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1、第六单元A AC Machines交流机Introduction简介The electrical machine that converts electrical energy into mechanical energy, and vice versa, is the workhorse in a drive system. A machine is a complex structure electrically, mechanically, and thermally.Although machines were introduced more than one hundred year
2、s ago, the research and development in this area appears to be never-ending. However, the evolution of machines has been slow compared to that of power semiconductor devices and power electronic converters.Traditionally, AC machines with a constant frequency sinusoidal power supply have been used in
3、 constant-speed applications, whereas DC machines were preferred for variable-speed drives. But in the last two or three decades, we have seen extensive research and development efforts for variable-frequency, variable-speed AC machine drive technology, and they will progressively replace DC drives.
4、 In most cases, new applications use AC drives.将电能转换成机械能或将机械能转换成电能的电机是传动系统中的主要组 成部分。从电学、机械学和热学的角度看，电机具有复杂的结构。虽然一百多 年前就开始使用电机，关于电机的研究与开发工作一直在继续。但是，与电力 电子器件和电力电子变换器相比，电机的发展十分缓慢。从传统观念上，由恒频 正弦电源供电的交流机一直用于恒速场合，而直流机则用于变速场合。但在最近 二、三十年，我们已经看到在变频、变速交流机传动技术上取得的研究与开发成 果，并且它们正逐渐取代直流传动。在大多数情况下，新设备都使用交流传动。AC mach
5、ines can generally be classified as follows:一般可将交流机分类如下：Induction machines: Cage or wound rotor （doubly-fed）, Rotating or linear;感应电机：鼠笼或绕线式转子（双馈），旋转或直线运动；Synchronous machines: Rotating or linear, Reluctance, Wound field or permanent magnet, Radial or axial gap （disk）, Surface magnet or interior （bu
6、ried） magnet, Sinusoidal or trapezoidal;同步电机：旋转或直线运动，启动、绕线式激磁（转子）或永磁磁铁，径向 或轴向气隙（圆盘状），凸磁极或内（隐）磁极，正弦波磁场或梯形波磁场；Variable reluctance machines: Switched reluctance, Stepper.变阻抗电机：开关磁阻电机，步进电机。Induction Machines感应电机Among all types of AC machines, the induction machine, particularly the cage type, is most co
7、mmonly used in industry. These machines are very economical, rugged, and reliable, and are available in the ranges of fractional horse power (FHP) to multi-megawatt capacity. Low-power FHP machines are available in single-phase, but poly-phasc (three-phase) machines arc used, most often in variable-
8、speed drives. Fig. 1-6A-1 shows an idealized three-phase, two-pole induction motor where each phase winding in the stator and rotor is represented by a concentrated coil. The three-phase windings are distributed sinusoidally and embedded in slots. In a wound-rotor machine, the rotor winding is simil
9、ar to that of the stator, but in a cage machine, the rotor has a squirrel cage-like structure with shorted end rings. Basically, the machine can be looked upon as a three-phase transformer with a rotating and short-circuited secondary. Both stator and rotor cores are made with laminated ferromagneti
10、c steel sheets. The air gap in the machine is practically uniform (non-salicnt pole).在所有的交流电机中，感应电机，尤其是鼠笼型感应电机，在工业上得到了 最广泛的应用。这些电机价格便宜、结实、可靠，并且从不到一个马力到数兆瓦 容量的电机都可买到。小容量电机一般是单相电机，但多相(三相)电机经常用于变速传动。图 1-6A-1给出了一台理想的三相、两极感应电机，图中定子和转子的每一个相绕 组用一个集中线圈来表示。三相绕组在空间上按正弦分布并嵌入在槽里。对绕线 式转子电机而言，转子绕组与定子绕组类似，但鼠笼式电机的转
11、子具有鼠笼状结 构，并且有两个短路环。基本上，感应电机可以看作是一个具有旋转并且短路的 二次绕组的一台三相变压器。定子和转子的核用层压铁磁钢片制成，电机内的气 隙实际上是均匀的(非凸极结构)。One of the most fundamental principles of induction machines is the creation of a rotating and sinusoidally distributed magnetic field in the air gap. Neglecting the effect of slots and space harmonics du
12、e to non-ideal winding distribution, it can be shown that a sinusoidal three-phase balanced power supply in the three-phase stator winding creates a synchronously rotating magnetic field.l The rotational speed can be given as equation (1-6A-1). Ne is called synchronous speed in i-pm and is the stato
13、r frequency in Hz. P is the pole numbers of a machine.(1-6A-1)感应电机的一个最基本的原理是在气隙中建立旋转和按正弦分布的磁场。如 果忽略槽和由于非理想分布的绕组产生的空间谐波的影响，可以证明，在三相定 子绕组中能以三相对称电源建立一个同步旋转的旋转磁场。旋转速度由公式 (1-6A-1)给出。Ne称作同步转速，单位是转/分，是定子频率，单位是赫兹。P是电机的极对数。The rotor winding will be subjected to a sweeping magnetic field, and have inducing cu
