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Hybrid excited synchronous machines (HESMs) combine permanent-magnet (PM) excitation and wound field (WF) excitation. The goal of hybrid excitation is to combine the advantages of PM excited machines and WF synchronous machines. HESM have been identified as one of the emerging technologies for modern energy conversion systems. They have been the subject of many review articles. The principle of hybrid excitation allows solving many drawbacks related to PM electric machines operation: flux weakening, energy efficiency, and PMs price fluctuation. It helps to introduce an additional degree of freedom in the design of synchronous machines, and allows therefore an easier adaptation of PM synchronous machines to a wider applications scope. To this additional degree corresponds the possibility of adjusting the contribution of the two magnetic field sources: PM and WF. The use of this technology for electric traction has been the subject of many scientific and technical contributions. In this contribution, the emphasis will be put on the use of these machines as generators in transportation applications and renewable energy applications. The design and operation of three particular structures will be presented. Two of them have been designed as generators for transportation applications, and the third one has been designed as generator for renewable energy conversion. All of them are flux switching hybrid excited synchronous machines (FSHESM). [ABSTRACT FROM AUTHOR]

In this paper, an analytical method for the computation of the electromagnetic field in the airgap of an inset permanent magnet synchronous machine is proposed. The originality lies in the fact that both the stator and rotor saliencies have been taken into account in the analytical procedure. The purpose in to compute both quickly and accurately the magnetic fluxes and instantaneous torque of the machine, in order to minimize torque ripples in an optimal predesign process. It is shown that the instantaneous torque is in good agreement with finite element results, for a shorter computation time. The model presented here can be used when the 2-D approximation of the machine is valid, which is the case for most of machines' topologies. [ABSTRACT FROM AUTHOR]

This paper presents a 3-D analytical model of an axial flux permanent-magnet synchronous machine, based on formal resolution of Maxwell equations. This method requires much less computation time than conventional 3-D finite elements, and is therefore suitable for optimization purposes. In a first part, the mathematical procedure used to compute the machine no-load flux is described in detail. This method is 3-D, and then takes into account the radial edge effects of the machine, as well as the curvature effects by a resolution in cylindrical coordinates. Moreover, the originality of this method lies in the fact that it is totally analytical. The obtained results are verified using 3-D finite elements, and compared with simpler analytical models of axial flux machines, taken from the literature. This work puts in evidence the advantages of the proposed model. In particular, it is shown that the radial edge effects are important for a correct estimation of the no-load flux. On the contrary, the curvature effects are a second-order phenomenon. [ABSTRACT FROM PUBLISHER]

We describe a 3-D analytical model based on formal resolution of Maxwell's equations of a permanent-magnet linear actuator, with circular-shaped magnets. We present all details of the 3-D analytical calculation for the no-load flux and then compare results obtained by this model to those obtained by 3-D finite-element analysis. The comparisons show a good agreement between the two models and so validate our analytical model. Unlike 3-D finite-element analyses, which are time consuming, the analytical models that we present in this paper are suitable for an optimization process of such a structure. [ABSTRACT FROM AUTHOR]

To further enhance the speed regulation range of the hybrid excited machine (HEM), the structure of a magnetic ring is optimized using a combination of the magnetic circuit method (MCM) and numerical analysis method in this paper, and a disc magnetic ring (DMR) is proposed. The magnetic density distribution of the proposed disc magnetic ring hybrid excited machine (DMRHEM) is compared to the radial-axial hybrid excited machine (RAHEM), and the superiority of alleviating a saturation problem in the proposed DMRHEM is determined. To improve the power density, the spoke-type permanent magnet (PM) rotor is applied. The influence of the proposed DMR on the HEM is analyzed, and the field adjustment capability of the proposed DMRHEM is better. Based on this, by combining the bypass principle, the analytical expressions for the relations between the rotor pole-pair number and the motor axial length/stator inner diameter (MAL/SID) as well as flux regulation capability are derived to further explore the superiority of the proposed DMRHEM. The influence mechanism of the rotor pole-pair number and the MAL/SID on the proposed DRMHEM is determined. The optimal MAL/SID and pole-pair number are obtained. [ABSTRACT FROM AUTHOR]

The contactless transmission between the conductor rotor and the permanent magnet (PM) rotor of an adjustable permanent magnet coupler (APMC) provides the device with significant tolerance for alignment errors, making the performance estimation complicated and inaccurate. The first proposal of an edge coefficient in this paper helps to describe the edge effect with better accuracy. Accurate equivalent magnetic circuit (EMC) models of the APMC are established for each region. Models of magnetic flux, magnetic resistance, and eddy current density are established by defining the equivalent dimensional parameters of the eddy current circuit. Furthermore, the concept of magnetic inductance is proposed for the first time, parameterizing eddy currents that are difficult to describe with physical models and achieving the modeling of the dynamic eddy current circuit. The magnetic resistance is subdivided into two parts corresponding to the output and slip according to the power relationship. Furthermore, eddy current loss and dynamic torque models are further derived. The method proposed in this paper enables the APMC to be modeled and calculated in a completely new way. The correctness and accuracy of the model have been fully demonstrated using finite element simulation and an experimental prototype. In addition, the limitations of the proposed method and the reasons are fully discussed and investigated. [ABSTRACT FROM AUTHOR]

