QUASI-Z-SOURCE INVERTER FED THREE-PHASE INDUCTION MOTOR

PHASE : I

2014

IMPLEMENTATION OF P&O

MPPT BASED QUASI-Z-SOURCE

INVERTER FED THREEPHASE

INDUCTION MOTOR

THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE AWARD OF THE

DEGREE OF MASTER OF ENGINEERING

IN POWER SYSTEMS ENGINEERING

OF THE ANNA UNIVERSITY CHENNAI

Submitted by

SASITHARAN K R

1373113

Under the Guidance of

<< NAME OF THE GUIDE >>

PROJECT

WORK

DEPARTMENT OF ELECTRICAL ENGINEERING

GOVERNMENT COLLEGE OF TECHNOLOGY

(An Autonomous Institution affiliated to Anna University Chennai)

COIMBATORE - 641 013

ACKNOWLEDGEMENT

It gives me immense pleasure in expressing my profound gratitude to

Dr. V. LAKSHMI PRABHA M.E, Ph.D., Principal, Government College of

Technology for the facility made available for the progress and completion of

my thesis.

I am extremely thankful to Dr. N. DEVARAJAN M.E., Ph.D., Professor

and Head, Department of Electrical Engineering for the permission and

encouragement accorded to carry out this thesis work.

I would like to express my sincere thanks to my guide

Dr. K. RANJITH KUMAR M.E., Ph.D., Assistant Professor of Electrical

Engineering for his enthusiastic guidance and his invaluable help during the

entire period of my project work.

I also thank my Faculty advisor, Dr. E. LATHA MERCY M.E., Ph.D.,

Associate Professor, Department of Electrical Engineering for her support

during the course of the project work.

I also thank all the other teaching and non-teaching staff members of

the Department of Electrical Engineering and Electronics and Instrumentation

Engineering for their cooperation during my thesis work.

Above all, I thank the Almighty God for his gracious blessings for the

successful completion of my thesis.

Finally I would like to dedicate the whole work to my parents for the

everlasting love and constant encouragement given by them during the

period, even being miles apart.

SYNOPSIS

The objective of this project work is performance of three phase

induction motor such as torque-speed characteristics are analyzed with

Quasi-Z-source inverter with controlled from Maximum power point tracking

(MPPT) algorithm to controls the switching during shoot through and non-

shoot through states.

The Quasi-Z-source inverter (QZI) is a single stage Power converter

derived from the Z-source inverter topology. This employs an impedance

network which couples the source and the inverter to achieve voltage boost

and inversion.

Solar panels have a non-linear voltage-current (V-I) characteristics,

with a distinct maximum power point, which depends on the environmental

factors, such as temperature and irradiance. Maximum power point tracking

(MPPT) algorithm is used to obtain the maximum Power from solar PV system

and controls the inverter switching during shoot through and non-shoot

through states.

In this work, performance of three phase induction motor such as

torque-speed characteristics are analyzed with Quasi-Z-source inverter. The

modeling of induction motor, PV array, Quasi-Z-source Inverter and MPPT

algorithm have been simulated in MATLAB/Simulink environment.

CONTENTS

CHAPTER

NO.

TITLE PAGE NO.

