PERMANENT MAGNET ASSISTED SYNCHRONOUS

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PERMANENT MAGNET ASSISTED SYNCHRONOUS RELUCTANCE MOTOR DESIGN AND PERFORMANCE IMPROVEMENT A Dissertation by PEYMAN NIAZI Submitted to the Office of Graduate…
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PERMANENT MAGNET ASSISTED SYNCHRONOUS RELUCTANCE MOTOR DESIGN AND PERFORMANCE IMPROVEMENT A Dissertation by PEYMAN NIAZI Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY December 2005 Major Subject: Electrical Engineering © 2005 PEYMAN NIAZI ALL RIGHTS RESERVED PERMANENT MAGNET ASSISTED SYNCHRONOUS RELUCTANCE MOTOR DESIGN AND PERFORMANCE IMPROVEMENT A Dissertation by PEYMAN NIAZI Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, Hamid A. Toliyat Committee Members, Prasad Enjeti Shankar. P. Bhattacharyya Reza Langari Head of Department, Costas Georghiades December 2005 Major Subject: Electrical Engineering iii ABSTRACT Permanent Magnet Assisted Synchronous Reluctance Motor Design and Performance Improvement. (December 2005) Peyman Niazi, B.S., Isfahan University of Technology (IUT), Isfahan, Iran; M.S., Khaje Nassir Toosi University of Technology, Tehran, Iran Chair of Advisory Committee: Dr. Hamid A. Toliyat Recently, permanent magnet assisted (PMa)-synchronous reluctance motors (SynRM) have been considered as a possible alternative motor drive for high performance applications. In order to have an efficient motor drive, performing of three steps in design of the overall drive is not avoidable. These steps are design optimization of the motor, identification of the motor parameter and implementation of an advanced control system to ensure optimum operation. Therefore, this dissertation first deals with the design optimization of the Permanent Magnet Assisted Synchronous Reluctance Motor (PMa-SynRM). Various key points in the rotor design of a low cost PMa-SynRM are introduced and their effects are studied. Finite element approach has been utilized to show the effects of these parameters on the developed average electromagnetic torque and the total d-q inductances. As it can be inferred from the name of the motor, there are some permanent magnets mounted in the rotor core. One of the features considered in the design of this motor is the magnetization of the permanent magnets mounted in the rotor core using the stator windings to reduce the manufacturing cost. iv At the next step, identification of the motor parameters is discussed. Variation of motor parameters due to temperature and airgap flux has been reported in the literatures. Use of off-line models for estimating the motor parameters is known as a computationally intensive method, especially when the models include the effect of cross saturation. Therefore in practical applications, on-line parameter estimation is favored to achieve a high performance control system. In this dissertation, a simple practical method for parameter estimation of the PMa-SynRM is introduced. Last part of the dissertation presents one advanced control strategy which utilized the introduced parameter estimator. A practical Maximum Torque Per Ampere (MTPA) control scheme along with a simple parameter estimator for PMa-SynRM is introduced. This method is capable of maintaining the MTPA condition and stays robust against the variations of motor parameters. Effectiveness of the motor design procedure and the control strategy is validated by presenting simulation and experimental results of a 1.5 kW prototype PMa-SynRM, designed and manufactured through the introduced design method. v To my dear dad and mom for their continuous support and devotion. To Shermin for her priceless love. Peyman Niazi vi ACKNOWLEDGMENTS My deep appreciation is first given to almighty God for blessing me with success in my efforts and blessing me with the erudition of several people whose advice, assistance and encouragement helped me throughout the completion of this thesis. I would like to express my heartfelt appreciation to my advisor, Prof. Hamid A. Toliyat, for his support and continuous help. His knowledge, invaluable guidance, understanding and patience inspired the completion of this thesis. I am very grateful to work with such an insightful and caring professor. My sincere gratitude also goes to the members of my graduate study committee: Prof. Prasad Enjeti, Prof. Shankar Bhattacharyya, and Prof. Reza Langari for their valuable advice and help through the years I spent at Texas A&M University. I would like to acknowledge the Department of Electrical and Computer Engineering at Texas A&M University for providing an excellent academic environment. Special thanks go to Ms. Tammy Carda, Ms. Linda Currin, Ms. Gayle Travis and Prof. Huang for all their efforts. Grateful acknowledgment is extended to LG Electronics Co. for their cooperation during this work and providing us with part of the experimental setup. I would like to extend my sincere appreciation to my fellow colleagues and friends at Advanced Electric Machine and Power Electronics Laboratory, past and present: Dr. Mehdi Abolhasani, Dr. S. M. Madani, Dr. Leila Parsa, Dr. Masuod Hajiaghajani, Dr. Sang-Shin Kwak, Salih Baris Ozturk, Sheab Ahmed, Steven Campbell, Salman Talebi, Rahul Khopkar, Bilal Akin, Dr. Namhun Kim, Dr. Lei Hao and Dr. Tilak vii Gopalarathnam. I honor their friendship and so many good memories throughout my time at Texas A&M University. Last but certainly not the least; I would like to thank my parents and my beloved Shermin, for their patience, care and endless devotion. I am very grateful to my dad for supporting me and teaching me to be strong. Also, I am deeply indebted to my mom for her patience and her prayers. I believe without them I would have been lost. I do not have the words to express my gratitude to Shermin for her emotional support and priceless love she has brought into my life through these years. During these years, whenever I was exhausted, hopeless and tired of struggling with the obstacles in my work, my prayers to God and the encouraging words of my loved ones were the only relief for me. No words can express my heartfelt gratitude to them for their endless love, care and sacrifice. viii TABLE OF CONTENTS Page ABSTRACT ..................................................................................................................... iii DEDICATION ...................................................................................................................v ACKNOWLEDGMENTS.................................................................................................vi TABLE OF CONTENTS ............................................................................................... viii