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1、Speed Control of DC Motor Abstract 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

2、, the 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 Φ = ∞. 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 Φ. Keyword

3、 DC Speed Feedback Brake Regulator Systems A 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

4、motor must provide 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

5、the output voltage 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 Braking In many speed control systems, e.g., rolling mills, mine winders, etc., the

6、 load has to be frequently 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

7、 not feasible with large 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

8、 is the best method, though not necessarily 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 d

9、elivered. Providing the supply system 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

10、to regenerate. Induction motor drives 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. Edd

11、y current braking can be applied to 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 brakin

12、g is applied. In dynamic braking, the 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 b

13、raking is applied down to the lowest speed. 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 m

14、any large AC hoist systems where the braking duty is both severe and prolonged. DC Motor Speed Control The 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, c

15、ontrol of armature voltage and field flux influences the motor speed. To reduce the speed to zero, either U=0 orΦ=∞.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 Φis reduced. The latter i

16、s the most practical way and is known as field weakening. Combinations of the two are used where a wide range of speed is required. A Single-Quadrant Speed Control System Using Thyristors A single-quadrant thyristor converter system is shown in Fig.1.For the moment the reader should ignore the rec

17、tifier BR2 and its associated circuitry (including resistor 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 side Since the circuit is a single-quadrant converter, the

18、speed of the motor shaft (which is the output from the system) 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 ga

19、te pulses are phased back to 180o, a resister can be connected 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

20、 by the pulses applied to its gate. The armature speed increases 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

21、right-hand side of Fig.23.1), and the feedback signal or output speed 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

22、 speed only if the armature resistance drop, IaRa, is small. Methods 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 refere

23、nce signal is of the opposite polarity to the armature voltage signal 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 c

24、ommutates to zero when its anode potential falls below the potential 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 durin

25、g the time interval when the instantaneous supply voltage is greater 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 sho

26、wn, the reverse blocking capability of the circuit is increased to allow low-voltage thyristor to be used. References: Fig.2 Illustrating the effect of motor back EMF on the Peak inverse voltage applied to the thyristor Fig.3 Armature voltage waveforms The waveforms shown in Fig.2 are ide

27、alized waveforms as much as they ignore the effects of armature inductance,commutator 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

28、.The effect of armature inductance is to force the thyristor to continue to conduct until 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 t

29、ransients having settled out by point E.The undulations on the waveform between E and F are due to commentator ripple. References 1.Landau ID(1999)From robust control to adaptive control.Control Eng Prac 7:1113–1124 2.Forssell U,Ljung L(1999)Closed-loop identification revisited. Automatica 35:121

30、5–1241 3.Soderstrom T,Stoica P(1989)System identification.Prentice Hall,Cambridge,UK 4.Horng JH(1999)Neural adaptive tracking control of a DC motor.Information Sci 118:1–13 5.Lyshevski SE(1999)Nonlinear control of mechatronic systems with permanent-magnet DC motors.Mechatronics 9:539–552 6.Yavin

31、 Y,Kemp PD(2000)Modeling and control of the motion of a rolling disk:e?ect of the motor dynamics on the dynamical model.Comput Meth Appl Mech Eng 188:613–624 7.Mummadi VC(2000)Steady-state and dynamic performance analysis of PV supplied DC motors fed from intermediate power converter.Solar Energy M

32、ater Solar Cells 61:365–381 8.Jang JO,Jeon GJ(2000)A parallel neuro-controller for DC motors containing nonlinear friction.Neurocomputing 30:233–248 9.Nordin M,Gutman P(2002)Controlling mechanical systems with backlash—a survey.Automatica 38:1633–1649 10.Wu R-H,Tung P-C(2002)Studies of stick-slip

33、 friction,pre-sliding displacement,and hunting.J Dyn Syst 124:111–117 11.Ogata K(1990)Modern control engineering.Prentice Hall,Englewood Cli?s,NJ 12.Slotine E,Li W(1991)Applied nonlinear control.Prentice Hall,Englewood Cli?s,NJ 13.Lee PL(1993)Nonlinear process control:applications of gen-eric mod

34、el control.Springer,Berlin Heidelberg New York 直流電動(dòng)機(jī)調(diào)速控制 摘要 調(diào)節(jié)系統(tǒng)的特征在于能保持輸出功率的穩(wěn)定。不同的速度控制系統(tǒng)可以使用不同的制動(dòng)系統(tǒng)，在有高起、制動(dòng)轉(zhuǎn)矩，快速響應(yīng)和快速度調(diào)節(jié)范圍要求的直流調(diào)速系統(tǒng)中，采用的是電氣制動(dòng)的方式。直流電機(jī)的速度控制取決于電樞電壓和磁通。要將轉(zhuǎn)速降為零，或者U=0或Φ=∞。后者是不可能的，因此只可通過(guò)電樞電壓的變化來(lái)降低轉(zhuǎn)速。要將轉(zhuǎn)速增加到較高值，可以增大U或減小Φ。 關(guān)鍵詞 直流調(diào)速 反饋 制動(dòng) 調(diào)節(jié)系統(tǒng) 調(diào)節(jié)系統(tǒng)是一類(lèi)通常能提供穩(wěn)定輸出功率的系統(tǒng)。 例如，電機(jī)速度調(diào)節(jié)器要能在