ACKNOWLEDGEMENT i

SYNOPSIS ii

CONTENTS iii

LIST OF FIGURES vi

LIST OF ABBREVIATIONS viii

1. INTRODUCTION

1.1 GENERAL 1

1.2 LITEACTURE SERWAY 3

1.3 OBJECTIVE OF THE PROJECT 4

1.3 BLOCK DIAGRAM

1.3.1 CONVENTIONAL SYSTEM 4

1.3.2 PROPOSED SYSTEM 5

1.4 BLOCK DIAGRAM EXPLANATION 5

2. SOLAR POWER GENERATION

2.1 PHOTOVOLTAIC SYSTEM 7

2.2 CHARACTERISTICS OF PV MODULE 7

2.3 SOLAR PV MODULE 10

2.4 MPPT CONTROL

2.4.1 INTRODUCTION 13

2.4.2 PERTURB AND OBSERVE METHOD 14

3. QUASI-Z-SOURCE INVERTER

3.1 INTRODUCTION 16

3.2 QUASI-Z-SOURCE NETWORK 16

3.3 OPERATING PRINCIPLE AND EQUIVALENT

CIRCUIT OF QZI

3.3.1 ACTIVE MODE 17

3.3.2 SHOOT THROUGH MODE 18

4. THREE-PHASE INDUCTION MOTOR

4.1 INTRODUCTION 21

4.2 PRINCIPLE OF COMPONENTS 21

4.3 PRINCIPLE OF OPERATION 22

4.4 ROTATING FIELD AND INDUCEED VOLTAGE 24

4.5 RUNNING OPERATION 27

4.6 SPECIFICATIONS OF INDUCTION MOTOR 28

5. SIMULATION RESULTS

5.1 INTRODUCTION 29

5.2 SIMULATION PARAMETERS 29

5.3 SIMULATION RESULTS

5.3.1 SIMULATION DESIGH AND OUTPUTS FROM WITHOUT MPPT CONTOL TECHNIQUES

31

5.3.2 SIMULATION DESIGH AND OUTPUTS FROM WITH MPPT CONTOL TECHNIQUES

37

6. CONCLUSION 42

REFERANCES 43

LIST OF FIGURES

FIGURE NO

FIGURE NAME

PAGE NO

1.1 CONVENTIONAL SYSTEM 4

1.2 PROPOSED SYSTEM 5

2.1 PHOTOVOLTAIC EFFECTS ON SOLAR CELL 8

2.2 SOLAR ARRAY 8

2.3 TYPICAL CHARACTERISTICS CURVE OF A SOLAR

CELL

9

2.4 PV-CELL MODULE 10

2.5 I-V CURVE OF SOLAR CELL 12

2.6 P-V CURVE OF SOLAR CELL 12

2.7 SIGN OF dP/dV AT DIFFERENT POSITIONS OF THE

POWER CHARACTERISTIC

14

2.8 PERTURB AND OBSERVE ALFORITHEM FLOW

CHART

15

3.1 QUSAI-Z-SOURCE INVERTER 17

3.2 EQIVALENT CIRCUIT OF QZSI IN ACTIVE MODE 18

3.3 EQIVALENT CIRCUIT OF QZSI IN SHOOT-

THROUGH MODE

18

4.1 THREE-PHASE INDUCTION MOTOR 21

4.3 MOVEING MAGNET CUTTING ACROSS A

CONDUCTING LADDER

24

4.4 ELEMENTARY STATOR HAVING TERMINALS A, B,

C CONNECTED TO A THREE-PHASE SOURCE

25

4.5 AIR-GAP FLUX DENSITY DISTRIBUTION 25

5.1 PV MODULE WITH INDUCTION MOTOR

PERFORMANCE FROM WITHOUT MPPT CONTROL

TECHNIQUE

31

5.1.1 PV MODULE VOLTAGE SOURCE SIMULATION 32

DESIGN

5.1.2 PV MODULE VOLTAGE SOURCE OUTPUT

WAVEFORM

32

5.1.3 PV MODULE WITH QUASI-Z-SOURCE SIMULATION

DESIGN

33

5.1.4 PV MODULE WITH QUASI-Z-SOURCE VOLTAGE

OUTPUT WAVEFORM

33

5.1.5 PV MODULE WITH INVERTER SIMULATION

DESIGN

34


VOLTAGE OUTPUT WAVEFORM

34


CURRENT OUTPUT WAVEFORM

35

5.1.8 PV MODULE WITH INDUCTION MOTOR

SIMULATION DESIGN

35

5.1.9 PV MODULE WITH INDUCTION MOTOR SPEED-

TORQUE CHARACTERISTICS OF MECHANICAL

OUTPUT WAVEFORM

36

5.1.10 PV MODULE WITH STATOR CURRENT OUTPUT

WAVEFORM

36

5.2 PV MODULE WITH INDUCTION MOTOR

PERFORMANCE FROM WITH MPPT CONTROL

TECHNIGUE

37


DESIGN WITH MPPT CONTROL

37



38

5.2.3 PV MODULE WITH INVERTER SIMLATION DESIGN 39



39



40

5.2.6 PV MODULE WITH INDUCTION MOTOR

SIMULATION WITH MPPT CONTROL TECHNIQUE

40

5.2.7 PV MODULE WITH INDUCTION MOTOR SPEED-

TORQUE CHARACTERISTICS OF MECHANICAL

OUTPUT WAVEFORM

41

5.2.8 PV MODULE WITH INDUCTION MOTOR STATOR


41

LIST OF TABLES TABLE NO TABLE NAME PAGE NO

2.1 ELECTRICAL CHARACTERISTICS DATA OF PV

MODULE

13

4.1 INDUCTION MOTOR SPECIFICATIONS 28

5.1 QZI PARAMETER AND THEIR VALUES 29

5.2 PV PANEL PARAMETERS AND THEIR VALUES 30

LIST OF ABBREVIATIONS

PV PHOTO VOLTAIC

MPPT MAXIMUM POWER POINT

TRACKEING

V-I VOLTAGE-CURRENT

AC ALTERNATE CURRENT

DC DIRECT CURRENT

QZI QUASI-Z-SOURCE INVERTER

ZSI Z-SOURE INVERTER

P&O PERTURB AND OBSERVE

VSI VOLTAGE SOURCE INVERTER

CSI CURRENT SOURCE INVERTER

IM INDUCTION MOTOR

CHAPTER 1

INTRODUCTION

1.1 GENERAL

Photovoltaic (PV) power generation has an important role to play due

to the fact that it is a green source. After their installation they generate

electricity from the solar irradiation without emitting greenhouse gases. They

can be installed in places with no other use, such as roofs and deserts, or

they can produce electricity for remote locations, where there is no electricity

network. The latter type of installations is known as off-grid facilities and

sometimes they are the most economical alternative to provide electricity in

isolated areas. However, most of the PV power generation comes from grid-

connected installations, where the power is fed in the electricity network. In

fact, it is a growing business in developed countries such as Germany which

in 2010 was by far the world leader in PV power generation followed by Spain,

Japan, USA and Italy. On the other hand, due to the equipment required, PV

power generation is more expensive than other resources. Governments are

promoting it with subsidies or feed-in tariffs, expecting the development of the

technology so that in the near future it will become competitive. Increasing the

efficiency in PV plants so that the power generated increases is the key

aspect, as it will increase the incomes, reducing consequently the cost of the

power generated, so that it approaches the cost of the power produced from

other sources.

