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Recently, the interest in consequent-pole flux-switching permanent magnet (CP-FSPM) machines has been increasing because of the flux-focusing PM arrangements and the removal of the flux-barrier effect. A simple and rigid outer-rotor salient pole rotor structure can be adopted in CP-FSPM machines, making them applicable for in-wheel direct-drive applications. In this study, three CP-FSPM machines with II-shaped (II-PM), V-shaped (V-PM), and straight U-shaped PM (SU-PM) arrays are analyzed and compared. Moreover, a CP-FSPM machine with inclined U-shaped PM (IU-PM) arrays is proposed to improve the flux-focusing effect and stator slot utilization. The working principles of CP-FSPM machines are analyzed by adopting a semi-analytical model. Combining the finite element analysis (FEA) results of air gap flux density and the analytical model of phase back electromotive force (EMF), the contributions of multiple working harmonics to the back EMF are quantitatively analyzed. Additionally, 6/16 and 6/17 CP-FSPM machines with different PM arrangements are globally optimized. Both the no-load and on-load performance of the optimized machines are included in the performance comparison. The results illustrate that the 6/16 and 6/17 machines exhibit their respective merits, and the IU-PM machine shows the best torque production ability in these CP-FSPM machines with the same design criteria. [ABSTRACT FROM AUTHOR]

Featured Application: Stand-alone wind power generator. In this paper, a novel mechanical flux-weakening design of a spoke-type permanent magnet generator for a stand-alone power supply is proposed. By controlling the position of the adjustable modulator ring mechanically, the total induced voltage, i.e., the amplitude of the back EMF vector sum can be effectively adjusted accordingly by the modulation effect. Consequently, the variable-speed constant-amplitude voltage control (VSCAVC) with a large speed range can be achieved. Compared to the electrical flux-weakening method, the mechanical flux-weakening method is easier to operate without the risk of PM demagnetization. The analytical model is presented, and the operation principles are illustrated. To analyze the performance of different combinations of stator/rotor pole pairs, four cases are optimized and analyzed using the finite element method for comparison. The characteristics of VSCAVC are analyzed. [ABSTRACT FROM AUTHOR]

When a permanent magnet synchronous motor (PMSM) is designed according to the traditional motor design theory, the performance of the motor is often challenging to achieve the desired goal, and further optimization of the motor design parameters is usually required. However, the motor is a strongly coupled, non-linear, multivariate complex system, and it is a challenge to optimize the motor by traditional optimization methods. It needs to rely on reliable surrogate models and optimization algorithms to improve the performance of the PMSM, which is one of the problematic aspects of motor optimization. Therefore, this paper proposes a strategy based on a combination of a high-precision combined surrogate model and the optimization method to optimize the stator and rotor structures of interior PMSM (IPMSM). First, the variables were classified into two layers with high and low sensitivity based on the comprehensive parameter sensitivity analysis. Then, Latin hypercube sampling (LHS) is used to obtain sample points for highly sensitive variables, and various methods are employed to construct surrogate models for variables. Each optimization target is based on the acquired sample points, from which the most accurate combined surrogate model is selected and combined with non-dominated ranking genetic algorithm-II (NSGA-II) to find the best. After optimizing the high-sensitivity variables, a new finite element model (FEM) is built, and the Taguchi method is used to optimize the low-sensitivity variables. Finally, finite element analysis (FEA) was adopted to compare the performance of the initial model and the optimized ones of the IPMSM. The results showed that the performance of the optimized motor is improved to prove the effectiveness and reliability of the proposed method. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the effect of the alternate flux bridge combining Halbach array in Vernier machines. The key novelty is that integrated with the Halbach array PM, the alternate flux bridge design can not only provide a flux path for low-order harmonics but also effectively improve the torque density of the machine. Together with the other three traditional structures under the same overall size, current density, and PM usage, the proposed structure is optimized by genetic algorithm (GA) to maximize the average torque and minimize the torque ripple. With the winding configuration of full-pitch (FP) and short-pitch (SP), the back-EMF, efficiency, power factor, and other performances of four machines with different topologies are analyzed and compared, respectively. With 2D time stepping finite element analysis (FEA) and experimental verification, the torque density of the proposed design reaches 40.11 KNm/m3, which is significantly higher than that of its existing counterparts. [ABSTRACT FROM AUTHOR]

A high-end permanent magnet (PM) synchronous motor's cogging torque is a significant performance measure (PMSM). During the running of the motor, excessive cogging torque will amplify noise and vibration. Therefore, the cogging torque must be taken into account while optimizing the design of motors with precise motion control. In this research, we proposed a local optimization-seeking approach (RSM+NSGA-II-LR) based on Response Surface Methodology (RSM) and Non-Dominated Sorting Genetic Algorithm-II (NSGA-II), which reduced the cogging torque of a permanent magnet synchronous motor (SPMSM). To reduce the complexity of optimization and increase its efficiency, the sensitivity analysis method was utilized to identify the structural parameters that had a significant impact on the torque performance. Second, RSM was utilized to fit the functional relationship between the structural parameters and each optimization objective, and NSGA-II was integrated to provide the Pareto solution for each optimization objective. The solution with a greater average torque than the initial motor and the lowest cogging torque was chosen, and a new finite element model (FEM) was created. On the basis of the sensitivity analysis, the structural factors that had the highest influence on the cogging torque were selected, and the RSM is utilized for local optimization to lower the cogging torque as much as feasible. The numerical results demonstrated that the optimization strategy presented in this study effectively reduced the cogging torque of the motor without diminishing the motor's average torque or increasing its torque ripple. [ABSTRACT FROM AUTHOR]

