Download docx - SWICHED RELUCTANCE MOTOR

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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

SRM is a doubly- salient, singly-excited motor. It has salient poles on both the

stator and rotor, but only one member (usually the stator) carries windings. The rotor

has no windings, magnets, or cage winding, but is built up from a stack of salient-pole

laminations. When a stator coil is energized, the rotor will move to the lowest magnetic

reluctance path. The reluctance of the motor varies with the position of the rotor. It has

desirable features including simple construction, high reliability and lower cost. These

inherent properties of SRM make it a viable candidate for various general purpose

adjustable speed applications.Fig.1 shows its typical structure. It can be seen that both

the stator and rotor have salient poles; hence, the machine is a doubly salient machine.

Fig.1 6/4 SRM

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1.2 BASIC STRUCTURE

Fig.2 Cross sectional view

The stator is made up of silicon steel stampings with inward projected poles. All

these poles carry field coils. The field coils of opposite poles are connected in series

such that their MMF’s are additive in nature. The rotor has no windings, magnets and

cage windings but it is built from a stack of salient pole laminations. It is preferred to

variable speed dc motor and Induction motor. Due to the absence of rotor windings,

SRM is very simple to construct, has a low inertia and allows an extremely high-speed

operation. The conventional SR machine has 6 stator and 4 rotor poles this

configuration has disadvantages such as torque ripple, acoustic noise.

1.3 OPERATION OF SWITCHED RELUCTANCE MOTOR

The rotor is aligned whenever the diametrically opposite stator poles are

excited. In a magnetic circuit, the rotating part prefers to come to the minimum

reluctance position at the instance of excitation. While two rotor poles are aligned to the

two stator poles, another set of rotor poles is out of alignment with respect to a different

set of stator poles. Then, this set of stator poles is excited to bring the rotor poles into

alignment. The Fig.3 shows the block diagram of SRM.

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Fig 3 Block Diagram of SRM

A torque is produced when one phase is energized and the magnetic circuit

tends to adopt a configuration of minimum reluctance, i.e. the rotor poles aligned with

excited stator poles in order to maximize the phase inductance. As the motor is

symmetric, it means that the one phase inductance cycle is compromised between the

aligned and unaligned positions or vice versa.

Fig.4 Principle of Operation

The stator pole axis AA’ and rotor pole axis aa’ are in alignment. Since the SRM

works on Variable reluctance path it searches for minimum reluctance path. At this

position inductance of B winding is neither maximum nor minimum. Next the phase B is

energized. Due to this the rotor develops a torque because of variable reluctance and

existence of variation in inductance. The direction of this torque is such that BB’ and bb’

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try to get aligned. If this torque is more than the opposing load torque and frictional

torque then the rotor starts rotating. Similarly phase winding C is energized and the

same process continues. Thus the rotor rotates.

1.4 CONCLUSION

Thus in this chapter the basics of SR machine has been discussed. The

structure, the principle of operation and the advantages of the SR machine have been

discussed.

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CHAPTER 2

THEORY OF SRM

2.1 INTRODUCTION

This chapter contains characteristics of Switched Reluctance motor. In this

section we discuss about the torque producing mechanisms and torque production rate

of the SRM.

2.2 TORQUE PRODUCTION MECHANISM

The instantaneous torque for any phase is expressed in terms of the rate of

change of co energy with respect to rotor position at some constant current, as given by

Te =[∂Wm /∂θ ]at i=constant (1)

where Te -Electromagnetic Torque.

∂Wm -rate of change of co energy.

∂θ - rate of change of rotor position angle.

The electromagnetic torque is produced due to the continuous excitation of the

phase windings A, B, C. Due to the energization of the phase windings the stator poles

and rotor pole come into alignment. Hence flux lines will flow from stator to rotor and

according to Faraday’s law when a current carrying conductor is placed in a magnetic

field it experiences a force. So the rotor experiences a force and it is driven into motion.

TORQUE EQUATION

The torque equation of a switched reluctance motor is given by

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T e=12i2∂L/∂θ

(2)

Where Te - Electromagnetic Torque in N-m

L - Inductance in Henry

і - Excitation current in A .

∂L/∂θ-Rate of change of inductance with respect to rotor position .

2.3 Reasons for Torque Ripple

Torque pulsations are most significant at the commutation instants when

torque production mechanism is being transferred from one active phase to another.

Toque ripple is produced due to the geometry of the SRM involving the shape of the

rotor and stator, the area of the air gap and length of the stator and rotor polar arc .

Hence torque ripple is produced due to the following two reasons

Geometry

Switching devices in the input side

%Ripple factor = (Tmax-Tmin) /Tavg * 100 (3)

The average torque produced is given by the formula

T i=1T ∫T avgdt (4)

where Ti – Instantaneous Torque in N-m

2.4 METHODS OF TORQUE RIPPLE MINIMIZATION

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The torque ripple can be minimized by various methods. By changing the

geometry of the machine and by designing new converters for proper switching of the

phase windings of the SRM.

