Design Of Permanent Magnet Machine Research Articles

Investigation of a less rare-earth permanent-magnet machine with the consequent pole rotor

Due to the rising price of rare-earth materials, permanent-magnet (PM) machines in different applications have a trend of reducing the use of rare-earth materials. Since iron-core poles replace half of PM poles in the consequent pole (CP) rotor, the PM machine with CP rotor can be a promising candidate for less rare-earth PM machine. Additionally, the investigation of CP rotor in special electrical machines, like hybrid excitation permanent-magnet PM machine, bearingless motor, etc., has verified the application feasibility of CP rotor. Therefore, this paper focuses on design and performance of PM machines when traditional PM machine uses the CP rotor. In the CP rotor, all the PMs are of the same polarity and they are inserted into the rotor core. Since the fundamental PM flux density depends on the ratio of PM pole to iron-core pole, the combination rule between them is investigated by analytical and finite-element methods. On this basis, to comprehensively analyze and evaluate PM machine with CP rotor, four typical schemes, i.e., integer-slot machines with CP rotor and surface-mounted PM (SPM) rotor, fractional-slot machines with CP rotor and SPM rotor, are designed to investigate the performance of PM machine with CP rotor, including electromagnetic performance, anti-demagnetization capacity and cost.

Analysis and Design of Triple-Rotor Axial-Flux Spoke-Array Vernier Permanent Magnet Machines

This paper focuses on the analysis and design of a triple-rotor axial-flux spoke-array vernier permanent magnet (TR-AFSAVPM) machine. By cooperating with spoke-array rotor and coil-wounded winding, power factor and torque density of the proposed machine are much improved and its copper utilization is reduced comparing with conventional vernier machines. First, the machine structure and its operation principles are reviewed. After that, analytical equations of its back-electromotive force and torque are derived to reveal the machine characteristics. Based on both quasi-3-D finite element analysis (FEA) and 3-D FEA, its high torque density performance is verified and a set of optimized machine sizing specifications is ultimately settled. A fractional slot axial-flux permanent magnet (VPM) machine and an axial-flux surface VPM machine are designed to compare with the proposed configuration. Analysis results show that the TR-AFSAVPM machine has high power factor viz., 0.96 and high torque density viz., 24.2 kNm/m3. A prototype has been designed and tested to validate the results. No-load test result is illustrated in this paper and the rated load experiment will be added in the future.

Ironless Machine Design for Wind-Based Microgeneration

This paper puts forward the design and analysis of an ironless permanent magnet machine for a micro wind power application. The proposed methodology includes comprehensive geometric, magnetic, and electrical dimensioning followed by detailed 2-D finite-element modeling of a synchronous generator. The configuration investigated in this paper shows the generators rotor fixed in the tip of the blades and illustrates the advantages of a large diameter for a microgeneration application.

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.

Electromagnetic Design of a High-Speed Solid Cylindrical Permanent-Magnet Motor Equipped With Active Magnetic Bearings

This paper presents the design in electromagnetic aspect of a high-speed solid cylindrical permanent-magnet (PM) machine equipped with magnetic bearings. First, the selection of PM machine structures is discussed. In specific, the analytical models of magnetic field for the solid cylindrical PM machine and ring PM machine are established; then, these two machine configurations are compared from the perspectives of magnetic design and rotor eddy-current losses, and the results show that the solid cylindrical PM machines have higher power density and lesser rotor eddy-current losses than ring PM machines. Subsequently, the rotor structures are described, and some integrated considerations in design of high-speed PM machines equipped with magnetic bearings are pointed out. Then, the configurations of magnetic bearings used for the machines are determined, and their analytical formulas of magnetic force are deduced. Ultimately, a 30 kW 60 000 r/min high-speed solid cylindrical PM motor equipped with magnetic bearings is designed and manufactured, and serial experimental tests are conducted on this prototype to verify the theoretical design and the practical performance of the machine.

Dynamic performance of the novel axial flux-switching permanent magnet motor

PurposeThe purpose of this paper is to investigate a novel axial flux-switching motor with sandwiched permanent magnet for direct drive electric vehicles (EVs), in which the torque density is increased and the cogging torque is decreased. For reducing the back-electromotive force (EMF) harmonics and cogging torque, a twisted structure is employed. To improve the dynamic performance of the axial field flux-switching sandwiched permanent magnet (AFFSSPM) motor a space vector modulation-direct torque and flux control scheme is proposed.Design/methodology/approachA multi-objective optimization is performed by means of artificial neural network and non-sorting genetic algorithm II to minimize the cogging torque while preserving the average torque.FindingsA comparative study between two proposed machines and the conventional flux-switching permanent magnet (FSPM) machine is accomplished and the static electromagnetic characteristics are analyzed. It is demonstrated that the proposed model with twisted structure has significantly improved performance over the conventional FSPM machine in back-EMF and efficiency. The proposed controller has a speed loop only and contains neither the current loop nor hysteresis control. The AFFSSPM motor exhibits excellent dynamic performance with this scheme.Originality valueThe axial flux-switching permanent-magnet machine is one of the most efficient machines but the AFFSSPM with sandwiched permanent magnet has not been specially reported to date. Thus in this paper, the authors report on optimal design of an axial flux-switching sandwiched permanent magnet machine for electric vehicles and investigate its dynamic performance.

