SPEED CONTROL OF THREE-PHASE INDUCTION MOTOR USING VARIABLE FREQUENCY DRIVE
ABSTRACT:
There are various methods for speed control of induction motors. This paper specifically describes one of the methods: speed control using variable frequency. The proposed system is a MATLAB Simulink model, which is a closed loop model designed to achieve desired speed control of a three-phase induction motor by varying its frequency. The Simulink model has four main blocks, namely the inverter, synchronous machine, proportional integral control and current hysteresis control. For accuracy of output results and simplicity, we have used dq to abc transformation block and sin function block. The inverter is comprised of six insulated-gate bipolar transistors (IGBTs), which are fired by gate pulses generated by current hysteresis control block. The inverter generates variable frequency and variable voltage output, which is given to motor terminals. The project presents the working principle of variable frequency drive (VFD), its performance, and the use of Pulse Width Modulation (PWM) in a three-phase inverter to control the frequency and thus the speed. The proposed method conformed to performance predictions and delivered the desired outputs.
TABLE OF CONTENTS
ABSTRACT ii
ACKNOWLEDGMENTS iii
LIST OF FIGURES v
LIST OF ABBREVIATIONS vi
1. INTRODUCTION 1
2. BACKGROUND AND BASIC UNDERSTANDING 2
3. VARIABLE FREQUENCY DRIVE OPERATING PRINCIPLE 8
4. COMPONENTS OF PROJECT MODEL 12
5. BLOCK DIAGRAM AND OUTPUT 19
6. CONCLUSION AND FUTURE WORK 23
REFERENCES 24
LIST OF FIGURES
1. Motor speed-torque chart 5
2. Basic block diagram of VFD 10
3. Hysteresis control block 17
4. Simulink model of VFD 21
5. Graph of desired speed 22
LIST OF ABBREVIATIONS
µA micro-Ampere
mA milli -Ampere
µV micro-Volt
mV milli-Volt
AC Alternating Current
BJT Bipolar Junction Transistor
CSI Current Source Inverter
DC Direct Current
DTC Direct Torque Control
EMF Electro Motive Force
HP Horse Power
IGBT Insulated Gate Bipolar Transistor
KW Kilo Watt
KV Kilo Volt
kHz kilo Hertz
LCI Load Commutated Inverter
LV Low Voltage
MOSFET Metal-Oxide Semiconductor Field Effect Transistor
MOSIGT Metal Oxide Semiconductor Insulated Gate Transistor
MV Medium Voltage
MW Mega Watt
PI Proportional Integral
PWM Pulse Width Modulation
SVPWM Space Vector Pulse Width Modulation
V/Hz Volts per Hertz
VFD Variable Frequency Drive
VSI Voltage Source Inverter
CHAPTER ONE: INTRODUCTION -
A variable-frequency drive (VFD) is a type of adjustable speed drive used in electro- mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage. VFDs are used in applications ranging from small appliances to the largest of mine mill drives and compressors. Over the last four decades, power electronics technology has reduced VFD cost and size and improved performance through advances in semiconductor switching devices, drive topologies, simulation, and control techniques, and control hardware and software. VFDs are available in several different low and medium
voltage AC-AC and DC-AC topologies. Variable speed drives are used for two main reasons: to improve the efficiency of motor-driven equipment by matching speed with the changing load requirements and to allow accurate and continuous process control over a wide range of speeds. This project specifically puts emphasis on one of the various methods of speed control of induction motor that is by changing frequency. The simulation of this VFD consists of four main units namely inverter, induction motor, PI (Proportional Integral) controller and hysteresis controller. In this project model, pulse width modulation technique is used to generate variable frequency.
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