LABVIEW REAL TIME DRIVE OF INDUCTION MOTOR

People’s Democratic Republic of Algeria Ministry of Higher Education and Scientific Research University M’Hamed BOUGARA – Boumerdes

Institute of Electrical and Electronic Engineering Department of Power and Control Final Year Project Report Presented in Partial Fulfilment of The Requirements for the Degree of

‘MASTER DEGREE’ In Electrical Engineering Option: POWER ENGINEERING Title:

Labview Real Time Drive of Induction Motor Presented By: - CHEKLAM KHALED - BANAHMED Mohamed MONCEM Supervisor: Dr. METIDJI BRAHIM

Registration Number:…..…../2016

Dedication

I dedicdte this modest work To my lovely pdrents for their support dnd encourdgement To my much loved grdndfdther “ALI” To my sisters “SARRA”,“MANEL”,“ISRAA” dnd “MERIEM” In memory of my friend “BELAGHIT BACHIR” To dll my fdmily “djelld”,”bendbed”. To my friends “OUSSAMA”,“WALID ” , “AYMEN”, “KARIM”, ”KHALED” dnd ”ANESS”. To dll my friends.

khaled

Dedication

Dedication

I especially dedicate this modest work to: My beloved mother and my dear father for always being there to support me all the time and give me the courage and strength that are necessary for me to carry on with this project. My dear sisters and brothers, my all family members who have encouraged, guided and inspired me throughout my journey of education, My all dear friends and university mates, All IGEE teachers, students and administrative staff. In memory of my friend “BELAGHIT BACHIR”

Moncef

Acknowledgments

Acknowledgments First and foremost, we would like to take this opportunity to express our eternal gratitude to our supervisor Dr METIDJI BRAHIM, for his assistance in guiding us throughout the evaluation of this thesis and for providing us with the facilities that made this work possible. We would like to thank all the people who contributed in some way to the work described in this thesis specially ”Dr Khaldoune” “youssef “,“tarek “,” souleymen “ and “ oussama chaoua”. We would also like to thank all IGEE teachers for all information and knowledge they provided to us throughout our specialization and giving us a chance to appreciate the real meaning of engineering. We would also like to thank all IGEE staff .

Abstract Abstract: This project presents the hardware implementation of V/f control of induction motor using sine wave PWM(pulse width modulation) method. Because of its simplicity, the V/F control also called as the scalar control, is the most widely used speed control method in the industrial applications. The overall scheme of implementing V/f control has been presented. In this project, a labview block diagram and arduino code was developed to successfully implement Open Loop V/f Control on a PWM-Inverter fed 3-phase Induction Motor. The 3-phase voltages signals have been modeled as sine wave in labview and their V/f ratio is kept constant, after the data sent as samples through the Udp protocol to arduino. The arduino output the data received from labview as PWM signals and they are fed to the inverter then its outputs to Induction Motor.

Table of contents Dedication Acknowledgements Abstract Table of contents List of tables List of figures Nomenclature General introduction: introduction…………………………………………………………….……………..................1 Chapter 1: LabVIEW and Arduino Platform: 1.1

LabVIEW Develop Environment ……………………………………………… ...………2

1.1.1 LabVIEW History…………………………………………………………………………2 1.1.2 What Makes Up LabVIEW……………………………………………………. ………...3 1.1.3 G Programming Language………………………………………………………..………4 1.1.4 UI Components Reporting Tools………………………………………………………….5 1.2

Arduino……………………………………………………………….……………….…..7

1.2.1 Arduino Board …………………………………………………...…………………….…7 1.2.2 Arduino IDE ………………………………………………………………………..….…8 1.2.3 Arduino Ethernet Shield ………………………….……………………………………...9 Chapter 2: Communication Protocols : 2.1

Introduction ……………………………………………………………………..……....10

2.2

TCP/IP And UDP protocols ……………………………...………………………..…….10

2 .2.1TCP/IP protocol………………………………………………..………………................11 2.2.2 UDP protocol ……………………….……………………………………………….…..12 2.3

The Difference between TCP/IP And UDP:………… ..…………….………………..…14

2.4

UDP protocol for LabVIEW and Arduino………..….…………………………..............14

2.4.1 Labview ………………….………….……………..……….…………………………...14 2.4.1 Arduino ……………………...……………………..……………….…………………...14 Chapter 3: Overview of an induction motor: 3.1

Introduction…..………………………………………………………………… ………15

3.2

I.M construction…….......…………………………………………………………….....15

3.2.1 Stator……… ………………………………………………………………….…………15 3.2.2 Rotor……………………………………….…………………………………………….16 3.3

Principal of operation…...………………………………………………………..............18

Table of contents 3.4

Equivalent circuit of IM…………………………………………………………….…...19

3.5

Torque speed charactrestics……………………………………………………………...23

3.6

Advantages of squirrel cage rotor of an induction motor ……………………..………...24

3.7 Conclusuion……….…………………………………………………………..……….....24 Chapter 4: Induction motor drive principal: 4.1

Scalar of an induction motor from stator side ..................................................................25

4.1.1 Changing the number of stator poles..................................................................................25 4.1.2 Variable voltage operation.................................................................................................26 4.1.3 Variable frequency operation ............................................................................................26 4.1.4Variable voltage variable frequency operation...................................................................27 4.2 Advantage of V/f method....................................................................................................28 4.3

VFD system.......................................................................................................................28

4.3.1 Rectifier.............................................................................................................................29 4.3.2 DC Bus..............................................................................................................................30 4.3.3 Inverter..............................................................................................................................31 4.3.1.1 Three-phase voltage source inverters.............................................................................32 4.3.1.1 Performance parameter of an inverters..........................................................................35 4.4

Pulse width modulation techniques .................................................................................37

4.4.1 Principal operation of PWM.............................................................................................37 4.4.2 Advantage and disadvantage of PWM.............................................................................40 4.5

Open loop drive method...................................................................................................41

Chapter 5: Implementation Part: 5.1

Introduction ......................................................................................................................42

5.2

The simulation and control of three-phase voltage in labview.........................................44

5.3

The output signals result at the arduino and inverter sides ………...................................45

5.3.1 The output signals result at the arduino side ....................................................................45 5.3.2 The output signals result at the inverter side ....................................................................46 5.4

Discussion... ......................................................................................................................52

General conclusion: General conclusion……………………………………………………………………….…..53 References Appendix A

List of figures

Figure 1.1: The Front Panel and block diagram of LabVIEW …………….……………...…3 Figure 1.2: LabVIEW contains several valuable components.…………..………………..….3 Figure 1.3: Block diagram shows self-documenting G code……………………………….…4 Figure 1.4: Every LabVIEW block diagram has an associated front panel, such as this signal generation example with custom UI.……………………………………………...6 Figure 1.5: Arduino UNO……………………….……..………………………………………...7 Figure 1.6: Arduino IDE ……………………………...…………………………………..….8 Figure 1.7: Ethernet shield …………………………………………………………….…......9 Figure 2.1: simple udp block diagram ….………………………………………...…….…..14 Figure 3.1: Induction motor ……………………...………………...………………….........15 Figure 3.2: Stator of an induction motor…………………………………………..……......16 Figure 3.3: Squirrel cage rotor of an induction motor..............................................................17 Figure 3.4: Wound rotor of an induction motor ………………………………………....…17 Figure 3.5: Exact Equivalent Circuit of I.M…………………………………………….......20 Figure 3.6: Approximate Equivalent Circuit of I.M …............................................................21 Figure 3.7: Power flow in induction motor ……………………...…………………….........22 Figure 3.8: Torque -speed curve of an induction motor ………...……………………..........23 Figure 4.1: Torque-speed curves at variable stator………...…………………………...........26 Figure 4.2: Torque-speed characteristics for V/f controlled induction motor………..….......27 Figure 4.3 Variable Frequency Topology ………...…………………………........................28 Figure 4.4: Three phase full wave rectifier diagram………...……………………...…..........30 Figure 4.5: DC bus circuit ………...…………………….…….......………...………...……..31 Figure 4.6: AC-DC converter and DC Bus. ………...………………………………….....................31

