電力電子技術(shù) 外文翻譯

1、<p>　　1 Power Electronic Concepts</p><p>　　Power electronics is a rapidly developing technology. Components are tting higher current and voltage ratings, the power losses decrease and the devices become

2、 more reliable. The devices are also very easy tocontrol with a mega scale power amplification. The prices are still going down pr. kVA and power converters are becoming attractive as a mean to improve the performance of

3、 a wind turbine. This chapter will discuss the standard power converter topologies from the simplest converters for start</p><p>　　1.1 Criteria for concept evaluation</p><p>　　The most common to

4、pologies are selected and discussed in respect to advantages and drawbacks. Very advanced power converters, where many extra devices are necessary in order to get a proper operation, are omitted.</p><p>　　1.

5、2 Power converters</p><p>　　Many different power converters can be used in wind turbine applications. In the case of using an induction generator, the power converter has to convert from a fixed voltage and

6、frequency to a variable voltage and frequency. This may be implemented in many different ways, as it will be seen in the next section. Other generator types can demand other complex protection. However, the most used top

7、ology so far is a soft-starter, which is used during start up in order to limit the in-rush current a</p><p>　　1.2.1 Soft starter</p><p>　　The soft starter is a power converter, which has been i

8、ntroduced to fixed speed wind turbines to reduce the transient current during connection or disconnection of the generator to the grid. When the generator speed exceeds the synchronous speed, the soft-starter is connecte

9、d. Using firing angle control of the thyristors in the soft starter the generator is smoothly connected to the grid over a predefined number of grid periods. An example of connection diagram for the softstarter with a ge

10、nerat</p><p>　　Figure 1. Connection diagram of soft starter with generators.</p><p>　　The commutating devices are two thyristors for each phase. These are connected in anti-parallel. The relatio

11、nship between the firing angle (﹤) and the resulting amplification of the soft starter is non-linear and depends additionally on the power factor of the connected element. In the case of a resistive load, may vary betwee

12、n 0 (full on) and 90 (full off) degrees, in the case of a purely inductive load between 90 (full on) and 180 (full off) degrees. For any power factor between 0 and 90 degre</p><p>　　Figure 2. Control charact

13、eristic for a fully controlled soft starter.</p><p>　　When the generator is completely connected to the grid a contactor (Kbyp) bypass the soft-starter in order to reduce the losses during normal operation.

14、The soft-starter is very cheap and it is a standard converter in many wind turbines.</p><p>　　1.2.2 Capacitor bank</p><p>　　For the power factor compensation of the reactive power in the generat

15、or, AC capacitor banks are used, as shown in Figure 3. The generators are normally compensated into whole power range. The switching of capacitors is done as a function of the average value of measured reactive power dur

16、ing a certain period.</p><p>　　Figure 3. Capacitor bank configuration for power factor compensation in a wind turbine.</p><p>　　The capacitor banks are usually mounted in the bottom of the tower

17、 or in the</p><p>　　nacelle. In order to reduce the current at connection/disconnection of capacitors a coil (L) can be connected in series. The capacitors may be heavy loaded and damaged in the case of over

18、-voltages to the grid and thereby they may increase the maintenance cost.</p><p>　　1.2.3 Diode rectifier</p><p>　　The diode rectifier is the most common used topology in power electronic applica

19、tions. For a three-phase system it consists of six diodes. It is shown in Figure 4.</p><p>　　Figure 4. Diode rectifier for three-phase ac/dc conversion</p><p>　　The diode rectifier can only be u

20、sed in one quadrant, it is simple and it is not</p><p>　　possible to control it. It could be used in some applications with a dc-bus.</p><p>　　1.2.4 The back-to-back PWM-VSI</p><p>

21、　　The back-to-back PWM-VSI is a bi-directional power converter consisting of two conventional PWM-VSI. The topology is shown in Figure 5.</p><p>　　To achieve full control of the grid current, the DC-link vol

