multilevel inverter fed switched reluctance motor · pdf filethe torque is produced by...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 20 (2016) pp. 10131-10138

© Research India Publications. http://www.ripublication.com

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Multilevel Inverter Fed Switched Reluctance Motor

1,a*Mohd Ruddin Ab Ghani, 1,bNabil Farah, 1 Nur Huda Mohd Amin, 1Syariffah Othman, 2Zanariah Jano

1Faculty of Electrical Engineering (FKE), 2Centre for Languages and Human Development, 1,2Universiti Teknikal Malaysia Melaka,

Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.

Abstract This paper analyzed three-level inverter in order to control the

Switched Reluctance Motor (SRM). The inverter was

controlled using space vector modulation SVM. The

multilevel inverter was utilized to feed the SRM to reduce the

Total Harmonics Distortion THD and compare it with another

power electronic circuit. The simulation was conducted using

MATLAB/SIMULINK software. The findings yielded that a

half bridge converter produced more harmonics than the

multilevel inverter. Therefore, the multilevel inverter circuit

was the best drive circuit to be used compared to half bridge

converter.

Keywords: SRM, Multilevel inverter, SVM, THD, inverter

INTRODUCTION

The most important element in the electrical motors is to

design a driver circuit that can efficiently drive the motor to

produce the desired output. In the case of the Switched

Reluctance Motor (SRM), countless researchers have focused

on producing suitable drivers for the SRM [1]-[3]. Various

types and constructions of the SRM motor have been

proposed. The main difference is in the phases employed, the

number of stator/rotor poles used and torque production

mechanism [2]. In this paper, the SRM motor parameters has

been fixed for all types of SRM that will be used. Table 1

shows the SRM motors parameters. Three types of SRM

motor discussed here are subject to two different control

mechanisms namely the power converter and multilevel

inverter which are compared in terms of construction and type

of control mechanism being used.

Table 1: SRM motor parameters

Stator resistance (ohm) 0.01

Inertia (kg.m.m) 0.082

Frication (N.m.s) 0.01

Initial speed and position [0 0]

Unaligned inductance(H) 0.67e-4

Aligned inductance (H) 23.6e-4

Saturated aligned inductance(H) 0.15e-4

Maximum current (A) 250

Maximum flux linkage (V.s) 0.486

The basic and simplest type of SRM motor has 6 stator poles

and 4 rotor poles which reflects its name, 6/4. The motion of

this motor is produced due to the variable reluctance in the air

gap between the stator and rotor windings. A single magnetic

field is produced due to the rotor winding activation then the

torque is produced by the tendency of the rotor to move to its

reluctance position. Figure 1 shows the 6/4 SRM motor in the

case of a rotor pole is aligned with a stator pole; due to the

field lines are orthogonal to the surfaces, hence, no torque will

be produced [4]. The difference between this motor and other

type of motor construction is only the number of phases

employed as well as the shape of the configuration.

Figure 1. 6/4 SRM motor

a. 8/6 SRM motor

This type of motor is similar to the previous motor. The basic

difference is the number of phases employed increases

whereas the parameters are the same as the 6/4’s SRM motor.

The operation principle to produce motion does not differ as

well. The SRM is known as a double salient motor with sold

laminated rotor core and stator independent phase winding

connected in series to make one phase of the motor. Figure 2

shows the 8/6 SRM motor construction.

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The torque is produced by activating the stator phase which

will attract the most adjacent rotor pole pair, then, minimize

the reluctance of the magnetic path. As a result, constant

torque is developed due to the activation of consecutive

phases of stator in succession. Therefore, the SRM is an

electrical motor in which the torque is produced due to the

tendency of its movable parts to move till the reluctance of the

excited winding is maximized [5].

b. 10/8 SRM motor

This is another different construction of the SRM motor that

employs more phases than the previous SRM constructions.

However, the parameters are similar to the 6/4 and 8/6 SRM

motor. The name of this motor is derived from the number of

stator and rotor poles used. The principle of torque production

is the same as the previous SRM construction where the

torque production depends on the tendency of the movable

part of the motor to move to position where the inductance of

the excited windings is maximized [6][7]. Figure 3 shows the

10/6 SRM motor construction.


