Slot-pole Combinations Research Articles

Analysis and Application of Two-Layer Unconventional Windings for PM-Assisted Synchronous Reluctance Motors

This paper presents a new winding configuration theory of conventional and unconventional slot-pole combinations that can be used to configure windings with any slot-pole combination. First, various two-layer windings can be divided into conventional balanced winding (CBW), unbalanced winding (UBW), unconventional even slot winding (UESW) and unconventional odd slot winding (UOSW). In addition, the winding configuration can be divided into two steps—slot sorting and slot distributions to phases—and the rule of winding distribution and connection of the four kinds of windings is given. Moreover, there are four models established corresponding to the four kinds of windings. The air-gap flux density and harmonic of models with double layer flux-barrier PM-assisted rotor and without flux-barrier rotor are analyzed and compared using two-dimensional transient finite element analysis (FEA). The effect of stator magneto motive force (MMF) on torque performance affected by winding configuration is analyzed by comparing air gap magnetic density under two kinds of rotors. The simulation of torque shows that UBW, UESW, and UOSW have a certain reducing effect on torque ripple in PMASynRM. Meanwhile, a brief comparison is made in terms of radial forces and power losses; the effects produced by UBW, UESW, and UOSW compared to CBW in these two aspects are acceptable.

Analysis of Split-Tooth Stator-Slot Permanent-Magnet Machines With Different PM Arrangements

In this paper, the split-tooth stator-slot permanent-magnet (ST-SSPM) machines with different PM arrangements are comprehensively analyzed. Four types of ST-SSPM machines are first introduced and classified by the positions and polarities of PMs. Then, the operation principles are elaborated and the slot-pole combinations are derived from the view of field modulation theory. Besides, four types of ST-SSPM machines with different slots and rotor poles are globally optimized to achieve maximum torque and minimum torque ripple. Furthermore, the electromagnetic performances of the optimal designs are thoroughly analyzed by using the finite-element analysis (FEA), including the cogging torque, back-EMF, steady torque, PM utilization ratio, loss, efficiency, and PM demagnetization. Finally, some conclusions are drawn based on the optimal designs and analyzed results.

Design and Validation of an Unconventional 39-Slot PM Synchronous Motor With Asymmetric and Unbalanced AC Windings

One of the main issues in manufacturing rotors for integer slot surface-mounted permanent magnet (PM) synchronous motors is the rotor skew. Motor manufacturers typically prefer to avoid skewing due to the added complexity and the difficulty in controlling the accuracy of the skewing and achieving the required outcome. This article proposes a design that minimizes torque ripple without using any kind of skewing in the rotor using asymmetric ac windings with unconventional stator slot-pole combinations. First, feasible slot and pole combinations are reviewed for PM synchronous motors. Theory behind unconventional asymmetric and unbalanced ac winding PM motors is presented. A lumped-parameter magnetic equivalent circuit for such unconventional stator is provided for a 1.7-kW PM motor. Detailed 2-D finite element analysis (FEA) is performed and compared with the lumped parameter model. A prototype motor is manufactured, and open-circuit as well as full-load tests are performed. Good agreement between the analytical, FEA, and test results is obtained.

Multi-Phase Fractional-Slot PM Synchronous Machines with Enhanced Open-Circuit Fault-Tolerance: Viable Candidates for Automotive Applications

This paper deals with the winding arrangement of multi-phase fractional-slot permanent magnet (PM) synchronous machines (FSPMSMs), with emphasis on the enhancement of their open-circuit fault-tolerance capability. FSPMSMs are reputed by their attractive intrinsic fault-tolerance capability, which increases with the number of phases. Of particular interest is the open-circuit fault-tolerance capability, which could be significantly enhanced through the parallel connection of the coils or suitable combinations of the coils of each phase. Nevertheless, such an arrangement of the armature winding is applicable to a limited set of slot-pole combinations. The present work proposes a design approach that extends the slot-pole combinations to candidates that are characterized by a star of slots including three phasors per phase and per winding period. It has the merit of improving the tolerance against open-circuit faults along with an increase in the winding factor of multi-phase machines. Special attention is paid to characterization of the coil asymmetry required for the phase parallel arrangement. A case study, aimed at a finite element analysis (FEA)-based investigation of the open-circuit fault-tolerance of a five-phase FSPMSM, is treated in order to validate the analytical prediction.

