Fractional-slot Concentrated-winding Permanent Magnet Research Articles

Harmonic Loss Reduction of Fractional Slot Concentrated Winding Permanent-Magnet Vernier Motor with Different Stator-Modular Designs

Harmonic Loss Reduction of Fractional Slot Concentrated Winding Permanent-Magnet Vernier Motor with Different Stator-Modular Designs

Design to Reduce Modulated Vibration in Fractional-Slot Concentrated-Windings PM Machines Considering Slot–Pole Combination

The superior torque performance and unsatisfactory vibration are the inherent contradiction issue in fractional-slot concentrated-windings (FSCW) permanent magnet (PM) machines. This article aims to reduce the modulated vibration in FSCW PM machines while preserving their great torque performance. First, the contradictory relationship between the torque performance and the vibration of FSCW PM machines is revealed from the perspective of the slot–pole combination. Then, the radial force modulation of the FSCW PM machine is investigated from the aspects of spatial order and magnitude modulation. Subsequently, a new vibration reduction design methodology is presented, which combines the optimal slot opening coefficient and modified slot–pole combination. Finally, the prototype of a 12-slot/14-pole FSCW PM machine is manufactured, and several simulated and experimental verifications are carried out to validate the theoretical analysis.

Multi-objective optimization of high torque density spoke-type PM machine for special vehicle drive system

PurposeThis paper proposes a spoke-type fractional-slot concentrated windings (FSCW) permanent magnet (PM) machine for special vehicle driving systems to obtain higher torque and power density, high efficiency and wide field-weakening range. To enhance the efficiencies of multi-objective optimization processes, the respond surface (RS) method and black-hole (BH) algorithm are used.Design/methodology/approachThe spoke-type FSCW PM machine is optimized to meet the requirements of the special vehicle driving system. The combination of the RS and BH algorithm is used to obtain high torque, low torque ripple and high efficiency.FindingsThe optimal spoke-type PM machine is obtained, and it has higher torque density, lower torque ripple, cogging torque and wider magnetic field weakening range. Finally, a 15-kW prototype machine is fabricated and tested to verify the results of the optimization method and finite-element analysis.Originality/valueThis paper designs a high torque density and efficiency spoke-type FSCW PM machine, which is superior for special vehicle driving systems. Meanwhile, the RS model combined with BH algorithm is applied to the field of electrical machine multi-objective optimal design.

Analysis and Reduction of Electromagnetic Vibration in Fractional-Slot Concentrated-Windings PM Machines

This article focuses on the electromagnetic vibration source and its reduction design in fractional-slot concentrated-windings (FSCWs) permanent magnet (PM) machines. First, the electromagnetic force and vibration characteristics of a 12-slot/10-pole FSCW PM machine are investigated. Then, four electromagnetic vibration sources are investigated and compared, in which the machine operating state is considered. The result shows that the electromagnetic force modulation and stator magnetomotive force (MMF) harmonics are the two sources that contribute most to the vibration underrated and heavy load condition, respectively. Afterward, two new designs to reduce the vibration caused by the electromagnetic force modulation and stator MMF harmonics are proposed, and the reduction principles are described in detail. Finally, the prototypes of the existing and proposed 12-slot/10-pole FSCW PM machines are manufactured. The tests are conducted to validate the theoretical analysis and proposed vibration reduction design.

The Mechanism Analysis on Open-Circuit Back EMF in Fractional-Slot Concentrated Winding Permanent Magnet Machines Using Air-Gap Field Modulation Theory

This article investigates the production mechanism of the open-circuit back-electromotive force (back EMF) in fractional-slot concentrated winding permanent magnet (FSCW-PM) machines based on the air-gap field modulation (AFM) theory. The relationship between spatial PM field harmonics and temporal back EMF harmonics is discovered by using a general model, which is suitable for both stator-PM and rotor-PM machines. The analysis results reveal that the FSCW-PM machines produce their open-circuit back EMF on the basis of AFM, which means that each back EMF harmonic is induced not only by a specific single spatial field harmonic but also by several different spatial field harmonics. Furthermore, a general winding factor calculation formula for FSCW-PM machines is derived together with the general calculation formula of all back EMF harmonics. Finally, the analysis is verified numerically by the finite element method and experimentally.

