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A number of transport vehicles have been fitted with electric traction motors and their inverters. The traction motor is required to continue to operate even if the inverter is under fault conditions. We propose a motor with two controllable rotors for a traction motor, which consists of 2 rotors and 1 stator. In this paper, we propose a fault-tolerant control method for a two-controllable-rotor motor using a 6-phase inverter. The operational principle of the two-controllable-rotor motor is described. The mathematical model under fault tolerant control is shown, and a fault-tolerant control method for the two-controllable-rotor motor is described. The proposed fault tolerant control method is verified by conducting finite element analysis and carrying out measurements on a prototype.

This paper proposes a rotor design method suitable for double-layer interior permanent magnet synchronous motor (DIPMSM), which can reduce electromagnetic torque ripple and at the same time reduce the electromagnetic noise of the motor. In previous studies, the inverse cosine function (ICF) was used to modify the rotor shape for making the air gap flux density distribution sinusoidal under no-load conditions, which can reduce the torque ripple. However, conventional ICF can only be used in a single-layer interior rotor structure. Consequently, this paper proposes a piecewise inverse cosine function (PICF) based on ICF, which can be applied to DIPMSM. To verify the improvement of the proposed method in the electromagnetic and noise aspects of the motor, the electromagnetic model and a noise prediction model of the 36-slot/8-pole motor are established by the finite element method. The PICF model is compared with the prototype in the aspects of electromagnetic performance and noise. The torque ripple is reduced by 54.16%, from ± 2.4 Nm to ± 1.1 Nm, and the electromagnetic noise is reduced by about 4.9 dB. Finally, the accuracy of the noise prediction model is verified by the noise test of the prototype.

Ultra-high-speed (UHS) surface-mounted permanent-magnet synchronous motors (SPMSMs) are widely used for driving air compressors. UHS SPMSMs can suffer from high stator iron loss and rotor eddy current loss due to their high rotational speed and changes in the magnetic flux density when loading. Since these losses do not have a linear trend but change according to the motor design parameters, mathematical models cannot always predict them. This study aims to design of UHS SPMSMs based on a kriging surrogate model that takes into account the stator iron loss and rotor eddy current loss. Since the kriging surrogate model is highly predictive for nonlinear inputs, it is the perfect candidate to take into account the stator iron loss and rotor eddy current loss. The design proposed in this study, allowed to minimize the size and losses of a motor that satisfied the power specification.

Aiming at the problem of excessive eddy current loss of permanent magnets in fractional slot concentrated winding permanent magnet synchronous motors (FSCW-PMSM) at high speed, a new PMSM with hybrid rotor structure for electric vehicles (EV) is proposed in the paper, the key is to introduce additional ferrite magnets in d and q axis magnetic flux paths, respectively. Furthermore, slotting on the rotor surface and genetic algorithm (GA) optimization are adopted to compensate for the side effects caused by the introduction of ferrite magnets and to obtain optimal parameters of the new motor. Compared with the traditional all-Nd-Fe-B structure, the proposed hybrid rotor structure can not only curb the magnet loss at high speed, but also present a cost-effective design approach for IPMSM for EV applications with less usage of expensive Nd-Fe-B magnets as well as enhanced reluctance torque capability.

According to IEC 60034-1, as the industrial applications, not only efficiency but also power factor are important performance index. As a direct on line motor to replace induction motor (IM), a line-start synchronous reluctance motor (LS-SynRM) have a high efficiency but a low power factor than that of IM. In this paper, the analysis and design of LS-SynRM are performed considering the rotor slot opening and bridges for improving the efficiency and power factor. The reference machine is selected with the 2.2kW IM, the performance of reference model is analyzed based on a finite element analysis (FEA). To analyze the effect of rotor slot opening and bridges, an optimal model of LS-SynRM is designed through two step design process. First, the design of rotor slot for synchronization is performed, second, the design of barriers using the response surface method (RSM) is performed under the same condition of the stator size of IM. Based on the basic model, the performances of LS-SynRM are analyzed according to the slot opening and bridges. Furthermore, the parametric analysis is performed, and the final model is designed considering the efficiency and power factor based on the design parameters. Finally, the final model is manufactured, and the experiment is performed to verify the FEA result.

A permanent magnet synchronous reluctance machine (PMSynRM) is studied in this paper. It has a stack of surface-mounted permanent magnet (SPM) rotor and a stack of synchronous reluctance (SynR) rotor, which are axially combined on the shaft. Unlike the traditional PM-assisted SynR machine (PMASynRM), the magnets are not located in the flux barriers of the SynR rotor, therefore, the magnets and flux barriers have no more geometric confliction between them. The two rotor stacks can be circumferentially shifted to any relative angle. Clearly, the shifting angle and the axial length ratio between the two rotor stacks, together with the phase angle of the armature current vector, influence the motor performance, and their optimal design is detailed in this paper. Analysis of the prototypes shows that the studied PMSynRM evidently exhibits higher torque density than the conventional PMASynRM.