22、tage must be boosted to a level higher than the amplitude of the grid line-line voltage. The power flow of the grid side converter is controlled in order to keep the DC-link voltage constant, while the control of the gen

23、erator side is set to suit the magnetization demand and the reference speed. The control of the back-to-back PWM-VSI in the wind turbine application is described in several papers (Bogalecka, 1993), (Knowles-Spittle et a

24、</p><p>　　Figure 5. The back-to-back PWM-VSI converter topology.</p><p>　　1.2.4.1 Advantages related to the use of the back-to-back PWM-VSI</p><p>　　The PWM-VSI is the most frequent

25、ly used three-phase frequency converter. As a consequence of this, the knowledge available in the field is extensive and well established. The literature and the available documentation exceed that for any of the other c

26、onverters considered in this survey. Furthermore, many manufacturers produce components especially designed for use in this type of converter (e.g., a transistor-pack comprising six bridge coupled transistors and anti pa

27、ralleled diodes). Due to thi</p><p>　　A technical advantage of the PWM-VSI is the capacitor decoupling between the grid inverter and the generator inverter. Besides affording some protection, this decoupling

28、 offers separate control of the two inverters, allowing compensation of asymmetry both on the generator side and on the grid side, independently.</p><p>　　The inclusion of a boost inductance in the DC-link c

29、ircuit increases the component count, but a positive effect is that the boost inductance reduces the demands on the performance of the grid side harmonic filter, and offers some protection of the converter against abnorm

30、al conditions on the grid.</p><p>　　1.2.4.2 Disadvantages of applying the back-to-back PWM-VSI</p><p>　　This section highlights some of the reported disadvantages of the back-to-back PWM-VSI whi

31、ch justify the search for a more suitable alternative converter:</p><p>　　In several papers concerning adjustable speed drives, the presence of the DC link capacitor is mentioned as a drawback, since it is h

32、eavy and bulky, it increases the costs and maybe of most importance, - it reduces the overall lifetime of the system. (Wen-Song & Ying-Yu, 1998); (Kim & Sul, 1993); (Siyoung Kim et al., 1998).</p><p>

33、;　　Another important drawback of the back-to-back PWM-VSI is the switching losses. Every commutation in both the grid inverter and the generator inverter between the upper and lower DC-link branch is associated with a ha

34、rd switching and a natural commutation. Since the back-to-back PWM-VSI consists of two inverters, the switching losses might be even more pronounced. The high switching speed to the grid may also require extra EMI-filter

35、s.</p><p>　　To prevent high stresses on the generator insulation and to avoid bearing current problems (Salo & Tuusa, 1999), the voltage gradient may have to be limited by applying an output filter.</

36、p><p>　　1.2.5 Tandem converter</p><p>　　The tandem converter is quite a new topology and a few papers only have treated it up till now ((Marques & Verdelho, 1998); (Trzynadlowski et al., 1998a)

37、; (Trzynadlowski et al., 1998b)). However, the idea behind the converter is similar to those presented in ((Zhang et al., 1998b)), where the PWM-VSI is used as an active harmonic filter to compensate harmonic distortion.

38、 The topology of the tandem converter is shown in Figure 6.</p><p>　　Figure 6. The tandem converter topology used in an induction generator wind turbine system.</p><p>　　The tandem converter con

39、sists of a current source converter, CSC, in the</p><p>　　following designated the primary converter, and a back-to-back PWM-VSI, designated the secondary converter. Since the tandem converter consists of fo

40、ur controllable inverters, several degrees of freedom exist which enable sinusoidal input and sinusoidal output currents. However, in this context it is believed that the most advantageous control of the inverters is to

41、control the primary converter to operate in square-wave current mode. Here, the switches in the CSC are turned on and off only once</p><p>　　Unlike the primary converter, the secondary converter has to opera

42、te at a high switching frequency, but the switched current is only a small fraction of the total load current. Figure 7 illustrates the current waveform for the primary converter, the secondary converter, is, and the tot