Analysis of a Novel Surface-Mounted Permanent Magnet Motor With Hybrid Magnets for Low Cost and Low Torque Pulsation

This article presents a novel surface-mounted permanent magnet motor (SPMM) with hybrid NdFeB-Alnico magnets to achieve low cost and low torque pulsation. Based on the analysis of the effects of stator magnetomotive force (MMF) on rotor magnets, the Alnico magnets can be properly configured to avoid demagnetization. To reduce torque pulsation, three models with different slot-pole combinations are proposed and compared, with the aid of the finite element method (FEM), and the results show that the torque pulsation of the 27-slot/4-pole model is the lowest, which is selected for further optimization. The multi-objective genetic algorithm (MOGA) is adopted to optimize the usage of Alnico and NdFeB magnets, thereby improving torque performance and reducing the cost. To verify the effectiveness of the optimization, the optimized model with hybrid NdFeB-Alnico magnets is compared with other models with only NdFeB magnets under the same operating conditions. As a result, it shows that the optimized model can significantly reduce the cost of magnets while maintaining excellent torque performance.

Cogging torque reduction based on segmented skewing magnetic poles with different combinations of pole‐arc coefficients in surface‐mounted permanent magnet synchronous motors

The calculation and reduction of cogging torque are fundamental to the evaluation and optimisation of motor performance. Considering that the accuracy of the cogging torque calculated by analytical method (AM) is low, an accurate calculation model of the effective air-gap length considering the actual stator slot structure and suitable for any motor is proposed, the cogging torque of 6p36s surface-mounted permanent magnet synchronous motor (SPMSM) are calculated accurately and verified by finite element method (FEM). Furthermore, the segmented skewing magnetic poles with different combinations of pole-arc coefficients are designed to weaken cogging torque, and the optimal combination of pole-arc coefficients and tilting angle of the adjacent magnetic poles are summarised by AM and particle swarm optimisation (PSO) algorithm. Finally, the cogging torques of six SPMSMs with different slot-pole combinations including 6p36s, 4p36s, 6p9s, 8p9s, 8p12s and 10p12s are analysed, and the results indicate that the cogging torque can be greatly weakened based on segmented skewing magnetic poles with different combinations of pole-arc coefficients, and other performances of the motors are basically not affected.

Synchronous Reluctance Machines for Automotive Cooling Fan Systems: Numerical and Experimental Study of Different Slot-Pole Combinations and Winding Types

In this paper a side-by-side comparison between synchronous reluctance machines (SynRMs) with concentrated and distributed windings is performed. The characteristics, parameters, and the installation space of a permanent magnet synchronous machine (PMSM) with concentrated windings used in a 13 V automotive cooling fan system (CFMs) are used as requirements and specifications. For that, eight SynRMs with different stator and rotor topologies are investigated and optimized by means of FE-based electromagnetic optimization. Knowing the challenges associated with the development of mechanically stable SynRM rotor structures, for two selected cross-sections in view of being prototyped, designs checks are performed to ensure robust operation at up to two times the required operating speed. The simulated results were verified by means of measurements performed using two different types of loading systems, i.e., with the real ventilator and using a DC machine as a load. Based on this, the relative differences between all three motor technologies in terms of important quantities (e.g., torque-speed characteristic, torque ripple, efficiency, power factor and ultimately the size) are highlighted.

Design Consideration of Fractional Slot Concentrated Winding Interior Permanent Magnet Synchronous Motor for EV and HEV Applications

This paper presents a comprehensive study on the fractional slot concentrated winding (FSCW) interior permanent magnet synchronous motors (IPMSMs) with different pole slot combination for the application of electric vehicle (EV) and hybrid electric vehicle (HEV). Three motors with the same dimension constraint and rated parameters are designed and optimized. With the optimized motors, winding factors and magnetomotive force (MMF), inductances, torque capacity, constant power speed range (CPSR), the losses, the efficiency, demagnetization capability and vibration are investigated and compared. The comparison results show that 12/8 motor and 12/10 motor have their respective unique advantages while 12/14 motor is not as good as the others.

