外文翻譯---永磁牽引電機(jī)的崛起

1、<p><b>　　外文原文</b></p><p>　　The Rise Of The Permanent-magnet TractioMotor</p><p>　　Technology offering benefits in terms of mass, size and energy consumption, the permanent-magne

2、t synchronous machine is increasingly being adopted for traction drives, despite the need for complex control systems and potential failure modes.</p><p>　　In the past couple of years, many of the bids for n

3、ew rolling stock placed with major international suppliers have proposed the use of permanent-magnet synchronous traction motors, which are smaller and lighter than the three-phase induction motors that have dominated th

4、e market in recent times.</p><p>　　Permanent-magnet motors first came to prominence with the use of two powered bogies from Alstom's AGV in the V150 trainset which broke the world speed record on April 3

5、 2007, but they have subsequently been used in a variety of applications, ranging from the Citadis-Dualis tram-train to SBB's Twindexx double-deck inter-city trainsets (Table I).</p><p>　　Although railwa

6、y operators are often viewed as conservative in the adoption of new technologies, the designers and manufacturers of rail traction systems tend to capitalise on the latest drive technologies, which are rapidly deployed i

7、n service if they promise significant performance improvements. This was the case for the early choppers supplying series-connected DC traction motors, separately-excited DC motors, synchronous AC motors and drives (as u

8、sed on the first generations of TGVs) and for</p><p>　　The permanent-magnet synchronous machine, with its associated control electronics, represents the latest such advance in traction technology. Millions o

9、f small PMSMs are already being used in the transmissions of hybrid cars, thanks to their low mass and good controllability. Larger machines offer a similar potential to enhance the overall performance of the railway tra

10、ction package. The technology is now beginning to be introduced into a variety of new rolling stock, but the integration of PMSM</p><p>　　Fundamental requirements </p><p>　　Petrol and diesel eng

11、ines for automotive applications generally require complex gearboxes to allow the prime mover to operate in the optimum speed band. By contrast, electric motors for rail traction are expected to operate effectively and e

12、fficiently over the entire speed range, allowing a permanent coupling to the axles and wheels, either directly or via a single ratio gearbox. This mechanically elegant solution results in highly reliable drives which nee

13、d relatively little maintenance.</p><p>　　Thus the first requirement placed on the design of traction motors is the ability to provide torque or tractive effort over a wide speed range, such as from 0 to 320

14、 km/h.</p><p>　　Whilst it is essential for the traction motor to operate reliably, it is equally important from the driver's and railway operator's perspective that modern traction systems control th

15、e torque accurately and smoothly throughout the speed range. Excellent torque control results in optimum use of available adhesion between wheel and rail, along with smooth acceleration and the ability to cruise at a con

16、stant speed and to brake the train electrically (dynamic braking).</p><p>　　Tractive effort, power and speed </p><p>　　The torque produced in a traction motor is translated into a linear force a

17、t the wheel-rail interface. This force, which causes the train to accelerate or brake dynamically, is normally referred to as the tractive effort. Fig 1 shows the TE curve of a typical drive system, together with the ass

18、ociated train or vehicle resistance curve. The TE curve intersects the resistance curve at the so-called balancing speed, that is, the theoretical maximum speed. Close to this speed, there is only a very s</p><

19、;p>　　Traction motors are generally designed to match a particular duty. The motor must produce the required full torque at zero speed and sustain this torque up to the so-called base speed, throughout region 1 of the

20、TE curve. Above this speed, the machine operates at its maximum power output, and in region 2 the tractive effort is therefore inversely proportional to the speed v. In the third region, tractive effort has to reduce in

21、inverse proportion to v² because of machine limitations.</p><p>　　Torque control </p><p>　　At low speeds, the motor can in theory provide a torque that is greater than that which can be tra

22、nsmitted by means of the adhesion available at the wheel-rail interface. However, this would overload the motor beyond the normally accepted level and must therefore be avoided either by driver action or an electronic co