2.4.1 REVIEW OF PREVIOUS METHODS FOR TORQUE RIPPLE MINIMIZATION

The concept of optimization of the geometry of the SRM has-been addressed

by several researchers [1], [2]. In addition to varying the combination of stator–rotor

poles, several design adjustments have been proposed to improve the efficiency of the

machine and minimize losses. Horst illustrated the stepped rotor construction for 12/4

and 6/2 and multiple teeth per pole [8].The stator and rotor teeth ratios have been

defined as 6(n):2(n),6(n):4(n), 6(n):8(n), 8(n):6(n), and 8(n):10(n), where n is a positive

integer from one to four. Gilman [3] described the pulsed duration modulated control

technique with reference to 4/6 SRM with stepped rotor construction. Kolomeitsev [4]

illustrated a 6/8 SRM with longitudinally different cross sectional shapes for stator and

rotor poles. He also explained bifurcated stator poles with 2n teeth and 2n+2 rotor

poles, where in an integer, through an example of 6/14 SRM. Kalpathi et al. showed a

6/14 SRM, closely resembling two teeth per pole configuration, to illustrate method of

torque ripple reduction. Morinigo [5] showed a 6/8 SRM with rotor laminations stacked

in a particular spiral pattern to deliver constant torque from three-phase sinusoidal

voltages. The torque ripple and the acoustic noise for the above mentioned

configurations is higher when compared to the new proposed 6/10 SR machine. The

average torque of the 6/10 SRM is higher than the available configurations hence the

torque ripple is lesser. The rotor poles are displaced from each other by an angle of 36 ◦

whereas in 6/4 machine they are displaced by 90◦.So the stator pole and rotor pole

come into alignment more quickly than the conventional SR machine.

2.4.2 SCOPE OF THE PROJECT

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The aim of the project is to model a new configuration of SR machine

with more number of rotor poles than stator poles by designing a new pole design

formula given by

Nr=2*Ns-2

Where Nr -No of rotor poles

Ns –No of stator poles

In order to reduce the torque ripple and improve torque production capability

this new configuration is proposed. In addition to this a New Material Type is suggested

to enhance the thermal capabilities and reduce the losses. A new Soft composite

magnetic material is suggested. Somaloy 500 is used for simulation purposes and it is

compared with various other materials.

2.4.3 CONTRIBUTIONS

A new configuration of SR machine is modeled with higher number of

rotor poles.

A new 6/10 configuration with Somaloy 500 material is presented in

the project.

2.5 MAGNETIZATION CURVE

In an SRM, reluctance (and, hence, inductance) is a function of excitation

current and rotor position. At an aligned position or at higher current levels, the

ferromagnetic material in the rotor and stator poles begins to saturate. Due to

secondary effects such as saturation, fringing, and leakage, nonlinearities are

introduced in the relationship between inductance, current and rotor position. At an

unaligned position, phase inductance has a minimum value due to high reluctance

offered by large air gap. Magnetic saturation is unlikely to occur at an unaligned

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position, and hence, the flux linkage shows a linear behavior until the start of overlap,

labeled as 100◦ rotor position. At a fully aligned position where rotor poles completely

overlap with stator poles, magnetic field density tends to saturate at high current levels

making flux linkage a nonlinear function of position and current.

Fig.5 Magnetization Curve

2.6 INDUCTANCE PROFILE

The aligned position (La)

Consider a pair of rotor and the stator poles to be aligned. Applying a current

to phase establishes a flux through stator and rotor poles. If the current continues to

flow through this phase, the rotor remains in this position, the rotor pole being ”stuck”

face to face to the stator pole. This position is called aligned position, and the phase

inductance is at its maximum value (Lmax or La) as the magnetic reluctance of the flux

path is at its minimum.

Intermediate rotor positions (Lint)

At intermediate positions the rotor pole is between two stator poles. In this

case the induction is intermediate between the aligned and unaligned values. If there is

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any overlap at all, the flux is diverted entirely to the closer rotor pole and the leakage

flux path starts to increase at the base of the stator pole on one side.

The unaligned position (Lu)

In the unaligned position, the magnetic reluctance of the flux path is at its

highest value as a result of the large air gap between stator and rotor. The Inductance is

at its minimum (Lmin or Lu). There is no torque production in this position when the

current is flowing in one the adjacent phases.

Fig.6 Inductance Profile

where R01 – Rising Inductance Region

R12 – Constant Inductance Region

R23 – Falling Inductance Region

2.7CONCLUSION

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The magnetization curve of the SRM is explained and the Inductance profile of

an SR machine is discussed. The toque production mechanism and the reasons for

torque ripple are also discussed.

CHAPTER 3

MODELLING OF SWITCHED RELUCTANCE MOTOR

3.1 INTRODUCTION

A step by step approach in using MagNet for magnetic field simulation of MCSRM is

described in this chapter.

3.2 PRE- PROCESSING

3.2.1 MODEL CREATION

STEP 1: Creating a new model.

Opening a new model

From the desktop, double click the MagNet icon.

The main window appears.