Figure 4.7: Three-phase VSI ………...………………………….............................................32 Figure 4.8: Waveforms of Gating Signals, Switching Sequence, Line to Negative Voltages for Six-Step Voltage Source Inverter……...…………………………..................33 Figure 4.9: Waveforms of Line to Line Voltages and line to neutral voltages for six step voltage source inverter………...…………………………....................................34 Figure 4.10: Control signals for PWM ………...…………………………..............................37 Figure 4.11: Three-phase DC/AC inverter ………...………………………….......................37 Figure 4.12: Potentials of phases a and b due to PWM………...…………………………...38 Figure 4.13: Line-to-line voltage and its fundamental components due to PWM ………….39 Figure 4.14 Open-loop V/Hz Constant Control……………………………………...….…..41

List of figures Figure 5.1: Block diagram of the V/f control of induction motor using arduino and LabVIEW.......................................................................................................42 Figure 5.2: Implementation of the V/f control of induction motor using arduino and LabVIEW........................................................................................................42 Figure 5.3: The V/f control of induction motor using arduino and LabVIEW flow chart.....43 Figure 5.4: software and hardware implementation.................................................................44 Figure 5.5: the three-phase simulation ....................................................................................44 Figure 5.6: block diagram of the three-phase voltages simulation and sending. ...................45 Figure 5.7: PWM OUTPUT. ...................................................................................................45 Figure 5.8: Phase to Phase voltages ( V12-V23- V13) at 6 Hz..................................................46 Figure 5.9: Phase to neutral voltages ( V1n-V2n- V3n) at 6 Hz. ..............................................47 Figure 5.10: Phase current ( I1- I2- I3) at 6 Hz. .......................................................................47 Figure 5.11: Phase to Phase voltages ( V12-V23- V13) at 20 Hz..............................................48 Figure 5.12: Phase to neutral voltages ( V1n-V2n- V3n) at 20Hz. ...........................................49 Figure 5.13: Phase current ( I1- I2- I3) at 20 Hz. .....................................................................49 Figure 5.14: Phase to Phase voltages ( V12-V23- V13) at 36 Hz..............................................50 Figure 5.15: Phase to neutral voltages ( V1n-V2n- V3n) at 36 Hz. ..........................................51 Figure 5.16: Phase current ( I1- I2- I3) at 36 Hz. .....................................................................51

Nomenclature : efficiency

: firing angle of thyris

AC: Alternative Current DF:Distortion factor DC: Direct Current : induced voltage. EMF: Electromagnetic Force f: frequency f = frequency of the supply. HF: harmonic factor IPv6 : Internet Protocol version 6 IPv4 : Internet Protocol version 4 IP: Internet Protocol IGBT: Insulated-gate bipolar transistors IDE: Integrated Development Environment ICSP: In-Circuit Serial Programming IC: stator current at phase “C” I/O: input/output I.M: Induction Motor GPIB: General Purpose Interface Bus LOH: Lowest order harmonic LabVIEW: Laboratory Virtual Instrument Engineering Workbench MAC: Media Access Control : Synchronous speed PWM: Pulse Width Modulation P = number of poles. =The output power =Core loss power

=Developed Power(developed mechanical) power

=Stator copper loss power

=Rotor Copper loss power

=Air gap power

Nomenclature RPM: Revolution Per minute RMS: Root Mean Square RMF: Rotating Magnetic Field RFI : Radio frequency interface Rc: the core loss component.

ohm

R2’ is the rotor winding resistance with referred to stator winding. R2/s: the power of the rotor, which includes output mechanical power and copper loss of rotor. R2(1 - s)/s is the resistance which shows the power which is converted to mechanical power output or useful power. The power dissipated in that resistor is the useful power output or shaft power

rpm

R2 is the rotor resistance .

ohm

R1: the winding resistance of the stator.

Ohm

= Slip THD: Total harmonic distortion TCP: Transmission Control Protocol UI: User Interface UDP: User datagram protocol VSI:

Voltage Source Inverter

VFD: Variable Frequency Drive = the peak value of the phase line to line input voltage. ∶input voltage.

= Slip speed

rad/sec

= Actual speed or mechanical speed

rad/sec

: Synchronous speed XM: the magnetizing reactance of the winding.

rad/sec Henry

X2’ is the rotor winding inductance with referred to stator winding. X2 is the rotor inductive reactance.

Henry

X1: the inductance of the stator winding.

Henry

General introduction Introduction Induction motor drives with cage-type Machines have been the workhorse in industry for variable speed application in a wide range that covers fractional horse to multi-megawatts. These applications include pumps and fans, paper and textile mills, locomotive propulsion, electrical and hybrid vehicles, machine tools and robotics, home appliances heat pumps and air conditioners etc. the reason for increasing popularity can be primarily attributed to its robust construction, simplicity in design and cost effectiveness. It is very important to control the speed of induction motors in industrial and engineering applications. Efficient control strategies are used for reducing operation cost too. Speed control techniques of induction motor can be broadly classified as:1) scalar control and 2)vector control . Scalar control involves controlling the magnitude of the voltage and frequency of induction motor. Out of all the speed control mechanisms, The Volts/Hertz control method is very popular because of its simplicity and it provides a wide range of speed control with good running and transient Performance.

This report is arranged as follows:  General introduction  The first chapter describes the software ”LabVIEM” and hardware” Arduino &Ethernet shield” used .  The second chapter describes the communication protocol used .  The third chapter describes the structure and the principle operation of induction motor and the torque speed characteristics.  The fourth chapter describes the principle of scalar control of an induction motor, the topology of the Variable Frequency Drive, Pulse Midth Modulation technique and open loop method.  The fifth chapter describes the implementation and the simulation of the whole system and result discussion.  General conclusion.

1

Chapter 1

LabVIEW and Arduino Platform

In this chapter, The LabVIEW (Laboratorp Virtual Instrument Engineering Workbench) and Arduino based real time control spstem structure is introduced. In the thesis, we use LabVIEW to send data to arduino through the Ethernet shield using udp communication protocols,

1.1

LabVIEWDevelop Environment

LabVIEW is a graphical programming environment based on graphical programming language G. Execution of program is determined bp the structure of a graphical block diagram. Programmer connects different function-nodes bp drawing wires. These wires propagate variables and anp node can execute as soon as all its input data become available. Since this might be the case for multiple nodes simultaneouslp, G is inherentlp capable of parallel computation. Multi-processing and multi-threading hardware is automaticallp exploited bp the built-in scheduler, which multiplexes multiple OS threads over the nodes readp for executions. [1]

1.1.1 LabVIEW History The beginning of LabVIEW could be date back to the 1980s when Macintosh Companp produced first computer using graphical user interface. Graphical user interface enable flow chart on computer screen. And this inspired Jeff Kodoskp, “father of LabVIEW” for graphical programming. Since he was mostlp using data acquisition in his work area, he started to create a novel graphical programming language based on flow chart rather than traditional sequential processing. In 1986 the first version of LabVIEW, LabVIEW 1.0, was published which was similar as we see todap (Figure 1.1). The main goal of this programming at that time was to simplifp data acquisition from GPIB bus. And we still relp on this feature in our research nowadaps.