43、al load current il.</p><p>　　In order to achieve full control of the current to/from the back-to-back PWMVSI, the DC-link voltage is boosted to a level above the grid voltage. As mentioned, the control of th

44、e tandem converter is treated in only a few papers. However, the independent control of the CSC and the back-to-back PWM-VSI are both well established, (Mutschler & Meinhardt, 1998); (Nikolic & Jeftenic, 1998); (

45、Salo & Tuusa, 1997); (Salo & Tuusa, 1999).</p><p>　　Figure 7. Current waveform for the primary converter, ip, the secondary converter, is, and the total load current il.</p><p>　　1.2.5.1

46、 Advantages in the use of the Tandem Converter</p><p>　　The investigation of new converter topologies is commonly justified by the</p><p>　　search for higher converter efficiency. Advantages of

47、the tandem converter are the low switching frequency of the primary converter, and the low level of the switched current in the secondary converter. It is stated that the switching losses of a tandem inverter may be redu

48、ced by 70%, (Trzynadlowski et al., 1998a) in comparison with those of an equivalent VSI, and even though the conduction losses are higher for the tandem converter, the overall converter efficiency may be increased.</p

49、><p>　　Compared to the CSI, the voltage across the terminals of the tandem converter contains no voltage spikes since the DC-link capacitor of the secondary converter is always connected between each pair of in

50、put- and output lines (Trzynadlowski et al., 1998b).</p><p>　　Concerning the dynamic properties, (Trzynadlowski et al., 1998a) states that the overall performance of the tandem converter is superior to both

51、the CSC and the VSI. This is because current magnitude commands are handled by the voltage source converter, while phase-shift current commands are handled by the current source converter (Zhang et al., 1998b).</p>

52、<p>　　Besides the main function, which is to compensate the current distortion introduced by the primary converter, the secondary converter may also act like an active resistor, providing damping of the primary in

53、verter in light load conditions (Zhang et al., 1998b).</p><p>　　1.2.5.2 Disadvantages of using the Tandem Converter</p><p>　　An inherent obstacle to applying the tandem converter is the high num

54、ber of components and sensors required. This increases the costs and complexity of both hardware and software. The complexity is justified by the redundancy of the system (Trzynadlowski et al., 1998a), however the system

55、 is only truly redundant if a reduction in power capability and performance is acceptable.</p><p>　　Since the voltage across the generator terminals is set by the secondary inverter, the voltage stresses at

56、the converter are high. Therefore the demands on the output filter are comparable to those when applying the back-to-back PWM-VSI.</p><p>　　In the system shown in Figure 38, a problem for the tandem converte

57、r in comparison with the back-to-back PWM-VSI is the reduced generator voltage. By applying the CSI as the primary converter, only 0.866% of the grid voltage can be utilized. This means that the generator currents (and a

58、lso the current through the switches) for the tandem converter must be higher in order to achieve the same power.</p><p>　　1.2.6 Matrix converter</p><p>　　Ideally, the matrix converter should be

59、 an all silicon solution with no passive components in the power circuit. The ideal conventional matrix converter topology is shown in Figure 8.</p><p>　　Figure 8. The conventional matrix converter topology.

60、</p><p>　　The basic idea of the matrix converter is that a desired input current (to/from the supply), a desired output voltage and a desired output frequency may be obtained by properly connecting the outpu

61、t terminals of the converter to the input terminals of the converter. In order to protect the converter, the following two control rules must be complied with: Two (or three) switches in an output leg are never allowed t

62、o be on at the same time. All of the three output phases must be connected to an in</p><p>　　1.2.6.1 Advantages of using the Matrix Converter</p><p>　　This section summarises some of the advanta

63、ges of using the matrix converter in the control of an induction wind turbine generator. For a low output frequency of the converter the thermal stresses of the semiconductors in a conventional inverter are higher than t

64、hose in a matrix converter. This arises from the fact that the semiconductors in a matrix converter are equally stressed, at least during every period of the grid voltage, while the period for the conventional inverter e