In [1], an error in Fig. 2 in Section II-B is corrected. In the original figure, Fig. 2(b) was exactly the same as Fig. 2(a). The correction is shown here. [ABSTRACT FROM AUTHOR]

Featured Application: This paper proposes a new hybrid vibration isolation system that combines an electromagnetic actuator, rubber passive vibration isolator, and magnetorheological damper, and it has a high bearing capacity, high output force, low power consumption, and good impact resistance. First, the overall design scheme of the hybrid vibration isolation system is introduced. The electromagnetic actuator is simulated with electromagnetic–mechanical coupling in the time–frequency domain. A dynamic stiffness test is carried out on the rubber vibration isolator. Then, the adaptive suppression filtered-x least mean square (ASFXLMS) algorithm is proposed to adjust the update of the control weight coefficients, by introducing a suppression factor to improve the robustness of the algorithm. Finally, a hybrid vibration isolation system-based active vibration isolation experimental platform is built, and multifrequency line spectra active–passive vibration isolation experiments are carried out. The results demonstrate that the hybrid vibration isolation system has good control effects in the time–frequency domain and shows a good robustness when subjected to impact. Targeting the problems of conventional active–passive hybrid vibration isolation systems, such as low output force, poor bearing capacity, large power loss and inability to withstand strong impacts, this paper proposes an active–passive hybrid vibration isolation system combining an electromagnetic actuator, rubber passive vibration isolator and magnetorheological damper. The overall design of the hybrid vibration isolation system is first introduced. Then, a two-dimensional electromagnetic frequency-domain simulation is carried out on the electromagnetic actuator to obtain the output characteristics. A three-dimensional modeling is conducted to simulate the electromagnetic–mechanical coupling in the time–frequency domain to obtain nephograms of the magnetic flux diffusion distribution and power loss. Then, a dynamic stiffness test is carried out on the rubber vibration isolator to obtain the dynamic stiffness characteristics and the damping angle curve. At the same time, an adaptive suppression filtered-x least mean square (ASFXLMS) algorithm is proposed to adjust the update of the control weight coefficients to ensure that the current signal does not exceed the effective operating range of the actuator when the electromagnetic actuator is subjected to strong external disturbances. Finally, a hybrid vibration isolation system-based active vibration isolation experimental platform is built, and multifrequency line spectra active–passive vibration isolation experiments are carried out. The results demonstrate that the hybrid vibration isolation system has good control effects in the time–frequency domain and shows good robustness when subjected to impact. [ABSTRACT FROM AUTHOR]

In this paper, a variable reluctance generator with segmental stator utilizing an assisted DC field for variable speed applications is proposed. In this work, analytical design, magnetic field analysis, and Parametric Sensitivity Analysis of the proposed machine are presented. The stator of suggested configuration, in addition to the distributed phase windings, is included the distributed assisted dc field coils, which are responsible for producing an adjustable magnetic flux in the generator. The segmental stator, the controllability of magnetic flux and generated voltage are the prominent features of the presented generator. Maintenance-free and easy accessibility of each stator segment due to utilizing the segmental stator, and high reliability due to the absence of brush and winding on the rotor is other features of the proposed machine. Finally, the Field Analysis using the finite element method is performed to verify the analytical design and sensitivity analysis. The results obtained from the FE analysis confirm the analytical design and the controllability of magnetic flux and generated voltage for the proposed configuration. [ABSTRACT FROM AUTHOR]

Aiming to design a generator with high reliability, high efficiency, and especially a constant output voltage over a wide speed range for hybrid electric vehicles (HEVs), this paper proposes a novel topology of a hybrid excitation doubly salient generator with separate windings (HEDSGSW). The topology herein utilizes a hybrid excitation type of PMs and DC windings to generate parallel magnetic circuits. In addition, PMs are embedded in the magnetic bridge to insulate the excitation windings with armature windings. This design can achieve compactness, efficiency, and especially constant output capability over a wide speed range. The geometry and flux regulation principles, including magnetic flux circuits, are elaborated. After comparing three power generation modes, the most suitable mode, namely, the doubly salient generation 2 (DSG2) mode, is confirmed to ensure a stable voltage output performance. Then, considering the non-uniformity effect of the stator and rotor slots, the no-load back electromotive force (EMF) expressions are derived based on the EMF to air-gap relative permeance method. Furthermore, a 1 kW HEDSGSW FEA model, with an output voltage of 42 V and a rated speed of 6000 rpm, is built to demonstrate the effectiveness of the proposed method. Finally, the operating properties of the HEDSGSW, such as no-load characteristics and adjustment characteristics, are analyzed to further verify the rationality of its magnetic flux circuit and the flexibility of the excitation regulation capability. [ABSTRACT FROM AUTHOR]

