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1、Speed Control of DC MotorAbstract Conditioning system is characterized in that output power to maintain stability. Different speed control system can use a different brake system, high starting and braking torque, quick response and quick adjustment range of degree requirements of DC drive system, t
2、he use of the electric braking mode. Depends on the speed control of DC motor armature voltage and flux. To zero speed, or U = 0 or = . The latter is impossible, it only changes through the armature voltage to reduce speed. To speed to a higher value can increase or decrease the U .Keyword DC Speed
3、Feedback BrakeRegulator SystemsA regulator system is one which normally provides output power in its steady-state operation.For example, a motor speed regulator maintains the motor speed at a constant value despite variations in load torque. Even if the load torque is removed, the motor must provide
4、 sufficient torque to overcome the viscous friction effect of the bearings. Other forms of regulator also provide output power; A temperature regulator must maintain the temperature of, say, an oven constant despite the heat loss in the oven. A voltage regulator must also maintain the output voltage
5、 constant despite variation in the load current. For any system to provide an output, e.g., speed, temperature, voltage, etc., an error signal must exist under steady-state conditions. Electrical BrakingIn many speed control systems, e.g., rolling mills, mine winders, etc., the load has to be freque
6、ntly brought to a standstill and reversed. The rate at which the speed reduces following a reduced speed demand is dependent on the stored energy and the braking system used. A small speed control system (sometimes known as a velodyne) can employ mechanical braking, but this is not feasible with lar
7、ge speed controllers since it is difficult and costly to remove the heat generated.The various methods of electrical braking available are:(1) Regenerative braking.(2) Eddy current braking.(3) Dynamic braking.(4) Reverse current braking(plugging)Regenerative braking is the best method, though not ne
8、cessarily the most economic. The stored energy in the load is converted into electrical energy by the work motor (acting temporarily as a generator) and is returned to the power supply system. The supply system thus acts as a”sink”into which the unwanted energy is delivered. Providing the supply sys
9、tem has adequate capacity, the consequent rise in terminal voltage will be small during the short periods of regeneration. In the Ward-Leonard method of speed control of DC motors, regenerative braking is inherent, but thyristor drives have to be arranged to invert to regenerate. Induction motor dri
