Ie4 Verim Sınıfı Senkron Relüktans Motor Tasarımı

Abstract

Dünyada hızla artan enerji talebi karşısında enerji kaynaklarının sınırlı kalması 21. Yüzyılda enerji problemlemini beraberinde getirmiştir. Bu sorun son yıllarda mevcut kaynakların etkin kullanılmasına başka bir deyiş ile enerji verimliliği kavramının hayatımızda önemli bir yere konumlanmasına sebep olmuştur. Günümüzde neredeyse bütün endüstriyel ürünler enerji verim sınıflarına göre üretilip sınıflandırılmaktadır. Enerji kaynak yönetimini etkin şekilde planlayabilmek adına hükümetler tarafından hazırlanan regülasyonlar aracılığıyla enerji verimli ürünlere yönelik çalışmalar yoğun olarak sürdürülmektedir. Enerji tüketim verileri incelendiğinde, elektrik motorlarının tüketim olarak endüstriyel, konut ve ticari alanlarda en yüksek tüketim yapan araçlar arasında yer aldığı gözlemlenmiştir. Elektrik motorları özelinde ise en çok kullanılan motor türünün asenkron motorlar olduğu bilinmektedir. Yapılan bir araştırmaya göre asenkron motorların verim seviyelerinde yapılacak 1%’lik bir artış yıllık 20 milyar kWh değerinde bir enerji kazanamına yardımcı olacaktır [1]. Endüstriyel motorlar için halihazırda tariflenen en üst verim düzeyi IE3 olarak adlandırılmıştır. Buna karşın regulasyonlar aracılığı ile IE3 verim seviyesinden daha yüksek verim düzeyine sahip IE4 verim sınıfı motorlar yakın zamanda endüstride kullanılmaya başlanacaktır. Özellikle 7.5 kW ve altı güçlerde verim seviyelerinde iyileştirmeler yaparak IE3 verim seviyesindeki bir motoru maliyet ve üretilebilirlik kısıtları altında IE4 verim seviyesine taşımak 7.5 kW üstü güçlere kıyasla oldukça zordur Yapılan bu çalışmada, IE3 verim düzeyinde üç fazlı 2.2 kW gücünde dört kutuplu bir asenkron motorun yerine geçebilecek IE4 verim seviyesinde bir senkron relüktans motor tasarım çalışması gerçekleştirilmiştir. Senkron relüktans motorlar, asenkron motor ve kalıcı mıknatıslı senkron motorlar ile aynı stator yapısını kullanan, rotorunda yer alan bariyerler yardımı ile d ve q eksen takımlarında oluşan relüktans farkı prensibine dayalı olarak moment üretimi gerçekleştiren motorları temsil etmektedir. Senkron relüktans motorlar asenkron motorlar ile kıyaslandığında rotorunda herhangi bir iletken malzeme bulunmaması sebebiyle rotorunda bakır kayıplarının olmaması, kalıcı mıknatıslı senkron motorlar ile kıyaslandığında ise rotorunda sürekli mıknatısa ihtiyaç duymadan çalışabilmesi sebebiyle maliyet avantajını beraberinde getirmektedir. Bu çalışmada yukarıda tariflenen mevcut asenkron motorun stator yapısı kullanılarak rotor yapısı yeniden tasarlanarak senkron relüktans motor modelleri oluşturulmuştur. Tasarımlar oluşturulurken, senkron relüktans motor için en önemli tasarım girdilerinden olan bariyer sayısı, bariyer şekli, izolasyon oranı açısından tasarımlar irdelenerek en iyi çözüm bulunmaya çalışılmıştır. Çalışmada sayısal analiz yöntemlerinden biri olan sonlu elemanlar yöntemi kullanılmıştır. Sonlu elemanlar yöntemi kullanan paket bir program aracılığı ile iki boyutlu modelleme ve analiz yapılarak manyetik devre sonuçlarına ulaşılmıştır. Modelleme ve analiz basamaklarının doğru bir şekilde yapıldığından emin olmak için test sonuçları varolan mevcut asenkron motorun sonlu elemanlar yöntemi kullanan paket program ile modelleme ve analizi gerçekleştirilmiştir. Test ve manyetik analiz sonuçlarının tutarlı olduğu tespit edilerek mevcut asenkron motordan yola çıkılarak senkron relüktans motor tasarım çalışmaları yapılmıştır. iki boyutlu modelleme ve analiz yapılması sebebiyle uç sargı etkileri gibi bir takım parametreler ihmal edilerek tasarım çalışmaları gerçekleştirilmiştir. Buna karşın senkron relüktans motor tasarımlarının iki boyutlu olarak modelleme ve analize tabi tutulması sebebiyle tasarım çıktılarının elde edilmesi için geçen süre üç boyutlu modelleme ve analize kıyasla oldukça zaman tasarrufu sağlamıştır. Çalışmanın son basamağında belirlenen ve iyileştirilen bir tasarım modeli için prototip üretimi gerçekleştirilmiştir. Prototip motor performans testleri gerçekleştirilmiştir. Sonuç olarak belirlenen model için manyetik analiz sonuçları ve performans test sonuçlarının tutarlı olduğu ve IE4 verim seviyesini gerçeklediği gözlemlenmiştir.