This work investigates the effect of design parameters of permanent magnet (PM) and flux barriers (FBs) in the rotor on the anti-demagnetization ability (ADA) of fractional slot concentrated windings interior permanent magnet (IPM) motors for electric scooters. A 2.5 kW IPM motor (12 slots and 8 poles) is designed for a wide speed range, and its ADA associated with different PM and FB arrangements is studied under high temperature and high current density operations. The analysis shows the relationship between the ADA and characteristic current (Ich, defined as the ratio of PM flux linkage to d-axis inductance). It is also found that proper designs of flux barriers can significantly improve the ADA of the IPM motor without much affecting Ich. Thus, the motor ADA and performance can be simultaneously improved. Finite element analysis is used for evaluation, and experiments are conducted to validate the analysis.

The rotor of self-bearing machines can be in an off-centered position as they lack of physical bearings. The air-gap length and effective area with respect to each phase become nonuniform, which results in inductance and back EMF non-linearities. Evaluation of self-bearing machines performance in time domain is inaccurate without a model that includes non-linear inductance and back EMF constants. To reflect non-linearities, finite element analysis (FEA) is often used. However, FEA requires large computational power to run in time-domain simulation. In this article, a 7-D lookup table (7-D LUT) model of inductance and back EMF constants, suspension forces, and torque is proposed for time-domain simulation, including non-linearity from the rotor translational and rotational displacement. Pre-evaluated FEA results are post-processed to construct the 7-D LUT model to enable fast and accurate time-domain simulation reflecting non-linearities from the input of rotary position (slotting effect), translational position in horizontal and vertical directions (unbalanced air-gap field effect), and magnetic saturation effect. A combined winding self-bearing machine is evaluated using the proposed method and verified with FEA and experimental results.

This article presents an improved analytical spatial harmonics subdomain (SHSD) model for analyzing the influence of individual spatial harmonics, in stator magneto-motive forces (MMFs), on the performance of multiphase cage rotor induction motors (CRIMs). The proposed SHSD model is an extension of conventional techniques that consider each MMF spatial harmonic, caused by stator slots with tooth-tips, to be individual excitations when quantitatively analyzing the resulting physical effects. The solution domain was divided into four subdomains (SDs) in 2-D polar coordinates, including 1) rotor bars described by the Helmholtz equation; 2) air gaps; 3) slot openings described by Laplace’s equation; 4) stator slots represented by pure forced vibration equations. Current density in the stator structure was decomposed in a Fourier series of position angles to obtain MMF spatial harmonics. This produced a set of pure forced vibration equations in the stator slots, which were first solved in 2-D polar coordinates rather than the typical Poisson’s equation. This approach establishes a relationship between electromagnetic performance and stator parameters, for further optimization of IMs and analysis of electromagnetic vibrations. The proposed analytical model was validated using a series of finite element simulations, which exhibited high accuracy and computational efficiency.

This article describes the characteristic calculation of induction motors with the same shaped rotor bars in equal spaces by considering hysteresis loops in stator and rotor cores. A fast calculation method based on the symmetrical bar shape is proposed to realize this calculation. The validity of the calculation is confirmed by experimental results. It is clarified that the accuracies of the calculated motor characteristics are improved by considering the reaction field caused by the hysteresis phenomenon and eddy currents in the core.

Permanent magnet (PM) machines with a harmonic utilization PM (HUPM) rotor show advantages in terms of magnet utilization and magnet weight reduction compared to common PM rotors. In this article, an analytic approach to estimate the electromagnetic torque, torque density, and magnet utilization of PM machines is presented. Two different rotor types, i.e., the surface-mounted PM (SPM) rotor and the HUPM rotor, have been chosen for analysis. The impact of geometry scaling on electromagnetic performances with a focus on torque characteristics and magnet utilization is studied. The 2-D finite element analysis (FEA) has been used to validate the analytical model. The analysis shows that the toque characteristics and the magnet weight of both machines are strongly affected by the outer machine dimensions and current loading. However, due to the higher utilization factor for the HUPM rotor, the magnet weight of this machine type can be reduced.

This article proposed a nonlinear analytical model (NAM) for external rotor permanent magnet synchronous motor (ER-PMSM) considering both rotor and stator saturation. The improved magnetic equivalent circuit (IMEC) is introduced to accurately describe the saturation effect of rotor and stator. The air gap reluctance is replaced by magnetic flux source, and, therefore, the size of IMEC can be reduced while keeping high accuracy. For the air gap field calculation, the analytical solution will be obtained based on the modified boundary condition from the IMEC. The complex permeance function is extended to represent the slotting effect of ER-PMSM. Hence, the NAM will be numerically solved from the combination of IMEC and analytical air gap solution. Both finite-element analysis (FEA) and experiment demonstrate that the proposed model has high accuracy and requires little time.