If MagNet is already running, on the file menu, click new to open a new model.

Name the model and save it.

STEP 2: SETTING UP THE WORKING ENVIRONMENT

INITIAL SETTINGS

Each new model reverts to the MagNet default settings for the preferred length, time,

frequency, temperature. For the proposed SRM model, only the preferred unit for length

is changed to millimeters and all other units are allowed as default.

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On the tools menu, click set units.

The default dialogue box appears.

From the length drop down list, select millimeter.

Click ok.

To accommodate the machine geometry on the screen then and there as the

drawing is proceeded; update automatically has to be made ON. To use this

facility, on the view menu , click update automatically.

STEP 3: Building the geometrical model

Building the geometry involves creation of the complete cross section of the machine.

This will be 2D model.

The steps in drawing the geometric model of the rotor in MagNet environment is

described below.

From the tools menu, click keyboard input bar.

On the draw menu, click circle (centre, radius).

In the keyboard input bar, enter the following coordinates to draw the inner and

outer diameter of the rotor.

Centre point 0, 0 Press Enter

Point on the radius of the circle 23, 0 Press Enter

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Enter the following coordinates to draw the inner and outer diameter of the stator.





Enter the following coordinates to create the air gap circles.


Point on the radius of the circle 53.625, 0 Press Enter


Point on the radius of the circle 53.375, 0 Press Enter

On the draw menu, click line.

This is done to draw stator and rotor poles.

In the keyboard input bar, enter the following coordinates to draw the poles of the

rotor.

Start coordinates 0, 0 Press Enter

Mid coordinates 53.625,16 Press Enter

End coordinates -50, 0 Press Enter

For the stator poles,


Mid coordinates 53.375, 14.5 Press Enter

End coordinates 50, 0 Press Enter

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On the edit menu, click select construction slice edges and select the lines

rotor pole and stator pole.

Select mirror command from the draw menu.

Give the mirror vector as (1, 0) and give apply transformation to a copy of the

selection.

Thus a copy of both the lines is obtained.

On the view menu select zoom command and delete the unwanted portions.

On the edit menu, click select construction slice edges.

Select segment edges on the draw menu.

Now we can delete the segments which are not required.

We will get a single stator and rotor pole.

This has to be rotated to get other poles.

On the edit menu select construction slice edges, select the stator poles.

Now, on the draw menu select rotate edges and give 60 degrees for the stator

poles.

Repeat the same for rotor poles but give 90 degrees for rotation angle.

Enter the following to draw the coils in the stator of the SRM model.

1. Select one side of the stator pole using select construction slices edges.

2. Right click on the selected line and go to properties.

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3. Then copy the start coordinate values in the keyboard input bar.

4. In the draw menu select line command.

5. Press Cartesian coordinates in the keyboard input bar and press relative

coordinates.

6. Then enter the following coordinates.

Start coordinates -2, 0 Press Enter

Mid coordinates 0, 5

-8, 0 Press Enter

End coordinates 0, -5 Press Enter

7. A cross section of coil is created.

8. Select the coil using select construction slice edges from the edit menu.

9. From the draw menu select mirror command and enter the following.

10.Mirror vector (1, 0) and select apply transformation to a copy of the selection.

11. From the edit menu, click select constructional slice edges and select the coils

on the either side of the stator pole.

12.From the draw menu, click rotate edges and enter the following.

13.Rotation angle=60 and then select apply transformation to a copy of the

selection.

3.2.2 ASSIGNING MATERIAL CHARACTERISTICS TO EACH PART OF SRM

Setting up the rotor component

1. On the view menu, click update automatically.

2. On the edit menu click select construction slice surfaces.

3. Select rotor of the geometric model you have drawn.

4. On the model menu, click make component in a line, and enter the following

details

Distance 90millimeters

Material LOSSIL 450

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Name Rotor

5. Click ok.

Setting up the stator component



3. Select stator of the geometric model you have drawn.


details


Material LOSSIL 450

Name stator

Setting up the shaft component



3. Select shaft of the geometric model you have drawn.


details

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Material CR10: cold rolled 1010 steel

Name Shaft

Setting up the air gap component



3. Select air gap of the geometric model you have drawn.


details

Distance 90 millimeters

Material AIR

Name air gap

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Setting up the coil component



3. Select 1 coil of the geometric model you have drawn.


details

Distance 90 millimeters

Material copper 5.77e7 Siemens/m

Name A1

5. Similarly create other coil components and name them A2, A3, A4.

6. Now select the coils A1, A2, A3, A4 in order and select make simple coil from

the model menu. A new coil component coil#1 appears in the project bar.

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7. Repeat step 1 to 6 is repeated for the coils B1, B2, B3, B4 and C1, C2, C3, C4 so

that coil#2 & coil#3 are created.

3.3 MESHING

Meshing is a software technique for dividing a 2D/ 3D region into a set of

small triangular or quadrilateral elements, and datasets are generated by the

techniques. In the FEA, the model is divided into a mesh of elements. The field inside

each element is represented by a polynomial with unknown coefficients. The FEA is the

solution of the set of equations for the unknown coefficients. The accuracy of the

solution depends upon the nature of the field and the size of the mesh elements.