35、負(fù)載轉(zhuǎn)矩變化時(shí)仍能保持電機(jī)轉(zhuǎn)速為恒定值。即使負(fù)載轉(zhuǎn)矩為零，電機(jī)也必須提供足夠的轉(zhuǎn)矩來(lái)克服軸承的粘滯摩擦影響。其他類(lèi)型的調(diào)節(jié)器也提供輸出功率，溫度調(diào)節(jié)器必須保持爐內(nèi)的溫度恒定，也就是說(shuō)，即使?fàn)t內(nèi)的溫度散失也必須保持爐溫不變。一個(gè)電壓調(diào)節(jié)其也必須保持負(fù)載電流值變化時(shí)輸出電壓值恒定。對(duì)于任何一個(gè)提供一個(gè)輸出，例如，速度、溫度、電壓等的系統(tǒng)，在穩(wěn)態(tài)下必須存在一個(gè)誤差信號(hào)。 電氣制動(dòng) 在許多速度控制系統(tǒng)中，例如軋鋼機(jī)、礦坑卷?yè)P(yáng)機(jī)等這些負(fù)載要求頻繁地停頓和反向運(yùn)動(dòng)的系統(tǒng)。隨著減速要求，速度減小的比率取決于存儲(chǔ)的能量和所使用的制動(dòng)系統(tǒng)。一個(gè)小型速度控制系統(tǒng)（例如所知的伺服積分器）可以采用機(jī)械制動(dòng)，但這對(duì)

36、大型速度控制器并不可行，因?yàn)樯岷茈y而且很昂貴。 可行的各種電氣制動(dòng)方法有： （1） 回饋制動(dòng)。 （2） 渦流制動(dòng)。 （3） 能耗制動(dòng) （4） 反接制動(dòng) 回饋制動(dòng)雖然并不一定是最經(jīng)濟(jì)的方式，但卻是最好的方式。負(fù)載中存儲(chǔ)的能量通過(guò)工作電機(jī)（暫時(shí)以發(fā)電機(jī)模式運(yùn)行）被轉(zhuǎn)化成電能并返回到電源系統(tǒng)中。這樣電源就充當(dāng)了一個(gè)收容不想要的能量的角色。假如電源系統(tǒng)具有足夠的容量，在短時(shí)回饋過(guò)程中最終引起的端電壓升高會(huì)很少。在直流電機(jī)速度控制渥特-勒奧那多法中，回饋制動(dòng)是固有的，但可控硅傳動(dòng)裝置必須被排布的可以反饋。如果轉(zhuǎn)軸速度快于旋轉(zhuǎn)磁場(chǎng)的速度，感應(yīng)電機(jī)傳動(dòng)裝置可以反饋。由晶閘管換流器而來(lái)的廉價(jià)變頻

37、電源的出現(xiàn)在變速裝置感應(yīng)電機(jī)應(yīng)用中引起了巨大的變化。 渦流制動(dòng)可用于任何機(jī)器，只要在軸上安裝一個(gè)銅條或鋁盤(pán)并在磁場(chǎng)中旋轉(zhuǎn)它即可。在大型系統(tǒng)中，散熱問(wèn)題是很重要的，因?yàn)槿绻L(zhǎng)時(shí)間制動(dòng)，軸、軸承和電機(jī)的溫度就會(huì)升高。 在能耗制動(dòng)中，存儲(chǔ)的能量消耗在回路電阻器上。用在小型直流電機(jī)上時(shí)，電樞供電被斷開(kāi)，接入一個(gè)電阻器（通常是一個(gè)繼電器、接觸器或晶閘管）。保持磁場(chǎng)電壓，施加制動(dòng)降到最低速。感應(yīng)電機(jī)要求稍微復(fù)雜一點(diǎn)的排布，定子繞組被從交流電源上斷開(kāi)，接到直流電源上。產(chǎn)生的電能繼而消耗在轉(zhuǎn)子回路中。能耗制動(dòng)應(yīng)用在許多大型交流升降系統(tǒng)中，制動(dòng)的職責(zé)是反向和延長(zhǎng)。 任何電機(jī)都可以通過(guò)突然反接電源以提供反向