Hybrid excitation is a technology that combines the advantages of field windings and permanent magnets for inducing magnetic flux. This article studies the benefits of hybrid excitation and provides an outlook on their possible applications, such as wind power generators and electric vehicle motors. Compared to permanent magnet-based machines, hybrid excitation gives a variable flux while still using the advantage of the permanent magnets for a portion of the flux. This article also looks into some different categories of machines developed for hybrid excitation. The categories are based on the reluctance circuit, the relative geometrical location of the field windings relative to the permanent magnets, or the placement of the excitation system. [ABSTRACT FROM AUTHOR]

This research work is aimed at the modification of in-wheel switched reluctance motor (Outer rotor-type SRM) with minimized torque ripple for electric vehicles. The geometry of stator and rotor poles affects the torque. Variation in the stator and rotor pole geometry causes change in the torque profile. To reduce the torque ripple and to increase the average torque, modification in the stator and rotor pole shoes is presented in this article. The stator and rotor pole shoes with notches and projections are proposed with the objective of minimization of torque ripple and maximization of average torque. Electromagnetic analysis of conventional and modified in-wheel SRM is done with computer-aided design software MagNet 7.1.1. From the finite element analysis results, the average torque and torque ripple values are derived. Prototype of 8/6, 1000 W in-wheel SRM with the notches and projections is fabricated. Experimentation is performed on the fabricated machine to measure the magnetic flux linkage, current and speed characteristics of the proposed in-wheel SRM. The precise determination of magnetic flux characteristics is significant to check the machine design and to accurately predict the action of modified in-wheel SRM. Static modeling results of the fabricated machine were coherent with the experimental values. [ABSTRACT FROM AUTHOR]

This study proposes a hybrid excited (HE) doubly salient machine with permanent magnets (PMs) located on stator slot openings. The HE machine inherits the high torque density of PM machines as well as flexible magnetic field regulation of wound field machines. Since the PMs are located at stator slot opening, the PM flux is shunted in the stator without DC excitation, and the machine exhibits high fault‐tolerant capability at high‐speed operation. The proposed machine is optimised, together with a comparison with a conventional stator slot PM HE machine. It is revealed that the proposed HE machine exhibits a significantly higher torque density under the same copper loss and PM usage. Finally, a prototype is fabricated, and experiments have been conducted to verify the accuracy of finite element simulation on the proposed machine topology. [ABSTRACT FROM AUTHOR]

Permanent magnet flux switching machines (FSPMs) have attracted considerable attention in recent years, due to their outstanding characteristics to operate as brushless AC drives. Since they are relatively new, there are particular challenges not only for their design procedure but also for their operating principle comprehension. This study highlights several issues on FSPMs from the basic operation description to their key design points. After a comprehensive description of FSPMs working principles, a detailed discussion is presented on their armature winding design. In addition, this study reviews various methods for their performance modification, including torque profile, electromotive force, and loss characteristics. This study also surveys field regulation technologies, modelling and design optimisation methods applied to FSPMs along with their fabrication and cost issues. [ABSTRACT FROM AUTHOR]

Here, machines having permanent magnets (PM) mounted in the stator are compared during fault operations such as armature winding short circuits. The magnet potential irreversible demagnetisation is also investigated due to the fact that the PMs are placed close to the armature coils (heat sources) and hence are prone to temperature-related demagnetisations. It is found that the doubly salient and flux reversal machines have inherently higher fault tolerant capabilities when compared with the switched-flux one. To the point of view of demagnetisation withstand capability, the doubly salient topology stands out as the most robust one while the switched flux is the weakest one. [ABSTRACT FROM AUTHOR]

In this study, a novel partitioned stator hybrid excited machine is proposed, in which the excitation sources including both permanent magnets (PMs) and field windings are allocated on the secondary stator that is separated from the original stator having armature windings. As a result, the available space is boosted to improve the torque density and flux regulation capability. Meanwhile, the rotor is simple without coil or PM. The PMs on the stator is placed on the slot openings between the two neighbour tooth tips, with which the uncontrolled voltage of the proposed machine is limited and it is favoured for safety-critical applications. The machine topology and operating principle are introduced in detail, and the basic electromagnetic performance is evaluated based on finite element method to validate the analysis. [ABSTRACT FROM AUTHOR]

This paper incorporates the idea of integrated field and armature windings into the design of novel hybrid excited machines with bi-directional flux modulating effect, which results in a new hybrid-excited machine concept that is referred as dual-electrical-port dc-coil-free hybrid-excited machine (DEP-DCF-HEM). In the proposed design, dc field windings are eliminated and dc bias currents are injected into the windings to generate dc excitation field. In addition, the armature windings are divided into dual electrical ports, and zero-sequence current flows between these two ports can adjust the air-gap field effectively. Compared with existing HEMs with additional dc coils, the proposed machines can achieve both higher torque density and wider flux weakening range. The presented design principle can be utilized in a variety of configurations of DEP-DCF-HEMs. Topologies with stator permanent magnet (PM), rotor PM, and dual PM are possible designs, which are all investigated in this paper. A dual PM DEP-DCF-HEM prototype is manufactured, and experimental measurements are conducted to verify its performances. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid excitation permanent magnet (PM) machine with an independent ac excitation port to extend the speed range and improve the torque capability. The proposed machine is characterized by an axial stator placed in one side of the rotor, which provides a shunted flux path of the radial stator. The prominent merit of the proposed machine is that it can make better utilization of the PM flux and offer a large flux regulation capability because the radial flux and the axial flux are in parallel to each other. Thorough analysis of the field distribution is performed by three-dimensional (3-D) finite-element analysis, and different operation modes of the proposed machine are illustrated and compared. Then, the flux regulation capability of the machine is analyzed using the simplified magnetic equivalent circuit, which is proved to give reasonable precision, indicating that the flux regulation ratio only depends on the design parameters of the ac excitation port. Finally, a 36-slot/six-pole prototype using the proposed configuration is built and tested. It is verified that the proposed machine exhibits excellent performance of flux regulation, thus offering a good potential to be used in wide-speed-range driving applications. [ABSTRACT FROM AUTHOR]

