Tijo Thomas

SEMINAR REPORT On RECTANGULAR WIRE WINDING AC MACHINES Submitted in partial fulfilment of the requirement for the award of the degree of BACHELOR OF TECHNOLOGY In ELECTRICAL AND ELECTRONICS ENGINEERING By TIJO THOMAS (Register Number: LPEC17EE028) Under the Guidance of Mrs. SUNILA. S ASSISTANT PROFESSOR Department of Electrical and Electronics Engineering COLLEGE OF ENGINEERING PATHANAPURAM DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING COLLEGE OF ENGINEERING PATHANAPURAM ELIKKATTOOR PO, KOLLAM – 689696 October 2019 DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING COLLEGE OF ENGINEERING PATHANAPURAM ELIKKATTOOR PO, KOLLAM – 689696 CERTIFICATE Certified that this is the bonafide report of seminar entitled ‘RECTANGULAR WIRE WINDING AC MACHINES’ by TIJO THOMAS (LPEC17EE028) in partial fulfilment for the award of Bachelor of Technology in Electrical and Electronics Engineering from APJ Abdul Kalam Technical University during the academic year-. Mrs. Sunila. S Mrs. Nisha Kuriakose Mr. Santhosh Raj R Seminar Guide Seminar Coordinator HOD Assistant Professor, Assistant Professor, Dept. of EEE Dept. of EEE, Dept. of EEE College of Engineering Pathanapuram College of Engineering Pathanapuram College of Engineering Pathanapuram ACKNOWLEDGEMENT I thank Professor Dr. S Ananda Resmi, our Principal, for helping me in completing this seminar. She also helped me implement the particular seminar. I thank her from the bottom of my heart for helping me in each step for completing the seminar. I express my sincere gratitude to Mrs. Sunila. S my seminar guide, Department of Electrical and Electronics engineering, for helping me conceive the idea of the seminar. I thank her from the bottom of my heart for helping me in each step for completing the seminar. I express my sincere gratitude to Mrs. Nisha Kuriakose, seminar coordinator; Department of Electrical and Electronics Engineering, for helping me conceive the ideas of the seminar. She also guided me to complete the particular seminar. I also express my gratitude for the valuable suggestions and advice during the course of work. I express my sincere gratitude to Mr. Santhosh Raj R, Head of the Department of Electrical and Electronics Engineering, for the valuable inputs he gave me for the completion of the work. I am happy to thank other faculty members, technical and administrative staff of the department of Electrical and Electronics Engineering for their valuable support and heartfelt cooperation. I thank my family and friends for giving me mental support and enabling me to work efficiently on the seminar. TIJO THOMAS ABSTRACT The rectangular wire winding AC electrical machine has drawn extensive attention due to their high slot fill factor, good heat dissipation, strong rigidity and short end-windings, which can be potential candidates for some traction application so as to enhance torque density, improve efficiency, decrease vibration and weaken noise, etc. In this paper, based on the complex process craft and the electromagnetic performance, a comprehensive and systematical overview on the rectangular wire windings AC electrical machine is introduced. According to the process craft, the different type of the rectangular wire windings, the different inserting direction of the rectangular wire windings and the insulation structure have been compared and analyzed. Furthermore, the detailed rectangular wire windings connection is researched and the general design guideline has been concluded. Especially, the performance of rectangular wire windings AC machine has been presented, with emphasis on the measure of improving the bigger AC copper losses at the high speed condition due to the distinguished proximity and skin effects. Finally, the future trend of the rectangular wire windings AC electrical machine is prospected. LIST OF CONTENTS 1. List of figures......................................................................................i 2. List of tables.........................................................................................ii 3. Chapter 1: Introduction..............................................................1 4. Chapter 2: Definition And Classification Of The Rectangular Wire Winding Ac Machine……………………………………….….3 2.1: Definition .........................................................................3 2.2: Classification.....................................................................4 5. Chapter 3: Production Craft Of The Rectangular Wire Winding………………………………………………………….5 3.1 Craft process............................................................................5 3.2 Inserting direction……………………………………………7 3.3 Insulation structure………………………………………..…8 6. Chapter 4: The Connection Of Rectangular Wire Winding………………………………………………………….10 7. Chapter 5: The Electromagnetic Performance And Thermal Management Of The Rectangular Wire Machine…………………….14 5.1 Electromagnetic performance………………………………..14 5.2 Thermal management………………………………..