Torque imporvement of IPM motors with skewing magnetic designs

Nội dung text: Torque imporvement of IPM motors with skewing magnetic designs

1. Nghiờn cứu khoa học cụng nghệ Torque imporvement of IPM motors with skewing magnetic designs Bui Minh Dinh1, Dinh Hai Linh2* 1School of Electrical Engineering, Hanoi Unviversity of Science and Technology; 2College of Electromechanical and Civil Engineering, Vietnam National University of Forestry. *Email: hailinh.vfu@gmail.com. Received 22 September 2021; Revised 20 October 2021; Accepted 12 December 2021. DOI: ABSTRACT In this paper, a type interior permanent magnet synchronous motor designs is proposed for sport scooter application to improve constant torque wide speed performance. Interior Permanent Magnet machines are widely used in automotive applications for their wide-speed range operation and low maintenance cost. An existing permanent magnet motor (commercial QS Motor) is 3 kW-3000 rpm. In order to improve torque and power in wide speed range, a IPM electric motor 5.5 kW -5000 rpm can run up to 100 km/h: An Step-Skewing Interior Permanent Magnet motor alternatives is designed and optimized in detail with optimal magnetic segment V shape. The electromagnetic charateristics of Interior Permanent Magnet motors with V shape are compared with the reference Surface Permanent Magnet motor for the same geometry parameter requirements. Detailed loss and efficiency result is also analyzed at rate and maximum speeds. A prototype motor is manufactured, and initial experimental tests are performed. Detailed comparison between Finite Element Analysis and test data are also presented. It is shown that it is possible to have an optimized Interior Permanent Magnet motor for such high-speed traction application. This paper will figure out optimal angle of magnetic V shape for maximum torque and minimum torque ripple. Keywords: Interior Permanent Magnet; Torque, V shape, Skewing design. 1. INTRODUCTION Permanent magnet (PM) synchronous motors are quite popular in many applications due to their distinctive benefits such as high efficiency, high torque density, smaller size, and relatively low current requirements [1-3]. They also have low vibration, and low acoustic noise levels compared to other types of electric motors [4-8]. It is also possible to obtain high torque quality in PM motors both at low and high speeds. Such issue is quite critical especially for high performance application such as servo motors, spindle motors and direct drive applications. There exist various methods in order to obtain high torque quality in PM motors [2-4, 6, 7]. These methods include design modifications both at rotor and stator sides such as using different slot/pole combinations, skewing rotor or stator, magnet grouping, adding auxiliary slots and so on. This paper focuses on the development of an Interior Permanent Magnet (IPM) spindle motor for E Scooter applications. An IPM motor is designed with step-skewing and V shape of permanent magnet . A finite element analysis (FEA) analyses are performed, and some parametric optimizations are realized to achieve better torque quality and performance. Comparison of the designed spindle motors with respect to the reference Surface Permanent Magnet (SPM) motor are also provided. Prototype motor is manufactured, and experimental tests are performed. It is shown that it is possible to have an improved IPM motor for such spindle application. 2. SPM AND IPM DESIGN In order to calculate rotor diameter and Slot length of IPM, an analytical equation can solve and give the result, the most important factor are L/D ratio and torque density must be estimated in optimal range. Tạp chớ Nghiờn cứu KH&CN quõn sự, Số 76, 12 - 2021 3
2. Kỹ thuật điều khiển & Điện tử T  D2 L. TRV (1) 4 stk 3 Where, D: Outter diameter rotor , Lstk: Stack length, TRV = 25 ữ 35 kNm/m The program is divided into three main parts: analytical calculation, exporting drawing and magnetic simulation. There are also some supporting parts including material library which also associate with FEMM library. Figure 1. Program Structure. Table 1. Motor specifications. No Parameters Value 1 Power (W) 5000 2 Speed (rpm) 0 ữ 5000 3 Stator (Slots) 36 4 Rotor (poles) 8 5 Rotor Outer Diameter (mm) 98 6 Stator Outer Diameter (mm) 150 7 Stack length (mm) 90 In this study, a SPM 5 kW- 3000 rpm surface mounted PM motor is used as a reference motor. Firstly, initial sizing of the motor is carried out. Electromagnetic analyses are performed for the reference motor and then two different IPM rotor designs are realized. I type IPM motor design alternatives are investigated in detail using FEA and several parametric optimizations are 4 B. M. Dinh, D. H. Linh, “Torque imporvement of IPM motor with skewing magnetic design.”