This study proposes a new three‐phase dual‐rotor middle‐stator brushless flux switching generator for 400Hz diesel‐driven aircraft ground power units. For the proposed machine, both field and armature windings are hosted in the stator in such a way that not only fulfils brushless structure, but also realises the flux switching function. Moreover, both windings have non‐overlapping concentrated windings to shorten the end‐windings and reduce the copper losses. In the meantime, the rotor has only slots without any active parts. First, the machine detailed design is provided, and its performance is analysed using finite element method. Also, a selection topology of both stator and rotor pole arcs is carried out, targeting maximum generated electromotive force, minimum harmonic content, and minimum cogging torque. Then, a prototype is implemented and experimented to confirm the feasibility of the proposed machine. [ABSTRACT FROM AUTHOR]

In this study, a new sensitivity analysis based on non‐linear varying‐network magnetic circuit (VNMC) method is proposed for an outer‐rotor I‐shaped permanent magnet flux‐switching motor. By integrating concept of sensitivity analysis into the non‐linear VNMC method, the whole design efficiency can be improved effectively by using the comprehensive sensitivity method and sequential non‐linear programming algorithm. In the optimisation process, two design objectives are selected, including machine output torque and torque ripple. Based on the sensitivity analysis, the parameters possessing the significant influence on the design objectives can be selected purposely, thus the overall amount of calculation is obviously reduced. After the determination of the sensitive parameters, the rest of optimisation can be realised efficiently by the non‐linear VNMC method. Finally, a prototype motor is manufactured and tested. Both theoretical analysis and experimental results confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This study overviews recent development of a new class of magnetically geared machine topologies, i.e. partitioned stator (PS) machines. They are developed from magnetic gears and magnetically geared machines, as well as stator permanent magnet (PM) machines (switched flux, flux reversal, and doubly saliency PM), wound field, or hybrid PM and field winding machines. Based on the operating principle, i.e. magnetic gearing effect/air‐gap field modulation and flux switching by the salient rotor iron poles, various PS machine topologies are developed. All have features of two stators, two air‐gaps, and one segmented ferromagnetic rotor identical to a magnetic gear's modulating rotor. Their inherent relationships are revealed, while their electromagnetic performance is compared. Both PM and wound field PS machines are discussed, together with hybrid excited PS‐PM machines and Vernier machines. It shows that all of these PS machines share the same torque production principle and the differences are mainly in PM configurations and relative positions of two stators. All PS machines have higher torque density per copper loss compared with their counterparts of single‐stator machines. PS switched flux PM machines can produce the highest torque density per copper loss. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid excitation synchronous machine (HESM) with magnetic shunting rotor is designed for electric vehicle traction applications with consideration of electromagnetic performance and mechanical strength. The HESM with magnetic shunting rotor is a topology of brushless HESM with extended magnetic bridge to embed field windings. The rotor core extends along the axial direction and the increase of rotor length is inevitable, which reduces torque density. In order to improve torque density, the excitation structure is optimized by built-in field windings and the HESM with one-end built-in field windings is presented. To improve the flux regulation capability and decrease the magnet consumption further, the HESM with dual-end built-in field windings is proposed and investigated. The comparative study of the performances of the original HESM and the HESMs with one/dual-end built-in field windings is carried out by three-dimensional finite element method (FEM). An original HESM prototype and a permanent magnet synchronous machine prototype have been developed and the experimental results, which agree well with the FE-predicted results, confirm the advantages of HESM and the validity of FEM used in predictions in this paper. [ABSTRACT FROM PUBLISHER]

Hybrid excitation synchronous machines (HESMs) are permanent magnet machines which allow the control of the air‐gap flux density. In this study, three new axial field HESM structures, each having two rotors and one stator, are proposed. The operation principles of these machines, considering weakening or supporting the air‐gap flux density, are described. The magnetostatic and transient analyses of the proposed models have been carried out by using finite element method. To have reliable analysis results, the stator length and input and output diameters of the models have been chosen to be identical. Results are compared in terms of efficiency, power density and range of flux control between each other and another axial field HESM in the literature. In conclusion, the proposed HESM models demonstrate satisfactory performance for the generator mode and they are suitable for wind energy applications. Furthermore, because of their field weakening operation ability they can be used as motors in the vehicle industry. [ABSTRACT FROM AUTHOR]