A Novel Approach to Transverse Flux Machine Construction

The article presents a concept for a new design of the well-known Transverse Flux Machine (TFM) made with the use of a flat core used in classical electrical machines. The proposed design was first analytically verified and was subsequently verified using the finite element method, which fully corroborated the results. The simulations show that a set of three single-phase TFM machines with slotted flat rotor yokes generates a torque over three times greater than that of an induction motor and twice as large as Fractional Slot Concentrated Winding—Permanent Magnet Synchronous Machines (FSCW-PMSM). The performed comparative calculations confirmed that the torque generated by machines operating on principles similar to TFM can generate a torque much greater than those currently in common use.

Secondary Eddy Current Losses Reduction in a Double-Sided Long-Primary Fractional Slot Concentrated Winding Permanent Magnet Linear Synchronous Motor

A novel design method for the primary structure of a double-sided long-primary fractional-slot concentrated winding permanent magnet linear synchronous motor (DSLP-FSCW-PMLSM) is proposed in this article. Different from the traditional symmetric primary structure, the primary structure obtained by the proposed design method has two asymmetric primary cores and two asymmetric primary windings. This unique structure can reduce the variation of the flux density caused by the primary core slotting, and can effectively reduce the slot harmonic contents of the armature reaction magnetic field; thus, it can significantly reduce secondary eddy current losses. First, the basic structure is introduced. The air-gap magnetic field of permanent magnet and armature reaction are analyzed in detail. Second, the performance of the proposed motor is analyzed by means of three dimensional finite element method and compared with the traditional motor. The focus is on secondary materials, secondary eddy current losses, thrust, pole arc coefficient, magnet skew angle, and efficiency. Last, experiments are conducted on two prototypes of DSLP-FSCW-PMLSM. The validity of the proposed topology is verified by the test results of static thrust, back electromotive force, and armature reaction air-gap magnetic field.

Sleeve design of permanent-magnet machine for low rotor losses

In this study, a novel rotor sleeve for permanent-magnet (PM) machines equipped with fractional-slot concentrated-windings (FSCW) is proposed. With the newly designed rotor sleeve, the rotor eddy-current (EC) losses are significantly reduced, and the torque density of the machine is improved. First, the rotor EC losses of a surface-mounted PM machine with the sleeve are analyzed. Meanwhile, the sleeve EC barriers and PM segmentation technologies for the suppression of the rotor EC losses are evaluated. Subsequently, an FSCW PM machine with the newly designed sleeve is proposed and optimized for a given set of specifications. Its electromagnetic and mechanical performances are evaluated by the finite element method (FEM). Finally, three assembling methods are presented and assessed comprehensively in terms of their merits and drawbacks.

Investigation of E-Core Modular Permanent Magnet Wind Turbine

Under the adverse trend of fossil energy attenuation and air pollution, wind power effectively alleviates the global energy crisis and environmental pollution. For wind turbines, especially large offshore wind turbines, their transportation, installation, and maintenance are very inconvenient. In order to solve this problem, this paper presents an E-core stator modular machine which inserts stator gap into the unwounded teeth of the fractional-slot concentrated winding (FSCW) permanent magnet (PM) machine. The winding factor of the new stator structure machine was derived. The electromagnetic models of 12-slot/10-pole and 12-slot/14-pole modular FSCW PM machines and traditional FSCW PM machines were established using the finite element analysis (FEA) software, and the open-circuit flux density, cogging torque, load torque, loss, and efficiency were simulated and analyzed. The results showed that the modular structure of E-core stator not only simplified the transportation, installation, and maintenance of wind turbines, but also optimized the electromagnetic performance of the 12-slot/14-pole machine, i.e., improved the output torque and operation efficiency.