The reluctance machine is a potential candidate for electrical vehicle propulsion because of its reliable structure, low cost, flexible flux regulation ability, and wide speed range. However, the torque density is unsatisfactory because of the poor excitation ability and low stator core utilization factor. To solve this problem, in this paper, a novel hybrid reluctance machine (HRM) with the skewed permanent magnet (PM) and the zero-sequence current is proposed for electric vehicles. The skewed PM has two magnetomotive force (MMF) components with different functions. The radial MMF component provides extra torque by the flux modulation effect. The tangential MMF component can generate a constant biased field in the stator core to relieve the saturation caused by the zero-sequence current and thus improve the utilization factor of the stator core. Therefore, torque improvement and the relief of stator core saturation can be simultaneously achieved by the skewed PM. In this paper, the machine structure and principle of the proposed machine are introduced. And ultimately, the machine's electromagnetic performances are evaluated under different PM magnetization directions and zero-sequence current angles by using finite element analysis (FEA). [ABSTRACT FROM AUTHOR]

In this work, a novel general pattern of assisted flux barriers in an asymmetric V-shape interior permanent magnet (AVIPM) machine is presented. The AVIPM machine has a symmetric permanent magnet (PM) structure and an asymmetric rotor core structure to realize the magnetic-field-shifting (MFS) effect. The general pattern can represent four possible types of assisted flux barriers at different positions on the rotor core and the final structure can be automatically determined by using optimization method. The advantage of the proposed optimization pattern is that the optimal design of assisted flux barriers in V-shape interior permanent magnet (VIPM) machines with high torque and low torque ripple can be generated within a short computing time. The proposed optimization method is applied to improve the structure of a conventional 8-pole 48-slot VIPM machine, which is commonly used for driving electric vehicles (EVs). A non-dominated sorting genetic algorithm II (NSGA-II) is used for the global optimization of both a VIPM machine and an AVIPM machine. The electromagnetic performance is computed using a finite element analysis (FEA). Moreover, a frozen permeability (FP) method is applied to perform an accurate separation of PM torque and reluctance torque. The results exhibit that the peak output torque of the AVIPM machine is increased by 8.7% compared to a conventional VIPM machine with the same PM volume due to the notable MFS effect. In the meantime, the AVIPM machine has a better overload capability due to the larger contribution of reluctance torque. Moreover, the proposed machine has high efficiency of over 97%. [ABSTRACT FROM AUTHOR]

The transverse flux tubular linear machine (TF-TLM) has merits of high power density and efficiency. However, excited by constant permanent magnet (PM), it is hard for TF-TLM to regulate its flux effectively, which restricts its further application in wave energy conversion (WEC). In contrast, the inherent higher order harmonics existing in the induced voltage may cause the additional loss and produce overvoltage, which should be eliminated to prompt power quality. Therefore, to strengthen the flux regulation capability of TF-TLM and improve the generated power quality, a novel hybrid-excited TF-TLM (HE-TFTLM) with complementary structure is proposed in this article. The key is that a parallel and complementary structure is constructed for hybrid excitations of both dc windings and PMs installed on the stator to enhance the flux regulation capability and eliminate the even-order harmonics in the induced voltage. In addition, the stator consequent-pole design boosts the output thrust density. According to the 3-D finite element analysis (FEA) results, output thrust force reaches 279.14 N, and the power density of the proposed machine can be effectively improved to 154 kW/m3 at rated excitation. [ABSTRACT FROM AUTHOR]

Vernier reluctance machine (VRM) with dc field coils in stator is a competitive rare-earth-free design for variable-speed industrial applications due to its robust structure and controllable excitation, while its torque density is relatively disadvantageous. To address this issue, this article proposes a new armature winding design method for VRM with dc field coils across two stator teeth. The key is to break the traditional winding design principle based on the flux modulation effect of fundamental dc field harmonic, and instead, reconstruct a novel harmonic winding to enhance the utilization factor of the modulated high-order dc field harmonics arising from the unique magnetomotive force distribution of dc field coils across two stator teeth. By this means, the torque density can be improved by 75.6% against the existing poor counterpart. In this article, the machine structure and operation principle are introduced, with emphasis on the high-order dc field harmonics distribution rule and its influence on the armature winding design. By finite element design and optimization, a comparative study is performed to evaluate the electromagnetic performance of VRMs using two different winding configurations with variable slot pole combinations. A prototype is fabricated and tested, and the results agree well with finite element analysis, which verifies the feasibility and advantages of the proposed winding design method. [ABSTRACT FROM AUTHOR]