14、rrent in the short-circuited rotor.2 The interaction of air gap flux and rotor mmf produces torque, make the rotor rotate. But the speed of the rotor is less than synchronous speed. So it called induction machine or asynchronous machine. To meet the various starting and running requirements of a var
15、iety of industrial applications, several standard designs of squirrel-cage motors are available from manufacturers5 stock. The torque-speed characteristics of the most common designs, readily available and standardized in accordance with the criteria established by the National Electrical Manufactur
16、ersJ Association (NEMA), are shown in Fig. 1-6A-2. The most significant design variable in these motors is the effective resistance of the rotor cage circuits.转子绕组切割磁场，就会在短路的转子中产生感应电流。气隙磁通和转子磁 动势的相互作用产生转矩使转子旋转。但转子的转速低于同步转速。因此称它作 感应电机或异步电机。为了满足各种工业应用中对启动和运行的要求，可从制造 厂家得到几种标准设计的鼠笼电机。最常见的转矩-速度特性，与国家电气制造
17、 协会的标准一致的，并很容易获得和定型的设计，如图1-6A-2所示。这些电机 中最有意义的设计变量是转子笼型电路的有效阻抗。Class A Motors These machines are suitable for applications where the load torque is low at start (such as fan or pump loads) so that full speed is achieved rapidly, thereby eliminating the problem of overheating during starting. In large
18、 machines, low-voltage starting is required to limit the starting current.A类电机这类电机适用于启动负载低(诸如风扇、泵类负载)以便能快速 达到全速，因而避免了启动过程电机过热的问题。对大容量电机而言，需要降压 启动以限制启动电流。Class B Motors Motors of this class are good general-purpose motors and have a wide variety of industrial applications. They are particularly suita
19、ble for constant-speed drives, where the demand for starting torque is not severe. Examples are drives for fans, pumps, blowers, and motor-generator sets.B类电机这类电机是很好的通用电机，有着广泛的工业应用。它们特别适 合对启动转矩要求不是特别严格的恒速驱动。比如驱动风扇、泵类负载、鼓风机 和电动发电机组。Class C Motors Class C motors are suitable for driving compressors, c
20、onveyors, and so forth.C类电机C类电机适合驱动压缩机、输送机等等。Class D Motors These motors are suitable for driving intermittent loads requiring rapid acceleration and high-impact loads such as punch presses or shears. In the case of impact loads, a flywheel is fitted to the system. As the motor speed falls appreciab
21、ly with load impact, the flywheel delivers some of its kinetic energy during the impact.D类电机此类电机适合驱动要求迅速加速的间歇性负载和冲床、剪床这样 的高冲击性负载。在驱动冲击性负载的情况下，在系统中加一个调速轮。当电机 转速随负载冲击有点下降时，在负载冲击期间调速轮释放它的一部分动能。Synchronous Machines同步电机A synchronous machine, as the name indicates, must rotate at synchronous speed, that i
22、s, the speed is uniquely related to (he supply frequency, as indicated in Equation (1-6A-1). It is a serious competitor to the induction machine invariable-speed drive applications.同步电机，正像名字所表示的，一定是像公式(1-6A-1)那样以同步速度旋转。对感应 电机恒速驱动应用而言，它是一位非常重要的竞争者。Fig. I-6A-3 shows an idealized three-phase, two-pole
23、wound field synchronous machine.The stator winding of the machine is identical to that of the induction machine, but the rotor has a winding (hat carries DC current and produces flux in the air gap that helps (he stator-induced rotating magnetic field to drag the rotor along with it. The DC field cu
24、rrent is supplied to the rotor from a static rectifier through slip rings and brushes, or by brushless excitation.Since the rotor always moves at synchronous speed, the synchronously rotating de-qe axes are fixed with the rotor, where the de axis corresponds to the north pole, as shown. There is no
25、stator-induccd induction in the rotor, and therefore, the rotor mmf is supplied exclusively by the field winding.This permits the machine to run at an arbitrary power factor at the stator terminal, that is, leading, lagging, or unity. On the other hand, in an induction machine, the stator supplies t
26、he rotor excitation (hat makes the machine power factor always lagging.图1-6A-3给出了台理想的三相、两极绕线式激磁的同步电机。同步电机的定子绕组 与感应电机的定子绕组一样，但同步电机的转子上有一个绕组，这个绕组通过直流电流，在 气隙中产生磁通，该磁通协助定子感应的旋转磁场来拉动转子与它一同旋转。直流激磁电流 由静态整流器通过滑环和电刷提供给转子，或由无刷励磁电源提供。因为转子总是以同步转 速旋转，同步旋转的de-qe轴与转子的相对位置是不变的，如图所示，de轴对应N极。在 转子中没有定子感应的感应电势，因此转子的磁动势
