Fırçasız doğru akım makinasının bilgisayar programı yardımıyla tasarımı

Abstract

Bu çalışmada sürekli mıknatıslı fırçasız doğru akım makinası incelenmiş ve iç rotorlu fırçasız doğru akım makinasının bilgisayar yardımıyla tasarımının yapılması konusu ele alınmıştır. îlk bölümde fırçasız doğru akım rnakinasının genel tanıtımı, doğru akım makinasıyla karşılaştırılması ve bu makinaya olan üstünlükleri anlatılarak konuya giriş yapılmıştır. İkinci bölümde fırçasız doğru akım makinası ası rotor yapısına göre ayrı ayrı incelenerek kullanım koşullarına göre karşılaştırmalı incelemesi yapılmıştır.. Bir sonraki bölüm fırçasız doğru akım rnakinasının tasarım yöntemini ve bu yöntem esnasında uygulanacak denklemlerin çıkarımını içermektedir. Bu çıkarım sonuçlarını kullanarak yapılan bilgisayar programının açıklaması ve kullanım prosedürü takib eden bölümde yer almaktadır. Son bölümde elde edilen sonuçlar belirtilmiştir.

A brushless motor, as its name suggests, is a motor without brushles, slip rings or mechanical commutators connected to windings on its rotor, such as is reuired in a conventional direct current motor. There are many motors which satisfy this basic definition. For example an alternative current induction motor is a brushless alternative current machine because current in the rotor windings is transmitted by electromagnetic induction as in the secondary winding of a transformer. The induction motor is not a brushless direct current motor because the performance is quite different than that of a direct current motor. A stepping motor has all the windings in the stationary portion, and the rotor has permanent magnets and soft iron poles. The rotor torque is developed as the magnetic polarity of the stator is determined by the energization of the phase coils, and as these phases are rotated, the poles of the rotor attempt to follow as in a synchronous manner. The step motor also has a very strange speed vs. torque relationship which is quite non-linear and much different than that of a conventional direct current motor. By definition, the brushless motor should produce a speed vs torque relationship which is linear and all of tthe performance equations for permanent magnet direct current motors should be satisfied Vi by the performance of the brushless motor. The direct current motor has phase windings on the armature which are mechanically commutated whereas, the brushless direct current machine motor has the phase -windings in the stator which are electronically commuated at he optimum angular rotational positions. A permanent magnet direct current motor with a mechanical commuation method contains permanent magnets in the stationary portion and copper -windings on the rotating portion. Notice that the permanent magnets are on the outside or in the stator portion while the -windings are in slots in the laminations on the rotor or armature which is the rotating portion of the motor. The magnets are on the rotating portion so that brushless or slip rings are not necessary because the -windings are in the stationary portion and do not rotate. As we -will see there are many versions of brushless motors. There are axial gap disc designs, inside rotor, outside roor and slotless design with many different -winding patterns as well as many different pole configurations. We -will atttempt to review most of the known brushless versions and provide some insight into the reasons for all of the various types and identify their usefulness. It should be clear by now that before a brushless motor design can commence there are several very important decisions which must be made. The reasons for this should be obvious from some of the previous discussion regarding the features of different types of brushless motors as well as the availability of different magnetic materials. Vii The method of commutation is also an important issue which should be considered in making the basic decisions about the design. The choice of an inside rotor, outside rotor, or a axial gap motor must be made first along with the magnet grade. Then the number of phases, the number of poles, the number of slots, and he winding configuration must be selected. The rotor&permanent magnet structure designed, then the stator and -winding is determined. A sort of a step by step procedure is provided as a suggestion for a typical brushless direct current motor design. 1- Servo or Continuous RPM 2- Inside, Outside or Axial Rotor 3- Select Magnet Grade 4- Select Number of Poles 5- Select Number Slots («fcphases) 6- Perform Rough Sizing Estimate 7- Select Air Gap &. Determine Magnetic Loading 8- Design Rotor && Determine Magnetic Loading 9- Layout Stator Lamination Dimensions 10- Solve for Conductors and Turns/Coils 11- Calculate Wire Size, Res/Phase &. Inductance 12- Check Temperature Rise, Curren Density, Demag 13- Re-check Performance 14- Reiterate Design Until Redefined If a fairly low RPM, constant speed or slightly variable speed brushless motor design is required, it would be wise to consider an axail rotor design. This would be paricularly true if zero cogging and smooth operation is required. Such applications would be as previously mentioned, record turn tables, compact disc players, floppy disc and video recorders. These designs using axial rotor motors would be very low in output power and the speed would be under 1.000 RPM. îf a very high torque low speed machine is desired, then a high pole count inside rotor design would be chosen using rare earth magnets. If a higher speed brushless motor is required which is constant and varies ever so slightly, an outside rotor brushless motor should be considered. Remember that the features of these designs have to do with ease of rnanufacturing and low cost. The inertia of the rotor is quite high which is desirable for such applications as fans and blowers. If a company which presently has the rnanufacturing technology for brush type direct current motors and would like to enter the brushless business, the outside rotor inside stator designs would be well suited to their rnanufacturing infrastructure. Fabricate which presently manufactures alternative current induction motors desires to enter brushless markets, a design with an inside rotor -would be well suited to the alternative current motor production equipment. Development and entry into brushless motors would be a very low risk venture because of the similar manufacturing equipment and infrastructure. If the brushless requirement is a servo with performance for factory automation, machine tools or aerospace there is little choice but to select the inside rotor brushless design using either high performance rare earth iX permanent magnets or an imbedded ferrite rotor design either of which would require a comletely new stator lamination to carry the high magnet flux. It is certainly important to take advantage of the modern personel computer in the design of brushless machines. The variables in magnetic circuit which include permanent magnets and electromagnets are so comlex that it is axtemely difficult for the human mind to keep tract of all their relationship to facilitate conception of new and innovative The use of the modern computers in design simulation is largely responsible for the acceleration in product development in this last half of the twentieth century. The motor designer must attemp to visualize the production of the electromagnetic fields in their cross linkage in the magnetic circuit that he is compelled to design, even though these problems knowwn as magnetic field problems can be expressed very precisely by a single set of four equations which are credited. The principles described in the preceding chapters are based upon the experience of the author and others in terms of the considerattions which determine the approach to the design of brushless permanent magnet motors for a wide variety of motor types used over a broad spectrum of applications. Much of the material presented is general in nature as much as possible as relating to several general types of brushless motor configurations.