PM Eddy Current Loss Research Articles

Analysis of MW-Level Offshore Wind Turbine Generators with Dual Star–Delta Fractional-Slot Windings

This paper investigates the use of fractional-slot concentrated windings (FSCWs) in large-scale (MW level) offshore wind generators. It focuses specifically on a power rating of 3 MW and uses an existing direct-drive synchronous PM machine (DD-SPM) with 480s/160p and dual three-phase integer-slot winding (ISW) as a baseline. A multiple of the common 12s/10p FSCW machine is used that matches the electrical frequency of the ISW machine, yielding a 192s/160p dual three-phase machine. The hybrid star–delta connection has grown increasingly popular owing to its unique harmonic cancellation properties, which can help reduce rotor and PM eddy current losses in FSCW machines. In this paper, two dual three-phase star–delta-wound machines are scaled to 3 MW and included in the investigation. Specifically, a 384s/160p dual three-phase and dual star–delta winding machine, which is a multiplication of the 24s/10p machine, and a 192s/176p dual three-phase and dual star–delta winding machine, which is a multiplication of the 24s/22p machine, are used. These machines are investigated using finite element analysis (FEA) and compared on the basis of their air-gap flux density harmonics, open-circuit electro-motive force (EMF), torque performance, and losses and power. It is found that the proposed 384s/160p dual star–delta winding machine has the best electromagnetic performance of all, with a stator power that is 1.2% greater than that of the baseline ISW machine. However, this machine has a coil pitch of 2 and so loses the manufacturing and fault-tolerant advantage of having concentrated windings. If concentrated windings are desired, then the proposed 192s/176p dual star–delta winding machine is the best choice, with the stator power only 2.6% less than that of the baseline ISW machine, but unfortunately still has significant rotor and PM eddy current losses.

Hybrid Network Model for PM Eddy Current Losses Considering Eddy Current Reaction Field and PWM Effects of PM Machine

Hybrid Network Model for PM Eddy Current Losses Considering Eddy Current Reaction Field and PWM Effects of PM Machine

Incorporating Harmonic-Analysis-Based Loss Minimization Into MPTC for Efficiency Improvement of FCFMPM Motor

According to air-gap field-modulation theory, multiple field harmonics are responsible for high torque density of field modulation (FM) motors. However, abundant field harmonics will undoubtedly increase motor losses, especially iron loss and PM eddy-current loss. Therefore, a harmonic-analysis-based loss minimization (HLM) method incorporated into model predictive torque control (MPTC) for efficiency improvement of FM motors is proposed in this article. First, by analyzing the loss generation mechanism, a harmonic-based online loss calculation model is built to serve for loss minimization control. Then, the reference flux for MPTC can be derived from the proposed HLM method, which avoids complexity of equivalent resistance tuning and improves accuracy of loss calculation compared to the conventional model-based loss minimization method which lacks attention on the harmonic-based loss analysis. Consequently, the HLM-MPTC strategy is finally determined and then applied in a flux-concentrating field-modulation permanent-magnet prototype to verify its validity. The experimental results evidence that the proposed HLM-MPTC can effectively achieve loss reduction and efficiency improvement.

Coupled Electromagnetic–Thermal Modelling of Dynamic Performance for Modular SPM Machines

This paper presents coupled electromagnetic (EM)–thermal modelling of the steady-state dynamic performances, such as torque speed curve and the efficiency map, for surface-mounted permanent magnet machines. One important feature of such a model is that it considers the demagnetization caused by magnet temperature rise at different rotor speeds. EM-only simulations, which often assume that the machines operate under constant temperature, have been widely used in the literature. However, the interaction between EM and thermal performances could lead to very different dynamic performance prediction. This is because the material properties, e.g., magnet remanence, coercivity, and copper resistivity are temperature-dependent. The temperature rise within electrical machines reduces torque/power density, PM eddy current losses, and iron losses but increases copper loss. Therefore, the coupled EM–thermal modelling is essential to determine accurate temperature variation and to obtain accurate EM performances of electrical machines. In this paper, the coupled EM–thermal modelling is implemented for both modular and non-modular machines to reveal the advantages of the modular machine under different operating conditions. The results show that the modular machine generally has better dynamic performance than the non-modular machine because the introduced flux gaps in alternate stator teeth can boost both EM and thermal performance.