A Solar cell or photovoltaic cell is an electrical device that converts the

energy of light directly into electricity by the photovoltaic effect. It is a form of

photoelectric cell, defined as a device whose electrical characteristics, such

as current, voltage or resistance vary when exposed to light. Solar cells are

the building blocks of photovoltaic modules otherwise known as solar panels.

Multiple solar cells in an integrated group constitute a solar photovoltaic

panel or solar photovoltaic module. Solar cells are usually connected in

series in modules, creating an additive voltage. Connecting cells in parallel

yields a higher current. However shadow effects may cause substantial

power loss. In order to achieve maximum power output from the panel

Maximum Power Point Tracking (MPPT) Algorithms are used.

The efficiency of a PV plant is affected mainly by three factors:

The efficiency of the PV panel (between 8-15%)

The efficiency of the inverter (95-98 %)

The efficiency of the MPPT algorithm (which is over 98%).

Improving the efficiency of the PV panel and the inverter is not easy as it

depends on the technology available, it may require better components, which

can increase drastically the cost of the installation. Instead, improving the

tracking of the MPPT with new control algorithms is easier, not expensive and

can be done even in plants which are already in use by updating their control

algorithms, which would lead to an immediate increase in PV power

generation and consequently a reduction in its price.

MPPT algorithms are necessary because PV arrays have a non linear

voltage-current (V-I) characteristic with a unique point where the power

produced is maximum. This point depends on the temperature of the panels

and on the irradiance conditions. Both conditions change during the day and

are also different depending on the season of the year. Furthermore,

irradiation can change rapidly due to changing atmospheric conditions such

as clouds. It is very important to track the MPP accurately under all possible

conditions so that the maximum available power is always obtained.

Since the power output of the solar panel belong to low power level

applications, a converter is added to boost up the output according to the

requirement. The load connected can be either a DC load or an AC load. In

case of Ac load connection an inverter circuit is added next to the converter.

But in most cases, a resistor plays the role of a load.

1.2 LITEACTURE SURWAY

Revathy.R et al., 2014 suggested by to generate residential power

using low power input of renewable energy like solar along with two-stage

QZI, single phase isolation transformer, and a voltage doubler rectifier and

three phase induction motor. The proposed cascaded qZSI can be applied

to almost all dc/ac, ac/dc, ac/ac and dc/dc power conversion schemes can

be used in demanding applications as power conditioners for solar panel.

Sibirahman T.P et al., 2014 described by a multicell SL Z-source

inerter is controlled the speed of an induction motor. To adding an extra

boosting flexibility by keeping the number of active semiconductors

unchanged, voltage-type and current-type Z-source inverters were earlier

proposed order to increase the boosting gains, simple boost control

method is employed in Multicell Switched-Inductor.

Nisha K.C.R et al., 2013 suggested using of embedded EZ-source

inverter system as a single stage power conversion system concept for

adjustable speed drives in photovoltaic applications and open-loop and

closed-loop control strategy of embedded EZSI system are performed.

Savitha P.B et al., 2014 proposed efficient PV module base on single

diode equivalent circuit model using software and compared the simulated

model results with manufacture’s specifications like peak current, peak

voltage, open circuit voltage and short circuit current are analysed using

WEBEL SOLAR W2300 250W Monocrystalline module.

Jong-Hyoung Park et al., 2009 proposed in PV system using a QZSI

for power reduction and power stage can be reduced in addition of shoot-

through stage which is a characteristics of QZSI and track the maximum

power to controlled methods such as MPPT, Point of Common Coupling

current control. Then the MPPT control technique with a modified P&O

method, the PCC current control for the regulation of the dc-link capacitor

voltage and the PWM methods for the system are analyzed.

1.3 OBJECTIVE OF THE PROJECT

The solar panel’s efficiency is usually around 40-60% and it is not easy to

harvest the maximum power from the solar panel as it is dependent on

irradiation which is an unstable factor. Moreover the panel output further

reduces when dust, cloud or other factor deposit on the panel. Thus an

improved MPPT scheme is proposed to maximize the power output.

The Objective of the project,

To compare performance of the conventional system with

the proposed system.

1.3 BLOCK DIAGRAM

1.3.1 CONVENTIONAL SYSTEM

Figure 1.1 Conventional Systems

1.3.2 PROPOSED SYSTEM

Figure 1.2 Proposed systems

1.4 BLOCK DIAGRAM EXPLANATION:

SOLAR PANEL:

. PV cells are the building blocks of all PV systems because they

are the devices that convert sunlight to electricity. When light falls on a PV

cell, it may be reflected, absorbed, or pass right through. But only the

absorbed light generates electricity. The energy of the absorbed light is

transferred to electrons in the atoms of the PV cell semiconductor material.