Reluctance machines with dc excitation coils have become a promising solution for electric vehicle propulsion system because of its robust rotor structure and good field-weakening ability. However, these machines usually suffer from relatively low torque density and efficiency. To solve this problem, this article proposes a novel hybrid reluctance machine with improved torque density and efficiency. The key novelty is to introduce skewed permanent magnets (PMs) in slot openings. The tangential component of skewed PMs can be used to relieve the dc saturation in the stator iron core, so that the $B-H$ working range can be extended and relatively high dc excitation can be applied in the proposed machine. Besides, the radial component of skewed PM provides extra torque component under flux modulation effect. Therefore, the proposed skewed PMs can achieve torque boost and core utilization improvement simultaneously. In this article, the dc-saturation-relieving effect of the proposed design is thoroughly investigated and verified by finite element analysis. [ABSTRACT FROM AUTHOR]

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

This article proposed a new slot-permanent-magnet (PM)-assisted hybrid reluctance generator (SPMa-HRG) with self-excited dc source for stand-alone wind power generation system. By introducing PM excitation in stator slot openings, enhanced torque density due to flux modulation effect can be achieved compared with the original reluctance topology. Moreover, the introduced PMs make it feasible to build a self-excited dc source to fed dc field winding without using extra power supply. In particular, a simple design of ac supply winding is proposed, by splitting a small portion of ac armature winding to provide electrical power to dc field winding through a diode rectifier and small-capacity H-bridge converter. Compared with using separate dc source, the device cost is reduced, and the system reliability is improved. In this article, the generator structure and operation principle are introduced. PM usage is optimized to obtain the optimal torque. The feasibility of the optimal design with self-excited dc source is verified by field-circuit coupled finite element analysis. [ABSTRACT FROM AUTHOR]

In this article, a novel pre-processing method is proposed for magnetic field approximation based on neural networks. The process of calculating magnetic fields based on neural networks is presented first. In order to save the training time and reduce the estimation error, an excitation distance function, which is inspired by an analytical formula of magnetic potential, is proposed to integrate the input data, such as the geometry, excitations, and boundaries. This pre-processing or roughly reduces the dimension of the input layer by three quarters, while the training process is accelerated by a more integrated input layer. Preliminary experiments show that the predicted results by the proposed pre-processing method are close to the ground truth, with a significant reduction of computation time compared with the traditional finite element method (FEM). [ABSTRACT FROM AUTHOR]

This article aims to propose a new hybrid reluctance machine equipped with relieving-dc-saturation (RDCS) ability for electric vehicle in-wheel drive. The proposed machine uses integrated ac and dc current excitation to eliminate extra dc field coils for the efficient torque generation. Besides, considering the inherent dc saturation in stator core caused by dc current excitation, slot PMs are artificially introduced to provide RDCS effect and thus boost torque density. Moreover, with a modular magnetic field configuration, the proposed topology exhibits excellent fault-tolerant potential at both open-circuit and short-circuit condition, making it suitable for safety-critical in-wheel vehicle propulsion. In this article, the machine configuration and operation principle are introduced, with emphasis on its RDCS effect and corresponding design consideration. Further, performance of this new topology is evaluated by both finite element analysis and prototype experiments. It is revealed that, with this RDCS ability, torque density of the proposed machine can be enhanced by about 25% under relatively high current density. [ABSTRACT FROM AUTHOR]

Owing to bidirectional field modulation effect, dual-permanent-magnet-excited (DPME) machine could offer improved torque capability, which has attracted increasing attention in recent years. However, conventional DPME machine only utilizes a small amount of abundant field harmonics to yield torque, which leads to limited torque enhancement. To solve this issue, a novel DPME machine with enriched working harmonics is proposed in this paper. The key of the proposed DPME machine is to design some non-uniformly distributed permanent-magnets and flux modulation poles on the stator. Thus, increased field harmonics are produced to produce effective torque, offering the potential to enhance torque. Firstly, the topology and feature of the machine are introduced. Moreover, operating principle is analyzed by using air gap field modulation theory. Then, the operating principle and torque enhancement are verified and evaluated by using finite-element method. At last, a corresponding principle machine is fabricated, and some experiments are performed for validation. [ABSTRACT FROM AUTHOR]

The transverse flux permanent-magnet (PM) linear machine has attracted much attention in high-performance direct-drive applications because of its high torque density and efficiency. However, due to its inherent large open-circuit flux leakage, the prominent cogging force makes it difficult to obtain a high accuracy in position and speed control, which restricts its potential for precision industrial processing applications. To overcome this problem, a novel transverse flux linear machine is proposed in this paper. The key is by creatively combining a consequent-pole mover design and a stator-segment-interlacing configuration in such a way that a parallel and complementary transverse magnetic circuit is realized for the moving PMs, which can effectively minimize the open-circuit leakage flux and cogging effect. In this paper, the machine structure, operation principle, and theoretical modeling are introduced, with its electromagnetic performance evaluated by using the finite-element method. A prototype is also built for the experimental verification, and relevant test results agree well with the finite-element predications. [ABSTRACT FROM AUTHOR]

