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Featured Application: The work specifically targets the enhancement of cooling mechanisms in high-power permanent magnet electrical machines, with a direct application in improving the thermal management of stator windings in such devices. This advancement can significantly benefit sectors like aerospace, where the efficiency, reliability, and longevity of electrical machines are critical. This paper investigates innovative methods for enhancing heat transfer efficiency in high-power permanent magnet electrical machines. The objectives are to quantify the effects of increasing the air speed, increasing the turbulence intensity, and introducing the spacing between windings on cooling performance. The cooling of stator windings is studied through experimental wind tunnel testing and Computational Fluid Dynamics (CFD) modelling. The CFD model is validated against wind tunnel measurements to within 4 Kelvin (K). The results demonstrate that each enhancement method significantly improves the cooling capability. Increasing the air speed from 10 m/s to 40 m/s reduces the winding hotspot temperature by 34%. Introducing a high turbulence intensity of 40% leads to a 21% lower hotspot temperature compared to 0.5% turbulence intensity. Creating a 1.5 mm spacing between coils also substantially improves convection and conduction heat transfer. Overall, combining these optimised design parameters yields over a 40% reduction in hotspot temperature compared to the original design. This research provides practical guidance for maximising heat transfer efficiency in high-power permanent magnet machines, without increasing complexity. The findings will lead to higher machine efficiency, reliability, and longevity for aerospace and other applications. [ABSTRACT FROM AUTHOR]

Winding inductance is a crucial parameter of machines, which plays an essential role in flux-weakening capability, reluctance torque, power factor, etc. In this article, winding inductance characteristics of flux-switching permanent magnet (FSPM) machines are investigated from the perspective of air-gap modulation magnetic field. With the aid of the general air-gap field modulation theory, the air-gap magnetic field contributed by an arbitrary energized winding of FSPM machines is modeled and analyzed. Then, an analytical expression of winding inductance is derived based on winding function and single-phase magnetic field, through which the relationship between winding inductance and single-phase magnetic field harmonics is unveiled. It is found that the direct current (dc) and 2nd harmonic components of winding inductances in FSPM machines are caused by the dc and 2nd time-harmonic components of primitive harmonics, respectively, which are essentially different from that of traditional interior permanent magnet or reluctance machines. Finally, experiments on a prototype three-phase 12/10 FSPM machine are conducted to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

The ac copper loss, which results from the skin effect, the proximity effect, and the bundle-level circulating current, is widely concerned in high-speed electrical machines since they grow rapidly with the frequency. While the skin effect can be easily suppressed by the utilization of thinner wires, the circulating current is generally restrained by a complicated transposition technique. Moreover, the transposition technique is better suited to the preformed winding other than the random-wound winding, hence, it is still difficult to suppress the circulating current ac loss in the random-wound winding. In this article, a practical transposition technique is proposed for the circulating current loss suppression for high-speed electrical machines with random-wound windings. To implement this technique, a specific winding former is designed and manufactured. The proposed transposition technique is verified in a 200 kW, 54 000 r/min high-speed permanent magnet machine, contributing to a reduction of 55.2% copper loss compared to the untransposed winding. The experiment result indicates that the proposed transposition technique is practical in engineering. [ABSTRACT FROM AUTHOR]

In the high-speed flux-switching permanent magnet (FSPM) machine, the ac copper loss issue in the armature winding conductor is very prominent, due to the high-frequency leakage magnetic field in stator slot, which seriously affects the machine performance. To model and calculate ac copper loss more accurately, a coupled electric circuit-magnetic field model is constructed based on 2D-finite element method, and consequently the influence of modeling methods and winding types on ac copper loss calculation of a 12-slot/10-pole (12/10) 54.7 kW/10 kr/min FSPM machine is investigated. First, ten simplified ac copper loss calculation models are established to deal with the problem of large consumption of calculation time and computer resources caused by the excessive number of wires, small size of winding conductors, high precision modeling, and mesh refinement. Second, the influences of voltage-/current-source and steady/rotating rotor are considered, and the ten models are evaluated in terms of computing time and accuracy. Third, based on the preferred model from the ten models, the effects of frequency, round/flat wires, and wire sizes on ac copper loss are further studied. Fourth, to investigate the influence of flux leakage at the end of winding on ac copper loss, a 3-D ac copper loss calculation model with different axial lengths of winding end space is established. Fifth, the change process of ac copper loss and transient temperature of winding under short time overload condition are obtained combined with the bidirectional coupling model between electromagnetic and thermal field method through multiple iterations of electromagnetic loss and temperature. Finally, the stator modules of round and flat copper wires are manufactured, respectively, and an experimental modular device is built to measure the ac copper loss, which confirms the improved accuracy of the predictions by the proposed model. [ABSTRACT FROM AUTHOR]

Consequent-pole (CP) permanent magnet (PM) configuration suffers asymmetric electromagnetic characteristics although it saves PM usage. The CP-based stator-PM synchronous machines are investigated in this paper, with particular reference to symmetrical issues. The electromagnetic performances of the CP-based stator-PM synchronous machines are firstly evaluated. Afterwards, the rule of even order harmonics cancellation is presented for different slot/pole number combinations and winding layouts, based on which symmetrical phase flux-linkages can be obtained although the unbalanced magnetic flux naturally occurs. Moreover, based on the three-dimensional finite element analysis, the unipolar end leakage-flux caused by the asymmetric magnetic field is identified, and the risk of the shaft magnetization is revealed. Finally, a pair of prototype machines are fabricated and measured to validate the analyses. [ABSTRACT FROM AUTHOR]