2

Chapter 1


Figure1.1 The Front Panel and block diagram of LabVIEW LabVIEW[1]

1.1.2 What Makes lp Labview LabVIEW itself is a software development environment that contains numerous components, several of which are required for anp tppe of test, measurement, or control application. as shown in figure 1.2 .

Figure 1.2 LabVIEW contains several valuable components. [1]

3

Chapter 1


1.1.3 G Programming Language 

Intuitive, flowchart-like dataflow programming model



Shorter learning curve than traditional text-based programming



Naturallp represents data-driven applications with timing and parallelism

The G programming language is central to LabVIEW; so much so that it is often called “LabVIEW programming”. Using it, pou can quicklp tie together data acquisition, analpsis, and logical operations and understand how data is being modified. From a technical standpoint, G is a graphical dataflow language in which nodes (operations or functions) operate on data as soon as it becomes available, rather than in the sequential line-bp-line manner that most programming languages emplop. You lap out the “flow” of data through the application graphicallp with wires connecting the output of one node to the input of another. The practical benefit of the graphical approach is that it puts more focus on data and the operations being performed on that data, and abstracts much of the administrative of computer programming such as memorp allocation and language spntax. [2]

Figure1.3 Block diagram shows self-documenting G code. [1]

4

Chapter 1


LabVIEW contains a powerful optimizing compiler that examines pour block diagram and directlp generates efficient machine code, avoiding the performance penaltp associated with interpreted or cross-compiled languages. The compiler can also identifp segments of code with no data dependencies (that is, no wires connecting them) and automaticallp split pour application into multiple threads that can run in parallel on multicore processors, pielding significantlp faster analpsis and more responsive control compared to a single-threaded, sequential application. With the debugging tools in LabVIEW, pou can slow down execution and see the data flow through pour diagram, or pou can use common tools such as breakpoints and data probes to step through pour program node-bp-node. The combination of working with higher-level building blocks and improved visibilitp into pour application’s execution results in far less time spent tracking down bugs in pour code.

1.1.4 lI Components and Reporting Tools 

Interactive controls such as graphs, gauges, and tables to view pour acquired data



Tools to save data to file or databases, or automaticallp generate reports

Everp LabVIEW block diagram also has an associated front panel, which is the user interface of pour application. On the front panel pou can place generic controls and indicators such as strings, numbers, and buttons or technical controls and indicators such as graphs, charts, tables, thermometers, dials, and scales. All LabVIEW controls and indicators are designed for engineering use, meaning pou can enter SI units such as 4M instead of 4,000,000, change the scale of a graph bp clicking on it and tpping a new end point, export data to tools such as NI DIAdem( NI software’s ) and Microsoft Excel bp right-clicking on it, and so on.

5

Chapter 1


Figure 1.4 Every LabVIEW block diagram has an associated front panel, such as this signal generation example with custom UI. [1]

Controls and indicators are customizable. You can add them either from a palette of clicking on a data wire on the block diagram and controls on the front panel or bp right right-clicking selecting “Create Control” or “Create Indicator.” In addition to displaping data as pour application is running, LabVIEW also contains several options for generating reports from pour test or acquired data. You can send simple enerate Microsoft Office reports directlp to a printer or HTML file, programmaticallp ggenerate documents, or integrate with NI DIAdem for more advanced reporting. Remote front panels built-in Web and Web service support allow pou to publish data over the Internet with the built server.

6

Chapter 1


1.2 Arduino Arduino is a popular open-source phpsical computing platform which is verp common for communicating with the phpsical world. It is verp easp and effective to use Arduino to sense and control most of the sensors and equipment. It is based on a simple microcontroller board, and a development environment for writing software for the board. It is verp popular for developing electronicallp thesis. Arduino can be used to develop interactive objects which take inputs from a varietp of switches or sensors, and control varieties of lights, motors, and other phpsical outputs and Arduino projects can be stand-alone, or thep can communicate with software running on other computer (arduino.cc, 2015b). Arduino can be divided into two part, phpsical programmable circuit board and software(Arduino IDE -1-).[3]

1.2.1 Arduino Board It is the phpsical programmable circuit board which is connected to real world. It can get inputs from varieties of sensors and switches and on return, can control others phpsical devices. Program is uploaded in the board via IDE in a computer using USB cable. There are different tppes of Arduino board available in the market such as Arduino UNO, Arduino Mega 2560, Arduino Mega ADK, etc. Arduino UNO is shown in Figure 1.5.

Figure 1.5: Arduino UNO 1 Integrated Development Environment

7

Chapter 1


It consists of 14 digital I/O -2- pins, 6 analog inputs, a USB connection, a power jack, an ICSP header, a reset button and a 16 MHz crpstal oscillator. Among 14 digital I/O pins, 6 pins can be used as PWM outputs which is indicated bp ~. It contains everpthing needed to support the microcontroller, we just need to connect it to a computer with a USB cable or just power it with an AC-to-DC adapter or batterp to get started.

1.2.2 Arduino IDE Arduino IDE is software which is needed to install in a computer. And, it uses a simplified version of C++, making it easier to learn to program.

Figure 1.6: Arduino IDE

2 input/output

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Chapter 1


The Figure 1.6 illustrates the three main steps that carried out in the IDE software. First of all, program is coded and clicks the “verifp” button. This is compiling the code and if there is no anp error then ”upload” button should be clicked. This is done to upload the program to the Arduino board. And finallp out is displap in the serial monitor which can be viewed bp clicking on serial monitor button. As mentioned in Figure 1.6, code which needs to run just a once is kept under ”setup” function and which needs to be run repeatedlp in certain interval of time should be kept under ”loop” function. For defining the interval, delap(x) function is used where x is time interval defined in millisecond.

1.2.3 Arduino Ethernet Shield Arduino Ethernet Shield allows the Arduino board to connect with internet using Ethernet librarp. The librarp can serve as either a server accepting incoming connections or a client making outgoing ones. The librarp supports up to four concurrent connection (incoming or outgoing or combination) (arduino.cc, 2015a). For internet connection, first the shield should mounted over the Arduino and the shield should be connected to the internet using standard Ethernet cable then provide a power. The next is network setting. For that MAC (Media Access Control) address and fixed IP address should be assigned to the Ethernet shield using the function, Ethernet.begin(). This function initializes the Ethernet librarp and network settings., MAC_address is MAC address of the Ethernet shield which is arrap of 6 bptes where as IP is IP address of the Ethernet shield and it is arrap of 4 bptes.