SRM DRIVE TOPOLOGY

The SRM drives have received a great attention for the past

two decades’. Several studies have been conducted to develop

new and sufficient drives to drive the SRM motor efficiently

and produce the desired output. The power convers have been

highlighted in most research on the SRM motors as different

types of power converters have been designed to be fed to the

SRM motor [8]. A study [9] develops a new topology which

uses power inverter to control the SRM motor. However,

these drive topologies have their own drawbacks. The most

apparent drawback is the percentage of the Total Harmonics

Distortion (THD) that a driver produces. In this paper, power

converter and multilevel inverter to drive topology were

proposed.

a. Half bridge converter topology

There are numerous converter drives which have been

developed to be fed to the SRM motor. The most flexible and

common topology to be used for the SRM is the half bridge

converter. This converter is fed by 240 vdc sources and

requires two switches and two diodes per phase. The turn on

and off angles and reference current are kept constant at 45

deg and 75 deg, 200 A respectively. This type of converter is

advantageous over other converter type in terms of energy

efficiency where the energy returns from the motor to the

source after turn-off of phase switching. Moreover, the control

mechanism of this converter is done independently for each

phase [10]. As the aim of this paper was to investigate the

control techniques for three different SRM constructions, the

control circuit of half bridge converter has different

configuration for each SRM construction. Figure 4 shows the

three-phase half bridge converter to drive the 6/4 SRM Motor.

Figure 4. Half bridge converter for 6/4 SRM

Figure 5 shows the four-phase half bridge converter fed to 8/6

SRM motor.

Figure 5. Half bridge converter for 8/6 SRM



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Figure 6 shows five-phase half bridge converter fed to 10/8

SRM motor.

Figure 6. Bridge converter for 10/8 SRM

During conduction periods, the active IGBTs apply positive

source voltage to the stator windings to drive positive currents

into the phase windings. During free-wheeling periods,

negative voltage is applied to the windings and the stored

energy is returned to the power DC source through the diodes

[11].

b. Multilevel inverter

The past SRM drives often use power converter. Several

attempts were made to develop new power electronic inverter

that utilizes the Voltage Source Inverter VSI [9]. In this paper,

new power electronics circuit was used to drive the SRM

motor using a multilevel inverter.

The concept of multilevel inverter is to produce multilevel

output voltages with less power switching loss and less

harmonic distortion.

A multilevel inverter can be constructed by connecting a set

of single full bridge inverter in series. Each bridge has its own

isolated dc sources which can solar cells or batteries. These

separated dc sources feeding the multilevel inverter can

generate almost sinusoidal waveform voltage. This type of

inverter can produce N level voltages (i.e for three level

inverter can generate three different voltage outputs +vdc, 0

and –vdc). Hence, the output voltage of an N-level multilevel

inverter is the sum of all the individual inverter outputs

[12][13]. Figure 7 shows the circuit of the 3-level inverter.

Figure 7. Circuit of the 3-level inverter

Modulation techniques of the multilevel inverter

In terms of the control strategy of the multilevel inverter,

numerous researchers in the power electronic field have

developed many modulation techniques. The famous and easy

modulation techniques are the Sinusoidal Pulse Width

Modulation (SPWM), and Space Vector Pulse Width

Modulation (SVPWM). The multilevel inverter switching

signal can be generated using these two methods with less

switching losses and harmonic distortion.

Sinusoidal Pulse Width Modulation (SPWM)

The multilevel inverter can be controlled by using the SPWM

where sinusoidal wave is compared with square waves to

generate the switching signal that will trigger the

semiconductors switches in time sequence considering the

phase between the phases shift three phase inverter legs. This

method uses N-1 level carrier signals to generate the N-level

inverter output voltage. In multilevel inverter, the frequency

modulation index, and the amplitude modulation index,

are defined as follows [14][15]:

1

2

Where =carrier signal frequency, = reference signal

frequency, = carrier signal amplitude, = reference signal

amplitude.

Figure 8 shows the SPWM carriers signal compared with

reference sinusoidal signal for three-level inverter.

