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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]

In this article, a simplified three-dimensional (3-D) hybrid analytical thermal model for surface-mounted permanent magnet (PM) synchronous machines is proposed and applied to investigate the influence of PM segmenting strategies on the spatial PM temperature distributions and hotspots. The developed 3-D hybrid thermal model synergies the lumped-parameter thermal model and analytical method and is able to estimate 3-D spatial temperature distributions and hotspots for both unsegmented and segmented surface-mounted PMs accounting for the uneven PM eddy current loss distributions. Meanwhile, by utilizing the proposed matrix-based post-processing methods, the developed hybrid analytical thermal model has a simple mathematical expression but persists in high estimation accuracy. Finally, the proposed hybrid analytical modelling method is validated by 3-D electromagnetic-thermal coupled FEA and experiments. [ABSTRACT FROM AUTHOR]

This article proposes and investigates two asymmetric consequent-pole hybrid excited flux reversal machine (AS-CP-HEFRM) topologies, which have same numbers of iron poles and permanent magnets (PMs) with concentrated ac and dc windings on each stator pole and a salient pole rotor. If PM number on one stator pole is larger than 1, PMs are magnetized radially in the same direction on one stator pole, while opposite on adjacent stator poles. The phenomenon of the phase shift between the flux linkages of dc and PM excitations in the AS-CP-HEFRMs is revealed for the first time, which will weaken the regulation of dc excitation field to PM produced field. The elimination condition of the phase shift is derived and verified by finite-element analysis in this article, which can be considered as design guidelines in AS-CP-HEFRMs. Airgap magnetic field space harmonics of AS-CP-HEFRM are also investigated and verified by finite-element analyses. Meanwhile, the relationship between the rotor pole number and the stator pole arc (PM ratio) is derived and verified by global optimization based on genetic algorithm for maximum average torque. The influence of stator/rotor pole number combinations is also studied and compared in terms of torque, torque ripple, and flux regulation capability. The torque components produced by airgap magnetic field space harmonics are calculated and compared. A prototype has been built and tested to validate the finite element calculations. [ABSTRACT FROM AUTHOR]

A novel asymmetric interior permanent magnet (AIPM) machine is proposed in this paper for electric vehicle application. It has a skewed V-shape permanent magnet (PM) cavity, two PMs with different dimensions and an additional flux barrier outside the V-shape cavity in each pole. This asymmetric rotor topology can inherently utilize the magnetic-field-shifting (MFS) effect to reduce the current angle difference between the maximum PM and reluctance torque components, thereby enhancing the maximum synthetic torque with the same PM usage. The influences of cavity positions in the proposed AIPM and an existing AIPM with extra flux barrier inside the V-shape cavity are investigated and compared using finite element analysis. It is found that the proposed structure with outside flux barrier has higher average torque than the one with inside flux barrier. Both AIPM topologies are designed with the same stator, rotor diameter, and PM usage as the conventional V-shape IPM benchmark for Prius 2010. Electromagnetic, mechanical and steady-state thermal performance of three machines are compared. The results confirm that the proposed AIPM machine can achieve significant torque enhancement due to utilizing MFS effect, compared with the existing AIPM and the IPM benchmark. Finally, a small prototype of the proposed AIPM machine is designed, manufactured and tested to validate the FE analysis. [ABSTRACT FROM AUTHOR]

A new simple rotor initial position detection method for permanent magnet machines is proposed in this article. It is based on the magnetic saturation effect, which is commonly used by existing methods. Different from the conventional methods utilizing phase current or phase voltage sensors, the dc-link voltage sensor is used to estimate the rotor initial position. In the proposed method, a specific excitation approach is used to enhance the performance and a so-called “equivalent injection position” is developed to simplify the estimation process. The proposed method can achieve a 30° estimation resolution. Besides, practical considerations, including the dc-link voltage measurement errors, dc-link resistance, dc-link capacitance, and dc-link voltage ripples, are discussed in this article. A guideline of voltage pulse selection is presented to minimize the impact of these practical issues. Moreover, it is found that as the dc-link resistance increases, the proposed method shows a better estimation performance than the conventional methods. Besides, the proposed method is insensitive to sensor measurement errors. The experimental results are given to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, spoke array permanent magnet (PM) flux reversal machines (SAPM FRM), which feature spoke array PMs distributed along the stator inner surface, are proposed to improve the torque density. Compared with the conventional surface mounted PM flux reversal machine (SPM FRM), the proposed SAPM FRM can produce about 100% larger torque with negligible torque ripple, as well as higher efficiency and higher power factor. Two prototypes have been built and tested to validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