….15 8. Chapter 6: The Restriction Of The Ac Copper Losses Of The Rectangular Wire Winding Machine…………………………………..17 9. Chapter 7: Conclusion……………………………………………20 10. Reference ………………………………………………………….21 LIST OF FIGURES 2.1 The diagram of the different winding type. (a) Stranded winding. (b) Rectangular wire winding........................................................................3 2.2 The diagram of the different winding structure. (a) Hair-Pin winding. (b) I-Pin winding...........................................................................................4 3.1 The diagram of the craft process.............................................................8 3.2 The diagram of the different inserting direction. (a) Radical direction. (b) Axial direction.........................................................................................9 3.3 The diagram of the different windings insulation structure. (a) S type. (b) B type. (c) U type..............................................................................................................10 4.1 The diagram of the different windings connection pattern. (a) Connection pattern one. (b) Connection pattern two..............................................................................................................13 4.2 The end-winding of the rectangular wire windings. (a) Adjacent layer connection. (b) End-to-end connection. (c) One double layer connection. (d) Single layer and double layer hybrid connection…………………………………………………….…………………14 4.3 The diagram of the end-winding structure………………………....15 5.1 The comparison of different winding machines. (a) Pulled winding. (b) Hairpin winding. (c) Concentrated winding.......................................................................................................16 5.2 The comparison of different winding machines. (a) The tendency of the AC/DC resistance versus frequency. (b) The tendency of the total losses versus frequency.........................................................................................17 5.3 The diagram of the spray oil at the endwinding........................................................................................................18 6.1 Different conductors per slot. (a) Four conductors. (b) Six conductors...................................................................................................20 i Department of Electrical and Electronics Engineering, PEC 6.2 AC copper losses with different conductors per slot...............................................................................................................20 6.3 AC copper losses with different conductor phase arrangements. (a)AAAA. (b)ABBB. (c)AABB. (d)AAAB. (e)ABAB. (f)ABBA……………………………………………………………………………21 6.4. Hybrid conductors distribution............................................................21 ii Department of Electrical and Electronics Engineering, PEC LIST OF TABLES Table 2.1.........................................................................................4 Table 2.2………………………………………………………….5 Table 3.2………………………………………………………….9 Table 3.3…………………………………………………………11 iii Department of Electrical and Electronics Engineering, PEC CHAPTER 1: INTRODUCTION Now a days, the requirement of the machine applying on the traction application is more and more strict in terms of the torque density, efficiency and other electromagnetic performance. The rectangular wire winding AC machine has aroused more and more attention due to their high power density and high torque density. Different from stranded windings the copper conductor cross section area of rectangular wire winding machine is much bigger, which means that the choose of copper conductor material should pay more attention considering the impact of conductor bending, rebound and insulation damage. The rectangular wire winding machine has been quickly developed in recent years due to their superior characteristics, which can be widely used in electric vehicles (EV) or hybrid electrical vehicles (HEV). Compared with the traditional stranded windings machine, the basic characteristics of the rectangular wire winding AC machine are as follows: 1) Short end-windings, compact structure, and low cost. 2) High slot fill factor and high torque density. 3) Good heat dissipation between the conductor and the slot. 4) Strong rigidity and good steadiness. 5) Low torque ripples and low acoustic noise And the manufacturing techniques and production are also different from stranded windings. Especially, it is found that at the high speed condition the AC copper losses of the rectangular wire windings are much serious due to the distinguished proximity and skin effects, weakening the advantage of the high efficiency, and it is an intractable problem to restrict the bigger AC losses. In this paper, based on the complex production craft and the detailed electromagnetic performance, a comprehensive and systematical overview on the rectangular wire windings AC electrical machine is introduced. The organization of this paper is as follows. First, the definition and classification of the rectangular wire winding AC machine, the craft process, the inserting direction and the insulation type of the rectangular wire winding is discussed, focusing on the difficulties and 1 Department of Electrical and Electronics Engineering, PEC key points of the production, as well as the machine performance. The general connection guideline of the rectangular wire winding has been concluded, combined with the different end-winding connection. And the electromagnetic performance and thermal management between the traditional stranded winding machine and the rectangular wire winding machine has been compared and analyzed in terms of the on-load capability, efficiency and cost, etc. Then, aiming to resolve the bigger AC losses, numerous restricting measures have been provided and several conclusions are drawn and the development tendency is proposed. 