The irreversible magnet demagnetisation phenomena are investigated, under both healthy and short‐circuit conditions for a switched flux permanent magnet (SFPM) machine. The temperature effects on permanent magnet material are taken into account and the influence of short‐circuit current over demagnetisation is evaluated. To calculate the short‐circuit current (mainly inter‐turn short circuit), the MATLAB/Simulink model has been employed. The aforementioned short‐circuit current is then fed to the finite‐element model, so the demagnetisation analysis can be carried out. Various fault scenarios are investigated, including a high speed and high fault severity. It is found that the short‐circuit current has limited effect on the magnet demagnetisation due to particular features of the SFPM machines. The mechanism of demagnetisation has been revealed and found out to be mainly due to temperature rise and poor PM materials utilisation. Experiments have been carried out to validate the MATLAB/Simulink model for short‐circuit current predictions. [ABSTRACT FROM AUTHOR]

This paper suggests a possible design of variable flux motor for adjustable speed operation. A method to calculate electrical parameters to meet variable speed conditions is suggested, and the basic motor shape is decided using the relationships between the calculated electrical parameters and motor geometry. The difference between coercivity of two types of magnet is used to control the flux. To prevent irreversible demagnetization of low-coercivity magnet, the approximate shape of magnet is decided by calculating the operating point of the magnet using an equivalent magnetic circuit. The optimum shape of magnet considering the nonlinear characteristics is suggested using a finite-element method. To validate the design, magnetizing/demagnetizing, and load operation tests are conducted. [ABSTRACT FROM PUBLISHER]

In this paper, a correction method is introduced to make a more accurate calculation of winding eddy‐current losses of high‐voltage direct current (HVDC) converter transformer. The assumption that winding eddy‐current losses of HVDC converter transformers follow the frequency with the exponent 2 proposed by IEC 61378‐2 Std. is thought to be inappropriate and the skin effect should be taken into consideration. The frequency characteristic of winding eddy‐current losses is proposed by analysing the distribution of magnetic flux in conductors, in which skin effect is taken into consideration. The correction method with a correction factor is then introduced to correct the assumption. To verify the validity of the correction method, a two‐dimension axisymmetric finite element analysis of a HVDC converter transformer is conducted. The geometrical complexity of windings and electrical connection are fully taken into account, it is shown that the correction method shows a significant advantage. Influence of different methods is revealed by applying the actual non‐sinusoidal load current and it is shown that the error of correction method is the least. At last, harmonic losses measurements are conducted on three coils to investigate the limits of the correction method. [ABSTRACT FROM AUTHOR]

Hybrid excited axial field flux‐switching machine (HEAFFSM) with permanent magnets (PMs) and excitation windings in its stator is a novel hybrid excited flux‐switching PM machine. The HEAFFSM combines the advantages of the hybrid excited synchronous machine and flux‐switching PM machine. In this study, the topology and operating principles of the HEAFFSM are analysed, and the electromagnetic characteristics (including the winding inductances, flux, and cogging torque) are obtained by the three‐dimensional finite‐element method. On the basis of the vector control method, the mathematical model of the HEAFFSM is deduced, and the operating performance of the HEAFFSM across its entire operating range is investigated. A new minimum‐copper‐loss (MCL) control strategy for the HEAFFSM drive system, which can operate in both flux‐enhancing and flux‐weakening conditions, is proposed and compared with the traditional control. The experimental results demonstrate that the MCL strategy maximises the range of speed regulation while minimises the copper loss of the HEAFFSM drive system. Moreover, the flux‐regulation capability and high power/torque density of the HEAFFSM are validated. [ABSTRACT FROM AUTHOR]

In this study, a mechanical flux adjusting technique for the switched flux permanent magnet (SFPM) machines is presented to improve the flux‐weakening capability by extending the speed range. The ferromagnetic material pieces, that is, flux adjusters (FAs), are located on the outside surface of the stator poles equipped with permanent magnet (PM) and used to weaken the PM flux via short‐circuit. To explore the most suitable machine topologies for such flux adjusting technique, the performance of conventional SFPM machines with different stator/rotor pole combinations, multi‐tooth, E‐core and C‐core SFPM machines is investigated and compared by employing the FAs. It shows that the maximum speed and flux‐weakening capability of the conventional SFPM machines can be significantly increased if the FAs are used. On the other hand, the multi‐tooth, E‐core and C‐core SFPM machines have inherently large inductance. Thus, the flux adjusting technique has less influence on their flux‐weakening performance. Besides two‐dimensional (2D) finite‐element analysis (FEA) and analytical methods, 3D FEA accounting for end‐effect is also used to predict the results. Finally, the analyses are validated by experiments. [ABSTRACT FROM AUTHOR]