This article presents an investigation and evaluation of an integrated flux-modulated machine for wind power generation. The integrated flux-modulated machine has two rotors which function as two contrarotating rotors connected to two sets of turbine blades. Hence, compared to conventional wind generators, more wind energy could be captured by this wind power generation system. Moreover, the integrated machine consists of two sets of stator windings. By regulating the currents in these windings, dual maximum power point tracking control strategy could be achieved. As a result, the wind power conversion efficiency is further improved. Moreover, this wind power generation system exhibits the advantage of high torque/power density due to the enhanced magnetic-gearing effect involved in the integrated flux-modulated machine. Hence, this machine is more suitable for direct-drive wind power generation, where the reliability is improved without the maintenance issues related to mechanical gearboxes. The topology and operating principle of the investigated machine are demonstrated in detail. Decoupled design of the two sets of windings is investigated, and a general rule to achieve decoupled windings by appropriate slot-pole combination selection is illustrated. The advantages of the investigated machine are confirmed in comparison to a benchmark machine. Finally, the investigated flux-modulated machine is prototyped. The validity of the operating principle and the simulation results are verified by experimental results. [ABSTRACT FROM AUTHOR]

As a promising candidate of the electrical continuously variable transmission, the integrated magnetic-field-modulated brushless compound-structure machine (IMFM-BCSM) has advantages of compact structure and no brush. The IMFM-BCSM is composed of a stator with two sets of windings, a permanent-magnet (PM) rotor and a modulation rotor. Due to its special operating principle, i.e., the magnetic field modulation principle, the back electromotive force (EMF) waveform distortion of the IMFM-BCSM is more serious than that of the conventional PM machine. To solve the above problem, a quasi-sinusoidal concentrated winding (QSCW) configuration is proposed and corresponding design method is further introduced. In order to observe the “filtering ability” of the QSCW, comparisons between QSCW configuration and fractional-slot concentrated winding configuration are carried out. The results show that when the QSCW configuration is employed, the no-load back EMF of the regular winding is more sinusoidal; the distortion degree is less affected by the rotor speeds; and the torque ripple is much smaller. Finally, a prototype is manufactured to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

A 60-slot/22-pole five-phase machine with hybrid single-/double-layer fractional slot winding is proposed to improve torque under third harmonic current injection condition. Design process of the proposed machine includes two steps of first combining two sets of 20-slot/22-pole machine windings and then shortening coil-pitch. Due to the special structure of the proposed machine, torque-contributing space harmonics in magnetomotive force (MMF) are improved, and redundant space harmonic in MMF which causes high eddy current loss in permanent magnets is suppressed. The proposed machine is evaluated under two modes of third harmonic current injection, namely constant rms and peak harmonic injection. Compared with 20-slot/22-pole machine, the proposed machine achieves higher torque and lower losses under both third harmonic current injection conditions. Besides, the performance of the proposed machine when injecting only the first or third harmonic current is also analyzed. [ABSTRACT FROM AUTHOR]

The conventional lap-winding high-speed permanent-magnet synchronous machine (HSPMSM) usually has a large interturn short-circuit (ITSC) current, seriously threatening the reliability. This article founds that the SC coil of the gramme-ring-winding HSPMSM is wound around the stator yoke, so the inductance of SC coil is considerable large and thus will cause a great reduction of ITSC current. The types of ITSC faults were first analyzed for a multistrand-gramme-ring-winding HSPMSM, and then, the ITSC characteristics and influencing factors were investigated based on finite-element (FE) method. The distribution of flux density is quite different from normal state, the SC current is far lower than that of the lap-winding HSPMSM, and the inductance of SC coil is fluctuant with rotation of rotor. By theoretical analysis of the inductance, the methods of increasing the height of stator yoke and using high-permeability CoFe alloy were proposed to further reduce the SC current. In addition, decreasing the strands number is beneficial to reduce the SC current density. [ABSTRACT FROM AUTHOR]

This article proposes a new hybrid-excited partitioned stator flux modulated machine with a dual-permanent magnet (HE-PSFMDPMM). The HE-PSFMDPMM employs consequent-pole (CP) permanent magnets (PMs) on the inner stator and Halbach array CP PMs on the rotor, which can yield abundant air-gap flux density working harmonics to increase the torque capability. Meanwhile, the field windings are housed in the inner stator to achieve flux weakening. The topology, working principle, and design optimization of HE-PSFMDPMM are investigated, respectively. The electromagnetic performances of HE-PSFMDPMM are analyzed and compared with that of a contrast model with conventional CP PMs on the rotor. The results indicate that by using dual-PM excitation, HE-PSFMDPMM can provide large flux linkage, high torque production with low torque ripple, and high efficiency. Meanwhile, a good flux weakening capability is obtained with the aid of direct current (dc) excitation. Moreover, compared with the contrast model, the proposed HE-PSFMDPMM with Halbach array CP PMs on the rotor can offer the merits of lower cogging torque and torque ripple, higher power factor, and better flux weakening capability. [ABSTRACT FROM AUTHOR]

A new partitioned stator hybrid excitation (HE) with an internal magnetic ring machine was proposed in this article. The key of the design is to adopt an inner magnetic ring to reduce the inside stator magnetic reluctance. As a result, the working magnetic field harmonics can be improved, which in turn improve the torque and flux regulation abilities. Besides, by following the design of partition stator, the space competition of permanent magnet, armature winding, and field winding can be effectively alleviated as compared with a single stator HE machine. The structure and operation principle of the conventional and proposed machines are described. Moreover, electromagnetic performances of both machines are compared by using finite element method. Theoretical and simulation analysis results show that the proposed machine can exhibit higher torque and enhanced flux regulation ability than the conventional one. [ABSTRACT FROM AUTHOR]