High-speed permanent magnet machine multi-physics fields design for turbine application

This paper presents the multi-physics fields research of a high-speed permanent magnet machine (HSPMM) for turbine application. At first, the design considerations for the HSPMM are introduced and presented. Then, the machine electromagnetic performances are comprehensively studied with machine stator slot numbers. Moreover, the influences from the PM magnetization methods and segmentation number on PM eddy current loss reduction are further investigated. Thermal analysis is also performed for the HSPMM with the cooling water fluid volume flow rate considered. In addition, rotor strength is studied for the HSPMM with several design factors on machine rotor strength performances further studied and researched.

Comparative Analysis of Dual-Rotor Modular Stator Axial-Flux Permanent Magnet Machines With Different Rotor Topologies

In this paper, the influence of rotor topology on the electromagnetic performances of dual-rotor axial-flux permanent magnet (DRAFPM) machines with modular stator (MS) and fractional slot non-overlapping winding (FSNW) is investigated by comparing four different rotor structures, including surface-mounted PM (SPM), consequent-pole PM (CPM), Halbach CPM (HCPM) and interior PM rotor (IPM) structures. In order to reduce the PM flux leakage in CPM rotor, the air-barrier introduced beside the PM is optimized by the three-dimensional finite-element method. Then, the main electromagnetic characteristics of the investigated machines, such as open-circuit airgap flux density, back-EMF, average torque, torque ripple, PM eddy-current loss and PM demagnetization are compared quantitatively. Consequently, the machine with SPM rotor accommodates the highest back-EMF and output torque; meanwhile, the CPM machine possesses the highest torque per PM volume and inductance of d-axis. Moreover, both CPM and IPM machine generate reluctance torque, and the IPM machine features larger salient pole ratio and stronger resistance to irreversible demagnetization, as well as the highest machine efficiency.

An Analytical Model and Optimization of a Novel Hybrid Rotor Machine for High Torque Density

This article proposes a novel hybrid rotor permanent magnet (HRPM) machine for the performance of torque and overload capability with the constraint of the rotor diameter. In order to optimize the electromagnetic performance, an analytical model (AM) is built by the magnetic equivalent circuit (MEC) of the rotor and stator considering the saturation and leakage flux effect. A good prediction accuracy is verified by the finite element method (FEM), even in high saturation condition. Based on the AM, the characteristics of the hybrid magnetic pole rotor are analyzed by the equivalent strategy that equivalent PM remanence and thickness of single pole in rotor. Furthermore, a response surface method (RSM) for multi-variate and multi-objective optimization is adapted to improve the electromagnetic performance because of the high torque density and PM material utilization. Finally, a comparison of the torque, PM eddy current loss and anti-demagnetization performance is investigated among surface-mount PM (SPM) machine, spoke-type PM (STPM) machine and HRPM machine. The comparison results show the hybrid PM rotor machine enhances higher torque density and overload capability. Finally, a 12 slot/10 pole HRPM machine is prototyped and tested to validate the analyses.

A Systematic Approach for Stator MMF Harmonic Elimination using Three-Layer Fractional-Slot Winding

A systematic approach based on a novel space-shifted three-layer winding (SSTLW) to eliminate both the sub- and superharmonics of fractional slot concentrated winding ac machines is presented. In this proposed three-layer fractional slot winding, the number of turns in one layer and the relative positions of other two layers are optimized to cancel subharmonics. The cancellation of superharmonics is achieved through series connection of two SSTLWs through effective doubling of the number of slots. The cancellation of the dominant sub- and superharmonics using this approach leads to reducing the total harmonic distortion, torque ripple, PM eddy current loss, and rotor core loss, while simultaneously improving power factor and saliency ratio. The proposed design methodology and ensuring improvements have been validated through finite element analysis for the widely used 12-slot/10-pole and 18-slot/14-pole permanent magnet synchronous machine (PMSM) configurations. A prototype three-layer winding is built for a 10-pole PMSM to validate the simulation results experimentally.