Increasing demand to energy in the 21st century brought the definition ‘energy problem’ as the resources are limited. More energy should be produced or less energy should be consumed with the same sources thus ‘energy efficiency’ entered into our lives. Today, all commercial products are strictly classified according to their energy efficiencies. In addition, these energy efficiency classes are strictly supervised with solid restrictions and regulations by governments and international organizations such as IEC or International Standards. When the energy demand is investigated, it is seen that electrical machines take a noticable percentage in it. Induction machines are the main motor type among commercial products. According to a recent research, a 1% increase in the induction machine efficiency would decrease the yearly demand by 20 billion kWh [1]. Currently, the highest commercial electrical machine efficiency class is identified as IE3 but with future regulations, this efficiency class would be IE4. Especially, for motor output powers under 7.5 kW, it is really hard to upgrade the efficiency class from IE3 to IE4. In this research paper, IE3 three phase 2.2 kW four pole induction machine is redesigned as synchronous reluctance motor (SynRM) with same output power but in IE4 energy efficiency class. SynRMs are type of electrical machines that uses the same stator structures with induction machines and permanent magnet motors. The difference is, when magnetic flux is generated, a difference between d and q axes are generated with help of specifically designed air barriers in rotor. Its basic working principle depends on the increased reluctance in q axis and minimum d axis reluctance. Its differences from switching reluctance motors are similar stator structures with other motor types and anisotropic distribution of saliency into rotor structure as air barriers. On the other hand both reluctance machines need a driver circuit. SynRMs can use a classical inverter motor driver circuit because of the general stator structure. Even SynRMs are as old as induction machines, the current developments in production and electronics technology made them a viable alternative to induction motors in late 20th and 21st century. When compared with induction machines, due to the lack of any conductive material in rotor, SynRMs have less copper losses and less temperature increases and also it is possible to design SynRMs more compact than induction machines because of its higher power/volume. And also it is possible to say that, due to the lack of any conductive material, rotor mass is lighter thus providing a less inertia and friction, ventilation losses. When compared with permanent magnet motors, it is cheaper because of the lack of magnets. SynRMs are temperature insensitive. The impact of high working temperatures effect less these motors than induction machines and permanent magnet because, high temperatures casuses increased resistance and negatively effects the permanent magnet properties. With these properties SynRMs, stands as a performance/price product between induction machines and permanent magnet motors. Today, SynRM is in the catalogues of many primary motor manufacturers and have a wide usage in industry. Currently, the widest usage is in variable speed systems such as pump and fan applications. Generally, the need of a driver circuit is a disadvantage for these motors but when variable speed applications and energy efficiency are considered, the usage of driver circuits is not a disadvantage. SynRM is also a hot topic in terms of scientific research. Since both cheaper and energy efficient motors are important, the development of this motor especially in terms of optimization is a frequent scientific topic. For example, by using ferrite magnets in air barriers, a hybrid permanent magnet SynRM is provided. With this hybrid structure it is possible to push energy efficiency limits to IE5 and IE6 classes. In this paper, the currently used commercial induction machine is redesigned as SynRM as stator structure and geometric dimensions are taken constants. While the designs are being formed, number of air barriers, air barrier geometry and isolation rate are taken as variables. Barrier numbers are investigated from one barrier to four barriers. As for shapes, angular, circular and circular-angular hybrid barrier shape are taken into account. By using these three variables, the best solution is