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

畢 業(yè) 設(shè) 計(jì) 外 文 文 獻(xiàn) 譯 文 及 原 文 學(xué) 生： 曹 文 天 學(xué) 號(hào)： 200806010211 院 （系）： 電氣與信息工程學(xué)院 專 業(yè)： 電氣工程及其自動(dòng)化 指導(dǎo)教師： 陳 景 文 2012年 6月 8日1 一種新型使用永磁同步發(fā)電機(jī)和 Z源逆變器的變速風(fēng)力發(fā)電系統(tǒng) 1 介紹 風(fēng)機(jī)發(fā)出的電作為能源使用在世界上已經(jīng)有了很顯著地增長(zhǎng)。隨著風(fēng)能變換系統(tǒng)（ WECSs）應(yīng) 用的增加，各種各樣適合它們的技術(shù)正在發(fā)展。正因?yàn)橛兄姸嗟膬?yōu)勢(shì)，永磁同步發(fā)電機(jī)（ PMSG）發(fā)電系統(tǒng)在風(fēng)力發(fā)電技術(shù)發(fā)展中已成為一種主流趨勢(shì)。從風(fēng)能中獲得最大能量以及在電網(wǎng)中得到高品質(zhì)的電能是風(fēng)能變換系統(tǒng)的兩個(gè)主要目標(biāo)。對(duì)于這兩個(gè)目標(biāo)，交 -直 -交變換器是風(fēng)能變換系統(tǒng)最好的拓?fù)浣Y(jié)構(gòu)之一。圖 1 展示了一種傳統(tǒng)的永磁同步發(fā)電機(jī)的交 -直 -交拓?fù)浣Y(jié)構(gòu)。這個(gè)結(jié)構(gòu)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?fù)浣Y(jié)構(gòu)中，升壓變換電路被控制用來跟蹤最大功率點(diǎn)（ MPPT），逆變電路用來給電網(wǎng)傳遞高品質(zhì)的電能。 圖 1 傳統(tǒng)的基于永磁同步電機(jī)并帶直流升壓斬波的風(fēng)能變換系統(tǒng) Z源逆變器目前被認(rèn)為替代現(xiàn)有的逆變拓?fù)浣Y(jié)構(gòu)有著固有的優(yōu)勢(shì)，例如電壓上升。這個(gè)逆變電路在相同的逆變相角（直通狀態(tài)）中，伴隨著兩個(gè)轉(zhuǎn)換開關(guān)的導(dǎo)通可以促進(jìn)電壓的上升能力。 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(jī)的風(fēng)能變換系統(tǒng)。這種系統(tǒng)的拓?fù)浣Y(jié)構(gòu)如圖 2所示。這種拓?fù)浣Y(jié)構(gòu)的升壓轉(zhuǎn)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?yàn)槎搪吠ㄟ^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(shí)間，逆變輸出功率的失真很小。 圖 2 有著 Z源逆變電路并且基于永磁同步電機(jī)的風(fēng)能變換系統(tǒng) 2 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(diǎn)跟蹤的系統(tǒng)。 2 Z源逆變電路 圖 3展示了 Z源逆變電路。在它的直流側(cè)有阻抗網(wǎng)絡(luò)，連接著電壓源與逆變器。阻抗網(wǎng)絡(luò)由兩個(gè)電感和兩個(gè)電容組成。傳統(tǒng)的電壓源逆變電路有六個(gè)有效矢量和兩個(gè)零矢量。然而， Z 源逆變電路僅有一個(gè)零矢量（狀態(tài)）。對(duì)于升壓來說，它被稱為直通矢量。在這種狀態(tài)下，負(fù)載端可以短路通過上下設(shè)備的任何一組橋臂，任何兩組橋臂，甚至所有的三組橋臂。 圖 3 電壓型 Z源逆變器 直流電壓可以表示成為 dci BVV （ 2-1） dcV是電壓源， B 是升壓系數(shù)，它決定于 )(21 1 0 TTB （ 2-2） 0T是間隔一個(gè)周期 T 的導(dǎo)通時(shí)間。輸出的電壓峰值向量acV為 )2( dcac VMBV （ 2-3） M 是調(diào)制系數(shù)，電容電壓可以表示為 dcCCC VTTTVVV )( 01121 （ 2-4） 01 TTT （ 2-5） iV和CV之間的關(guān)系為 dcCi VVV 2（ 2-6） 電感的電流紋波可以這樣計(jì)算 )( 0101 TTTTI （ 2-7） 圖 4展示了 Z源逆變器基本的 PWM控制方法。 這種方法需要SCV和SCV兩個(gè)額外的直線作為直通信號(hào)。當(dāng)載波信號(hào)高于SCV或低于SCV，逆變電路會(huì)產(chǎn)生一個(gè)直通矢量。SCV可表示為 TTVSC 1 （ 2-8） 3 圖 4 Z源逆變器的 PWM控制方法 在風(fēng) 能變換系統(tǒng)中，帶著輸入電容（aC、bC和cC）的二極管整流橋作為 Z 源逆變器的直流源部分。這個(gè)結(jié)構(gòu)如圖 5所示。當(dāng)二極管整流與逆變器處于直通狀態(tài)時(shí)，輸入電容抑制浪涌電壓可能會(huì)產(chǎn)生線電感。 圖 5 帶二極管整流橋的 Z源逆變器 在任何時(shí)刻，只用擁有最大電位差的兩相會(huì)導(dǎo)通，導(dǎo)通電流從永磁同步發(fā)電機(jī)側(cè)流向阻抗網(wǎng)絡(luò)側(cè)。圖 6展示每個(gè)周期六種可能的狀態(tài)。在任何狀態(tài)下，一個(gè)上橋臂，一個(gè)下橋臂和一個(gè)與它 們相連的電容是導(dǎo)通的。例如，當(dāng)電位差在 a 相與 b 相達(dá)到最大，二極管paD和nbD以及它們相連的電容aC導(dǎo)通，如圖 7所示。 4 圖 6 整流器的六種導(dǎo)通狀態(tài) 圖 7 當(dāng)電位差在 a相與 b相達(dá)到最大時(shí)的等效電路圖 在每一個(gè)導(dǎo)通周期內(nèi)，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（paD和nbD）是關(guān)斷的，直流側(cè)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(gè)有效矢量或兩個(gè)零矢量當(dāng)中，因此，可將帶二極管 （paD和nbD）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(fù)載電流ii在電路工作于零矢量時(shí)為零。 圖 8 Z源逆變電路處于第一種模式的等效電路圖 5 圖 9 Z源逆變電路處于第一種模式的等效電路圖 3 控制系統(tǒng) 控制系統(tǒng)的結(jié)構(gòu)如圖 10所示。控制系統(tǒng)由兩部分組成： 1）電網(wǎng)功率的控制， 2）最大功率點(diǎn)的跟蹤。 圖 10 風(fēng)能變換系統(tǒng)的控制方框圖 1）電網(wǎng)功率的控制 在同步參考系中的功率方程為 )(23 qqdd ivivP （ 3-1） )(23 qddq ivivQ （ 3-2） 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(biāo) 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，qv就等于零。那么，有功與無功功率就可以表示為 6 dd ivP 23（ 3-3） qd ivQ 23（ 3-4） 根據(jù)上式，分別控制直軸和交軸電流就可以實(shí)現(xiàn)控制有功和無功功率。 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(yīng)設(shè)為零。