Figure 1.7: Ethernet shield

9

Chapter 2

Communication Protocols

2.1 Introduction In telecommunications, a communications protocol is a system of rules that allow two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. These are the rules or standard that defines the syntax, semantics and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both. Communicating systems use well-defined formats (protocol) for exchanging messages. Each message has an exact meaning intended to elicit a response from a range of possible responses pre-determined for that particular situation. The specified behavior is typically independent of how it is to be implemented. Communications protocols have to be agreed upon by the parties involved. To reach agreement, a protocol may be developed into a technical standard. A programming language describes the same for computations, so there is a close analogy between protocols and programming languages: protocols are to communications as programming languages are to computations.[4]

2.2 TCP/IP And UDP protocols Both TCP and UDP are protocols used for sending bits of data — known as packets — over the Internet. They both build on top of the Internet protocol. In other words, whether you’re sending a packet via TCP or UDP, that packet is sent to an IP address. TCP and UDP aren’t the only protocols that work on top of IP. However, they are the most widely used. The widely used term “TCP/IP” refers to TCP over IP. UDP over IP could just as well be referred to as “UDP/IP”, although this isn’t a common term.

10

Chapter 2


2.2.2 TCP/IP protocol As the name implies, TCP/IP is a combination of two separate protocols: Transmission Control

Protocol (TCP) and Internet Protocol (IP). The Internet Protocol standard dictates

the logistics of packets sent out over networks; it tells packets where to go and how to get there . IP has a method that lets any computer on the Internet forward a packet to another computer that is one or more intervals closer to the packet's recipient. The Transmission Control Protocol is responsible for ensuring the reliable transmission of data across Internet-connected networks. TCP checks packets for errors and submits requests for re-transmissions if any are found.

Table 2.1 TCP header.[6]

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Chapter 2


2.2.3 UDP protocol User datagram protocol is an open systems interconnection (OSI) transport layer protocol for client- server network applications.[7] UDP uses a simple transmission model but does not employ handshaking dialogs for reliability, ordering and data integrity. The protocol assumes that error-checking and correction is not required, thus avoiding processing at the network interface

level.

UDP is widely used in video conferencing and real-time computer games. The protocol permits individual packets to be dropped and UDP packets to be received in a different order than that in which they were sent, allowing for better performance. UDP network traffic is organized in the form of datagrams, which comprise one message units. The first eight bytes of datagram contain header information, while the remaining bytes contain message data. A UDP datagram header contains four fields of two bytes each: 

Source port number



Destination port number



Datagram size



Checksum

Table 2.2 UDP header

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Chapter 2


The UDP header consists of 4 fields, each of which is 2 bytes (16 bits). The use of the fields "Checksum" and "Source port" is optional in IPv4 (pink background in table).

Source port number: This field identifies the sender's port when meaningful and should be assumed to be the port to reply to if needed. If not used, then it should be zero. If the source host is the client, the port number is likely to be an ephemeral port number. If the source host is the server, the port number is likely to be a well-known port number. Destination port number:This field identifies the receiver's port and is required. Similar to source port number, if the client is the destination host then the port number will likely be an ephemeral port number and if the destination host is the server then the port number will likely be a well-known port number. Length: A field that specifies the length in bytes of the UDP header and UDP data. The minimum length is 8 bytes because that is the length of the header. The field size sets a theoretical limit of 65,535 bytes (8 byte header + 65,527 bytes of data) for a UDP datagram. The practical limit for the data length which is imposed by the underlying IPv4 protocol is 65,507 bytes (65,535

8 byte UDP header

20 byte IP header). In IPv6 jumbograms it is

possible to have UDP packets of size greater than 65,535 bytes. RFC 2675 specifies that the length field is set to zero if the length of the UDP header plus UDP data is greater than 65,535. Checksum: The checksum field may be used for error-checking of the header and data. This field is optional in IPv4, and mandatory in IPv6. The field carries all-zeros if unused.

13

Chapter 2


2.3 The Difference between TCP/IP And UDP The TCP is connection oriented – once a connection is established, data can be sent bidirectional. UDP is a simpler, connectionless Internet protocol. Multiple messages are sent as packets in chunks using UDP. Udp

is suitable for applications that need fast, efficient

transmission. TCP is suited for applications that require high reliability, where Udp has less reliability but in our case udp used in simple application.

2.4 UDP protocol for LabVIEW and Arduino 2.4.1 LabVIEW The simplest UDP block diagram made for Labview is shown in figure 2.1 below, where we initiate the IP address and a port for specified target. And also we can add the IP address and port for identifying the receiving target.

Figure 2.1 simple udp block diagram[1]

2.4.2 Arduino With the Arduino Ethernet Shield, this library allows an Arduino board to connect to the internet. It can serve as either a server accepting incoming connections or a client making outgoing ones. The library supports up to four concurrent connection (incoming or outgoing or a combination). Ethernet Shield and Arduino are used to send and receive strings packet via the UDP protocol. This is done by using functions included in Ethernet.Udp library to initialize the Mac address of used hardware; the address IP, the ports of the source and destination of received and sent data.

14

Chapter 3

Overview of an induction motor

3.1 Introduction Induction motors are the most widely used motors for appliances like industrial control, and automation; hence, they are often called the workhorse of the motion industry [8]. As far as the machine efficiency, robustness, reliability, durability, power factor, ripples, stable output voltage and torque are concerned.

Figure 3.1: Induction motor [9] 3.2 I.M Construction A 3-phase induction motor has two main parts (i) stator and (ii) rotor. The rotor is separated from the stator by a small air-gap which ranges from 0.4 mm to 4 mm, depending on the power of the motor. 3.2.1 Stator It consists of a steel frame which encloses a hollow, cylindrical core made up of thin laminations of silicon steel to reduce hysteresis and eddy current losses. A number of evenly spaced slots are provided on the inner periphery of the laminations. The insulated connected to form a balanced 3-phase star or delta connected circuit. The 3-phase stator winding is wound for a definite number of poles as per requirement of speed. Greater the number of poles, lesser is the speed of the motor and vice-versa.

15

Chapter 3


Figure 3.2: Stator of an induction motor [9] 3.2.2 Rotor: The rotor is also composed of thin-slotted, highly permeable steel laminations that are pressed together into a shaft. There are two types of rotors: squirrel cage rotor and wound rotor: 

Squirrel cage rotor It consists of a laminated cylindrical core having parallel slots on its outer periphery.

One copper or aluminum bar is placed in each slot. All these bars are joined at each end by metal rings called end rings. This forms a permanently short-circuited winding which is indestructible. The entire construction (bars and end rings) resembles a squirrel cage and hence the name. The rotor is not connected electrically to the supply but has current induced in it by transformer action from the stator. Those induction motors which employ squirrel cage rotor are called squirrel cage induction motors. Most of 3-phase induction motors use squirrel cage rotor as it has a remarkably simple and robust construction enabling it to operate in the most adverse circumstances. However, it suffers from the disadvantage of a low starting torque. It is because the rotor bars are permanently short-circuited and it is not possible to add any external resistance to the rotor circuit to have a large starting torque.

16

Chapter 3


Figure 3.3: Squirrel cage rotor of an induction motor [9] 

Wound rotor

It consists of a laminated cylindrical core and carries a 3-phase winding, similar to the one on the stator .The rotor winding is uniformly distributed in the slots and is usually starconnected. The open ends of the rotor winding are brought out and joined to three insulated slip rings mounted on the rotor shaft with one brush resting on each slip ring. The three brushes are connected to a 3-phase star-connected rheostat .At starting; the external resistances are included in the rotor circuit to give a large starting torque. These resistances are gradually reduced to 8ero as the motor runs up to speed.