When enough photons are absorbed by the negative layer of the photovoltaic

cell, electrons are freed from the negative semiconductor material. A solar

panel of 178 W is designed using input source to generate the rated Power

from PV panel.

QUASI-Z-SOURCE INVERTER:

Quasi-Z-Source Inverter (QZSI) acquires all the advantages of

traditional z-source inverter. The impedance network couples the source and

the inverter. The impedance network couples the source and the inverter to

achieve voltage boost and the inversion in a single stage. By using this new

topology, the inverter draws a constant current from the PV panels, causes

less EMI problems and reduced source stress compared to the traditional ZSI.

PERTURB AND OBSERVE MPPT:

The controller adjusts the voltage by a small amount from the

array and measures power; if the power increases, further adjustments in that

direction are tried until power no longer increases. This is called the Perturb

and Observe method. It is also called as Hill climbing method. Perturb and

Observe method may result in top-level efficiency, provided that a proper

predictive and adaptive hill climbing strategy is adopted.

LOAD:

The load used for an Induction motor. Squirrel cage type of

induction motor should be considered this type of load. Cost wise, it should be

very low. Maintains and constructions should be very simple. Performance is

better, compared through the other type of motors.

CHAPTER 2

SOLAR POWER GENERATION

2.1 PHOTOVOLTAIC SYSTEM

Photovoltaic (PV) cells, or solar cells, take advantage of the

photoelectric effect to produce electricity. PV cells are the building blocks of

all PV systems because they are the devices that convert sunlight to

electricity. When light falls on a PV cell, it may be reflected, absorbed, or pass

right through. But only the absorbed light generates electricity. The energy of

the absorbed light is transferred to electrons in the atoms of the PV cell

semiconductor material. When enough photons are absorbed by the negative

layer of the photovoltaic cell, electrons are freed from the negative

semiconductor material. Due to the manufacturing process of the positive

layer, these freed electrons naturally migrate to the positive layer creating a

voltage differential, similar to a household battery.

When the two layers are connected to an external load, they electrons

flow through the circuit creating electricity. Each individual solar energy cell

produces only 1-2 watts. To increase power output, cells are combined in a

weather-tight package called a solar module. These modules (from one to

several thousand) are then wired up in serial and/or parallel with one another,

into what's called a solar array, to create the desired voltage and amperage

output required by the given project. With their newfound energy, these

electrons escape from their normal positions in the atoms and become part of

the electrical flow, or current, in an electrical circuit. A special electrical

property of the PV cell provides the force, or voltage, needed to drive the

current through an external load, such as a light bulb.

Figure 2.1 Photovoltaic effects on a solar cell

Figure 2.2 Solar Array

Multiple Solar PV modules can be wired together to form a Solar PV

array. Solar PV modules and arrays produce direct current (DC) electricity.

They can be connected in both series and parallel to produce any required

voltage and current combination. Because a single Solar PV panel can only

produce a limited amount of power, many installations contain several panels.

Solar PV panels that are electrically connected together are often referred to

as an array. The panels are mounted at a fixed angle facing south, or they

can be mounted on a tracking device that follows the sun, allowing them to

capture the most sunlight. Many solar panels combined together to create one

system is called a solar array. For large electric utility or industrial

applications, hundreds of solar arrays are interconnected to form a large

utility-scale PV system.

2.2 CHARACTERISTICS OF PV MODULE

The silicon solar cell gives output voltage of around 0.7 V under open

circuit condition. To get a higher output voltage many such cells are

connected in series. The typical characteristic curve of a PV solar cell is

shown below

Figure 2.3 Typical characteristic curve of a solar cell

The characteristic of a PV module is non-linear which makes it difficult

to determine the maximum power point. In order to extract maximum power

from the PV module, it must always be operated at or very close to where the

power is highest. This point is referred to as Maximum power point (MPP) and

it is located around the bend or knee of the IV characteristic. The operating

characteristics of a PV panel consist of two regions: the current source region

and voltage source region. As observed from the characteristic curve, in the

current source region, the output current remains almost constant as the

terminal voltage changes and in the voltage source region the terminal

voltage varies only minimally over a wide range of output current.

The characteristics vary with solar insolation and temperature. The

output power is directly proportional to the irradiance. As such, a smaller

irradiance will result in reduced power output from the solar panel. However it

is also observed that only the output current is affected by the irradiance.

When the irradiance or light intensity is low, the flux of photon is less than

when the sun is bright and the light intensity is high, thus more current is

generated as the light intensity increases. The change in voltage is minimal

with varying irradiance. Irradiance mainly affects the output current and the

temperature mainly affects the terminal voltage.

2.3 SOLAR PV MODELLING

The equivalent circuit of a PV cell is as shown in Figure 2. Where Iph

represents the cell photo current, I0 represents the diode saturation current, I

and V are cell output current and cell output voltage respectively. Rp is shunt

resistance, Rs is series resistance. They ideal PV module for one diode circuit.