Investigation of Asymmetric and Unbalanced Winding Structures for 3-Phase Permanent Magnet Synchronous Machines

In this study, an investigation of winding structures is performed for 3-phase unbalanced and asymmetric winding permanent magnet (PM) machines including different slot-pole combinations. There are two different cases for unbalanced winding (UBW) structure: 1) Stator slot number of the machine is divisible by three, 2) Stator slot number of the machine is not divisible by three. Only the first case is examined in this paper. The unbalanced winding layouts are created for minimum unbalance and maximum winding factor. Total magneto motive force (MMF) distributions for nine different slot-pole combinations and their harmonic contents are presented. Variation of the amount of unbalance for different slot-pole combinations is also provided in the paper. Key issues arising from the asymmetric and unbalanced windings such as degree of asymmetric and unbalanced magnetic pull are explored. A prototype motor with 39-slots and 12-poles has been manufactured for experimental verification. A comparison between the finite element analysis (FEA) results and experimental results is presented for the prototype motor for both no-load and on-load conditions. It is shown that the asymmetric and unbalanced winding PM motors have significant potential for applications requiring smooth torque operation.

Optimal Design of the Bearingless Induction Motor

The bearingless version of the induction motor (IM) has unacceptable performance for high speed or significant power applications. This is due to design challenges that are unique to the bearingless IM, including fundamental topology differences, rotor current induced by the suspension field, and a lack of techniques that can rapidly and accurately model the machine. This article presents a complete investigation into the design topology, modeling, and optimization of bearingless IMs to identify high-efficiency, power-dense designs for a high speed industrial compressor system. Key differences in the design of the bearingless IM from that of the classical line-fed IM are explored and an analytic design approach is proposed. A pole-specific rotor and a combined stator winding are used to improve the machine performance. Computationally efficient finite element modeling techniques are proposed and evaluated based on their ability to accurately calculate bearingless IM design performance metrics. An optimization framework is developed around these advancements using the multiobjective evolutionary algorithm based on decomposition. This article exercises this framework to explore the design space of four different slot-pole combination bearingless IMs for a 50 kW, 30 000 r/min compressor. High performance designs are identified that achieve $>96\%$ efficiency with a torque density competitive with high performance servo motors that use contact bearings.

Output power improvement of a vernier motor using field winding configuration

In this paper, a field winding vernier (FWV) machine is proposed to get higher back electromotive force (EMF) than surface permanent magnet vernier (SPMV) machine. First, the magneto motive force (MMF) equation of FWV machine is derived to obtain the requisite field current to produce the same back EMF as SPMV machine. Using the derived equation, the surface current density is also estimated and compared with the maximum allowable current density to examine the possibility of improving the back EMF of the FWV machine and find the slot-pole combination that is advantageous for the FWV structure. Using the obtained information, three models of SPMV and FWV machines are designed, finite element analysis are performed, and it is verified that proposed FWV machine has the capability of producing higher back EMF than SPMV machine.

Design and fabrication of an outer rotor permanent magnet synchronous generator with fractional winding for micro‐wind turbines

Permanent magnet synchronous generators (PMSGs) have been widely used in micro-wind turbines (MWTs) for direct-drive applications. The generating maximum power from the PMSGs used in the MWTs is desired. However, cogging torque (CT) and design form of the PMSGs prevent this. Therefore, various methods are applied to reduce the CT of PMSGs in the literature. Some of them are inapplicable and some are the ones that cause power loss. In this study, to overcome the expressed causes, a new design, fabrication, and application of an outer rotor PMSG with fractional winding having a slot–pole combination technique for MWTs have been suggested, designed, and implemented on an MWT. As a result of the new design combination of ±1 or ±2 between the numbers of stator slot (N S) and the number of pole-pairs (2p), the ratio of the CT value to the nominal torque value in the new prototyped outer rotor PMSG was found as 6.25%. Finally, the operating power can generate 1029 W through the prototype PMSG with fractional winding having a slot–pole combination technique integrated into the direct-drive MWT system.