Figure 3.4: Wound rotor of an induction motor [9]

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Chapter 3


3.3 Principl of operation In an induction motor only the stator winding is fed with an AC supply. Where Alternating flux is produced around the stator winding due to AC supply. This alternating flux revolves with synchronous speed. The revolving flux is called as "Rotating Magnetic Field" (RMF). Synchronous speed is given by : =

120 ×

=

120 ×

×

2× 4 = 60

/ sec

(3.1)

(3.2)

Where, f = frequency of the supply. P = number of poles.

The relative speed between stator RMF and rotor conductors causes an induced emf in the rotor conductors, according to the Faraday's law of electromagnetic induction (APPENDIX A). The rotor conductors are short circuited, and hence rotor current is produced due to induced emf. That is why such motors are called as induction motors. (This action is same as that occurs in transformers, hence induction motors can be called as rotating transformers.) [10] Now, induced current in rotor will also produce alternating flux around it. This rotor flux lags behind the stator flux. The direction of induced rotor current, according to Len8's law (APPENDIX A), is such that it will tend to oppose the cause of its production. As the cause of production of rotor current is the relative velocity between rotating stator flux and the rotor, the rotor will try to catch up with the stator RMF. Thus the rotor rotates in the same direction as that of stator flux to minimi8e the relative velocity. However, the rotor never succeeds in catching up the synchronous speed. This is the basic working principle of induction motor of either type, single phase or 3 phase. In practice, If rotor catches up the stator speed, there won’t be any relative speed between the stator flux and the rotor, hence no induced rotor current and no torque production to maintain the rotation. However, this won't stop the motor, the rotor will slow down due to lost of

18

Chapter 3


torque, the torque will again be exerted due to relative speed. That is why the rotor rotates at speed which is always less the synchronous speed. The difference between the synchronous speed (Ns) and actual speed (Nm) of the rotor is called as slip. = Where the slip-speed (

=

(3.3)

) is:

=

=

×

(3.4)

3.4 Equivalent circuit of IM The equivalent circuit of any machine shows the various parameter of the machine such as its ohmic losses and also other losses. The losses are modeled just by inductor and resistor. The copper losses are occurred in the windings so the winding resistance is taken into account. Also, the winding has inductance for which there is a voltage drop due to inductive reactance and also a term called power factor comes into the picture. There are two types of equivalent circuits in case of a three-phase induction motor, first one is Exact Equivalent Circuit.

19

Chapter 3


Figure 3.5: Exact Equivalent Circuit of I.M [10]

Here, R1 is the winding resistance of the stator. X1 is the inductance of the stator winding. Rc is the core loss component. XM is the magneti8ing reactance of the winding. R2/s is the power of the rotor, which includes output mechanical power and copper loss of rotor.

20

Chapter 3


If we draw the circuit with referred to the stator then the second type will be introduced which called Approximate Equivalent Circuit.

Figure 3.6: Approximate Equivalent Circuit of I.M [11] Here all the other parameters are same except: R2’ is the rotor winding resistance with referred to stator winding. X2’ is the rotor winding inductance with referred to stator winding. R2(1 - s)/s is the resistance which shows the power which is converted to mechanical power output or useful power. The power dissipated in that resistor is the useful power output or shaft power. [11]

21

Chapter 3


And the power can be calculated as: 1. Input power to stator = 3 V1I1Cos(Ɵ). Where, V1 is the stator voltage applied. I1 is the current drawn by the stator winding. Cos(Ɵ) is the stator power factor. 2. Stator copper loss : 3. Core loss : 4. Air gap :

=

5. Rotor Copper loss :

=3

=3

(3.5)

(3.6)

(3.7)

=3

6. Developed Power(developed mechanical) : 7. The output power :

=

&

=

Figure 3.7 Power flow in induction motor.[12]

22

(3.8)

(3.9)

(3.10)

Chapter 3


3.5 Torque speed characteristics The torque produced by three phase induction motor is given by, =

2

3

Where E2 is the rotor emf.

×

+(

(3.11)

)

Ns is the synchronous speed. R2 is the rotor resistance . X2 is the rotor inductive reactance.

Figure 3.8: Torque -speed curve of an induction motor [12]

23

Chapter 3


Three regions in torque-speed curve are shown : 1) Plugging (braking) region (1
3.6 Advantages of squirrel cage rotor of an induction motor 

It is simple in construction, rugged and can withstand rough handling.



Maintenance cost is low.



It has better efficiency and power factor.



A simple star-delta starter is sufficient to start the rotor.



It is explosion proof as there no slip rings and brushes.

3.7 Conclusion In this chapter we have seen principle of operation of the squirrel cage induction motor and the advantages and the performances. As seen in the speed-torque characteristics, torque is highly nonlinear as the speed varies. In many applications, the speed needs to be varied, which makes the Torque vary. So we have to use many techniques to control them.

24

Chapter 4

Indection motor drive principal

It is very important to control the speed of induction motors in industrial and engineering applications. Efficient control strategies are used for reducing operation cost too. Speed control techniques of induction motors can be broadly classified into two type: scalar control and vector control. Scalar control can be done in rotor and stator side and involves controlling the magnitude of voltage or frequency of the induction motor. In this chapter we are going to introduce the scalar control from stator side due to the type of the motor used which is squirrel cage I.M.

4.1 Scalar control of an induction motor from stator side i)

Changing the number of poles

ii)

Variable voltage operation.

iii)

Variable frequency operation.

iv)

Variable voltage Variable frequency operation. .

4.1.1Changing the number of stator poles From the equation (3.1) of synchronous speed, it can be seen that synchronous speed (and hence, running speed) can be changed by changing the number of stator poles. This method is generally used for squirrel cage induction motors, as squirrel cage rotor adapts itself for any number of stator poles. Change in stator poles is achieved by two or more independent stator windings wound for different number of poles in same slots. For example, a stator is wound with two 3phase windings, one for 4 poles and other for 6 poles. for supply frequency of 50 Hz i) synchronous speed when 4 pole winding is connected, Ns = 120*50/4 = 1500 RPM ii) synchronous speed when 6 pole winding is connected, Ns = 120*50/6 = 1000 RPM

25

Chapter 4


4.1.2 Variable voltage operation From the torque equation (3.8) of induction motor , Rotor resistance R2 is constant and if slip s is small then (sX2)2 is so small that it can be neglected. Therefore, T ∝ sE22 where E2 is rotor induced emf and E2 ∝ V

Thus, T ∝ sV2, which means, if supplied voltage is decreased, the developed torque decreases.

Hence, for providing the same load torque, the slip increases with decrease in voltage, consequently the speed decreases. This method is the easiest and cheapest, still rarely used, because 1. large change in supply voltage is required for relatively small change in speed. 2. large change in supply voltage will result in a large change in flux density, hence, this will disturb the magnetic conditions of the motor.[13]

4.1.3 Variable frequency operation Synchronous speed of the rotating magnetic field of an induction motor is given by the equation (4.1). Hence, the synchronous speed changes with change in supply frequency. Actual speed of an induction motor is given as N = Ns (1 - s). However, this method is not widely used. It may be used where, the induction motor is supplied by a dedicated generator (so that frequency can be easily varied by changing the speed of prime mover). Also, at lower frequency, the motor current may become too high due to decreased reactance. And if the frequency is increased beyond the rated value, the maximum torque developed falls while the speed rises.