10、ves can regenerate if the rotor shaft is driven faster than speed of the rotating field. The advent of low-cost variable-frequency supplies from thyristor inverters have brought about considerable changes in the use of induction motors in variable speed drives.Eddy current braking can be applied to
11、any machine, simply by mounting a copper or aluminum disc on the shaft and rotating it in a magnetic field. The problem of removing the heat generated is severe in large system as the temperature of the shaft, bearings, and motor will be raised if prolonged braking is applied.In dynamic braking, the
12、 stored energy is dissipated in a resistor in the circuit. When applied to small DC machines, the armature supply is disconnected and a resistor is connected across the armature (usually by a relay, contactor, or thyristor).The field voltage is maintained, and braking is applied down to the lowest s
13、peed. Induction motors require a somewhat more complex arrangement, the stator windings being disconnected from the AC supply and reconnected to a DC supply. The electrical energy generated is then dissipated in the rotor circuit. Dynamic braking is applied to many large AC hoist systems where the b
14、raking duty is both severe and prolonged.DC Motor Speed ControlThe basis of all methods of DC motor speed control is derived from the equations:the terms having their usual meanings. If the IaRa drop is small, the equations approximate to or 。Thus, control of armature voltage and field flux influenc
15、es the motor speed. To reduce the speed to zero, either U=0 or=.The latter is inadmissible; hence control at low speed is by armature voltage variation. To increase the speed to a high value, either U is made very large or is reduced. The latter is the most practical way and is known as field weaken
16、ing. Combinations of the two are used where a wide range of speed is required.A Single-Quadrant Speed Control System Using ThyristorsA single-quadrant thyristor converter system is shown in Fig.1.For the moment the reader should ignore the rectifier BR2 and its associated circuitry (including resist
17、or R in the AC circuit), since this is needed only as a protective feature and is described in next section.Fig.1 Thyristor speed control system with current limitation on the AC sideSince the circuit is a single-quadrant converter, the speed of the motor shaft (which is the output from the system)
18、can be controlled in one direction of rotation only. Moreover, regenerative braking cannot be applied to the motor; in this type of system, the motor armature can suddenly be brought to rest by dynamic braking (i.e. when the thyristor gate pulses are phased back to 180o, a resister can be connected
19、across the armature by a relay or some other means).Rectifier BR1 provides a constant voltage across the shunt field winding, giving a constant field flux. The armature current is controlled by a thyristor which is, in turn, controlled by the pulses applied to its gate. The armature speed increases