Effect of time‐harmonic current on the harmonic leakage inductance of fractional slot concentrated winding permanent magnet synchronous motor

Harmonic leakage inductance occupies a high proportion in the synchronous inductance of fractional slot concentrated winding permanent magnet synchronous motor (FSCW-PMSM), and the synchronous inductance determines the operating performance of the motor. To calculate the harmonic leakage inductance and synchronous inductance of the FSCW-PMSM fed by inverters, two-dimensional finite element analysis and the analytical method are used to study the influence of time-harmonic current on the harmonic leakage inductance of the three-phase FSCW-PMSM in this study, and the influence mechanism is revealed. The relationship between the time-harmonic magnetic field and space harmonic magnetic field is obtained, and the harmonic leakage coefficient and the working harmonic coefficient with different slot-pole combinations are investigated. The results show that the time-harmonic current can reduce the harmonic leakage inductance and increase the magnetising inductance, but has little effect on the synchronous inductance under the unsaturated condition. A prototype was manufactured and tested to verify the accuracy of the analysis model. The research results provide beneficial help for the design of the three-phase FSCW-PMSM fed by inverters.

Design Optimization of an Electric Machine for a 48-V Hybrid Vehicle With Comparison of Rotor Technologies and Pole-Slot Combinations

Through analytical equations followed by a systematic optimization study using high-fidelity finite-element (FE) models, the torque capability of three common synchronous machine technologies—namely, a permanent magnet (PM) synchronous machine (PMSM) with V-shaped rare-earth rotor magnets, a PMSM with deep V-shaped ferrite rotor magnets, and a synchronous reluctance machine (SynRM) with four layers of conforming flux barriers are compared for an application in a 48-V mild hybrid electric car. The optimization of the deep V-shaped ferrite PMSM automatically resulted in a spoke-type PM layout for maximum torque production. Yet, an optimized SynRM with conforming flux barriers was achieved that could produce a higher torque than ferrite PMSM. One machine technology is selected and six variants of it, with two rotor PM layouts each with three alternative pole-slot combinations, are subsequently subjected to a large-scale FE model-based drive-cycle design optimization. Various pole-slot combinations are methodically compared in terms of drive-cycle losses, active material cost, torque ripple, and PM demagnetization level. More than 20 000 designs were analyzed over ten energy-centric torque-speed points to identify an optimal design solution. The results of multiphysics analysis incorporating electromagnetics, computational fluid dynamics, and structural analyses are provided, including a study on three different water jacket concepts. A final design is prototyped and primary experimental results are provided.

A new fault-tolerant switched flux machine with hybrid permanent magnets

This paper put forward a new fault-tolerant hybrid switched-flux PM (HSFPM) machine design employing the synergy of NdFeB and Ferrite Magnet. The key of the proposed HSFPM designed machine is the unique design E-core laminated stator with the hybrid magnet to ensure a drastic reduction of NdFeB magnet without compromising the output performances and efficiency in the conventional SFPM machine design to avert the huge demand of NdFeB and its associated volatile high price increase. Additionally, the fault-tolerant stator teeth designed principle implemented in the proposed HSFPM machine provides enhanced segregation among the various phases and ensures continuity of operation with acceptable operating performance under fault-condition. For fair evaluation and comparison, both the proposed HSFPM and the conventional SFPM (CSFPM) machine have the same slot-pole combination, winding arrangements, and stator/rotor dimensions except for the unique outer-stator of the proposed design. Meanwhile, compared to the CSFPM machine, the proposed HSFPM machine design makes use of only 60% of the PM (NdFeB) length. Finally, the evaluation of the no-load in conjunction with the load condition performances was carefully investigated by the Finite Element Method (FEM) of the ANSYS Maxwell software. The results depicted that the proposed HSFPM exhibits similar sinusoidal back electromotive force, comparable output torque, and slightly higher efficiency compared to that of the CSFPM machine.

Research on weakening measure of radial electromagnetic force waves in permanent magnet synchronous motors by inserting auxiliary slots

The accurate calculation and analysis of electromagnetic force waves are especially crucial for comprehensively predicting and weakening the electromagnetic vibration of electrical machines. In this study, a fast and accurate calculation method of radial electromagnetic force density of surface-mounted permanent magnet synchronous motor (PMSM) is presented, the radial electromagnetic force density including amplitude, frequency and order is obtained and the accuracy is verified. Comprehensively considering that the effects of the auxiliary slots on cogging torque and torque ripple, the weakening measure of radial electromagnetic force waves by inserting auxiliary slots is research, and the optimal determinations of the number and the structural parameters of auxiliary slots in PMSMs with different slot–pole combinations are summarised, and six PMSMs with 6-pole/36-slot (6p36s), 4p36s, 6p9s, 8p9s, 8p12s and 10p12s are analysed to verify the universality of the conclusions.