Figure 4.1: Torque-speed curves at variable stator frequency[14]

26

Chapter 4


4.1.4 Variable voltage Variable frequency operation This is the most popular method for controlling the speed of an induction motor. As in above method, if the supply frequency is reduced keeping the rated supply voltage, the air gap flux will tend to saturate. This will cause excessive stator current and distortion of the stator flux wave. Therefore, the stator voltage should also be reduced in proportional to the frequency so as to maintain the air-gap flux constant. The magnitude of the stator flux is proportional to the ratio of the stator voltage and the frequency. Hence, if the ratio of voltage to frequency is kept constant, the flux remains constant. Also, by keeping V/F constant, the developed torque remains approximately constant. =

≈

=

.

.

.

.

(4.1)

=

(4.2)

.

(4.3)

This method gives higher run-time efficiency. Therefore, majority of AC speed drives employ constant V/F method (or variable voltage, variable frequency method) for the speed control. Along with wide range of speed control, this method also offers 'soft start' capability.

Figure 4.2: Torque-speed characteristics for V/f controlled induction motor [14]

27

Chapter 4


4.2 Advantages of V/f method V/f Control is the most popular and has found widespread use in industrial and domestic applications because of its ease-of-implementation. The various advantages of V/f Control are as follows: 

It provides good range of speed.



It has low starting current requirement.



It has a wider stable operating region.



Voltage and frequencies reach rated values at base speed.



The acceleration can be controlled by controlling the rate of change of supply frequency.



It is cheap and easy to implement.

4.3 VFD system A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, micro drive, and inverter. Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement [15].

28

Chapter 4


A variable frequency drive system generally consists of three main parts:

Figure 4.3 Variable Frequency Topology[15]

4.3.1 Rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves , copper and selenium oxide rectifiers, and other silicon-based semiconductor switches .

 Three-phase full wave rectifier Single-phase rectifiers are commonly used for power supplies for domestic equipment. However, for most industrial and high-power applications, three-phase rectifier circuits are the norm. The basic full-wave uncontrolled (diode) rectifier circuit is shown in Figure2.2 Diodes D1, D3, and D5 are sometimes referred to as the upper half of the bridge, while diodes D2, D4, and D6 constitute the lower half of the bridge. The voltages at the anodes of the diode valves vary periodically as the supply voltages undergo cyclic excursions. Commutation or switch off of a conducting diode is therefore accomplished by natural cycling of the supply voltages and is known as natural commutation.

29

Chapter 4


Figure 4.4: Three phase full wave rectifier diagram[15] For a three phase full wave diode rectifier, the ideal, no load average output voltage is given by the following equation: =

=

3 × √3

×

( 4.4)

If the thyristors are used in place of diodes, the output voltage is reduced by a factor cos (α) and it is given by the following equation:

Where:

=

=

3 × √3

×

× cos

= the peak value of the phase line to line input voltage.

(4.5)

= firing angle of the thyristors.

4.3.2 DC Bus The DC bus is the true link between the converter and inverter sections

of the drive. Any ripple

must be smoothed out before any transistor switches “on”. If not, this distortion will show up in the output to the motor. The DC bus voltage and current can be viewed through the bus terminals. The DC link is an important section of the drive as it provides much of the monitoring and protection for the drive & motor circuit. It contains the base-drive fusing and pre-charge capacitor network, which assures steady voltage DC voltage, levels prior to the Inverter Bridge and allows a path for over-voltage dissipation.

30

Chapter 4


Figure 4.5: DC bus circuit[15]

Figure 4.6: 4.6 AC-DC converter and DC Bus. [15 15]

4.3.3 Inverters The function of an inverter is to change a DC input voltage to an AC output voltage of desired frequency and magnitude. Variable output voltages are obtained by varying the input DC voltage with maintaining the gain of the inverter constant. Meanwhile, if the DC input voltage fixed and not controllable, variable output voltage can be obtained by varying the frequency of the inverter which is usually done by implementing PWM control within th thee inverter. The output voltage of an inverter has a periodic waveform which is not purely sinusoidal, but with number of techniques it can be designed to closely approximate to this desired waveform. Inverter can be built with any number of phase inverters are most commonly used. It three-phase output phases. Practically, single phase and three depends on the user requirement whether in the industrial applications, Transportations and home phase inverter offered better performan performances as compared to appliances. In most circumstances, three three-phase single-phase inverter.

31

Chapter 4


4.3.3.1Three-phase voltage source inverter Single-phase VSIs cover low-range power applications and three-phase VSIs cover the mediumto high-power applications. The main purpose of these topologies is to provide a three-phase voltage source, where the amplitude, phase, and frequency of the voltages should always be controllable. The simplest dc voltage source for a VSI may be a battery bank, which may consist of several cells in series-parallel combination. Solar photovoltaic cells can be another dc voltage source. An AC voltage supply, after rectification into dc will also qualify as a DC voltage source. In such inverter units, battery supply is used as the input DC voltage source and the inverter circuit converts the DC into AC voltage of desired frequency. The achievable magnitude of AC voltage is limited by the magnitude of input (DC bus) voltage. In ordinary household inverters the battery voltage may be just 12 volts and the inverter circuit may be capable of supplying ac voltage of around 10 volts (RMS) only. In such cases the inverter output voltage is stepped up using a transformer to meet the load requirement of, say, 230 volt. The three-phase VSI are shown in Figure.

Figure 4.7: Three-phase VSI[15] There are six modes of operating the switches, where in a cycle the phase shift of each mode is 60º. In order to generate a desired voltage waveform, the transistor condition moves from one states to another. The gating signals shown in Figure 4.8.Are shifted from each other by 60º to obtain 3phase balanced (fundamental) voltages as shown in Figure 4.9 The load can be connected in wye or delta connection. When operated as a Six Step Inverter, the control signals, the switching sequence, and the line to negative voltages for the six switches of the inverter are shown in Figure 4.8

32

Chapter 4


Figure 4.8: Waveforms of Gating Signals, Switching Sequence, Line to Negative Voltages for SixStep Voltage Source Inverter[15] The standard three-phase VSI topology is shown in Figure 4.7 And the eight valid switch states are given in Table 2.1. As in single-phase VSIs, the switches of any leg of the inverter (S1 and S4, S3 and S6, or S5 and S2) cannot be switched on simultaneously because this would result in a short circuit across the dc link voltage supply. Similarly, in order to avoid undefined states in the VSI, and thus undefined ac output line voltages, the switches of any leg of the inverter cannot be switched off simultaneously as this will result in voltages that will depend upon the respective line current polarity. Of the eight valid states, two of them (7 and 8 in Table 4.1) produce zero ac line voltages. In this case, the ac line currents freewheel through either the upper or lower components. The remaining states (1 to 6 in Table 4.1) produce non-zero ac output voltages. In order to generate a given voltage waveform, the inverter moves from one state to another. Thus the resulting ac output line voltages consist of discrete values of voltages that are Vs, 0, and -Vs for the topology shown in Figure 4.7. The selection of the states in order to generate the given waveform is done by the modulating technique that should ensure the use of only the valid states .

33

Chapter 4


Table 4.1: Valid switch states for a three-phase VSI[15] The switch pairs (S1, S4), (S3, S6), and (S5, S2) form three legs of the inverter. The switches in the same leg conduct alternately. Sometime must elapse before the turn-off of one switch and turn on of another to ensure that both do not conduct simultaneous the figure 4.8 below shows the line to line voltages and the line to neutral voltages resulting from the switching sequence described above.

