Induced Emf and Magnetic Flux

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Direct Torque and Indirect Flux Control of Brushless DC Motor with Non-sinusoidal Back-EMF without position sensor Abstract: In this paper, the position sensorless direct torque and indirect flux control (DTIFC) of BLDC motor with nonsinusoidal (non-ideal trapezoidal) Back-EMF has been extensively investigated using three-phase conduction scheme with six-switch inverter. In the literature, several methods have been proposed to eliminate the low-frequency torque pulsations for BLDC motor drives such as Fourier series analysis of current waveforms and either iterative or least-mean-square minimization techniques. Most methods do not consider the stator flux linkage control, therefore possible high-speed operations are not feasible. In this work,by using sliding mode observer the mechanical rotor position is removed. The proposed sensorless DTC method controls the torque directly and stator flux amplitude indirectly using d–axis current. Since stator flux is controllable, flux-weakening operation is possible. Moreover, this method also permits to regulate the varying signals. Simple voltage vector selection look-up table is designed to obtain fast torque and flux control. Furthermore, to eliminate the low-frequency torque oscillations, the new method has been used to estimate the electromagnetic torque. Simulation results confirm that the proposed three-phase conduction DTC of BLDC motor drive with six-switch inverter scheme. Keywords: Brushless dc (BLDC) motor, sliding mode observer, direct torque control (DTC), stator flux control, fast torque response. 1. Introduction Permanent magnet brushless machines are widely used for servo drives, ship propulsion systems and traction drives. Brushless AC (BLAC) drive back-EMF waveform is sinusoidal and is supplied with SPWM voltage source inverter, while the Brushless DC (BLDC) stator phase currents are rectangular and its back-EMF is trapezoidal due to concentrated windings. BLDC motor has better efficiency, higher torque density, lower cost and simpler structure, compared to BLAC motors. Further, BLAC drive requires an accurate encoder sensor, while BLDC drive needs to discrete position sensor such as Hall Effect device. Cost reduction of variable speed drives is growing interest over these years. Elimination of the position sensor are important subjects in low cost drives. Up to now, many researches have been reported to control of BLDC motor using six-switch three-phase inverter (SSTPI). Direct torque control (DTC) scheme was first proposed by Takahashi [1] and Depenbrock [2] for induction motor drives in the mid 1980s. More than a decade later, in the late 1990s, DTC techniques for both interior and surface-mounted synchronous motors (PMSM) were analyzed [3]. More recently, application of DTC scheme is extended to BLDC motor drives to minimize the low-frequency torque ripples and torque response time as compared to conventional PWM current controlled BLDC motor drives [4], [5] and [6]. In [4], [5] and [6], the voltage space vectors in a two-phase conduction mode are defined and a stationary reference frame electromagnetic torque equation is derived for surface-mounted permanent magnet synchronous machines with non-sinusoidal back-EMF (BLDC, and etc.). It is shown in [5] that only electromagnetic torque in the DTC of BLDC motor drive under two-phase Induced Emf and Magnetic Flux Induced Emf and Magnetic Flux Bởi: OpenStaxCollege The apparatus used by Faraday to demonstrate that magnetic fields can create currents is illustrated in [link] When the switch is closed, a magnetic field is produced in the coil on the top part of the iron ring and transmitted to the coil on the bottom part of the ring The galvanometer is used to detect any current induced in the coil on the bottom It was found that each time the switch is closed, the galvanometer detects a current in one direction in the coil on the bottom (You can also observe this in a physics lab.) Each time the switch is opened, the galvanometer detects a current in the opposite direction Interestingly, if the switch remains closed or open for any length of time, there is no current through the galvanometer Closing and opening the switch induces the current It is the change in magnetic field that creates the current More basic than the current that flows is the emfthat causes it The current is a result of an emf induced by a changing magnetic