Figure 2.4: PV cell model

The mathematical model of PV array for single diode circuit can be

represented by the following equation [1]:

A. Photo Current (Iph):

Iph depends on the solar irradiation and cell’s operating temperature

according to the below equation.

(2.1)

B. Reverse Saturation Current (Irs):

Reverse saturation current of PV system can be determined by the

given equation.

(2.2)

C. Diode Saturation Current (I0):

Saturation current of PV system varies with the cell temperature can be

determined by given equation.

(2.3)

D. output current (I):

The equation for output current of the PV system of single diode model

presented in Figure 1 is given by,

(2.4)

From the above equations,

Isc is cell’s short circuit current(A),K is the temperature

coefficient(0.0017A/K),Tc is the operating temperature(°C), Tref is the

reference temperature(°C), H is solar isolation (kW/m2), q is charge of electron

(1.6×10-19C), Voc is open circuit voltage(V), Ns is number of cells connected in

series(36), k is Boltzmann constant(1.38×10-23 J/K), A is ideal factor(1.6), Ego

is band gap energy(1.1eV), Np is number of parallel connection of cell(1).

Figure 2.5: Current vs. Voltage curve of solar cell

Figure 2.6: Power vs Voltage curve of solar cell

In this paper Trina solar make 178Wp PV module is taken and the

name-plate details are given in Table 2.1.

Table 2.1: electrical characteristics data of Viridian solar 178Wp PV

module

Description Rating

Rated Power

380Wp

Maximum Power Voltage(Vmp)

35.0 V

Maximum Power Current (Imp)

7.7 A

Open Circuit Voltage (VOC)

45.2 V

Short Circuit Current (ISC)

8.4A

2.4 MAXIMUM POWER POINT TRACKING

2.4.1 INTRODUCTION

Maximum power point tracking, frequently referred to as MPPT, is an

electronic system that operates the PV modules such that the modules

produce all the power they are capable of. MPPT is not a mechanical tracking

system that “physically moves “the modules to make them point directly at the

sun. It only varies the electrical operating point of the modules so that they

deliver the maximum available power.

The following are the different MPPT methods to maximize the output

power and fix its value to the highest in the steady state. They are:

1. Perturb and observe,

2. Incremental conductance,

3. Parasitic capacitance,

4. Voltage based peak power tracking,

5. Current based peak power tracking.

2.4.2 PERTURB AND OBSERVE METHOD

The controller adjusts the voltage by a small amount from the array and

measures power; if the power increases, further adjustments in that direction

are tried until power no longer increases. This is called the Perturb and

Observe method. It is also called as Hill climbing method. Perturb and

Observe method may result in top-level efficiency, provided that a proper

predictive and adaptive hill climbing strategy is adopted. In Figure 2.7, if the

operating voltage of the PV array is perturbed in a given direction and dP/Dv >

0, it is known that the perturbation moved the array's operating point toward

the MPP.

Figure 2.7 Sign of dP/dV at different positions on the power

characteristic

Figure 2.8 shows the flowchart of P&O algorithm method. The P&O

algorithm would then continue to perturb the PV array voltage in the same

direction. If dP/dV< 0, change in operating point moves the PV array away

from the MPP, and the P&O algorithm reverses the direction of the

perturbation. The advantage of the P&O method is that it is easy to

implement. However, it has some limitations, like oscillations around the MPP

in steady state operation, slow response speed, and even tracking in wrong

way under rapidly changing atmospheric conditions.

Figure 2.8 Perturb and observe algorithm

CHAPTER 3

QUASI-Z-SOURCE INVERTER

3.1 INTRODUCTION

The quasi z-source inverter (QZSI) is a single stage power converter derived

from the z-source inverter topology, employing a unique impedance network.

The conventional VSI and CSI suffer from the limitation that triggering two

switches in the same leg or phase leads to a source short and in addition, the

maximum obtainable output voltage cannot exceed the dc input, since they

are buck converters and can produce a voltage a voltage lower than the dc

input voltage. Both z-source inverters and quasi-z-source inverters overcome

these drawbacks; by utilizing several shoot-through zero states. A zero state

is produced when the upper three or lower three switches are fired

simultaneously to boost the output voltage. Sustaining the six permissible

active switching states of a VSI, the zero states can be partially or completely

replaced by the shoot through states depending upon the voltage boost

requirement.

Quasi-Z-Source Inverter (QZSI) acquires all the advantages of traditional z-

source inverter. The impedance network couples the source and the inverter.

The impedance network couples the source and the inverter to achieve

voltage boost and the inversion in a single stage. By using this new topology,

the inverter draws a constant current from the PV panels, causes less EMI

problems and reduced source stress compared to the traditional ZSI.

3.2 QZSI NETWORK

The QZSI circuit differs from that of a conventional ZSI in the LC impedance

network interface between the source and inverter. The unique LC and diode

network connected to the inverter bridge modify the operation of the circuit,

allowing the shoot-through state which is forbidden in traditional VSI. This

network will effectively protect the circuit from the damage when the shoot-

through occurs and by using the shoot-through state, the (quasi) Z-source

network boosts the dc-link voltage.