2 Department of Electrical and Electronics Engineering, PEC CHAPTER 2: DEFINITION AND CLASSIFICATION OF THE RECTANGULAR WIRE WINDING AC MACHINE 2.1 Definition Consisted with the new winding structure, the rectangular wire winding AC machine has been quickly developed in recent years due to the superior characteristic, which can be widely used in the electrical vehicle (EV) or hybrid electrical vehicle (HEV) application, such as the Chevrolet Blot 2017 and Toyota Prius IV. Different from the traditional stranded winding machine, which the stator winding is formed by coiling the continuous round wire in slots. The rectangular wire winding machine refers in particular to the stator winding having the different conductor shape, different forming technic, different connection pattern is shown in figure 2.1. And the detailed difference between the stranded winding and the rectangular wire winding has been compared and concluded in Table 2.1. Fig 2.1 The diagram of the different winding type. (a) Stranded winding. (b) Rectangular wire winding. 3 Department of Electrical and Electronics Engineering, PEC TABLE 2.1 THE DISTINCTION OF DIFFERENT WINDING STRUCTURE 2.2 Classification Among the different production craft and the winding structure, there are two major rectangular wire winding, named as the Hair-Pin winding and the I-Pin winding, respectively, depicted in Fig 2.2, where one Hair-Pin winding can be considered as jointing two I-Pin windings. Fig 2.2 The diagram of the different winding structure. (a) Hair-Pin winding. (b) I-Pin winding. 4 Department of Electrical and Electronics Engineering, PEC According to the distinctive structure, the preforming craft existing in the Hair-Pin winding can be removed in the I-Pin winding. What’s more, the other production craft including the inserting, welding and twisting are also different. Especially, the Hair-Pin winding machine cooperating with shorter end-winding, compact structure and higher torque density. And the detailed difference between the Hair-Pin winding and the I-Pin winding has been compared and concluded in Table 2.2. TABLE 2.2 THE DISTINCTION OF DIFFERENT RECTANGULAR WIRE WINDING 5 Department of Electrical and Electronics Engineering, PEC CHAPTER 3: PRODUCTION CRAFT OF THE RECTANGULAR WIRE WINDING In this section, the production techniques in terms of the craft process, inserting direction and the insulation structure have been introduced, which not only have an influence of the production speeds and economic efficiency, but also play an important role in guaranteeing the reliability and performance of the machine. 3.1. Craft process Compared with the traditional stranded winding machine, the complexity and the accuracy requirement of production craft in the rectangular wire winding machine have been increased due to using the special materials and winding structure. The detailed production technology of the Hair-Pin winding machine has been researched with explaining the characteristic of each craft step, as shown in Fig 3.1, which pointed out that it is the key to keeping the reliability of end-winding welding and insulation. What’s more, the employ of the copper material with the bigger cross section area should take the negative influence of the bending and rebound into consideration. The main process is as follows: 1) Inserting the insulation paper into slots so as to produce the insulation stack, and the different slot insulation structure will be introduced hereafter; 2) Straightening the wire and stripping the paint, where the former aims to eliminate the plastic deformation and the manufacture error, and the latter aims to make the preparation of the conductors contacting such as welding craft; 3) Shaping and forming the wire, which means to produce the forming rectangular wire winding unit that will be inserted in the stator slots. 6 Department of Electrical and Electronics Engineering, PEC 4) Inserting the forming wire windings into the stator slots, which the detailed inserting location is determined by the conductor phase per slot, where the star of the slots in the traditional stranded can still be used. 5) Twisting and welding the end of rectangular wire windings. The twisting direction and welding not distribution have a vital impact of the end-winding structure. 6) Checking the reliability of the welding and insulation, avoiding the failure occurrence, such as the lack of welding and pseudo soldering. According to the mechanical stress and thermal distribution under different running conditions, an assessment of the machine reliability has been provided. And a method of quality monitoring of laser welding in the hairpin windings machine has been introduced. Compared with the traditional stranded winding machine, the maintainability of the rectangular wire winding machine has been decreased, i.e. once some trouble have been occurred, the overall machine wound be damaged. Nevertheless, cooperating with the proper craft, the rectangular wire winding machine has the advantage of high production rate, which is of benefit to mass production. 