23、ntrol system.</p><p>　　Early DC traction drives were controlled by adjusting the supply voltage using series resistances and by changing the motor group configuration. Today, both DC commutator motors and cl

24、assic synchronous and asynchronous AC motors are controlled electronically, by varying either the voltage or the voltage and frequency. Modern power drives with relatively simple algorithms achieve very good control of t

25、ractive effort throughout the speed range.</p><p>　　Power control of permanent-magnet synchronous machines can easily deliver good performance in the constant-torque region, but this needs complex algorithms

26、 to control the machine in the constant power region.</p><p>　　AC and DC motors, as well as PMSMs, fundamentally rely on the same physics to generate accelerating and braking torques. Hence the control strat

27、egies are similar to some extent. In all types of machines, the torque is created through the interaction between two magnetic fields. To generate a torque, there must be an appropriate electrical angle (ideally 90°

28、) between the two magnetic fields. These fields can be generated by currents flowing through windings or by permanent magnets.</p><p>　　Although today's traction applications mostly use three-phase induc

29、tion motors, it is important to understand the nature and behaviour of the magnetic fields in the stator and rotor of the different types of machine.</p><p>　　In a conventional DC traction motor, the north a

30、nd south poles of the stator field are always oriented in the same direction while the rotor field is maintained at a 90° (electrical) angle by the action of the commutator. In a series-connected machine, the same c

31、urrent flows through the stator and rotor windings (Fig 3), while a separately-excited machine allows the armature and stator fields to be controlled independently (Fig 4).</p><p>　　In a classic synchronous

32、three phase machine, the rotor field is produced by a current supplied via slip rings, and the orientation of the field is determined by the physical position of the rotor winding (Fig 5). The stator field is created by

33、currents flowing in the stator windings and rotates at the speed determined by the inverter frequency. The angle between stator and rotor fields increases as more torque is produced, but the rotor speed is the same as th

34、at of the stator field. A braking a</p><p>　　In an asynchronous three-phase machine, the magnetic field rotating in the stator induces currents in the rotor cage (Fig 6) that, in turn, generate a magnetic fi

35、eld which interacts with the stator field to produce either motoring or braking torque. In motoring, the rotor speed is lower than the rotating stator field speed set by the inverter, and in braking it is faster. No torq

36、ue is produced if the two speeds are the same. This difference can be expressed as slip frequency or percentage slip.</p><p>　　In a PMSM, the rotor field is created by magnets that are either distributed on

37、the surface of the rotor or buried in openings in the rotor laminations (Fig 7). The latter arrangement offers greater mechanical strength and much lower eddy-current losses in the rotor. The material with the strongest

38、magnetic properties is Neodymium Iron Boron (Nd2Fe14B). The stator field is generated by means of a relatively standard three-phase multipole winding on a laminated core.</p><p>　　In all electric machines, t

39、he rotating magnetic field leads to the generation of voltages that oppose the supply voltage(s), the so-called back EMF. At zero speed this is zero, but it grows linearly with speed. Thus the supply voltage must be incr

40、eased to maintain a constant torque in region 1.</p><p>　　The torque supplied or absorbed by an electric machine is given by the product of the magnetic flux and current. It is the role of the electronic pow

41、er converter to condition the DC or single-phase AC supply voltage such that a suitable current or currents flow in the motor. Many different types of converters are available, but most modern traction systems use insula

42、ted gate bipolar transistors (IGBTs) and some form of pulse-width modulation.</p><p>　　In the region of constant tractive effort, the voltage (and frequency in the case of induction machines) applied to the

43、terminals needs to increase linearly with motor speed so as to maintain the product of flux and current, that is the torque, at a constant level. Beyond the base speed, the applied voltage cannot be increased further due

44、 to the limitations of the power electronics and the insulation capability of the machine. However, mechanically, the machine can go faster.</p><p>　　So region 2 is entered by field weakening, thereby reduci

45、ng the level of back EMF or, in the case of a PMSM, counteracting its influence. In DC machines this is achieved by reducing the current flowing through the field windings (see the resistance RFW in Fig 3) and in a conve

