aravind naragund, 4kv13ecd01

VISVESVARAYA TECHNOLOGICAL UNIVERSITY

BELAGAVI- 590018, Karnataka

A PROJECT REPORT

ON

POWER QUALITY IMPROVEMENT IN DC DRIVES BY

SUPPRESSING HARMONICS

A Dissertation work submitted in partial fulfillment for the award of the degree of

MASTER OF TECHNOLOGY

IN

COMPUTER APPLICATION IN INDUSTRIAL DRIVES

Submitted by

ARAVIND NARAGUND

USN: 4KV13ECD01

Under the Guidance of

Prof. K.V. DEVADAS. B.E.,M.Tech.,MISTE

Professor & HOD

Department of E & E Engineering

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

K.V.G. COLLEGE OF ENGINEERING SULLIA, D.K., PIN-574 327, KARNATAKA

2014-2015

ABSTRACT

The vast majority of the electromagnetic contamination issues made in power system are

because of the non-linear attributes of load and fast switching of power electronic

devices gadgets which are utilized as a part of converter circuits. The diode bridge

rectifiers/converters which are used in electrical DC drives system, produces significant

harmonic voltages and currents.The diode bridge rectifiers are also considered as a major

contributor to the power system harmonics that are the major power quality issues. These

harmonics causes various detrimental effects such as increasing the copper loss, iron

loss, dielectric loss, thermal stress and hence reduces the efficiency of power system

equipments.

This project presents various techniques like passive filter, shunt active filter,

sinusoidal pulse width modulation and multipulse converters for harmonics reduction.

The power quality parameters such as “Total Harmonic Distortion of voltage” (THDV)

and “Total Harmonic Distortion of current” (THDI) has determined in each case of

above said techniques for different ratings of DC motor and also extended the work to

higher pulse converters (up to 96 pulse).

By using MATLAB/Simulink for simulation, the clear comparison of power

quality parameters has made between before and after application of above discussed

techniques. Simulation results obtained shows that there is reduction in total harmonic

distortion (THD) with application of power quality improvement techniques.

ACKNOWLEDGEMENT

A dissertation work of this nature with the co-ordination and support from many, for its

successful completion and I am fortunate enough in this direction. It gives me great

pleasure to acknowledge and express my deep sense of gratitude to those who have

helped me throughout this work.

I would like to articulate my profound gratitude and indebtedness to my project

guide Prof. K.V. DEVADAS, who is also Head of the Department of Electrical and

Electronics Engineering, KVG College of Engineering, Sullia for his excellent guidance,

encouragement and support throughout the course. I consider it to be an honour for

working under him.

I extend my heartfelt gratitude to Mr. KIRAN B.V., Assistant Professor and

Project coordinator, Department of Electrical and Electronics Engineering KVG College

of Engineering, Sullia, who has been a great source of inspiration and for his help &

encouragement.

I am also thankful to Dr. N.A. JNANESH, Principal, KVG College of

Engineering, Sullia, for providing an opportunity to study in this great Institution.

I am indebted to Late Dr. KURUNJI VENKATRAMANA GOWDA and

Dr. RENUKA PRASAD K.V., General Secretary of A.O.L.E for providing an

environment with all facilities that helped me in completing my project.

I sincerely thank faculty members of the Department of Electrical and Electronics

Engineering, KVG College of Engineering, Sullia, for helping me in completing this

dissertation work successfully.

Most importantly, I would like to express my deepest thanks to my family for

giving me a life of opportunities and their care, support, encouragement, and inspiration

all along in my academic endeavors.

Last but not the least, My sincere thanks to all of my friends who have patiently

extended all sorts of help for accomplishing this undertaking.

CONTENTS

CHAPTER No. TITLE PAGE No.