在第二條路徑中，為了控制有功功率，用一個(gè)外部的電容電壓控制回路來設(shè)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(duì)于這種控制有兩種方法： 1）電容電壓（cV）的控制 2)直流電壓（iV）的控制。 第一種控制方法（控制模型 1如圖 10所示），電容電壓保持在參考值不變。在控制回路中，當(dāng)直通時(shí)間改變，dcV和iV將會(huì) 改變。然而，另一種方法（控制模型 2如圖 10所示），直流電壓（iV）的參考量被設(shè)定。在這種方法中，當(dāng)直通時(shí)間改變，dcV和cV將會(huì)改變。在直通狀態(tài)下，逆變電路的輸入電壓為零，這使iV成為一個(gè)很難控制的變量。因此，如公式（ 2-6）所示，通過控制cV間接控制iV。 2）最大功率點(diǎn)跟蹤 風(fēng)機(jī)的機(jī)械功率傳遞公式為 321 mpm VACP （ 3-5） 是空氣密度； A 是風(fēng)力機(jī)葉片迎風(fēng)掃掠面積； mV 是風(fēng)速； pC 是風(fēng)能利用系數(shù)，定義為風(fēng)力機(jī)輸出功率和風(fēng)能功率的比例，取決于葉片的空氣動(dòng)力學(xué)特性。圖 11展示了風(fēng)速變化時(shí)發(fā)電機(jī)的轉(zhuǎn)速與風(fēng)力機(jī) 輸出功率之間的聯(lián)系。可以看出，不同風(fēng)速時(shí)最大功率所對(duì)應(yīng)的發(fā)電機(jī)轉(zhuǎn)速不同。 圖 11 風(fēng)速變化時(shí)機(jī)械功率與轉(zhuǎn)子轉(zhuǎn)速的關(guān)系 永磁同步發(fā)電機(jī)的穩(wěn)態(tài)感應(yīng)電壓與轉(zhuǎn)矩方程為 at IKT （ 3-6） 7 eKE （ 3-7） 是轉(zhuǎn)子速度， aI 是定子電流。同時(shí)，我們知道 222 )( sa LIVE （ 3-8） V 是永磁同步發(fā)電機(jī)的端電壓， sL 是其電感。整流后的直流電壓為 VV dc 63 （ 3-9） 根據(jù)式（ 3-7）、（ 3-8）、（ 3-9）可得 22 )(63tsedc KTLKV （ 3-10） 轉(zhuǎn)矩決定于發(fā)電機(jī)轉(zhuǎn)速和風(fēng)速。因此根據(jù)式（ 3-10），對(duì)于直流電壓會(huì)得到一個(gè)關(guān)于轉(zhuǎn)速和風(fēng)速的函數(shù)式。 最后 ，通過設(shè)置直流電壓就可以調(diào)節(jié)發(fā)電機(jī)轉(zhuǎn)速。 8 A New Variable-Speed Wind Energy Conversion System Using Permanent-Magnet Synchronous Generator and Z-Source Inverter 1 INTRODUCTION Wind turbines usages as sources of energy has increased significantly in the world. With growing application of wind energy conversion system(WECSs), 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. Extracting maximum power from wind and feeding the grid with high-quality electricity are two main objectives for WECSs. To realize these objectives, the ac-dc-ac converter is one of the best topology for WECSs. Fig.1 shows a conventional configuration of ac-dc-ac topology for PMSG. This configuration includes diode rectifier, boost dc-dc converter and three-phase inverter. In this topology, boost converter is controlled for maximum power point tracking(MPPT) and inverter is controlled to deliver high-quality power to the grid. Fig.1. Conventional PMSG-based WECS with dc boost chopper 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 boost capability with the turning ON of both switches in the same inverter phase leg (shoot-through state). In this paper, a new PMSG-based WECS with Z-source inverter is proposed. The proposed topology 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 of inverter is allowed. Also, in this configuration, inverter output power distortion is reduced, since there is no need to phase leg dead time. 9 Fig.2. Proposed PMSG-based WECS with Z-source inverter 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. 2 Z-Source Inverter 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 composed 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 that is called shoot-through vector. In this state, load terminals are shorted through both the upper and lower devices of any one phase leg, any two phase legs, or all three phase legs. Fig.3. Voltage-type Z-source inverter The voltage of dc link can be expressed as dci BVV （ 2-1） Where dcVis the source voltage and B is the boost factor that is determined by )(21 1 0 TTB （ 2-2） Where 0Tis the shoot-through time interval over a switching cycle T. The output peak phase voltage acVis )2( dcac VMBV （ 2-3） Where M is the modulation index. The capacitors voltage can expressed as 10 dcCCC VTTTVVV )( 01121 （ 2-4） Where 01 TTT （ 