A novel parallel hybrid excited (HE) machine with wide flux regulation range is proposed in this paper. The flux paths of permanent magnet (PM) and field winding are separated to avoid irreversible demagnetization and achieve improved flux regulation capability. Since the field winding and armature winding are located in the same stator slots, open-winding drive circuit can be employed to feed biased ac excitation in one set of winding and solve the spatial confliction of conventional hybrid excited machine. Finite element (FE) method is utilized to analyze the electromagnetic performances of the proposed HE machine, in comparison with the original HE machine. It is revealed that the proposed HE machine exhibits lower PM excited back-electromotive force (EMF), which is beneficial to high speed fault tolerant operation. Besides, the torque density can be higher with flux enhancing, albeit with reduced PM usage. Finally, a prototype is manufactured and tested to validate the FE predictions. [ABSTRACT FROM AUTHOR]

Hybrid permanent-magnet (PM) variable-flux memory (VFM) machines employ both high coercive force PM, i.e., the constant PM (CPM), and low coercive force PM, i.e., the variable PM (VPM). The high energy-product CPM guarantees the benefits of high torque density of the conventional PM machines, while the PM magnetization state of the VPM is flexibly regulated to match various operation requirements. In fact, the two kinds of PMs can be magnetically connected in either parallel or series, with which the machine characteristics are quite different. In this paper, based on the two-dimensional and three-dimensional finite-element analyses, a pair of VFM machines with parallel and series connections, respectively, are investigated with specific reference to identify their difference in end effects. The comparison results show that the series hybrid PM VFM machine suffers more serious end leakage flux. The prototype machines are manufactured and tested to validate the analyses and predictions. [ABSTRACT FROM AUTHOR]

Permanent magnet (PM) machine has received much attention recently. However, unbalanced magnetic force (UMF) may occur in PM machines with some slot/pole number combinations even when there is no rotor eccentricity, which can cause high vibration and noise. In order to reduce the rated on-load UMF, three 3-slot/2-pole PM machines with different auxiliary slots are investigated and compared in this paper. In the first two machines, namely, machines 1 and 2, the auxiliary slots are inserted in the middle of the stator teeth, while their sizes are optimized under different working conditions, i.e., no-load and rated on-load conditions. In contrast, both position and size of auxiliary slots are optimized under the rated on-load condition in the third machine viz., machine 3. Compared with the conventional prototype machine, the maximum rated on-load UMFs are reduced by 6.3%, 50.7%, and 96.6%, and the rated output torques are decreased by 0.7%, 11.5%, and 4% in these three machines, respectively. In addition, the other electromagnetic performances, such as flux linkage, back electromagnetic force, cogging torque, rated output torque, and torque ripple, are compared. The influence of working conditions is investigated, and the experiments are also carried out to validate the numerically predicted results. [ABSTRACT FROM AUTHOR]

This paper proposes two novel partitioned stator (PS) memory machines based on flux-reversal and switched-flux topologies, respectively. The proposed machines geometrically feature two separate stators with armature winding and hybrid PM excitations, i.e., NdFeB and low coercive force PMs. The proposed PS machines can offer increased available inner stator space for hybrid PM, which is beneficial to the torque improvement. The machine topologies are introduced first in terms of possible PM types with parallel magnetic circuits. The design considerations for hybrid PM are analytically analyzed. Then, the electromagnetic characteristics of the two proposed machines are comprehensively compared by using finite element (FE) method. The commercially available Toyota Prius 2010 machine is referenced as a benchmark for comparison with the optimal PS machine having identical overall dimension in potential context of traction applications. Finally, The FE analyses are validated by experiments on a small-scaled demonstration machine. [ABSTRACT FROM PUBLISHER]

A series hybrid variable flux memory (VFM) machine employing two kinds of permanent magnets (PMs) on alternate rotor poles is investigated. This VFM machine features controllable PM flux and thus good flux-weakening capability, as well as improved torque density. However, it is found that the unipolar end leakage flux occurs if the two kinds of PMs are not balanced. According to the analyses of series connection between two PMs based on the fundamental magnetic circuit, the mechanism of the unbalanced rotor poles and the unipolar end leakage flux is revealed. Further, the rule of obtaining balanced poles is identified and the effects of operating conditions are presented. A series hybrid VFM machine prototype is fabricated and tested. [ABSTRACT FROM AUTHOR]