Magnet provides you with the control over the size of the meshing elements. We can

change the size of the elements for the entire model or just the area of interest.

1. On the view menu, click initial 2D mesh.

2. The initial 2D mesh appears in the view window

3.4 POST PROCESSING

Analyzing the results

1. In the solver menu, click static 2D.

2. For viewing the result the following steps are followed.

Click the field option in the project bar. The field menu will be displayed

and in that click the flux functions to view the flux to view the flux plot.

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Click the results page to note the values of flux linkage in various coils.

The flux linkage values are noted for various rotor positions.

The respective flux plots, flux linkage plot, torque plot, inductance plot are

obtained.

DESIGN OF 6/10 SRM

For the design of 6/10 SRM continue the above mentioned steps for

Stator design. For changing the number of poles we have to decrease

the rotor pole width hence for drawing rotor pole use the following co-

ordinates.

In the keyboard input bar, enter the following coordinates to draw the poles of the

rotor.


Mid coordinates 53.625,12 Press Enter

End coordinates -50, 0 Press Enter

On the edit menu, click select construction slice edges and select the lines

rotor pole.

Select mirror command from the draw menu.

Give the mirror vector as (1, 0) and give apply transformation to a copy of the

selection.

Thus a copy of both the lines is obtained.

On the view menu select zoom command and delete the unwanted portions.

On the edit menu, click select construction slice edges.

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Select segment edges on the draw menu.

Now we can delete the segments which are not required.

We will get a single rotor pole.

This has to be rotated to get other poles.

On the edit menu select construction slice edges, select the rotor poles.

Now, on the draw menu select rotate edges and give 36 degrees for the rotor

poles.

After assigning the material properties the model looks like this.

3.5 CONCLUSION

Thus a step by step procedure for creating a model using MagNet was discussed.

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CHAPTER 4

TORQUE RIPPLE MINIMIZATION USING GEOMETRY MODIFICATION

4.1 INTRODUCTION

A new configuration of SRM with ten rotor poles is presented and 6/10

configuration is modeled for torque ripple minimization and to increase the torque

production rate. By increasing the number of rotor poles the torque production density is

increased compared to conventional 6/4 SRM.

4.2 OPERATION OF 6/10 SRM

The operation of the 6/10 design is similar to the concept involved in

conventional SRMs. When excitation is applied to a stator phase, there are two adjacent

rotor poles that can potentially be attracted to the stator pole. However, it must be noted

that there is a significant difference in the magnitude of attraction. For example, when

the rotor is aligned with phase A, then exciting phase B will influence mostly one rotor

pole pair that is only 12◦ away rather than influencing another rotor pole pair that is 24◦

away. This produces continuous rotation without any dead zone. Since the torque

production at an unaligned position is comparatively low, this does not have a major

negative influence on the torque.

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Fig.7 6/10 SRM

4.3 TORQUE PRODUCTION

The angular travel per stroke or excitation for the 6/10 prototype SRM is 12 ◦

in comparison to 30◦ for the 6/4 test SRM, leading to higher fundamental frequency. It is

apparent that the 6/10 prototype SRM needs 2.5 times more strokes for a mechanical

revolution, which is an advantage since the average torque is proportional to the

magnetic co energy and the number of strokes. The 6/10 prototype SRM design was

optimized for 120◦conduction interval and θon/θoff as 30◦/150◦. This does not necessarily

work for the 6/4 test SRM, and optimized θon/θoff is found from the intersection of

individual static torque profiles and was set to 50◦/170◦.

The operation of the SRM in practice is limited to a maximum continuous

current rating, as defined by the thermal response. A comparison of flux linkages for a

current rated within the thermal limits is shown in Fig.8 which shows that the area under

the flux linkage curve is comparable for both the SRMs. As a result, the average torque

can be higher for the 6/10 prototype SRM due to a higher stroke factor.

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Fig.8 Comparison of 6/4 & 6/10

Flux Linkage Characteristics of 6/4 SRM and 6/10 SRM

4.4 COMPARISON OF 6/4 SRM AND 6/10 SRM

Torque ripple is defined from instantaneous torque T i as the difference

between the maximum and minimum torques, ex-pressed as percentage of the average

torque. This can be expressed as

Torque Ripple=Tmax-Tmin×100%

Tave

In order to make a fair comparison between the two machines, similar limits

were imposed on the width, volume, outer diameter, and electrical power of the new

configuration. In order to incorporate the increased number of poles without violating

any of the constraints, the poles were optimized to have acceptable widths with optimal

conduction angles. In addition to higher peak torque, some other benefits of 6/10

prototype SRM can be observed from the shape of the torque profiles with respect to

the rotor position. The Fig.8 also shows that the instantaneous torque at most positions

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is higher for 6/10 prototype SRM than that of 6/4 test SRM. Therefore, it produces

higher average torque with comparable.

