Transverse Flux Permanent Magnet Machine Research Articles

Design and Performance Analysis of Permanent Magnet Claw Pole Machine with Hybrid Cores

Permanent magnet claw pole machine (PMCPM) is a special kind of transverse flux permanent magnet machine. Compared with other electrical machines, it has the advantages of high torque density and high efficiency for high speed operation. However, because of its complex irregular structure, the manufacturing process using silicon sheets is complicated. Soft magnetic composite material (SMC) is manufactured by powder metallurgy technology, which can produce various shapes of stator core structures, so it is easier to produce various irregular shapes of the stator core. However, the raw SMC material is relatively expensive, and the mechanical strength of SMC is weak. In this paper, a PMCPM with hybrid cores is proposed. With the adoption of hybrid silicon sheet — SMC cores and amorphous alloy — SMC cores, the torque ability of PMCPM can be improved greatly and it can have higher efficiency for more wide operation frequency. Meanwhile, its mechanical strength has been improved and it can be designed for high torque direct drive applications as it is a modular machine. Furthermore, three methods are proposed to reduce the additional eddy current loss which resulted from the employment of hybrid cores in PMCPM.

Design optimization of a novel linear transverse flux switching permanent magnet generator for direct drive wave energy conversion

Linear transverse flux permanent magnet machines (LTFPMs) are categorized as high force density topologies, which are suitable candidates for direct drive and low-speed applications. This paper introduces a novel LTFPM topology, which also proposes advantages of the flux-switching machines. This proposed linear transverse flux switching PM machine (LTFSPM) has two long passive translators located at the armature's top and bottom sides. The topology offers a high value of force density, and also, it is a cost-effective topology due to its double-sided passive translator. Furthermore, the PMs are fully utilized in the magnetic circuit, the end winding length is negligible, and the iron cores can be laminated easily. In this paper, the operation principle of the topology is explained and its magnetic circuit is discussed. To reduce the computational time of optimization procedure, a double-layer method is adopted, which provides high robustness, low computational time, and high precision. Results of the finite element method indicate that the proposed machine can be considered a potential candidate for linear motion applications especially direct drive wave energy conversion systems, which require high force density values.

Cogging Torque Minimization in Transverse Flux Permanent Magnet Generators using Two-step Axial Permanent Magnet Segmentation for Direct Drive Wind Turbine Application

Transverse flux permanent magnet machines (TFPMs) are categorized as synchronous machines that benefit from having high value of torque density and capablity of accommodating high pole numbers. These characteristics make TFPMs suitable candidates for low-speed applications where high torque density value is requred such as direct drive wind turbine application. Despite the aforementioned advantages, TFPMs suffer from intrinsically high cogging torque value which is an important concern for wind turbine application. This paper focuses on axial PM segmentation technique to minimized cogging torque of TFPM topologies. Concept of the proposed method is discussed using analytical equations and optimum segmentaion angle is formulized. Non-linear magnetic equivalent circuit (MEC) is adopted where the PM segmentation, armature reaction, rotor transition and iron saturation effect are carefully modeled. The results of the MEC simulation are compared with the finite element method (FEM) results in terms of accuracy and computational time. The results from the analysis indicate that the proposed MEC method is almost ten times faster than FEM with reasonable level of precision. Taguchi method is adopted as a fast-response optimization method to improve the generator torque characteristics. The results show that the cogging torque has reduced by 97% with respect to the initial design while the average torque has only dropped by 8% which is an acceptable side effect due to the significant improvement in machine cogging torque.

Mitigation of cogging torque in transverse‐flux permanent‐magnet machines with flux concentrators by step skewing of stator pole

The objective of this article is to study how the stator step skewing method can lead to the reduction of the cogging torque of a transverse-flux permanent-magnet (TFPM) machine with flux concentrators. Three structures are analysed and compared in terms of their influence of the skewed displacement on the cogging torque using the three-dimensional finite element method (3D-FEM). Thereafter, to validate the FEM results, cogging torque is calculated by applying a Schwarz–Christoffel (SC) conformal mapping. To apply this transformation, the 3D TFPM generator structure with axially magnetised permanent magnets (PMs) is converted into a 2D structure with radially magnetised PMs and the cogging torque of the machine is predicted using both the analytical method and 3D-FEM. The accuracy of the approach is demonstrated by the adequate agreement between the results obtained through this SC mapping and those of the 3D-FEM. In addition, two 100 W prototyped TFPM machines are designed, simulated, manufactured and tested to validate the effects of the step-skewed stator yoke on the predicted cogging torque and back-EMF.