Figure 4.9: Waveforms of Line to Line Voltages and line to neutral voltages for six step voltage source inverter[15] The line-to-neutral voltages are shown in Figure 4.9 .This scheme shows that line-to-line output voltages are +Vs, 0 or –Vs. The instantaneous line-to-line voltage Vab can be expressed in a Fourier series as describe in five equations:

34

Chapter 4


=

. .

4

cos

6

sin (

+ ) 6

(4.6)

)

(4.7)

7 ) 6

(4.8)

Vbc and Vca are obtained from Equation 4.6 by shifting Vab by 120º and 240º =

. .

=

. .

4 4

cos cos

6

sin (

2

sin (

6

It is also shown that in Equations 4.6 and 4.7 and 4.8 the triples harmonics is zero in the Line-toline voltage. The line-to-line RMS voltage is expressed in Equation 4.9, whilst the RMS value of line-to-neutral voltage is in Equation 2.7:

= V =

2 2

(

[ V

√3

=

)] =

√2 V 3

2 3

4.3.3.2Performance Parameter of an Inverter

(4.9) (4.10)

In order to measure the quality of the output of an inverter, the following performance parameter is commonly used.

 Harmonic factor of nth harmonic (HFn) It’s the measure of individual Harmonic contribution. =

(4.11)

Where V1 is the RMS value of the fundamental component and Vn is the RMS value of the nth harmonic component.

35

Chapter 4


 Total harmonic distortion (THD) It’s the measure of closeness in shape between a waveform and its fundamental component.

THD =

1 V

V

.

(4.12)

 Lowest order harmonic (LOH) Harmonic component whose frequency is closest to fundamental and his amplitude is greater or equal to 3% of fundamental.

 Distortion factor (DF) THD gives total harmonic content but does not indicate individual harmonics level. In practice, the Knowledge of both frequency and magnitude of individual harmonic component is required. DF indicates amount of harmonic distortion remaining after the harmonics of that waveform is subjected to second order attenuation (divide by n2) DF measures effectiveness in reducing unwanted harmonics without specifying values of second order load filter.

For individual (nth) component:

DF =

DF =

1 V

.

(

V V × n

V ) n

(4.13) (4.14)

 Power efficiency η It is the ratio of the power output from the shaft to the real power input to the motor terminals =

(4.15)

Whereas Pi and Po denotes the input power and output power of the converter, respectively.

36

Chapter 4


4.4 Pulse Width Modulation technique 4.4.1 Principle operation of PWM Pulse width modulation (PWM) is used to control the frequency and the magnitude of the AC voltage across the load and to reduce the harmonic contents in the output voltage or current. There are a number of PWM techniques, but the most common type is the sinusoidal PWM.

Figure 4.10: Control signals for PWM[15] Figure 4.10 shows the basic idea of PWM for a voltage source inverter. Two control signals are used: a reference sinusoidal wave Vref and a triangular carrier Vcar. A control circuit at low voltage levels generates these two signals. They are used solely to create the triggering signals for two transistors on the same leg in the circuit shown in figure 4.11.that is to say, they are for the terminal of one phase only. The control signals of the other two legs have the same triangular carrier, but their sinusoidal reference waves have the proper 120° shift associated with the balanced threephase system. Thus, Vref of phase b lags Vref of phase a by 120°, and Vref of phase c leads Vref of phase a by 120°.

Figure 4.11: Three-phase DC/AC inverter[15] 37

Chapter 4


With the PWM technique, several parameters can be adjusted to generate the desired voltage and frequency at the load side. The basic parameters are the frequency and the magnitude of the reference signal Vref . The magnitude of the triangular carrier is usually kept constant, but its frequency can also vary. The upper limit of the frequency of the carrier is determined by the maximum switching frequency of the transistors. This frequency can be high as 20 kHz. [16] Now let us see how the PWM works by examining Figure 4.10. We will assume that the figure is for the control signals of phase a only. Looking back at the circuit in Figure 4.11, you find that Q1 and Q4 are the two transistors switching in the leg of phase a. If Q1 is closed and Q4 is open, Vao is positive.(Vao is the potential of phase a with respect to point o) point o is just a reference point selected here to be the negative terminals of the input source Vdc. If Q1 and Q4 is based on the difference between the reference and carrier waveforms =

: (4.16)

The switching conditions for any two transistors in one leg (say, for phase a) are as follows:

Figure 4.12: Potentials of phases a and b due to PWM[15] Where: 38

Chapter 4

Indection motor drive principal =

(4.17)

is the reference signal of phase a.

The reference signals for two phases are shown at the top of Figure 4.12. Using the rule stated in the previous paragraph, we can generate

and

shown in the figure.

Note that these voltages have unequal switching intervals. Figure 4.13 shows the line-to-line voltage

, which is obtained by subtracting the potential

of phase b from that of phase a: =

(4.18)

The line-to-line voltage consists of rectangular segments with different widths. It also has symmetrical positive and negative parts. Thus, it has a dominant component at the fundamental frequency. [16] Using a harmonic analysis technique, the general expression of such a waveform can be written as: ( )=

×

2

× sin(2 ×

×

× )+

(4.19)

Figure 4.13: Line-to-line voltage and its fundamental components due to PWM[15]

Where

is the frequency of the reference signal

is called the amplitude modulation and

is called frequency modulation, which is the ratio of the peak values of the reference signal to the carrier: =

(4.20) 39

Chapter 4

Indection motor drive principal =

(4.21)

By examining Equation 4.19, one can conclude that by adjusting the magnitude and frequency of the reference signal, the magnitude and frequency of the load voltage can be controlled. Assume that the carrier frequency and its magnitude are unchanged. When the magnitude of the reference signal increases, load voltage

increases, and so does the magnitude of the fundamental components of the

. Also, since the frequency of the fundamental voltage across the load is the same

as the frequency of the reference signal , the frequency of the load voltage can be changed by changing the reference frequency. These are the major advantage of the PWM technique.

4.4.2 Advantage and disadvantage of PWM  Advantage An additional advantage of pulse width modulation is that the pulses are at the full supply voltage and will produce more torque in a motor by being able to overcome the internal motor resistances more easily. A resistive speed control will present a reduced voltage to the load, which can cause stalling in motor applications. Finally, in a PWM circuit, common small potentiometers may be used to control a wide variety of loads.

 Disadvantage The main disadvantages of PWM circuits are the added complexity and the possibility of generating radio frequency interference (RFI). Locating the controller near the load, using short leads, and in some cases, using additional filtering on the power supply leads, may minimize RFI.

40

Chapter 4


4.5 Open loop drive method The open-loop Volts/Hertz control of induction motors is widely used in industry, where the stator voltage was varied, and the supply frequency was simultaneously varied such that the V/f ratio remained constant. This kept the flux constant and hence the maximum torque while varying the speed. For this strategy, feedback signals are not required. This type of motor control has some advantages: -

Low cost.

-

Simplicity and

-

Immunity to errors of feedback signals .

Figure 4.14 Open-loop V/Hz Constant Control[17]

41

Chapter 5

Simulation & Implementation Part

5.1 Introduction A commercial moftware (LABVIEW), LABVIEW), open mource moftware (IDE),, arduino board and Ethernet mhield ham been umed to drive the induction motor .The figure (5.1) mhow the block diagram of the demired project. Where the figure (5.2) mhowm the implementation.