3. Nghiờn cứu khoa học cụng nghệ also performed before finalizing the design. The IPM and SPM motor specifications used in this study are given in table I. Reference motor is an integral slot motor with 36/8 slot/pole combinations. The layout of stator and rotor lamination is shown in figure 2. The 36 stator slots, 8 magnetic poles and the distributed winding double layers have been designed in below figure. Figure 2. Rotor Design of IPM. In order to minimize torque ripple, 4 step skewing rotor was designed in figure 3. The skewing angle is from -1.875 mechnical degrees to +1,875 mechnical degrees based on many steps running. Figure 3. Four Slices step-skewing rotor of IPM. Electromagnetic material for stator, rotor and permanent magnetic have applied for this design as in table 2. The IPM weight of magnet is lower 0.2 kg and the stator core and winding are keep the same. Table 2. IPM dimenssion parameters. No Parameters Value No Parameter Value 1 Stack height (mm) 90 10 Number of magnets poles 8 2 Gap Length (mm) 0.5 11 Outside diameter rotor (mm) 100 3 Number of Slots stator 36 12 Inside diameter rotor (mm) 40 4 Outside diameter stator (mm) 150 13 Thickness of magnets (mm) 3 5 Inside diameter stator (mm) 101 14 Position of magnet (mm) 37 6 Tooth width stator (mm) 4 15 Width of magnets (mm) 14 7 Slot opening width stator (mm) 1 16 Angle of magnets 1200 8 Core back width stator (mm) 9.8 17 Clearance between Magnets (mm) 3 9 Tooth tang depth stator (mm) 1,5 - - Tạp chớ Nghiờn cứu KH&CN quõn sự, Số 76, 12 - 2021 5
4. Kỹ thuật điều khiển & Điện tử With optimal skewing angle, electromagnetic torque and efficiency performances have been evaluated in follow plotes. The torque and efficiency curves vs speed with skewed and non- skewed magnetic rotor are compared in fig 4. Figure 4. Compare the torque, efficiency, power and copper loss of skewed and non-skewed magnetic rotor IPM. Table 3. Performance comparison. SPM-Non Parameters IPM- Skewed Skewed Unit Average torque 24.014 24.985 Nm Average torque 23.83 24.81 Nm Torque Ripple 2.6991 1.098 Nm Torque Ripple [%] 11.231 4.3998 % Electromagnetic Power 5033.5 5226.5 Watts Input Power 5259.3 5804.5 Watts Output Power 4853.7 5086.9 Watts Total Losses (on load) 405.63 717.58 Watts System Efficiency 87.638 92.287 % Shaft Torque 63.175 64.288 Nm Average torque, output power, efficiency of IPM with are shown in table 3 at speed 3000 rpm. The surface magnetic mount structure is not robust at high speed due to radial forces. Efficiency of SPM is 87.6% and current density is 11 A/mm2 is quite high. So cooling method must be considered. The stator and rotor dimensions are important for analytical model to calculate electromagnetic performance such as toque, power and efficiency. 6 B. M. Dinh, D. H. Linh, “Torque imporvement of IPM motor with skewing magnetic design.”