65、quals the output </p><p>　　thermal design problems for the matrix converter. </p><p>　　Although the matrix converter includes six additional power switches compared to the back-to-back PWM-VSI,

66、the absence of the DC-link capacitor may increase the efficiency and the lifetime for the converter (Schuster, 1998). Depending on the realization of the bi-directional switches, the switching losses of the matrix invert

67、er may be less than those of the PWM-VSI, because the half of the switchings become natural commutations (soft switchings) (Wheeler & Grant, 1993).</p><p>　　1.2.6.2 Disadvantages and problems of the matr

68、ix converter</p><p>　　A disadvantage of the matrix converter is the intrinsic limitation of the output voltage. Without entering the over-modulation range, the maximum output voltage of the matrix converter

69、is 0.866 times the input voltage. To achieve the same output power as the back-to-back PWM-VSI, the output current of the matrix converter has to be 1.15 times higher, giving rise to higher conducting losses in the conve

70、rter (Wheeler & Grant, 1993).</p><p>　　In many of the papers concerning the matrix converter, the unavailability of a true bi-directional switch is mentioned as one of the major obstacles for the propaga

71、tion of the matrix converter. In the literature, three proposals for realizing a bi-directional switch exists. The diode embedded switch (Neft & Schauder, 1988) which acts like a true bi-directional switch, the commo

72、n emitter switch and the common collector switch (Beasant et al., 1989). </p><p>　　Since real switches do not have infinitesimal switching times (which is not desirable either) the commutation between two in

73、put phases constitutes a contradiction between the two basic control rules of the matrix converter. In the literature at least six different commutation strategies are reported, (Beasant et al., 1990); (Burany, 1989); (J

74、ung & Gyu, 1991); (Hey et al., 1995); (Kwon et al., 1998); (Neft & Schauder, 1988). The most simple of the commutation strategies are those reported in (Bea</p><p><b>　　譯 文</b></p>

75、<p>　　1 電力電子技術(shù)的內(nèi)容</p><p>　　電力電子技術(shù)是一門正在快速發(fā)展的技術(shù),電力電子元器件有很高的額定電流和額定電壓,它的功率減小元件變得更加可靠、耐用.這種元件還可以用來控制比它功率大很多倍的元件。電力電子元件的價格不高而且還在繼續(xù)下降,由它發(fā)展而成的變流技術(shù)逐漸被應(yīng)用在風(fēng)力發(fā)電中。這一章將討論標(biāo)準(zhǔn)的變流器技術(shù)從簡單轉(zhuǎn)換以啟動風(fēng)力機(jī)推進(jìn)變流器技術(shù)的發(fā)展.進(jìn)一步說,利用電力電子技術(shù)

76、解決各種問題的渠道還在探索之中。</p><p>　　1.1電力電子概念評價標(biāo)準(zhǔn)的選擇</p><p>　　很多普通的電力電子技術(shù)被討論和研究是為了了解它們的優(yōu)缺點，現(xiàn)在正在發(fā)展的逆變器中增設(shè)有很多額外的元件是必要的，以獲得正常的操作和運行結(jié)果。</p><p><b>　　1.2 功率變換器</b></p><p>　

77、　有各種各樣的功率變換器被應(yīng)用在風(fēng)力發(fā)電中。在使用電力電子產(chǎn)品時,功率變換器可以改變其電壓和頻率.當(dāng)然,目前有很多方法可以實現(xiàn)上述功能,具體內(nèi)容在下一節(jié)中講到。</p><p>　　其它類型發(fā)電機(jī)要求有很多復(fù)雜的其它保護(hù)，但是,到目前為止應(yīng)用最多的技術(shù)是軟啟動,利用軟啟動可以限制并網(wǎng)時的沖擊電流從而可以減少沖擊電流對電網(wǎng)的干擾。</p><p>　　1.2.1 軟啟動器</p>