A separate-stator modular machine with biased flux is proposed in this paper. In this machine, the windings and the permanent magnets are located in two separate parts of the stator, which favors the heat dissipation and magnetic saturation reduction of the machine. With the specially designed stator structure, a biased flux can be introduced to flexibly regulate the excitation field by injecting a zero-sequence current into the phase windings, so that a wide operation speed range can be achieved. Moreover, a modular structure is adopted to simplify the automated manufacture assembly. In this paper, the machine configuration and the working principle are first illustrated. The effect of the design parameters on its torque capability is then investigated. A coupled electromagnetic-thermal optimization method based on the genetic algorithm and finite-element method is proposed to improve the torque performance of the machine. [ABSTRACT FROM AUTHOR]

In this paper, a new permanent magnet (PM) linear motor is proposed. This motor has a special structure with complementary stator flux, which helps to reduce the flux leakage and improve the utilization of the PM. The PMs are installed in a leaning manner, which increases the effective area of the PMs and enhances the field excitation. Hence, the force density of the motor can be improved and it will be, especially suitable for applications within a limited space. The motor structure and working principle are first explained. The design of the motor is then comprehensively investigated. An electromagnetic optimization method based on tabu search algorithm and finite-element method is proposed for the motor to improve its force density. [ABSTRACT FROM AUTHOR]

In this paper, both the steady-state and dynamic performances of the double-stator permanent magnet brushless (DS-PMB) machines, including the surface-mounted topology (DS-SPMB) and the interior topology (DS-IPMB), are quantitatively compared with that of the traditional single-stator SPMB (SS-SPMB) machine. Based on the same electric loading and magnetic loading, the DS-SPMB and DS-IPMB machines are designed to have the same output power, while the DS-SPMB and SS-SPMB machines are of the same peripheral dimensions. The steady-state and transient characteristics of these machines are simulated by using the circuit-field-torque time-stepping finite element method. Finally, the preferred machine, namely, the DS-SPMB one, is prototyped and tested for experimental verification. [ABSTRACT FROM AUTHOR]

With the increasing popularity of hybrid electric vehicles (HEVs), the demands of improving the fuel economy and energy efficiency of HEVs are enlarged. The technology electrical continuously variable transmission (E-CVT) system provides the opportunity to fulfill this requirement. However, conventional E-CVT with planetary gears suffer from frictional loss, high maintenance, and audible noise. Therefore, a series of gearless E-CVT propulsion systems are developed. Thereinto, a double-rotor single-stator brushless E-CVT having high torque density, reduced stator end winding length, and reduced copper loss was recently proposed. However, only torque of the E-CVT system is optimized by the genetic algorithm in the previous study. This paper adopts a differential evolution algorithm coupled with finite element method to optimize torque, energy efficiency, torque ripples, and multiobjective of the E-CVT system by reconfiguring the height of rotors, the areas of slots, and the height of yoke. It is simulated that by only tuning the weighting factors, the permanent magnetic machine in the E-CVT system can operate in the highest torque mode, highest energy efficiency mode, lowest torque ripples mode, and multiobjective optimization mode. [ABSTRACT FROM PUBLISHER]

This paper presents an optimal design methodology of a dual-mechanical-port bidirectional flux-modulated machine for electric continuously variable transmission in hybrid electrical vehicles. The machine utilizes bidirectional flux modulation effect to combine two rotors and one stator together, aiming to realize electrical and mechanical power flexible split and combination. Due to the complexity of the machine structure, conventional optimization methods using analytical model are inapplicable. Therefore, an effective and practical method that combines the genetic algorithm and finite-element method (GA-FEM) is proposed to optimize the design of the machine in this paper. Since the computational cost increases exponentially with the increasing of number of design parameters, to reduce the computational cost in the optimization process, the design parameters are divided into two levels basing on a sensitivity analysis. And, then, the sensitive parameters are optimized using the GA-FEM coupled method. Finally, a prototype is fabricated to verify the effectiveness of the optimal design. [ABSTRACT FROM PUBLISHER]

Severe leakage flux is a long-existed drawback in the transverse-flux permanent magnet machines (TFPMs), which results in a low permanent magnet (PM) utilization rate and prominent cogging torque in TFPMs. Aiming to solve this problem, this paper presents a novel consequent-pole transverse-flux machine (CP-TFM). The key is to artificially shift the upper and lower salient-pole rotors with a half-pole pitch and connect them with a ring-shaped core. Therefore, a complementary magnetic circuit is constructed to reduce the flux leakage between the adjacent poles as well as improve the PM utilization rate. To verify the feasibility of design, a 3-D finite-element model is established and its electromagnetic performance is evaluated. With the same peripheral dimension and copper loss, a quantitative comparison is carried out between the proposed CP-TFM and conventional TFPM. Finite-element simulation results reveal that compared to its contrast, the proposed solution can almost double the PM utilization ratio and effectively reduce the cogging torque. [ABSTRACT FROM AUTHOR]