27、仅由激磁绕组提供。这使得电机在定子 侧可以任意的功率因数运行，即引前、滞后或同相。从另一角度说，在感应电机中，定子给 转子提供励磁使得电机功率因数总是滞后。The mechanism of torque production is somewhat similar to that of an induction machine. The machine shown is characterized as a salient pole because of the nonunifonn air gap around the rotor, which contributes to asymmetr
28、ical magnetic reluctance in (he d and q axes. This is in contrast to a machine with a cylindrical rotor structure having a uniform air gap (such as an induction motor), defined as a nonsalient pole machine.3 For example, low-speed synchronous generators in hydro-electric power stations use salient p
29、ole machines, whereas high-speed generators in steam-power stations use nonsalient pole machines. In addition to field winding, the rotor usually contains an amortisseur, or damper winding, which is like short-circuited squirrel cage bar in an induction motor. The machine is more expensive but effic
30、iency is somewhat higher.Wound field machines are normally used for high-power (multi-megawatt) drives.转矩产生的原理有点类似于感应电机。如图所示的同步电机是四极式同步机，因为转子 周围的气隙是不均匀的，不均匀的气隙在d轴和q轴上造成了不对称的磁阻。与其(凸极式 同步机)对应的另一种电机是有均匀气隙的圆柱体形转子结构的电机(与异步机相似),定义为 隐极式同步电机。例如，水电站使用的低速发电机是凸极同步机，而火力发电厂使用的高速 发电机是隐极式同步机。除激磁绕组之外，转子通常有一个阻尼器，或叫阻
31、尼绕组，它就像 感应电机中短路的鼠笼棒。同步机更昂贵但效率也高一些。绕线式激磁绕组同步机通常用于 大功率(数兆瓦)驱动。ariable Reluctance Machine (VRM)变阻抗电机A variable or double reluctance machine (VRM), as the name indicates, has double saliency, meaning it has saliency in the stator as well as in the rotor.As mentioned before, the VRM has two classificatio
32、ns: switched reluctance machine (SRM) and stepper motor. The stepper motor is basically a digital motor, i.e., it moves by a fixed step or angle with a digital pulse. Small stepper motors are widely used for computer peripheral-type applications. However, since the machine is not suitable for variab
33、le-speed applications, there will not be any further discussion of it.变阻抗或双阻抗电机，正像名字所表示的那样，有两个凸极，这意味着电机的定子和 转子都是凸极结构。如前所述，变阻抗电机有两种：开关磁阻电机和步进电机。步进电机基 本上是一种数字电机，即它根据数字脉冲运动固定的步数或角度。小型步进电机广泛用于计 算机外围设备。然而，由于步进电机不适合调速应用场合，不再作进一步讨论。There has been interest in switched reluctance motor drives in the literatu
34、re, and recently, great effort has been made to commercialize them in competition with induction motors.Fig. 1-6A-4 shows the cross-section of a four-phase machine with four stator-pole pairs and three rotor-pole pairs (8/6 motor). The machine rotor docs not have any winding or PM. The stator poles
35、have concentrated winding (instead of sinusoidal winding), and each stator-pole pair winding, as shown in the figure, is excited by a converter phase. For example, the stator-polc pair A-A is energized when the rotor pole-pair a-a approaches it to produce (he torque by magnetic pull, but is de-energ
36、ized when pole alignment occurs.4 All four machine phases are excited sequentially and synchronously with the help of a rotor position encoder to get unidirectional torque.The magnitude of torque can be given as: .Where m = inductance slope and i = instantaneous current. The current i can be maintai
37、ned constantly by during the inductance slope. At high speeds, the rotor-induced CEMF is high.有关文献对开关磁阻电机驱动十分关注，最近做了许多工作来使其商品化以参与和感应 电机的竞争。图1-6A-4给出了有四对定子极对数、三对转子极对数的四相开关磁阻电机的 截面图。电机转子没有任何绕组或永磁磁铁。定子极上有集中绕组(不是正弦分布绕组)， 每一对定子极绕组，如图所示，由变换器的一相供电。例如，当转子极对a-a，接近定子极对A-A，时，定子极对A-A，被通电，通过磁拉力产生转矩，当两个极对重合时，定子极对
38、A-A, 断电。借助于转子位置编码器，电机的四对绕组顺序、与转子同步供电，得到单向转矩。可 给出转矩的幅值。式中m=感应速率，i=瞬时电流。感应速率恒定则电流i为常数。高速 运行时，转子感应的反电动势也高。The favorable attributes of this electronic motor are simplicity and robustness of construction; potentially, it is somewhat cheaper than other classes of machines. However, the torque generation is pulsating in nature and there are serious acoustic noise problems.这种电机的优点是结构简单、坚固；也可能它比其它电机要便宜一些。但是，这种电机 有转矩脉动和严重的噪声问题。