LIST OF FIGURES i

LIST OF TABLES iv

NOMENCLATURE v

1 INTRODUCTION 1

1.1 Literature Survey 2

1.2 Scope and Objective of the Present Work 4

1.3 Organization of the Dissertation Report 4

2 POWER QUALITY IMPROVEMENT

TECHNIQUES

5

2.1 Passive Filters 5

2.2 Active Filters 6

2.2.1 Shunt Active Filter 6

2.3 Pulse Width Modulation 8

2.4 Multipulse Converters 10

2.4.1 12-Pulse Converter 11

2.4.2 24, 36, 48 and 96-Pulse converters 12

3 MATHEMATICAL MODELING 13

3.1 Separately Excited DC Motor 13

3.2 Modeling of Separately Excited DC Motor 14

4 DEVELOPMENT OF MATLAB/SIMULINK

MODELS

16

4.1

4.2

Simulation Tools

MATLAB/Simulink Models of Proposed Work

16

16

5 SIMULATION RESULTS AND DISCUSSIONS 27

5.1 Simulated Results before Application of Filters 27

5.2 Simulated Results with Application of Passive Filter 28

5.3 Simulated Results with Application of Shunt Active

Filter

29

5.4 Simulated Results before Application of PWM Signals 30

5.5 Simulated Results with Application of PWM Signals 31

5.6 Simulated Results of Multipulse Converters 32







5.6.7 Comparison of THDI and THDV for Multipulse

Converters with Different Ratings of DC Motor

38

5.7 Discussions 40

6 CONCLUSION AND SCOPE FOR FUTURE

WORK

41

6.1 Conclusion 41

6.2 Scope for Future Work 41

BIBLIOGRAPHY

APPENDIX

PROJECT OUTCOME

LIST OF FIGURES

FIGURE No. TITLE PAGE No.

1.1 Three phase bridge rectifier supplying a separately

excited DC motor

1

1.2 Source Current Waveform 1

2.1 Diode bridge rectifier 5

2.2 Line voltage and Output voltage 6

2.3 Block diagram for shunt active filter 7

2.4 Waveforms showing operation of shunt active filter 7

2.5 Voltage source converter topology for active filters 8

2.6 Schematic diagram of three phase controlled rectifier 9

2.7 Sinusoidal Pulse Width Modulation 10

2.8 Schematic diagram of 12-pulse converter 12

3.1 Separately excited DC motor 13

3.2 Equivalent circuit of separately excited DC motor 14

4.1 Simulation model of 6-pulse diode bridge rectifier

supplying aseparately excited DC motor

17


supplying a separately excitedDC motor with passive

filter

17


supplying a separately excitedDC motor with application

of shunt active filter

18

4.4 Simulation model of 6-pulse controlled rectifier

supplying a separately excitedDC motor before

application of PWM signals.

19

4.5 Simulation model of 6-pulse controlled rectifier

supplying a separately excitedDC motor with application

of PWM signals.

20


supplying a separately excitedDC motor

21


supplying a separately excitedDC motor.

22



23



24



25



26

5.1 Source current of 6-pulse diode bridge rectifier 27

5.2 FFT analysis for source current of 6-pulse diode bridge

rectifier (THDI=15.27%)

27

5.3 Source current of 6-pulse diode bridge rectifier with

passive filter

28


rectifier with passive filter (THDI=4.16%)

28

5.5 Source current of 6-pulse diode bridge rectifier with

application of shunt active filter

29


rectifier with application of shunt active filter

(THDI=0.91%)

29

5.7 Source current of 6-pulse controlled rectifier before

application of PWM signals

30

5.8 FFT analysis for source current of 6-pulse controlled

rectifier before application of PWM signals

(THDI=0.43%)

30

5.9 Source current of 6-pulse controlled rectifier with

application of PWM signals

31

5.10 FFT analysis for source current of 6-pulse controlled

rectifier with application of PWM signals

(THDI=0.20%)

31

5.11 FFT analysis for source current of 4-pulse converter

(THDI=37.16%)

32

5.12 FFT analysis for source voltage of 4-pulse converter

(THDV=6.35%)

32


(THDI=10.04%)

33


(THDV=6.04%)

33


(THDI=5.06%)

34


(THDV=4.06%)

34


(THDI=4.10%)

35


(THDV=2.10%)

35


(THDI=3.91%)

36


(THDV=1.92%)

36


(THDI=2.40%)

37


(THDV=1.14%)

37

5.23 Comparison of %THDI for Multipulse Converters 38

5.24 Comparison of %THDV for Multipulse Converters 39

LIST OF TABLES

TABLE No. TITLE PAGE No.

2.1 Harmonics present in 6, 12, 24, 36, 48, and 96-pulse

converters

11

5.1 Comparison of THDI for Multipulse Converters 38

5.2 Comparison of THDV for Multipulse Converters 39

NOMENCLATURES

Symbols Definition

: Back EMF of the motor

: Armature current

: Field current

: Armature inductance

: Armature resistance

: Load torque

: Applied terminal voltage to the DC motor

Ac : Amplitude of carrier voltage

Ar : Amplitude of reference voltage

Cf : Filter capacitor

h : Harmonics order

Ic : Harmonics compensating current

IL : Load current

ILH : Harmonic part of the load current

ILR : Real part of the load current

Is : Supply current

p : Pulse number

V : AC supply voltage

Vc : Carrier voltage

VL : Load voltage

Vr : Reference voltage

: Viscous friction of motor

: Rotational inertia of motor

: Internaltorque of the motor

: Motor speed

1

CHAPTER 1

INTRODUCTION

DC motor drives of very wide power range have been used in various industries and in

robotics. The application of DC motor drives are ranging from very precise, high

performance position controlled drives in robotics to variable speed drives for adjusting

flow rates in process industries. Since DC supply is not directly available, the DC motor

is fed from AC supply through bridge rectifier. It is shown in figure 1.1.