5. Nghiờn cứu khoa học cụng nghệ Constant torque wide speed performances of IPM with skewed and non skewed magnet have calculated in figure 5. The torque-speed curves of IPM skewing is prolonged than the IPM -non skewd curves with limited current of 25A/72VDC because the back EMF waveforms is smaller and more sinusoidial. Figure 5. IPM and SPM. Figure 6 shows back-EMFs at maximum speed 5000 rpm at no load as fig 2. Harmonic Distortion Back EMF Phase Voltage is 1.6%. Figure 6. Back EMF waveform. Figure 7 shows torque ripple waveform of 2.5% and average torque is 25 Nm at maximum speed 5000 rpm. Figure 7. Torque waveform versus electric angle. Tạp chớ Nghiờn cứu KH&CN quõn sự, Số 76, 12 - 2021 7
6. Kỹ thuật điều khiển & Điện tử Figure 8. Shaft torque versus electric angle and Efficiency. The torque ripple of the V shape IPM prototype model is approximately 2% less than torque ripple results of the IPM model with 4 step-slice skewing. If increasing number of magnet segments, the torque ripples can be more reduced however the manufactures are facing some challenges in placing magnet pieces by machanical jig or frame. An efficiency map of IPM proposal is plotted in peak torque and peak power modes with maximum DC current of 100A and 72 VDC in figure 8. Maximum efficiency loop of 97% is possible achieve at high speed and low torque. This effect is from V shape magnet angle design. 3. IPM MANUFACTURED AND EXPERIMENTAL TEST IMPLEMENTATION The rotor lamination and interrior magnet core were implemented by wire cutting and jig assembly in figure 9. Figure 9. IPM rotor. The IPM V shape magnet is manufactured and tested to validated back EMF in no-load and average torque at maximum speed. Rotor lamination have manufacture by wire cutting before placing magnet and shaft assembly. The back-to-back test bench of DC generator and IPM 5 kW IPM motor has setup as figure 10. Figure 10. IPM motor test bench. The whole hardware of torque and speed sensors was built together, and torque results are displayed in interface control as figure 11. 8 B. M. Dinh, D. H. Linh, “Torque imporvement of IPM motor with skewing magnetic design.”
7. Nghiờn cứu khoa học cụng nghệ Figure 11. IPM motor control interface. The torque and speed curves have been tested and measured in dynamic condition with pre- setup speed and current. The maximum speed test result was implemented at 5000 rpm and average torque of 15 N.m as figure 12. Figure 12. Torque and speed results. Full torque vs speed of the IPM motor under different load and voltage by auto run test system as EU drive cycle will be obtained by industrial lab and test bench. 4. CONCLUSION In this study, two different types of interior permanent magnet motor and surface magnet moted designs are investigated for E sport Scooter. An existing SPM motor is used as a reference motor. Different V shape IPM motor topologies are developed for the same application. Extensive FEA analyses and parametric optimizations are performed, and results are compared with the reference SPM motor. V-type IPM motor is manufactured and tested since it has better torque quality and wider constant power region. Detailed comparison between FEA and test data are presented. It is seen that good agreement between the test data and FEA simulations are obtained. It is concluded that v-type IPM motor has more benefits as opposed to SPM and conventional spoke type IPM Tạp chớ Nghiờn cứu KH&CN quõn sự, Số 76, 12 - 2021 9