20、as the pulses are phased forward (which reduces the delay angle of firing), and the armature speed reduces as the gate pulses are phased back.The speed reference signal is derived from a manually operated potentiometer (shown at the right-hand side of Fig.23.1), and the feedback signal or output spe
21、ed signal is derived from the resistor chain R1 R2, which is connected across the armature. (Strictly speaking, the feedback signal in the system in Fig.23.1 is proportional to the armature voltage, which is proportional to the shaft speed only if the armature resistance drop, IaRa, is small. Method
22、s used to compensate for the IaRa drop are discussed in Reading Material.)Since the armature voltage is obtained from a thyristor, the voltage consists of a series of pulses; these pulses are smoothed by capacitor C. The speed reference signal is of the opposite polarity to the armature voltage sign
23、al to ensure that overall negative feedback is applied.A feature of DC motor drives is that the load presented to the supply is a mixture of resistance, inductance, and back EMF Diode D in Fig.1 ensures that the thyristor current commutates to zero when its anode potential falls below the potential
24、of the upper armature connection, in the manner outlined before. In the drive shown, the potential of the thyristor cathode is equal to the back EMF of the motor while it is in a blocking state. Conduction can only take place during the time interval when the instantaneous supply voltage is greater
25、than the back EMF.Inspection of Fig.2 shows that when the motor is running, the peak inverse voltage applied to the thyristor is mush greater than the peak forward voltage. By connecting a diode in series with the thyristor, as shown, the reverse blocking capability of the circuit is increased to al
26、low low-voltage thyristor to be used.References:Fig.2 Illustrating the effect of motor back EMF on thePeak inverse voltage applied to the thyristorFig.3 Armature voltage waveformsThe waveforms shown in Fig.2 are idealized waveforms as much as they ignore the effects of armature inductance,commutator
27、 ripple,etc.Typical armature voltage waveforms are shown in Fig.3.In this waveform the thyristor is triggered at point A, and conduction continues to point B when the supply voltage falls below the armature back EMF.The effect of armature inductance is to force the thyristor to continue to conduct u
28、ntil point C,when the fly-wheel diode prevents the armature voltage from reversing. When the inductive energy has dissipated (point D), the armature current is zero and the voltage returns to its normal level, the transients having settled out by point E.The undulations on the waveform between E and