field, whether or not there is a path for current to flow Faraday’s apparatus for demonstrating that a magnetic field can produce a current A change in the field produced by the top coil induces an emf and, hence, a current in the bottom coil When the switch is opened and closed, the galvanometer registers currents in opposite directions No current flows through the galvanometer when the switch remains closed or open An experiment easily performed and often done in physics labs is illustrated in [link] An emf is induced in the coil when a bar magnet is pushed in and out of it Emfs of opposite signs are produced by motion in opposite directions, and the emfs are also reversed by reversing poles The same results are produced if the coil is moved rather 1/4 Induced Emf and Magnetic Flux than the magnet—it is the relative motion that is important The faster the motion, the greater the emf, and there is no emf when the magnet is stationary relative to the coil Movement of a magnet relative to a coil produces emfs as shown The same emfs are produced if the coil is moved relative to the magnet The greater the speed, the greater the magnitude of the emf, and the emf is zero when there is no motion The method of inducing an emf used in most electric generators is shown in [link] A coil is rotated in a magnetic field, producing an alternating current emf, which depends on rotation rate and other factors that will be explored in later sections Note that the generator is remarkably similar in construction to a motor (another symmetry) Rotation of a coil in a magnetic field produces an emf This is the basic construction of a generator, where work done to turn the coil is converted to electric energy Note the generator is very similar in construction to a motor 2/4 Induced Emf and Magnetic Flux So we see that changing the magnitude or direction of a magnetic field produces an emf Experiments revealed that there is a crucial quantity called the magnetic flux, Φ , given by Φ = BA cos θ, where B is the magnetic field strength over an area A, at an angle θ with the perpendicular to the area as shown in [link] Any change in magnetic flux Φ induces an emf This process is defined to be electromagnetic induction Units of magnetic flux Φ are T ⋅ m2 As seen in [link], B cos θ = B⊥, which is the component of B perpendicular to the area A Thus magnetic flux is Φ = B⊥A, the product of the area and the component of the magnetic field perpendicular to it Magnetic flux Φ is related to the magnetic field and the area over which it exists The flux Φ = BA cos θ is related to induction; any change in Φ induces an emf All induction, including the examples given so far, arises from some change in magnetic flux Φ For example, Faraday changed B and hence Φ when opening and closing the switch in his apparatus (shown in [link]) This is also true for the bar magnet and coil shown in [link] When rotating the coil of a generator, the angle θ and, hence, Φ is changed Just how great an emf and what direction it takes depend on the change in Φ and how rapidly the change is made, as examined in the next section Section Summary • The crucial quantity in induction is magnetic flux Φ, defined to be Φ = BA cos θ, where B is the magnetic field strength over an area A at an angle θ with the perpendicular to the area • Units of magnetic flux Φ are T ⋅ m2 • Any change in magnetic flux Φ induces an emf—the process is defined to be electromagnetic induction 3/4 Induced Emf and Magnetic Flux Conceptual Questions How the multiple-loop coils and iron ring in the version of Faraday’s apparatus shown in [link] enhance the observation of induced emf? When a magnet is thrust into a coil as in [link](a), what is the direction of the force exerted by the coil on the magnet? Draw a diagram showing the direction of the current induced in the coil and the magnetic field it produces, to justify your response How does the magnitude of ... IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 16, NO. 2, APRIL 2011 351 Direct Torque and Indirect Flux Control of Brushless DC Motor Salih Baris Ozturk, Member, IEEE, and Hamid A. Toliyat, Fellow, IEEE Abstract—In this paper, the position-sensorless direct torque and indirect flux control of brushless dc (BLDC) motor with nonsinu- soidal back electromotive force (EMF) has been extensively inves- tigated. In the literature, several methods have been proposed for BLDC motor drives to obtain optimum current and torque control with minimum