This article presents a novel doubly fed doubly salient permanent magnet machine (DFDSPMM) with armature windings wound around stator and rotor teeth. Compared with the conventional doubly salient permanent magnet machine (DSPMM), this machine locates an extra winding in the rotor slots as armature winding to fully use its rotor slot space, thus leading to an increase in the output torque. The structure and operational principle of the proposed machine are analyzed at first. Then, the feasible stator/rotor-pole number combinations are discussed. Furthermore, the electromagnetic characteristics of the investigated machines are predicted based on the 2-D finite element (FE) analysis. It shows that higher torque density and lower cogging torque can be achieved by the proposed DFDSPMMs with improved stator/rotor-pole number combinations. Moreover, the proposed DFDSPMMs are compared against a surface-mounted permanent magnet machine (SPMM) to reveal comprehensive performance. Finally, the prototype is built and tested to validate the 2-D FE predictions.

The integrated magnetic-field-modulated brushless double-rotor machine (IMFM-BDRM) can be a promising candidate for the electrical-continuously variable transmission (e-CVT) in hybrid electric vehicles (HEVs) due to its brushless and compact structure. However, the large permanent-magnet (PM) eddy current loss and the conflict between torque density and mechanical strength limit its application. In this article, an IMFM-BDRM with an improved PM rotor is proposed to solve those problems. First, the structure of the proposed machine is introduced, and the magnetic field modulation mechanism is analyzed by the magnetic circuit method. The research shows that the modulated magnetic fields in the proposed IMFM-BDRM are produced mainly because of the variation in the flux paths, which is quite different from that in the traditional IMFM-BDRMs. Second, the electromagnetic performances are analyzed by the finite-element method. The effects of the structure parameters of the two rotors on torque performance are further investigated. Finally, to evaluate the overall performance of the proposed IMFM-BDRM, a traditional IMFM-BDRM with the same stator is designed to compare their performances. The comparison results show that the proposed machine has more advantages of output torque, PM loss, and efficiency than the traditional IMFM-BDRM.

In this article, a new low-cost small-scale three-phase brushless motor topology is proposed. This is a new topology for self-excitation of brushless wound rotor synchronous motor investigated initially for rated speed. For brushless excitation, the stator is designed to contain two windings, namely, three-phase armature winding and exciter winding. The rotor consists of two windings, that is, harmonic winding and field winding, and a diode rectifier. An inverter feeds the three-phase armature winding which is connected in series through an uncontrolled three-phase rectifier to a single exciter winding. When the current is supplied from the inverter, both the armature and exciter windings are energized eventually producing a flux in the air gap. Since the flux produced by the exciter winding is not synchronized with the field winding, it produces a harmonic to be intercepted by the harmonic winding on the rotor. Eventually, the voltage produced in the harmonic winding is used to feed dc current to the field winding for brushless operation. The results obtained by 2-D finite-element analysis (FEA) validate the brushless operation of the motor. The proposed motor is analyzed basically for topology verification with the FEA results. Since the topology can be verified, further effort can be put to investigate such low-cost topologies for brushless wound rotor synchronous motor. It can be an alternative to a costly permanent magnet synchronous motor for specific applications.

In this paper, a novel 6-stator-pole double-rotor hybrid excited axial switched-flux permanent magnet (DR-HEASFPM) machine is proposed for electrical vehicles. Based on 3-D finite element analysis, the influence of 10-, 11-, 13-, and 14-rotor-pole on the electromagnetic performance of DR-HEASFPM machine, including the magnetic field distribution, flux-linkage, back-EMF, flux regulation principles and capability, is comparatively investigated. The results show that the 6/10-, Ll-pole DR-HEASFPM machines exhibit higher PM flux-linkage and back-EMF. Moreover, the back-EMF of 6/11-pole machine is more sinusoidal and the flux-regulation capability is more excellent, which is suitable for wide speed-regulation application.

This article deals with electromagnetic forces of permanent magnet synchronous motors (PMSMs) with inclined and parallel rotor eccentricity. The electromagnetic forces have the spatial orders of the main components (multiples of pole numbers) and the sideband components when the rotor is eccentric. Although other studies have reported that each amplitude of an upper and a lower sideband is different, the causes of the asymmetry have not been fully investigated. The rotor eccentricity leads to changes in the gap permeance, the working point of the rotor magnets, and the distribution of gap magnetic flux density. By considering these effects in detail, we develop a new analytical expression of electromagnetic force, which expresses the asymmetry of a pairs of sidebands. The expression is compared with 3-D magnetic field analyses of PMSMs with inclined and parallel rotor eccentricity. As a result, it is found that upper sideband amplitudes are larger than lower sideband amplitudes, and the ratio of an upper sideband to the lower sideband of parallel eccentricity is larger than that of inclined eccentricity.

This article presents the rotor optimization in an interior permanent magnet synchronous machine (IPMSM) with high-strength non-grain-oriented (NGO) silicon steel material. Different from simple replacement with high-strength NGO, this article presents a customized design to make the best use of rotor iron core material. Specific optimization of the rotor topology is presented, followed with simulation verification by finite element method (FEM). Based on the simulation results, the benefits and limitations of the optimization design with the replacement of high-strength NGO are listed. In order to further overcome the limitations of the presented optimization design, magnetic characteristics of the high-strength NGO laminations subjected to various tensile stresses are measured in the experiment. Finally, experimental results are analyzed, and the conclusions to employ high-strength NGO for IPMSM are summarized.

