Mıknatıslı anahtarlamalı relüktans makinesinin kontrolü ve performans analizi
Control and performance analysis of permanent magnet switched reluctance machine
Yazar: FARUK DURAK
Danışman: YRD. DOÇ. DR. FUAT KÜÇÜK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Elektrik Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering

Özet:
Anahtarlamalı Relüktans Makinesi (ARM) asenkron ve senkron makinelere kıyasla
daha basit yapılı, daha sağlam ve üretimi daha ucuz bir makinedir. ARM'ler değişken
hızlı uygulamalarda yüksek performans sağlar. Rotorunda sargı olmaması nedeniyle
ARM'nin verimi aynı güçteki asenkron ve senkron makinelerden daha yüksek
olabilmektedir. Sargısız rotorun bir diğer avantajı ise atalet momentinin oldukça düşük
olması ve yüksek hız seviyelerine kolayca çıkabilmesidir.
ARM'nin yukarıda bahsedilen avantajlarına rağmen analitik modelleme yapılması
oldukça zordur. Günümüzde tasarım ve analizi bilgisayar üzerinde koşturulan sonlu
elemanlar tabanlı yazılımlar ile yapılmaktadır. Klasik ARM'ler üzerine yapılmış pek
çok çalışma mevcut olmakla beraber bunların çoğunluğu ticarileşme fırsatı
bulamamıştır. ARM'nin maliyetinin asenkron ve senkron makinelere göre çok düşük
olasına rağmen ihtiyaç duyduğu güç elektroniği sürücü devresinin piyasada seri
üretiminin bulunmamasının getirdiği maliyet artışı mevcuttur. ARM'ler üzerine
yapılan çalışmalar arttıkça yakın gelecekte sözkonusu maliyet artışının önleyecek
yöntemler geliştirilebileceği ve böylece ARM'lerin özellikle değişken hız
uygulamalarında tercih edilebileceği düşünülmektedir.
Bu çalışmanın motivasyon kaynağını ARM'lerde ciddi bir maliyet artışına neden
olmadan güç üretiminin arttırılabileceği düşüncesi oluşturmuştur. Güç ve moment
artışı klasik ARM'deki stator üzerine yerleştirilen maliyeti ucuz mıknatıslar sayesinde
sağlanmıştır. Bu mıknatısların sağladığı diğer avantajlar ise klasik ARM'nin hız
cevabını, moment dalgalılığını iyileştirmesi ve faz arızası esnasında devamlı dönüşü
sağlayacak yeterli moment üretimine olanak sağlamasıdır. Yapılan çalışma neticesinde
ARM'nin yapısında ucuz mıknatıslar yerleştirilerek performansının arttırılabileceği ve
aynı zamanda güvenirliğinin daha da iyileştirilebileceği görülmüştür.
Bu çalışmada, 1. bölümde tezin literatürdeki yeri ve çalışmanın amacı verilmiş daha
sonra 2.Bölümde ARM'ler hakkında teorik bilgi verilmiştir. 3. Bölümde; 6/4 yapıdaki
bir ARM ile yine aynı motorda statora Alnico-5 mıknatıs yerleştirilerek elde edilmiş
SMARM'nin AutoCAD programı ile yapılmış çizimleri verilmiştir. Tasarlanan bu iki
motorun FEMM programı aracılığıyla manyetik analizi yapılmıştır. FEMM
programında ilk önce belirli bir akı ve rotor konumunda iken motorda oluşan akım ve
moment daha sonra bu değerler ile iki boyutlu akı ve moment tabloları
oluşturulmuştur.4. bölümde motor ve asimetrik yarım köprü doğrultucunun
matematiksel olarak modelleri Simulink de oluşturulmuş ve FEMM den alınan akı ve
moment tabloları kullanılarak kullanılarak oluşturulan model yardımıyla motorların
çalışması incelenmiştir. Oluşturulan modelde akım ve hız kontrolleri uygulanmıştır.
Daha sonra 5. Bölümde sürekli halde, değişken yük koşullarında ve son olarak arıza
durumunda analiz yapılmıştır. Sonuç kısmında ise standart ARM'de
mıknatıs kullanılması durumunda motorda olan iyileştirmeler belirtilmiş ve öneri
olarak SMARM'nin geleceği üzerinde yorumlarda bulunulmuştur

Abstract:
Switched Reluctance Machines (SRMs) comes to the fore with its simplicity and
robustness. Their manufacturing cost are relatively lower than their counterparts,
induction and synchronous machines. SRMs can show high performance within a wide
speed range and thus very suitable for variable speed applications. Owing to absence
of winding on rotor, their efficiencies can be higher than Induction and Synchronous
Machines with same power range. The other advantage of winding-less rotor is that
rotor inertia is low. Thus, the SRM responses to instant speed change very fast and can
be run at maximum speed levels that its counterparts never reach.
Like synchronous machines, SRMs runs at synchronous speed. The continuous
rotation can be achieved by synchronizing excitation current pulses with rotor position.
Although their basic characteristics are quite similar to the separately excited DC
machines, they do not possesses a brush-commutator assembly.
SRMs are highly nonlinear machines due to salient structures of both stator and rotor.
Therefore, obtaining their analytical model for all operation range is extremely hard.