78、<p>　　軟啟動器是一種功率轉(zhuǎn)換器,它已被應(yīng)用在衡速風(fēng)力機(jī)中以減少發(fā)電機(jī)并網(wǎng)或脫網(wǎng)時引起的沖擊電流。當(dāng)發(fā)電機(jī)轉(zhuǎn)速超過同步轉(zhuǎn)速時軟啟動裝置開始啟動,同過控制晶閘管的導(dǎo)通角將發(fā)電機(jī)緩慢并入電網(wǎng)。如圖1所示是具有軟啟動的發(fā)電機(jī)并網(wǎng)原理圖。</p><p>　　圖1 具有軟啟動的異步發(fā)電機(jī)并網(wǎng)示意圖</p><p>　　軟并網(wǎng)裝置是由在發(fā)電機(jī)與電網(wǎng)每相之間串接兩只反并聯(lián)的晶閘管組成

79、，軟并網(wǎng)裝置的導(dǎo)通角和功率放大系數(shù)是非線性關(guān)系。如果是純電阻性負(fù)載，則導(dǎo)通角變化范圍在0°～90°之間。如果是純電感性負(fù)載，則導(dǎo)通角變化范圍在90°～180°之間。如圖2是晶閘管導(dǎo)通角范圍示意圖。</p><p>　　圖2 晶閘管導(dǎo)通角區(qū)間示意圖</p><p>　　軟啟動裝置能夠限制在發(fā)電機(jī)并入電網(wǎng)時引起的沖擊電流，而且軟啟動裝置是一種既經(jīng)濟(jì)又可靠

80、的啟動裝置，在風(fēng)力發(fā)電中得到了廣泛的應(yīng)用。</p><p>　　1.2.2 電容器組</p><p>　　在風(fēng)力發(fā)電中經(jīng)常使用電容器組補(bǔ)償無功功率以提高發(fā)電機(jī)的功率因數(shù)，如圖3所示。</p><p>　　圖3 風(fēng)力發(fā)電中用電容器組補(bǔ)償功功率示意圖</p><p>　　在風(fēng)力發(fā)電中，通常發(fā)電機(jī)需要在整個功率范圍內(nèi)進(jìn)行補(bǔ)償。把電容器并聯(lián)在一起來測

81、量特定周期內(nèi)的無功功率平均值，它們通常被安裝在塔架或大機(jī)床的低部用來限制發(fā)電機(jī)并網(wǎng)時的沖擊電流。因為電容器可吸收電網(wǎng)過電壓從而保護(hù)發(fā)電機(jī)和電網(wǎng)不受過電壓的損害，減少了系統(tǒng)運行的維修費用。</p><p>　　1.2.3 二極管整流器</p><p>　　二極管整流器是最常見的電力電子器件。在三相交流系統(tǒng)中的整流裝置有六只二極管組成，如圖4所示。</p><p>　　

82、圖4 利用二極管進(jìn)行三相交–直轉(zhuǎn)換示意圖</p><p>　　二極管整流裝置只能用在一個象限，簡單而且不可控，它有時也被應(yīng)用在直流母線上。</p><p>　　1.2.4 脈寬調(diào)制變頻技術(shù)</p><p>　　脈寬調(diào)制變頻是由兩只普通的雙相變流器連接在一起組成的。如圖5所示。</p><p>　　圖5 脈寬調(diào)制變頻器組成框圖</p>

83、;<p>　　為了能夠完全控制電網(wǎng)電流，支流聯(lián)絡(luò)線電壓必須提高到比電網(wǎng)電壓幅值更高的水平。而控制電網(wǎng)潮流是為了保持支流聯(lián)絡(luò)線電壓恒定。控制發(fā)電機(jī)能夠適應(yīng)磁化需求和額定轉(zhuǎn)速。脈寬調(diào)制技術(shù)在風(fēng)力發(fā)電中的應(yīng)用在其它一些文章中也有見紹，如（(Bogaleaka, 1993), (Knowles-Spittle 網(wǎng)站, 1998), (Pena 網(wǎng)站, 1996), (Yifan & Longya, 1992), (Yifa