Design Optimization of a Transverse Flux Halbach-Array PM Generator for Direct Drive Wind Turbines

Due to high power density of the transverse flux permanent magnet machines (TFPMs), they are potential candidates for direct drive wind turbine (DDWT) applications. But the TFPMs usually suffer from high values of cogging torque and torque ripple which are troublesome in DDWTs. Aiming to improve conventional TFPM torque profile, using Halbach-array of PMs is proposed. To select the optimum array, sensitivity analysis is carried out and the optimum array type is selected considering the machine performance and manufacturing feasibility. In order to minimize the cogging torque and achieve the maximum available power density, Design of Experiments (DOE) optimization method is carried on the stator-side parameters. The final design is prototyped and tested where the experimental results are compared with the conventional TFPM and the simulation results. The results indicate that by using the proposed transverse flux Halbach-array PM generator the cogging torque drops dramatically without deteriorating the machine average torque.

Mitigation of cogging torque in TFPM machines with flux concentrators and evaluation of the structures by using the SC method

In this study, the effect of adding of new stator and rotor slots on cogging torque of a transverse-flux permanent-magnet (TFPM) machine with flux concentrators is studied. To reduce the cogging torque, the widths and the positions of the slots of concern are improved through three-dimensional finite element method (3D-FEM). After that, to validate the 3D-FEM results, cogging torque is determined by applying a Schwarz–Christoffel (SC) conformal mapping. To apply this transformation, the 3D TFPM structure with axially magnetised PM is converted into a 2D structure with radially magnetised PMs and cogging torque of the machine is predicted using both the analytical method and 3D-FEM. The agreement in the obtained results through this SC mapping and the 3D-FEM method is the indicative of the accuracy of the efforts.

A Review on Transverse Flux Permanent Magnet Machines for Wind Power Applications

Transverse flux permanent magnet (TFPM) machines are a potential candidate for direct-drive wind power application due to high torque and power densities. The operating principle of TFPM machines is firstly described with various topologies available in literature, with the placement of magnets as a criterion for the classification of TFPM machine topologies. This review includes characteristics, power factor improvement, cogging torque minimization, material consideration, modelling techniques, and scalability. Different wind turbine concepts with direct-drive machines, control techniques and power converter topologies are also considered in this paper.

Impact of Number of Phases on Electromagnetic Torque Characteristics of Transverse Flux Permanent Magnet Machines

This paper presents an investigation on the influences of number of phases of Transverse Flux Permanent Magnet (TFPM) machines on the characteristics of developed electromagnetic torque. Electromagnetic torque is expressed in terms of the Fourier series of phase currents and internal voltages. After some algebraic and trigonometric calculations, a general equation is obtained that establishes a relationship between the electromagnetic torque ripples, number of phases and harmonic contents of both internal voltages and phase currents. This result is significant when it is required to design a few specific number of identical single-phase TFPM machines which finally they will be assembled such that to build a multi-phase machine with a minimum torque ripple. The design parameters of a case study Claw Pole TFPM machine are introduced with some details and a few FE based simulation results are given as the validations of the analytical approach of the present paper. The simulation results show clearly the impact of each harmonic of the internal voltages and phase currents on the torque ripple for various numbers of phases leading the designer to find out which number of single-phase machine combinations is the optimum one regarding the torque ripple.

Torque ripple reduction in homopolar poly‐phase transverse flux machine

The problem of high ripple in output torque is inherent to switched reluctance and permanent magnet machines compared to conventional machines. Torque ripple is undesirable as it leads to increased audible noise, speed ripple, and fatigue. Torque ripple is more prominent in complex machines like TFMs. This paper aims to tackle the problem of torque ripple in the homopolar poly-phase transverse flux permanent magnet machine by machine design approach. Rotor pole shaping, increase in number of repetitions, and increase in number of phases have been considered to reduce torque ripple. The 3-D finite element simulations have been carried out for the considered variations in geometry. Results of nature of air-gap flux density at no-load, cogging torque, average torque, and % ripple in the output torque are used to comment on the effectiveness of the torque ripple reduction techniques. The objective of this research is to reduce the torque ripple in the output torque to 10%. The technique/combination of techniques resulting in reduced torque ripple has been suggested to be implemented in the prototype.