Dynamic torque ripple is a complex function of switching frequency, control

technique, turn-on and turnoff angles, and operating points. Machine geometry also

significantly affects the torque ripple performance. Therefore, the evaluation of static

torque ripple provides us with valuable information. For three-phase machines such as

the 6/4 test and 6/10 SRMs, the conduction angle needs to be at the least 120◦

electrical in order to produce torque at every position. Rise and fall times of current

profile also need to be considered for the selection of conduction interval, turn-on angle

θon, and turn of angle θoff.

4.5 DIMENSIONS OF 6/10 SRM

Stator Inner Diameter: 66 mm

Stator Outer Diameter: 76 mm

Rotor Inner Diameter: 23 mm

Rotor Outer Diameter: 41mm

Stator Pole arc : 26°

Rotor Pole arc : 24°

Air gap length : 0.25 mm

Stack length : 45 mm

4.6 CONCLUSION

In this chapter the principle of operation of 6/10 SRM has been discussed.

The Flux linkage characteristics of both the machines are compared and torque

production rates of both the machines are compared.

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CHAPTER 5

STATIC ANALYSIS AND SIMULATION RESULTS

5.1INTRODUCTION

The machine design and analysis was done using MAGNET V6. The 6/10 SR

machine and the 6/4 SR machine were analyzed using finite element analysis. Static 2D

analysis was done and the results are presented.

5.2 OUTPUTS OF CONVENTIONAL 6/4 MACHINE

5.2.1 FLUX PLOT

The Flux plot for the conventional 6/4 machine is given with phase A energized.

Excitation current –10 A.

Aligned position

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Fig.9 Flux Plot of 6/4 SRM

Mid Aligned Position


Un Aligned Position


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5.2.2 MAGNETIZATION CURVE

The Flux Linkage Characteristics for various rotor positions with varying

excitation current is plotted.

Fig.12 Flux Linkage Characteristics of 6/4 SRM

5.2.3 INDUCTANCE Vs ROTOR POSITION

The Inductance Vs Rotor position graph is taken by exciting phase A with an

excitation current of 10 A furthermore the torque values can also be found out.

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Fig.13 Inductance Vs Rotor Position of 6/4 SRM

5.2.4 TORQUE PROFILE

The torque profile for 6/4 SRM is given with PHASE A excited .The torque

profile graph presents three sets of torque values taken for excitation current 1A, 2A,

and 3A.The Fig.14 represents the torque profile of 6/4 SR Machine.

Fig.14 Torque Profile 6/4 SRM

.

5.3 OUPUT WAVEFORMS OF 6/10 SRM

5.3.1 FLUX PLOT

The Flux plot for the 6/10 SR machine is given with phase A energized. With

Excitation current – 10 A.

ALIGNED POSITION

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MID ALIGNED POSITION


UNALIGNEDPOSITION


5.3.2 MAGNETIZATION CURVE

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The Flux Linkage Characteristics for various rotor positions with varying

excitation current is plotted. The Flux Linkage graph is plotted for rotor position degrees

ranging from 0-180 degrees

Fig.18 Flux Linkage Characteristics of 6/10 SRM

5.3.3 INDUCTANE Vs ROTOR POSITION

The Inductance Vs Rotor position graph is taken by exciting phase A

with an excitation current of 2 A, furthermore the torque values can also be found out.

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Fig.19 Inductance Vs Rotor Position of 6/10 SRM

5.3.4 TORQUE PROFILE

The torque profile for 6/4 SRM is given with PHASE A excited .The torque

profile graph presents three sets of torque values taken for excitation current 1A, 2A ,

3A .

Fig.20 Torque Profile 6/10 SRM

5.4 CONCLUSION

From the static analysis of the 6/4 and 6/10 SR machines the torque

values are obtained and graphs are plotted. From the torque profiles of both the

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machines it is evident that 6/10 SRM produces more torque than 6/4 machine. The

values of torque are listed in a table for comparison.

Table 1: Torque values of 6/4 SRM Table 2: Torque values of 6/10 SRM

Current in A

Tmax in N-m

1 0.25

2 0.7

3 1.75

For any ampere of excitation current, the new geometry of SRM gives a

increased maximum torque. For 3A of stator excitation, the conventional 6/4 SRM a

maximum torque of 1 N-m, whereas the new 6/10 geometry gives 1.75 N-m. Due to

higher number of rotor poles than stator poles the motor rotates faster since the rotor

poles come into alignment with the rotor poles more quickly than the conventional

6/4 SRM. Hence the torque produced is higher than that of the conventional 6/4

SRM. The value of ∂θ is not very low as it is the case of conventional 6/4 SRM, so

the torque value produced is higher.

Current in A Tmax in N-m

1 0.1

2 0.4

3 1

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CHAPTER 6

TRANSIENT ANALYSIS OF 6/10 SRM

6.1 TRANSIENT ANALYSIS

Transient dynamics analysis, sometimes called ‘Time-History Analysis’, is a

technique used to determine the dynamic response of a structure under the action of

any general time dependant loads. The transient analysis of the switched reluctance

motor is done to analyze the behavior of torque at various rotor position angles and

under various load conditions.