From a new stator-flux perspective, a comparative study between the series and parallel hybrid excitation machine (PHEM) is conducted and it is revealed that in PHEMs there still exist distinct stator-flux harmonic components during high-speed flux weakening operation, which could be further utilized to improve the torque capability at high-speed range. Inspired by this idea, an auxiliary winding is creatively introduced into PHEMs to recycle and utilize the magnetic field energy generated during the field regulation. A new design case is presented in this paper, in which two sets of armature windings with different pole pair numbers are arranged to realize the function of flux weakening operation and energy recycling, respectively. The feasibility of this new hybrid solution is evaluated by using the finite-element analysis. Furthermore, a prototype is manufactured and relevant experiments are performed. The experimental results agree well with the theoretical analysis and simulation results, which verify that the recycled energy can be effectively used to boost the output torque and power of PHEMs in the high-speed region. [ABSTRACT FROM AUTHOR]

For the purpose of saving energy resources, it is extremely expected to develop highly efficient electric motors. Different types of permanent magnet (PM) arrangement can significantly affect the performance of the motors. Conventionally, the arrangement of the PMs is determined by designer’s experience. This paper focuses on the optimal design of PM arrangement in PM synchronous motors (PMSMs). We present a general pattern of the PM arrangement in PMSM. By varying the parameters of the general pattern, it can produce different types of PM arrangement in the rotor. The employed approach combines the global optimization method with the finite-element method for solving the optimization of the PM structures. Based on the proposed general pattern and optimization methods, the best PM arrangement in the motor can be automatically determined. In order to reduce computing loading, this paper employs the response surface models for reducing the computing time of objective functions. In the end, numerical tests are designed to showcase the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A novel gearless and brushless power-split transmission system is proposed for a variable speed constant frequency wind power generation application. The key is to design a special hybrid axial–radial flux focusing structure, which has an improved utilization of permanent magnet (PM) materials. This design integrates the merits of two popular concepts—the direct-drive PM generator and the doubly fed induction generator. It is direct driven, with high torque density and in the meanwhile, it needs only a partial-scale converter. To improve the stability of the system, five phase currents are used for the control winding. A time stepping finite-element method is used to analyze the dynamic performance of the proposed system. [ABSTRACT FROM AUTHOR]

This paper proposes and implements a new single-phase magnetless flux switching machine (FSM) for rooftop wind power generation. The key is to integrate an outer-rotor FSM and an inner-rotor FSM with shared stator yoke and stator drum windings. In such a way, this proposed machine can not only realize flux switching function to regulate magnetic flux effectively, but also incorporate the field and armature windings within one stator to reduce the copper losses and improve the overall machine efficiency. Meanwhile, the structure is compact and rotors can be directly driven by blades to capture the wind power. The machine design guidelines from both magnetic and electric aspects are illustrated, the machine characteristics are analyzed by using time-stepping finite-element method, and the system performances are evaluated based on mathematical modeling. Both simulation and prototyping test are conducted to verify the validity of the proposed machine and system. [ABSTRACT FROM AUTHOR]

In this paper, an efficient and effective magnetic circuit model is developed for the analysis of a magnetless double-rotor flux switching motor. First, a magnetic circuit network for the proposed machine is built, and formulas for the calculation of the magnetic components in the circuit, including the permeances of teeth, yokes, slots, leakage permeances, and air-gap permeances, are derived. Then, by applying Kirchhoff’s current law to each node in the network, nodal analysis is used to solve the matrix equation. All the circuit variables, and hence the complete motor magnetic characteristics are being considered. When the rotor rotates, the air-gap permeances are adjusted accordingly, and the above calculations are repeated, so as to find the complete static performance of the motor. Last, the validity and the effectiveness of the proposed method are verified using both the experimental results and the simulation results obtained from the time-stepping finite-element method. [ABSTRACT FROM AUTHOR]

Finite-element method (FEM) has been widely used to analyze the performance of electric devices. Due to the nonlinear permeability of iron materials, Newton–Raphson method is usually used in FEM for nonlinear iteration. To accelerate the nonlinear convergence, one effective technique is proposed. The method is to use different relaxation factors for materials in the electric device. The difference between this proposed method and conventional method is that in conventional method only one relaxation factor is used for all solutions. With the proposed method the total computing time of iteration process of FEM can be reduced effectively. The proposed algorithm is tested on a highly saturated transformer to showcase its effectiveness. [ABSTRACT FROM AUTHOR]

This paper proposes a novel magnetic-geared tubular linear machine for tidal and wave energy conversion. The key of the proposed machine is to embed the armature windings into slots adjacent to the modulating segments of a linear magnetic gear (LMG). The compact component designed can serve simultaneously as the modulating poles in the LMG and the armature stator in the generator. When compared with its existing counterparts, the proposed machine has an improved force density and a simpler mechanical structure by virtue of its gearing effect. Moreover, Halbach permanent-magnet (PM) array is used to build up the PM arrays in both the inner mover and outer mover of the LMG, resulting in increase in thrust force density, reduction in cogging force, and high machine efficiency. The working principle of the proposed machine is introduced, and the electromagnetic performance is investigated quantitatively using the time-stepping finite-element method. [ABSTRACT FROM AUTHOR]