Here, the diode bridge rectifier has connected at the front-end in DC power

supply. Generally DC smoothing capacitor has connected across the rectifier‟s output.

When the input voltage to diode bridge rectifier is higher than the voltage of capacitor,

the diodes starts conducting and AC voltage is converted to the DC voltage across the

capacitor. This results in a current waveform as shown in Figure 1.2.Obviously, this is

not a pure sinusoidal current waveform. Thus the diode bridge rectifier produces

harmonics in source voltage and current that results power quality issues.

2

According to IEEE standard 1159- 1995, Power quality is defined as “concept of

powering and grounding sensitive equipment in a manner that is suitable for operation of

that equipment”. Power quality is considered with variations in voltage and/or current

from their ideal. The ideal voltage waveform is a sinusoidal wave of constant frequency,

which is also called as fundamental component. But when there is voltage distortion, the

frequency of non-fundamental components is multiples of fundamental frequency. The

presence of non-fundamental components causes harmonic distortion. i.e. non-sinusoidal

waveform.

Total Harmonic Distortion is defined as the RMS value of the waveform

remaining when the fundamental is removed. i.e. total harmonic distortion is a sum of the

distorted waveform. The THD is given by

According to the limits set by IEEE standard 519-1992, any individual harmonics

and total harmonic distortion (THD) should be less than 3% and 5% respectively.

To overcome the above limitations, most of the high-rated electrical drives are

used with multipulse rectifiers as front end converters.

1.1 Literature Survey

Many investigations have been carried out on the power quality improvement techniques

and harmonics reduction.

In this paper [1], cancellation of harmonics in a power converter has studied.

Here the difficulty found in determining the switching angle that has to generate the

expected fundamental output voltage and it should not produce specially selected

harmonics. In contrast to the known works done earlier, here all keys to the problems are

found. That is obtained by translating the transcendental equations which stipulates the

harmonic cancellation problem into corresponding set of polynomial equations. All the

solutions for these equivalent problems are determined by means of resultants of

mathematical theory. In specific, it seems that there are new solutions that have not been

stated in the earlier literature. The comprehensive solutions for both unipolar and bipolar

3

switching configuration to cancel the fifth and seventh harmonics are specified. Lastly,

the unipolar situation is again considered where the fifth, seventh, eleventh, and

thirteenth harmonics are eliminated along with confirmatory experimental results [1].

This paper [2] presents harmonic phenomenon. The fourier series is the tool for

harmonics studies in order to understand waveforms behavior owing to nonlinear loads.

The harmonic concepts, definition of harmonic quantities, associated harmonics

difficulties in power distribution systems are described. Moreover, filter applications

such as passive filter in overcoming harmonic problems are discussed. This paper also

investigate the recent developments for active power filter uses power electronic

switching to generate harmonic currents from nonlinear load is then described [2].

This paper [3] presents simplicity in defining the PCC and proposes a method by

which IEEE Std 519 can be connected at the planning step when the exact interest

current is obscure. IEEE Std 519 was initially acquainted in 1981 to deliver direction on

dealing with harmonics injected by power converters and other nonlinear loads so that of

power quality difficulties are avoided. It is being applied by referring engineers and

imposed by utilities more often in current years as the use of adjustable frequency drives

and other nonlinear loads has developed. Two of the more difficult parts of applying

IEEE Std are (i) defining an proper point of common coupling (PCC) and (ii) building up

an interest current at the planning step. This is for the reason that the standard don't

convey a brief importance of the PCC and the proposed significance of interest current is

an esteem that must be controlled by estimations taken after establishment. This paper

presents the writer‟s-best interpretation of IEEE Std 519. It efforts to deliver simplicity

in the determination of the PCC and suggestions a methods by which IEEE Std 519 can

be connected at the planning step when the accurate interest current is obscure [3].

4

1.2 Scope and Objective of the Present Work

The main aim of this project work is to reduce the harmonics in AC supply voltages and

currents of DC drives system fed from three phase AC supply through diode bridge

rectifier.

The objectives of the proposed project work are

1. To develop simulation models for the power quality improvement techniques like

passive filter, shunt active filter, sinusoidal pulse width modulation, and

multipulse converters

2. To carry out the comparative study of all the power quality improvement

techniques on the basis of simulation results.

1.3 Organization of the Dissertation Report

Chapter 1 Discusses electrical DC drives system and how it introduces harmonics in AC

supply voltages and currents. It also presents literature survey, „Scope and Objective of

the present work‟.

Chapter 2 presents various power quality improvement techniques used for

harmonics reduction in DC drives system and also discussed in detail.