46、ntional synchronous machine it is achieved by reducing the current supplied to the rotor. In an induction machine, field weakening happens automatically as the supply frequency is increased while the supply voltage is ke

47、pt </p><p>　　In region 3, the flux and current are reduced at a greater rate than in the constant power region to avoid exceeding the machine's electrical or mechanical limits. In the separately-excited

48、DC motor, for example, the armature current is also reduced as a function of speed.</p><p>　　Advantages and drawbacks </p><p>　　The main reason why permanent-magnet machines are being more and m

49、ore widely adopted for railway traction drives is that they offer very significant advantages compared with equivalent three-phase induction motors. The level of efficiency is 1% to 2% higher across 80% of the operating

50、range. The specific power is 30% to 35% greater, resulting in a machine that is about 25% smaller and lighter for the same power rating.</p><p>　　Whereas in an asynchronous motor heating of the rotor is caus

51、ed by the inherent slip power, this is virtually eliminated with a PM drive, avoiding the need for rotor cooling. Normally, PM machine stators are completely sealed and cooled by means of a heat transfer fluid, thus lead

52、ing to potentially more reliable drives. PMSMs also allow dynamic braking down to very low speeds and, in theory, it should be possible to produce a self-controlled retarder by electro-mechanically short-circuiting the &

53、lt;/p><p>　　Of course, these benefits are not available without compromise. There are seven main drawbacks to the use of permanent-magnet traction motors, although appropriate mitigation measures have been deve

54、loped.</p><p>　　Limitations on the size and cost of the four-quadrant converter and machine do not allow operation across the whole speed range by the simple expedient of supplying the machine with a voltage

55、 that is sufficiently higher than the back EMF to permit the flow of current required to achieve the desired torque. This constraint is solved by means of field weakening, creating the constant torque and constant power

56、regions. Since the field generated by the permanent magnets cannot be adjusted, field wea</p><p>　　These extra currents cause copper losses in the stator windings that negate, to some extent, the efficiency

57、gains that are achieved by the use of the low-loss permanent-magnet rotor.</p><p>　　In order to be able to control the currents that create the field weakening effect, it is necessary for the electronics to

58、know the position of the rotor, to an accuracy of between 1° and 2° (the field angle). For a four-pole machine this requires a mechanical resolution of better than 1.5°. If a sensor is used, its integrity

59、and reliability must be extremely high to ensure adequate performance. Sensorless approaches can be used, such as that developed by Schrödl1, but these can lead to a reduct</p><p>　　The magnetic flux is

60、 temperature-dependent in that the field strength reduces by about 1% per 10K increase in rotor temperature. With PMSMs operating over a temperature range of 200K (-40°C to a maximum permissible 160°C), this ca

61、n have a significant impact. Hence it is necessary for the electronics to monitor the operating temperature and to take this into account when controlling the electrical supply to the machine.</p><p>　　Each

62、PMSM requires its own individual highly-dependable electronic power controller to ensure that currents are injected at the right moment. However, modern traction systems increasingly use individual controls for each moto

63、r to optimise performance, so this is less of a consideration.</p><p>　　Irreversible demagnetisation occurs if very high currents flow in the machine at high temperatures, even if the rotor does not reach th

64、e Curie temperature of between 310°C and 370°C. Potentially more critical, though, a short-circuit in the stator windings can lead to the destruction of the machine, because the moving permanent magnet field wi

65、ll continue to induce high currents in the stator. However, demagnetisation helps to mitigate this problem.</p><p>　　Similarly, in no-load operation, when the train is coasting, the permanent-magnet rotor co

66、ntinues to induce currents in the stator core. These eddy currents, together with hysteresis effects, result in iron losses, which reduce the overall efficiency of the machine.</p><p>　　The rare-earth magnet

67、s used in PMSMs are magnetically strong but relatively delicate, both mechanically and thermally. The rotor construction is thus more complex than in the case of rotors for induction motors, and the design processes must