Multiphase PMSM With Asymmetric Windings for More Electric Aircraft

This article presents a multiphase permanent magnet synchronous motor (PMSM) for the more electric aircraft propulsion. The stator winding of the motor is composed of multiple sets of multiphase windings with different parameters. The purpose of the motor design is to modify the distribution of the high-efficiency area of the motor by reasonably matching the winding parameters of each set, thereby making the motor more suitable for the working condition of more electric aircraft and improving the working efficiency of the motor. This article analyzes the selection principle of slot-pole combination and the influence that asymmetric windings have on the motor magnetic field. Three basic matching modes are proposed: equal torque matching, equal power matching, and equal speed matching. The motor model is established, with the external characteristics, efficiency, and dynamic response of different matching modes being compared and analyzed. The results show that equal torque matching and equal speed matching can reduce the total loss of the motor in a complete flight working condition, whereas equal power matching is not suitable for more electric aircraft.

Analytical Model for Cogging Torque Calculation in Surface-Mounted Permanent Magnet Motors With Rotor Eccentricity and Magnet Defects

This article proposes a novel analytical model which combines subdomain method and magnet equivalent circuit (MEC) method to predict the cogging torque of surface-mounted permanent magnet (SPM) motors with rotor eccentricity and magnet defects in any slot-pole combination cases. Firstly, the general solution of open-circuit magnetic field distribution in a slotless SPM motor with magnet defects is derived. Then, the motor is divided into several subdomains along the air-gap circumferential direction to consider the non-uniform air-gap caused by rotor eccentricity, where the air-gap lengths of each subdomain are considered to be uniform. Finally, the methods of conformal mapping and MEC combined with equivalent current is used to consider the effect of slotting and saturation, which is beneficial to improve the calculation precision. The magnetic field distributions and cogging torque calculated by the proposed model are consistent with the results of finite element analysis (FEA). Compared with the FEA, the proposed model can perform fast calculations of air-gap flux density and cogging torque under rotor eccentricity and magnet defects for SPM motors, which can be utilized for optimizing the motor towards fault tolerance.

Design and analysis of a kind of rotor ironless high torque density machine using Alnico magnet

Conventional non-rare-earth permanent magnet (PM) electrical machine can hardly achieve comparable performance with the neodymium iron boron (NdFeB) machine due to the low coercivity and remanence. To solve this problem, a new kind of electrical machine using only Alnico magnet is proposed in this study. The novel rotor topology eliminates rotor iron core, and thus effectively limits armature reaction and improves torque density. A kind of rapid assessment method for the demagnetisation effect of q current in different slot–pole combinations through magnetomotive force and winding factor is presented and verified by 2D finite-element analysis. The optimisation of critical dimensions is demonstrated, and the trade-off between high PM utilisation and low demagnetisation effect is emphasised. After that, the good torque–current linearity and robust to demagnetisation characteristics of the proposed topology are proved through a comparison with two rare-earth-free machines. Finally, the performance comparison with a manufactured conventional NdFeB machine under the same volume constraints is provided. The result suggests that the proposed machine has a higher power factor, lower eddy-current loss, and rare-earth PM machine comparable torque density.

Design and Analysis of PMSM Traction Motor for Passenger Car Applications

In recent years, owing to the severity of global warming and deduction in petroleum resources quicken the researches to move on sustainable energy resources. Thereby E-mobility has been picturized and fully electric vehicle technology is the major research area nowadays. This paper presents the design methodology of electric traction motor requirement by considering vehicle dynamics and passenger car parameters. Pertaining to the vehicle desired performance, the maximum optimal power is computed. Followed by that power, torque Vs speed profile is determined and the same is compared with the urban and extra-urban drive cycle to estimate the average power and torque. Then the Interior PMSM 2D Finite Element Method (FEM) analysis is planned to carry out with the geometries obtained from analytical calculations for two different slot-pole combinations. The performance differences such as torque Vs speed profile, No-load Back EMF and torque ripple are investigated.