Effect of stator slot openings in axial flux permanent magnet machines

The width of the stator slot openings near the air gap has a large influence on the power loss in the stator core and in the permanent magnets of axial flux permanent magnet synchronous machines. On the one hand, the increase in stator slot openings results in lower power loss in the stator iron. On the other hand, it also results in increased loss in the permanent magnets. Also the torque is reduced for large but also for very small slot openings. This paper deals with axial flux machines of the YASA type: yokeless and segmented armature. It is shown that the slot openings contribute to an unequal flux density level over the different laminations in the stator core. The effect on the power loss and the flux distribution is shown

Slot opening displacement technique for cogging torque reduction of axial flux brushless DC motor for electric two-wheeler application

Introduction. Reduction of cogging torque is the crucial design consideration of axial flux brushless DC (BLDC) motor, particularly for low-speed applications. Aim. The slot opening displacement technique is presented in this article to reduce cogging torque in axial flux BLDC motors suitable for electric two-wheeler applications. Methods. Double rotor single stator configuration of axial flux BLDC motor is the most suitable for such vehicular applications. Initially double rotor single stator 250 W, 150 rpm axial flux BLDC motor is designed with stator slot opening in middle position and considered as reference motor for further analysis. To evaluate the cogging torque profile of the reference motor 3D finite element modeling and analysis are performed. The design is enhanced by dividing all stator teeth into groups and displacing the slot openings of each group in opposite direction with respect to the adjacent group. Results. The influence of slot opening displacement on cogging torque is evaluated with finite element modeling and analysis. As cogging torque is reduced from 1.23 N×m to 0.63 N×m, the slot opening displacement technique is found to be effective in reducing cogging torque of axial flux BLDC motor.Вступ. Зменшення зубчастого обертаючого моменту є важливим фактором при проектуванні безщіткових двигунів постійного струму (БЩДПС) з осьовим потоком, особливо для низькошвидкісних застосувань. Мета. У цій статті представлений метод зміщення отвору щілини для зменшення зубчастого моменту в БЩДПС з осьовим потоком, придатних для застосування в електричних двоколісних транспортних засобах. Методи. Конфігурація двигуна постійного струму з осьовим потоком з двома роторами та одним статором є найбільш підходящою для таких транспортних засобів. Початково спроєктований двороторний двигун БЩДПС з одним статором потужністю 250 Вт, 150 об/хв з осьовим потоком з отвором в статорному пазу в середньому положенні вважається еталонним двигуном для подальшого аналізу. Для оцінки профілю зубчастого обертаючого моменту еталонного двигуна виконується 3D-моделювання та аналіз методом скінченних елементів. Конструкція вдосконалена за рахунок поділу всіх зубів статора на групи та усунення пазових отворів кожної групи у протилежному напрямку по відношенню до сусідньої групи. Результати. Вплив зміщення отвору паза на зубчастий обертаючий момент оцінюється за допомогою моделювання та аналізу методом скінченних елементів. Оскільки зубчастий обертаючий момент зменшується з 1,23 Н×м до 0,63 Н×м, метод зміщення відкриття щілини виявився ефективним для зниження зубчастого обертаючого моменту двигуна БЩДПС з осьовим потоком

Eddy-current loss in the rotor magnets of permanent-magnet brushless machines having a fractional number of slots per pole

We develop an analytical model for predicting the eddy-current loss in the rotor magnets of permanent-magnet brushless machines that have a fractional number of slots per pole, when either all the teeth or only alternate teeth are wound, and in which the unwound teeth may be narrower than the wound teeth. The model enables the magnetic field distribution in the air gap and magnet regions to be determined, by neglecting the eddy-current redistribution effect and assuming that the eddy currents are resistance limited. It can account for space-harmonic magnetomotive forces (MMFs) resulting from the winding distribution and time-harmonic MMFs due to nonsinusoidal phase currents, as well as for the effect of curvature and circumferential segmentation of the magnets. We have validated the model by finite-element analysis, and used it to investigate the eddy-current loss in the magnets of three surface-mounted magnet brushless motors that have similar slot and pole numbers, and employ identical rotors but different stators, when they are operated in brushless ac (BLAC) and dc (BLDC) modes. We show that the stator winding configuration, as well as the operational mode, significantly influence the resultant eddy-current loss