Chapter 3 presents the mathematical modeling of separately excited DC shunt

motor in detail.

Chapter 4 presents introduction about the simulation tools. The development of

MATLAB/Simulink models of the proposed work is shown and explained clearly.

Chapter 5 presents the simulated results of proposed work, and comparison of

results for multipulse converters.

Chapter 6 consists of conclusion and scope for future work.

5

CHAPTER 2

POWER QUALITY IMPROVEMENT TECHNIQUES

Power quality can be improved by mitigation of harmonics. The harmonic mitigation

techniques can be classified into precautionary (preventive) solutions and corrective

(remedial) solutions. Phase cancellation or harmonic control in power converters, and

usage of low distortion loads are preventive solutions. Usage of harmonic filters for

compensation of harmonics, reactive power and unbalance are corrective solutions. The

best solutions for harmonic present in the system are filters. The following are types of

the filters generally used for harmonics reduction.

1. Passive filters and

2. Active filters

Apart from application of filters, other techniques used for harmonics reduction are

1. Pulse Width Modulation (PWM) and

2. Multipulse converters

2.1 Passive Filters

In Passive filters, only passive elements are used in addition to the diode bridge rectifier,

to improve the shape of the line current. Obviously, the output voltage is not

controllable.

Figure2.1 shows the diode bridge rectifier that is having non-sinusoidal input AC

line current due to high capacitance value of the capacitor Cf which is used to reduce

ripple in the supply voltage VL of the load. Consequently, the diodes of the rectifier are

conducting for short period of time intervals and hence the input AC line current is

having narrow pulses with harmonic content.

6

Without adding additional components, shape of the line current can be improved

by using low capacitance value for output capacitor Cf. When capacitor of low

capacitance is used, the diodes of rectifiers are conducted for long period of time

intervals and hence ripple in the output DC voltage is more. This solution can be applied

if the load accepts a largely pulsating DC supply voltage.

In the figure 2.2, the output voltage waveforms for two different values of

capacitors highlight the above concept.

The method discussed above do not decrease the harmonics in AC line current

and ripple in the output DC voltage completely. However, another alternative to decrease

harmonics is “Active filter” in order to overcome the above limitations.

2.2 Active Filters

For active filters, active switches are used in conjunction with reactive elements in order

to increase the effectiveness of the line current shaping and to obtain controllable output

voltage. Based on the functions to be performed at different applications to solve

different problems, the active power filters are classified as follows.

1. Shunt Active Filter

2. Series Active Filter and

3. Shunt-Series Active Filter (combination of shunt and series active filters)

2.2.1 Shunt Active Filter

The shunt active filter acts as source of current to provide compensating current for

harmonics in the load current. The harmonics in the load current are cancelled by

introducing the equal and opposite harmonic compensating current provided by the shunt

active filter.

7

1. Basic Operating Principle

Figure 2.3 shows the block diagram of shunt active filter. The shunt active filter is

connected in parallel with the AC supply lines. It consists of PWM inverter with

capacitor (C) at the DC bus. The PWM inverter converts DC into harmonics

compensating current (IC) which is then injected into AC supply lines. Thus it prevents

the harmonic currents flowing from non-linear load into the AC supply.

The current (IL) drawn by non-linear load can be decomposed as

IL = ILR + ILH……………… 2.1

Where, ILR is real part of the load current and ILH is the harmonic part of the load

current. The function of the shunt active filter is to introduce the compensating current IC.

The compensating current IC eliminates the harmonic part of the load current. That is

given by

IC = ILH……………… 2.2

Figure 2.4 shows the waveforms of AC supply voltage (V), current (IL) drawn by

non-linear load, desired supply current (IS) and the compensating current (IC) injected by

the active filter containing all the harmonics, to make supply current sinusoidal.

8

2. Voltage Source Converter

Figure 2.5 shows schematic of voltage source converter topology for shunt active filter.

The voltage source converter consists of power electronics devices and capacitor as

voltage source at the DC bus. Two types of control signals can be applied to the power

electronics devices that are 180 0 conduction and 120 0conduction. The 1800 conduction

has better utilization of the switches and is the preferred method.

In 1800 conduction method, each device conducts for 180 0and three devices

remains on at any instant of time. There are six modes of operation in a cycle and

duration of each mode is 60 0. The gating signals to the power electronics devices are

shifted from each other by 60 0. The most commonly used technique for gating the power

electronics devices is Pulse Width Modulation (PWM) technique. The PWM technique

applied to voltage source inverter is to convert the DC bus voltage into AC voltage of an

arbitrary waveform. There are many PWM techniques. By using PWM techniques, it‟s

possible to control the output.