Influence of Introducing the Rotor MMF Harmonic on Torque Performance of Spoke Type Permanent Magnet Motor With FSCW

This article proposes a torque optimization method that introduces the rotor magnetomotive force (MMF) harmonics, aiming to increase the average torque without increasing the cogging torque and torque ripple. A spoke type permanent magnet direct drive motor with fractional slot concentrated winding (FSCW) is designed. The FSCW can improve the utilization rate of the winding, but at the same time, it brings a wealth of MMF harmonics. First, the electromagnetic torque expression is derived using the principles of magnetic energy and virtual power. It means that the constant electromagnetic torque is generated when the stator and rotor MMF harmonics with the same space and time order are the same as the main wave speed. The analytical method is then used to analyze the influence of the stator and rotor MMF harmonics on the electromagnetic torque of the three-phase FSCW permanent magnet motor. On this basis, a rotor shape that introduces the third rotor MMF harmonics is proposed. Finally, the finite element software is used to compare and analyze the torque performance of motor before and after optimization. The finite element simulation and experiment results prove the correctness and effectiveness of the method.

Unequal Teeth Design to Reduce Electromagnetic Vibration in Fractional-Slot Concentrated-Windings Permanent-Magnet Machine

This paper presents a new stator topology of fractional-slot concentrated-windings permanent-magnet (FSCWPM) machine in order to reduce the electromagnetic vibration. First of all, the space orders and corresponding frequencies of the lowest order radial force of FSCW-PM machines is studied. A 12-slot/10-pole FSCW-PM machine is used as an example, and its lowest order radial force harmonics are calculated by analytical method and finite element method, respectively. Then, in order to minimize the amplitude of the vibration acceleration, a new stator structure of 12-slot/10-pole machine is designed, by which the amplitude of the lowest order radial force is greatly reduced. Afterwards, the modal and vibration experiments are performed. The result shows that the 2SUPnd/SUP order radial force with 2f0 frequency contributes most to overall vibration. Finally, vibration simulation models of both machines are established, the results show that the machine with unequal teeth design effectively reduce the electromagnetic vibration.

Computationally Efficient Strand Eddy Current Loss Calculation in Electric Machines

A fast finite element (FE) based method for the calculation of eddy current losses in the stator windings of randomly wound electric machines is presented in this paper. The method is particularly suitable for implementation in large-scale design optimization algorithms where a qualitative characterization of such losses at higher speeds is most beneficial for identification of the design solutions that exhibit the lowest overall losses including the ac losses in the stator windings. Unlike the common practice of assuming a constant slot fill factor s <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> for all the design variations, the maximum s <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> in the developed method is determined based on the individual slot structure/dimensions and strand wire specifications. Furthermore, in lieu of detailed modeling of the conductor strands in the initial FE model, which significantly adds to the complexity of the problem, an alternative rectangular coil modeling subject to a subsequent flux mapping technique for determination of the impinging flux on each individual strand is pursued. Rather than pursuing the precise estimation of ac conductor losses, the research focus of this paper is placed on the development of a computationally efficient technique for the derivation of strand eddy current losses applicable in design optimization, especially where both the electromagnetic and thermal machine behavior are accounted for. A fractional-slot concentrated winding permanent magnet synchronous machine is used for the purpose of this study due to the higher slot leakage flux and slot opening fringing flux of such machines, which are the major contributors to strand eddy current losses in the windings. The analysis is supplemented with an investigation on the influence of the electrical loading on ac winding loss effects for this machine design, a subject that has received less attention in the literature. Experimental ac loss measurements on a 12-slot 10-pole stator assembly will be discussed to verify the existing trends in the simulation results.

Effect of Local Tangential Force on Vibration Performance in Fractional-Slot Concentrated Winding Permanent Magnet Synchronous Machines

This paper aims to disclose the noticeable effect of local tangential force on vibration performance in fractional-slot concentrated-winding permanent magnet synchronous machines (PMSMs). The mechanism to induce vibrations by tangential force is revealed at first. It is found that tangential force is able to deflect the yoke through the tooth's lever arm effect. This phenomenon is detailedly explained through finite element simulation and analytical description of the microscopic deformation in this paper. With the aid of a 10-pole/12-slot PMSM, the quantitative contribution of tangential force to the vibration is also investigated through simulation, vibration synthesis, and experiments. Results show that due to the strong lever arm effect and not so small force amplitudes as commonly expected, the contribution of tangential force to final vibration is comparable to that of radial force. Besides that, the synthesized vibrations indicate the contribution of tangential force decreases with the increase of non-zero spatial order, in a way similar to radial force. In order to underpin the findings, more situations such as with different pole-slot combinations are also analyzed at last.