68、 be adapted accordingly. The control of the supply to the stator windings is also more complex since multiple feedback loops and signal transformations are required (Fig 8).</p><p>　　Although this list of po

69、tential drawbacks may seem extensive, there are many applications where the benefits of PMSMs greatly outweigh the disadvantages, which makes these machines highly attractive to traction designers. The smaller dimensions

70、 and lighter weight are beneficial where space in bogies is limited, such as where it is desired to integrate the drive in a stub-axle without a gearbox. The significantly better efficiency and much lower rotor losses of

71、fer significant benefits in terms of</p><p>　　Hence we can expect to see a much wider adoption of permanent-magnet traction motors in the coming years, in the same way that three-phase induction motors were

72、taken up with increasing popularity from the mid-1980s onwards.</p><p>　　The authors would like to thank Dr Harald Neudorfer and Markus Neubauer of Traktions-systeme Austria, and Dr Colin Goodman of BCRRE fo

73、r their assistance in the preparation of this article.</p><p><b>　　中文翻譯</b></p><p><b>　　永磁牽引電機(jī)的崛起</b></p><p>　　永磁同步電機(jī)，即使需要復(fù)雜的控制系統(tǒng)和潛在的失效模式，但鑒于其提了質(zhì)量、尺寸和能耗方面的益處

74、，越來(lái)越多地應(yīng)用于牽引傳動(dòng)裝置。</p><p>　　在過(guò)去的幾年中，許多大型國(guó)際供應(yīng)商競(jìng)相投標(biāo)那些使用永磁同步牽引電機(jī)的機(jī)車(chē)車(chē)輛，這種電機(jī)相比近期已經(jīng)占據(jù)市場(chǎng)的三相異步電動(dòng)機(jī)體積更小，重量更輕。 由于應(yīng)用了Alstom公司AGV的V150小火車(chē)的兩個(gè)強(qiáng)有力裝置。永磁同步牽引電機(jī)名聲大噪，而這個(gè)小火車(chē)曾在2007年4月3日打破了世界速度紀(jì)錄，但它們隨后被使用在各種各樣的裝置上，從Citadis車(chē)到SBB的

75、Twindexx雙層城際列車(chē)。</p><p>　　在采用新技術(shù)方面，鐵路運(yùn)營(yíng)商往往被視為是保守的，但鐵路牽引系統(tǒng)的設(shè)計(jì)者和制造商傾向于利用最新的驅(qū)動(dòng)技術(shù)，如果這些技術(shù)有望帶來(lái)顯著的性能改進(jìn)，就會(huì)很快地被應(yīng)用。正如早期的斬波器提供情況串聯(lián)的直流牽引電機(jī)，分別激式直流電動(dòng)機(jī)，交流同步電動(dòng)機(jī)和驅(qū)動(dòng)器（使用第一代的TGVs）和各代的鼠籠式異步（）三相驅(qū)動(dòng)器。隨著技術(shù)的不斷發(fā)展，牽引驅(qū)動(dòng)器變得更高效，更可控，從而能更好地

76、利用現(xiàn)有的附著力，同時(shí)降低能源消耗。</p><p>　　永久磁鐵同步機(jī)及相關(guān)的控制電子裝置，代表了最新的牽引技術(shù)。由于質(zhì)量輕及良好的可控性，數(shù)以百萬(wàn)計(jì)的小型永磁同步電機(jī)被應(yīng)用在混合動(dòng)力汽車(chē)的變速器上。較大的機(jī)器使得提高鐵路牽引包整體性能成為了可能。這項(xiàng)技術(shù)現(xiàn)在開(kāi)始被引入各種新的機(jī)車(chē)車(chē)輛，但集成的永磁同步電機(jī)牽引包所帶來(lái)的一些重大技術(shù)挑戰(zhàn)必須克服。 用于汽車(chē)應(yīng)用的汽油和柴油發(fā)動(dòng)機(jī)通常需要復(fù)雜的齒輪箱，以允