Computationally Efficient Optimization of a Five-Phase Flux-Switching PM Machine Under Different Operating Conditions

This paper investigates the comparative design optimizations of a five-phase outer-rotor flux-switching permanent magnet (FSPM) machine for in-wheel traction applications. To improve the comprehensive performance of the motor, two kinds of large-scale design optimizations under different operating conditions are performed and compared, including the traditional optimization performed at the rated operating point and the optimization targeting the whole driving cycles. Three driving cycles are taken into account, namely, the urban dynamometer driving schedule (UDDS), the highway fuel economy driving schedule (HWFET), and the combined UDDS/HWFET, representing the city, highway, and combined city/highway driving, respectively. Meanwhile, the computationally efficient finite-element analysis (CE-FEA) method, the cyclic representative operating points extraction technique, as well as the response surface methodology (in order to minimize the number of experiments when establishing the inverse machine model), are presented to reduce the computational effort and cost. From the results and discussion, it will be found that the optimization results against different operating conditions exhibit distinct characteristics in terms of geometry, efficiency, and energy loss distributions. For the traditional optimization performed at the rated operating point, the optimal design tends to reduce copper losses but suffer from high core losses; for UDDS, the optimal design tends to minimize both copper losses and PM eddy-current losses in the low-speed region; for HWFET, the optimal design tends to minimize core losses in the high-speed region; for the combined UDDS/HWFET, the optimal design tends to balance/compromise the loss components in both the low-speed and high-speed regions. Furthermore, the advantages of the adopted optimization methodologies versus the traditional procedure are highlighted.

Loss Calculation and Thermal Analysis for Nine-Phase Flux Switching Permanent Magnet Machine

This paper investigates the accurate loss calculation and thermal analysis for a nine-phase flux switching permanent magnet (FSPM) machine. First, the 3 D finite element method (FEM) model is developed to calculate the PM eddy current loss, in which magnet axial segmentation is taken into account. In order to calculate the iron loss quickly and precisely, the magnetic flux leakage coefficient is proposed in this paper to modify the 2 D calculation model of iron loss. Both the dc-biased magnetic induction and the rotational magnetization are taken into account. Then, the key parameters for thermal modeling, such as the convective heat-transfer coefficient between external frame and ambient, and the coefficient of convection heat transfer in the end region, are derived, based on which a dissymmetric 3 D FEM are used for thermal calculation of nine-phase FSPM machine. Finally, experiments on a prototype machine at the rated generation operation condition are carried out to verify the effectiveness of the developed model.

Iron Loss and Efficiency Analysis of Interior PM Machines for Electric Vehicle Applications

An interior permanent magnet (IPM) machine with ∇+U shape rotor topology is proposed for electric vehicle applications whose iron loss and efficiency are compared to that of typical V shape and ∇ shape machines. The air-gap flux density, flux-density waveform, and its harmonics on stator core and rotor core are analyzed. It can be obtained that ∇+U shape rotor topology has the lowest total harmonic distortion. The torque ripple, core loss, core loss density, PM eddy-current loss, d - and q -axis inductances, saliency ratio, characteristic current, and efficiency of three IPM machines are analyzed and compared. It is demonstrated that the efficiency of ∇+U shape IPM machine is higher than V shape and ∇ shape machines, particularly under high-speed operation, because the iron loss of the ∇+U shape machine is the lowest. With the increase of PM layer, the PM eddy-current loss is increased, PM segmentation can effectively reduce the PM eddy-current loss. Finally, the ∇+U shape IPM machine is prototyped to verify the results of the finite element analysis.

