DIRECT TORQUE CONTROL OF A THREE PHASE INDUCTION MOTOR USING HYBRID CONTROLLER A THESIS Submitted by RAJESHWARI JADI (Reg.No: M070105EE) In partial fulfillment for the award of the Degree of MASTER OF TECHNOLOGY IN ELECTRICAL ENGINEERING (Computer Controlled Industrial Power) Under the guidance of Mrs. SUNITHA R DEPARTMENT OF ELECTRICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY CALICUT NIT CAMPUS PO, CALICUT KERALA, INDIA 673601 May 2009
ACKNOWLEDGEMENT It gives me immense pleasure to profusely thank my guide Mrs. Sunitha R, Lecturer, Department of Electrical Engineering, for the unflagging zeal with which she guided me in carrying out the project work. It has been a proud privilege to work under her. I am deeply indebted for her invaluable guidance, constant encouragement, constructive criticism and inspiring suggestions throughout the course of my project work. I express my gratitude to Dr. Paul K. Joseph, Professor and Head of Electrical Engineering Department and Dr. Ashok S., Asst. Professor Department of Electrical Engineering for their valuable guidance and support to carry out this work. I also express my gratitude to the entire faculty and the staff members of Electrical Engineering Department for their cordial co-operation throughout the fulfillment of this work. Finally it gives me great pleasure to acknowledge all my friends who directly and indirectly helped me in the successfully completion of this work. Rajeshwari Jadi Date: NIT Calicut
DECLARATION I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published written by another person nor material which has been accepted for that of any other degree or diploma of any university or any institute of learning, except where due acknowledgment has been made by me in the text. Place: NIT Calicut Date: Name: Rajeshwari Jadi Reg.No: M070105EE
CONTENTS Contents Page.No ABSTRACT i LIST OF FIGURES ii LIST OF TABLES v MAJOR SYMBOLS vi LIST OF ABBREVIATIONS vii Chapter 1 INTRODUCTION 1 1.1 A Look Back On Electrical Machine Drives and Motivation 1 1.2 Project objective 3 1.3 Organization of the thesis 4 Chapter 2 LITERATURE SURVEY 5 Chapter 3 DIRECT TORQUE CONTROL OF INDUCTION MACHINE 9 3.1 Introduction 9 3.2 Principle of DTC 11 3.3 Space vector concept 11 3.4 Concept of direct torque control 14 3.4.1 Control of flux 15 3.4.2 Control of torque 16 3.4.3 Switching logic selection table 17 3.5 DTC controller modeling 20 3.6 Features, advantages and disadvantages 20 3.6.1 The main features of DTC 20 3.6.2 The main advantages of DTC 21 3.6.3 The main disadvantages of DTC 21 3.7 Summary 21 Chapter 4 DYNAMIC MODELLING OF INDUCTION MOTOR 22 4.1 Introduction 22 4.2 Mathematical modeling of induction motor with stator 22
4.3 Summary 26 Chapter 5 SPEED CONTROL USING DTC, HYBRID CONTROLLER AND SIMULINK MODELING 27 5.1 Introduction 27 5.2 DTC Controller modeling 27 5.3 Simulink Block diagrams 28 5.4 Speed control of IM with a speed sensor 29 5.4.1 Direct Torque Control of Induction Motor with PI controller 29 5.4.2 Fuzzy Logic Controller (FLC) 29 5.4.3 New Hybrid Controller 34 5.5 Sensor less speed control of Induction motor 36 5.6 Summary 37 Chapter 6 SIMULATION RESULTS AND DISCUSSIONS 38 6.1 Introduction 38 6.2 Conventional Direct Torque Control of Induction Motor 38 6.2.1 Start-up with No Load 38 6.2.2 Effect of Flux Hysteresis Band and Torque Hysteresis Band 40 6.3 Speed control of IM with a speed sensor 42 6.3.1 Speed control of IM with DTC/PI controller 42 6.3.2 Speed control of IM with DTC/PI type FLC controller 47 6.3.3 Speed control of IM with DTC/PD type FLC+I controller 53 6.3.4 Speed control of IM with Hybrid controller 58 6.4 Sensor less Speed control of IM 63 6.4.1 Speed control of IM with DTC/PI controller 63 6.4.2 Speed control of IM with DTC/PI type FLC controller 68 6.4.3 Speed control of IM with DTC/PD type FLC+I controller 72 6.4.4 Speed control of IM with Hybrid controller 76 6.5 Summary 80
Chapter 7 CONCLUSIONS AND FUTURE SCOPE OF WORK 81 7.1 Conclusions 81 7.2 Future scope of Work 81 REFERENCES 82
ABSTRACT This thesis presents the implementation of a high performance Direct Torque Control (DTC) of Induction Motor (IM) drives using a Hybrid controller. The objective of this work is to improve the speed control of 3-phase induction motors using a Hybrid controller. The newly developed hybrid control law consists of proportional-integral (PI) control at steady state, PI-type fuzzy logic control at transient state, and a simple switching mechanism between steady and transient states, to achieve satisfied performance under steady and transient conditions. The speed control of the IM is achieved by using a speed sensor and sensorless speed control. A complete simulation of the conventional DTC and closed-loop for speed control of a 3-phase IM will be tested using a software package Matlab/SimuLink. The features of the presented new hybrid controller will be highlighted by comparing the performance of various control approaches, including PI control, PI-type fuzzy logic control (FLC), and combination of PD-type FLC and I control, for DTC-based induction motor drives. It will be shown that the presented induction motor drive is with fast tracking capability, less steady state error, and robust to load disturbance while not resorting to complicated control method or adaptive tuning mechanism. Direct Torque Control (DTC) is one of the most excellent control strategies of torque control/ speed control in induction machine. It is considered as an alternative to the field oriented control (FOC) or vector control techniques. These two control strategies are different on the operation principle but their objectives are the same. In this method the stator voltage vectors will be selected according to the differences between the reference and actual torque and stator flux linkage. Here only the stator current and voltages will be needed to calculate the actual torque and the flux linkages. The status of the torque and flux linkages will be given to the optimal switching logic. This optimal switching logic will be used for the switching of the inverter. The inverter output will give the controlled voltage vectors that will be given to the induction motor. By properly adjusting the inverter switching the speed of the motor will be controlled. The performance of this control method will be demonstrated by simulations performed using a versatile simulation package, Matlab/Simulink. Direct Torque Control of induction machine with hysteresis controller and switching table inverter is developed and simulated in MATLAB-SIMULINK. Several numerical simulations have been carried out in a steady state and transient operation on a speed control mode. i