torque pulsations. Most methods are complicated and do not consider the stator flux linkage control, therefore, pos- sible high-speed operations are not feasible. In this study, a novel and simple approach to achieve a low-frequency torque ripple-free direct torque control (DTC) with maximum efficiency based on dq reference frame is presented. The proposed sensorless method closely resembles the conventional DTC scheme used for sinusoidal ac motors such that it controls the torque directly and stator flux amplitude indirectly using d-axis current. This method does not require pulsewidth modulation and proportional plus integral reg- ulators and also permits the regulation of varying signals. Further- more, to eliminate the low-frequency torque oscillations, two actual and easily available line-to-line back EMF constants (k ba and k ca ) according to electrical rotor position are obtained offline and con- verted to the dq frame equivalents using the new line-to-line park transformation. Then, they are set up in the look-up table for torque estimation. The validity and practical applications of the proposed sensorless three-phase conduction DTC of BLDC motor drive scheme are verified through simulations and experimental results. Index Terms—Brushless dc (BLDC) motor, direct torque con- trol (DTC), fast torque response, low-frequency torque ripples, nonsinusoidal back electromotive force (EMF), position-sensorless control, stator flux control, torque pulsation. I. I NTRODUCTION T HE permanent-magnet synchronous motor (PMSM) and brushless dc (BLDC) motor drives are used extensively in several high-performance applications, ranging from servos to traction drives, due to several distinct advantages such as high power density, high efficiency, large torque to inertia ratio, and simplicity in their control [1]–[3]. In many applications, obtaining a low-frequency ripple-free torque and instantaneous torque and even flux control are of primary concern for BLDC motors with nonsinusoidal back Manuscript received May 30, 2009; revised September 11, 2009 and January 2, 2010; accepted February 6, 2010. Date of publication March 25, 2010; date of current version January 19, 2011. Recommended by Technical Editor M.-Y. Chow. S. B. Ozturk is with the Faculty of Engineering and Architecture, Okan University, Akfirat Campus, Tuzla/Istanbul 34959, Turkey (e-mail: salihbaris@ gmail.com). H. A. Toliyat is with the Department of Electrical and Computer Engineer- ing, Texas A&M University, College Station, TX 77843-3128 USA (e-mail: toliyat@ece.tamu.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMECH.2010.2043742 electromotive force (EMF). A great deal of study has been devoted to the current and torque control methods employed for BLDC motor drives. One of the VNU Journal of Science, Mathematics - Physics 25 (2009) 153-159 153 The effect of cobalt substitution on structure and magnetic properties of nickel ferrite Nguyen Khanh Dung 1, *, Nguyen Hoang Tuan 2 1 Industry University, Ho Chi Minh City, 12 Nguyen Van Bao, Ward 4, Go Vap District, Hochiminh city, Vietnam 2 Can Tho University, 3-2 Street, Can Tho city, Vietnam Received 15 August 2009 Abstract. A series of cobalt doped nickel ferrite with composition of Ni 1-X Co X Fe 2 O 4 with x ranges from 0.0 to 0.8 (in steps of 0.2) was prepared by using co-precipitation method and subsequently sintered, annealed at 600 0 C for 3h. The influence of the Co content on the crystal lattice parameter, the stretching vibration and the magnetization of specimens were subsequently studied. XRD and FTIR were used to investigate structure and composition variations of the samples. All samples were found to have a cubic spinel structure. TEM was used to study morphological variations. The results indicate that the average particle sizes are between 29÷35 nm. B-H hysteresis measurement was carried out at room temperature under field of 5 kOe and this measurement with the increase of Co 2+ concentration yields the monotonic increase of saturation magnetization (M S ) and coercive field (H C ). Ferrites with such behavior are important for magnetic recording media, microwave applications, environment and medical biology [1-3]. In view of this, we have studied the various properties of Co doped Ni ferrite. 