This paper proposes a novel variable flux memory (VFM) machine, in which the “constant” permanent magnet (CPM) with high coercive force and the “variable” PM (VPM) with low coercive force are alternatively located in the interior-PM rotor. Thus, the VPMs and CPMs are magnetically connected in series, with which the CPMs can assist the VPMs to withstand the unintentional demagnetization caused by armature reaction. Therefore, a high armature current can be applied to the machine. Meanwhile, the reluctance torque is retrieved. Thus, a high torque density can be obtained. Based on two-dimensional finite element analysis, first, the electromagnetic performance of the proposed VFM machine in two extreme magnetization states is evaluated in detail. Then, the demagnetization and remagnetization characteristics are investigated, in which the working points of VPMs are illustrated. Furthermore, the advantages of improved efficiency of the proposed VFM machine are demonstrated. A prototype machine is manufactured and tested to validate the predictions. [ABSTRACT FROM AUTHOR]

The partitioned stator switched-flux permanent magnet (PM) (SFPM) (PS-SFPM) machine is a novel stator-PM machine in which PMs and armature windings are separately placed in two different stators. Compared with the conventional SFPM machine with a single stator in which both PMs and armature windings are located, the PS-SFPM machine can generate higher torque density due to the utilization of the machine's inner space. In this paper, the magnetic gearing effect in the PS-SFPM machine is investigated in terms of air-gap field harmonics based on a simple magnetomotive force (MMF)-permeance model. It is found that the PS-SFPM machine is one type of magnetically-geared machine, in which the modulations of rotor iron pieces to the open-circuit PM and armature reaction fields are similar to those found in the magnetic gear and the conventional magnetically geared machine. The pole-pair numbers and rotating speeds of the air-gap field harmonics obtained by the MMF-permeance model are verified by finite element (FE) analysis. More than 93% of the average electromagnetic torque is contributed by the main air-gap field harmonics having pole-pair numbers (2i - 1)\boldsymbol p PM and \rm| N\rm{r} \,\pm \, (2i-1)pPM| ( i = 1,2,3) in a PS-SFPM machine with pPM-pole-pair PMs and Nr-rotor-pole. A prototype machine is fabricated and tested to verify the FE analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a partitioned stator switched flux memory machine (PS-SFMM) with triple magnets to enable expedient flux control with reduced converter power rating. Meanwhile, the torque/magnet cost ratio of the machine has been significantly improved without much compromise of the torque capability. Three kinds of permanent magnets (PMs), NdFeB, SmCo, and AlNiCo, are hybridized, and hence the irreversible demagnetization of vulnerable AlNiCo PMs can be well prevented by SmCo magnets. The machine configurations with dual PM (DPM) and triple PM (TPM) are described first. Thereafter, the performance improvement mechanism is unveiled and addressed in the perspective of hysteresis curves as well as simplified magnetic circuits. In addition, the electromagnetic characteristics of the proposed machine with triple-magnet design are investigated and compared with those having DPMs. Finally, two PS-SFMM prototypes with DPM and TPM are manufactured and tested to verify the theoretical analyses. [ABSTRACT FROM PUBLISHER]

The hybrid-excited stator slot permanent magnet (HSSPM) machines have good flux regulation capability due to the dc excitation. This makes them attractive candidates for variable speed applications. In this paper, the choices of stator/rotor pole combinations for an arbitrary number of armature phases are discussed. The three-phase 12-10/11/13/14 stator/rotor poles HSSPM machines with single- and double-layer windings are further investigated. Their open-circuit characteristics, torque, inductances, and unbalanced magnetic forces are comparatively studied using 2-D finite-element analysis (FEA). Finally, the 2-D FEA is experimentally validated. [ABSTRACT FROM AUTHOR]

A new flux reversal permanent magnet (FRPM) linear machine known as the partitioned stator FRPM (PS-FRPM) linear machine is proposed. The structure and the operation principle of the machine are described, and the major design parameters are optimized for maximum thrust force. A periodic model is also used in the analysis in order to highlight the significant effect of the longitudinal end effect on the machine performance, particularly in terms of unbalanced magnetic circuit and cogging force. Furthermore, the proposed machine is compared with the conventional FRPM linear machine. It is concluded that higher thrust force, less cogging force, and consequently less thrust force ripple can be obtained by the proposed machine. [ABSTRACT FROM PUBLISHER]