29、 F are due to commentator ripple.References1.Landau ID(1999)From robust control to adaptive control.Control Eng Prac 7:111311242.Forssell U,Ljung L(1999)Closed-loop identification revisited. Automatica 35:121512413.Soderstrom T,Stoica P(1989)System identification.Prentice Hall,Cambridge,UK4.Horng JH
30、(1999)Neural adaptive tracking control of a DC motor.Information Sci 118:1135.Lyshevski SE(1999)Nonlinear control of mechatronic systems with permanent-magnet DC motors.Mechatronics 9:5395526.Yavin Y,Kemp PD(2000)Modeling and control of the motion of a rolling disk:e?ect of the motor dynamics on the
31、 dynamical model.Comput Meth Appl Mech Eng 188:6136247.Mummadi VC(2000)Steady-state and dynamic performance analysis of PV supplied DC motors fed from intermediate power converter.Solar Energy Mater Solar Cells 61:3653818.Jang JO,Jeon GJ(2000)A parallel neuro-controller for DC motors containing nonl
32、inear friction.Neurocomputing 30:2332489.Nordin M,Gutman P(2002)Controlling mechanical systems with backlasha survey.Automatica 38:1633164910.Wu R-H,Tung P-C(2002)Studies of stick-slip friction,pre-sliding displacement,and hunting.J Dyn Syst 124:11111711.Ogata K(1990)Modern control engineering.Prent
33、ice Hall,Englewood Cli?s,NJ12.Slotine E,Li W(1991)Applied nonlinear control.Prentice Hall,Englewood Cli?s,NJ13.Lee PL(1993)Nonlinear process control:applications of gen-eric model control.Springer,Berlin Heidelberg New York直流电动机调速控制摘要 调节系统的特征在于能保持输出功率的稳定。不同的速度控制系统可以使用不同的制动系统，在有高起、制动转矩，快速响应和快速度调节范围要求
34、的直流调速系统中，采用的是电气制动的方式。直流电机的速度控制取决于电枢电压和磁通。要将转速降为零，或者U=0或=。后者是不可能的，因此只可通过电枢电压的变化来降低转速。要将转速增加到较高值，可以增大U或减小。关键词 直流调速 反馈 制动调节系统调节系统是一类通常能提供稳定输出功率的系统。例如，电机速度调节器要能在负载转矩变化时仍能保持电机转速为恒定值。即使负载转矩为零，电机也必须提供足够的转矩来克服轴承的粘滞摩擦影响。其他类型的调节器也提供输出功率，温度调节器必须保持炉内的温度恒定，也就是说，即使炉内的温度散失也必须保持炉温不变。一个电压调节其也必须保持负载电流值变化时输出电压值恒定。对于任何
35、一个提供一个输出，例如，速度、温度、电压等的系统，在稳态下必须存在一个误差信号。电气制动在许多速度控制系统中，例如轧钢机、矿坑卷扬机等这些负载要求频繁地停顿和反向运动的系统。随着减速要求，速度减小的比率取决于存储的能量和所使用的制动系统。一个小型速度控制系统（例如所知的伺服积分器）可以采用机械制动，但这对大型速度控制器并不可行，因为散热很难而且很昂贵。可行的各种电气制动方法有：（1） 回馈制动。（2） 涡流制动。（3） 能耗制动（4） 反接制动回馈制动虽然并不一定是最经济的方式，但却是最好的方式。负载中存储的能量通过工作电机（暂时以发电机模式运行）被转化成电能并返回到电源系统中。这样电源就充当
36、了一个收容不想要的能量的角色。假如电源系统具有足够的容量，在短时回馈过程中最终引起的端电压升高会很少。在直流电机速度控制渥特-勒奥那多法中，回馈制动是固有的，但可控硅传动装置必须被排布的可以反馈。如果转轴速度快于旋转磁场的速度，感应电机传动装置可以反馈。由晶闸管换流器而来的廉价变频电源的出现在变速装置感应电机应用中引起了巨大的变化。涡流制动可用于任何机器，只要在轴上安装一个铜条或铝盘并在磁场中旋转它即可。在大型系统中，散热问题是很重要的，因为如果长时间制动，轴、轴承和电机的温度就会升高。在能耗制动中，存储的能量消耗在回路电阻器上。用在小型直流电机上时，电枢供电被断开，接入一个电阻器（通常是一个
37、继电器、接触器或晶闸管）。保持磁场电压，施加制动降到最低速。感应电机要求稍微复杂一点的排布，定子绕组被从交流电源上断开，接到直流电源上。产生的电能继而消耗在转子回路中。能耗制动应用在许多大型交流升降系统中，制动的职责是反向和延长。任何电机都可以通过突然反接电源以提供反向的旋转方向（反接制动）来停机。在可控情况下，这种制动方法对所传动装置都是使用的。它主要的缺点就是当制动等于负载存储的能量时，电能被机器消耗了。这在大型装置中就大大增加了运行成本。直流电机速度控制所有直流电机速度控制的基本关系都可由下式得出：各项就是她们通常所指的含义。如果IaRa很小，等式近似为或。这样，控制电枢电压和磁通就可影