7 Department of Electrical and Electronics Engineering, PEC Fig 3.1 The diagram of the craft process 3.2. Inserting direction Relating to the production difficulty, the machine structure and performance, the inserting direction of the rectangular wire windings can be divided into two types, that is, the radical direction and the axial direction, depicted in Fig 3.2, where the radical inserting direction is same as to the traditional stranded windings which is inserted from the slot opening to the slot bottom. Therefore, limited to the bigger cross section area of the copper conductors, the slot shape of the rectangular wire winding machine is always the parallel slot structure consisting with the open slot, which cause the bigger torque ripples and acoustic noise, as well as deteriorated the AC copper losses. 8 Department of Electrical and Electronics Engineering, PEC Fig 3.2 The diagram of the different inserting direction. (a) Radical direction. (b) Axial direction The axial inserting direction, that is, the inserting direction is from one port of the stator stack steel, named as inserting port, can employ the semi-closed slot structure avoiding the open slot, which is useful to improve the torque ripples, acoustics noise and AC copper losses. However, the twisting can only be accomplished after the rectangular wires have been inserted in the slots, which furtherly raises the production difficulty. The electromagnetic performance of the machine consisting with the different slot opening shape and different winding structure has been compared and analyzed, shown as Table 3.2. TABLE 3.2 Comparison Of Different Inserting Directions 9 Department of Electrical and Electronics Engineering, PEC 3.3. Insulation structure The insulation performance is the foundation to keep the machine reliability. Considering the complex production craft, some scholars have designed different insulation structure with emphasis on the damage risk during the welding process. The insulation structure can be classified into three types, i.e. S type, B type and U type, shown in Fig 3.3, corresponding to Chevrolet Voltec 2011、Chevrolet Spark 2014、Chevrolet Blot 2017, respectively. The S type insulation structure has been gradually phased out due to the existence of the potential safety hazard in the insulation corner. The B type insulation structure has been widely used in recent years due to overcoming the safety problem. Especially, in view of the conductors per slot are on phase where the voltage difference between the conductors can be neglect, the insulation structure between the conductors can be eliminated, which can furtherly increase the slot fill factor and torque density. Fig 3.3 The diagram of the different windings insulation structure. (a) S type. (b) B type. (c) U type 10 Department of Electrical and Electronics Engineering, PEC General Electric Corporation has invented an insulation structure, where two U type insulation possessing inverse direction has been superposed cooperating with the slot width increase, which has the little influence of the machine performance. Table 3.3 compared the difference among the different insulation structure. TABLE 3.3 Comparison Of Different Insulation Structure 11 Department of Electrical and Electronics Engineering, PEC CHAPTER 4: THE CONNECTION OF RECTANGULAR WIRE WINDING The rectangular wire winding machine has applied the special winding connection configuration, that is, the rectangular wire distributed at the noninserting port has been connected with welding technology. And the corresponding port is named as the welding port. It is important to reasonably design the end-winding structure including the twisting direction and the welding location, which is related to the production difficulty and machine size, as well as the machine reliability and electromagnetic performance. Different from the traditional stranded windings which the coil turns is flexible, the copper conductor number per slot in the rectangular wire winding machine is fixed, which means the number of parallel paths should be more and more possible so as to fulfill the limitation of the inverter voltage and current. Especially, the winding connection should pay more attention to avoid the circulating currents within the parallel paths. Therefore, a lot of works have been done relating to the rectangular wire winding connection configuration. The different rectangular wire winding connection pattern has been provided with the general design guideline: 1) Determining the slot/pole combination of the stator, the number of conductor per slot, the number of parallel paths and the conductors phase per slot; 2) Determining the connection of the elementary winding, that is, the winding unit having the minimum conductors covered all the layers and all the slots per pole per phase; 3) Determining the coil pitch, twisting direction and the conductor welding relationship according to the elementary winding. Then the detailed winding can be designed and manufactured. Especially, the end-winding connection diagram of two different elementary windings with four conductors per slot, eight pole pairs and two slots per pole per phase has been drawn in Fig 4.1 (a) and (b), where the solid line and the dashed line represent the welding port and the inserting port of the stack steel, respectively. It can be seen that the 12 Department of Electrical and Electronics Engineering, PEC coil pitch of the two winding connection pattern is flexible so as to match the requirement of the elementary winding and guarantee the maximum parallel paths number without the circulating currents. What’s more, the rectangular wire winding shape, the twisting direction, welding position and the distribution of the outgoing lines are also different. Thus, the production difficulty, cost and reliability of the machine can be improved by considering the winding connection. 