38、的旋轉(zhuǎn)方向（反接制動(dòng)）來(lái)停機(jī)。在可控情況下，這種制動(dòng)方法對(duì)所傳動(dòng)裝置都是使用的。它主要的缺點(diǎn)就是當(dāng)制動(dòng)等于負(fù)載存儲(chǔ)的能量時(shí)，電能被機(jī)器消耗了。這在大型裝置中就大大增加了運(yùn)行成本。 直流電機(jī)速度控制 所有直流電機(jī)速度控制的基本關(guān)系都可由下式得出： 各項(xiàng)就是她們通常所指的含義。如果IaRa很小，等式近似為或。這樣，控制電樞電壓和磁通就可影響電機(jī)轉(zhuǎn)速。要將轉(zhuǎn)速降為零，或者U=0或Φ=∞。后者是不可能的，因此只可通過(guò)電樞電壓的變化來(lái)降低轉(zhuǎn)速。要將轉(zhuǎn)速增加到較高值，可以增大U或減小Φ。后者是最可行的方法，就是我們通常所知道的弱磁場(chǎng)。在要求速度調(diào)節(jié)范圍寬的場(chǎng)合可綜合使用這兩種方法。 使用晶

39、閘管的單向速度控制系統(tǒng) 一個(gè)單相晶閘管逆變器系統(tǒng)如圖1所示。讀者應(yīng)該先忽略整流器BR2和它的相關(guān)電路（包括交流回路中的電阻器R），因?yàn)檫@部分只有在具有保護(hù)功能時(shí)才需要，將在下一節(jié)介紹。 圖1 單向晶閘管逆變器系統(tǒng) 因?yàn)樵撾娐肥且粋€(gè)單向轉(zhuǎn)換器，只能在一個(gè)旋轉(zhuǎn)方向控制電機(jī)軸（系統(tǒng)的輸出）的速度。而且，回饋制動(dòng)不能用于電機(jī)；在這種系統(tǒng)類(lèi)型中，電機(jī)電樞可以通過(guò)電氣制動(dòng)靜止（例如，當(dāng)晶閘管門(mén)極脈沖反向時(shí)，電阻可通過(guò)一個(gè)繼電器或其他裝置連接到電樞上）。 整流器BR1給并聯(lián)勵(lì)磁繞組提供一個(gè)穩(wěn)定電壓，產(chǎn)生穩(wěn)定的磁通。電樞電流由一個(gè)晶閘管控制，該晶閘管又由加在它們極上的脈沖控制。脈沖正向時(shí)（減小起動(dòng)

40、延時(shí)角）電樞轉(zhuǎn)速增加，門(mén)極脈沖反相時(shí)電樞轉(zhuǎn)速減小。 速度參考信號(hào)可從人工操作的電位器（如圖1右側(cè)所示）上獲得，反饋信號(hào)或輸出轉(zhuǎn)速信號(hào)可從連接在電樞上的電阻器鏈上獲得。（嚴(yán)格的講，圖1系統(tǒng)中反饋信號(hào)只有當(dāng)電樞電組的壓降很小時(shí)，才與軸轉(zhuǎn)速成正比的電樞電壓成正比。用于補(bǔ)償IaRa壓降的方法將在閱讀材料中討論。）因?yàn)殡姌须妷菏菑囊粋€(gè)晶閘管上獲得的，該電壓包括一系列由電容器C濾波的脈沖。速度參考信號(hào)與電樞電壓信號(hào)極性相反，以確保施加的都是負(fù)反饋。 直流電機(jī)裝置的一個(gè)特征就是需要供電的負(fù)載時(shí)電阻、電導(dǎo)的混合，并且在圖1中反電動(dòng)勢(shì)二極管D確保當(dāng)晶閘管陽(yáng)極電勢(shì)低于前面敘述的電樞連接方式的上限時(shí)，晶閘管電流

41、應(yīng)換向?yàn)榱?。在所示拖?dòng)系統(tǒng)中，當(dāng)晶閘管處于斷開(kāi)狀態(tài)時(shí)，其陽(yáng)極電勢(shì)等于電機(jī)反電動(dòng)勢(shì)。只有在瞬時(shí)電源電壓大于反向電勢(shì)的間隔時(shí)它才會(huì)導(dǎo)通。圖2所示的檢測(cè)表明電機(jī)運(yùn)行時(shí)晶閘管上峰值反向電壓大于峰值正向電壓。如圖所示，在晶閘管上串聯(lián)一個(gè)二級(jí)管，電路的反向關(guān)斷能力就會(huì)增強(qiáng)，所以允許使用低壓晶閘管。 圖2晶閘管對(duì)電機(jī)反電動(dòng)勢(shì)的影響 圖3電樞電壓波形 圖2所示的波形是理想的波形，因?yàn)楹雎粤穗姌须姼?、換向器紋波等因素的影響。典型的電樞電壓波形如圖3所示。在該波形中，晶閘管在A點(diǎn)觸發(fā)，一直到B點(diǎn)電源電壓低于電樞反電動(dòng)勢(shì)時(shí)導(dǎo)通。電樞電感的作用使晶閘管保持到C點(diǎn)飛輪二極管使電樞電壓反向之前導(dǎo)通。當(dāng)電感能量消失（D點(diǎn)），電樞電流為零，電壓恢復(fù)到它的正常水平，這個(gè)暫態(tài)過(guò)程最后穩(wěn)定在E點(diǎn)。點(diǎn)E、F之前的紋波是由換向器引起的紋波。