searched. There are some variables that are not taken into account such as thickness of end rotor bridges and existence of barrier bridges. There are many researches made on SynRMs but first research made by Kostko, J.K. with a paper named “Polyphase Reaction Synchronous Motors”. In this paper, first theory of SynRMs are made and also first patent taken by Kostko himself in 1923 but as can be guessed in 1923, SynRM was not able to industrial induction machines due to lack of line start capabilities and relatively low efficiencies. Almost forty years later, a new work was made by Cruickshank, A.J.O., Menzies, R.W. and Anderson, A.F. in name of “Axially Laminated Anisotropic Rotors for Reluctance Motors introduced axially laminated SynRM. Axially laminated SynRM was more efficient than Kostko’s design and it could challenge the induction machines. Axially laminated SynRM was popular during 1960s and 1970s because of its capabilities but its manufacturing was a huge problem. Axially alignment of laminations needs a whole new production line so it wasnt industrially viable. Another work by Cruickshank, Menzies and Anderson put the mathematical theory of axially laminated SynRM. In this work, it still can be observed that axially laminated SynRM are a little behind the induction machines, they have higher saliency ratios than transverse laminated SynRM. In another work made by Honsinger, V.B. in name of “The Inductances Ld and Lq of Reluctance Machines” has put the general analytical model of SynRM in 1971. With this research it is possible to calculate the axes inductances analytically. Before this research, gaining high saliency ratios and torque values was arbitrary. In 1990s, SynRM has revived because of the latest developments in driver systems and production technologies. Papers written by Lipo, T.A. and Miller, T.J.E., has actually put that with driver systems SynRM is a viable alternative to induction machines especially in variable speed applications.Lipo’s researches were on the torque ripple optimization and Miller was working on driver design for SynRM. By the time, Vagati was also researching on saliency ratio improvements. Works made by Kamper, M.J., remarks the importance of finite element method to analyse and optimise SynRM. Another FEM work made by -, Magnussen and Sadarangani provides an understanding to optimization of barrier shape. Another interesting work is about a permanent magnet assisted SynRM which is designed for home appliance applications which shows that permanent magnet assisted SynRM can also be a viable alternative to permanent magnet machines. In paper, Finite Elements Method (FEM) is used as numerical method. FEM is a numerical method that allows us to investigate the problems. It is based on the discretization of a surface/product/material into finite elements and calculation of energies inside each discretized element. After calculation of energies, it is possible to calculate the potentials and fields. After calculation, it can be rebuilt to see the whole results.In contrary to its predecessor Finite Difference Method (FDM), FEM provides faster and more precise results than FDM. FDM, discretizes systems into equidistant grids, on the other hand, FEM discretizes systems into finite elements with dense elements for rapidly changing regions; sparse elements into slowly changing regions. By this method it is possible to obtain a flexibility. Today, FEM is the best computational method to analyze complex systems with help of powerful and comprehensive computer systems and programs. Thus results are taken with a program that allows both designing and analysing of an electrical machine. To ensure that the results are related, induction machine is designed and analysed with FEM program and the results are compared with available test results. After the confirmation of results are related, SynRM are designed and analysed. While analysing with FEM, end turns are omitted thus that two dimensional discretization can be made. Two dimensional analysis give faster results and less memory usage. At the last step of research, a prototype is produced based on the most efficient FEM model. According to the analyses models with four air barriers and angular barrier geometry have shown better performance than other models. As a result it is observed that, motor prototype test results and finite element analysis models are related and the production of a SynRM wtih IE4 energy efficiency class.