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1、Speed Control of DC MotorRegulator 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 m
2、ust 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 must ou
3、tput 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 system, e.g., rolling mills mine winders, etc., the load has to b
4、e 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
5、with large speed controllers since it is difficult and costly to remove the heat generated. The various methods of electrical braking avaiable are:(1) Regenerative braking.(2) Eddy current braking.(3) Dynamic braking.(4) Reverse current braking(plugging).Regenerative braking is the best method, thou
6、gh 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
7、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
8、 motor driver can regenerate if the rotor shaft is driven faster than speed of the rotating field. The advent of low-cost variable variable-frequency supplies from thyristor inverters have brought about considerable charges in the use of induction motors in variable speed drives. Eddy current brakin
9、g can be applied to any machine, simply by mounting a copper or aluminium 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, bearing, and motor will be raised if prolonged braking is applied.In
10、dynamic breaking, the stored energy is 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
11、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 system wher
12、e the braking duty is both severe and prolonged. Any electrical motor can be brought to a standstill by suddenly reconnecting the supply to reverse the direction of rotation (reverse current braking). Applied under controlled conditions, this method of braking is satisfactory for all drivers. Its ma
13、jor disadvantage is that the electrical energy consumed by the machine when braking is equal to the stored energy in the load. This increases the running cost significantly in large drives.Equal pulse width PWM law VVVF (Variable Voltage Variable Frequency) installs in the early time is uses PAM (Pu
14、lse Amplitude Modulation) to control, its inventor part which the technology realizes but only can output the frequency adjustable square-wave voltage not to be able to adjust the pressure. The pulse width PWM law are precisely in order to overcome, is in the PWM law which the PAM law this shortcomi
15、ng development comes the simplest one kind. It is each pulse width equal pulse row took the PWM wave, through a change pulse row cycle may the frequency modulation, the change pulse width or the duty factor may adjust the pressure, uses the suitable control method then to cause the voltage and the f
16、requency coordination change. Is opposite in the PAM law, this method merit simplified the electric circuit structure, enhanced the input end power factor, but simultaneously also has in the output voltage besides the fundamental wave, but also contains the big harmonic component.Stochastic PWM That
17、 time the high efficiency transistor mainly for the bipolarity Daring ton triode, the carrier frequency generally did not surpass 5kHz, the vibration which the electrical machinery winding electromagnetism noise and the overtone created has aroused peoples interest. In order to obtain the improvemen
18、t, the stochastic PWM method arises at the historic moment. Its principle is the stochastic change turn-on frequency causes the electrical machinery electromagnetism noise to be limited to approximately the belt white noise (in linear frequency coordinate system, various frequencies energy distribut
19、ion is even), although the noise a decibel number has not always changed, but weakens greatly take the fixed turn-on frequency as the characteristic colored noise intensity. Because of this, even if in IGBT by widespread application today, has had to limit regarding the carrier frequency is comparin
20、g the low frequency the situation, stochastic PWM still had its special value; On the other hand explained eliminates the machinery and the electromagnetism noise best method enhances the operating frequency blindly, the stochastic PWM technology was precisely provides an analysis, has solved this k
21、ind of question brand-new mentality.Spatial voltage vector control PWM Spatial voltage vector control PWM (SVPWM) also calls the magnetic flux sine PWM law .It take the three-phase profile whole production effect as the premise, take approaches the electrical machinery air gap the ideal circular rot
22、ary field path as the goal, has the actual magnetic flux with the inventor different switch pattern to approach the base director circle magnetic flux, by theirs comparison result decided the inventor the switch, forms the PWM profile. This law embarks from the electric motor angle, regards as the i
23、nventor and the electrical machinery a whole, inscribes the polygon to approach the circle the way to carry on the control, causes the electrical machinery to obtain the peak-to-peak value constant circular magnetic field (sine magnetic flux).The concrete method divides into the magnetic flux split-
24、ring type and the magnetic flux closed loop type. The magnetic flux split-ring law synthesizes an equivalent voltage vector with a two non-vanishing vector sum null vector, if the sampling time enough is small, may synthesize the random voltage vector. When this law output ratio-voltage sine-wave mo
25、dulation enhances 15% close, sum of the harmonic current effective value smallest. The magnetic flux closed loop type introduces the magnetic flux feedback, controls the magnetic flux the size and the change speed .Estimates the magnetic flux after the comparison and assigns the magnetic flux, accor
26、ding to the error decided has the next voltage vector, forms the PWM profile. This method has overcome the magnetic flux split-ring method insufficiency, when has solved the electrical machinery low speed, the stator resistance affects the major problem, reduced the electrical machinery pulsation an
27、d the noise. But because has not introduced the torque the adjustment, the system performance has not had the fundamental improvement.Vector Control PWMThe vector control also called the magnetic field direction detection control, its principle is asynchronous motor under three-phase coordinate syst