Slot opening displacement technique for cogging torque reduction of axial flux brushless DC motor for electric two-wheeler application

Introduction. Reduction of cogging torque is the crucial design consideration of axial flux brushless DC (BLDC) motor, particularly for low-speed applications. Aim. The slot opening displacement technique is presented in this article to reduce cogging torque in axial flux BLDC motors suitable for electric two-wheeler applications. Methods. Double rotor single stator configuration of axial flux BLDC motor is the most suitable for such vehicular applications. Initially double rotor single stator 250 W, 150 rpm axial flux BLDC motor is designed with stator slot opening in middle position and considered as reference motor for further analysis. To evaluate the cogging torque profile of the reference motor 3D finite element modeling and analysis are performed. The design is enhanced by dividing all stator teeth into groups and displacing the slot openings of each group in opposite direction with respect to the adjacent group. Results. The influence of slot opening displacement on cogging torque is evaluated with finite element modeling and analysis. As cogging torque is reduced from 1.23 N×m to 0.63 N×m, the slot opening displacement technique is found to be effective in reducing cogging torque of axial flux BLDC motor.Вступ. Зменшення зубчастого обертаючого моменту є важливим фактором при проектуванні безщіткових двигунів постійного струму (БЩДПС) з осьовим потоком, особливо для низькошвидкісних застосувань. Мета. У цій статті представлений метод зміщення отвору щілини для зменшення зубчастого моменту в БЩДПС з осьовим потоком, придатних для застосування в електричних двоколісних транспортних засобах. Методи. Конфігурація двигуна постійного струму з осьовим потоком з двома роторами та одним статором є найбільш підходящою для таких транспортних засобів. Початково спроєктований двороторний двигун БЩДПС з одним статором потужністю 250 Вт, 150 об/хв з осьовим потоком з отвором в статорному пазу в середньому положенні вважається еталонним двигуном для подальшого аналізу. Для оцінки профілю зубчастого обертаючого моменту еталонного двигуна виконується 3D-моделювання та аналіз методом скінченних елементів. Конструкція вдосконалена за рахунок поділу всіх зубів статора на групи та усунення пазових отворів кожної групи у протилежному напрямку по відношенню до сусідньої групи. Результати. Вплив зміщення отвору паза на зубчастий обертаючий момент оцінюється за допомогою моделювання та аналізу методом скінченних елементів. Оскільки зубчастий обертаючий момент зменшується з 1,23 Н×м до 0,63 Н×м, метод зміщення відкриття щілини виявився ефективним для зниження зубчастого обертаючого моменту двигуна БЩДПС з осьовим потоком

Comprehensive analysis and evaluation of cogging torque in Axial Flux Permanent Magnet machines

Evaluation and minimization of cogging torque in Axial Flux Permanent Magnet (AFPM) machines become essential specially in direct drives for low speed applications. This paper presents a comprehensive analysis of the cogging torque in AFPM machines designed for low speed applications and mitigation methods are proposed. Evaluation methodologies of the cogging torque based on Finite Element Analysis (FEA) computations are discussed and applied to a double-sided, internal rotor, AFPM reference machine. From the performance comparison of Maxwell stress tensor and virtual work methods on the evaluation of cogging torque, it is possible to conclude that the latter overestimates the amplitude of the cogging torque into a considerable extent.info:eu-repo/semantics/publishedVersio

Investigation of novel multi-layer spoke-type ferrite interior permanent magnet machines