This paper proposes a novel algorithm which made it feasible to predict the harmonic fault signatures under dynamic eccentricity in Permanent-Magnet synchronous machines with concentrated non-overlapping winding for any slot-pole combination. In the literature, only the appearance of the fractional harmonic components related with the pole number has been proposed but there are no studies to predict which exact components will rise in each topology. Initially, a mathematical equation is derived for the machine EMF under dynamic eccentricity based on the air gap permeance model. Later on, the terms of this equation are inserted in a Fault Signature Block Binary Array in which the position of each cell expresses a specific harmonic frequency component. After substitution of the machines parameters, the array results with zero and nonzero terms. The positions of the nonzero terms express the frequency components excited by this particular fault. 3-D FEA and experimental results of a Permanent-Magnet Axial-Flux Machine are used to validate the proposed algorithm. [ABSTRACT FROM AUTHOR]

Voltage induced in the dc winding by the armature field in wound field switched flux (WFSF) machines will induce voltage perturbation in the voltage supply and cause dc winding current ripple and field excitation fluctuation. This will challenge the dc voltage controller and deteriorate the control performance, especially when the load and/or the rotor speed are high. In this article, the dual three-phase armature winding design with a phase-shift of 30 electrical degrees is employed in the partitioned stator WFSF machines to reduce the on-load dc winding-induced voltage. Analytical deductions and finite element (FE) results demonstrate that the dominant sixth-order-induced voltage harmonic can be suppressed to zero. Hence, the peak-to-peak induced voltage in the 12/11- and 12/13-pole partitioned stator WFSF machines can be reduced by 83.35% and 82.53%, respectively. Due to the improvement of winding factors, the torque densities are 4.85% and 5.60% higher, respectively. Prototypes are built and tested to verify the analytical and FE results. [ABSTRACT FROM AUTHOR]

Wound rotor induction machine (WRIM) connected to stator and rotor voltage source converters (VSCs), known as the double-inverter-fed WRIM drive, can be viewed as two virtual squirrel cage induction machine drives, when seen from air-gap. In this article, this feature of WRIM is explored to develop an improved dual direct torque vontrol (DDTC) technique such that, two individual and independent conventional DTC controllers can be directly employed to control the stator and rotor VSCs. The improved technique is inculcated with all the benefits of conventional DTC controller, especially the benefit of zero dependence on rotor position. Furthermore, the increased torque ripple with the conventional DTC controllers is mitigated by modifying the switching tables (STs) such that, the voltage vectors emulated in the air-gap are equivalent to a 3-level neutral point clamped VSC. The STs are developed by analyzing the WRIM as an open-end winding induction machine (OEWIM). To demonstrate the performance of the proposed DDTC technique, the experimental results obtained from 3 kW WRIM are presented, under various transients and steady-state conditions. The reduction in the torque ripple is demonstrated by estimated torque ripple waveforms, at different speeds. [ABSTRACT FROM AUTHOR]

Online stator winding insulation monitoring is becoming an important topic in recent years and many online monitoring methods have been proposed. In these methods, the online common-mode impedance spectrum method can monitor the condition of the ground-to-wall insulation accurately based on the switching harmonics and no additional signal injection equipment is needed. However, the existing method has the limit that it can only detect the overall insulation aging condition. The coils at the line end are subjected to a higher voltage and their insulation degrades faster than the part closer to the neutral end. It is a common practice to change connections to reverse the line and neutral ends to extend the insulation life for Y-connection stator winding machines. In this condition, the existing method would give false alarm because it estimates the severity of aging at different positions of the winding as a whole unit. In this article, the proposed method monitors the parallel capacitance in the frequency range both below and above the resonance frequency. Using multifrequency information, the proposed method can distinguish the insulation aging at different locations, which improves the performance of this monitoring method. The offline and online experimental results both validate the proposed method. [ABSTRACT FROM AUTHOR]

A dual-stator Vernier permanent magnet (DSVPM) machine is proposed in this article for improving the power factor. Compared with the conventional single-stator Vernier permanent magnet (SSVPM) machine with the surface-mounted permanent magnet rotor, the proposed DSVPM machine has the higher power factor and the overload capacity. The reason for the higher power factor and the overload capacity in DSVPM machines is explained theoretically in this article by air gap permeance theory, and the advantages of the power factor and overload capacity of DSVPM machine are verified by the finite element analysis (FEA) through 18-slots and 34-poles SSVPM and DSVPM FEA model. The rotor eddy current losses, core losses and magnet demagnetization ratio of the DSVPM and SSVPM machines are also studied in this article, the FEA results reveal eddy current and core losses and magnet demagnetization ratio are all lower in the proposed DSVPM machine. The power factor of DSVPM machine variation with the magnet thickness and pole ratio (the ratio of the rotor pole pair number to the stator pole pair number) is also researched by the theoretical and FEA methods. In this article, a surface-mounted permanent magnet machine with fractional-slot concentrated-winding is designed to compare the torque density and cost with DSVPM machine. The sandwiched rotor structure of the proposed DSVPM machine is discussed and the structural analysis by three-dimensional FEA is carried out to prove the feasibility of rotor support, the result reveal that the rotor structure has the sufficient strength. [ABSTRACT FROM AUTHOR]

In this article, two novel dual-stator machines with different biased permanent magnet (PM) configurations are developed and comparatively studied. For the proposed machines, the PMs are only located in the inner stator, but with different configurations, that is, surface-mounted PM (SPM) and interior PM (IPM), respectively. The machine topologies and operating principle are introduced first. Then, the electromagnetic characteristics, including open-circuit performance, torque characteristics, field-weakening capability, loss, and efficiency, are comprehensively analyzed and compared by finite-element method (FEM). The experimental validation is conducted to verify the FEM analyses. [ABSTRACT FROM AUTHOR]

In this article, the split-tooth stator-slot permanent-magnet (ST-SSPM) machines with different permanent magnet (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 the 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 electromotive force (EMF), steady torque, PM utilization ratio, loss, efficiency, and PM demagnetization. Finally, some conclusions are drawn based on the optimal designs and analyzed results. [ABSTRACT FROM AUTHOR]