77、許原動(dòng)機(jī)操作的最佳速度頻帶。相比之下，用于軌道牽引的電動(dòng)馬達(dá)被期望在整個(gè)速度范圍內(nèi)能夠有效和高效地運(yùn)作，使一個(gè)永久耦合的車(chē)軸和車(chē)輪，直接地或通過(guò)一個(gè)單一的比變速箱。這種機(jī)械優(yōu)雅的解決方案能帶來(lái)高度可靠的驅(qū)動(dòng)器，而這種驅(qū)動(dòng)器需要相對(duì)較少的維護(hù)。因此，牽引電機(jī)設(shè)計(jì)的第一個(gè)要求是在很寬的速度范圍內(nèi)，如從0到320公里每小時(shí)能夠提供轉(zhuǎn)矩或牽引力。 現(xiàn)代牽引系統(tǒng)對(duì)牽引電動(dòng)機(jī)穩(wěn)定地運(yùn)作是必不可少的。同樣重要的是，從駕駛者的和鐵路運(yùn)營(yíng)商的角度

78、，現(xiàn)代牽引系統(tǒng)又能在寬泛的速度范圍內(nèi)準(zhǔn)確而又平穩(wěn)地控制轉(zhuǎn)矩。良好的轉(zhuǎn)矩控制可導(dǎo)致車(chē)輪和鋼軌之間有效附著力的最佳利用，平穩(wěn)的加速度及以恒度巡航和電力剎車(chē)的能力的獲得（動(dòng)態(tài)制動(dòng)）。</p><p>　　牽引力，動(dòng)力和速度 牽引電動(dòng)機(jī)產(chǎn)生的轉(zhuǎn)矩在輪軌接口處被轉(zhuǎn)換成一個(gè)線性力。這個(gè)力通常被稱(chēng)為作為牽引力，它會(huì)導(dǎo)致列車(chē)的加速或動(dòng)態(tài)制動(dòng)。圖1示一個(gè)典型的驅(qū)動(dòng)系統(tǒng)的TE曲線，以及與之相關(guān)聯(lián)的鐵路列車(chē)或車(chē)輛的阻力曲線。T

79、E曲線與阻力曲線相交于所謂的均衡速度，即理論上的最大速度。如圖1中的紅色箭頭所示：越接近這個(gè)速度，使火車(chē)加速可利用的牽引力越小。圖2所示：驅(qū)動(dòng)器產(chǎn)生的功率和所需的推進(jìn)功率即是速度和牽引力的乘積（相互作用的結(jié)果）。 牽引電機(jī)要遵循特定的要求去設(shè)計(jì)。在整個(gè)區(qū)域1的TE曲線上，電機(jī)必須在零速度產(chǎn)生所需的全轉(zhuǎn)矩，并持續(xù)這一轉(zhuǎn)矩至所謂的基本速度。超過(guò)這個(gè)速度，機(jī)器在其最大輸出功率上工作，因此在區(qū)域2可見(jiàn)牽引力和速度。在區(qū)域3上??，由于機(jī)

80、器的限制性，使?fàn)恳p少，與v²成反比。 轉(zhuǎn)矩控制 電機(jī)在低速條件下，可以提供的理論轉(zhuǎn)矩是大于那些利用輪軌界面上有效粘附的可傳送裝置。然而，這將使電機(jī)超載，并超出通常可以接受的水平，因此，必須避免由駕駛員或電子控制系統(tǒng)操作。 早期直流牽引驅(qū)動(dòng)器是通過(guò)使用串聯(lián)電阻調(diào)節(jié)電源電壓，并通過(guò)改變電機(jī)的組配置來(lái)控制的。如今，無(wú)論</p><p>　　對(duì)一個(gè)典型的三相同步機(jī)來(lái)說(shuō)，轉(zhuǎn)子磁場(chǎng)是通過(guò)