The permanent magnet synchronous machines have been attracting more and more attention due to the advantages of high torque density, outstanding efficiency and maturing technologies. Under the urges of mandatory energy efficiency requirements, they are considered as the most potential candidates to replace the comparatively low-efficient induction machines which dominate the industrial market. However, most of the high performance permanent magnet machines are based on high cost rare-earth materials. Thus, there will be huge demands for low-cost high-performance permanent magnet machines. Ferrite magnet is inexpensive and abundant in supply, and is considered as the most promising alternative to achieve the goal of low cost and high performance. In consideration of the low magnetic energy, this thesis explored the recent developments and possible ideas of ferrite machines, and proposed a novel multi-layer spoke-type interior permanent magnet configuration combining the advantages of flux focusing technique and multi-layer structure. With comparable material cost to induction machines, the proposed ferrite magnet design could deliver 27% higher power with 2-4% higher efficiency with exactly the same frame size. Based on the data base of International Energy Agency (IEA), electricity consumed by electric machines reached 7.1PWh in 2006 [1]. Considering that induction machines take up 90% of the overall industrial installation, the potential energy savings is enormous. This thesis contributes in five key aspects towards the investigation and design of low-cost high-performance ferrite permanent magnet machines. Firstly, accurate analytical models for the multi-layer configurations were developed with the consideration of spatial harmonics, and provided effective yet simple way for preliminary design. Secondly, the influence of key design parameters on performance of the multi-layer ferrite machines were comprehensively investigated, and optimal design could be carried out based on the insightful knowledge revealed. Thirdly, systematic investigation of the demagnetization mechanism was carried out, focusing on the three key factors: armature MMF, intrinsic coercivity and working temperature. Anti-demagnetization designs were presented accordingly to reduce the risk of performance degradation and guarantee the safe operation under various loading conditions. Then, comparative study was carried out with a commercial induction machine for verification of the superior performance of the proposed ferrite machine. Without loss of generality, the two machines had identical stator cores, same rotor diameter and stacking length. Under the operating condition of same stator copper loss, the results confirmed the superior performance of the ferrite machine in terms of torque density, power factor and efficiency. Lastly, mechanical design was discussed to reduce the cost of mass production, and the experimental effort on the prototype machine validates the advantageous performance as well as the analytical and FEA predictions

General Analytical Magnetic Model for Partitioned-Stator Flux-Reversal Machines With Four Types of Magnetization Patterns

International audienceA Partitioned Stator-Flux Reversal Permanent Magnet Machine (PS-FRPMM) is a new combination of a stator PM machine and a magnetically geared machine and has the specifications of both machines in terms of robust structure and torque density. In this paper a comprehensive 2-D analytical model is developed for PS-FRPMM based on subdomain technique. The presented model has the capability to accurately and quickly investigate the effects of design parameters on the machine performance. The 2-D analytical model is evaluated on two case studies with 12 stator teeth and 10 rotor poles, and 18 stator teeth and 13 rotor poles, with four different magnetization patterns. The influences of various design parameters such as the rotor slot width, slot opening width and the segment ratio of the PMs in the 2-segment magnetization pattern have been investigated on the quantities such as the instantaneous torque, torque ripple, Unbalanced Magnetic Force (UMF) and Electromotive Force (EMF). For evaluating the presented analytical model, 2-D Finite Element Method (FEM) with and without saturation effects has been used. The comparative study between the analytical and numerical models shows good agreement. Finally, a 3-D FEM has been used and the results of 2-D analytical model and 3-D FEM are compared in term of the accuracy and computational time. The results show that the presented model has lower computational time compared to the 2-D and 3-D FE method, while its accuracy is acceptable under different circumstances such as saturation

Comparison of three analytical methods for the precise calculation of cogging torque and torque ripple in axial flux PM machines

A comparison between different analytical and finite-element (FE) tools for the computation of cogging torque and torque ripple in axial flux permanent-magnet synchronous machines is made. 2D and 3D FE models are the most accurate for the computation of cogging torque and torque ripple. However, they are too time consuming to be used for optimization studies. Therefore, analytical tools are also used to obtain the cogging torque and torque ripple. In this paper, three types of analytical models are considered. They are all based on dividing the machine into many slices in the radial direction. One model computes the lateral force based on the magnetic field distribution in the air gap area. Another model is based on conformal mapping and uses complex Schwarz Christoffel (SC) transformations. The last model is based on the subdomain technique, which divides the studied geometry into a number of separate domains. The different types of models are compared for different slot openings and permanent-magnet widths. One of the main conclusions is that the subdomain model is best suited to compute the cogging torque and torque ripple with a much higher accuracy than the SC model