This article proposes a new axial dual-stator flux-switching permanent magnet (FSPM) machine for high-speed applications. The machine adopts a fractional slot distributed winding, which has a higher winding factor, efficiency, and torque density. First, the high-speed FSPM machine topology and operating principle are introduced. By employing the winding complementarity principle, the unfavorable even harmonics of a single stator in the FSPM machine can be counteracted, resulting in an essentially sinusoidal permanent magnet (PM) flux-linkage as well as effectively reduced cogging torque and torque ripple. Second, based on the 3-D finite element method (FEM), both the no-load and on-load electromagnetic performances are obtained. Compared with the other three FSPM machines, the advantages of the proposed machine are highlighted. Finally, a high-speed FSPM prototype is manufactured and a test platform is built to measure the no-load and on-load performances, which verifies the theoretical analysis and simulated results. [ABSTRACT FROM AUTHOR]

In this article, a new dual-winding dual-flux-concentrated magnetic-field-modulated brushless compound-structure machine (DDMFM-BCSM) is proposed by combining the magnetic-field modulated brushless dual-rotor machine (MFM-BDRM) and permanent magnet synchronous machine (PMSM) into one. Proposed machine has two sets of windings in stator slots and spoke-type PMs on dual rotors. Besides, there are flux barriers on the inner rotor to improve the performance of MFM-BDRM part. Based on magnetic field modulation principle, the main harmonics of the flux density in inner and outer air gap are calculated by analytical method and simulated by finite element method (FEM). The performance of the proposed machine, including MFM-BDRM part, PMSM part, and the whole DDMFM-BCSM, is analyzed. In order to analyze the influence of flux barriers on the performance of DDMFM-BCSM, a DDMFM-BCSM without flux barriers is designed to compare their performance, including torque, loss, and power factor. [ABSTRACT FROM AUTHOR]

In this article, the analysis of induction machines using five separated subdomains including the rotor slot, rotor slot opening, airgap, stator slot opening, and stator slot regions is considered. The Maxwell equations of each region are solved considering the boundary conditions. Uniform distributions of the current density in the rectangular slots of both the rotor and stator are considered to find the energy of the winding and to calculate the machine inductances using the energy equation. The calculated flux density of each subdomain is used to find the flux distribution. The calculated magnetic flux intensities are required to estimate the saturation level of the motor cores and correct the saturation-related values such as the leakage and magnetizing inductances. The machine core losses are calculated based on the Steinmetz equation at the no-load condition. The calculated inductances and resistances are used in the equivalent circuit of the squirrel-cage induction machine (SCIM) for the performance prediction. The results demonstrate the reliability of the saturation model in the prediction of the saturation influence in a wide range of magnetization levels. The accuracy of the proposed model in the prediction of the performance of the SCIM is validated using two-dimensional (2-D) and 3-D finite-element analysis results. A sensitivity analysis with 75 different geometries was conducted to show the capability of the model for the performance prediction of a wide range of induction machines. [ABSTRACT FROM AUTHOR]

Partial demagnetization is a condition that may occur in Permanent Magnet machines due to overloading or thermal stress. Whenthis happens, the magnetic field locally weakens leading to an asymmetry of the air-gap field. This asymmetry will cause harmonics, which will be expressed as extra losses and mechanical oscillations. Moreover, since the field becomes weaker, more current is required to serve the load leading to less efficiency, increased losses and consequently increase of the temperature, which will cause further progression of the demagnetization severity until a total machine breakdown. Several methods have been proposed in the literature for the online detection of the demagnetization, however they have not related the fault to the manufacturing characteristics of the machine, which play an important role on the expected harmonic index and the associated fault signatures. This paper presents for the first time a detailed analytical investigation of the expected harmonics in the stator current spectrum in case of demagnetization, as a function of the stator winding and number of poles. The analytical results are verified by extensive simulations via the finite element method and experimental testing. [ABSTRACT FROM AUTHOR]

Direct cooling of the windings in a motor using oil offers more effective thermal management than conventional alternatives and can therefore increase the torque density of electric machines; however, this technique is limited by the thermophysical properties of the oil. The use of a direct winding heat exchanger allows a glycol-water coolant mixture to be used, which leads to a significant improvement in heat transfer and a reduction in the pumping losses compared to direct oil cooling. This article proposes ceramic 3-D printed direct winding heat exchangers (3D-DWHX), which can significantly improve the cooling of windings in electric machines due to the unique geometries enabled by 3-D printing. Ceramics are also capable of withstanding extremely high temperatures, which extends the application of the proposed 3D-DWHX. A closed-form analytical thermal model incorporating the temperature dependence of winding losses is proposed and used with empirical heat transfer correlations to design a microfeature enhanced 3D-DWHX. The ceramic 3D-DWHX was built and tested in a motorette that demonstrated a continuous current density of 35.7 ARMS/mm2, corresponding to a continuous specific power in the reference electric machine of at least 12.1 kW/kg while keeping the maximum winding temperature below 200 °C. [ABSTRACT FROM AUTHOR]

In this article, split-tooth stator slot permanent magnet (PM) machines, which have high fault-tolerant capability, are proposed. Compared with the existing 12-slot 10-pole (12S10P) stator slot PM machine, the torque can be improved by 66% by properly choosing the split tooth number and other geometric parameters. It is found that two split teeth stator slot PM machine (ST2) shows the best torque characteristics among the stator slot PM machines with different split tooth number. To further illustrate the merits and demerits of ST2, a conventional 6S4P surface mounted PM machine (SPMM) and a 6S4P variable flux reluctance machine serve as the benchmarks to compare with the 6S11P ST2, at both open circuit condition and load condition. The 6S11P ST2 shows 68% higher torque over the 6S4P VFRM. Although the torque of the 6S11P ST2 is around half of the 6S4P SPMM, the former has 70% higher torque per PM volume than the latter. Furthermore, demagnetization analyses under three-phase short-circuit and pure d-axis currents show that the 6S11P ST2 has much better demagnetization withstand capability over the 6S4P SPMM. A Prototype is manufactured and tested to validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