Figure 3.1 Quasi Z source Inverter

The impedance network of QZSI is a two port network. It consists of inductors

and capacitors connected as shown in figure. This network is employed to

provide an impedance source, coupling the converter to the load. The dc

source can be battery, diode rectifier, thyristor converter or PV array. The

QZSI topology is shown the figure 3.1.

3.3 OPERATING PRINCIPLE AND EQUIVALENT CIRCUIT OF QZSI

The two modes of operation of a quasi z-source inverter are:

(1) Non-shoot through mode (active mode).

(2) Shoot through mode.

3.3.1 ACTIVE MODE

In the non-shoot through mode, the switching pattern for the QZSI is

similar to that of a VSI. The inverter bridge, viewed from the DC side is

equivalent to a current source. , the input dc voltage is available as DC link

voltage input to the inverter, which makes the QZSI behave similar to a VSI.

Figure 3.2 Equivalent circuit of QZSI in Active mode

3.3.2 SHOOT THROUGH MODE

In the shoot through mode, switches of the same phase in the inverter bridge

are switched on simultaneously for a very short duration. The source however

does not get short circuited when attempted to do so because of the presence

LC network, while boosting the output voltage. The DC link voltage during the

shoot through states, is boosted by a boost factor, whose value depends on

the shoot through duty ratio for a given modulation index.

Figure 3.3 Equivalent circuit of QZSI in Shoot through Mode

Assuming that during one switching cycle, T, the interval of the shoot through

state is T0; the interval of non-shoot-through states is T1; thus one has T= T0

+ T1 and the shoot through duty ratio, D = T0 / T1.

During the interval of the non-shoot through states, T1

(3.1)

During the interval of the shoot-through states, T0,

(3.2)

(3.3)

At steady state, the average voltage of the inductors over one switching cycle

is zero.

(3.4)

From (3.1) and (3.3),

(3.5)

(3.6)

Thus,

(3.7)

From (3.4), (3.6) and (3.7), the peak dc-link voltage across the inverter bridge

is

(3.8)

Where B is boost factor of the QZSI. This is also the peak voltage across the

diode. The average current of the inductors L1, L2 can be calculated by the

system power rating P,

(3.9)

According to Kirchhoff’s current law and (3.9), we also can get that,

(3.10)

Hence QZSI inherits all the advantages of the ZSI. It can buck or boost a

voltage with a given boost factor. It is able to handle a shoot through state,

and therefore it is more reliable than the traditional VSI. It is unnecessary to

add a dead band into control schemes, which reduces the output distortion. In

addition, there are some unique merits of the QZSI when compared to the

ZSI.

CHAPTER 4

THREE PHASE INDUCTION MOTOR

4.1 INTRODUCTION

Three-phase induction motors are the motors most frequently

encountered in industry. They are simple, rugged, low-priced, and easy to

maintain. They run at essentially constant speed from zero to full-load. The

speed is frequently-dependent and, consequently, these motors are not easily

adapted to speed control. However, variable frequency electronic drives are

being used more and more to control the speed of commercial induction

motors.

4.2 PRINCIPAL COMPONENTS

A three-phase induction motor has two main parts: a stationary stator

and a revolving rotor. The rotor is separated from the stator by a small air gap

that ranges from 0.4mm to 4mm, depending on the power of the motor.

Figure 4.1 three-phase induction motor

The Stator consists of a steel frame that supports a hollow, cylindrical

core made up stacked laminations. A number of evenly spaced slots, punched

out of the internal circumference of laminations, provide the space for the

stator winding.

The Rotor is also composed of punched laminations. These are

carefully stacked to create a series of rotor slots to provide space for the rotor

winding. We use two types of rotor windings: (1) conventional 3-phase

windings made of insulated wire and (2) squirrel-cage windings. The type of

windings gives rise to two maintains classes of motors: squirrel cage induction

motors (also called cage motors) and wound-rotor induction motors.

A Squirrel-cage rotor is composed of bare copper bars, slightly longer

then the rotor, which are pushed into the slots. The opposite ends are welded

to two copper end rings, so that all the bars are short-circuited together. The

entire construction resembles a squirrel cage, from which the name is derived.

In small and medium-sized motors, the bars and end-rings are made of

diecast aluminium, molded to form an integral block.

A Wound rotor has 3-phase windings, similar to the one of the stator.

The winding is uniformly distributed in the slots and is usually connected in 3

wire wye. The terminals are connected to three slip rings, which turn with the

rotor. The revolving slip-rings and associated stationary brushes enable us to

connect external resistors in serious with the rotor winding. The external

resistors are mainly used during the start up period; under normal running

conditions, the three brushes are short-circuited.

4.3 PRINCIPLE OF OPERATION

The operation of a 3-phase induction motor is based upon the

application of Faraday’s law and Lorentz force on a conductor. The behaviour

can readily be understood by means of the following example.