4.1 The diagram of the different windings connection pattern. (a) Connection pattern one. (b) Connection pattern two The rectangular wire winding machine has been produced in some famous corporations and applied into the EV/HEV application. Remy company has used the end-winding adjacent layer connection, which can be thought as connecting multiple double layer windings, except that jumper lines have been used to stride to different double layer. Different from Remy, Hatichi has invented the end-winding connection, which the conductors distributed at the slot opening and the slot bottom have been welded into one double layer. The winding connection in Honda Spirior can be considered as dividing all the conductors per slot into one double layer. Toyota Prius has the single layer and double layer hybrid winding connection, where the conductors distributed at the slot opening and bottom have been welded in 13 Department of Electrical and Electronics Engineering, PEC one layer. The different end-winding connection distributed at welding port mentioned above have been drawn in Fig 4.2, with 48 slots, 8 poles and 4 conductors per slot, where the three colours represent the three phases, respectively. Fig 4.2 The end-winding of the rectangular wire windings. (a) Adjacent layer connection. (b) End-to-end connection. (c) One double layer connection. (d) Single layer and double layer hybrid connection What’s more, in order to maintain the stability of the end-winding connection and optimize the distribution of the outgoing lines, some special equipment has been employed, such as the connection ring. The detailed forming 14 Department of Electrical and Electronics Engineering, PEC rectangular wire windings possessing different coil pitch, including fullpitch, short-pitch and long-pitch have been comprehensively studied with 72 slots, 6 conductors per slot and 3slots per pole per phase, where the endwinding connections have the different types. A creative winding stator which can solve the contradiction between the machine size and performance has been given. Furtherly, the type of forming winding and the production cost can be decreased, using the optimized end-winding connection. An improved Hair-Pin winding has been introduced, where the end-winding shape has been reasonably designed like the steps, shown in Fig 4.3, which can avoid the interference between the adjacent end-windings and furtherly decrease the machine size. Fig 4.3 The diagram of the end-winding structure 15 Department of Electrical and Electronics Engineering, PEC CHAPTER 5 THE ELECTROMAGNETIC PERFORMANCE AND THERMAL MANAGEMENT OF THE RECTANGULAR WIRE MACHINE 5.1. Electromagnetic performance In order to furtherly evaluate the rectangular wire winding machine, the performance of the machine in terms of the on-load capability, efficiency, flux-weakening characteristic and so on, has been systematically researched. The electromagnetic performance, production difficulty and the cost of the traditional stranded winding machine and the rectangular wire winding have been compared and analysed shown in Fig 5.1, where the red line and blue line represent the peak torque and the rated torque, respectively. It indicated that the hairpin winding machine due to the bigger slot fill factor can be the good choice to boost the torque density and power density. Fig 5.1 The comparison of different winding machines. (a) Pulled winding. (b) Hairpin winding. (c) Concentrated winding 16 Department of Electrical and Electronics Engineering, PEC Furthermore, the AC copper losses have also been investigated, the rectangular wire winding having the bigger conductor cross section lead the distinguished proximity and skin effects, which deteriorated the advantage of the smaller DC resistance especially at the high frequency condition. And the detailed DC resistance, AC resistance and total losses have been compared in Fig 5.2. Also the copper losses of the same machine except the different winding structure have been compared, which pointed out that the AC copper losses of the rectangular wire winding machine with 4 conductors per slot would excess the stranded winding machine when the speed is up to 4000rpm. 5.2 The comparison of different winding machines. (a) The tendency of the AC/DC resistance versus frequency. (b) The tendency of the total losses versus frequency 5.2. Thermal management : The cooling technic is the key to guarantee the machine quality, as overheating will result in degradation of insulation materials, magnet demagnetization and life loss of the machine. Thus, it has drawn more attention to the thermal management of the machine. At present, the water cooling and oil cooling are the two major cooling types of rectangular wire 17 Department of Electrical and Electronics Engineering, PEC winding machine. Especially, the spray oil cooling at the endwinding has been applied in the Chevrolet Voltec, depicted in Fig 13, which can dramatically improve the heat dissipation and enhance the torque density due to the bigger rectangular wire winding interval compared with the stranded winding. Fig 5.3 The diagram of the spray oil at the end-winding 18 Department of Electrical and Electronics Engineering, PEC