Today, their design and analysis are carried out by using finite element based computer
aided tools. A large amount of researches have been done on the design and control
strategies of SRMs. However, most of them could not find a chance to be
commercialized. Although an SRM itself has lower cost than its counterparts, a power
electronic drive circuit usually required to be run. The problem is that possible drive
circuit topologies are not serially produced as package. Therefore, the user should
individually construct the required drive circuit, which inevitably increases the drive
circuit cost. As the researches on SRMs increase, some possible methods may be
developed for reducing the overall machine cost so that the SRMs can be more
preferable, especially for variable speed applications.
Recently, most of the researches on SRMs focus on improving the performance of the
SRM in the control stage rather than improvement in the machine design stage.
Therefore, investigations on SRM design are still limited and there is a need for filling
this gap.
The motivation of this thesis relies on the idea that may allow to increase power
capability of SRMs without serious increase in manufacturing cost. The increase in
power as well as in torque can be obtained by inserting permanent magnets on stator
of a classical SRM. Placing permanent magnets on stator does not affect rotor inertia.
Thus, constructed permanent magnet machine still shows the feature of low inertia.
The other advantages of using permanent magnets are to improve speed response and
reduce torque ripples. Additionally, these magnets can significantly improve the
developed torque in the machine during a possible failure in a phase and let the
machine continuously rotate and thus increase reliability of the SRM.Although various type permanent magnets are available in the market, NdFeB
magnets, which are rare-earth type magnets, are predominantly used in the design of
permanent magnet machines. This is because NdFeB magnets have high residual flux
as well as high resistance to demagnetization. However, NdFeB magnets are very
expensive and thus inevitable increase the design cost of permanent magnet machines.
Therefore, alternative magnets should be investigated for SRM application.
Analysis in this research demonstrates that a permanent magnet switched reluctance
machine (PMSRM) can possess the mentioned advantages by using cheap permanent
magnets rather than using expensive magnets such NdFeB magnets. Among the
alternative magnets, Alnico magnets, which are non-rare earth type magnets, have
potential to be used for performance increase since their residual flux is as high as
those of NdFeB magnets and their price are much lower than NdFeB magnets. The
main drawback of Alnico magnets is that they can be easily demagnetized with a
reverse magnetic field. Reverse magnetic field in an electric machine often occurs
when there are bidirectional current flows through windings. However, SRMs are
often controlled in a way that phase windings carry unidirectional current. An
Asymmetric Half Bridge (AHB) converter, which is accepted to be classical converter
SRMs, is suitable for PMSRM as well. It provides natural protection for Alnico
magnets while allowing an independent phase control.
In order to investigate static characteristics of PMSRM, a 6/4 version has been
designed and analyzed in FEMM. Current and rotor position has been taken as
reference parameters to obtain flux and torque tables. These data are then employed to
form a model to be used for further analysis of designed PMSRM in Matlab/Simulink.
A control unit, drive circuit as well as machine model has been constructed for 6/4
PMSRM in order to investigate its dynamic behavior at various operation conditions.
The PMSRM has been controlled through a AHB converter whose gate signals are
generated by considering current and speed control. A current control loop is built on
the basis of hysteresis current control algorithm. On the other hand, a PWM algorithm
has been used to achieve speed control. Both classical SRM and PMSRM are simulated
with the same conditions to verify the effectiveness of using permanent magnets. The
simulation results demonstrate that PMSRM has superiorities on the classical SRM.
Besides a power increase is observed, the torques ripples due to nature of the machine
has been remarkably reduced. Another advantage of using permanent magnets has
been observed at transient speed response, which means PMSRM has better
acceleration and deceleration behavior.
The works in this thesis has been organized as 6 sections:
In the first section, history of SRM has been firstly summarized and then previous
researches on SRMs has been briefly mentioned and criticized. Some important
industrial applications of SRMs has been given. The current researches and design
trends on SRMs have been discussed. The need of designing a new type SRM machine
is well described and motivation of this thesis has been highlighted.
The second section has been reserved for theoretical explanation of SRMs. The
general structure as well as operating principle of SRMs have been introduced and
related equivalent circuit and mathematical expressions have been given. The possible
converter topologies that are required to operate SRMs have been also mention in this
section.
Third section gives the design and analysis stages of a 6/4 SRM and PMSRM via finite
element based software called FEMM. The technical and magnetic specifications of both machines have been also given in this section. The conditions of static magnetic
analysis have been well described and methods of obtaining flux and torque tables
have been explained. Additionally, the magnetic behavior of both machines have been
examined and comparatively given to make further discussion.
In the fourth section, overall Matlab/Simulink model of SRM/PMSRM simulation has
been given. Particularly, constructing a dynamic model of PMSRM together with AHB
converter and applied control algorithms have been introduced. Each part of modeling
employed in Matlab/Simulink has been thoroughly illustrated and discussed. The way
of obtaining proper gate signals for converter switches have been well described.
In the fifth section, simulation results for various conditions have been discussed in
detail. The effects of using permanent magnets in the machine has been thoroughly
investigated. The reasons of improved performance in the case of PMSRM have been
well addressed. Additionally, the fault tolerant analysis results of both machines have
been given and they have been comparatively discussed in detail.
The last section has been reserved for conclusion. Superiorities and design constraints
of PMSRM have been discussed. Comments on possible improvements on the results
and future work on this thesis has been clearly stated.