81、滑環(huán)提供的電流產(chǎn)生的，磁場(chǎng)的方位是由轉(zhuǎn)子線圈的物理位置決定的。定子磁場(chǎng)通過(guò)定子線圈中流動(dòng)的電流所產(chǎn)生的，并以由逆變器頻率確定的速度旋轉(zhuǎn)。隨著定子和轉(zhuǎn)子磁場(chǎng)之間的角度增加，產(chǎn)生更多的扭矩，但轉(zhuǎn)子和定子磁場(chǎng)的速度是相同的。角度變小，制動(dòng)變強(qiáng)。 在異步三相電機(jī)中，定子磁場(chǎng)是通過(guò)轉(zhuǎn)子籠（圖6）的旋轉(zhuǎn)所提供的感應(yīng)電流產(chǎn)生的，反過(guò)來(lái)說(shuō)，即產(chǎn)生的磁場(chǎng)與定子磁場(chǎng)相互作用，從而產(chǎn)生驅(qū)動(dòng)或制動(dòng)轉(zhuǎn)矩。在驅(qū)動(dòng)方面，轉(zhuǎn)子的轉(zhuǎn)速是低于逆變器設(shè)置的定子磁場(chǎng)的

82、旋轉(zhuǎn)速度，并且在制動(dòng)方面其也是較快的。如果兩者的速度相同，則不產(chǎn)生轉(zhuǎn)矩。這種差異可以表示為轉(zhuǎn)差頻率或百分比滑移。</p><p>　　在永磁同步電機(jī)中，轉(zhuǎn)子磁場(chǎng)是由??分布在轉(zhuǎn)子的表面上或埋在轉(zhuǎn)子疊片（圖7）開(kāi)口上的磁鐵所產(chǎn)生的。后者可提供更大的機(jī)械強(qiáng)度和低得多的轉(zhuǎn)子的渦流損耗。釹鐵硼(Nd2Fe14B)是一種具有最強(qiáng)磁特性的材料。定子磁場(chǎng)是通過(guò)一種相對(duì)標(biāo)準(zhǔn)的三相多極線圈上的層疊鐵心產(chǎn)生的。 在所有的電機(jī)

83、中，旋轉(zhuǎn)磁場(chǎng)產(chǎn)生的電壓與電源電壓（s）是相反的，即所謂的反電動(dòng)勢(shì)的電壓。其在零速時(shí)為零，但它隨速度線性增長(zhǎng)。因此，為保持區(qū)域1中恒定的轉(zhuǎn)矩，電源電壓必須增加。 由電機(jī)提供或吸收的轉(zhuǎn)矩被認(rèn)為是磁通和電流相互作用的結(jié)果。正如合適的電流或電機(jī)中電流流動(dòng)一樣，電功率轉(zhuǎn)換器的作用是以直流或單相交流電源電壓為條件的。許多不同類(lèi)型的轉(zhuǎn)換器是可用的，但最現(xiàn)代化的牽引系統(tǒng)使用絕緣柵雙極晶體管（IGBT）和某種脈沖寬度調(diào)制形式。</p>

84、<p>　　在恒定的牽引力范圍內(nèi)，施加到端子的電壓（及這種情況下感應(yīng)電機(jī)的頻率）必須隨電動(dòng)機(jī)的速度而線性增加，以便保持磁通和電流相互作用的產(chǎn)物（即轉(zhuǎn)矩）在一個(gè)恒定的的水平。超出基本速度，由于電力電子和機(jī)器絕緣能力的局限性，所施加的電壓不能進(jìn)一步增加。而機(jī)械、機(jī)器確可以走得更快。 因此，區(qū)域2輸入磁場(chǎng)減弱，從而降低反電動(dòng)勢(shì)的水平，或抵消永磁同步電機(jī)的影響。直流電機(jī)是通過(guò)減少流經(jīng)場(chǎng)繞組的電流（在圖3中看到的電阻RFW）