2.3 Pulse Width Modulation

Diode bridge rectifiers are widely used in industries and domestic appliances because of

its advantages like low cost, simple design, robustness and absence of controller.

However, the diode bridge rectifier is also having certain disadvantages such as poor

power quality due to high level of harmonics in AC supply current, malfunction of

sensitive equipments, increased losses, and inefficient use of electric power. To

9

overcome these problems, many techniques have been proposed for diode bridge

rectifiers. Apart from techniques like passive filters and active filters, the best technique

is pulse width modulation for controlled rectifiers.

Figure 2.6 shows the schematic diagram of three phase controlled rectifier

consisting of six IGBT devices on three legs of the rectifier. The input of rectifier is

connected to the three phase AC source and DC motor is connected to the output of

rectifier. The gating signals for IGBT devices are generated from pulse width modulation

technique.

By using PWM technique, the switching devices (IGBT) are made on and off

many times in a half cycle and also by changing the pulse width, the output has

controlled. There are different methods of varying the widths of pulses and the most

common one is the sinusoidal pulse width modulation (SPWM) shown in fig.2.7. In

SPWM method, the triangular carrier voltage Vc is compared with the sinusoidal

reference voltage Vr to generate pulse widths. The Ac and Ar are the amplitudes of carrier

voltage and reference voltage respectively. The widths of the pulses are varied by

changing the amplitude Ac of carrier voltage or the modulation index (M) from 0 to 1.

The modulation index is defined as,

10

In SPWM technique, pulse widths are varied that is suitable for elimination or

reduction of harmonics.

2.4 Multipulse Converters

In power electronics terminology, multipulse converter can be defined as a converter

operating in a three phase system is having more than six pulses. Generally the pulse

number is a multiple of six, i.e. the multipulse converter consists of several three phase

diode bridge rectifiers connected either in series or parallel on the output side. So 12, 18,

24-pulse converters etc. are possible.

When several diode bridge rectifiers are connected in series or parallel with

proper degree of phase shift between them, the harmonics cancellation takes place such

that the line currents drawn by a p-pulse converter has a harmonics of order h is given by

Where, k=1, 2, 3 …….

11

The magnitudes of the harmonic components are inversely proportional to their

harmonic order i.e. magnitude of hth

order harmonic is . Hence, higher order

harmonics have small magnitudes and less total harmonic distortion as compared to

lower order harmonics.

Table 2.1: Harmonics present in 6, 12, 24, 36, 48, and 96-pulse converters

Multipulse converters results in two major accomplishments, namely

1. Reduction of AC input line current harmonics and

2. Reduction of DC output voltage ripple.

2.4.1 12-Pulse Converter

Figure 2.8 shows the schematic diagram of 12-pulse converter. The 12-pulse converter

needs a phase shifting transformer having three windings (a primary winding and two

separate secondary windings). A primary winding is connected in star fashion and fed

from three phase supply. One of the secondary winding is connected in star fashion and

another secondary winding is connected in delta fashion. This provides the 300 phase

shift between them. The 12-pulse rectifier is made of two sets of three phase diode

bridge rectifiers which are connected to the two separate secondary windings of the

phase shifting transformer. The two sets of diode bridge rectifiers are connected in series

on DC side and then it is fed to the DC motor.

12

2.4.2 24, 36, 48 and 96-Pulse converters

Higher pulse converter configuration is also possible by using same principle as that of

12-pulse converter. The 12-pulse was obtained with a 300 phase shift between the

secondary windings of the phase shifting transformer. The higher pulse configuration can

be obtained by connecting suitably phase shifted transformers in parallel.

24-pulse converter needs two phase shifting transformer and four sets of diode

bridge rectifiers. 24-pulse converter can be implemented by connecting two 12-pulse

rectifiers with phase shift of 150 from each other. Obviously, it has less harmonics of

order i.e. 23, 25, 47, 49…

Similarly, 36, 48, and 96-Pulse converters can be implemented by connecting

suitable number of phase shifting transformer and diode bridge rectifiers with proper

degree of phase shift between them.

Although theoretically higher pulse converter configurations are possible, but it

increases the complexity of rectifier topology and also it‟s difficult to justify the

rectifiers above48pulse.

13

CHAPTER 3

MATHEMATICAL MODELING

This chapter deals with the separately excited DC motor and its mathematical modeling.