Low-speed flux-modulated permanent-magnet (PM) machines do not need to conform to the conventional design rule which requires identical number of pole-pairs in both stator and rotor. In flux-modulated machines, special ferromagnetic segments in the airgap are used to modulate the magnetic field. In this paper, a general rule to compare different types of electric machines as well as measures to improve the torque density in these machines are presented. In this paper, the energy conversion capacity of different machines with the same physical size and the same operating temperature-rise are compared. An adaptive-order method for modeling the load—temperature-rise relationship is presented to reduce the computing time for this inverse problem. Three power-electronic-driven PM electric machines, which are, namely, a traditional PM machine, a radial-flux-modulated machine (RFMM), and an axial-flux-modulated machine (AFMM), are analyzed and compared based on their temperature distribution and electromagnetic torque density using magnetic field and thermal field computation. Experimental results of an AFMM prototype are used to validate the temperature-rise which is computed using 3-D finite-element method (3-D FEM). [ABSTRACT FROM PUBLISHER]

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]

Electric motors fabricated with aluminum–nickel–cobalt (AlNiCo) permanent magnets (PMs) can be operated over a wide speed range, as the strong nonlinear demagnetization characteristics of AlNiCo allow effective and efficient airgap flux control. This paper presents a linear hysteresis model which is derived from the Preisach model for AlNiCo PMs, to be incorporated into the time-stepping finite element method to study the motor performance, especially transient performance, accurately and effectively. The proposed method can significantly reduce the computing time without scarifying the accuracy of the Preisach model. The validity and accuracy of the proposed method are verified by both simulation and experimentation. [ABSTRACT FROM PUBLISHER]

A novel dual-stator bidirectional-flux modulated permanent magnet (PM) machine is presented in this paper. The key of the design is to locate consequent PM poles in both stator and rotor sides and the merit is that the magnetic flux produced by either the rotating or stationary PMs and dual-stator windings can be modulated by the stator teeth and rotor iron segments. It is shown that with this flux modulation effect and improved reluctance torque effect, the torque density of the machine can be increased. The bidirectional flux modulation theory and operation principle of the machine are explained and analyzed using time-stepping finite element method. [ABSTRACT FROM AUTHOR]

This paper presents a novel gearless and brushless power split transmission system for variable-speed constant-frequency wind power generation application. The core element of this system is a novel axial-flux doubly fed dual-rotor permanent magnet machine. The key of the design is to utilize the flux modulation principle to modulate the magnetic flux in an axial-flux machine and use doubly fed stator winding to control the rotor rotation. This design combines the merits of direct-drive machines and doubly fed generators. As the mechanical problems related to brushes, slip rings, and gear boxes are successfully overcome, the operational reliability of the system is improved. The stator winding of the proposed system can be directly connected to the power grid, and the power rating of its associated frequency converter is reduced. Time-stepping finite-element method is used to analyze the dynamic performance of the proposed system. [ABSTRACT FROM AUTHOR]

This paper presents a novel magnetless double-rotor flux switching motor for low cost cooling fan application. By creatively incorporating concentrated toroidal windings into a double-rotor middle-stator structure, the proposed motor not only realizes the flux switching feature, but also shortens the end-windings to improve its operational efficiency. To achieve a better performance, the motor dimensions, especially the stator and rotor pole arcs, are optimized. Meanwhile, with the introduction of a stepped air-gap, the torque at any rotor position is boosted and problems with zero output torque at starting is successfully avoided. The final optimized motor is analyzed using finite element method, and its validity is confirmed by the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, an electric machine with dual permanent magnet (PM) structures in both stator and rotor is proposed. Multi-pole PMs are buried both in stator and rotor slots of the proposed machine and the magnetic field is modulated through the stator and rotor teeth. This machine with dual magnetic flux modulation can be categorized as one special case of flux-modulating machines. A time-stepping finite-element method combined with space vector pulse width modulation-based vector control method is used to analyze the steady-state and transient performance of the machine and its control system. [ABSTRACT FROM AUTHOR]

A novel double-stator, double-rotor brushless electrical continuously variable transmission (E-CVT) system is proposed. This machine incorporates an inner stator which can fully utilize the space inside the inner rotor so as to reduce the volume of the machine. This design is based on magnetic flux modulating and magnetic gear effect to make the E-CVT system work in different operating modes. Different control modes of this proposed machine are also discussed and analyzed, including pure electric mode, hybrid mode, and battery charging mode. Time-stepping finite element method (TS-FEM) is used to analyze the dynamic performance of the machine. TS-FEM simulation results are reported to verify the validity of the proposed design. [ABSTRACT FROM AUTHOR]