Hybrid-excited permanent magnet (PM) machines utilise the coordinated operation between the PM and the field excitation current. To enhance the effectiveness of the field excitation current, iron flux bridges are applied to hybridexcited switched-flux PM machines. This study proposes a new control strategy in which the d-axis current is utilised, while the field excitation current is controlled towards zero rather than negative in the flux-weakening mode. These reference currents are determined by the voltage error regulation method. The special magnetic circuit can effectively reduce the d-axis flux-linkage by either partially short-circuiting the PM flux via the iron bridge or removing the field excitation current. The proposed method exhibits advantages, such as highly enhanced torque response in the constant torque region, extended speed range, robustness against machine parameters, and higher efficiency in fluxweakening region. The feasibility of the proposed method is verified by detailed experimental results. [ABSTRACT FROM AUTHOR]

This study investigates the electromagnetic performance of a hybrid excited switched flux permanent magnet (SFPM) machine using the frozen permeability (FP) method. The flux components due to PMs, field excitation windings and armature windings have been separated using the FP method. It has been used to separate the torque components due to the PMs and excitations, providing a powerful insight into the torque generation mechanism of hybrid excited SFPM machines. It also allows the accurate calculation of d- and q-axis inductances, which will then be used to calculate the torque, power and power factor against rotor speed to compare the relative merits of hybrid excited SFPM machines with different types of PMs (i.e. NdFeB, SmCo and Ferrite). This offers the possibility of choosing appropriate PMs for different applications (maximum torque or maximum speed). Although only one type of hybrid excited PM machine has been employed to carry out the investigations, the method used in this study can also be extended to other hybrid excited PM machines. The predicted results have been validated by tests. [ABSTRACT FROM AUTHOR]

This study investigates the electromagnetic performance of a hybrid excited switched flux permanent magnet (SFPM) machine using the frozen permeability (FP) method. The flux components due to PMs, field excitation windings and armature windings have been separated using the FP method. It has been used to separate the torque components due to the PMs and excitations, providing a powerful insight into the torque generation mechanism of hybrid excited SFPM machines. It also allows the accurate calculation of d‐ and q‐axis inductances, which will then be used to calculate the torque, power and power factor against rotor speed to compare the relative merits of hybrid excited SFPM machines with different types of PMs (i.e. NdFeB, SmCo and Ferrite). This offers the possibility of choosing appropriate PMs for different applications (maximum torque or maximum speed). Although only one type of hybrid excited PM machine has been employed to carry out the investigations, the method used in this study can also be extended to other hybrid excited PM machines. The predicted results have been validated by tests. [ABSTRACT FROM AUTHOR]

This paper presents two novel designs of magnetic flux‐modulated mnemonic (MFMM) machines which incorporate magnetic gearing effect and flux‐mnemonic concept together. Both of these two machines can perform large torque production at low‐speed because of the magnetic gearing effect, and can readily achieve flexible flux‐controllability by temporarily applying current pulses to magnetise/demagnetise aluminium‐nickel‐cobalt magnets so as to expand the constant‐power region operation effectively. One machine has permanent magnets (PMs) on its rotor and outer stator which is referred as the dual‐layer PM MFMM (DPM‐MFMM) machine; bi‐directional field modulating effect is artfully incorporated in this machine to guarantee effective coupling between the magnetic fields excited by the armature windings and those excited by the two sets of PMs. The second machine employs all the PMs on the outer stator and the rotor is only made up of ferromagnetic segments. In other words, it is a single‐layer PM‐MFMM (SPM‐MFMM) machine, and the rotor carries the flux modulating poles. The configurations and working principles of both machines are discussed. The electromagnetic performances are comprehensively studied and quantitatively compared using finite element method (FEM). [ABSTRACT FROM AUTHOR]

Several switched flux permanent magnet (SFPM) machines with mechanically movable flux adjusting technique are proposed, analyzed, and compared for applications which demand high speed and efficiency. By using ferromagnetic pieces-–one per every stator pole or every alternative stator pole, which are named as flux adjusters (FAs) and located on the outside surface of the stator—the airgap flux density can be weakened and therefore the operation speed range and flux weakening capability can be improved. The influence of using all or alternative FAs on the open circuit results, electromagnetic performance, and torque–speed characteristics of the SFPM machine is investigated through three SFPM machines with different stator/rotor pole combinations, i.e., 12/10, 12/13, and 12/14. Moreover, although using FAs in all stator poles can significantly improve the flux weakening capability, alternative FAs can also achieve remarkable improvement although higher torque ripple is observed. Additionally, it has been found that the 12/13 combination is considered to be the most suitable candidate for alternative FAs technique. In addition to 2-D finite-element analysis (FEA) and analytical methods, 3-D FEA results accounting for the end-effect are presented. Furthermore, experiments are performed to validate the results. [ABSTRACT FROM AUTHOR]