The DC motors are used in various applications such as defence, industries,

robotics etc. The preferences are because of their simplicity, high starting torque, near

linear operation and ease of speed control. DC drives are less complex with a single

power conversion from AC to DC. DC motors have a long tradition used as adjustable

speed machines and a wide range of options have evolved for this purpose. DC motors

have armature and field circuits, both of which carry direct current. The mutual electric

connections between these circuits give rise to different types of DC motors, they are,

1. Separately excited DC motor and

2. Self-excited DC motor

3.1 Separately Excited DC Motor

Figure 3.1 shows the separately excited DC motor, where the field winding and armature

winding are excited or supplied separately. The accurate control of torque and flux gives

rise to better performance that can be achieved as the field and armature current are

controlled separately. By varying field current, it‟s possible to control the field flux. If

the field is assumed to be constant the resulting torque is proportional to the current in

the armature, there by varying only armature current, dynamic performance of the motor

is controlled.

14

3.2 Modeling of Separately Excited DC Motor

The DC motor is modeled by obtaining the differential equations that are related to the

performance parameters of the motor.

In figure 3.2, the equivalent circuit of separately excited DC motor is shown.

The basic equations of torque and back EMF of a motor are

….……..…3.1

…………...3.2

Where, is a motor constant.

Taking Laplace transforms of above equations

….……..…3.3

….……..…3.4

The armature voltage and torque equations are given by

….……..…3.5

….……..…3.6

Taking Laplace transforms of equation (3.5)

….……..…3.7

Therefore,

Ia(S) ….……..…3.8

15

Substituting equation (4) in (8),

Ia(S) ….……..…3.9

Where, is the electrical time constant of the armature.

Taking laplace transforms of equation (3.6)

….……..…3.10

Therefore,

(S) ….……..…3.11

Substituting equation (3) in (11),

(S) ….……..…3.12

Where, is the mechanicaltime constant of the system.

16

CHAPTER 4

DEVELOPMENT OF MATLAB/SIMULINK

MODELS

This chapter presents introduction about simulation tools. The development of

MATLAB/Simulink models of the proposed work are shown and explained clearly.

4.1 Simulation Tools

Simulation is an easy way to minimize the time required for developing the models and it

also confirms the correct and fulfillment of serious steps. At presence there are some

simulation tools are available but all are not working with different systems in the same

integrated environment. Here, MATLAB/Simulink and SimPowerSystem are used which

works with electrical, power electronics and control systems in the same integrated

environment.

4.2 MATLAB/Simulink Models of Proposed Work

Figure 4.1 shows the MATLAB/Simulink model of 6-pulse diode bridge rectifier. The

diode bridge rectifier is fed from the three phase source through a three phase V-I

measurement block. The scope2 and scope3 blocks show the source voltage and current

waveforms. The armature of the DC motor is connected to the rectifier output. The scope

connected to the current measurement block shows the rectifier output current. The

voltage measurement block connected across the rectifier output shows the DC voltage

in scope1. The field of the DC motor is connected to the DC voltage source block.

17

Figure 4.2 shows the model of 6-pulse diode bridge rectifier with passive filter. In

addition to figure 4.1, the passive element such as a capacitor has connected across the

rectifier‟s output in figure 4.2.

18

Figure 4.3 shows the simulation model of 6-pulse diode bridge rectifier with

application of shunt active filter. In addition to the fig.4.2, the shunt active filter is

connected in parallel at the input side of the rectifier in fig. 4.3.

19

Figure 4.4 shows the 6-pulse controlled rectifier. Here, six IGBT/diode switches

are used in rectifier bridge instead of diodes as in the fig.4.5. The gating signals of these

six switches are generated from six separate pulse generator blocks.

20

Figure 4.5 shows the model of 6-pulse controlled rectifier with application of

PWM signals. In this model, a discrete PWM generator block provides gating signals to

all the six IGBT/diode switches.

21

Figure 4.6 shows the MATLAB/Simulink model of 4-pulse diode bridge rectifier.

The 4-pulse diode bridge rectifier is fed from the two phases of the three phase source

block. The armature of the DC motor has connected to the rectifier‟s output and field of

the motor is supplied by the DC voltage source block.

22

Figure 4.7 shows the 12-pulse uncontrolled rectifier model which is developed in

MATLAB/Simulink. It is seen in the figure that it has two series connected three phase

diode bridges. The phase shifting transformer consists of three windings, a primary

winding and two secondary windings. A primary winding is connected to the three-phase

source. The two series connected three phase diode bridges are connected to the two

separate secondary windings of the phase shifting transformer. The output of 12-pulse

converter is DC power which is fed to DC motor.

23

Figure 4.8 shows the MATLAB/Simulink model of the 24-pulse converter, where

two 12-pulse converters are connected in series on the DC side to form 24-pulse

converter. The two 12-pulse converters are connected to the two separate three phase

transformers (each transformer has three windings) with a 15 degree phase shift between

them. The two three phase transformers are fed from the same three phase source.