Figure 8. The SPWM carriers signals of three-level inverter

Space Vector Pulse Width Modulation (SVPWM)

Space Vector Modulation (SVM) is an algorithm for the

control of pulse width modulation (PWM). The idea behind

SVPWM is to create a rotating space vector that will be used

for various applications. One method to be used in inverter is

the switching times [16].

The space vector of a three-level inverter is shown in Figure

9.



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Figure 9. The three-level inverter voltage vector

In this paper three different multilevel circuit is used to drive

three different types of SRM motor. Figure 10 shows the

circuit of three-level inverter three-phase used to drive the 6/4

SRM motor.

Figure 10. Three-level inverter fed to 6/4 SRM

Figure 11 shows the four phase three-level inverter fed to

8/6 SRM motor.


Figure 12 shows the five phase three-level inverter fed to

10/8 SRM motor.


SIMULATION RESULTS

The aim of this paper was to study and control three different

constructions of switched reluctance motor namely 6/4, 8/6

and 10/8. First of all, these three types were constructed in

MOTOR SOLVE software with fixed parameters and then

constructed using MATLAB/Simulink. Two different drive

circuit were utilized; half bridge converter and multilevel

inverter.

a. Results of Motor Solve

Figure 13 shows the output flux of the SRM using motor solve

which is the same for the three construction types, 6/4, 8/6 and

10/8 because all the parameters are fixed. Figure 14 shows the

output of Torque VS rotor angle which are the same for the

three types of SRM.

Figure 13. Static complete analysis for flux linkage



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Figure 14. SRM torque against rotor angle

b. Matlab/Simulink Results

First of all, the output of drive and control circuit are

presented and compared in terms of Total Harmonics

Distortion THD %.

1. Half bridge converter topology

The half bridge converter with two IGBT and two free-

wheeling diode was fed to the SRM motor. Figure 15 shows

the output current of one phase of half bridge converter and

Figure 16 shows the THD% of the half bridge converter one

phase.

Figure 15. Output current of half bridge convert

Figure 16. THD of current of half bridge converter

By applying this converter to the SRM motor, the output flux

of motor are shown in Figure 17.

Figure 17. The output flux of SRM motor

In addition, the output of armature current, torque and motor

speed are shown in Figures 18, 19 and 20 respectively.

Figure 18. Armature current of SRM fed by half bridge

converter

Figure 19. The output torque of SRM fed by half bridge

converter



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Figure 20. The output speed of SRM fed by half bridge

converter

2. Multilevel inverter topology

In this paper, the three-level inverter was used, modulated by

the space vector. The three-level inverter had four IGBT in

each phase. Figure 21 shows the output current of one phase

of three-level inverter followed by THD current of the same

inverter in Figure 22.

Figure 21. Three-level inverter output current

Figure 22. Current THD of three-level inverter

The multilevel inverter was fed to the SRM and the output

flux of the motor are shown in Figure 23.

Figure 23. Output flux of SRM fed by multilevel inverter

Besides, the armature current, output torque and speed of the

SRM motor are presented in Figures 24, 25 and 26

respectively.

Figure 24. Armature current of SRM fed by multilevel

inverter

Figure 25. Output torque of SRM fed by multilevel inverter



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Figure 26. Output speed of SRM fed by multilevel inverter

DISCUSSION

Based on the simulation results, the multilevel inverter is best

suited for the SRM motor due to the best outputs results

produced and the less harmonics contents in output compared

to the half bridge converter. Figure 27 shows the comparison

between the half bridge converter and multilevel inverter in

terms of THD.

Figure 27. THD comparison of multilevel inverter VS half

bridge converter

CONCLUSION

This paper aims to develop multilevel inverter and use it as a

driver circuit for the switched reluctance motor SRM. A half

bridge converter has been compared to multilevel inverter.

The findings yield that the half bridge converter produces

more harmonics than the multilevel inverter. Therefore, the

multilevel inverter circuit is the best drive circuit to be used

compared to half bridge converter.

ACKNOWLEDGMENT

The authors would like to gratefully acknowledge the funding

support provided by Universiti Teknikal Malaysia Melaka

(UTeM) under the research grant No:

PJP/2016/FKE/HI5/S0148/Malaysia, UTeM.

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