Magnet Eddy-Current Loss Analysis of Interior PM Machines for Electric Vehicle Application

The magnet eddy-current losses of six interior permanent magnet (IPM) machines are investigated for electric vehicle applications in this paper. The armature field, eddy-current density of magnet, the influence of PM depth, the distance of PM layers, and the number of PM segmentation are studied by finite-element analysis. It is demonstrated that increasing the PM depth of first layer and the distance of PM layers can provide more soft iron space for the armature-reaction flux, which can reduce the magnet eddy-current loss. PM segmentation can effectively reduce the PM eddy-current loss, because the eddy-current paths are divided into smaller loops, increasing the effective resistance. An IPM machine with segmented PM is prototyped to verify the analysis.

On the investigation of the magnetic forces of CWPMM

Purpose– The purpose of this paper is to investigate the magnetic forces generated by a 12 slot/10 pole concentrated winding PM machines, considering a comparative study between two topologies: a surface mounted permanent magnet (SPM) machine and an interior PM (IPM) machine.Design/methodology/approach– Following a description of the main characteristics of the concentrated winding permanent magnet machines (CWPMMs) under comparison, an investigation of the magnetic forces developed by both machines under study is carried out using finite element analysis (FEA).Findings– A 2D FEA-based investigation has highlighted that the SPM machine develops higher magnetic forces than the IPM one. However, and following a 3D FEA, it has been found that the distribution of the magnetic forces along the air gap of the SPM machine is almost homogenous while it is concentrated in two opposite positions in the air gap of the IPM machine.Research limitations/implications– This work has treated almost all features of the machines under comparison, except the power losses. These should be investigated with emphasis on the PM eddy current losses is so far as the harmonic content of the armature air gap MMF is high.Practical implications– The list of the selection criteria of CWPMMs should be extended to the magnetic force cancellation in order to fulfill the requirements of many applications such as the automotive ones.Originality/value– The paper proposes a combined electromagnetic-mechanical approach to investigate the magnetic forces generated by CWPMMs using 2D and 3D FEA.

Air gap MMF based prediction of eddy current loss in the PMs of concentrated winding brushless machines

Purpose – The purpose of this paper is to an analytical approach-based prediction of the eddy current loss in the PMs of a concentrated winding machine equipped with 12 slots in the stator and ten poles in the rotor. Design/methodology/approach – The investigation of the PM eddy current loss has been carried out using an analytical model and a 2D time-stepped transient finite element analysis (FEA). Findings – It has been found, in the case of the treated machine, that just the subharmonic of rank 1 and the harmonic of rank 7 have significant contributions to the eddy current loss in the PMs. Research limitations/implications – A shift between the results yielded by the developed analytical model and those computed by FEA has been noticed. This limitation is mainly due to the slotting effect which has been omitted in the analytical model. Practical implications – Fractional slot PM machines are currently given an increasing attention in automotive applications. The prediction of their iron loss in an attempt to rethink their design represents a crucial efficiency benefit. Originality/value – The analytical prediction of the eddy current loss in each PM then in all PMs and their validation by FEA represent the major contribution of this work.

Comparaison de deux bobinages pour la propulsion d’un véhicule hybride urbain

The use of permanent magnet synchronous machines (PMSM) for in-wheel electrical motorization of an urban hybrid vehicle has been studied in this article. Two types of winding, distributed and concentrated winding around a tooth, have been considered for the winding of the PMSM. Different electromagnetic sizes such as the resistance, the inductances, the iron losses, the PM eddy-current losses and teeth magnetic forces have been considered for the comparison of the two machines performances. The study shows the advantages of concentrated winding in comparison with the distributed winding, such as the diminution of the cogging torque, the reduction of no-load emf harmonics and the increase of the flux weakening range due to the increase of the inductance. However, it is important to notice the drawbacks of concentrated winding: the high level of PM eddy-current losses and large variation of stator teeth magnetic forces. These undesired effects are due to the harmonics of magnetic field produced by the concentrated winding.