Lately, there has been increased interest in hybrid excitation electrical machines. Hybrid excitation is a construction that combines permanent magnet excitation with wound field excitation. Within the general classification, these machines can be classified as modified synchronous machines or inductor machines. These machines may be applied as motors and generators. The complexity of electromagnetic phenomena which occur as a result of coupling of magnetic fluxes of separate excitation systems with perpendicular magnetic axis is a motivation to formulate various mathematical models of these machines. The presented paper discusses the construction of a unipolar hybrid excitation synchronous machine. The magnetic equivalent circuit model including nonlinear magnetization curves is presented. Based on this model, it is possible to determine the multi-parameter relationships between the induced voltage and magnetomotive force in the excitation winding. Particular attention has been paid to the analysis of the impact of additional stator and rotor yokes on above relationship. Induced voltage determines the remaining operating parameters of the machine, both in the motor and generator mode of operation. The analysis of chosen correlations results in an identification of the effective control range of electromotive force of the machine. [ABSTRACT FROM AUTHOR]

The hybrid excitation synchronous machine (HESM) with magnetic shunting rotor is a new topology of brushless HESM. To optimize the excitation construction, improve the flux control capability, and decrease the magnet consumption as well, two types of HESMs with different air-gap features are further proposed and investigated in this paper. First, configuration of the HESM with axial auxiliary air-gaps is presented. The comparative study of axial auxiliary air-gap scheme with respect to radial one is carried out. Three-dimensional (3-D) finite-element analysis (FEA) of the HESM is performed to achieve the field distribution, air-gap flux density and flux control characteristic, which indicates the HESM with axial auxiliary air-gaps also has good flux control capability and moreover enlarged excitation housing. Afterwards, construction and flux control principle of the new HESM with axial non-uniform air-gaps are introduced. A prototype HESM is developed, and the experimental results of open-circuit characteristic and terminal characteristic, which agree with the 3-D FEA results, verify the satisfactory field control performance, desirable power output capability, and the improved flux control capability of the HESM at negative excitation current as well. [ABSTRACT FROM PUBLISHER]

In this paper, an analytical approach for the prediction of the armature reaction field of field-excited flux-switching (FE-FS) machines is presented. The analytical method is based on the magnetomotive force (MMF)-permeance theory. The doubly-salient air-gap permeance, developed here, is derived from an exact solution of the slot permeance. Indeed, the relative slot permeance is obtained by solving Maxwell's equations in a subdomain model and applying boundary and continuity conditions. In addition, during a no-load study, we found that, regarding the stator-rotor teeth combination, phase distributions were modified. Hence, in this paper, phase MMF distributions, for q phases, several stator-rotor combinations and also phase winding distribution (single- or double-layers) are proposed. We compare extensively magnetic field distributions calculated by the analytical model with those obtained from finite-element analyses. Futhermore, the model is used to predict the machine inductances. Once again, FE results validate the analytical prediction, showing that the developed model can be advantageously used as a design tool of FE-FS machine. [ABSTRACT FROM AUTHOR]

Switched-flux permanent magnet (PM) (SFPM) machines have attracted considerable interest in recent years, since the flux focusing can be utilized, both armature windings and PM excitation sources are on the stator, while the salient pole rotor is very simple and robust. In SFPM machines, the high variable flux densities throughout the stator core result in iron loss being a significant proportion of the total losses. This paper presents a novel modular-rotor SFPM machine that facilitates a reduction in iron loss for a marginal reduction in output torque. The modular rotor also offers a reduction in rotor mass over the conventional-rotor topology. The electromagnetic performance of both conventional- and modular-rotor SFPM machines is analyzed by 2-D finite element analyses and is verified by measurements on small-scaled prototype SFPM machines. [ABSTRACT FROM AUTHOR]

This paper investigates the torque characteristics of permanent-magnet flux switching (PMFS) machines with rotor step skewing. The cogging torque, torque ripple, and average output torque of a PMFS machine with a common stator and different rotor pole widths and rotor pole numbers are first established using two-dimensional (2-D) finite element analysis (FEA). A cost-effective rotor step skewing technique is then proposed to reduce the cogging torque and torque ripple of the machine with two different rotors. The results have revealed that the least step number and angle for optimal torque ripple mitigation of the PMFS machine are determined by the harmonic contents of the torque pulsation and the rotor pole number. The influences of load conditions on the machine torque characteristics are carried out by varying current excitations. The corresponding three-dimensional (3-D) FEA models are constructed and experimental prototypes are built for validations. [ABSTRACT FROM PUBLISHER]

This paper presents a general and accurate approach to determine the no-load flux of field-excited flux-switching (FE-FS) machines. These structures are inherently difficult to model due to their doubly-slotted air gap. This analytical approach is based on magnetomotive force-permeance theory. The analytical model developed is extensively compared to field distribution obtained with 2-D finite element (2-D FE) simulations. The good agreement observed between analytical model and 2-D FE results emphasizes the interest of this general approach regarding the computation time. Hence, this analytical approach is suitable for optimization process in pre-sizing loop. Furthermore, based on the field model, classical electromagnetic performances can be derived, such as flux linkage and back-electromotive force (back-EMF) and also, unbalanced magnetic force. Once again, FE results validate the analytical prediction, allowing investigations on several stator-rotor combinations, or optimization of the back-EMF. [ABSTRACT FROM PUBLISHER]