6.2 STEPS INVOLVED IN TRANSIENT ANALYSIS

The Motion component is designed by coupling the shaft and the rotor .The load is

given in the Motion component. The load with respect to time is also mentioned in

the motion component block.

The Transient solver option is set. The start time and the end time are specified. The

solver options are also specified, Newton Raphson method of solving is used and

the polynomial order is specified.

The load is specified in the motion component and the value with respect to time is

also specified.

The three windings are switched simultaneously with an interval of 60 degrees each

by use of a Position controlled switch. The windings are excited by current sources

and input parameters are given.

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6.3 TRANSIENT ANALYSIS IN MAGNET V6

MagNet provides a technique to model the electrical equivalent circuit of the

stator of the Switched Reluctance Motor.

To draw the electrical equivalent, first click on New circuit window option under

the Circuit menu. The circuit window appears as shown.

The coils of the stator are represented here with the same name given during the

creation of the model. The pane on the right side of the window is the drawing

area where the circuit is to be built.

All the components required to draw the circuit are available under the Draw

menu itself.

PCS-Position Controlled Switch forms a part of the control circuitry and is used to

turn- on and turnoff the stator phases depending upon the input obtained from rotor

position sensor. Though there is no actual rotor position sensor available, a virtual

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sensor is assumed to be present and hence the conduction angles for each phase

are given as the corresponding switch positions prior to solving. This is necessary

because according to the reluctance principle only one phase remains turned on at

any instant of rotor position. If this technique of utilizing the equivalent circuit for

analysis is not made use of then solving can be done only for a single phase

conduction period (0-30°). The conduction sequence for the model under study is

given below:

Table no: 3 Switching Sequence

TURN-ON

ANGLE

TURN-

OFF

ANGLE

PHASE

0 30 3

30 60 2

60 90 1

90 120 3

12

0

150 2

15

0

180 1

18

0

210 3

21

0

240 2

24

0

270 1

37

27

0

300 3

30

0

330 2

33

0

360 1

Double-click the PCS-1 switch corresponding to phase ‘A’ and in the

properties dialog box which appears, enter the turn on and turn off

angles. Disable the periodic checkbox.

SIMULATION RESULTS

6.4 COMPARISON OF TORUE PROFILES OF 6/4 SRM AND 6/0 SRM

The Load torque is given and the input current and voltages are set for the 6/4

SRM machine. Input Parameters for the 6/4 machine are as follows.

V=105 V

J=10 Kg/mm2

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TL=10 N-m

Өon=0

Өoff=60

Fig.21 Torque Profile of 6/4 SRM

Fig.22 Torque Profile of 6/10 SRM

6.5 CONCLUSION

From the above graphs it is clearly observed that a 6/10 machine produces

more torque when compared to the conventional machine 6/4 machine. When a load

torque of 10 N-m is given the 6/10 SR machine produces 12 N-m whereas the

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conventional 6/4 SR machine produces 10.5 N-m. Hence the 6/10 configuration

produces more torque per unit volume when compared of 6/4 conventional machine.

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Chapter-7

SOFT COMPOSITE MAGNETIC MATERIAL

7.1 INTRODUCTION

Soft magnetic composites (SMCs), which are used in electromagnetic

applications, can be described as ferromagnetic powder particles surrounded by an

electrical insulating film. SMC components are normally manufactured by conventional

PM compaction combined with new techniques, such as two step compaction, warm

compaction, multi-step and magnetic annealing followed by a heat treatment at

relatively low temperature. These composite materials offer several advantages over

traditional laminated steel cores in most applications.

7.2 MATERIAL CHARECTERISTICS

In order to examine and improve the efficiency of the SRM new kind of

material is suggested for the analysis. Five types of material are compared here, the

material are as follows

A) Somaloy 500 (SMC)

B) M19 Silicon Steel

C) Lossil 450

D) Carpenter Silicon steel

E) Nd-fe

Electrical steel lamination is the most commonly used core material in

electrical machines. Electrical steels are typically classified into grain-oriented electrical

steels and non-oriented electrical steels. Electromechanical steels currently used in the

manufacture of electrical machines posses high induction of magnetic saturation

(Bs~2T), low coercive force (Hc< 100A/m), and they are characterized by low total

losses, Electrical sheet steels have been the dominant choice for the soft iron

41

components in electrical machines subject to time varying magnetic fields. The new soft

iron powder metallurgy materials can be considered as an alternative for magnetic core

of the electrical machines.

Fig.23 Soft magnetic composites (SMCs)

ADVANTAGES OF SMC

Reduced copper volume as a result of increased fill factor and reduced end

winding length and reduced copper loss as a result of the reduced copper

volume.

Reduced high frequency tooth ripple losses since the SMC has essentially very

low eddy current losses.

Potential for reduced air gap length as a result of the tight tolerances maintained

in manufacturing SMC material.

Modular construction allows the possibility of easy removal of an individual

modular unit for quick repair or replacement.