Surface-mounted permanent magnet synchronous motors (SPMSMs) usually adopt a retaining sleeve for ultrahigh-speed (UHS) applications. The retaining sleeve usually has high electrical conductivity and cannot be segmented. Accordingly, the rotor eddy current loss is high. Moreover, the higher the eddy current loss, the higher is the rotor temperature. Therefore, the rotor eddy current loss should be considered in the design stage. However, the eddy current loss is generally calculated through three-dimensional finite-element analysis (3-D FEA) and considered cumbersome because of the high computation time. This article proposes a simple estimation method for the rotor eddy current loss of a UHS SPMSM according to the motor size. In this study, the mechanically stable cross-sectional structure of the rotor was fixed, and a formula for predicting the eddy current loss of the rotor based on motor size was devised. In this method, the basic electromagnetic formula for eddy current and the frozen permeability method were utilized. The proposed method was validated via comparisons with the results of 3-D FEA.

In the conventional flux reversal permanent magnet (FRPM) machine, half of the permanent magnets (PMs) produce the leakage flux at each operation moment, which results in poor utilization of magnets. In order to improve the magnetic flux utilization in the FRPM machine, this article proposes a novel consequent-pole FRPM machine topology with Halbach array magnets in the top of rotor slot, where Halbach array magnets in the rotor slot are employed to guide the flux into the rotor teeth to reduce the leakage flux. Therefore, compared with the conventional FRPM machine, the proposed counterpart exhibits larger back-electromotive force (back EMF) and torque density. In this article, the structure and operation principle of the proposed FRPM machine are investigated based on a classical 12-slot/17-pole FRPM machine topology. Furthermore, the electromagnetic performances of the proposed machine, including back EMF, electromagnetic torque, losses, flux-weakening, and overload capabilities are obtained and compared with the conventional machine by the finite-element method (FEM).

This article presents an analytical solution procedure to investigate the geometrical impact of the magnet and the rotor core on the performance of slotted, surface-mounted permanent magnet (PM) synchronous motors. In particular, four different motor configurations with loaf-shape/regular arc-shape magnets mounted on the octagon/circular rotor surface are investigated, and their no-load (i.e., PM flux density, back EMF, and the cogging torque) and on-load (i.e., armature flux density, winding inductance, and electromagnetic torque) performance metrics are compared. The analysis is carried out analytically by using the concept of the surface magnetization current (SMC) and the superposition theorem. First, the stator slots are nullified, and Poisson’s equation is solved on a slot-less surface. The effect of the stator slots is then included by injecting equivalent SMC on the stator bore. For verification purposes, analytical results are validated via the finite element (FE) and experimental measurements on the motor prototype.

The segmented-stator dual-rotor axial flux permanent magnet motor (AFPMM) in this article adopts two-segment Halbach permanent magnets (PMs) in the rotor and soft magnetic composite materials in the stator core, so it has the advantages of high torque density and high efficiency. This article proposes an optimization method for AFPMMs combining analytical optimization and nonlinear optimization, based on the analytical calculation of the magnetic field and electromagnetic performance. To realize analytical calculations, the AFPMM is regarded as the superposition of equivalent linear PM motor slices at different radii. The magnetic field is calculated using the slotless 2-D equivalent model and the slotted air gap relative permeability. Compared with finite-element analysis (FEA), the analytical calculation of the electromagnetic characteristics has acceptable accuracy and faster speed. The multiobjective optimization program for the AFPMM aims at lighter motor mass and lower loss. In analytical optimization, the expression of the optimal axial magnetization coefficient of the two-segment Halbach array and the expression of the minimum rotor core thickness is deduced to improve the optimization speed and results. Then, the nonlinear optimization algorithm is used to solve the multiobjective optimization problem.

In this article, the application of a nonlinear complex De Gersem-type polyharmonic finite-element (FE) model in the steady-state analysis of three-phase solid-iron rotor induction motors is discussed. Effective magnetic permeability, dependent on the fundamental time harmonic of the magnetic field, is used for the representation of the magnetic saturation effects. A new coupling scheme for the air-gap mesh nodes is proposed in order to make the model more time-competitive with the time-stepping model in cases where the number of air-gap nodes must be high. By means of comparative analysis of computed electromagnetic torque and harmonic losses, it is shown that omitting some nodes at the interface boundary results in the reduction of the execution time by a factor of 100 with only a slight loss of accuracy.

In this paper, a novel hybrid permanent magnet variable flux memory machine using two-part rotor is proposed whose rotor comprises an AlNiCo part and a NdFeB part adjacent to each other on the same shaft. With the proposed topology, flexible flux controllability can be achieved since the magnetization state of AlNiCo can be adjusted by a temporary current pulse. The detailed operating principles are described, and the split ratio and some key design parameters are optimized. Then, the electromagnetic performance of the proposed machine with emphases on back electromotive force, flux density, flux-weakening performance, and torque characteristics is investigated. Finally, 3-D finite-element validation is implemented and a machine prototype has been manufactured and tested to validate the analyses.

