Sincap kafesli asenkron makinenin basitlendirilmiş vektör kontrolü
Başlık çevirisi mevcut değil.
- Tez No: 75313
- Danışmanlar: PROF. DR. EMİN TACER
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Elektrik Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Elektrik Mühendisliği Bilim Dalı
- Sayfa Sayısı: 114
Özet
ÖZET Sincap kafesli asenkron makineler basit yapısı, yüksek verimliliği, az bakım gerektirmesi, üretim maliyetinin düşüklüğü nedeniyle en çok tercih edilen makineler olmuştur. Ancak karmaşık matematiksel modeli sebebiyle kontrolleri, doğru akım makineleri kadar kolay değildir. Mikroişlemci ve güç elektroniği alanındaki gelişmeler asenkron makinenin kontrolünü kolaylaştırmıştır. Bu gelişmeler sayesinde sincap kafesli asenkron makinenin moment ve akısı vektör kontrolü ile serbest uyarmalı doğru akım makinesinde olduğu gibi ayrı ayrı kontrol edilebilmektedir. Bu tezde sincap kafesli asenkron makinenin basitleştirilmiş vektör kontrolü anlatılmıştır. Öncelikle asenkron makinenin üç fazlı modeli ele alınıp matematiksel modelin karmaşıklığı görülmüştür. Bu nedenle asenkron makinenin matematiksel modeli uzay fazörleri yardımı ile rotor, stator akısı ve manyetik akı yönlendirmeli eksen takımlarında elde edilmiştir. Daha sonra rotor akısı yönlendirilmiş eksen takımındaki eşitlikler basitleştirilerek, stator referans akımlarının ve hız sensörünün kullanıldığı sincap kafesli asenkron makinenin elde edilen basit modeli ve bu şekildeki kontrolü Matlab ve Simulink yardımı ile incelenmiştir. Sonuçlar kontrolsüz asenkron makine ile karşılaştırılmıştır. xi
Özet (Çeviri)
SUMMARY SIMPLIFIED VECTOR CONTROL OF SQUIRREL-CAGE INDUCTION MACHINES The induction machines also known as the asynchronous machines are commonly preferred in industry. In recent years, especially the squirrel-cage induction machines take first place in industrial applications. In 1887 Nikola Tesla built the first induction machine in America, in which a two phase alternating current and some fixed electromagnets, instead of a permanent magnet, were used to generate a rotating field. In the past d.c. motors were used extensively in areas where variable speed operation was required, since their flux and torque could be controlled easily by the field and armature current. In particular, the separately excited d.c. motor has been used mainly for applications where there was a requirement of fast response and four quadrant operation with high performers near zero speed. However, d.c. motors have certain disadvantages, which are due to the existence of the commutator and brushes. That is, they require periodic maintenance; they cannot be used in explosive or corrosive environments and they have limited commutator capability under high speed, high voltage operational conditions. These problems can be over come by the applications of alternating current motors, which can have simple and rugged structure, high maintainability and economy; they are also robust and immune to heavy overloading. Their small dimension compared with d.c. motors allows a.c motors to be designed with higher output ratings for low weight and low rotating mass. The squirrel cage induction machines need complex control algorithms due to their non-linear dynamic model. The speed of supply fed induction motors cannot be continuously varied without additional equipment or without incurring large power losses. However, as a result of progress in the field of power electronics and induction machines became more practical. Some of the advantages of the using of microprocessor or digital techniques are:. Cost reduction in control electronics. Standard hardware is required and the only changes are the software.. Very high accuracy, excellent repeatability, linearity and stability with different setting ranges.. Centralised operator communications, monitoring, and diagnostic.. Complex, high speed arithmetic and capability of decision making.. Powerful system software for on-line measurements, control parameter setting (current control parameter setting, speed control parameter setting) and testing. Automatic location of hardware faults with the help of system and user software. The induction motor drive system is basically a multivariate system, therefore in principle the state variable control theory should be applicable. The dynamic model of yhe induction motor is non-linear because of the speed of rotor in the voltage equations of the stator and rotor and the some parameters of the induction machine may vary with saturation of vary with saturation, temperature and skin effect, adding further non- linearity to the system. If a microcomputer or other digital circuits are used in the control system, then additional sampling characteristics must be added. The discrete time effect of the converters and controllers can be neglected if the machine response is sluggish. Which is normally the case. A simple and popular volts/hertz speed control method for an induction motor system consists of a phase-controlled rectifier with three- phase ac supply, L-C filter, and voltage fed or current fed inverter. This is a scalar control, which relates to the magnitude control of a variable only, and the command and feedback signals are d.c. quantities which are proportional to the respective variables. When the control of an induction machine needs fast transient responds or torque at standstill, the vector control seems the only efficient solution. Therefore, vector control techniques with fast microcomputers or microprocessors have made possible the high performance application of induction machine. Vector controls techniques incorporating fast microprocessors have made possible the application of induction drives for high performance applications where traditionally only d.c. drives where applied. In the past such control techniques would have not been possible because of the complex