Permanent magnet (PM) tubular machines have been applied to many applications, since they offer high force density with no end winding and no net attractive force between the mover and the stator. In this paper, two novel PM tubular machines named partitioned stator interior PM (PS-IPM) and partitioned stator surface-mounted PM (PS-SPM) tubular machines are proposed. Both the proposed machines are optimized for maximum thrust force, and their electromagnetic performance has been compared. It is found that the PS-IPM tubular machine has higher thrust force capability and better magnet utilization compared with the PS-SPM tubular machine. However, due to lower cogging force, the PS-SPM tubular machine has fewer thrust force ripples. Furthermore, the effect of the cross-coupling magnetic saturation on PM flux linkage, and the $d$ -axis and $q$ -axis inductances for both the proposed machines is investigated. It is demonstrated that the PM flux linkage and the $d$ -axis and $q$ -axis inductances are affected by the cross-coupling magnetic saturation. Moreover, the force–velocity characteristics of the proposed machines are calculated and compared. It is observed that both the machines have good constant power operation capability. [ABSTRACT FROM PUBLISHER]

This paper presents a quantitative comparative study on the two novel memory machines (MMs) with two sets of different magnets on the stator, which are derived from the switched flux (SF) and the variable reluctance (VR) topologies, respectively. The machine topologies, the operating principles, and the design considerations are described. The hybrid magnet sizing is analytically optimized with the aid from a simplified magnetic circuit. Then, the major parametric optimization is conducted on the two machines sharing identical outer diameter and stack length, as well as the copper loss constraint. The electromagnetic performance of the two optimally designed models is analyzed and comprehensively compared, which confirms the advantage of the SF topology for MMs. [ABSTRACT FROM AUTHOR]

A novel stator hybrid-excited, parallel flux path, synchronous machine of doubly salient topology is proposed. It has the novel features of: 1) hybrid dc field and permanent magnet (PM) excitation in the stator; 2) magnets placed in the slots between adjacent salient stator poles; and 3) the magnetic poles of PMs arranged, such that the flux premagnetizes the stator, but it is in a direction to oppose the dc excitation flux. The electromagnetic characteristics of the machine are analyzed on open-circuit and load. Since the new machine topology is developed from the variable-flux machine (VFM), a comparison of their electromagnetic torque and machine losses is conducted. The average electromagnetic torque of the hybrid-excited machine can be increased by 18% for fixed copper loss in comparison with the VFM due to the reduction of magnetic saturation in the stator. It is also shown that at high temperatures some risk of PM demagnetization exists when excited with dc and armature currents due to fringing flux that exists between the stator and the rotor poles. However, this affects only a very small area of the PMs. The performance of the hybrid-excited machine is predicted by a 2-D finite-element analysis and experimentally validated. [ABSTRACT FROM AUTHOR]

The mechanism and the influence of the on-load terminal phase voltage distortion by the armature reaction in interior permanent magnet (IPM) machines with fractional-slot concentrated windings (FSCWs) are investigated in this paper, by taking a 12-slot/8-pole machine as an example. The phenomenon is presented first, which shows that the peak voltage will be much higher than the fundamental value, especially under the flux-weakening operation. Then, the mechanism is investigated with the aid of the frozen permeability method. Due to the geometric feature of the FSCW IPM rotor, the armature reaction flux will asymmetrically enhance the local magnetic saturation in the tooth-tips and the rotor lamination region near the rotor ribs, which disrupt the smooth variation of phase flux linkage and lead to a voltage distortion. With the increasing of current advancing angle ( $\beta $ ), this effect will become more obvious and result in the higher distortion level. Furthermore, the influences of voltage distortion on the machine torque performance are investigated, which show that it will only contribute to the torque ripple in the constant torque region, but will largely reduce the flux-weakening operation region compared with the ideal one calculated by the fundamental voltages only. Finally, a prototype is manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

The on-load voltage distortion in fractional slot surface-mounted permanent magnet machines refers to the phase terminal voltage distorted by armature reaction. With the aid of frozen permeability method, the mechanism of this phenomenon has been investigated based on a 12-slot/8-pole model as an example, showing that the local magnetic saturation in tooth-tips is the main cause, especially when small or closed slot openings are adopted. Then, its impacts on machine performance under vector control have been investigated. If the dc-link voltage is sufficient to satisfy all distorted voltage, i.e., operating in constant torque region, the phenomenon mainly contributes to torque ripple. However, it becomes more problematic in the flux weakening region if the dc-link voltage is limited. Both base-speed and torque-speed curve will significantly differ from the expected results calculated by fundamental voltages. Meanwhile, if the machine operates beyond the base speed, or considering the limited bandwidth in real systems, the phase currents may be distorted, which consequently increase the current harmonics and reduce the average torque. Finally, a prototype machine is manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

