Serbest uyarmalı doğru akım motorunun mikrokontrolör tabanlı dört bölgeli hız kontrolü
Speed control of a separately excited dc motor in four quadrants based on microcontroller
- Tez No: 66866
- Danışmanlar: DOÇ. DR. METİN GÖKAŞAN
- Tez Türü: Yüksek Lisans
- Konular: Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve Kontrol, Computer Engineering and Computer Science and Control
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Kontrol ve Bilgisayar Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 82
Özet
ÖZET Bu tez çalışmasında, bir doğru akım (d. a.) sürücü sistemin dört bölgede hız kontrolü gerçekleştirilmiştir. Öncelikle d. a. sürücü sistemlerin gelişimi tanıtılmış ve günümüzde kullanılan yöntemlerden kısaca bahsedilmiştir. Birinci bölümde, ilk olarak kullanılan hız kontrollü d. a. sürücünün temel prensibi anlatılmıştır. Daha sonraları geliştirilen ve günümüzde de çok nadir de olsa halen kullanılmakta olan Ward-Leonard hız kontrol sisteminin prensip şeması verilerek çalışması anlatılmıştır. Yarıiletken teknolojisinin hızlı gelişmesiyle tristörlerin kullanıldığı hız kontrollü d. a. sürücü sistemlerin blok şeması çizilmiş ve çalışması anlatılarak avantaj ve dezavantajları verilmiştir. Mîkrokontrolörlerin kullanılmasıyla gerçekleştirilen sayısal kontrol uygulamalarında analog işaretlerin okunması ve gerekli kontrol işaretlerinin üretilmesi ile ilgili kısaca bilgiler verilmiştir. Kontrol sistemlerinde, matematiksel modellerin sistemi tam olarak ifade etmesi çok önemlidir. İkinci bölümde, uyarma ve endüvi sargılarının birbirinden bağımsız olarak beslendiği, kontrol sistemlerinde çok kullanılan serbest uyarmak d. a. motorunun eşdeğer devresi verilerek lineerleştirilmiş matematiksel modelini gösteren tanım denklemleri verilmiştir. Üçüncü bölümde ise tam kontrollü döğrultucunun transfer fonksiyonu elde edilmiştir. Dördüncü bölümde dijital kontrol sistemi tanıtılarak PID kontrolörün dijital olarak nasıl gerçekleştirileceği anlatılmıştır. Beşinci bölümde gerçekleştirilen hız kontrol sisteminin prensip şeması verilmiş ve kontrol sisteminin yazılımına ilişkin akış diyagramı ile donanımına ilişkin devreler hakkında bilgiler verilmiştir. Son bölüm olan altıncı bölümde gerçekleştirilen sistemin özelliklerinden ve getirdiği bazı kolaylıklardan bahsedilmiştir.
Özet (Çeviri)
SUMMARY In this thesis, the speed control of a separately excited direct current (dc) motor is aimed. For this purpose, information about the dc drives is given firstly. Then, the state of the art is explained about dc drives at present. Dc motors have been used in variable speed drives for a long time. The versatile control characteristic of dc motors have contributed to their extensive use in industry. Alternating current (ac) motors can provide high starting torques, which are required for traction drives. Control over a large speed range both below and above the rated speed can be easily achieved. The methods of control are simpler and less expensive than those of ac motors. Although commutators prohibit their use in certain applications, such as high speed drives and operation in hazardous atmospheres, dc motors play a significant role in many industrial drives. Dc motors range in size from tiny units turning fens in electronic apparatus to 10000-hp motors driving the rolls in steel mills. Other applications include fork lifts, punch presses, and battery-powered vehicles. The most flexible control is obtained by means of a separately excited dc motor, in which the armature and field circuits are provided with separate sources. This arrangement produces speed-torque characteristics approximating closely to the ideal characteristics. For the armature source a controlled rectifier or a chopper is required. If the field current is to be controlled, similar provision must be made for the field circuit. XIThyristor dc drives frequently require sophisticated control systems. Both analog and digital feedback controls are used. In order to exploit the full potential of thyristor control, electrical braking, both dynamic and regenerative is widely used at present in the most thyristor-controlled dc drives. The techniques of thyristor control of dc drives have developed rapidly in recent years. Microcomputer control of complex drives systems can provide great operating flexibility. The technology is now highly advanced. Careful design of a control system with microcomputer can significantly reduce the controller hardware cost. This advantage will become more and more significant with continuation of the present trends in microcomputer technology. In today applications, system designers are using more powerful microcontrollers with higher speed and more functional integration