1. Introduction NiFe 2 O 4 has cubic inverse spinel structure with Ni 2+ ions occupy octahedral B – site and Fe 3+ ions occupy both tetrahedral A – sites and octahedral B – sites [4]. Nickel ferrite has been prepared by standard ceramic route. That are particle size micrometer, low saturation magnetization and low coercivity. To our knowledge, the systematic investigation of the magnetic and electrical properties of Ni 1-X Co X Fe 2 O 4 with x varied from 0 to 0.8 in steps of 0.2 has not been reported so far. Further Ni-Co ferrite shows the good magnetostrictive properties among all the ferrite family. The studies on doping of good magnetostrictive material into the highly resistive nickel ferrite is one of the important phase for consideration of challenging magnetoelectric materials. Therefore by keeping this view in our mind we have proposed the studies on structural analysis and magnetic properties of Co–Ni ferrite with the above mentioned compositions by co – precipitation method, a new method for preparation of ferrite [5-6]. The results shown prepared Ni 1-X Co X Fe 2 O 4 powder ferrite had the particle sizes in nanometers and good magnetic properties: - Saturation Magnetization M S about 47-67 emu/g, ______ * Corresponding author. E-mail: nkdung@yahoo.com N.K. Dung, N.H. Tuan / VNU Journal of Science, Mathematics - Physics 25 (2009) 153-159 154 - Coercivity H C from 31 Oe (with x=0.0) to 871 Oe (with x=0.8), - Average longitudinal Magnetostriction λ // = (80-120).10 -6 - Magnetomechanic Quality Q=3100 (with x=0.0) 2. Experimental 2.1. Synthesis of Ni-Co powder ferrite A series of cobalt doped nickel ferrite with composition of Ni 1-X Co X Fe 2 O 4 with x ranges from 0.0 to 0.8 (in steps of 0.2) was prepared by co-precipitation method. For i DEFECT INDUCED NOVEL ELECTRICAL, MAGNETIC AND OPTICAL PROPERTIES OF TiO 2 THIN FILMS GROWN BY PULSED LASER DEPOSITION TARAPADA SARKAR (M.Tech., INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN SCIENCE DEPARTMENT OF PHYSICS NATIONAL UNIVERSITY OF SINGAPORE 2015 ii DECLARATION I hereby declare that thesis is my original work and it has been written by me in it’s entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has not also been submitted for any degree in any university previously. Tarapada Sarkar 15 August 2015 iii ACKNOWLEDGEMENTS The completion of my dissertation and subsequent Ph.D. has been a long journey. It was a journey of 4 yrs and 6 months which taught me a lesson that life doesn’t stand still, nor wait until you are finished. Many things have happened and changed in the time in which I have been involved with this project. Many have questioned whether I would finish my dissertation, and have doubted my commitment to it. I, on the other hand, losing confidence so many times that I could not keep count of, jumping here and there, computers crashing, needing to work as much as possible, so many sleepless night and pure frustration had to push on. With all this, I knew that I will complete my Ph.D. I just had to do it in my own time and on my own terms. I am grateful to a lot of people who have been instrumental in enabling me to reach my goal. It humbles me to acknowledge them. If I have to name one man for whom I am writing this thesis and this acknowledgement, he has to be my supervisor, Prof. T. Venkatesan. Venky, as he is called by one and all has been one of the biggest influences in my life. I consider myself to be extremely fortunate to have known, worked together with and been supervised by Venky. He has encouraged me in all my efforts and endeavours. He has managed to keep me motivated in my research. Venky has been extremely patient with me. Venky has had a tremendous contribution in my development as an individual. I also want to take this opportunity to acknowledge my co-supervisor, Prof. Ariando. Prof. Ariando has been extremely supportive and had taken keen interest in my research activities. Thanks to Prof J.M.D Coey for the invaluable feedback and inputs in my research work. I thank to Dr. Sankar Dhar and Dr. Arkajit Roy Barman, my mentors, who helped me a lot in my 1 st two years of Ph.D. They have been of extraordinary help iv in helping me manage my research work and giving direction to it. Their critical inputs have definitely helped me in taking my work to the next level. I thank Prof. A. Rusydi for his help in understanding the use of optical and x-ray spectroscopy for looking at defects in TiO 2 . They have been of tremendous help with experiments as well as theoretical understandings of my subject. I also thank Prof. H. Yang for the many fruitful discussions and the opportunities to work together. I want to thank