This paper presents the simplified analytical optimization and comparison between electrically excited (EE) and permanent-magnet (PM) machines in terms of torque per volume T/V and torque per weight T/G for low-speed applications when their copper loss and overall size are the same. Analytical torque models for both machines are individually developed and optimized to obtain the optimal flux density ratio, split ratio, and maximum torque densities. Furthermore, the variation of optima with the number of poles and machine size is also investigated. The analytical analyses are validated by both finite-element analyses and experiments. It is concluded that torque densities of PM machines can be more than \sqrt2 times higher than those of EE machines. For EE machines, there is an optimal pole number to maximize torque densities, and large volume applications are preferred. In actual applications, EE machines are more likely to compromise the torque density to meet the thermal constraints. It also shows that the optimal T/G designs have significantly higher split ratio and are more cost- and weight-effective than the optimal T/V designs. [ABSTRACT FROM PUBLISHER]

In sensorless control of permanent-magnet brushless ac machines, it is necessary to identify the initial rotor position prior to start-up of the machine. Although saliency-tracking-based sensorless techniques are proven to be a good candidate to estimate the initial rotor position in sensorless control, magnetic polarity identification is another important issue. Since the machine saliency undergoes two cycles in a single electrical period, the estimated position information based on machine saliency has an angle ambiguity of \pi. With the aid of magnetic saturation effect, this paper proposes a robust initial rotor position estimation scheme, which utilizes both d- and q-axis carrier currents, instead of only the q-axis carrier current, in conventional pulsating-carrier-signal-injection-based sensorless control algorithm. Integrated with conventional carrier-signal-injection-based sensorless algorithm, the proposed technique could obtain the initial rotor position for both standstill and free-running rotors. Finally, the experimental results confirm the effectiveness and robustness of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper proposes a permanent magnet machine having mixed high-cost NdFeB and low-cost ferrite magnets with modular unequal magnet height poles, i.e., the modular Hat- and T-type magnet poles, together with optimized Halbach magnetization. The investigation shows that the modular T-type magnet poles with mixed magnet grade and unequal side-magnet height exhibit significant potential to achieve low torque ripple, relatively large electromagnetic torque, and high magnet usage efficiency simultaneously. [ABSTRACT FROM AUTHOR]

In order to improve the electromagnetic performance and ease the manufacture process, particularly stator winding, it is often preferable to employ a modular stator, e.g., individual stator tooth/back-iron segments, or separate stator tooth segments and back-iron segments. However, due to manufacture limits, there always exhibit additional air gaps between the stator teeth and back-iron segments. In practice, such gaps are likely to be nonuniform due to manufacture tolerances. This paper investigates the influence of uniform and nonuniform additional gaps on the cogging torque of permanent-magnet machines having either unskewed or step-skewed rotors. It is found that the presence of these gaps increases the cogging torque magnitude due to increased flux leakage through the tooth tips, while the uneven gaps can cause a significant increase in both the peak and periodicity of cogging torque waveform, which causes the skew method ineffective, as confirmed by both finite-element analyses and experiments. [ABSTRACT FROM PUBLISHER]

The paper presents an analytical model for predicting the open-circuit magnet eddy-current loss due to slotting in surface-mounted permanent-magnet machines based on the exact subdomain field model. The spatial and temporal characteristics of field harmonics due to slotting and corresponding eddy-current harmonics in the magnet are analyzed in both stator and rotor reference frames. The contribution of interaction between eddy-current harmonics having the same frequency but different spatial order to magnet loss is revealed for the first time by an analytical model. The magnet loss can be under- or overestimated if the interaction is neglected. The developed model is capable of providing both high accuracy and insights of loss generation. The influence of the slot and pole number combination, slot-opening to slot-pitch ratio, pole-arc to pole-pitch ratio, circumferential segmentation, and rotational symmetry order on the open-circuit magnet is investigated using the developed model. The finite-element results validate high accuracy of the developed analytical model. [ABSTRACT FROM PUBLISHER]

The significant influence of slot opening on the optimal stator and rotor pole combination and on the electromagnetic performance of the switched-flux permanent magnet (SFPM) machine is observed and investigated in this paper. A new SFPM brushless machine with remarkable slot opening relative to the magnet thickness is developed to reduce the magnet usage and to increase the slot area. Its stator slot opening is almost several times of that in the conventional SFPM machine, but its magnet usage is only half. However, the new machine exhibits \sim40% larger back EMF and electromagnetic torque than those of the conventional machine, while its cogging torque and torque ripple are significantly lower. [ABSTRACT FROM AUTHOR]

A subdomain model considering the influence of tooth-tips is developed for predicting the armature reaction field in surface-mounted permanent-magnet machines having either non-overlapping or overlapping windings. In the developed model, the field domain is divided into three types of subdomains, viz. air gap including magnet, slot openings, and slots. The expression of the vector potential distribution in each subdomain is obtained by the variable separation method, and the field solution is obtained by applying the boundary and interface conditions. Compared with the conventional subdomain model, the subdomain model considering the tooth-tips predicts similar flux density in the air gap and magnets, but exhibits much higher accuracy for the flux density in the slot openings and slots. The finite-element results validate the analytical prediction. [ABSTRACT FROM PUBLISHER]