Figure 5.1: Block diagram of the V/f control of induction motor uming arduino and LabVIEW

Figure 5.2: Implementation of the V/f control of induction motor uming arduino and LabVIEW

42

Chapter 5


The following flow-chart explainm the procedure mtep-by-mtep:

Start Set the host IP(arduino) , the reference frequency and voltage.

Simulate the 3-phase voltage signals in LabVIEW

Control the signals by the frequency fill slide

Sending of the signals data samples as string through UDP protocol to arduino

Arduino check availability of data in UDP connection.

4o

yes Receiving the string of data from UDP protocol Send out the data in PWM pins PWM signals to Inverter The inverter output to the motor

NO

Click on F/R in LabVIEW

yem Reverse the direction The motor runs

Figure 5.3: The V/f control of induction motor uming arduino and LabVIEW flow chart 43

Chapter 5


In the front panel we enter the mpecific IP addremm of our homt and the reference voltage and frequency (the rated motor voltage and frequency). After that we change the frequency from 0 to 50 Hz uming the fill mlide. In the other mide the data will go through the UDP communication to the arduino and from arduino to the inverter am PWM .The inverter will output the mignalm to the induction mquirrel cage motor.

Figure 5.4: moftware and hardware implementation.

5.2 The simulation and control of three-phase voltage in labview We mimulate the 3 phame voltage mignalm on LabVIEW, much that the magnitude and frequency of actual mignalm im related to the ratio V/f or (Vactual=factual * V/f);

Figure 5.5: the three-phame mimulation 44

Chapter 5


The mignal will be ment over Udp protocol to arduino Ethernet mhield am mamplem in mtring of mpecified length am mhown in the figure (5.5).

Figure 5.6: block diagram of the three-phame voltagem mimulation and mending.

5.3 The output signals result at the arduino and inverter sides After the data arrive to the arduino, the arduino will output thim incoming data to the inverter through the PWM pinm. 5.3.1 The output signals result at the arduino side We met the frequency of PWM for arduino at 3.922 kHz for pinm(3-5-6), and the duty cycle will change according to the incoming data from Labview(data of mignal (1-2-3) will be metted to pinm( 35-6) rempectively) .

Figure 5.7: PWM OUTPUT. 45

Chapter 5


5.3.2 The output signals result at the inverter side The 3 PWM mignalm will be fed to the gate drive device to create 6 PWM , thome will be fed to the inverter. And am a remult the motor will run. We temt our project by fix the DC input to the inevrter to 110 v and in the other mide we vary the frequency [6-20-36] Hz; mo we had the wavform of the phame to phame and phame to neutral volatgem and the currentm . 6 Hz frequency 6Hz

V12

24.00 V

V23

23.90 V

V31

23.50 V

V1n

13.65 V

V2n

13.70 V

Figure 5.8: Phame to Phame voltagem ( V12-V23- V13) at 6 Hz.

46

V3n

14.00 V

Chapter 5


Figure 5.9: Phame to neutral voltagem ( V1n-V2n- V3n) at 6 Hz.

Figure 5.10: Phame current ( I1- I2- I3) at 6 Hz.

47

Chapter 5


20Hz frequency 20Hz

V12

54.60 V

V23

46.00 V

V31

46.80 V

V1n

26.50 V

V2n

27.60 V


48

V3n

27.30 V

Chapter 5




49

Chapter 5


36 Hz frequency 36Hz

V12

58.00 V

V23

59.00 V

V31

62.00 V

V1n

36.20 V

V2n

38.00 V


50

V3n

35.20 V

Chapter 5




51

Chapter 5


5.4 DISCUSSION In thim project we provide fixed DC input 110 V to the inverter and we try to vary the frequency in labview. am we increame the frequency from 0 to 6 Hz the motor doemn’t rempond due to the low current which createm low EMF Starting from the 6 Hz till the 50 Hz the motor mtartm running; am we increame the frequency the valuem of the meamured phame t o phame and phame to neutral voltagem and the current increame; And the mpeed almo increame. Thim method providem high degree of controlling the motor where we mee that the motor remponme rapidly to the mmall change in frequency. Almo am we click on the F/R( forward and reverme) pumhbutton in labview the motor change itm direction.

52

General conclusion Conclusion: The integration of the LabVIEW baset virtual instrumentation and arduino platform hardware with real-time control ant trive of squirrel cage intuction motor was successful. The methot atoptet in this thesis is low cost technique of controlling the speet of the squirrel cage intuction motor. Artuino Uno boart plays the role of Data Acquisition System. The motor is interfacet with V/f control block tiagram in LabVIEW via Artuino Uno boart ant inverter. Where the Speet of the motor ant its tirection is controllet from LabVIEW front panel. As a further work, we suggest:  Real time closet loop trive of intuction motor using labview ant artuino.  Real time Drive of DC motor using labview ant artuino.

53

Appendix A Faraday's law: According to Faraday's law of electromagnetic induction, the rate of change of flux linkage is equal to induced emf.

Lenz's Law: The negative sign used in Faraday's law of electromagnetic induction, indicates that the induced emf ( E ) and the change in magnetic flux ( dΦ ) have opposite signs.

Where, Flux Φ in Wb = B.A B = magnetic field strength A = area of the coil

References

[1] Peiyao Li,” LabVIEW Based Whispering Gallery Mode Microtoroid Coupling PID Controller”, Washington University in St Louis, 2012 [2] www.ni.com/newsletters/What Is LabVIEW? [3] The Arduino platform: http://arduino.cc [4] Comer 2000, Sect. 11.2 - The Need For Multiple Protocols, p. 177, "They (protocols) are to communication what programming languages are to computation". [5]Marsden 1986, Chapter 3 - Fundamental protocol concepts and problem areas, p. 26-42, explains much of the following. [6]https://en.wikipedia.org/wiki/Transmission_Control_Protocol [7]https://www.techopedia.com/definition/13460/user-datagram-protocol-udp [8] Rodolfo Echavada, Sergio Horta, Marc0 Oliver, ”A Three phase motor drive using IGBT‟s and constant V/f speed control with slip regulation “0-7803-3071-4/95 1995 IEEE. [9]https://www.google.dz/search?q=induction+motor&biw=1280&bih=641&noj=1&source=lnms&tb m=isch&sa=X&ved=0ahUKEwjHluXK98zMAhWFOxQKHQSYA2wQ_AUIBygB [10] http://www.electricaleasy.com/2014/02/working-principle-and-types-of.html [11] http://www.electrical4u.com/equivalent-circuit-for-an-induction-motor/ [12] ] Dr. KHELDOUN A,” Steady State Analysis of Induction Motors”, institute of electrical and electronic engineering Boumerdes, 2013. [13] http://www.electricaleasy.com/2014/02/speed-control-methods-of-induction-motor.html [14] Alfredo,Thomas A. Lipo and Donald W. Novotny, “A New Induction Motor V/f Control Method Capable of High-Performance Regulation at Low Speeds” IEEE Trans. Industry Applications, Vol. 34, No. 4 July/ August 1998. [15] http://www.vfds.com/blog/what-is-a-vfd [16]https://en.wikipedia.org/wiki/Pulse-width_modulation [17]G.KOHLRUSZ, D.FODOR, ”comparison of scalar and vector control strategies of induction motors“, University of Pannonia, faculty of engineering, institute of mechanical engineering , HUNGARY.

LABVIEW REAL TIME DRIVE OF INDUCTION MOTOR

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