85、實(shí)現(xiàn)的，常規(guī)的同步機(jī)則是通過(guò)減少轉(zhuǎn)子供給的電流來(lái)實(shí)現(xiàn)的。當(dāng)電源頻率增加，而電源電壓保持恒定時(shí)，感應(yīng)機(jī)的磁場(chǎng)削弱會(huì)自發(fā)進(jìn)行。由于永久磁鐵產(chǎn)生的轉(zhuǎn)子磁場(chǎng)的作用，永磁同步電機(jī)弱磁是很難發(fā)生的。</p><p>　　區(qū)域3中的磁通和電流比恒定功率區(qū)域中的磁通和電流以更大的速率減少，以避免超過(guò)機(jī)器的電力或機(jī)械限制。例如在單獨(dú)他勵(lì)直流電動(dòng)機(jī)中，電樞電流作為速度的函數(shù)也會(huì)減少。</p><p><

86、b>　　優(yōu)點(diǎn)和缺點(diǎn)：</b></p><p>　　永久磁鐵的機(jī)器越來(lái)越廣泛應(yīng)用于鐵路牽引機(jī)的主要原因是相比三相異步電動(dòng)機(jī)，它們擁有非常顯著的優(yōu)勢(shì)。在80％工作范圍內(nèi)，其工作效率要高1％至2％。在相同功率等級(jí)的條件下，相比一臺(tái)特定能源只有25%的機(jī)器，其特定的電源是30％至35％以上。</p><p>　　而異步電動(dòng)機(jī)中轉(zhuǎn)子的熱量是由固有轉(zhuǎn)差功率引起的，這實(shí)際上可由PM驅(qū)動(dòng)

87、器消除，避免了轉(zhuǎn)子冷卻的需要。通常情況下，PM機(jī)器定子完全密封，并由傳熱流體的裝置進(jìn)行冷卻，從而產(chǎn)生了潛在的更加可靠的驅(qū)動(dòng)器。永磁同步電機(jī)還允許動(dòng)態(tài)制動(dòng)下降到非常低的速度，并且理論上它應(yīng)該是能夠通過(guò)電 - 機(jī)械短路的定子繞組產(chǎn)生自我控制的減速器。 當(dāng)然，這些好處也并不是毫無(wú)缺憾。即使已經(jīng)制定了適當(dāng)?shù)木徑獯胧来艩恳姍C(jī)的使用仍存在七個(gè)主要的缺點(diǎn)，。 由于四象限轉(zhuǎn)換器和機(jī)器的尺寸和成本的限制，使其在整個(gè)速度范圍內(nèi)不容許通

88、過(guò)簡(jiǎn)單的應(yīng)急手段。相比反電動(dòng)勢(shì)，以允許所需的流過(guò)電流和足夠高的電壓供給機(jī)器以達(dá)到期望的轉(zhuǎn)矩。解決這個(gè)問(wèn)題主要通過(guò)弱磁，恒轉(zhuǎn)矩和恒功率區(qū)實(shí)現(xiàn)。由于無(wú)法調(diào)整永久磁鐵產(chǎn)生的磁場(chǎng)，磁場(chǎng)削弱要通過(guò)注入到與設(shè)定磁場(chǎng)相對(duì)抗的旋轉(zhuǎn)永久磁鐵的定子繞組的電流來(lái)實(shí)現(xiàn)。 在定子繞組中，這些額外的電流會(huì)導(dǎo)致銅損。在一定程度上能使由使用低損耗的永久磁鐵轉(zhuǎn)子所產(chǎn)生的效率增益變得無(wú)效。</p><p>　　為了能夠控制磁場(chǎng)減弱效應(yīng)產(chǎn)生的

89、電流，了解電子轉(zhuǎn)子的位置及1°和2°（視場(chǎng)角）之間的準(zhǔn)確性是必要的。對(duì)于四極電機(jī)所需要的機(jī)械分辨率在1.5°以上。傳感器使用時(shí)，為確保有足夠的性能其完整性和可靠性必須非常高。如同開(kāi)發(fā)的Schrödl1，傳感器方法的使用可導(dǎo)致控制精度的減少。 磁通具有溫度依賴性，當(dāng)轉(zhuǎn)子溫度每增加10K磁場(chǎng)強(qiáng)度會(huì)降低約1％。當(dāng)永磁同步電機(jī)運(yùn)行溫度超過(guò)200K（-40°C的溫度范圍內(nèi)的最大允許160&