The split ratio, i.e., the ratio of stator bore radius to stator outer radius, is an important design parameter for permanent-magnet (PM) linear machines, as it significantly influences the thrust force capability and efficiency. The optimal split ratio for maximum thrust force is investigated analytically for both surface-mounted PM (SPM) and interior PM (IPM) E-core linear oscillating actuators. It utilizes simple lumped magnetic circuit models and accounts for the magnetic saturation, the curvature effect, the fringing effect, and the armature reaction effect which may greatly affect the accuracy of the analytical model for the optimal split ratio. The optimal split ratio for both SPM and IPM prototype actuators is found to be around 0.55. The developed analytical models are validated by both finite-element analyses and measurements. [ABSTRACT FROM AUTHOR]

This paper presents the design, analysis and experimental validation of a single-phase tubular E-core interior permanent magnet (1PM) linear oscillating actuator (LOA). Firstly, the topology is described and its electromagnetic performance, in terms of the air-gap flux density, flux-linkage, back-emf coefficient and thrust force-displacement characteristic, is analyzed by finite element analyses. It shows that it is simple to manufacture compared to E-core SPM actuators and solves the problem of significant leakage flux in C-core actuators. In addition, the E-core 1PM actuator is capable of producing reluctance force due to the salient mover structure, which enhances the spring stiffness and is conducive to the oscillation, although has no contribution to the output power. The influence of the magnet pole ratio and split ratio on the performance of the 1PM LOA is investigated, and the optimal parameters have been identified with reference to the peak value and flatness of the excitation force-displacement characteristic. Finally, the predicted thrust force characteristics are validated by measurements on a prototype actuator. [ABSTRACT FROM AUTHOR]

This article investigates the effect of airgap length on the electromagnetic performance of direct-drive surface mounted permanent magnet Vernier (SPM-V) machines with different power ratings. Using 3 kW machine as an example, its performance is comprehensively compared with a conventional SPM machine with the same airgap lengths using two-dimensional finite-element analysis. For each airgap length, the slot/pole number combination for the SPM-V machine is investigated to achieve the optimal performance compared to the conventional SPM machine. In order to make the study more generic, the slot/pole number and the airgap length variations are expressed as normalized pole pitch, i.e., $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ (ratio of rotor pole pitch to electromagnetic airgap length). The results show that for 3 kW machines, $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 is a good design criterion for the SPM-V machines to achieve higher average torque and efficiency than the conventional SPM machines. In addition, a reasonably good power factor (>0.9 in this case) can be achieved. Although the power factor of SPM-V machines drops significantly at multi-MW power level, i.e., 3 and 10 MW, the criterion $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 still results in achieving a performance closest to their optimal capability. However, when $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2, special consideration should be paid to avoid potential irreversible magnet demagnetization at multi-MW power levels. [ABSTRACT FROM AUTHOR]

This article investigates the impact of scaling on the electromagnetic performance of surface-mounted permanent-magnet Vernier (SPM-V) machines with a main focus on open-circuit induced Electro Motive Force (EMF). Three different power ratings, i.e., 3 kW, 500 kW, and 3 MW, have been chosen for this article. For each power rating, the SPM-V machines are analyzed for different slot/pole number combinations to compare their optimal performance with a conventional SPM machine. Step-by-step development of an analytical equation is presented for the prediction of induced EMF taking into account the interpole leakage of rotor permanent-magnets. 2-D finite-element analysis (FEA) has been used to validate the analytical equation across different power ratings. The analytical equation is thereafter utilized to study the influence of different geometric parameters on the performance of the SPM-V machines. It reveals that the back EMF and torque of SPM-V machines, for a given normalized pole pitch (rotor pole pitch to magnetic airgap length), are unaffected by the increase in airgap length due to scaling. However, the power factor of SPM-V, unlike the conventional SPM, reduces significantly with the increase in electrical loading due to the scaling effect. The analytical model for induced EMF and the 2-D FEA predicted results are validated by experiments using conventional SPM and SPM-V machine prototypes. [ABSTRACT FROM AUTHOR]