38、响电机转速。要将转速降为零，或者U=0或=。后者是不可能的，因此只可通过电枢电压的变化来降低转速。要将转速增加到较高值，可以增大U或减小。后者是最可行的方法，就是我们通常所知道的弱磁场。在要求速度调节范围宽的场合可综合使用这两种方法。使用晶闸管的单向速度控制系统一个单相晶闸管逆变器系统如图1所示。读者应该先忽略整流器BR2和它的相关电路（包括交流回路中的电阻器R），因为这部分只有在具有保护功能时才需要，将在下一节介绍。图1 单向晶闸管逆变器系统因为该电路是一个单向转换器，只能在一个旋转方向控制电机轴（系统的输出）的速度。而且，回馈制动不能用于电机；在这种系统类型中，电机电枢可以通过电气制动静止
39、（例如，当晶闸管门极脉冲反向时，电阻可通过一个继电器或其他装置连接到电枢上）。整流器BR1给并联励磁绕组提供一个稳定电压，产生稳定的磁通。电枢电流由一个晶闸管控制，该晶闸管又由加在它们极上的脉冲控制。脉冲正向时（减小起动延时角）电枢转速增加，门极脉冲反相时电枢转速减小。速度参考信号可从人工操作的电位器（如图1右侧所示）上获得，反馈信号或输出转速信号可从连接在电枢上的电阻器链上获得。（严格的讲，图1系统中反馈信号只有当电枢电组的压降很小时，才与轴转速成正比的电枢电压成正比。用于补偿IaRa压降的方法将在阅读材料中讨论。）因为电枢电压是从一个晶闸管上获得的，该电压包括一系列由电容器C滤波的脉冲。速
40、度参考信号与电枢电压信号极性相反，以确保施加的都是负反馈。直流电机装置的一个特征就是需要供电的负载时电阻、电导的混合，并且在图1中反电动势二极管D确保当晶闸管阳极电势低于前面叙述的电枢连接方式的上限时，晶闸管电流应换向为零。在所示拖动系统中，当晶闸管处于断开状态时，其阳极电势等于电机反电动势。只有在瞬时电源电压大于反向电势的间隔时它才会导通。图2所示的检测表明电机运行时晶闸管上峰值反向电压大于峰值正向电压。如图所示，在晶闸管上串联一个二级管，电路的反向关断能力就会增强，所以允许使用低压晶闸管。图2晶闸管对电机反电动势的影响图3电枢电压波形图2所示的波形是理想的波形，因为忽略了电枢电感、换向器纹
41、波等因素的影响。典型的电枢电压波形如图3所示。在该波形中，晶闸管在A点触发，一直到B点电源电压低于电枢反电动势时导通。电枢电感的作用使晶闸管保持到C点飞轮二极管使电枢电压反向之前导通。当电感能量消失（D点），电枢电流为零，电压恢复到它的正常水平，这个暂态过程最后稳定在E点。点E、F之前的纹波是由换向器引起的纹波。五分钟搞定5000字毕业论文外文翻译，你想要的工具都在这里!在科研过程中阅读翻译外文文献是一个非常重要的环节，许多领域高水平的文献都是外文文献，借鉴一些外文文献翻译的经验是非常必要的。由于特殊原因我翻译外文文献的机会比较多，慢慢地就发现了外文文献翻译过程中的三大利器：Google“翻译
42、”频道、金山词霸（完整版本）和CNKI“翻译助手。具体操作过程如下： 1.先打开金山词霸自动取词功能，然后阅读文献； 2.遇到无法理解的长句时，可以交给Google处理，处理后的结果猛一看，不堪入目，可是经过大脑的再处理后句子的意思基本就明了了； 3.如果通过Google仍然无法理解，感觉就是不同，那肯定是对其中某个“常用单词”理解有误，因为某些单词看似很简单，但是在文献中有特殊的意思，这时就可以通过CNKI的“翻译助手”来查询相关单词的意思，由于CNKI的单词意思都是来源与大量的文献，所以它的吻合率很高。 另外，在翻译过程中最好以“段落”或者“长句”作为翻译的基本单位，这样才不会造成“只见树
43、木，不见森林”的误导。四大工具： 1、Google翻译： google，众所周知，谷歌里面的英文文献和资料还算是比较详实的。我利用它是这样的。一方面可以用它查询英文论文，当然这方面的帖子很多，大家可以搜索，在此不赘述。回到我自己说的翻译上来。下面给大家举个例子来说明如何用吧比如说“电磁感应透明效应”这个词汇你不知道他怎么翻译，首先你可以在CNKI里查中文的，根据它们的关键词中英文对照来做，一般比较准确。 在此主要是说在google里怎么知道这个翻译意思。大家应该都有词典吧，按中国人的办法，把一个一个词分着查出来，敲到google里，你的这种翻译一般不太准，当然你需要验证是否准确了，这下看着吧，
44、把你的那支离破碎的翻译在google里搜索，你能看到许多相关的文献或资料，大家都不是笨蛋，看看，也就能找到最精确的翻译了，纯西式的！我就是这么用的。 2、CNKI翻译： CNKI翻译助手，这个网站不需要介绍太多，可能有些人也知道的。主要说说它的有点，你进去看看就能发现：搜索的肯定是专业词汇，而且它翻译结果下面有文章与之对应（因为它是CNKI检索提供的，它的翻译是从文献里抽出来的），很实用的一个网站。估计别的写文章的人不是傻子吧，它们的东西我们可以直接拿来用，当然省事了。网址告诉大家，有兴趣的进去看看，你们就会发现其乐无穷！还是很值得用的。 3、网路版金山词霸（不到1M）： 4、有道在线翻译：翻
45、译时的速度：这里我谈的是电子版和打印版的翻译速度，按个人翻译速度看，打印版的快些，因为看电子版本一是费眼睛，二是如果我们用电脑，可能还经常时不时玩点游戏，或者整点别的，导致最终SPPEED变慢，再之电脑上一些词典（金山词霸等）在专业翻译方面也不是特别好，所以翻译效果不佳。在此本人建议大家购买清华大学编写的好像是国防工业出版社的那本英汉科学技术词典，基本上挺好用。再加上网站如：google CNKI翻译助手，这样我们的翻译速度会提高不少。具体翻译时的一些技巧（主要是写论文和看论文方面） 大家大概都应预先清楚明白自己专业方向的国内牛人，在这里我强烈建议大家仔细看完这些头上长角的人物的中英文文章，这
46、对你在专业方向的英文和中文互译水平提高有很大帮助。 我们大家最蹩脚的实质上是写英文论文，而非看英文论文，但话说回来我们最终提高还是要从下大工夫看英文论文开始。提到会看，我想它是有窍门的，个人总结如下： 1、把不同方面的论文分夹存放，在看论文时，对论文必须做到看完后完全明白（你重视的论文）；懂得其某部分讲了什么（你需要参考的部分论文），在看明白这些论文的情况下，我们大家还得紧接着做的工作就是把论文中你觉得非常巧妙的表达写下来，或者是你论文或许能用到的表达摘记成本。这个本将是你以后的财富。你写论文时再也不会为了一些表达不符合西方表达模式而烦恼。你的论文也降低了被SCI或大牛刊物退稿的几率。不信，你可以试一试 2、把摘记的内容自己编写成检索，这个过程是我们对文章再回顾，而且是对你摘抄的经典妙笔进行梳理的重要阶段。你有了这个过程。写英文论文时，将会有一种信手拈来的感觉。许多文笔我们不需要自己再翻译了。当然前提是你梳理的非常细，而且中英文对照写的比较详细。 3、最后一点就是我们往大成修炼的阶段了，万事不是说成的，它是做出来的。写英文论文也就像我们小学时开始学写作文一样，你不练笔是肯定写不出好作品来的。所以在此我鼓励大家有时尝试着把自己的论文强迫自己写成英文的，一遍不行，可以再修改。最起码到最后你会很满意。呵呵，我想我是这么觉得的。