Time stepping finite-element method can be used to compute the electromagnetic torque on the rotor of electric machines. During calculation, the magnetic field equations are solved for finding the field distribution, and Maxwell stress tensor method is usually used for force distribution. However, the solutions from the two different sets of mathematical systems cannot guarantee the energy input and output of the system are balanced. In some cases unrealistic results may occur in that, for example, the calculated efficiency is higher than 100%. In particular, the accuracy of force computation is largely dependent on the mesh qualities and relative position changes along the integration path. In this paper, an algorithm of power balanced torque computation based on considerations of energy conservation is presented. The main salient merit of this method is that it guarantees the input energy and output energy are balanced as the rotor moves, and the computed torque is less sensitive to mesh quality and position changes. [ABSTRACT FROM PUBLISHER]

A novel electrical continuously variable transmission (E-CVT) system is presented and analyzed based on harmonic spectra analysis of magnetic fields. Two rotors and one stator are integrated within one electric machine so as to keep the whole system compact. The main merits of this proposed torque transmission machine are its brushless structure, improved torque density, reduced stator end winding length, and reduced copper loss. The operating principle of the machine is described and its steady-state and transient performances are analyzed using time-stepping finite element method (TS-FEM). FEM results are used to confirm and validate the superior performance of the proposed machine. [ABSTRACT FROM AUTHOR]

Magnetic gears (MGs) are devices which operate through the interaction of magnetic fields produced by multipole magnets to transmit torque with high efficiency. Compared with mechanical gears, it requires no moving contact for the force transmission, hence there are no mechanical fatigue and no mechanical loss and less acoustic noise. There is no need for lubrication and hence MG requires minimal maintenance. However, the heavy use of permanent magnetic (PM) materials leads to a high production cost. In this paper, a novel mesh adjustable finite-element algorithm is proposed to optimize the magnetic gear dimensions in order to maximize the torque output for a given amount of PMs. With the proposed mesh adjustable finite-element algorithm, the coordinates of mesh nodes are moved according to dimensional changes, without compromising the mesh quality. The merit is that no re-mesh is required during the process of optimization, which can significantly reduce the computing time while retaining the robustness of the algorithm. By combining the proposed approach with particle swarm optimization (PSO) algorithm, a reliable convergence to the finding of global optimum is achieved. This proposed method is applied to optimize the dimensions of a coaxial magnetic gear with surface mounted PMs. Optimal results confirm the validity and effectiveness of the proposed algorithm. [ABSTRACT FROM PUBLISHER]

Magnetic fluid hyperthermia (MFH) is a promising cancer therapy by virtue of its good depth penetration. As the injected magnetic fluids of MFH are inevitably distributed in the tumor as well as in normal tissues nearby, it is difficult to accurately heat and ablate the targeted tumor without damaging the surrounding healthy tissues. Based on the observation that magnetic nanoparticles are only heated by alternating fields and not by static dc fields, it is possible to exploit such findings in MFH therapy to provide an efficient cure for cancer patients. To avoid unnecessary heating of healthy tissues, a novel system is proposed to set up a dc magnetic field around the tumor target. At the same time, the system creates a field-free region (FFR) with negligible static magnetic field in the target area. The target area can then be fully heated by an alternating field whereas the nearby tissues are not heated. In this paper, a novel ac and dc magnetic field combined MFH system, targeting the treatment area, is presented to produce an accurately focused magnetic field to abate the tumor cells. The proposed method is validated using finite element analysis. [ABSTRACT FROM PUBLISHER]

A parameterized mesh generation and refinement method is presented for parameter sweeping analysis of electromagnetic designs. The advantages of the method are distinct in that the method is remeshing-free, thus it can significantly reduce the numerical simulation time during the finite element analysis (FEA) process. The refinement procedure is accomplished in an adaptive manner to concentrate the mesh vertices to regions with large solution variations. A high quality mesh can be obtained and kept by using this method with triangular finite elements. An example of parameter sweeping for optimal electric motor design is given to showcase the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

The significance of eddy-current in high-speed permanent magnet machines cannot be underestimated in that it has serious implications on the machine's efficiency or even demagnetizes the PMs because of an overheating problem. It is necessary to accurately estimate the eddy-current losses and find an optimal design to minimize the losses and improve the machine's performance. In this paper, the axial segmentation of the PMs is first employed to cut off the eddy-current axial paths. Then, a conductive shield is introduced to smooth the time varying magnetic field in the conductive sleeve and the PMs in order to reduce the eddy-current losses. A nodal method based network-field coupled multislice time-stepping finite element method (TS-FEM) is proposed to analyze the steady-state and dynamic characteristics of the high-speed PM machine; its merit is that sub-block matrixes of the circuit equations are more convenient to be established compared with that of mesh method. Analysis of eddy-current losses in the rotor is reported. [ABSTRACT FROM PUBLISHER]