In this paper, a proposal for a field weakening method for a permanent-magnet synchronous motor is evaluated. The method consists in inserting giant magnetostrictive elements between permanent magnets. The magnetic permeability of these magnetostrictive parts is modified when the speed increases. The field leakages around the permanent magnets are consequently increased, thus reducing the electromotive forces in the armature windings. An original modeling approach, based on the concept of equivalent stress, is proposed in order to evaluate this field weakening solution. [ABSTRACT FROM PUBLISHER]

Two motors are studied and optimized for transportation applications. The objective is to design motors whose external model is well suited for conventional vector control. Hence, in the design procedure, the emphasis is on the back-electromotive force (EMF) waveforms and external parameters. The first topology is a surface-mounted (nonsalient pole) motor with segmented magnets reducing significantly selected harmonics. The second is an inset magnet type (salient pole) motor with surface poles particularly shaped to reduce the harmonic content of the air gap flux density. For both motors, the principle of pulse width modulation is used for the harmonic reduction in the design process. The interest of these motors lies in the sinusoidal waveform of their back EMF allowing a simple vector control even at field-weakening region for high speeds. [ABSTRACT FROM PUBLISHER]

Permanent magnet (PM) brushless machines having magnets and windings in stator (the so-called stator-PM machines) have attracted more and more attention in the past decade due to its definite advantages of robust structure, high power density, high efficiency, etc. In this paper, an overview of the stator-PM machine is presented, with particular emphasis on concepts, operation principles, machine topologies, electromagnetic performance, and control strategies. Both brushless ac and dc operation modes are described. The key features of the machines, including the merits and drawbacks of the machines, are summarized. Moreover, the latest development of the machines is also discussed. [ABSTRACT FROM PUBLISHER]

Flux-switching permanent magnet (FSPM) machine is a relatively novel brushless machine, which exhibits inherently sinusoidal PM flux-linkage, back-EMF waveforms and high torque capability. However, the air-gap field density is difficult to be regulated since it is produced by the stator magnets alone. Hence, hybrid-excited flux-switching (HEFS) machine is proposed by introducing a set of field windings into an original FSPM machine. However, in HEFS machines the flux linkages of armature windings vary in inverse proportion to the air-gap flux density when significantly saturated, which is different from the conventional machines. So in this paper, the oversaturated phenomenon in HEFS machines is explained and the effect of saturation, especially due to magnet material, on the relationship between air-gap flux density and armature flux linkage is investigated based on 2-D finite element analysis. Also, an effective stator-tooth-width coefficient (kstw) is defined to evaluate the oversaturated effect quantitatively. [ABSTRACT FROM AUTHOR]

In this paper, a nonlinear magnetic network model (NMNM) is proposed to predict the electromagnetic performance of a hybrid-excitation flux-switching (HEFS) machine, in which the modeling of the magnetic motive forces (MMF) due to field windings is specifically investigated. The proposed NMNM enables the predictions of air-gap flux-density distributions, flux linkage, back-electromotive force (back-EMF), and inductances of both armature and field windings under different excitation conditions, including pure magnets, pure field currents, and hybrid excitations. The predicted results from the NMNM model are validated by 2-D finite element analysis. [ABSTRACT FROM AUTHOR]

In safety critical aerospace applications, fault-tolerant drives can help reach the necessary system reliability levels without replicating the entire drive system and thus minimizing the overall system weight. Machine selection and design for fault tolerance has to be considered at an early stage to ensure optimal performance at a system level. This paper looks at the fault-tolerant properties of permanent-magnet flux-switching machines (PMFSMs) and proposes a new configuration able to fulfill the fault-tolerant requirements. PMFSMs have the distinct property of having a robust rotor construction with the permanent magnets embedded in the stator while having their operational characteristics similar to those of synchronous permanent-magnet machines. While these machines have numerous inherent advantages for achieving a high power density, in their basic form, they are not tolerant to short-circuit winding failures. This paper will look at a novel stator structure able to achieve a 1-p.u. winding inductance and will subsequently look at design iterations to maximize the torque density. [ABSTRACT FROM AUTHOR]

A novel E-core switched-flux permanent-magnet (SFPM) brushless machine is proposed, and its electromagnetic performance is compared with that of the conventional SFPM brushless machine. The operation principle of the E-core SFPM machine will be first described, and the influence of stator and rotor pole number combinations is investigated, while the electromagnetic performance of the optimized E-core SFPM machine is predicted by finite-element analyses and validated by experiment. It is shown that the number and volume of magnets in the E-core SFPM machine is significantly reduced, only half of that in the conventional machine, while the phase back electromotive force and torque of the E-core machine are \sim 15% larger than those of the conventional machine. [ABSTRACT FROM AUTHOR]

A novel E-core hybrid-excited switched-flux permanent-magnet (SFPM) brushless machine is proposed based on an E-core SFPM machine, which has significantly less magnet and higher torque density than those of a conventional SFPM machine. The proposed machine has a simple structure. The main flux path of dc excitation does not affect the magnet excitation because it is not through magnets. The combination of stator and rotor pole numbers of the proposed machine is optimized, and the flux-enhancing and flux-weakening capabilities are investigated by 2-D finite-element analyses and experimentally validated. [ABSTRACT FROM PUBLISHER]

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]