b” is the largest.</p><p>

45、　　In each conduction interval, inverter operates in two modes. In mode 1, the inverter is operating in the shoot-through state. In this mode, the diodes ( and ) are off, and the dc link is separated from the ac line. Fig

46、. 8 shows the equivalent circuit in this mode. In mode 2, the inverter is applying one of the six active vectors or two zero vectors, thus acting as a current source viewed from the Z-source circuit with diodes ( and ) b

47、eing on. Fig. 9 shows the equivalent circuit in this mode. The</p><p>　　Fig.8. Equivalent circuit of the Z-source inverter in mode 1 </p><p>　　Fig.9. Equivalent circuit of the Z-source inverter

48、in mode 2</p><p>　　3 CONTROL SYSTEM</p><p>　　The structure of the control system is shown in Fig. 10. The control system is composed of two parts: 1) control of power delivered to the grid and 2

49、) MPPT.</p><p>　　Fig.10. Block diagram of proposed WECS control system</p><p>　　1）Control of Power Delivered to the Grid</p><p>　　The power equations in the synchronous reference f

50、rame are given by</p><p><b>　?。?-1）</b></p><p><b>　　（3-2）</b></p><p>　　where P and Q are active and reactive power, respectively, v is grid voltage, and i is

51、 the current to the grid. The subscripts “d” and “q” stand for direct and quadrature components, respectively. If the reference frame is oriented along the grid voltage, will be equal to zero. Then, active and reactive

52、power may be expressed as</p><p><b>　?。?-3）</b></p><p><b>　?。?-4）</b></p><p>　　According to earlier equations, active and reactive power control can be achie

53、ved by controlling direct and quadrature current components, respectively.</p><p>　　Two control paths are used to control these currents. In the first path, with given reactive power, the q-axis current refe

54、rence is set. To obtain unit power factor, the q-axis current reference should be set to 0. In the second path, an outer capacitor voltage control loop is used to set the d-axis current reference for active power control

55、. This assures that all the power coming from the rectifier is transferred to the grid. For this control, two methods are proposed: 1) capacitor voltage () c</p><p>　　In the first control method (control mod

56、e 1 in Fig. 10), capacitor voltage is kept constant at reference value. In the control loop, when shoot-through time changes, and will change. However, in other method (control mode 2 in Fig. 10), a reference value is s

57、et for dc-link voltage (). In this method, with changing shoot-through time, and will change. The input voltage of inverter is zero in shoot through state, which makes a difficult variable to control. Consequently, (2-

58、6) is used to contro</p><p>　　2）Maximum Power Point Tracking</p><p>　　The mechanical power delivered by a wind turbine is expressed as</p><p><b>　　（3-5）</b></p>&

59、lt;p>　　Whereis the air density, A is the area swept out by the turbine blades, is the wind velocity, and is the power coefficient defined as the ratio of turbine power to wind power and depends on the aerodynamic c

60、haracteristics of blades. Fig. 11 represents the relation between generator speed and output power according to wind speed change. It is observed that the maximum power output occurs at different generator speeds for dif

61、ferent wind velocities.</p><p>　　Fig.11. Mechanical power versus rotor speed with the wind speed as a</p><p><b>　　parameter</b></p><p>　　The steady-state-induced voltage

62、 and torque equations of PMSG are given by</p><p><b>　　（3-6）</b></p><p><b>　?。?-7）</b></p><p>　　where is rotor speed and is stator current. Also, we have&l

63、t;/p><p><b>　?。?-8）</b></p><p>　　where V is terminal voltage of PMSG and is its inductance. The rectified dc-link voltage may be obtained using</p><p><b>　?。?-9）<

64、/b></p><p>　　From (3-7) to (3-9), the rectified dc voltage may be written as</p><p><b>　?。?-10）</b></p><p>　　The torque is determined by the generator speed and the w

65、ind speed, therefore according to (3-10), it is possible to obtain a prediction for the dc voltage as a function of the generator speed and the wind speed. As result, the generator speed can be regulated by setting the d