This paper presents a novel interior permanent magnet brushless doubly fed generator (IPM-BDFG) for wind power applications, which is based on the magnetic field modulation theory. The basic structure and working principle of the IPM-BDFG are put forward first. As the rotor structure has a great influence on the performance of the IPM-BDFG, the merits of the IPM rotor are discussed by comparing with the surface-mounted rotor. In order to solve the asymmetry phenomena and reduce the harmonics caused by the introduction of field modulation ring, a three-segmented structure for the outer rotor is adopted. Finally, the performances of the proposed IPM-BDFG are validated by using finite-element analysis (FEA). The FEA results show that the IPM-BDFG with segmented outer rotor has excellent performances and owns good potential in the applications of future large-scale wind power generation systems.

Magnetic equivalent circuit (MEC) modeling is a challenging work to machines with novel structures, although it is an effective tool in the design process. The parameterized dynamic MEC modeling method is developed in this paper for the analysis of a novel rotor-segmented axial-field switched reluctance machine (RS-AFSRM). The “parameterization” is the feature leading the general MEC models in each interval of the rotor position, and the “dynamic” characteristic depends on the change of the flux patterns in the air region with the rotor displacement. By the proposed MEC model, the RS-AFSRM is analyzed on the smooth transition with efficient computation. The results obtained through the developed MEC models are verified by both the static and motion-coupled analyses.

A continuous demand for more efficient and more compact drives is pushing the popularity of high-speed permanent magnet synchronous machines (PMSMs). However, high rotational speeds and extreme power densities imply that an appropriate cooling of the rotor may be difficult. This is all the more important because of the risk of demagnetization when permanent magnets are operated at high temperatures. Therefore, it is paramount to reduce the losses in the rotor of high-speed machines as much as possible. One technique to reduce the eddy-current losses is introducing a shielding cylinder, i.e., a conductive sleeve that is wrapped around the magnets. However, when badly designed, such a shielding cylinder may increase, rather than decrease, the losses. Therefore, an in-depth study of the effect of the shielding cylinder on the eddy-current losses in high-speed PMSMs is required. By studying how the eddy-current losses are affected by the shielding cylinder’s thickness and its conductivity, this paper aims at providing more insight in how the eddy-current losses can be reduced. Moreover, the study of the eddy-current losses is repeated for different stator sources to evaluate the importance of accounting for the actual control strategy during the machine’s design.

There were many attempts to design the rotor bar shape to increase the starting torque in squirrel cage induction motor, and it is well known that deep slot of rotor bar increases the starting torque. However, this deep slot increases the leakage flux so that it hurts the running efficiencies. To increase the running efficiency, it is necessary to keep shallow slot of rotor bar. This paper presents a new design of rotor bar to improve the starting torque without decreasing motor efficiency. The influence of current density of rotor bar on starting torque and rotor copper loss is analyzed so as to design the shapes of rotor bar. In the design, the starting torque was improved by increasing the rotor resistance at startup, and the rotor reactance was maintained during operation. The result showed the improvement of the starting torque without reducing the running efficiency.

In this article, a novel exterior-rotor multiple teeth enhanced-torque switched reluctance motor (SRM) is proposed, which exploits permanent magnets (PMs) inside the end teeth of the neighboring stator poles. First, the topology of the proposed motor, namely PM-SRM, is introduced and its working principle is illustrated. Then, based on the magnetic equivalent circuit (MEC) of the motor, it is proven that the PMs contribute to increase the air-gap flux density and regulate the stator poles flux density. As a result, the output torque of the motor is increased as well. The electromagnetic analyses of the proposed PM-SRM are performed using 3-D finite-element analysis. To validate the improved performance of the proposed PM-SRM, it is compared with its PMless counterpart and a classical 12/10-pole SRM in terms of the output torque and power, losses, and efficiency. It is shown that the proposed motor outperforms the two compared motors in terms of the output power and torque, and efficiency. Finally, a prototype of the motor is fabricated and tested to evaluate the predicted results. Both simulation and experimental results demonstrate the high torque and power production capability of the proposed PM-SRM.

Power split system is the key power transmission component in hybrid electric vehicles (HEVs). This paper presents a new consequent-pole inserted permanent magnet (PM) double-rotor machine., which is suitable as the power split system for HEV. The key is to insert the interior radical magnetized PM with the same polarity into the rotor's iron core., so the mechanical structure of the proposed machine is more robust. Also., the working principle is analyzed., and the structure is optimized. In addition., the performances of the conventional machine and proposed type are quantitatively compared. The result shows that proposed machine has more advantages to be applied for the power split system in HEVs.

This article describes the development of an exact analytical model for predicting magnetic field distribution within active parts of a dual-rotor (DR) permanent magnet (PM) synchronous machine with a Halbach array. The model is based on the accurate solution of Laplace’s and Poisson’s partial differential equations (PDEs) using a method of separation of variables. The model also allows the calculation of the DR machine flux linkage, back electromotive force (bEMF), and electromagnetic torque at on load and cogging torque at a no-load condition. The model can be used at the initial stage of designing a DR PM machine for the estimation of electromagnetic parameters and the optimization of machine geometry.