2-5） Relation between iVand cVcan be written as dcCi VVV 2（ 2-6） And current ripple of inductors can be calculated by )( 0101 TTTTI （ 2-7） Fig. 4 illustrates the simple PWM control method for Z-source inverter. This method employs two extra straight lines as shoot-through signals, SCVand SCV. When the career signal is greater than SCVor it is smaller than SCV, a shoot-through vector is created by inverter. The value of SCVis calculated by TTVSC 1 （ 2-8） Fig.4. PWM control method for Z-source inverter In the proposed WECS, a diode rectifier bridge with input capacitors (aC,bCand CC) 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 the line inductance during diode commutation and shoot-through mode of the inverter. 11 Fig.5. Z-source inverter fed with a diode rectifier bridge At any instant of time, only two 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, one of lower diodes, and the corresponding capacitor are active. For example, when the potential difference between phases “a” and “b” is the largest, diodes paDand nbDconduct in series with capacitor aC, as shown in Fig. 7. Fig.6. Six possible conduction intervals for the rectifier Fig.7. Equivalent circuit when the potential difference between phases “a” and “b” is the largest. 12 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 (paDand nbD) are off, and the dc link is separated from the ac line. Fig. 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 (paDand nbD) being on. Fig. 9 shows the equivalent circuit in this mode. The load current iis zero during zero vectors. Fig.8. Equivalent circuit of the Z-source inverter in mode 1 Fig.9. Equivalent circuit of the Z-source inverter in mode 2 3 CONTROL SYSTEM 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) MPPT. 13 Fig.10. Block diagram of proposed WECS control system 1） Control of Power Delivered to the Grid The power equations in the synchronous reference frame are given by )(23 qqdd ivivP （ 3-1） )(23 qddq ivivQ （ 3-2） where P and Q are active and reactive power, respectively, v is grid voltage, and i is 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, qvwill be equal to zero. Then, active and reactive power may be expressed as dd ivP 23（ 3-3） qd ivQ 23（ 3-4） According to earlier equations, active and reactive power control can be achieved by controlling direct and quadrature current components, respectively. Two control paths are used to control these currents. In the first path, with given reactive power, the q-axis current reference 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. This assures that all the power coming from the rectifier is transferred to the grid. For this 14 control, two methods are proposed: 1) capacitor voltage (CV) control and 2) dc-link voltage (iV) control. In the first control method (control mode 1 in Fig. 10), capacitor voltage is kept constant at reference value. In the control loop, when shoot-through time changes, dcVand iVwill change. However, in other method (control mode 2 in Fig. 10), a reference value is set for dc-link voltage (iV). In this method, with changing shoot-through time, dcVand CVwill change. The input voltage of inverter is zero in shoot through state, which makes iVa difficult variable to control. Consequently, (2-6) is used to control iVindirectly by controlling CV. 2） Maximum Power Point Tracking The mechanical power delivered by a wind turbine is expressed as 321 mpm VACP （ 3-5） Where is the air density, A is the area swept out by t