One of the main tasks during the design of a superconducting electrical machine is the estimation of losses in the superconducting coils. These losses can be decisive in such applications since they influence the cooling power requirements and the overall efficiency of the machine. In this article, we focus on the dissipation in the stator superconducting coils of a synchronous machine. The calculations are done within the framework of the SupraGenSys project, which aims to develop a new superconducting generator for the wind energy sector. A detailed study of the ac losses in the stator coils is carried out based on a basic design that considers the main constraints of this application. The objective is to look for an optimum solution for the level and distribution of losses as a second step in the design process. The T-A formulation of Maxwell's equations is used in a 2-D finite-element model to analyze the behavior of the magnetic field around the coils and calculate losses. Particular attention is given to the position of the coils inside a slot and several coil configurations are presented. It is shown that certain coil arrangements lead to a significantly lower total loss, a more uniform loss distribution, which ultimately leads to the possibility of increasing the operating temperature. [ABSTRACT FROM AUTHOR]

In this article, the field modulation effect (FME) of consequent-pole permanent magnet (CPM) machine is revealed and investigated from the perspective of a double-side slotting effect (DSSE), which can characterize and elaborate its torque production mechanism. Since the CPM machine features that both PM and armature fields are modulated by stator /rotor teeth, which generates more field harmonics contributing to the torque production compared with conventional surface-mounted PM (SPM) machine. A simplified PM magneto-motive force (MMF)-permeance based model is first established to confirm the effective working harmonics of the CPM machine. The contributions of dominant air-gap field harmonics to the torque production are then demonstrated and quantified based on Maxwell stress tensor (MST) method. The impacts of FME on the torque performance of the CPM machines with different stator-slot/rotor pole combinations are subsequently investigated by the finite element (FE) method and compared with those of conventional SPM counterparts. Besides, the influences of rotor PM parameters on the FME of the CPM machine are also evaluated. Finally, the experimental measurements on a 12-slot/14-pole CPM machine prototype are carried out to validate the theoretical and FE analyses. [ABSTRACT FROM AUTHOR]

Transient voltage distribution due to steep-fronted surges must be taken into account during the machine's design as it can lead to main and turn insulation failure. In medium voltage machines, the end-windings region has a considerable percentage of the coil length and plays an important role during transient studies. This article has the purpose of verifying the influence of end-windings on the transient voltage distribution by using a three-phase simulation model in which transient magnetic fields and electric circuit elements are coupled. The transient simulation and the calculation of the electrical parameters used in the model are done employing the Finite Elements Method (FEM). To verify the influence on the results, simulations for different surge rise times are performed, considering and neglecting the end-windings model. As main results, the intercoil and interturn voltages are analyzed for all turns from the three phases of one winding group. The model is validated by measurement results. It is shown that the end-windings, indeed, affect the transient voltage distribution for both, interturn and intercoil voltages, regarding the rate of rising (slope), instant, and the amplitude of the peak voltages. Moreover, all three phases are affected by the end-windings, especially for the turn-to-turn voltages. [ABSTRACT FROM AUTHOR]

This article introduces a self-excitation technology for field wound synchronous machines (FWSMs) to eliminate conventional components required by brushless and brushed static excitation systems. This technology is based on the utilization of pre-existing airgap flux harmonics, so no exciter or brush is required. The energy of these airgap harmonics at the slotting frequency is captured using rotor-mounted harvesting coils. A power electronic converter is then used to rectify the induced harvesting coil voltage and regulate the field winding current of the FWSM. Simulation results are presented showing the efficacy of the proposed method for a prototype FWSM under various loading conditions. For demonstration, a full-scale 5.4-MVA synchronous generator is used for design and validation. [ABSTRACT FROM AUTHOR]

An invasive diagnostic technique is proposed in this article for the detection and discrimination of turn-to-turn faults in the stator and rotor windings of synchronous machines during the startup period. For this purpose, search coils are installed in the machine to sense the rotational magnetic field along the air-gap circumference, while the difference in the related induced voltages (differential voltages) reveals its distortion, using it as a criterion for the detection of the faulty condition. Nevertheless, the rotor speed is a time-variant parameter, which changes from zero at the starting instant up to its rated value at a synchronous speed. Consequently, during the generator startup, the frequency of the induced voltages in the search coils needs to be updated continuously for obtaining reliable values for the differential voltages. A simple method is presented to achieve this goal by detecting the sequential zero crossing of the voltage waveforms. The proposed method is verified through simulation and experimental results. They show that the proposed diagnostic technique is capable of detecting and discriminating stator and rotor turn-to-turn faults during the machine startup period, both in generating and motoring conditions, with suitable accuracy and security. In addition, the region of stator turn-to-turn faults can be easily identified. [ABSTRACT FROM AUTHOR]

This article analyses the electromagnetic performance of dc-biased current vernier reluctance machines (DCB-VRMs) with distributed windings. Taking example of 12-stator slot machines, the coil connection and current configuration are illustrated. Moreover, the back electromotive force (EMF), torque capability, etc., are analyzed by finite-element analysis (FEA). In addition, the torque density of DCB-VRMs equipped with distributed and nonoverlapping windings are compared. The results show that some combinations of distributed winding machines present a higher torque capability thanks to the higher pole ratio. [ABSTRACT FROM AUTHOR]