CHAPTER 6 :THE RESTRICTION OF THE AC COPPER LOSSES OF THE RECTANGULAR WIRE WINDING MACHINE Considering the disadvantage of the AC bigger copper losses of the rectangular wire winding machine at the high speed condition, a lot of outstanding woks have been done. First, in order to investigate the origin of the AC copper losses, the relationship between of the machine structure parameters and the copper losses. The eddy-current losses and thermal analysis of an inverter-fed cage induction machine with a multi-conductor stator winding have been presented, which pointed out the installment of the magnetic wedges at the slot opening is a simple way to reduce the eddy-current loss. And the influence of the air gap size and the winding position on the copper losses has been researched, which indicated that increasing the distance between the winding and the air gap can improve the copper losses. And based on the foundation that the AC copper losses at the slot opening is serious, positioning the conductors near the slot bottom, reducing the slot opening size and applying the transposition method can reduce the copper losses effectively. The conductors shape has also an impact of the AC copper losses.In view of the conductor layer number per slot, the related research has been carried out, which pointed out that the increase of the conductor layer number can significantly decrease AC copper losses so as to improve the machine performance at the high speed condition. The AC copper losses of Chevrolet Spark 2014 and Chevrolet Bolt 2017 have been compared, using 4 conductors and 6 conductors per slot, respectively, where the diagram of the conductors distribution and the copper losses are depicted in Fig 6.1 and Fig 6.2. 19 Department of Electrical and Electronics Engineering, PEC 6.1 Different conductors per slot. (a) Four conductors. (b) Six conductors 6.2 AC copper losses with different conductors per slot Furthermore, some scholars have found that the conductors phase per slot has a vital impact of copper losses where six different conductor phase arrangements have been compared with 4 conductors per slot , shown in Fig 17, which indicated that conductor phase arrangements of ABAB and ABBA have the minimum AC copper losses. However, the conductor phase arrangement of the same phase has the most serious condition. Thus, it is necessary to reasonably design the winding connection taking the AC copper losses into consideration. 20 Department of Electrical and Electronics Engineering, PEC Fig 6.3 AC copper losses with different conductor phase arrangements. (a)AAAA. (b)ABBB. (c)AABB. (d)AAAB. (e)ABAB. (f)ABBA An optimal twisting criterion has been proposed which achieved the minimization of the copper losses due to parasitic circulating currents and reduced the number of twists and the length of the coils. Hybrid rectangular bar windings consisting of copper bars which are located close to slot bottom and aluminum bars which are located close to the slot opening have been introduced, which can not only decrease the copper losses, but also reduce the machine mass. Fig 6.4. Hybrid conductors distribution 21 Department of Electrical and Electronics Engineering, PEC CHAPTER 7: CONCLUSION This paper has presented the overview of the rectangular wire winding machine with a focus on the production craft and electromagnetic performance. What’s more, the winding type, inserting direction, insulation structure and winding connection have been researched, combined with the production technology. Furthermore, the electromagnetic performance and thermal management of the machine having the different winding structure have been compared and analyzed, which indicated the superior characteristic of the rectangular wire winding machine that satisfies the requirement of the EV/HEV application. Especially, in view of the weakness of the bigger AC copper losses, some methods have been provided so as to furtherly improve the machine efficiency. In a word, the rectangular wire winding machine has the vast development prospect due to the high torque density, high power density and so on. 22 Department of Electrical and Electronics Engineering, PEC REFERENCE [1] F. Momen, K. Rahman and Y. Son, "Electrical Propulsion System Design of Chevrolet Bolt Battery Electric Vehicle," in IEEE Transactions on Industry Applications, vol. 55, no. 1, pp. 376-384, Jan.-Feb. 2019. [2] M. Popescu, J. Goss, D. A. Staton, D. Hawkins, Y. C. Chong and A. Boglietti, "Electrical Vehicles—Practical Solutions for Power Traction Motor Systems," in IEEE Transactions on Industry Applications, vol. 54, no. 3, pp-, May-June 2018. [3] T. Ishigami, Y. Tanaka and H. 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Lee and H. Lee, "Optimum Design of the Electric Vehicle Traction Motor Using the Hairpin Winding," 2012 IEEE 75th Vehicular Technology Conference (VTC Spring), Yokohama, 2012, pp. 1-4. [29] L. Hao, "Design and analysis of IPM machine with bar wound fractional slot distributed winding for automotive traction application," 2013 IEEE Energy Conversion Congress and Exposition, Denver, CO, 2013, pp. 598-605. [30] S. Jurkovic, K. Rahman, B. Bae, N. Patel, and P. Savagian, “Next generation chevy volt electric machines; design, optimization and control for performance and rare-earth mitigation,” IEEE Energy Conversion Congress and Exposition(ECCE), pp-, 2015. 25 Department of Electrical and Electronics Engineering, PEC