Dr. K. Gopinadhan. Gopi has been the epitome of sincerity whom all graduate students in our lab have tried to idolize. Gopi has helped me a lot with transport measurements and helped me understand the intricate physics related. I would also want to thank Dr. S. Saha. We have been good friends in the few days that we have known each other. He has helped me with Raman measurements and with understanding of the data. I thank Dr. C.B. Tay- Chuan Beng is a very helpful individual and is always ready to help with PL measurements. I must thank Dr. W. Lú- Weiming has helped me a lot with SQUID measurements and also with PLD depositions. I have been fortunate enough to have some of the most wonderful, talented and helpful lab-mates. I want to thank Mallikarjuna rao Motapothula, Anil Annadi, Liu Zhiqi, Yong Liang Zhao, ELECTROMIGRATION-INDUCED FAILURE CHARACTERISTICS OF GMR SPIN-VALVES AND MAGNETIC MULTILAYERS FOR THE ELECTRICAL RELIABILITY OF SPINTRONIC DEVICES JING JIANG (M. Eng., Hefei University of Technology, P. R. China) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE January 2011 ACKNOWLEDGEMENT ACKNOWLEDGEMENT I would like to take this opportunity to thank all those who have helped and supported me in completing the work within this dissertation. First and foremost, I would like to give my utmost gratitude to my supervisor, Assistant Professor Seongtae Bae, for his kind and consistent concern, support and guidance in the project and also all the valuable discussion on the experimental results. He is a generous and caring mentor, always willing to offer a helping hand when I encountered difficulties over the past few years. Moreover, his active attitude and precise spirit of doing research have great influence on my personality. I appreciate his precious advice and counseling. Without his encouragement and understanding, I would not have been able to achieve this research goal. I am also grateful to be in a caring, supportive and cooperative research team. I’d like to thank Dr Sunwook Kim, Dr Howan Joo, Mr. Minghong Jeun, Ms. Naganivetha Thiyagarajah, Ms. Lin Lin, and Ms. Ping Zhang for their help in carrying out the experiment. I would especially like to thank Mr. Dinggui Zeng working closely with me in BML, Mr. Bee Ling Tan in DSI helping me the AES characterization and Dr Hojun Ryu from ETRI (Korea) helping me the TEM analysis. Their valuable assistance and support have been indispensable for my research work. I would also like to express my heartfelt appreciation for all the staffs in BML and ISML for their efforts in maintaining the functionality of the equipments, caring for the welfare of the students, and making our life here safe and pleasant. In addition, deep appreciation also goes to my friends in Singapore and China for having faith in me and i ACKNOWLEDGEMENT encouraging me to pursue my research goal. Last but not least, I would not have survived the PhD process without the support and understanding from my parents. Equally noble and important is my beloved husband Yongshan Yuan, who accompanies me throughout the most severe time. Without his patience, continuous support and encouragement, all these things would have never been possible. ii TABLE OF CONTENTS TABLE OF CONTENTS ACKNOWLEDGEMENT . i TABLE OF CONTENTS . iii SUMMARY vi LIST OF FIGURES . viii LIST OF TABLES . xiv CHAPTER INTRODUCTION . 1.1 Background and Motivation 1.2 Objectives and Work Done . 10 1.3 The Outline of this Thesis . 12 References . 14 CHAPTER ELECTROMIGRATION AND GIANT MAGNETORESISTANCE RELEVANT TOPICS . 20 2.1 General Aspects of Electromigration in Thin Films . 20 2.1.1 Theoretical Development of Electromigration . 20 2.1.2 Grain Boundary Diffusion and Atomic Flux Divergence 24 2.1.3 Structural Factor . 28 2.1.3 Current Crowding and Thermal Gradient Effects 32 2.1.4 Self Healing Effect . 37 2.2 Inter-diffusion in Magnetic Multi-layers ... Any change in magnetic flux Φ induces an emf the process is defined to be electromagnetic induction 3/4 Induced Emf and Magnetic Flux Conceptual Questions How the multiple-loop coils and iron ring... 2/4 Induced Emf and Magnetic Flux So we see that changing the magnitude or direction of a magnetic field produces an emf Experiments revealed that there is a crucial quantity called the magnetic. .. magnetic flux is Φ = B⊥A, the product of the area and the component of the magnetic field perpendicular to it Magnetic flux Φ is related to the magnetic field and the area over which it exists The flux