Stator is easily recyclable since the stator can again be compressed back into

powered form with pressure and the copper windings can be readily removed.

42

Simulation Results

7.3 STATIC ANALYSIS WITH DIFFERENT CORE MATERIALS

The static analysis of 6/10 SRM is given with simulation results, so as to

compare which material yields more torque and produces fewer losses.

SIMULATION OF VARIOUS MATERIALS

A) Somaloy 500

B) M19 Laminated Steel C) Lossil 450

l

D) Carpenter Silicon Steel E) Nd-Fe

Fig.24 Simulation of A,B,C,D and E

43

7.4 TORQUE PROFILES OF SOMALOY 500 AND M19 LAMINATED STEEL

The static analysis for the 6/10 SRM using five different materials were done.

The torque profiles of Somaloy 500 and M19 Laminated steel are presented below. The

static analysis was done by exciting one of the phase winding. Exciting phase winding A

with current I=10 A.

TORQUE PROFILE OF SOMALOY 500

Fig.25 Torque Profile of Somaloy 500

TORQUE PROFILE OF M19 LAMINATED STEEL

Fig.26 Torque Profile of M19 Laminated Steel

44

The torque values of various materials are presented in the table below.

Table no: 4 Torque values

MATERIAL TORQUE IN N-m

SOMALOY 500 3.9

M19 LAMINATED STEEL 4.5

CARPENTER SILICON STEEL 1.9

LOSSIL 450 2.1

Nd-Fe 0.01237

The Flux Linkage values are also listed below in the table for various kinds of material.

Table no: 5 Flux Linkage values

MATERIAL FLUX LINKAGE IN Wb-m

SOMALOY 500 1.3



LOSSIL 450 0.63

Nd-Fe 0.0023

The inductance values of various kinds of materials is presented in the below table.

Table no: 6 Inductance Values

MATERIAL INDUCTANCE IN HENRY

SOMALOY 500 0.13



LOSSIL 450 0.037

Nd-Fe 0.00023

45

The maximum and minimum value of inductances for various kinds of materials

is listed below.

Table no: 7 Maximum and Minimum Inductance Values

MATERIAL MAXIMUM

INDUCTANCE IN

HENRY

MINIMUM INDUCTANCE

IN HENRY

SOMALOY 500 0.13 0.042

M19 LAMINATED STEEL 0.19 0.054

CARPENTER SILICON

STEEL

0.064 0.036

LOSSIL 450 0.063 0.037

Nd-Fe 0.00023 0.00002

Even though the torque values of Somaloy 500 is lesser compared to the value of M19

Laminated steel the total average loss of the system is comparatively lesser for

Somaloy 500. This can be found from the Static analysis of the SRM machine using

Magnet V6 software.

The total loss can be found from the below equation

Ploss = PCu+ PF e + Pmech

The total average loss of the two materials is presented below. The total

average loss of the SR machine is found from the FEA using Magnet V6 software. The

distribution for Somaloy 500 is more even when compared to the M19 Laminated silicon

steel. The flux lines travel from the North Pole to South Pole more evenly in case of

46

Somaloy 500, whereas in M19 laminated steel the losses are more so the flux lins are

unevenly distributed. Here the total average loss is found by doing the Time harmonic

analysis and the value of losses are displayed in the screen. The simulation results for

the Total average losses is presented in Fig.27 and Fig.28

Fig.27 Total loss of Somaloy 500

Fig.28 Total loss of M19 Laminated Steel

47

The Total average loss of the machine for the two materials is illustrated below in a

table.

Table no: 8 Total Average Losses

Material Total Average Loss in W

Somaloy 500 1.80391e+007

sM19 Laminated Steel 4.7876 e+007

7.5 CONCLUSION

Hence, even though the torque value is slightly lesser, the losses in

Somaloy 500 are reduced when compared to M19 Laminated steel. Hence it has better

thermal characteristics and the temperature distribution is more in Somaloy 500.

48

CHAPTER 8

TORQUE RIPPLE CALCULATION

8. 1 INTRODUCTION

Torque ripple is defined from instantaneous torque Ti as the difference between

the maximum and minimum torques, expressed as percentage of the average torque.

This can be expressed as

Torque ripple=Tmax-Tmin

Tavg

The torque ripple of the 6/10 SRM is lesser than that of conventional 6/4 SRM because

of the average torque produced is more for 6/10 SRM. The average torque can be

found out using the formula.

Tavg=S*∂Wm

2*π

Where S=m*Nr

m=no of phases

Nr=No of rotor poles

∂Wm=Rate of change of co energy

The angular travel per stroke or excitation for the 6/10 prototype SRM is 12 ◦

in comparison to 30◦ for the 6/4 test SRM, leading to higher fundamental frequency. It is

apparent that the 6/10 prototype SRM needs 2.5 times more strokes for a revolution,

which is an advantage since the average torque is proportional to the magnetic co

energy and the number of strokes So the average torque produced by 6/10 SRM is

more compared to 6/4.