24

Figure 4.9 shows the MATLAB/Simulink model of the 36-pulse converter. It can

be seen from the figure that it consists of three series connected subsystem blocks

(subsystem1, subsystem2, subsystem3) where each subsystem is having 12-pulse

converter with a three phase transformer. The three 12-pulse converters with a phase

shift of 10 degrees from each other can provide 36-pulse converter. All the three sub

system block inputs are connected to the same three phase source. The outputs of three

subsystem blocks are connected in series and then it is fed to the DC motor.

25

Figure 4.10 shows the MATLAB/Simulink model of the 48-pulse converter. In

addition to 36-pulse converter, one more subsystem of 12-pulse converter with a three

phase transformer is added to 48-pulse converter. i.e. 48-pulse converter consisting of

four subsystem blocks (subsystem1, subsystem2, subsystem3, subsystem4) and each

block having 12-pulse converter with a three phase transformer. The four 12-pulse

converters are phase shifted by 7.5 degrees from each other.

26

Figure 4.11 shows the MATLAB/Simulink model of the 96-pulse converter,

where two subsystems are connected in series on the output side. Each subsystem

consists of four 12-pulse converters with a three phase transformer. Totally eight 12-

pulse converter with phase shift of 3.75 degrees between them can provide 96-pulse

converter.

27

CHAPTER 5

SIMULATION RESULTS AND DISCUSSIONS

In this chapter, the simulated results of proposed work are shown and discussions are

made on it.

5.1 Simulated Results before Application of Filters

28

5.2 Simulated Results with Application of Passive Filter

29

5.3 Simulated Results with Application of Shunt Active Filter

30

5.4 Simulated Results before Application of PWM Signals

31

5.5 Simulated Results with Application of PWM Signals

32

5.6 Simulated Results of Multipulse Converters


33


34


35


36


37


38

5.6.7 Comparison of THDI and THDV for Multipulse Converters with

Different Ratings of DC Motor

Table 5.1: Comparison of THDI for Multipulse Converters

Motor

rating

(in HP)

%THDI

4-pulse 6-pulse 12-pulse 24-pulse 36-pulse 48-pulse 96-pulse

10 7.24 3.11 2.76 2.44 2.13 2.50 2.28

20 7.21 2.79 2.22 2.20 2.03 2.38 2.02

30 5.92 2.56 2.10 2.04 1.96 1.94 1.82

40 5.11 2.41 1.95 1.93 1.92 2.35 1.98

39

Table 5.2: Comparison of THDV for Multipulse Converters

Motor

rating

(in HP)

%THDV

4-pulse 6-pulse 12-pulse 24-pulse 36-pulse 48-pulse 96-pulse

10 6.33 1.51 2.06 1.46 1.07 1.12 1.21

20 6.42 1.67 1.50 1.37 1.14 1.07 1.16

30 6.34 1.60 1.47 1.34 1.21 1.20 1.09

40 6.26 1.53 1.37 1.30 1.24 1.04 1.34

40

5.7 Discussions

Figure 5.1 to 5.22 show the simulated results of 5-HP DC motor. The block parameters

of common components and devices in all the simulation models are same. These

parameters are shown in the appendix.

Figure 5.1 shows the source current of 6-pulse diode bridge rectifier before

application of filters. It can be seen from the figure that the waveforms of three phase

source currents are distorted and they are not pure sinusoidal. THD for source currents is

calculated by FFT analysis which is shown in figure 5.2. The THD obtained is 15.27%.

It is seen in the figure 5.3 that the source currents of diode bridge rectifier with

passive filter are less distorted as compared to figure 5.1. Figure 5.4 shows the FFT

analysis of source current of 6-pulse diode bridge rectifier with passive filter. With the

application of passive filter, the THD is reduced from 15.27% to 4.16%.

With the application of shunt active filter to diode bridge rectifier has further

improved the shape of source current waveforms which are shown in figure 5.5. The

THD is further reduced to 0.91% that is shown in figure 5.6.

Figure 5.7 shows the source current of 6-pulse controlled rectifier before

application of PWM signals. For the source current of controlled rectifier, the THD

obtained is 0.43% that is shown in figure 5.8.

It is seen in the figure 5.9 that the source current waveforms became almost pure

sinusoidal. With the application of PWM signals to controlled rectifier, the THD is

reduced to 0.20% that is shown in figure 5.10

Figure 5.11 to 5.22 show the THD of source current and voltage for multipulse

converters. It is seen from table 5.1 and 5.2 that as the number of pulses increases the

THD decreases, which is also graphically represented in figure 5.23 and 5.24.