Design of a Novel Consequent-Pole Transverse-Flux Machine With Improved Permanent Magnet Utilization

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.

Design, Analysis and Fabrication of a Novel Transverse Flux Permanent Magnet Machine with Disk Rotor

The purpose of this paper is to propose a novel design for the transverse flux permanent magnet (TFPM) disk-rotor generator with E and I-shaped cores (TFPMDEIG). Disk-shape structure increases the machine’s power factor, allows for high rotational speeds, decreases centrifugal force over permanent magnets, and is employed in wind turbines, due to its compact structures. As for other advantages for this structure, one can point to the fact that there are as many windings as machine’s pole pairs; these windings become parallel by observing the polarity. In other words, the total power of this machine is distributed between pole pairs, increasing the overall reliability of the machine. In this paper, first, the initial design algorithm and the basic formulas governing the behavior of the proposed structure using the equivalent magnetic circuit for each pole are provided, and the three-dimensional finite element method (3D-FEM) is used for verification of the algorithm. To validate the simulation results (3D-FEM), then, a prototype has been fabricated and experienced. The experimental results are in good agreement with simulation results.

Design Considerations of PM Transverse Flux Machines With Soft Magnetic Composite Cores

The design considerations of permanent-magnet transverse flux machines (PMTFMs) with soft magnetic composite (SMC) cores are investigated in this paper. A simplified torque equation of the PMTFMs is deduced first. It is shown that the torque coefficient is directly related to the air-gap flux density, the number of pole pairs, and the stator slot width, etc. To accurately illustrate the influences of these parameters on motor performance, electromagnetic and mechanical analyses are completed by using the 3-D finite element method. For the laboratory prototype, SMC cores can be manufactured by two methods, namely, wire cutting and mould pressing. It is found that wire cutting method deteriorates the magnetic properties of SMC cores and lowers the machine performance. The performance predictions of the PMTFMs are compared for these two methods in this paper. The calculation results are verified by the experimental results.

Cogging Torque Minimization of SMC PM Transverse Flux Machines Using Shifted and Unequal-Width Stator Teeth

This paper proposes a method to minimize the cogging torque of a permanent-magnet transverse flux machine (PMTFM) with soft-magnetic-composite cores, using the shifted stator disks and unequal stator teeth pairing. Fourier analysis is performed to find the major cogging torque component so as to reduce it by shifting the stator disks. The unequal stator teeth pairing technique that is traditionally used in the radial and axial flux machines is employed to reduce the cogging torque of PMTFMs in this paper. Three different configurations are studied. The cogging torque and the electromagnetic torque are calculated by the three-dimensional finite-element method and verified by the experiment results.

Design and optimization of a surface mounted transverse flux permanent magnet machine

Transverse flux permanent magnet machine (TFPM) is well known for its achievable high torque density and flexible topologies, which makes it especially suitable for wind power generation, electric vehicle and direct drive area. Existing TFPM topologies, however, are subject to high flux leakage and cogging torque. This paper deals with the design and optimization of a three phase surface mounted transverse flux permanent machine (SM-TFPM) to reduce flux leakage and cogging torque, the solutions of adjusting the interval between magnets and inserting auxiliary stator are suggested to realize the restriction of both flux leakage and cogging torque. The finite element analysis (FEA) results show the obvious effects, and the FEA design is validated via prototype experiment by using TMS320F28335 based controller and induction machine load. Based on the abovementioned researches, a further multi-objective optimization is applied by using differential evolution (DE) algorithm and the optimization results are compared with the previous design to demonstrate the improved performance

Performance Analysis of a Permanent Magnet Transverse Flux Generator With Double Coil

One of the disadvantages of permanent magnet (PM) transverse flux machines is high magnetic flux leakage in the stator and rotor cores. To improve the magnetic circuit of this class of machines, a generator with double coil was designed and built to research the problem. The machine topology is different from the topologies previously introduced in the literature. The main difference was in the stator and rotor configurations. The stator of the generator is divided by two parts: 1) outer and 2) inner. Two coils were placed in the inner and outer stators. The rotor with PMs was placed between the two stators. To diminish magnetic flux leakage in the stator and to decrease machine’s weight, magnetic poles were placed in aluminum housings. This resulted in high-density eddy currents induced in the housings, and a significant raise of the temperature. The housing of the machine was modified. The prototype test showed that the modified version of the stator contributed to a significant decrease in temperature. Electromechanical parameters and cogging torque of the proposed generator is also studied and presented in this paper.

