機械 外文翻譯 外文文獻 英文文獻 直流電動機調速控制

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, 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 = . 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 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 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 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 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 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 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 delivered. 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 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.Eddy 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 braking 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 braking 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 many large AC hoist systems where the braking 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 influences 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 weakening. 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 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 sideSince the circuit is a single-quadrant converter, the 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 gate 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 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 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 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 reference 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 commutates 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 during 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 shown, 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 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 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 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 transients having settled out by point E.The undulations on the waveform between E and 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(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 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 nonlinear 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.Prentice 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直流電動機調速控制摘要 調節(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系統(tǒng)，在有高起、制動轉矩，快速響應和快速度調節(jié)范圍要求的直流調速系統(tǒng)中，采用的是電氣制動的方式。直流電機的速度控制取決于電樞電壓和磁通。要將轉速降為零，或者U=0或=。后者是不可能的，因此只可通過電樞電壓的變化來降低轉速。要將轉速增加到較高值，可以增大U或減小。關鍵詞 直流調速 反饋 制動調節(jié)系統(tǒng)調節(jié)系統(tǒng)是一類通常能提供穩(wěn)定輸出功率的系統(tǒng)。例如，電機速度調節(jié)器要能在負載轉矩變化時仍能保持電機轉速為恒定值。即使負載轉矩為零，電機也必須提供足夠的轉矩來克服軸承的粘滯摩擦影響。其他類型的調節(jié)器也提供輸出功率，溫度調節(jié)器必須保持爐內的溫度恒定，也就是說，即使爐內的溫度散失也必須保持爐溫不變。一個電壓調節(jié)其也必須保持負載電流值變化時輸出電壓值恒定。對于任何一個提供一個輸出，例如，速度、溫度、電壓等的系統(tǒng)，在穩(wěn)態(tài)下必須存在一個誤差信號。電氣制動在許多速度控制系統(tǒng)中，例如軋鋼機、礦坑卷揚機等這些負載要求頻繁地停頓和反向運動的系統(tǒng)。隨著減速要求，速度減小的比率取決于存儲的能量和所使用的制動系統(tǒng)。一個小型速度控制系統(tǒng)（例如所知的伺服積分器）可以采用機械制動，但這對大型速度控制器并不可行，因為散熱很難而且很昂貴。可行的各種電氣制動方法有：（1） 回饋制動。（2） 渦流制動。（3） 能耗制動（4） 反接制動回饋制動雖然并不一定是最經濟的方式，但卻是最好的方式。負載中存儲的能量通過工作電機（暫時以發(fā)電機模式運行）被轉化成電能并返回到電源系統(tǒng)中。這樣電源就充當了一個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，在短時回饋過程中最終引起的端電壓升高會很少。在直流電機速度控制渥特-勒奧那多法中，回饋制動是固有的，但可控硅傳動裝置必須被排布的可以反饋。如果轉軸速度快于旋轉磁場的速度，感應電機傳動裝置可以反饋。由晶閘管換流器而來的廉價變頻電源的出現(xiàn)在變速裝置感應電機應用中引起了巨大的變化。渦流制動可用于任何機器，只要在軸上安裝一個銅條或鋁盤并在磁場中旋轉它即可。在大型系統(tǒng)中，散熱問題是很重要的，因為如果長時間制動，軸、軸承和電機的溫度就會升高。在能耗制動中，存儲的能量消耗在回路電阻器上。用在小型直流電機上時，電樞供電被斷開，接入一個電阻器（通常是一個繼電器、接觸器或晶閘管）。保持磁場電壓，施加制動降到最低速。感應電機要求稍微復雜一點的排布，定子繞組被從交流電源上斷開，接到直流電源上。產生的電能繼而消耗在轉子回路中。能耗制動應用在許多大型交流升降系統(tǒng)中，制動的職責是反向和延長。任何電機都可以通過突然反接電源以提供反向的旋轉方向（反接制動）來停機。在可控情況下，這種制動方法對所傳動裝置都是使用的。它主要的缺點就是當制動等于負載存儲的能量時，電能被機器消耗了。這在大型裝置中就大大增加了運行成本。直流電機速度控制所有直流電機速度控制的基本關系都可由下式得出：各項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轉速。要將轉速降為零，或者U=0或=。后者是不可能的，因此只可通過電樞電壓的變化來降低轉速。要將轉速增加到較高值，可以增大U或減小。后者是最可行的方法，就是我們通常所知道的弱磁場。在要求速度調節(jié)范圍寬的場合可綜合使用這兩種方法。使用晶閘管的單向速度控制系統(tǒng)一個單相晶閘管逆變器系統(tǒng)如圖1所示。讀者應該先忽略整流器BR2和它的相關電路（包括交流回路中的電阻器R），因為這部分只有在具有保護功能時才需要，將在下一節(jié)介紹。圖1 單向晶閘管逆變器系統(tǒng)因為該電路是一個單向轉換器，只能在一個旋轉方向控制電機軸（系統(tǒng)的輸出）的速度。而且，回饋制動不能用于電機；在這種系統(tǒng)類型中，電機電樞可以通過電氣制動靜止（例如，當晶閘管門極脈沖反向時，電阻可通過一個繼電器或其他裝置連接到電樞上）。整流器BR1給并聯(lián)勵磁繞組提供一個穩(wěn)定電壓，產生穩(wěn)定的磁通。電樞電流由一個晶閘管控制，該晶閘管又由加在它們極上的脈沖控制。脈沖正向時（減小起動延時角）電樞轉速增加，門極脈沖反相時電樞轉速減小。速度參考信號可從人工操作的電位器（如圖1右側所示）上獲得，反饋信號或輸出轉速信號可從連接在電樞上的電阻器鏈上獲得。（嚴格的講，圖1系統(tǒng)中反饋信號只有當電樞電組的壓降很小時，才與軸轉速成正比的電樞電壓成正比。用于補償IaRa壓降的方法將在閱讀材料中討論。）因為電樞電壓是從一個晶閘管上獲得的，該電壓包括一系列由電容器C濾波的脈沖。速度參考信號與電樞電壓信號極性相反，以確保施加的都是負反饋。直流電機裝置的一個特征就是需要供電的負載時電阻、電導的混合，并且在圖1中反電動勢二極管D確保當晶閘管陽極電勢低于前面敘述的電樞連接方式的上限時，晶閘管電流應換向為零。在所示拖動系統(tǒng)中，當晶閘管處于斷開狀態(tài)時，其陽極電勢等于電機反電動勢。只有在瞬時電源電壓大于反向電勢的間隔時它才會導通。圖2所示的檢測表明電機運行時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)一個二級管，電路的反向關斷能力就會增強，所以允許使用低壓晶閘管。圖2晶閘管對電機反電動勢的影響圖3電樞電壓波形圖2所示的波形是理想的波形，因為忽略了電樞電感、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點觸發(fā)，一直到B點電源電壓低于電樞反電動勢時導通。電樞電感的作用使晶閘管保持到C點飛輪二極管使電樞電壓反向之前導通。當電感能量消失（D點），電樞電流為零，電壓恢復到它的正常水平，這個暫態(tài)過程最后穩(wěn)定在E點。點E、F之前的紋波是由換向器引起的紋波。