41

CHAPTER 6

CONCLUSION AND SCOPE FOR FUTURE WORK

6.1 Conclusion

Power quality related issues and different harmonic suppression techniques are discussed

in detail. The harmonic reduction techniques such as passive filter shunt active filter,

pulse width modulation and multipulse converters models are developed and simulated

in MATLAB/Simulink environment. The simulation results obtained are analyzed and it

is proved that with application of filters the THD has reduced. For controlled rectifiers, it

has shown the effectiveness of PWM technique for harmonic elimination in distorted

source current. The performance comparison of multipulse converters has been carried

out on the basis of simulation results obtained for different ratings of motor. It is found

that as the number of pulses increased the THD decreases remarkably. Thus the power

quality has improved.

6.2 Scope for Future Work

Experimental investigations can be done on simulated models of all power quality

improvement techniques which have been presented in the present work by developing a

prototype model in the laboratory to verify the simulation results.

In this project work, only the series connection of multiple rectifiers is considered

to increase the pulse number. With the series connection, the output voltage of the

multipulse converter is the sum of the individual output voltages of each rectifier,

whereas with parallel connection, the output current of the multipulse converter is the

sum of individual output currents of each rectifier. However, connecting rectifiers in

parallel is more complex due to fluctuations in DC voltage which cause circulating

currents to flow. To remedy this, these types of multipulse converters typically require

the use of an interphase transformer which absorbs the difference in the DC voltage

between individual rectifiers.

42

BIBLIOGRAPHY

[1] John N. Chiasson, Leon M. Tolbert, Keith J. McKenzie, Zhong Du, “A Complete

Solution to the Harmonic Elimination Problem”, IEEE Transactions on

PowerElectronics, vol. 19, no.2, march 2004 (491-499).

[2] M.Izhar, C.M. Hadzer,S.Masri and S.Idris, “A Study of the Fundamental

Principles to Power System Harmonic”, National Power and Energy Conference

2003 Proceedings, Bangi Malaysia. (Page no: 225-231).

[3] Tony Hoevenaars, Kurt LeDoux, Matt Colosino, “Interpreting IEEE Std 519 and

Meeting its Harmonic Limits in VFD Applications”, Paper No. PCIC-2003-15.

[4] Math H J Bollen, “Understanding Power Quality Problems; Voltage sags and

interruptions”, Wiley India, 2011.

[5] MATLAB: High-Performance Numeric Computation and Visualization Software

– Reference Guide, TheMathWorks Inc., April 1993.

[6] SIMULINK: The Dynamic System Simulation Software-User‟s Guide, Math

Works Inc., April 1993.

[7] F. Z. Peng, H. Akagi, and A. Nabae, “Study of active power filters using quad

series voltage source PWM converters for harmonic compensation”,IEEE

Transactions on Power Electronics, vol. 5, no. 1, Jan. 1990, pp. 9–15.

[8] B. Singh, A. Chandra, and K. Al-Haddad, “Computer-aided modeling and

simulation of active power filters”, Electrical Machines and Power Systems, vol.

27, 1999, pp. 1227–1241.

[9] D.A.Paice, “Power Electronic Converter Harmonics- Multipulse Methods for

Clean Power”. New York: IEEE Press, 1996.

43

APPENDIX

Details of different ratings of DC motor used for simulating the present work are given

below. Table A.1 shows the machine parameters for different ratings of DC motor.

Details of different ratings of DC motor

1. 5-HP: 240V, 1750RPM, Field 150V

2. 10-HP: 240V, 1750RPM, Field 300V

3. 20-HP: 240V, 1750RPM, Field 300V

4. 30-HP: 240V, 1750RPM, Field 300V

5. 40-HP: 240V, 1750RPM, Field 300V

Table A.1: Machines parameters

Motor

rating

(in

HP)

Ra

(Ω)

La

(H)

Rf

(Ω)

Lf

(H)

Laf

(H)

J

(kg.m2)

B

(N.m.s)

Tf

(N.m)

5 0.78 0.016 150 112.5 1.234 0.05 0.01 0

10 1.086 0.01216 180 71.47 0.6458 0.04251 0.003406 1.046

20 0.4114 0.004895 105.9 27.65 0.4038 0.08321 0.004313 2.105

30 0.2275 0.002866 102.3 20.82 0.401 0.1239 0.005219 3.164

40 0.1514 0.002012 92.78 16.32 0.369 0.1646 0.006126 4.223

Where,

Ra :Armature resistance

La : Armature Inductance

Rf : Field Resistance

Lf : Field Inductance

Laf : Field – Armature Mutual Inductance

J : Total Inertia

B : Viscous Friction Coefficient

Tf : Coloumb Friction Torque

44

PROJECT OUTCOME

This paper “POWER QUALITY IMPROVEMENT IN DC DRIVES BY

SUPPRESSING HARMONICS” was presented in TEQIP II funded National

Conference on Advances in Electrical Engineering (NCAEE-2015) at NMAM Institute

of Technology Nitte.

aravind naragund, 4kv13ecd01

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