Fractional-slot slot harmonic only windings (SHOW), featured by multi-layer and varied coil turn ratios, contain only the torque-generating component and its slot harmonics in stator magnetomotive force (MMF), which makes them attractive. This paper establishes general design principles of SHOW considering different slot/pole combinations and makes detailed comparisons between SHOW and double layer (DL) windings for surface-mounted permanent magnet (SPM) machines. Firstly, fractional slot windings are classified into several categories. Similarity in distribution factors of MMF harmonics is illustrated, based on which, harmonics elimination principle of SHOW is explained. Then, general equations for calculating optimal coil turn ratios for SHOW are derived. Practical ratios approximating the optimal ones are also presented and evaluated. Furthermore, in order to show the superiorities of SHOW, 12-slot/10-pole (12s10p) and 24S10P SPM machines with SHOW are comprehensively studied and compared with their DL counterparts in terms of torque ripple, overload capability, rotor magnet loss, stator iron loss and radial electromagnetic force harmonics. Finally, 12S10P and 24S10P prototypes with SHOW are fabricated and tested for verifications. [ABSTRACT FROM AUTHOR]

This article provides an applicable method to predict the distribution of the electric potential inside the winding of an electrical machine with a reasonable set of parameters. It extends the understanding of the winding impedance in terms of the inter-winding behavior and gives us the opportunity to properly design the insulation system during the development phase of an electrical machine. Predictions are backed up by measurements and an in-depth look at the measurement setup. The results proof nonuniform potential distribution and show that the potential difference between individual turns exceeds the amplitude of the phase voltage. Our findings also establish an interrelation between the winding impedance and the potential oscillations inside the winding. The article provides an introduction to the fundamental process of voltage stress on electrical machine windings and discusses drivers for upcoming challenges in the field of winding insulation and partial discharges. [ABSTRACT FROM AUTHOR]

This article proposes a novel doubly fed flux reversal machine (DF-FRM) with two sets of armature windings wound on both stator and rotor teeth. The proposed DF-FRM can provide much higher torque density than conventional FRM due to better utilization of rotor space. Moreover, the DF-FRM exhibits higher fault tolerance and it can still offer almost the desired output torque of FRM during fault operation, albeit one set of armature windings is malfunctioning. The machine topology as well as operation principles of a 12-stator-slot/14-rotor-slot DF-FRM is introduced and explained. Furthermore, the electromagnetic performances of FRM and DF-FRM with optimized structure aiming at maximum torque density are analyzed and compared using finite element (FE) method. The results show that DF-FRM can yield 60% higher torque density than the conventional FRM. Finally, a prototype is manufactured and tested to validate the FE results. [ABSTRACT FROM AUTHOR]

Vernier permanent-magnet (VPM) machines which have high torque density and high efficiency have been extensively used in direct drive. This article attempts to propose a new winding form and compare it with a traditional winding form as a part of fractional slot winding in the VPM machines to provide a design guideline in the aspect. Different winding forms are compared with the same copper loss and the same design. The design guideline of winding forms is provided by multiobjective generation algorithm (GA) optimization. Maximum torque value and minimum torque ripple are the optimization objectives in the GA optimization process. In addition, several models of the modularized motor with the new winding form based on the fractional-slot windings are compared, and the suitable application range of these models are discussed. [ABSTRACT FROM AUTHOR]

This article compares two important methods for the synthesis of the winding layout of ac machines. Both methods apply in general to integral-slot and fractional-slot windings, including nonoverlapping windings so they can both be claimed to unify the synthesis task. Both of them also maximize the winding factor at the working harmonic. This article gives several examples including the calculation of the winding factor by the little-known closed-form expression of Klíma, which also applies in general to the entirety of this class of windings. Exact agreement with the calculation based on the slot-star corroborates the results. [ABSTRACT FROM AUTHOR]

Tooth coil windings, in particular when using a double layer structure, present opportunities for in-slot liquid cooling. Since the windings are not overlapping, access to the slot from the end section for coolant liquids is enabled. In this article, a solution for in-slot and in-stator direct oil cooling for a tooth coil winding machine is presented. The coils are prewound on bobbins and inserted on the stator teeth. The novelty of the design consists in the integration of the cooling, using a thermally conductive epoxy resin to create the channels within the slot as well as the positioning of the stator yoke cooling channels. A 50-kW machine for an automotive traction application is designed, manufactured, and tested. Conjugate heat transfer simulations are used in the design process in combination with finite-element analysis for the loss mapping. The thermal model is verified with measurements at 6-L/min oil flow and 17.5 A/mm2 continuous and 35 A/mm2 30-s peak. The thermal model is then used to establish a continuous operating point at 25 A/mm2. [ABSTRACT FROM AUTHOR]

Flux estimation of single winding induction machines (SWIMs) operating in a zero-speed region is challenging, since in this operation region, the voltage drop on the stator resistance value, which varies with the operating point, is not negligible. Furthermore, in this operation region, because of the interference between higher band frequencies of a dc-rejection filter with low-pass filter of the stator currents, the dc-offset of measured currents may distort the true values of the stator current. Dual stator winding induction machines (DSWIMs), which have two sets of three-phase windings with different number of pole pairs and adapt a standard squirrel cage rotor, have overcame the associated problems of SWIMs in the zero-speed region. Nevertheless, DWSIMs have lower power rating than SWIMs if they use the same stator and rotor frames. In this article, an optimal design procedure is proposed for DSWIMs, which benefits the advantages of DSWIMs and surmounts the rate reduction problem as much as possible. In this regard, the optimal flux levels ratio of winding sets and the best pole pair ratio are determined first. Afterward, the winding specifications are designated to have maximum output power, while the DSWIM advantages, especially the zero-speed region operation capability, remain valid. A DSWIM is designed, simulated in ANSYS/MAXWELL and fabricated based on the proposed method and utilizing commercially available standard stator and rotor frames. Experimental assessments verify that the DSWIM prototype has improved the rate-reduction problem up to 19% in comparison to similar proposed DSWIMs. [ABSTRACT FROM AUTHOR]