which are produced to control systems. A microcontroller individually has a Central Processing Unit-CPU, a memory unit and intensive peripherals such as Analog to Digital Converter-ADC and Digital to Analog Converter-DAC. Therefore, it can be suitable for digital control systems by adding some extra components. Microcontrollers read some feedback signals, such as voltage, current or speed, through measuring circuits and limit them, They send information to accelerate or decelerate the motor or, produce control signals for the switching elements in driving circuits. Control algorithms for the system can be written or non-measurable signals can be obtained using measurable ones easily. Some modern control algorithms which are very difficult or sometimes impossible to realize with analog circuits can be realized. It is very important for a designer to be able to make changes in the control system without having changed anything in the hardware and only changing the control algorithm. In order to understand and control complex systems one must obtain a mathematical model describing those systems. Therefore it is necessary to analyse the relationship between the system variables and to obtain the mathematical model. Since the systems xuunder consideration are dynamic in nature, the descriptive equations are usually differential equations. A great majority of physical systems are linear within some range of the variables. However, all systems ultimately become nonlinear as the system variables are increased without limit. In practice, The complexity of the systems and the ignorance of all the relevant factors necessitate the introduction of assumptions concerning the system operation. Therefore scientist often find useful to consider physical system, delineate some necessary assumptions, and linearize the system. Then, by using the physical laws describing the linear equivalent system, one can obtain a set of linear differential equations. Finally, utilizing mathematical tools we obtain a solution describing the operation of the system. In order to obtain a mathematical model of a dc motor it is useful to neglect the second order effects, such as hysteresis and the voltage drops across the brushes. These assumption are necessary to avoid the complexity of the system, and to linearize it. The mathematical model of the separately excited dc motor can be given by the following equations. In this linearized model, the flux density generated by the field winding is assumed to be the linear function of the field current. But, in general, the relationship between the flux density and the field current is not linear. diJt) vf(t) = Rfif(t) + Lf-^- (1) vo(0 = *Â(0+4^p+£a (2) m = J~+Pa>{İ) + TL (3) Ea=Gfif(t)m(t) (4) Te = Gfif{t)ia(t) (5) X1USince the aim in this work is to control digitally the speed of dc motor fed by a dual converter by a microcontroller, it is necessary to know the transfer function of the used component also. This provides to analyze the whole closed loop control system easily. By using the dynamic equation of the motor above, its transfer function is obtained under the condition of constant field current, as (?(*) = W(s)G///Va(s) JLas2+s(PLa+JRa) + /ma+(GfIfy (6) and the block diagram of the separately excited dc motor can be shown as in figure- 1. TM w® Figure- 1. Block diagram of separately excited dc motor controlled by rotor voltage. In three-phase drive systems, the armature current can be continuous because of the inertia of the load and motor. By linearization of the transfer characteristic and taking into account the effect of the dead time on dynamic converter properties, we can express the converter output relation for no-load operation, AEa(s)= Kde-SJ< AE, (7) If time Td is much smaller than the dominant time constants in closed circuit control, then, to simplify the analysis, the dead time term in the transfer function is replaced by XIVa first order inertia term with time constant Td. In such a case, the converter 's transfer function becomes A£» Kd AEc(s) l+sTd (8) for the continuous current operation. The digital speed control implementation of the separately excited dc motor in four quadrants is shown in the figure-2. Display Microcontroller ~l Input output interface l_ Reference speed Start /stop Synchronizing circuit -dD-i 3 -phase supply Motor current A/D Current. Transformer Gate pulse generator GroupTselector Speed input module Speed sensor Figure-2. Block diagram of the speed control of separately excited dc motor by using microcontroller. In the control system, PID controller was used as a digital controller and it was realized by programming in parallel. XV
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