In this paper, the partitioned stator (PS) structure is extended to variable-flux memory machines, forming two newly emerged PS switched-flux memory machines (PS-SFMMs) with series and parallel hybrid magnet configurations. From the perspective of geometry, both two PS-SFMMs share identical outer stator and rotor segments, while two different types of permanent magnet (PM) arrangements are employed in the inner stationary part. Thus, the developed machines can inherent the geometric separation of the armature winding and PM excitations from the PS design, thus achieving acceptable torque capability, and excellent air-gap flux control. A comparative study between PS-SFMMs with series and parallel structures is established. First, the topologies and operating principle are introduced, respectively. In addition, the design tradeoffs and PM sizing of the two PS machines are revealed and optimized with a simplified magnetic circuit model. Then, the electromagnetic characteristics of PS-SFMMs with different magnetic circuits are investigated and compared with the finite-element (FE) method. The FE results are validated by the experiments on a parallel prototype. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical method that combines the superposition concept and the subdomain method to predict the cogging torque of permanent magnet (PM) machines with a rotor eccentricity. The original eccentric machine is first divided into several sections along the air-gap circumferential direction. Then, the equivalent air-gap lengths of all sections will be determined and individually used to build up a series of concentric models representing each section. By the superposition method, the air-gap flux density of the original eccentric machine can be synthesized from that of every concentric model predicted through the subdomain method. Consequently, the cogging torque can be predicted by the integral of Maxwell stress tensor based on the synthesized air-gap flux density. To prove the efficacy of the proposed method, two fractional-slot PM machines with different slot/pole number combinations are taken as examples, together with the validation of a finite-element analysis. [ABSTRACT FROM AUTHOR]

Linear flat switched flux permanent magnet (SFPM) brushless machines have significant potential for many applications including transportation, automobile and aerospace. Novel E-core and C-core linear SFPM machines are proposed and optimized by individual parameter optimization, when the copper loss and volume is fixed, in this paper by finite element (FE) analysis. Then, the results of the individual parameter optimizations are examined by a global optimization with genetic algorithm. Furthermore, the magnet thickness of all the machines and the middle teeth of the E-core machines are analyzed individually. Finally, the electromagnetic performance of the novel machines are analyzed and compared with the conventional machine. It shows that both E-core and C-core machines require significantly smaller magnet volume since only about half the number of permanent magnets is required. Furthermore, the C-core machines have the largest back-EMF and force density due to the largest slot area, and the E-core machines are suitable for fault-tolerant operations while the 6/11 mover/stator pole E-core SFPM machine has the smallest cogging force. [ABSTRACT FROM PUBLISHER]

We present a simple lumped magnetic circuit model for interior permanent-magnet (IPM) machines with multisegment and multilayer permanent magnets. We derived analytically the open-circuit air-gap field distribution, average air-gap flux density, and leakage fluxes. To verify the developed models and analytical method, we adopted finite-element analysis (FEA). We show that for prototype machines, the errors between the FEA and analytically predicted results are <1% for multisegment IPM machines and <2% for multilayer IPM machines. By utilizing the developed lumped magnetic circuit models, the IPM machines can be optimized for maximum fundamental and minimum total harmonic distortion of the air-gap flux density distribution. [ABSTRACT FROM AUTHOR]

Flux-switching permanent magnet (FSPM) motors have a doubly salient structure, the magnets being housed in the stator and the stator winding comprising concentrated coils. They have attracted considerable interest due to their essentially sinu- soidal phase back electromotive force (EMF) waveform. However, to date, the inherent nature of this desirable feature has not been investigated in detail. Thus, a typical three-phase FSPM motor with 12 stator teeth and ten rotor poles is considered. It is found that, since there is a significant difference in the magnetic flux paths associated with the coils of each phase, this results in harmonics in the coil back EMF waveforms being cancelled, resulting in es- sentially sinusoidal phase back EMF waveforms. In addition, the influence of the rotor pole-arc on the phase back EMF waveform is evaluated by finite-element analysis, and an optimal pole-arc for minimum harmonic content in the back EMF is obtained and verified experimentally. [ABSTRACT FROM AUTHOR]

In this paper, the influences of design parameters on the on-load demagnetization behavior of a switched flux hybrid magnet memory machine (SF-HMMM) are evaluated, which aims to provide a useful design guideline to avoid this performance degradation. The machine topology and on-load demagnetization phenomenon are described, respectively. Furthermore, some key design parameters are selected to optimize to elevate the operating point of the low coercive force (LCF) permanent magnets (PMs). Then, some geometric modifications are suggested to alleviate the on-load demagnetization effects. Finally, an SF-HMMM prototype is fabricated and tested to experimentally verify the finite-element analysis. [ABSTRACT FROM AUTHOR]