LIST OF FIGURES..........................................................................................................xii LIST OF TABLES ..........................................................................................................xvi CHAPTER I INTRODUCTION......................................................................................1 A. Overview ...........................................................................................1 B. Evolution of Synchronous Reluctance Motor ...................................4 1. Conventional design....................................................................8 2. Segmental design.........................................................................9 3. Double barrier design ................................................................10 4. Axially-laminated design ..........................................................12 5. Transversally-laminated design.................................................14 6. Permanent magnet assisted SynRM ..........................................15 C. Modern Synchronous Drives...........................................................16 D. Research Objectives ........................................................................18 E. Thesis Outline .................................................................................20 II DESIGN OF A LOW COST PERMANENT MAGNET ASSISTED SYNCHRONOUS RELUCTANCE MOTOR .........................................22 A. Introduction .....................................................................................22 B. Mathematical Model of SynRM......................................................25 1. The d-q equation of synchronous reluctance machine ..............25 2. The steady state equations for a synchronous reluctance motor .........................................................................................27 3. Phasor equations for a synchronous reluctance machine ..........28 ix TABLE OF CONTENTS (Continued) CHAPTER Page 4. Torque expression for constant Volt/Hertz and constant current operation .......................................................................29 5. Maximum power factor .............................................................30 C. Design Criteria ................................................................................35 1. Computer aided design..............................................................36 i. Why we need computer aided design..................................36 ii. The nature of the design process .........................................37 2. Finite element approach ............................................................39 i. Energy functional ................................................................40 ii. Finite element formulation ..................................................43 iii. Boundary conditions ...........................................................46 v. Solution techniques .............................................................47 vi. Parameter from field............................................................49 D. Design Procedure ............................................................................51 1. Design strategy..........................................................................51 2. Design tool ................................................................................53 i. Effect of the single flux barrier width .................................55 ii. Effect of the flux barrier location........................................58 iii. Effect of the flux barrier insulation ratio.............................61 iv. Effect of the pole span on the pole pitch ratio.....................63 v. Effect of the air-gap length..................................................64 vi. Effect of the mechanical strutting .......................................65 E. Proposed Motor ...............................................................................68 F. Experimental Reslts.........................................................................77 G. Conclusion.......................................................................................80 III ON-LINE PARAMETER ESTIMATION OF PM-ASSISTED SYNCHRONOUS RELUCTANCE MOTOR .........................................82 A. Introduction .....................................................................................82 B. Parameter Identification Algorithms ...............................................83 C. Parameter Estimation ......................................................................84 D. Multiple Reference Frame...............................................................92 E. Modified Parameter Estimation Method .........................................94 1. Low pass filter...........................................................................94 F. Simulation and Experimental Results .............................................97 G. Conclusion.....................................................................................102 x TABLE OF CONTENTS (Continued) CHAPTER Page IV ROBUST MAXIMUM TORQUE PER AMPERE (MTPA) CONTROL OF PM-ASSISTED SYNCHRONOUS RELUCTANCE MOTOR ......................................................................103 A. Introduction ...................................................................................103 B. Maximum Torque Per Amper Control ..........................................106 C. MTPA Control System..................................................................110 D. Simulation Study ...........................................................................113 E. Experimental Results.....................................................................117 F. Conclusion.....................................................................................121 V CONCLUSION AND EXTENSION .....................................................122 A. Conclusion.....................................................................................122 B. Suggestions and Extensions ..........................................................126 REFERENCES...............................................................................................................128 VITA ..............................................................................................................................136 xi LIST OF FIGURES FIGURE Page 1- 1 Basic three phase, two pole reluctance variable motor, single saliency SynRM. ..5 1- 2 Basic three phase, two pole reluctance variable motor, double saliency switch reluctance motor. ....................................................................................................5 