Consider a series of conductors of length l, whose extremities are

short-circuited by two bars A and B (Fig.4.3 a). A permanent magnet placed

above this conducting ladder, moves rapidly to the right at speed v, so that its

magnetic field B sweeps across the conductors. The following sequence of

events then takes place:

1. A voltage E=Blv is induced in each conductor while it is being cut by

the flux (Faraday law).

2. The induced voltage immediately produces a current I, which floes

down the conductor underneath the pole face, through the end-bars,

and back through the other conductors.

3. Because the current carrying conductor lies in the magnetic field of the

permanent magnet, it experiences a mechanical force (Lorentz force);

4. The force always acts in a direction to drag the conductor along with

the magnetic field.

If the conducting ladder is free to move, it will accelerate toward

the right. However, as it picks up speed, the conductors will be cut less

rapidly by the moving magnet, with the result that the induced voltage

E and the current I will diminish. Consequently, the force acting on the

conductors will also decrease. If the ladder were to move at the same

speed as the magnetic field, the induced voltage E, the current I, and

the force dragging the ladder along would all become zero.

In an induction motor the ladder is closed upon itself to form a squirrel-

cage (Fig.4.3 b) and the moving magnet is replaced by a rotating field.

The field is produced by the 3-phase currents that flow in the stator

windings, as we will now explain.

(a)

(b)

Figure.4.3 moving magnet cutting across a conducting ladder

4.4 THE ROTATING FIELD AND INDUCED VOLTAGES

Consider a simple stator having 6 salient poles, each of which

carries a coil having 5 turns (Fig.4.4.). coils that are diametrically

opposite are connected in series by means of three jumpers that

respectively connect terminals a-a, b-b, and c-c. This creates three

identical set of windings AN, BN, CN, which are mechanically spaced

at 120 degrees to each other. The two coils in each winding produce

magneto motive forces that act in the same direction.

Figure.4.4 Elementary stator having terminals A, B, C connected

to a 3-phase source (not shown). Currents flowing from line to neutral

are considered to be positive.

The three sets of windings are connected in wye, thus forming a

common neutral N. Owing to the perfectly symmetrical arrangement,

the line to neutral impedances are identical. In other words, as regards

terminals A, B, C, the windings constitute a balanced 3-phase system.

For a two-pole machine, rotating in the air gap, the magnetic field being

sinusoidal distributed with the peak along the center of the magnetic

poles. The result is illustrated in fig.4.5. The rotating field will induce

voltages can be obtained by using Faraday laws of induction.

Figure.4.5 Air gap flux density distribution

The flux density distribution in the air gap can be expressed as:

(4.1)

The air gap flux per pole, ɸp, is:

(4.2)

where,

l is the axial length of the stator.

r is the radius of the stator at the air gap.

Let us consider that the phase coils are full-pitch coils of N turns, it is

obvious that as the rotating field moves the flux linkage of a coil will vary. The

flux linkage of a coil will vary. The flux linkage for coil aa’ will be maximum

and zero at the flux linkage λo will vary as the cosine of the angle

hence;

(4.3)

Therefore, the voltage induced in phase coli aa’ is obtained from faraday law

as:

(4.4)

The voltage induced in the other phase coils are also sinusoidal, but phase-

shifted from each other by 120 electrical degrees. Thus,

(4.5)

(4.6)

From equation (4.4), the rms value of the induced voltage is:

(4.7)

Where, f is the frequency in hertz. Equation (4.7) has the same form as

that for the induced voltage in transformers. However, ɸp in equation (4.7)

represents the flux per pole of the machine. Equation (4.7) shows the rms

voltage per phase. The N is the total number of series turns per phase with

the forming a concentrated full-pitch winding.

In an actual AC machine each phase winding is distributed in a number

of slots for better use if the iron and copper and to improve the waveform. For

such a distributed windings, the EMF induced in various coils placed in

different slots are not in time phase, and therefore the phasor sum of EMF is

less than their numerical sum when they are connected in series for the phase

winding. A reduction factor Kw, called the winding factor, must therefore be

applied. For most three-phase machine windings Kw is about 0.85 to 0.95.

therefore, for a distributed phase winding, the rms voltage per phase is

(4.8)

Where, Nph is the number of turns in series per phase.

4.5 RUNNING OPERATION

If the stator windings are connected to a three-phase supply and the

rotor circuit is closed, the induced voltages in the rotor windings produce rotor

currents that interact with the air gap field to produce torque. The rotor, if free

to do so, will then start rotating.

According the lens law, the rotor rotates in the direction of the rotating

field such that relative speed between the rotating field and the rotor windings

decreases. The rotor will eventually reach a steady-state speed n that is less

than the synchronous speed ns, at which the stator rotating field rotates in the

air gap. It is obvious that at n=ns, there will be no induced voltage and current

in the rotor circuit and hence no torque.