28、em stator current Ia, Ib and Ic , through the three-phase/two phase transformation, equivalent becomes under two static coordinate systems alternating current Ia1 and Ib1, again through presses the rotor magnetic field direction detection revolving transformation, equivalent becomes under the synchr
29、onized revolving coordinate system direct current Im1 and It1 (Im1 is equal to the direct current motor exciting current; It1 is equal to the armature electric current which is proportional with the torque), then the imitation direct discharge motive control method, realizes to the motor control. It
30、s essence is the motor equivalent is the direct current motor, separately to the speed, the magnetic field two components carries on the independent control. Through the control rotor flux linkage, then the decomposition stator current obtains the torque and the magnetic field two components, after
31、coordinate transformation, realization orthogonal or decoupling control.But, because the rotor flux linkage accurately observes with difficulty, as well as the vector transformation complexity, causes the actual control effect often with difficulty to achieve theoretical analysis effect, this is the
32、 vector control technology in the practice insufficiency. In addition, It must directly or indirectly obtains the rotor flux linkage to be able to realize the stator current decoupling control in space position, needs to dispose the rotor position or the velocity generator in this kind of vector con
33、trol system, this gives many application situations to bring inconveniently obviously.The analytical functions of the armature reaction of permanent magnet brushless DC motor with concentrated coils are proposed by using the method of image, concerning with the configuration of these machines. This
34、approach is different from the method of equivalent distributed current sheet and more suitable for the electric machines, which have concentrated coils and deeper slots. Under different control mode, the analytical functions of the armature reaction are different.Brushless DC motor (BLDCM) with per
35、manent excitation, in which electrical commutator is used instead of mechanical, has not only the same good characteristics of speed control as traditional DC motor, but also the good characteristics of AC Motor. Brushless DC motors have found wide application due to their high power density and eas
36、e of control. Moreover, the machines have high efficiency over wide speed range. Recently it has been quickly developed.SCM control of permanent magnet brushless DC motor speed control system applicable to electric bicycles, and other low-power work. Redundant power and can return to collapse. The s
37、ystem has good speed performance, high power factor, energy saving, small size, light weight, and other advantages.According to the permanent magnet brushless DC motor control of the PWM pulse width, speed sensor and passed through eighth speed digital dynamic display of speed, through hardware and
38、software support, for the entire system design requirements.Brushless DC Motor DriveIdeal Torque ProductionAs stated earlier, a brushless DC motor generally describes a motor having a trape-zoidal back EMF. For this case, the phase currents are rectangular pulses, sometimes loosely identified as squ
39、arewave currents. While (8.3) can be used to describe torque production for this motor, it is easier to understand this configuration graphically as shown in Fig. 8-2, where the three phases have been labeled A, B, and C respectively.In the figure, the back EMF shapes, i.e ., the back EMFs divided b
40、y speed, are trape-zoids having 2/3 duty cycle. That is, for each 180!aE the back EMF shape is constan over 120!aE. The current associated with each back EMF is composed of rectangula pulses having a 2/3 duty cycle, where the nonzero portions of the pulses are aligned with the flat areas of the resp
41、ective back EMF shapes and the polarity of the current matches that of the back EMF. Following (8.2), the constant torque produced is shown at the bottom of the figure. Over each 60!aE segment, positive current flows I one phase, negative current flows in another, and no current flows in the third p
42、hase. The letters below the constant torque line signify the two phases carrying current, with the overbar denoting negative current flow or flow out of a phase. Every 60!aE where the back EMF in a phase makes a transition, the current in one phase remains unchanged, while the current in another goe
43、s to zero, and the current in the thirdbecomes nonzero. Over 360!aE, there are six transitions or commutations before the sequence repeats. As a result, this motor drive is often called a .six step drive.DC Motor Speed Control The basis of all methods of DC motor speed control is derived from the eq
44、uations:EU=E+IaRathe terms having their usual meanings. If the IaRa drop is small, the equations approximate to UorU/ 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 b
45、y 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.直流电机速度控制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
46、能在负载转矩变化时仍能保持电机速度为恒定值。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。其它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，即使炉内的热量散失也必须保持炉温不变。一个电压调节器必须也保持负载电流值变化时输出电压恒定。对于任何一个提供一个输出，例如速度、温度、电压等的系统，在稳态下必定存在一个误差信号。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）可以采取机械制动，但这对大型速
47、度控制器并不可行，因为散热很难并且很昂贵。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）反向（接）制动。回馈制动虽然并不一定是最经济的方式，但却是做好的方式。负载中存储的能量通过工作电机（暂时以发电机模式运行）被转化成电能并被返回到电源系统中。这样电源就充当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沃特-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。如果轴转速快于旋转磁场的速度，感应电机传动装置可以反馈。有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
48、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
49、，这种制动方法对所有传统装置都是适用的。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。等脉宽PWM法 VVVF(Variable Voltage Variable Frequency)装置在早期是采用PAM（Pulse Amplitude Modulation）控制技术来实现的，其逆变器部分只能输出频率可调的方波电压而不能调压。等脉宽PWM法正是为了克服PAM法的这个缺点发展而来的，是PWM法中最为简单的一种。它是把每一脉冲的宽度均相等的脉冲列作为PWM波，通过改变脉冲列的周期可以调频，改变脉冲的宽度或占空比可以调压，采用适当控制方法即可使电压与频率协调变化。相对于PAM法，该方法的优点是简化了电路结构，提高了输入端的功率因数，但同时也存在输出电压中除基波外，还包含较大的谐波分量。随机PWM 在上世纪70年代开始至上世纪80年代初，由于当时大功率晶体管主要为双极性达林顿三极管，载波频率一般不超过5k