With the continuous improvement of magnetic and mechanical properties of soft magnetic composite (SMC) material, there is a trend to develop novel electrical machines with SMC cores for some special applications. Among these electrical machines, permanent magnet claw pole machine (CPM) has been extensively studied over the past few decades. As linear global winding has been used in this machine, it can be regarded as a linear winding CPM (LWCPM). To improve the performance of LWCPM, a new S-shape winding CPM (SWCPM) is proposed in this article. The main stator structures of the LWCPM and SWCPM are optimized to achieve maximum torque ability. Compared with LWCPM, SWCPM provides higher average torque, power factor, and higher efficiency. The main disadvantage of the proposed SWCPM is its lower flux weakening ability. 3-D finite element model is used to evaluate the performance of the proposed LWCPM and SWCPM. The accuracy of the 3-D finite element model is verified by using a previous prototype. [ABSTRACT FROM AUTHOR]

In this article, a novel doubly-fed flux-switching permanent magnet (DF-FSPM) machine is proposed, whose armature windings are wound on both stator poles and rotor teeth. Different from the conventional FSPM machine in which the armature windings are only located in the stator, the rotor slot area is fully utilized in the DF-FSPM machine to improve the electrical loadings and, thus, the torque density. Moreover, it has the potential of fault-tolerant operation, since it comprises two sets of armature windings, which can work individually. The topology and the operating principle of the machine are introduced with reference to a 12-stator-pole/10-rotor-tooth DF-FSPM machine. The electromagnetic performances of the optimized DF-FSPM machine and its FSPM counterpart machine are compared, including the induced voltage, inductances, torque capability, flux weakening capability, efficiency, and power factor. It shows that the DF-FSPM machine can exhibit about 46.5% higher torque density than the FSPM machine, while its torque production per magnet volume is also improved by about 39.6%. In addition, the efficiency and power factor of the DF-FSPM machine are higher than those of the FSPM machine. Finally, experimental validation is conducted on a prototype machine. [ABSTRACT FROM AUTHOR]

An electronic pole-changing winding induction machine with eight and four poles for a 48-V starter-generator application is studied in this article. Starter-generators require high torque capability for short durations at low speed for cranking, a wide flux weakening region for regeneration, as well as high torque density, so that the machine may be integrated into a drive train with minimum change to the existing system. In this article, it is shown that when pole-changing windings are used, the axial length of the machine can be reduced compared to the baseline induction machine design, resulting in a more compact machine. The effects of shorter stack length and pole-changing windings on the performance of the induction machine are studied. Efficiency, loss, and power factor maps are calculated with analytical and finite-element methods and experimentally validated to compare the performance of the pole-changing winding induction machine with a baseline design under various operating conditions. [ABSTRACT FROM AUTHOR]

This article presents a novel use of three-dimensional printed direct winding heat exchangers (3-D-DWHX) to improve the thermal management of the stator in high power density electric machines. The 3-D-DWHX is in direct contact with the stator windings, enabling high continuous current densities. The use of dielectric polymer for the heat exchanger allows direct contact with the windings without an additional insulation material. By occupying the otherwise unused space between double layer concentrated windings, there is no significant impact on the electromagnetic design, and a smaller machine can be realized. The result is an increased continuous power rating and power density of electric machines. The polycarbonate-aluminum flake 3-D-DWHX was validated in a nonencapsulated motorette test, achieving a continuous current density of 20.4 ARMS/mm2 for a hotspot temperature of 148 °C. Finite element analysis shows that the same design, when encapsulated, can achieve 33.3 ARMS/mm2 current density with a hotspot temperature of 195 °C, corresponding to a continuous specific power of 11.8 kW/kg. [ABSTRACT FROM AUTHOR]

A systematic approach based on a novel space-shifted three-layer winding (SSTLW) to eliminate both the sub- and superharmonics of fractional slot concentrated winding ac machines is presented. In this proposed three-layer fractional slot winding, the number of turns in one layer and the relative positions of other two layers are optimized to cancel subharmonics. The cancellation of superharmonics is achieved through series connection of two SSTLWs through effective doubling of the number of slots. The cancellation of the dominant sub- and superharmonics using this approach leads to reducing the total harmonic distortion, torque ripple, PM eddy current loss, and rotor core loss, while simultaneously improving power factor and saliency ratio. The proposed design methodology and ensuring improvements have been validated through finite element analysis for the widely used 12-slot/10-pole and 18-slot/14-pole permanent magnet synchronous machine (PMSM) configurations. A prototype three-layer winding is built for a 10-pole PMSM to validate the simulation results experimentally. [ABSTRACT FROM AUTHOR]

The requirement for electrical machines with high power/torque density has stimulated the development of high efficient cooling systems to dissipate the heat within the machines. This article presents a new water cooling topology for thermal management of a permanent-magnet synchronous machine (PMSM) with concentrated windings. The advanced cooling configuration consists of several water cold plates radially inserted into the core laminations. Therefore, the heat sources in laminations and windings are close to the coolant. Three-dimensional electromagnetic finite-element analysis and the computational fluid dynamics are used to evaluate the performance of the PMSM. In order to evaluate the effectiveness of the proposed cooling configuration, one PMSM with the proposed cooling configuration and the other with the regular water jacket (WJ) are designed and built under the similar sizes and specifications. The simulated and tested results show that the winding temperature can be reduced by over 20 °C using this cooling technique compared to using the WJ at the rated condition. [ABSTRACT FROM AUTHOR]

Dual stator winding induction machines (DSWIMs), which have two sets of three-phase windings with unequal pole pairs in their stator and a standard squirrel cage rotor, have overcame the narrow speed operation region and circulating current problems exists in other types of dual winding machines. These advantages are resulted from the independent operation of their winding sets. The independent operation of winding sets will be guaranteed if the flux saturation is avoided. This letter proposes a novel reference frame angle determination technique that not only guarantees the flux saturation avoidance but also results in flux optimization in DSWIMs. Despite pervious methods, the proposed method does not require position or speed sensor and it is easily applicable in various control schemes and in different reference frames. This method is implemented in a flux and torque vector control system for driving a 3.3 kW DSWIM. The experimental results confirm the effectiveness of the proposed method. Moreover, by implementing the proposed method, the torque sharing between the two winding sets is properly done according to the power rating of each of them. [ABSTRACT FROM AUTHOR]