Star and Delta Hybrid Connection of a FSCW PM Machine for Low Space Harmonics

Fractional-slot concentrated-winding (FSCW) permanent magnet (PM) machines have been widely studied in recent years. This is mainly due to the several advantages, including high power density, high efficiency, short end turns, high fill factor, low cogging torque, good flux-weakening and fault-tolerant performance. However, the key challenges of utilizing FSCW-PM machines are the abundant stator magnetomotive force (MMF) harmonics. In this paper, the multiphase star–delta hybrid connection (SDHC) windings configuration that can eliminate some stator MMF harmonics is systematically studied. First, the general relationship between the number of slots and phases which are appropriate for the SDHC windings configuration is derived. In addition, the particular principle of the MMF harmonics elimination by the SDHC windings configuration is researched. In order to verify the analysis results, four three-phase SDHC FSCW-PM machines with different slot–pole combinations are built and calculated by the finite-element method. Finally, experiments on a prototype three-phase 12-slot ten-pole FSCW-PM machine are carried out for validation.

Reduction of Tooth Harmonic in Fractional-Slot Concentrated-Winding Permanent-Magnet Machines Using New Stator Design

Fractional-slot concentrated windings (FSCWs) are characterized with many advantages. However, their magnetic fields have rich space harmonics. These harmonics, especially tooth harmonics, have negative effect on machine performances. This paper proposes a new method to reduce the tooth harmonics in FSCW permanent-magnet (PM) machine, in which the magnetic distribution in air-gap will be affected by winding span radian. Also, a new stator structure is designed on the method. By using the new stator design, each order tooth harmonic can be reduced significantly and the working harmonic can also be increased slightly. Simultaneously, the unbalanced radial magnetic force can be significantly weakened. The basic principle of tooth harmonic reduction method can be analyzed by using the stator structure of the FSCW machine with single layer windings. Then, a three phase 18-slot/16-pole FSCW machine with double layer windings is newly designed, which can effectively weaken the tooth harmonic components of FSCW machines. It is shown that, under the fixed electrical and geometrical constrains, the designed FSCW machine has better performances, such as loss, vibration and noise, than the conventional ones.

Three‐phase current injection method for mitigating turn‐to‐turn short‐circuit fault in concentrated‐winding permanent magnet aircraft starter generator

Fractional-slot concentrated-winding (FSCW) permanent magnet synchronous machines, which are characterised with high power density, fault tolerance and wide constant-power speed range, are gaining more and more attention in the aircraft starter generator (SG) systems. Nevertheless, the short-circuit (SC) fault, especially the turn-to-turn SC fault, is the obstruct crux in aviation applications. This study is aimed to demonstrate the feasibility of FSCW permanent magnet SG (PMSG) in dealing with turn-to-turn SC fault. The law of FSCW-PMSG SC fault is analysed and verified by finite-element analysis (FEA), including the influence on turn-to-turn SC current by the number of the shorted turns and the coil position in the slot. The three-phase current injection control is employed to mitigate the SC fault in PMSG when a turn-to-turn SC fault occurs. A 24-slot, 16-pole FSCW-PMSG with spoke-type rotor topology is designed to confirm the ability of inhibiting turn-to-turn SC current without the risk of irreversible demagnetisation. Both FEA and experimental results are presented, verifying the effectiveness of the three-phase current injection control in restraining the turn-to-turn SC current for FSCW PMSG in an acceptable range.