1- 3 Flux barrier type rotor of reluctance motor of the sixties .....................................6 1- 4 Four-pole conventional salient pole design............................................................9 1- 5 Four-pole isolated segmental rotor design. ..........................................................10 1- 6 Four-pole double-barrier rotor design ..................................................................12 1- 7 Four-pole axially-laminated rotor design.............................................................13 1- 8 Four-pole transversally-laminated rotor design ...................................................14 1- 9 Four-pole transversally-laminated PM assisted rotor design ...............................16 2- 1 Modern transversally laminated rotor for synchronous reluctance motors ..........23 2- 2 Axially laminated rotor for synchronous reluctance motors ................................23 2- 3 Two-pole synchronous reluctance motor .............................................................25 2- 4 Phasor diagram for synchronous reluctance machine. .........................................27 2- 5 Power factor vs. saliency ratio (K) of a synchronous reluctance motor when the motor is controlled with the maximum power factor control scheme............33 2- 6 Typical triangular finite element connected to other finite elements...................44 2- 7 Mesh generated by a Maxwell® ..........................................................................44 2- 8 Stator structure .....................................................................................................52 2- 9 Illustration of design parameters. .........................................................................54 2- 10 Modification of one flux barrier width.................................................................55 xii LIST OF FIGURES (Continued) FIGURE Page 2- 11 The torque of a single flux barrier rotor as a function of the rotor angle barrier width.....................................................................................................................57 2- 12 The maximum, minimum and average normalized torque values as a function of flux barrier width. ............................................................................................57 2- 13 The flux plots with flux barrier widths of a) 2mm, b) 8mm. ...............................58 2- 14 The direction of the flux barrier movement .........................................................59 2- 15 The torque of a single flux barrier rotor as a function of the rotor angle.............60 2- 16 The maximum, minimum and average torque as a function of the flux barrier location. ................................................................................................................60 2- 17 Rotor with 3 barrier and different insulation ratio, a) Wtot=0.2, b) Wtot=0.4, c) Wtot=0.8 ................................................................................................................62 2- 18 The maximum, minimum and average torque as a function of the insulation ratio.......................................................................................................................62 2- 19 The rotor structure with a pole span caused by the q-axis cut-out. ......................63 2- 20 The behavior of the torque as a function of the pole span ratio (τp/ τ) . ..............64 2- 21 Behavior of output torque as a function of the rotor angle and airgap.................65 2- 22 Behavior of output torque as a function of the rotor angle and radial rib width ..67 2- 23 Behavior of output torque as a function of the rotor angle and tangential rib width.....................................................................................................................67 2- 24 Rotor flux barriers geometry of optimized SynRM. ............................................69 2- 25 Proposed PMaSynRM. .........................................................................................69 2- 26 Magnetization of PM through the stator windings...............................................70 2- 27 Air gap flux density and PM flux while stator has one turn winding. .................71 xiii LIST OF FIGURES (Continued) FIGURE Page 2- 28 Proposed stator .....................................................................................................72 2- 29 Variation of d-q axes fluxes vs. stator current vector amplitude..........................73 2- 30 Calculated d-q axes inductances ..........................................................................73 2- 31 (Ld -Lq) vs. current for PMa-SynRM and SynRM................................................74 2- 32 Saliency ratio (Ld / Lq) vs. current........................................................................75 2- 33 Saturation effect due to the PM of the rotor.........................................................75 2- 34 Line-to-line back-EMF in PMa-SynRM. .............................................................76 2- 35 Torque-angle curves of the PMa-SynRM and SynRM. .......................................77 2- 36 Stator and rotor laminations of the proposed PMa-SynRM. ................................78 2- 37 Actual back-EMF line voltage at 1800 rpm. ........................................................79 2- 38 Torque-angle curves of the PMa-SynRM ............................................................79 3- 1 A four pole PMa-SynRM rotor. ...........................................................................87 3- 2 B-H characteristics of ferrite. ...............................................................................87 3- 3 Sensitivity of estimated Lq to the change of PM flux and stator resistor at 3600 rpm. .............................................................................................................89 3- 4 Sensitivity of estimated Ld to the change of stator resistor at 3600 rpm..............89 3- 5 Back-EMF due to permanent magnets in phase A. .............................................91 3- 6 Normalized harmonics of line-line back-EMF due to PMs .................................91 3- 7 Block diagram of control system along the parameter estimator.........................95 3- 8 Block diagram of the parameter estimator ...........................................................96 xiv LIST OF FIGURES (Continued) FIGURE Page 3- 9 d-q axes inductances and (Ld-Lq) vs. current. .....................................................96 3- 10 Approximated permanent magnets back-EMF used in the simulati
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