Multidisciplinary Design Analysis and Optimization of a PM Transverse Flux Machine With Soft Magnetic Composite Core

This paper presents a multidisciplinary analysis and a design optimization approach for a permanent magnet (PM) transverse flux machine (TFM) with a soft magnetic composite (SMC) core. First of all, electromagnetic, thermal, and modal analyses, and the manufacturing method of the SMC cores, are investigated for this machine. Meanwhile, a lumped 3-D thermal network model is developed for the thermal analysis. Then, a multidisciplinary optimization design model is proposed to minimize the material cost and to maximize the output power based on the proposed multidisciplinary analysis models. The numerical solutions obtained from electromagnetic and thermal analyses are validated by comparing them with the previous experimental results. As shown, the performance of this PM-SMC TFM can be improved greatly using the proposed approach. Finally, a finite-element model is employed to verify the performances obtained from optimal results in terms of thermal and modal analyses.

A Novel Transverse Flux Permanent Magnet Generator With Double C-Hoop Stator and Flux-Concentrated Rotor

Transverse flux permanent magnet (TFPM) machine possesses the characteristic feature of decoupled electric load and magnetic load to obtain high power density. A novel TFPM generator (TFPMG) with double C-hoop stator and flux-concentrated rotor is proposed for low-speed applications, such as direct-drive power generation, which has larger torque capability and more poles than traditional double-side TFPMGs. The structure and operation principles of the generator are described in detail. The 3-D finite-element method (3-D FEM) is employed to compute the no-load magnetic field distributions. The analytical results, including flux density waveform, electromotive force (EMF) waveform, and inductance waveform of the armature winding, are obtained to verify the principle and feasibility of the proposed generator. The cogging torque is also analyzed and optimized by the 3-D FEM. A prototype is fabricated, and some experiments are conducted. The experimental results of back EMF and waveforms of current and voltage with different loads verify the FEM analysis previews well.

High Torque Density Transverse Flux Machine Without the Need to Use SMC Material for 3-D Flux Paths

This paper presents a new transverse flux permanent magnet machine. In a normal transverse flux machine, complicated 3-D flux paths often exist. Such 3-D flux paths would require the use of soft magnetic composites material instead of laminations for construction of the machine stator. In the new machine topology proposed in this paper, by advantageously utilizing the magnetic flux path provided by an additional rotor, use of laminations that allow 2-D flux paths only will be sufficient to accomplish the required 3-D flux paths. The machine also has a high torque density and is therefore an attractive solution for various direct drive applications.

Influence of various structural factors of claw pole transverse flux permanent magnet machines on internal voltage using finite element analysis

This paper presents the influence of several structural factors and parameters involved in the design of Claw Pole Transvers Flux Permanent Magnet Machines (TFPMs) on their internal voltage. Knowing the influence of each factor is very important for an effective process of design and optimization for these machines. In this paper by using the complete design algorithm of Claw Pole TFPM, only one parameter is changed at a time and its influence on the internal voltage is analyzed. Output torque is also studied, because the internal voltage has effect on both the average and the ripple of output torque. The most important factors and parameters which are considered are: 1) number of poles; 2) length of air gap; 3) ratio of magnet arc to flux concentrator arc in each pole of rotor; 4) shape of pole shoe of stator and 5) area of rotor pole covered by stator pole. Due to geometrical complexities of TFPMs, analytical methods fail to describe the behavior of these machines. For this reason, in this paper finite element analysis is used both in the design and analysis of TFPMs.

Cogging Torque Optimization of Flux-Switching Transverse Flux Permanent Magnet Machine

In this paper, cogging torque characteristics in both single-phase and three-phase flux switching transverse flux permanent magnet machines (FS-TFPMM) are analyzed by 3-D finite element method (FEM). It is found that the cogging torque of the FS-TFPMM is significantly influenced by the ratios of stator and rotor core circumferential widths to pole pitch, $k_{s}$ and $k_{r}$ . When $k_{r}>1-k_{s}$ , the cogging torque waveform has additional two zero-crossing points, whilst its amplitude is significantly reduced. The optimal ratios of $k_{s}$ and $k_{r}$ are selected to reduce the cogging torque and to maximize the permanent magnet flux linkage. A 380 W three-phase prototype is designed, manufactured, and tested to verify the optimization.