8. Kỹ thuật điều khiển & Điện tử motor for such high speed E sport motorbycycle applications. The IPM motor is designed with step-skewing and V shape of permanent magnet at 5000 rpm and has average torque equal 15N.m REFERENCES [1]. Yunpeng Si; Yifu Liu; Chunhui Liu; Zhengda Zhang; Mengzhi Wang; Qin Lei, “A Constant Current Based Interior Permanent Magnet (IPM) Synchronous Motor Drive Control Strategy”, IEEE Energy Conversion Congress and Exposition, INSPEC Accession Number. 20135262 (2020), pp. 2641-2648. [2]. Junqiang Zheng; Wenxiang Zhao; Christopher H. T. Lee;Jinghua Ji;Gaohong Xu, “Improvement torque performances of interior permanent-magnet machines”, CES Transactions on Electrical Machines and Systems, Volume. 3, Issue. 1(2019), pp.12-18. [3]. Jonas Bruckschlửgl; Johannes Germishuizen; Andreas Kremser, “Design optimisation of IPM machines considering the constant power range”, 19th International Symposium on Electromagnetic Fields in Mechatronics, Electrical and Electronic Engineering, INSPEC Accession Number. 19632550 (2019). [4]. Q. Chu and Z. Q. Zhu, “Reduction of On-Load Torque Ripples in Permanent Magnet Synchronous Machines by Improved Skewing,” IEEE Trans. On Magnetics, vol. 49, no.7 (2013), pp. 3822- 3825. [5]. T. Li and G. Slemon, “Reduction of Cogging Torque in Permanent Magnet Motors,” IEEE Trans. On Magnetics, vol. 24, no.6 (2013), pp. 2901-2903, Jul. [6]. X. Ge, Z. Q. Zhu, G. Kemp, D. Moule and C. Williams, “Optimal step-Skew Methods for Cogging Torque Reduction Accounting for Three-Dimensional Effect of Interior Permanent Magnet Machines,” IEEE Trans. On Energy Conversion, vol. 32, no. 1 (2017), pp. 222-232. [7]. J. Urresty, J. Riba, L. Romeral and A. Garcia, “A Simple 2-D FiniteElement Geometry for Analyzing Surface-Mounted Synchronous Machines With Skew Rotor Magnets,” IEEE Trans. On Magnetics, vol. 46, no.11 (2010), pp. 3948-3954. [8]. R. Islam, I. Husain, A. Fardoun and K. McLaughlin, “Permanent Magnet Synchronous Motor Magnet Designs With Skewing for Torque Ripple and Cogging Torque Reduction,” IEEE Trans. Ind. Appl., vol. 45, no. 1 (2009), pp. 152-160. TểM TẮT CẢI THIỆN Mễ MEN ĐỘNG CƠ ĐỒNG BỘ NAM CHÂM VĨNH CỬU GẮN CHèM VỚI NAM CHÂM RÃNH NGHIấNG Trong bài bỏo này, động cơ đồng bộ nam chõm vĩnh cửu gắn chỡm ứng dụng cho xe mỏy điện thể thao được thiết kế nhằm cải thiện khả năng mụ men khụng đổi ở dải tốc độ cao. Động cơ động cơ đồng bộ nam chõm vĩnh cửu gắn chỡm được sử dụng rộng rói trong ứng dụng cho ụ tụ nhờ khả năng giữ cho mụ men khụng đổi ở tốc độ cao và chi phớ bảo dưỡng thấp. Động cơ nam chõm vĩnh cửu đó được thương mại húa của hóng QS Motor cú thụng số kỹ thuật là 3 kW-3000 vũng/phỳt. Động cơ đồng bộ nam chõm vĩnh cửu gắn chỡm được thiết kế là 5,5 kW -5000 vũng/phỳt,cú thể chạy tới 100km/h bằng việc tối ưu gúc sếp nam chõm chữ V và ghộp dạng chộo rónh. Đặc tớnh điện từ của động cơ đồng bộ nam chõm gắn chỡm cú nam chõm chữ V được so sỏnh với động cơ đồng bộ nam chõm gắn bề mặt khi cú cựng một thụng số kớch thước hỡnh học. Kết quả về hiệu suất và tổn hao sắt được phõn tớch ở dải tốc độ cực đại . Một mẫu động cơ nam chõm vĩnh cửu theo thiết kế tối ưu đó được chế tạo và đo kiểm đỏnh giỏ. Kết quả phõn tớch theo phương phỏp phõn tớch phần tử hữu hạn đươc so sỏnh với kết quả thử nghiệm. Kết quả thực nghiệm khảng định sự tối ưu húa của thiết kế động cơ nam chõm vĩnh cửu ở dải tốc tộ cao. Bài bỏo cũng đó đưa ra gúc sếp nam chõm tối ưu là để tối đa mụ men trung bỡnh và tối thiểu mụ men nhấp nhụ. Từ khúa: Động cơ đồng bộ nam chõm vĩnh cửu; mụ men, hỡnh dạng chữ V; thiết kế chộo rónh. 10 B. M. Dinh, D. H. Linh, “Torque imporvement of IPM motor with skewing magnetic design.”