90、#176;C），就會(huì)有顯著的影響。因此，控制機(jī)器的電力供應(yīng)，考慮電子監(jiān)控的工作溫度這一點(diǎn)是必要的。 永磁同步電機(jī)需要自己獨(dú)立的高可靠電子電源控制器，以確保電流在合適的時(shí)刻注入。然而，越來(lái)越多的現(xiàn)代牽引系統(tǒng)使用單獨(dú)控制的電機(jī)以優(yōu)化性能，這是缺乏考慮的。 即使轉(zhuǎn)子達(dá)不到310℃和370℃之間的居里溫度，如果機(jī)器在高溫下通過(guò)高強(qiáng)度電流，亦會(huì)發(fā)生不可逆退磁。潛在的更關(guān)鍵的是由于運(yùn)動(dòng)的永磁體磁場(chǎng)將繼續(xù)誘導(dǎo)定子中的高強(qiáng)度電流，故定子

91、繞組的短路可導(dǎo)致機(jī)器的損壞。然而，退磁有助于緩解這一問(wèn)題。</p><p>　　類(lèi)似地，無(wú)負(fù)荷運(yùn)行過(guò)程中，當(dāng)列車(chē)滑行時(shí)，永久磁鐵轉(zhuǎn)子會(huì)繼續(xù)減少定子鐵芯中的感應(yīng)電流。這些渦流，加上磁滯效應(yīng)會(huì)導(dǎo)致鐵損，從而降低機(jī)器的整體效率。</p><p>　　用于永磁同步電機(jī)的稀土永磁材料磁性強(qiáng)，但相對(duì)性的細(xì)膩。因此，轉(zhuǎn)子結(jié)構(gòu)是比在感應(yīng)電動(dòng)機(jī)的轉(zhuǎn)子結(jié)構(gòu)更加復(fù)雜，其設(shè)計(jì)流程，必須相應(yīng)地調(diào)整。向定子繞組供給的

92、控制也更復(fù)雜，因?yàn)槎鄠€(gè)反饋回路和信號(hào)轉(zhuǎn)換是必需的（圖8）。</p><p>　　盡管這一清單中潛在的缺點(diǎn)可能看起來(lái)廣泛，有許多應(yīng)用場(chǎng)合的永磁同步電機(jī)的好處大大超過(guò)這些缺點(diǎn)，這使得這些機(jī)器對(duì)牽引設(shè)計(jì)師極具吸引力。較小的尺寸和較輕的重量是有利的，因?yàn)檗D(zhuǎn)向架的空間是有限的，如它是理想的驅(qū)動(dòng)器集成在未經(jīng)變速箱存根車(chē)軸。顯著的效率提高和更低的轉(zhuǎn)子損耗對(duì)性能和降低能源消耗是有益的。一個(gè)很好的例子是在本文開(kāi)頭提到的使用永磁同步

93、電機(jī)V150的小火車(chē)。電力車(chē)上的異步電機(jī)不得不裝置在主架（RG5.07 P71）上，而永磁同步電機(jī)可能被安裝在中級(jí)車(chē)對(duì)之間的鉸接轉(zhuǎn)向架，以降低傳輸系統(tǒng)的復(fù)雜性和質(zhì)量。</p><p>　　從20世紀(jì)80年代中期起，三相異步電動(dòng)機(jī)日益普及，因此我們可以預(yù)期在未來(lái)幾年內(nèi)，永磁牽引電機(jī)以同樣的方式，會(huì)被廣泛地采用。 在編寫(xiě)本文時(shí)，作者在此要感謝醫(yī)生哈拉爾德Neudorfer和馬庫(kù)斯·紐鮑爾Trakti