hardware and software required solving the complex control problem.As for d.c. machine, in a.c. machine both the phase angle and the modulus of the current has to be controlled, in other words, the current vector has to be controlled. In d.c. machines, the orientations of the field flux and armature m.m.f. is fixed by the commutador and the brushes. In induction machines the field flux and the spatial angle of the armature m.m.f. require external control. With vector control of a.c. machines, the torque and flux producing current components are decoupled and the transient response characteristics are similar to those of a separately excited d.c. machine. The control system adapts to any load disturbances or reference value variations as fast as d.c. machine. To apply vector control methods; first off all, the mathematical model of an induction machine must be obtained. As it is mentioned above, the dynamic performance of an induction machine is complex because of the coupling effects between the stator and rotor phases where the coupling coefficients vary with rotor position. Therefore, the mathematical model of the machine can be described by differential equations with time varying coefficients. As a first stage, the mathematical model of a three-phase induction machine on ABC phase axis will be developed. This model in natural axis is based on the following assumptions:. Rotor winding or bars are replaced symmetrically on rotor periphery. Symmetrical winding on stator. Uniform air gap. Neglecting skin and end-effects. The number of effective turns of stator windings and the number of effective turns of rotor windings are equal. Hysteresiz and fuko losses are negligible. Almost stationary magnetic field and sinusoidal distribution of the induction in the air gap. Neglecting inverter dead time and no delay due to signal processing, and the effect of space harmonics. According to the above assumptions, the differential equations in other words the mathematical model, which describes the dynamic behaviour of the electrical and mechanical parts of the induction machine in ABC axis, can be written. But these equations have time varying coefficients because of the sinusoidal variation of mutual inductance with the displacement. xivThere are essentially two general methods of vector control, direct and indirect methods. The direct method was developed by F. Blaschke, and the other was developed by K. Hasse. One of the prime task in vector control is to decouple the torque and flux based from modulus of stator current and keep them in qudrature to one another at all times in reference frame that is related to the rotor coordinates. That requires sensing the three phase stator currents. The principle of the various forms of vector control of a.c. machines can be well understood by comparing the production of electromagnetic torque in d.c. machine and a.c machines. For this purpose first the space phasors of various quantities (m.m.f, currents, flux linkages...) will be introduced by utilising physical and mathematical considerations. In this thesis, vector control of induction machine is discussed, considering rotor-flux-oriented control, stator- flux-oriented control and magnetising-flux-oriented control by using space-phasor theory. These three control methods are simplified. Simulation of simplified rotor-flux- oriented control is studied in computer. In this thesis, first chapter contains a introduction by taking into account the above consideration. In second chapter, the mathematical model of the machine is obtained on ABC phase axis. In third chapter, the space phasors of various quantities (stator m.m.f, stator currents, magnetising current, stator flux linkages...) are obtained by physical considerations. This followed by a discussion of the mechanism of electromagnetic torque production in d.c. and a.c machines and an explanation based on space-phasor theory. Then, the voltages equations are formulated in a general reference frame. In fourth chapter, three types of vector control are presented by considering space phasor-theory. These are the rotor-flux-oriented control, stator- flux-oriented control, and magnetising-flux-oriented control methods. For purpose, voltage equations obtained by using general reference frame, for three methods. Similarly torque equations obtained by using same method. The expression for the electromagnetic torque contains a flux-producing current component and a torque-producing current, which are in space quadrature, and this expression for the electromagnetic torque of d.c. machine. But control algorithms obtained are quite complicated for implementation and still require the measurement or indirect observation of several process quantities (stator currents, flux amplitude, flux frame location, speed and torque). Some simplification steps were taken to overcome these disadvantages. These are:. Flux is constant xv. Stator transient inductance and derivative direct axis of stator current are neglected. In fifth chapter, the induction machine model is obtained in the stationary reference frame fixed to stator, in per-unit system, and machine is simulated in computer and the results of simulation are given In sixth chapter, simplified rotor-flux-oriented vector control with speed sensor is analysed. For this control method:. In order to avoid flux measurement or calculation, the control laws reformulated using constant flux reference in stead of actual value.. Another simplification is based on the use of reference value for currents instead of measured actual values. Finally, a very simple algorithm is found. Then this control method is simulated in computer. The control algorithm is: Uaxrrf =°s1smf Uyxref = ^s1syref + ^s^mr'sxref syref Û) =© H Tr1snaef In the last chapter, the results of studied are given. xvi
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