Analysis of Fractional-Slot Concentrated Winding PM Vernier Machines With Regular Open-Slot Stators

Permanent magnet (PM) vernier (PMV) machines have been extensively researched for direct-drive applications due to their inherently high torque density. This paper presents a quantitative investigation on fractional-slot concentrated winding PMV (FSCW-PMV) machines with regular open-slot stator topology. Based on winding theory, the configuration of two winding types, i.e., nonoverlapping winding and FSCW with two-slot coil pitch are analytically derived for PMV machines, respectively. Through finite element analysis, comparative study of FSCW-PMV machines, regular integral slot winding PMV machines, and regular PM machines are performed. It is found that the flux modulation effect also exists in regular nonoverlapping winding PM machines. In other words, the regular nonoverlapping winding PM machine also belongs to the PMV machine family. The PMV machine with two-slot coil pitch is newly proposed, and turns out to be a promising PMV machine topology with competitive torque capability and power factor. Finally, a prototype of 18-slot, 14-rotor pole pair, and 4-stator pole pair PMV machine with two-slot coil pitch is built. Experimental results show that the torque density of the prototype can reach 20.0 kNm/m3 and the power factor is 0.91.

Design, Analysis, and Experimental Validation of a Permanent Magnet Synchronous Motor for Articulated Robot Applications

Based on the base module of Universal Robotics, this paper deals with a 16-pole, 18-slot fractional-slot concentrated-winding permanent magnet synchronous machine (PMSM) for articulated robot applications considering several pole-slot combinations and using an optimum design. The selected PMSM considering the pole-slot combination is optimized and compared both analytically and experimentally. The experimental results confirmed that the proposed PMSM can achieve improved performance at the rated state. Repeatability test results of the proposed smart actuator with a link-attached sphere-mounted retroreflector sensor met the goal of within $100~\mu \text{m}$ according to a laser tracker. The analysis results are in good agreement with the experimental results within the maximum 2.5% error in terms of the efficiency. The design, analysis, and experiment with the PMSM for articulated robot applications were conducted successfully.

Ventilation and Thermal Improvement of Radial Forced Air-Cooled FSCW Permanent Magnet Synchronous Wind Generators

This paper presents coupled fluid-thermal analyses to improve the ventilation and thermal performance of radial forced air-cooled fractional-slot concentrated-winding (FSCW) permanent magnet synchronous wind generators (PMSWGs) using the computational fluid dynamics (CFD) method. Three-dimensional coupled fluid-thermal CFD models are established based on the governing conservation equations of the solved solid machine parts and the air domain. The losses are applied into the CFD models as the heat sources and the boundary conditions are determined. Based on the proposed method, the fluid and temperature field of the machines with different air cooling channel numbers and channel widths are calculated, and the ventilation and thermal performance are compared to determine the optimal channel number. Further, an alternative cooling structure with radial winding holes through the slot center to dissipate heat from the winding directly is proposed. The results show that it is a promising alternate, especially for the FSCW PMSWGs to decrease the winding temperature and ventilation losses. The proposed CFD method is validated by experiments implemented on a standard product of integral-slot distributed-winding (ISDW) PMSWGs with the same ventilation system.

Analytical Modeling of Interturn Short Circuit for Multiphase Fault-Tolerant PM Machines With Fractional Slot Concentrated Windings

Interturn short-circuit faults that occur inside stator coils are difficult to cope with compared with terminal short-circuit faults. A general analytical model for interturn short-circuit faults is developed that employs a novel T-type equivalent circuit. When this model is used to investigate the impact of interturn short-circuit faults in permanent-magnet (PM) machines with fractional slot concentrated windings (FSCW), the model delivers fault response predictions that agree very well with results from the finite element analysis. The model is used to show that the 24-slot/14-pole FSCW PM machine is vulnerable to very high interturn fault currents, even when the remaining turns are shorted, offsetting its advantage of low magnetic coupling between phases. FSCW-PM machines that employ aligned coils in phase windings can effectively suppress their interturn fault currents. Experimental verifications are provided for the 24-slot/22-pole FSCW PM prototype machine (with two aligned coils per phase) under the single-turn short-circuit fault.