A memory machine (MM) equipped with hybrid permanent magnets (PMs), i.e., NdFeB and low coercive force PMs, exhibits acceptable torque capability at low speeds and high efficiency at high speeds. Previous literatures have addressed that the constant power speed range (CPSR) of MMs can be further extended by online PM flux control and the requirement of the flux-weakening (FW) inverter current can be reduced as well. Nevertheless, how to coordinate the d-axis vector FW and PM magnetization control over a whole operating range in a reasonable manner remains unreported. Therefore, this paper proposes and implements a stepwise magnetization control strategy on a dc-magnetized MM based on the operating characteristics under various PM magnetization states and speed ranges. The configuration, principle, and mathematical model of the investigated machine are introduced first. Then, the proposed control strategy is established by dividing the operating envelop into several FW regions and an appropriate FW control scheme is utilized at each stage. It demonstrates that the CPSR can be effectively extended by simply applying the demagnetizing current pulses in several steps. This simplifies the control efforts considerably without resorting to continuous PM flux control and frequent actions of the switching devices. The effectiveness of the proposed control strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]

Variable flux permanent magnet synchronous machine (PMSMs) (VF-PMSMs) are gaining importance, especially in automotive applications. The use of such machines will require the development of methods to estimate the permanent-magnet (PM) magnetization state. PM magnetization state estimation methods reported in literature include back-electromagnetic (EMF) compatibility and high-frequency signal injection. One advantage of high-frequency signal injection methods is that they can operate over the whole speed range, with practically no interference with the regular operation of the machine. Magnetization estimation using high-frequency injection relies on the variation of the d-axis high-frequency inductance with the saturation produced by the magnets. Alternatively, the changes of the magnet electrical resistance due to the magnetoresistive effect can also be used for this purpose. These methods have been tested with different materials, including NdFeB, AlNiCo, and SmCo magnets. NdFeB magnets are usually protected from oxidation using NiCuNi coating. However, NiCuNi also shows magnetoresistance effect and can therefore affect the performance of the method when used with magnets having NiCuNi coating. This paper studies the effects of PM coating on the performance of methods, which estimate the magnetization state of the magnet using the magnetoresistance effect by means of high-frequency signal injection. The analysis will include NdFeB, AlNiCo, and SmCo magnets. [ABSTRACT FROM PUBLISHER]

In this paper, novel dual-stator switched-flux hybrid magnet machines (DS-SF-HMMMs) are proposed. Two sets of armature winding are employed so as to improve the space utilization and torque density. Meanwhile, two kinds of permanent magnets (PMs), i.e., neodymium–iron–boron and low-coercive-force magnets, are placed on either a common stator or separate stators. The proposed machines can provide the merits of high torque density in DS machines, and excellent flux adjusting capability in memory machines. The topologies and operating principle of the DS-SF-HMMMs having different PM arrangements are introduced and highlighted, respectively. In order to overcome the drawbacks of the original “U”-shaped PM type, two alternate designs are presented to increase the copper area in the inner stator and facilitate the manufacturability. In addition, the equivalent magnetic circuits for various machine models are formulated to reveal the field regulation principle. Then, the electromagnetic characteristics of various available DS-SF-HMMMs are evaluated and compared by the finite-element (FE) method. The stator/rotor pole combinations of the selected machine are analytically optimized in order to maximize the torque density. Finally, two prototypes are manufactured and tested to verify the FE analyses. [ABSTRACT FROM PUBLISHER]

A novel switched-flux (SF) surface-mounted permanent magnet (PM) memory machine is proposed by incorporating the flux-memorizable concept into the SF structure. It employs a temporary current pulse to magnetize/demagnetize the aluminum–nickel–cobalt (Al–Ni–Co) PMs so that the air-gap flux can be regulated online for extending its high-speed constant-power region. An analytical hysteresis modeling method is formulated and implemented by numerical nonlinear approximation of hysteresis loops, and then coupled with time-stepping finite element method to perform the analyses of both static and transient flux-regulatable characteristics. The preciseness of the coupling solution and the validity of machine design are verified by experimental results. [ABSTRACT FROM AUTHOR]

A novel axial field flux-switching permanent magnet (AFFSPM) machine with a doubly-salient structure is presented as a wind power generator. One rotor is sandwiched between two stators in which both windings and permanent magnets are placed. This novel generator is suitable for the wind power generation system because of its shorter axial length and higher power density. A three-phase 12/10-pole 0.6 kW AFFSPM generator is designed. The power-size equation of the machine is deduced, and the size of generator is determined. Based on the 3-D finite element method, the electromagnetic performances of the generator are investigated. According to the theoretical calculation, a prototype is manufactured and the experiments are done. The analysis results are consistent with the experimental ones well. [ABSTRACT FROM AUTHOR]