49

8.2 COMPARISON OF TORQUE RIPPLE OF 6/10 AND 6/4 SRM

TORQUE RIPPLE OF 6/4 SRM AND TORQUE RIPPLE OF 6/10 SRM

Table no: 9 Torque Ripple of 6/4 SRM and 6/10 SRM

Current in A Tmax in N-m Tmin in N-m Tavg in N-m Torque Ripple

6/4

SRM

6/10

SRM

6/4

SRM

6/10

SRM

6/4

SRM

6/10

SRM

6/4

SRM

6/10

SRM

0.5 0.04 0.06 0.003 0.035 0.03 0.04 1.98 0.625

1 0.15 0.22 0.053 0.02 0.13 0.19 2.99 0.48

1.5 0.32 0.47 0.303 0.26 0.27 0.41 2.4 0.51

2 0.55 0.79 0.1 0.38 0.47 0.68 2.05 0.6

2.5 0.84 1.16 0.12 0.58 0.72 0.96 1.07 0.6

3 1.18 1.75 0.047 1.15 0.99 1.23 3.04 1.9

Thus it is concluded that the torque ripple in the 6/10new configuration is

reduced 60% when compared to the conventional 6/4 SRM for any phase excitation.

For an excitation of 0.5A the torque ripple of the conventional 6/4 SRM is 1.98

whereas the torque ripple of the new 6/10 configuration is 0.625.

0.625/1.98*100=31.6%

From this it is evident that the torque ripple is reduced by 60% for the new

configuration. Also in this chapter we had already discussed about the increase in

the average torque due to the increase in number of strokes. Average torque is

inversely proportional to the torque ripple so if Tavg increase torque ripple decreases.

Thus the torque ripple of the machine is greatly reduced in the new 6/10 SRM

because of the increased average torque.

50

8.3 CONCLUSION

The torque ripple for the 6/4 SR machine is higher when compared to

6/10 configuration. The torque ripple values were calculated by finding the maximum

and minimum values of torque from the Static analysis of the SR machine

configurations. The static analysis was done using various input current values starting

from 0.5A to 3A.

51

CHAPTER 9

CONCLUSION

This paper has presented a new family of SRMs, which have higher number of

rotor poles than stator poles. Using a newly defined Pole Design (PD) formula, a new

combination of the stator–rotor pole has been proposed. Due to an increase in the

number of rotor poles without increasing the number of stator phases, these

configurations have shown superior performance with higher torque per unit volume,

comparable torque ripple, and lower manufacturing costs when compared to a

conventional SRM with comparable number of phases without the need for specialized

power electronic circuitry. Simulation results have been presented to compare a novel

6/10 SRM designed using the PD formula with a conventional 6/4 SRM in terms of flux

linkage, constructional features, and output torque. This proposed new 6/10

configuration of SRM has been designed using Magnet V6. The Analysis was done by

using Finite Element Analysis.

The 6/10 machine has more advantages than the 6/4 SRM in three aspects.

Torque Ripple

Average Torque

Torque Producing Capability.

52

REFERENCES

1 A. V. Radun, “Design considerations for the switched reluctance motor,”

IEEE Trans. Ind. Appl., vol. 31, no. 5, pp. 1079–1087, Sep./Oct. 1995.

2 .S.-H. Mao and M.-C. Tsai, “A novel switched reluctance motor with C-core stators,”IEEE

Trans. Magn., vol. 41, no. 12, pp. 4413–4420,,DEC 2005.

3 3.R. E. Gilman, “Pulse duration modulated switched reluctance motor con-trol,” U.S.

Patent 5 789 883, Aug. 4, 1998.

4 S. F. Kolomeitsev, “Variable reluctance electric motor,” U.S. Patent 5 719 456, Feb. 17,

1998.

5 F. B. Morinigo, “Switched reluctance motor delivering constant torque from three phase

sinusoidal voltages,” U.S. Patent Application 20020125783, Jun. 12, 2007.

6 T. J. E. Miller,Switched Reluctance Motors and Their Control. Oxford,U.K.: Magna Phys.

Publ., 1993, p. 4, 5.

7 P. N. Materu and R. Krishnan, “Steady-state analysis of the variable-speed switched-

reluctance motor drive,” IEEE Trans. Ind. Electron., vol. 36, no. 4, pp. 523–529, Nov.

1989.

8 G. E. Horst, “Redundant switched reluctance motor,” U.S. Patent 5 239

217, Aug. 24, 1993

9 Novel Switched Reluctance Machine Configuration With Higher Number of Rotor Poles

Than Stator Poles: Concept to Implementation Piyush C. Desai, Student Member, IEEE,

Mahesh Krishnamurthy, Member, IEEE,Nigel Schofield, Member, IEEE, and Ali Emadi,

Senior Member, IEEE

10 10 Two Dimensional Magnetic and Thermal Analysis of High Speed Switched

Reluctance Motor Using Soft Magnetic Composite Material K. Vijayakumar, R.

Karthikeyan, G.K.Sathishkumar, R. Arumugam, Member IEEE