There is always uncertainty in industrial manufacturing. These uncertainties have an undesirable impact on the products if deterministic optimization approaches are employed. In order to have products as desired, uncertainties must be quantified in the design process. This paper presents a robust design optimization of an outer rotor surface mounted permanent magnet motor with particular application in the hybrid vehicle using the design for six-sigma methodology. Due to very long computational time of robust optimization, a ten high-dimensional surrogate model of the system using the Box–Behnken response surface methodology (RSM) is integrated with the particle swarm optimization (PSO). This causes a significant improvement in the effectiveness and efficiency of optimization. The results acquired from RSM are verified by their simulation using the finite-element method, and the accuracy of RSM is proved. Finally, the deterministic and robust optimized motors are simulated in mass production using Monte Carlo analysis, and six-sigma quality achievements are demonstrated.

Electric continuously variable transmission (e-CVT) device is a key component in hybrid electric vehicles (HEVs), which serves to perform the energy transmission among the initial combustion engine, battery, and output shaft. This paper presents a novel consequent-pole PM magnetic-geared double-rotor machine (CPDRM) that utilizes the magnetic gearing effect to transmit the power with a high efficiency. The artistry of CPDRM is to insert a dc winding within the center of the stator on the circumferential direction. Therefore, the machine can extend the constant-power region by changing the current direction and amplitude of dc windings. Meanwhile, the flux density within the air gap is changed accordingly. Then, the working principle of CPDRM and the flux change process are illustrated by employing the magnetic circuit method. Finally, a finite-element method model is constructed to verify the performances of the CPDRM under different operating modes. The result shows that the proposed machine has an excellent flux-weakening ability, and it can serve as a suitable candidate as an e-CVT component for HEVs.

Being much more rugged than a rotor made of traditional steel sheets, a solid rotor is frequently used in high-power high-speed induction machines (IMs). Furthermore, by a solid-rotor machine, a higher rotating speed can be achieved. However, the solid rotor also has certain disadvantages, the relatively high solid-rotor eddy-current losses being the most serious one. Basically, solid-rotor eddy-current losses are mainly induced by time–spatial air-gap flux density high-order harmonics. The suppression of the high-order harmonics is the key means to mitigate the rotor eddy-current losses. In this paper, a novel computational model is proposed for evaluating the rotor harmonic eddy-current losses of a 2 MW, 12 000 r/min IM. The model was built on a special machine referred to as a virtual permanent magnet harmonic machine (VPMHM). The model was constructed by applying the finite-element method (FEM), and it is based on the time–spatial harmonics produced by a rotating magnet with sinusoidal magnetization. The VPMHM model links the air-gap flux density harmonics directly to the specific rotor eddy-current losses. Furthermore, according to the proposed model, three options, namely, the use of air-gap permeance modifying notches on the stator teeth, semimagnetic wedges, and their combination, were investigated in detail for mitigating the rotor eddy-current losses in the motor nominal operating point. The results and conclusions in this paper are based on the FEM analysis.

By utilizing magnetic field space modulation magnetic gearboxes (MGs) are able to create speed amplification without any physical contact [1–3]. An example of a flux-focusing coaxial MG is illustrated in Fig. 1. This coaxial MG consists of an inner rotor 1 that contains $p_{1} = 4$ pole-pairs an outer rotor 3 with $p_{3} = 13$ pole-pairs and a central ferromagnetic segment central rotor 2 that consists of $n_{2} = 17$ pieces. The $n_{2}$ ferromagnetic segments serve to modulate the inner and outer rotor magnetic fields. In order to create the highest level of field coupling between the inner and outer rotors the number of ferromagnetic segments must be chosen to satisfy $n_{2} = p_{1}+p_{3}$. With this condition satisfied the rotor angular velocity relationship between each rotor is $\mathrm{w}_{2} \mathrm{p}_{2} = \mathrm{w}_{3} \mathrm{p}_{3}+ \mathrm{w}_{1} \mathrm{p}_{1}$ where the subscript denotes rotor number. If the outer rotor is fixed $( \omega _{3} = 0)$ the torque will be maximized and the gearing ratio will be $\mathrm{w}1 = $ Gw 2 where $\mathrm{G} = n_{2}/ p_{1}$. For the example MG shown in Fig. 1 the gear ratio is $\mathrm{G} = 4.25$. In order to try to increase the torque density of a MG a range of different coaxial type rotor typologies have recently been investigated [4–14]. Along with the flux focusing MG design two other coaxial radial type MG rotor typologies that have been shown to create high torque density are the flux concentration Halbach rotor typology [15] and the consequent pole triple-PM rotor MG typology [16]. In this paper, these two design typologies are compared for the first time. The objective is to provide an idealized comparative analysis of the two competing typologies and then present the experimental design and testing of the best design.

This paper investigates the no-load iron loss, on-load loss, and thermal performance of a high-speed surface-mounted permanent-magnet synchronous machine with an amorphous metal stator core (AMSC) and a titanium alloy retaining sleeve by numerical methods. The electromagnetic properties of the AMSC are tested by an experimental platform. The distributions of no-load iron loss, rated-load loss, and the thermal behavior of the motor are investigated under converter supply conditions. Finally, the loss and thermal performances of the prototype are tested and compared with the corresponding simulation results to verify the accuracy of the calculation results and the superiority of the prototype.