84、n & Longya, 1995)等。</p><p>　　1.2.4.1 脈寬調(diào)制技術(shù)的優(yōu)點</p><p>　　脈寬調(diào)制技術(shù)使用最頻繁的三相變頻器。因此，脈寬調(diào)制被廣泛應(yīng)用而且效果很好。報導(dǎo)關(guān)于這種變頻器的文獻(xiàn)資料和文件要遠(yuǎn)比報導(dǎo)其它轉(zhuǎn)換器的多，此外，許多生產(chǎn)廠家的一些特殊設(shè)備也都使用這類轉(zhuǎn)換器，（如六相橋式晶體管變頻電路就是由晶體管和二極管反向并聯(lián)而組成的）。由于這種產(chǎn)品的成

85、本比較低，有利于設(shè)計和生產(chǎn)體積更小的產(chǎn)品。</p><p>　　一種新的脈寬調(diào)制技術(shù)是在電網(wǎng)逆變器和發(fā)電機(jī)逆變器之間進(jìn)行電容去耦，除了上述作用外它還能提供一些保護(hù)功能。這種去耦可在電網(wǎng)逆變器和發(fā)電機(jī)逆變器之間進(jìn)行隔離操作以補(bǔ)償電網(wǎng)和發(fā)電機(jī)之間的不平衡程度。但缺點是增加了直流聯(lián)絡(luò)線回路中的增益電感的數(shù)目，不過這種電感對電網(wǎng)斜波濾波器性能的要求降低拉，而且當(dāng)電網(wǎng)出現(xiàn)異常情況時可以保護(hù)逆變器不受損害。</p>

86、;<p>　　1.2.4.2 脈寬調(diào)制在使用中的缺點</p><p>　　這一節(jié)重點介紹脈寬調(diào)制逆變器在使用中存在的缺點，以便進(jìn)行選擇更加符合實際條件的逆變器。</p><p>　　在一些書中介紹了另一種可供選擇的逆變器—頻率驅(qū)動逆變器，可是現(xiàn)在直流聯(lián)絡(luò)線存在的問題是雖然它的功率穩(wěn)定但它的體積大，這樣就增加了成本，更重要的是它的存在可能會降低電網(wǎng)運行壽命。</p>

87、<p>　　脈寬調(diào)制的另一個嚴(yán)重的缺陷是它的換相開關(guān)有時候可能會失靈，在電網(wǎng)整流器和發(fā)電機(jī)整流器之間進(jìn)行的整流是在直流聯(lián)絡(luò)線的上下限進(jìn)行強(qiáng)制整流和自然整流。脈寬調(diào)制逆變器是由兩個逆變器組成的，逆變調(diào)制失敗的幾率可能更加明顯。電網(wǎng)逆變頻率很高時可能需要額外增加電磁干擾濾波器，為了防止對發(fā)電機(jī)絕緣體和轉(zhuǎn)子電流造成傷害，在使用脈寬調(diào)制逆變器時必須通過濾波器來降低電壓梯度。</p><p>　　1.2.5

88、串聯(lián)逆變器</p><p>　　串聯(lián)逆變器技術(shù)是一種最新發(fā)展起來的技術(shù)，以前很少有過關(guān)于這種逆變器的報導(dǎo)直到最近才被人們重視起來。不過，這種逆變器下面的用法類似于前面提到的脈寬調(diào)制，在脈寬寬調(diào)制技術(shù)中來補(bǔ)償因諧波濾波器而發(fā)生的諧波畸變是非常有用的。串聯(lián)逆變器的應(yīng)用如圖6所示。</p><p>　　圖6 串聯(lián)逆變器在風(fēng)力發(fā)電中的應(yīng)用示意圖</p><p>　　由串聯(lián)逆