Multiphase drives are convenient for high-power/high-current applications as they allow the reduction of the phase current for given rated power and phase voltage. Due to their redundant structure, the multiphase drives have intrinsic open-phase fault-tolerant operation capability. This situation may happen when one or more power electronic units are turned off after a fault event, and the drive configuration allows phase disconnection. In this case, the healthy machine phases can be overloaded to keep the torque constant and without any pulsations. The goal of the work is the evaluation of the thermal parameters of the stator windings of multiphase machines to be used in the analysis of both short thermal transients and steady-state operation, during normal and open-phase faults. The approach has general validity and can be applied to any ac multiphase machine having a distributed winding configuration. The prototype used for the experimental tests is an asymmetrical 12-phase induction machine, having four 3-phase stator sets with isolated neutral points. The stator windings thermal model is obtained experimentally, by considering the mutual heat exchange phenomena among the windings when one or more winding sets are disconnected. This thermal model allows at evaluating the proper machine overloading for short thermal transients and steady-state operation in case of open-phase faults. [ABSTRACT FROM AUTHOR]

This paper presents an integrated control strategy for a starter/generator (S/G) system based on five-phase dual-stator winding induction machine (FPDWIM). The FPDWIM has a cage-type rotor and two sets of stator windings. One is a five-phase control winding (CW), and the other is a five-phase power winding (PW). In the starting mode, the FPDWIM works as a motor. The CW provides both active power and reactive power to drive the engine. In the generating mode, the CW mainly handles reactive power while the PW outputs active power. To achieve the integration of the starting and generating controls, indirect CW-flux-oriented control (ICWFOC) to operate in both starting and generating modes is proposed in this paper. In starting mode, the CW current and flux are controlled to output a constant starting torque; while in the generating mode, both CW and PW dc bus voltages are regulated. In this way, the principles and structures of the control strategies in both modes are compatible, resulting in a simpler implementation and improved performance. With the proposed control strategy, the system can complete the starting–generating operation with a smoother transition process. Simulation and experimental results are compared to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

A flux-based technique is proposed for the on-line detection, localization and discrimination of stator and rotor turn-to-turn faults in synchronous generators, using the measured air-gap rotational magnetic field. Simple magnetic field sensors (MFSs) are installed in the stator slots at different regions, and the corresponding induced voltages are measured. Several differential voltages are then obtained to give a picture of the rotational magnetic field symmetricity, whose distortions indicate the presence of the stator or rotor faults. The proposed diagnostic technique is presented in detail and validated initially by simulation results obtained with a finite element simulation package and afterwards through the experimental tests. The obtained results demonstrate that the proposed technique can be used to detect and discriminate stator and rotor turn-to-turn faults with appropriate sensitivity. In addition, the region of the stator turn-to-turn faults can be identified as well. [ABSTRACT FROM AUTHOR]

This paper proposes a novel, low-cost, effective way to improve the thermal performance of electrical machines by extending a part of the back-iron into the slot. This modification helps in reducing the thermal resistance path from the center of the slot to the coolant; however, its thermal benefits must be clearly evaluated in conjunction with the electromagnetic aspects, due to the higher iron losses and flux leakage, and furthermore such an extension occupies space, which would otherwise be allocated to the copper itself. Taking a case study involving an existing 75-kW electric vehicle traction motor, the tradeoffs involving the losses, flux leakage, output torque, torque quality, and the peak winding temperature with and without back-iron extension are compared. Finally, experimental segments of the aforesaid motor are tested, verifying a significant 26.7% peak winding temperature reduction for the same output power with the proposed modification. [ABSTRACT FROM AUTHOR]

The nine-phase six-terminal induction machine has recently been proposed as a promising contender to the conventional six-phase asymmetrical winding machine in terms of torque density, phase current quality, stator winding simplicity, and fault-tolerant capability. However, the relatively lower dc-link voltage utilization of a single neutral arrangement in multiphase machines with multiple three-phase windings represents, in general, a technical challenge when compared to windings with isolated star points. Therefore, this paper proposes a new pseudo six-phase winding layout suitable for medium-voltage high-power induction machines, which employs quadruple three-phase stator winding sets, while providing the same terminal behavior of a nine-phase six-terminal winding. Additionally, like the traditional six-phase winding, two possible neutral arrangements can be configured. The proposed winding configuration provides the same dc-link voltage utilization as in conventional dual three-phase winding machines with isolated neutrals. The effect of the circulating zero-sequence current component experienced with a single neutral arrangement can also be avoided. A 1.5 Hp prototype induction machine is used to experimentally validate the proposed six-phase winding layout under both healthy and fault conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a novel on-line rotor position estimation method for an aircraft wound-field synchronous starter/generator (WFSSG) in the low-speed region. The method is based on the fact that mutual inductance between stator and rotor windings of the main machine (MM) varies with the rotor position, so it is independent of magnetic saliency. High-frequency (HF) rotating voltage is imposed in the stator windings of the MM, and the rotor position information is extracted from the HF response current signals in the stator windings of the main exciter (ME) in WFSSG. Theoretical expressions of the HF response current signals containing rotor position information in the rotor and stator windings of the ME are derived. Then, harmonics in the ME stator windings are analyzed, and optimum frequencies of the injected HF voltage for MM and excited voltage for the ME are obtained. Also, a novel signal processing method without time delay is adopted to improve the signal-to-noise ratio of the extracted rotor position information. The performance of the proposed method is verified by the experimental results, and accurate rotor position can be estimated even if the magnetic saliency of the MM changes greatly during the start-up process. [ABSTRACT FROM AUTHOR]