Stator winding inter-turn (SWI) short-circuit fault and broken rotor bar (BRB) fault are two common faulty modes of the squirrel cage induction motors (SCIMs). These faults have various impacts on the motor performance and may be rooted in each other; therefore, they may be presented at the same time in an SCIM. This paper proposes an exact analytical model for the SCIMs, which is able to include the SWI and BRB faults presenting simultaneously or individually with variable severities. Multiple coupled circuit modeling is applied to achieve such analytical model. The magnetic saturation effect is included in the model by applying appropriate air gap function and the rotor bars skew effect is taken into account by using 2-D winding function theory. Simulation results as well as the corresponding experimental results approve the presence of the same harmonics in the stator line currents due to the proposed faults. However, more detailed study gives solution for discrimination of the faults. The attained analytical model can be applied to examine the performance of the related fault diagnosis methods and to design novel fault diagnosis techniques including the model-based ones.

This paper proposes and analyzes the design philosophies of the single-phase main exciter (ME) for an aircraft wound-rotor synchronous machine and investigates its operating characteristics in both generating and starting modes. The fundamental structure and starting–generating system are discussed. The load features of single-phase ME are summarized. The ME has the characteristics of linear current amplifier and approximately constant current source the generating mode, which can be used in the wide range of working temperature. Detailed waveforms and finite-element analysis verify that excitation current $I_{\mathrm {ef}}$ is almost irrelevant to speed but in direct proportion to frequency in the starting mode. Besides, simulated data indicate that the energy transferring efficiency between ME stator and rotor can reach about 55% by the single-phase ac excitation method. Finally, the experimental verification is carried out, and the simulated and experimental data and waveforms of single-phase ME agree well with each other.

This paper presents a composite solid rotor applied to improve the starting and synchronization capabilities of the line-start permanent magnet synchronous motor (LSPMSM). The rotor is mainly composed of solid steels to employ their high starting torque. A squirrel cage and some air slots are designed to be added on the rotor surface. During the starting process, the cage carrying eddy currents constitutes a branch in parallel with that of the solid steel, and hence decreases the total rotor impedance. Meanwhile, the surface slots enlarge the eddy current area of the solid steel and further reduce the rotor resistance. All these rotor parameters turning smaller lead to a higher induction torque, and thus enhance the motor performances of starting and synchronization. A set of comparisons about rotor parameters, induction torques, and speed-time responses are implemented among the LSPMSMs with the composite solid rotor and other solid ones lacking cage or slots. Results of the comparisons validate the advantages of the cage slot attachment as well as the motor performance improvement by applying the composite solid rotor.

Several brushless topologies for wound rotor synchronous machines (WRSMs) have been presented in recent years to replace the brushes and slip-ring assembly in conventional WRSMs [1–4]. The brushless operation of the WRSM presents these machines as an alternative to the permanent magnet synchronous machines (PMSMs) because of their low cost and competitive performance as compared to the PMSMs. However, the drawback of the brushless wound rotor synchronous machines (BL-WRSMs) is their low starting torque because of the absence of the excitation source on their rotor. Although, the BL-WRSM achieves the rated torque at the base speed but low starting torque under the base speed makes these machines less suitable for variable speed applications. A PM assisted BL-WRSM was presented in [5] to overcome the problem of the low starting torque and to provide better performance under full-load conditions. However, the presence of the PM on each pole increases the cost of the machine. Moreover, the leakage flux is increased in PM assisted machines. These issues can be resolved by the consequent pole (CP) machines [6]. In this paper, a consequent pole hybrid brushless wound rotor synchronous machine (CPH-BLWRSM) is proposed to overcome the problem of low starting torque, and to reduce the PM usage as compared to the PM assisted machines. A 2-D finite element analysis is performed to validate the proposed CPH-BL-WRSM and its performance is compared with the existing BL-WRSM and PM assisted BL-WRSM.

The temperature rise of the rotor caused by harmonic eddy-current loss constrains the performances of high-speed permanent magnet (PM) motors. Excessive temperature rise can even result in irreversible demagnetization in the PM. An analytical model for the rotor harmonic eddy-current loss of high-speed surface-mounted PM motors in consideration of eddy-current reaction fields, harmonic currents, stator slotting, and different rotation states of the rotor is proposed, which can be utilized to reliably calculate and evaluate the rotor harmonic eddy-current loss. The accuracy and effectiveness of this analytical model are validated by using the finite-element method and a proposed experimental method.

This paper deals with the feasibility of developing an external-rotor synchronous reluctance motor for a low-speed direct-drive domestic application. Here, an attempt is made to identify the rotor geometry which provides high peak, average torque, and the saliency ratio in comparison with those of equivalent external-rotor switched reluctance motor (Ex-R SRM) which has already been developed and tested for the same application. In this context, six different rotor geometries are considered for the feasibility study and their performance characteristics are predicted using finite-element analysis. These results are compared with the equivalent size of Ex-R SRM, and finally, a feasible rotor geometry is proposed for further investigation and for the prototype designing.