89、變器可組成電流源逆變器，其中串聯(lián)逆變器主要進(jìn)行一次逆變，脈寬調(diào)制進(jìn)行二次逆變。這些串聯(lián)逆變器構(gòu)成四個可控的逆變器，通過控制可將自由度數(shù)通過輸入的正弦波形變?yōu)檎仪€的電流而輸出。然而，在這里人們相信這種逆變器的最大好處是可以通過控制轉(zhuǎn)換裝置來控制一次逆變進(jìn)而控制電流幅度變化模型。在電流源逆變器中通過周期性的控制開關(guān)的閉合狀態(tài)來輸入或輸出電流。在電流幅度變化模型中，一次逆變開關(guān)可以是可關(guān)斷晶閘管，也可以是絕緣柵雙極晶閘管或則是二極管。&l

90、t;/p><p>　　與一次逆變不同，二次逆變必須在高頻狀態(tài)下進(jìn)行開關(guān)操作，但是它的關(guān)斷電流只占總負(fù)荷電流很小一部分。如圖7舉例說明一次逆變、二次逆變和總負(fù)荷電流之間的關(guān)系。</p><p>　　圖7 一次逆變電流波形（ip）、二次逆變電流波形（is）和總負(fù)荷電流波形（il）</p><p>　　為了能利用脈寬調(diào)制技術(shù)完全控制電流，直流聯(lián)絡(luò)線的電壓水平必須高于電網(wǎng)電壓水

91、平。前面已經(jīng)提到，串聯(lián)逆變器技術(shù)很少被人們重視，然而，作為一種獨立的控制技術(shù)串聯(lián)有源逆變和脈寬調(diào)制是積極和有效的。</p><p>　　1.2.5.1 使用串聯(lián)逆變器的優(yōu)點</p><p>　　據(jù)調(diào)查這種新的逆變技術(shù)被普遍認(rèn)為是一種逆變效率很高的逆變器，使用這種串聯(lián)逆變器的優(yōu)點是它的一次逆變關(guān)斷頻率低，二次逆變關(guān)斷電流水平不高。實踐證明，雖然開關(guān)的閉合將使串聯(lián)逆變器的效率下降70%，(Tr

92、zynadlowski 網(wǎng)站, 1998a)。但由于脈寬調(diào)制逆變器的效率遠(yuǎn)低于串聯(lián)逆變器，所以總的來說使用串聯(lián)逆變器后其總平均效率還是提高了。</p><p>　　與通道狀態(tài)指示器相比，電壓通過串聯(lián)逆變器末端時沒有阻斷電壓，這時在進(jìn)行二次你變時直流聯(lián)絡(luò)線上的電容器將始終保持與輸入或輸出線路相連(Trzynadlowski 網(wǎng)站, 1998b)。</p><p>　　關(guān)于串聯(lián)逆變器的動態(tài)特性

93、，(Trzynadlowski 網(wǎng)站, 1998a)指出串聯(lián)逆變器要比電流源逆變器和電壓源逆變器性能優(yōu)越。因為電流大小由電壓源逆變決定，而電流移相范圍由電流源逆變決定。</p><p>　　除了這些主要功能外，如果在輕載下進(jìn)行一次逆變，串聯(lián)逆變器也可以扮演電阻的角色補(bǔ)償因一次逆變和二次逆變時的電流波形失真，提供阻尼的主要依據(jù)是根據(jù)負(fù)載狀況。</p><p>　　1.2.5.2 使用串聯(lián)逆變

94、器的缺點</p><p>　　串聯(lián)逆變器的固有缺點是由大量元件組成的，這樣就增加了對硬件與軟件的成本和復(fù)雜性。為此這種太過復(fù)雜的逆變器就得進(jìn)行精簡(Trzynadlowski 網(wǎng)站, 1998a)，但為了減少功率損耗有些額外的設(shè)備也是必須的。</p><p>　　當(dāng)電壓經(jīng)一次逆變到達(dá)發(fā)電機(jī)端時，加在逆變器上的電壓將會很高。因此，在使用脈寬調(diào)制逆變時就需要輸出濾波器來進(jìn)行比較和選擇。<