A novel solution for sensorless starting of conventional surface mounted PM motors is proposed. The strategy of the proposed scheme is to creatively formulate a combination of electromagnetic field with transient finite element method (FEM). The proposed solution is an improvement over and above conventional methods in that it is based on rotor position detection at zero speed with high frequency signal injection and back EMF detection. Previous researches tend to consider the induced signal from different winding terminals independently. The proposed methodology however exploits the induced voltage signals from two of the motor winding terminals, using the third terminal as the signal injection point. The strategy also eliminates the process of polarity tests. The relationship between the dependency of induced signals and the rotor position angle is summarized, and a simple motor starting scheme is proposed. Effects arising from the transient characteristics of the injected/induced signals are fully addressed using FEM. [ABSTRACT FROM PUBLISHER]

This paper presents a novel sub-matrix transformation method on mesh rotation problems in the finite element analysis (FEA) of electric machines. This proposed approach is simple, convenient and readily implementable. For each rotor position, only the transformation matrix which has fixed regular pattern versus the rotor position displacement needs to be modified. Transformation matrices with first-order element, second-order element as well as with periodic and anti-periodic boundary conditions have been developed. By using sub-matrix transformation, the mesh coupling can be realized automatically, efficiently and with minimal computing burden, since all the coefficients of the FEA system equation are stored in the sub-matrixes and they do not need to be re-assembled for different rotor positions. Formulae derivation and theoretical analysis are presented together simulation results to verify the validity of proposed method. [ABSTRACT FROM PUBLISHER]

A sensitivity analysis method for the equivalent parameter extraction of transient magnetic field problems with internally coupled circuits is presented. In contrast to conventional methods using physical meaning and physical relationships for parameter extraction, this method is based on a collection of mathematical system equations which include transient magnetic field equations and internal circuit equations. The extracted parameters include the collective effects of eddy currents, internal circuits, and mechanical motion. Compared with previous sensitivity analysis methods which extract only the equivalent inductance, the proposed algorithm extracts also the equivalent resistance. A laminated transformer with internal circuit is reported to validate and showcase the proposed method. [ABSTRACT FROM PUBLISHER]

Conventional transient finite-element methods (FEM) of magnetic field and electric circuit coupled problems often result in unbalanced power computation. In the worst case, the output power may be even miscomputed to be larger than the input power which violates all fundamental laws of physics. Eddy-current loss computation in laminated iron cores is usually carried out in a postprocessing algorithm, and thus the effect of eddy-current on both the system equations and other physical quantities cannot be included conveniently. This paper studies the power-balanced computation in FEM from two important aspects, which are, namely, the time integration algorithms and the inclusion of eddy-current loss in laminated iron cores of the system equations. A novel approach is presented, which retains the power balance property (i.e., all power, including the losses, are considered and balanced in both input and output) in the time integration process, to include the eddy-current loss effect in the FEM system equations. It also insures the solution is stable. Consequently, the input power, losses, and output power of the electromagnetic systems are balanced, and the accuracy of the solutions, especially the efficiency, is guaranteed. A numerical experiment is carried out on a laminated transformer to verify the accuracy of the proposed method. [ABSTRACT FROM PUBLISHER]

A novel mesh-insensitive methodology for magnetic force computation is presented. The force value is obtained by integration on several layers of mesh elements around the objects on which the force needs to be computed. The number of layers can be automatically determined during computation and the force computation on objects touching each other can also be evaluated accurately. The computation results are compared with those obtained using traditional Maxwell stress tensor method and normal virtual work method. The results confirm that the sensitivity of the computed force to the mesh quality is greatly reduced and the accuracy of the force computation is increased. [ABSTRACT FROM PUBLISHER]

In transient magnetic field computation, it is highly desirable if the stray capacitances among all conductors can be computed and their effects addressed conveniently. Because of the existence of floating conductors, the general finite element (FE) solver of Poisson's equation, which is a commonly used magnetic field solver, cannot be used to extract the capacitance matrix directly. In this paper, methods to deal with floating conductors in the electrostatic field for field solution, and capacitance matrix extraction using finite element method (FEM) are compared; their merits and shortcomings are discussed. A method to compute the electric field and extract the capacitance matrix to include the effect of floating conductors inside the solution domain is put forward. The merit of the proposed algorithm is that the general FE solver can be used without the need for any special program modification. A FE formulation to automatically include the capacitances in transient magnetic field is presented. By using the proposed method, users only need to input the information as how the conductors are connected. All the stray capacitances among conductors are automatically included in the solution of transient magnetic field with the proposed algorithm. [ABSTRACT FROM PUBLISHER]

A novel low-speed axial-flux-modulated motor is proposed for in-wheel applications in hybrid electric vehicles. The proposed motor breaks the traditional design rule which stipulates that the pole-pair numbers of the stator and the rotor must be equal. Special ferrite segments in the air gap are used to modulate the magnetic field. It has the merit of having a very high torque density at low speed. It can be fitted into very limited space, such as inside the wheel rim of electric vehicles. Compared with radial-flux-modulated motors (RFMM), its manufacturing and assembling process are simple and easy. Its performance is compared with that of an RFMM using two-dimensional and three-dimensional finite-element methods and the comparison results verify the validity of this proposed machine design. [ABSTRACT FROM AUTHOR]