Vacuum technology is necessary for semiconductor industry, medical industry and food industry [1]. The vacuum technology is also necessary for the new space industry and other advanced industries [2]. Turbo molecular pumps with high speed rotors are key technology for these industries. Turbo molecular pumps are usually composed of active magnetic bearings, a high speed rotor and its controllers. Thus, the mechanism is very precise and complicated, which leads to high price. In this study, high critical temperature (T c ) superconducting magnetic bearings (SMBs) [3] [4] are tried to apply to a high speed rotor for turbo molecular pump because of some merits.

The fractional slot concentrated winding consequent pole (CP) permanent magnet (PM) synchronous machines can improve the PM utilization ratio. However, the even-order harmonics exist in phase back electromotive forces (EMFs) for specific slot and pole number combinations, resulting in high torque ripple. Therefore, the multilayer winding is employed in this paper to reduce the torque ripple by suppressing the even-order harmonic back EMFs. The principles of both even-order harmonic back EMFs and torque ripple suppression by the four-layer windings are illustrated. The electromagnetic characteristics of the CP PM machine with four-layer windings are compared with that of PM machines with the traditional and CP rotors by finite-element analysis. It is demonstrated that the four-layer winding can suppress the even-order harmonic back EMFs and torque ripple in the machine with CP rotor. The prototypes of both the traditional rotor and CP rotors with four-layer wingdings are manufactured and tested to verify the theoretical analysis.

Brushless doubly fed machine (BDFM), is a new type of machine with special structure, shows promising features for the field of variable frequency speed regulation and wind power generation due to its inherent characteristics, which has the advantages of reliable operation, adjustable power factor, lower operation and maintenance costs as well as requiring a smaller capacity converter [1], [2]. Since core loss has an important effect on efficiency and temperature distribution, it is vital to accurately calculate such component in an optimal design procedure. Furthermore, rotor core loss is also a significant factor which can affect the performance characteristics of BDFM due to the complex magnetic field distribution and relatively high value of slip. Specifically, a novel hybrid rotor structure which is combined with magnetic barrier and assisted cage has better coupling ability than the commonly used rotor structures such as cage rotor and reluctance rotor is presented but it also increases the difficulty of core loss calculation. E&S model is a vector magnetic hysteresis property model [3], [4], in which H (magnetic field intensity) is dependent not only on B (magnetic flux density) but also on time derivative of B. Increase of core loss when the phase difference between B and H occurs, is well expressed in this method, while the conventional analysis was not able to consider the phase difference between B and H. Furthermore, the total core loss including both alternating and rotational losses can be directly calculated from the fundamental terms of obtained $B_{x}$, $B_{y}$, $H_{x}$ and $H_{y}$ without other fitting data, which can improve the core loss computation accuracy of BDFM with hybrid rotor in contrast with conventional core models. In this paper, an improved E&S model based on a 2-D rotational magnetic property analysis for core loss of BDFM with hybrid rotor is proposed by considering the high-order harmonic magnetic field. The finite element analysis model of BDFM with hybrid rotor is established. The core loss calculation results are compared with the simulation results to verify the correctness and feasibility of the proposed E&S model. Fig. 1 shows the finite element model, hybrid rotor of prototype and special points distribution diagram of BDFM with hybrid rotor. As shown in Fig. 1 (a)-(b), the cage bars are added on the non-magnetic layer of the radial magnetic barrier rotor, and the cage bars are respectively divided into concentric cage bar and common cage bar. There are two kinds of rotating magnetic fields with different poles and frequencies in the air-gap of BDFM, which renders that the air-gap magnetic density harmonic contents are rich and the magnetic properties of each part of core are different. According to the basic principle, structure characteristics and magnetic field distribution of BDFM with hybrid rotor, some special points of stator and rotor are analyzed and calculated. The relationship between B vector and H vector, and the relationship between the waveform of $B_{x}$, $B_{y}$ and the waveform of $H_{x}$, $H_{y}$, obtained by the combination of the improved E&S model and finite element analysis, is shown in Fig. 1 (c), which is seen that the phase between B and H is different. The improved E&S model can consider higher order harmonic magnetic field than the conventional E&S model. As shown in Fig. 2 (a), the stator and rotor core loss calculation process of BDFM with hybrid rotor is described by the flow diagram. The datum of $B_{x}$, $B_{y}$, $H_{x}$, $H_{y}$ are obtained by the combination of the improved E&S model and finite element method, and all order harmonic of $B_{x}$, $B_{y}$, $H_{x}$, $H_{y}$ are computed by fourier series expansion. Therefore, the total core loss of BDFM with hybrid rotor can be calculated by the formula in the flow diagram, where, $\rho$ is the magnetic material density, T is the period, $m$ is the amount of the special points, $n$ is the harmonic order, and $M_{i}$ is the mass. In addition, in order to verify the accuracy of the core loss calculation, the 2-D finite element model of BDFM with hybrid rotor is established, and the simulation results are shown in Fig. 2 (b). The validity and feasibility of the improved E&S model is verified by comparing with the simulation results. In addition, the full paper will present the detailed calculation procedure and analysis.