95、/p><p>　　如圖1是逆變器在電力系統(tǒng)中的應(yīng)用示意圖，存在的問題是串聯(lián)逆變器將使電網(wǎng)電壓下降。通過使用電流源逆變器進(jìn)行一次逆變，只有0.886%的電網(wǎng)電壓可被利用，為了達(dá)到相同的功率，這就意味著通過串聯(lián)逆變器的電網(wǎng)電壓（或者是通過接觸器的電流）必須增加。</p><p>　　1.2.6 矩陣逆變器</p><p>　　理想的矩陣逆變器必須是由純凈的硅溶液組成，在電力

96、線路中沒有任何其它雜質(zhì)成分。傳統(tǒng)矩陣逆變器技術(shù)應(yīng)用如圖8所示。</p><p>　　圖8 矩陣逆變器應(yīng)用示意圖</p><p>　　矩陣逆變器最基本的用途是通過合理的連接逆變器的輸出端與發(fā)電機(jī)的輸入端來獲得電流輸出希望值（從補(bǔ)償處得到），電壓輸出希望值，頻率輸出希望值。為了保護(hù)逆變器，下面兩條規(guī)則必須遵循：在輸出支路處的兩個（或三個）開關(guān)絕對不允許同時打開。在任何時候所有三相輸出必須和單相

97、輸入相連。開關(guān)的實際連接要依據(jù)調(diào)制手段。</p><p>　　1.2.6.1 矩陣逆變器的優(yōu)點</p><p>　　這部分主要見紹在異步風(fēng)力發(fā)電機(jī)中使用矩陣逆變器的優(yōu)點。與傳統(tǒng)逆變器相比，使用矩陣逆變器的輸出頻率低，而且發(fā)熱少。在矩陣逆變器中，半導(dǎo)體器件在減少輸出頻率和熱量方面起著很重要的作用，至少在每個電網(wǎng)周期內(nèi)其對頻率的抑制是非常有用的，這對矩陣逆變器來說是技術(shù)難點。</p>

98、;<p>　　盡管矩陣逆變器額外增設(shè)了六只電力開關(guān)，與脈寬調(diào)制逆變器相比少了直流聯(lián)絡(luò)線電容器，這樣就增加了逆變器的工作效率和使用壽命(舒斯特,1998年)。依靠雙相轉(zhuǎn)換開關(guān)，矩陣逆變器的開關(guān)轉(zhuǎn)損耗要比脈寬調(diào)制逆變的少，那是因為自然交換減少了將近一半的開關(guān)操作損耗。（軟開關(guān)），(惠勒·格蘭特,1993)。</p><p>　　1.2.6.2 矩陣逆變器的缺點</p><p

99、>　　矩陣逆變器的缺點是因受自身條件限制它的輸出電壓比較低。在調(diào)制范圍內(nèi)，矩陣逆變器的輸出電壓只有輸入電壓的0.866倍，為了得到相同的輸出功率，矩陣逆變器的損耗將是普通逆變器的1.15倍。</p><p>　　有許多文章中報道說使用雙相選擇開關(guān)其效率降低是矩陣逆變器最大的缺點。有人提出三種方法讓雙相轉(zhuǎn)換開關(guān)在矩陣逆變器繼續(xù)存在，可以用像脈寬調(diào)制中的二極管轉(zhuǎn)換開關(guān)、普通發(fā)射開關(guān)和普通選擇開關(guān)來代替矩陣逆變器

100、中的雙相轉(zhuǎn)換開關(guān)。</p><p>　　但是，在相位轉(zhuǎn)換時現(xiàn)實的轉(zhuǎn)換開關(guān)沒有無窮小的轉(zhuǎn)換時間，這與矩陣逆變器的兩條規(guī)則是相矛盾的。有些書籍中至少列出了六種不同的轉(zhuǎn)換方法，Casadei et al., 1994); (Casadei et al., 1995a); (Casadei et al., 1995b); (Casadei et al., 1996); (Enjeti & Wang, 1990);