In a P-pole machine, one cycle of variation of the current will make the

mmf wave rotate by 2/P revolutions. The revolutions per minute n (rpm) of the

travelling wave in a P-pole machine for a frequency f cycles per second for

the currents are:

(4.9)

The difference between the rotor speed n and the synchronous speed ns, of

the rotating field is called the slip s and is defined as

(4.10)

4.6 SPECIFICATIONS OF INDUCTION MOTOR

In my thesis work, induction motor should be taken from load source

and torque-speed characteristics have been analysed from shoot through and

non-shoot through stages on Quasi-Z-source Inverter, then motor can be

performed. Following specifications should be specified from 1HP induction

motor.

Table no 4.1 Induction motor specifications

DESCRIPTION RATEING

Rated Power 1HP

Rated Voltage 415 Vrms

Number of Poles 2

Rated Frequency 50hz

Mutual Inductance 0.610H

Interia Constant 0.0051JKgm2

Friction factor 0.06Nms

CHAPTER 5

SIMULATION RESULTS

5.1 INTRODUCTION

Traditionally, Quasi Z-source inverter by coupling the inverter circuit to

an Induction Motor. To performing, with and without stages controlled the

MPPT controller and speed-torque characteristics should be performed

through this two stages from PV module.

5.2 SIMULATION PARAMETERS

.Table 5.1 shows the parameters of Quasi- Z-source inverter and

corresponding values used in the simulation.

Table 5.1 Quasi-Z-source inverter Parameters and their values

PARAMETERS

VALUES

Magnetizing inductance

400mH

Capacitor

400 µF

Input Voltage

385 V

Output Frequency

50 Hz

Turn Ratio( )

2:1

Switching Frequency

5000 Hz

Output Load

1HP Induction Motor

.Table 5.2 shows the parameters of PV Module and corresponding

values used in the simulation.

Table 5.2 PV Panel parameter and their values

PARAMETERS

VALUES

Number of cells

75

Open circuit voltage ( )

45.2V

Short circuit Current ( )

8.4

Voltage at maximum power point ( )

35.0

Current at maximum power point ( )

7.7

Standard solar intensity

1000

Standard temperature

25

5.3 SIMULATION RESULTS

5.3.1 SIMULATION DESIGN AND OUTPUT’S FROM WITHOUT MPPT

CONTROL

Figure 5.1, shows the given PV diagram with simulation results should

be presented through the without MPPT control techniques from QZI fed

induction motor. Following simulation diagram should be analyzed with

without MPPT stage, PV systems voltage output waveform and quasi-z-

source inverter voltage output waveform, inverter voltage and current output

waveforms and speed-torque characteristics of induction motor and stator

performance of induction motor can be presented.

Figure.5.1 PV module with Induction Motor performance from without

MPPT

Figure.5.1.1 PV module voltage source simulation design

Figure.5.1.2 PV module voltage source output waveform

Figure.5.1.3 PV module with Quasi-Z-source simulation design

Figure.5.1.4 PV module with Quasi-Z-source voltage output

waveform

Figure.5.1.5 PV module with Inverter simulation design

Figure.5.1.6 PV module with Inverter simulation voltage output

waveform

Figure.5.1.7 PV module with Inverter simulation current output waveform

Figure.5.1.8 PV module with Induction Motor simulation diagram

Figure.5.1.9 PV module with Induction Motor Speed-Torque

(Mechanical) output waveform

Figure.5.1.10 PV module with Induction Motor stator current output

waveform

5.3.2 SIMULATION DESIGN AND OUTPUT’S FROM WITH MPPT

CONTROL

Figure 5.2, shows the given PV diagram with simulation results should

be presented through with MPPT control techniques from QZI fed induction

motor. Following simulation diagram should be analyzed with MPPT stage,

PV systems voltage output waveform and quasi-z-source inverter voltage

output waveform, inverter voltage and current output waveforms and speed-

torque characteristics of induction motor and stator performance of induction

motor can be presented.

Figure.5.2 PV module with Induction Motor Performance from with

MPPT control

Figure.5.2.1 PV module with Quasi-Z-source simulation design

with MPPT control

Figure.5.2.2 PV module with Quasi-Z-source output waveform

Figure.5.2.3 PV module with Inverter simulation design with MPPT control

Figure.5.2.4 PV module with Inverter simulation voltage output

waveform

Figure.5.2.5 PV module with Inverter simulation current output Waveform

Figure.5.2.6 PV module with Induction Motor simulation diagram

with MPPT control

Figure.5.2.7 PV module with Induction Motor Speed-Torque

(Mechanical) output waveform

Figure.5.2.8 PV module with Induction Motor stator current output

waveform

CHAPTER 6

CONCLUSION

6.1 CONCLUSION

A detailed analysis on Quasi-Z-source inverter has been presented. It

employs a unique impedance network to couple the inverter main circuit to the

PV module; collected rated power will be operated from Induction Motor. The

operating principle and characteristics are analyzed.

This project focused on analysis of speed-torque characteristics of

three-phase induction motor with Quasi-Z-source. The modelling of induction

motor, PV array, and Quasi-Z-source Inverter and MPPT algorithm has been

simulated in MATLAB/Simulink environment.

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QUASI-Z-SOURCE INVERTER FED THREE-PHASE INDUCTION MOTOR

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