Closed-form Method for Multi-stage Axial Flux Permanent Magnet Machine: Design and Analysis

Designing an axial flux permanent magnet machine is complex and computationally intensive. This paper proposes a new closed-form method for concurrent design and analysis of a multi-stage axial flux permanent magnet machine. The method will provide a simpler modeling solution to machine designers. By calculating magnetic and electric properties, the design space of an axial flux permanent magnet is created for initial design. This paper demonstrates the feasibility of the new closed-form method by showing that the results obtained from the proposed method correlate with the finite element analysis results. The design space is also evaluated and analyzed by taking into account various parameters, including copper losses, permanent magnet density, phase voltages, and torque waveform. Finally, a multi-objective analysis is performed to compare two different designs of an axial flux permanent magnet machine. The proposed method also provides a useful guide for the initial design state.

Design and analysis of a 3D-flux flux-switching permanent magnet machine with SMC cores and ferrite magnets

Since permanent magnets (PM) are stacked between the adjacent stator teeth and there are no windings or PMs on the rotor, flux-switching permanent magnet machine (FSPMM) owns the merits of good flux concentrating and robust rotor structure. Compared with the traditional PM machines, FSPMM can provide higher torque density and better thermal dissipation ability. Combined with the soft magnetic composite (SMC) material and ferrite magnets, this paper proposes a new 3D-flux FSPMM (3DFFSPMM). The topology and operation principle are introduced. It can be found that the designed new 3DFFSPMM has many merits over than the traditional FSPMM for it can utilize the advantages of SMC material. Moreover, the PM flux of this new motor can be regulated by using the mechanical method. 3D finite element method (FEM) is used to calculate the magnetic field and parameters of the motor, such as flux density, inductance, PM flux linkage and efficiency map. The demagnetization analysis of the ferrite magnet is also addressed to ensure the safety operation of the proposed motor.

Evaluation of parameter sensitivities for flux-switching permanent magnet machines based on simplified equivalent magnetic circuit

Most of the published papers regarding the design of flux-switching permanent magnet machines are focused on the analysis and optimization of electromagnetic or mechanical behaviors, however, the evaluate of the parameter sensitivities have not been covered, which contrarily, is the main contribution of this paper. Based on the finite element analysis (FEA) and simplified equivalent magnetic circuit, the method proposed in this paper enables the influences of parameters on the electromagnetic performances, i.e. the parameter sensitivities, to be given by equations. The FEA results are also validated by experimental measurements.

Comprehensive multi‐objective scalarisation optimisation of a permanent magnet machine with correlation parameters stratified method

With the increasingly high requirements in high-quality motor driving system, the multi-objective optimisation of permanent magnet (PM) machines has become a hot issue in recent years. However, such multi-objective optimisation is often concerned with high-dimensional optimisation problems and the obtained Pareto optimal points are non-single, hence it is relatively complex and difficult to obtain a definite result in the design of PM machine. In this study, a comprehensive multi-objective scalarisation optimisation approach with the correlation parameters stratified method is proposed, where not only the impacts of each design parameter on objectives are investigated, but also the interactions among the design parameters themselves are considered and analysed in detail. In addition, by introducing the weight factors of the desired objectives, the multi-objective optimisation is transformed into a simplified scalar optimisation problem. Then, an interior PM machine with L-shaped PMs is investigated by using the proposed method. Finally, based on the optimised result, a prototype machine is built and tested. Both simulation and experiment results verify the validity of the proposed method.

Double-Rotor Flux-Switching Permanent Magnet Machine With Yokeless Stator

In this paper, novel design of a flux-switching permanent magnet machine (FSPMM) with a yokeless stator and two rotors has been proposed. The proposed machine has been found to perform on par with a 6-slot/13-pole C-core conventional FSPMM in terms of torque output. Additionally, the proposed machine has no significant unbalanced magnetic forces, which is a major challenge in conventional FSPMM with odd number of rotor poles. Step-by-step parametric optimization has been performed using finite-element models of the machine in order to achieve the highest torque with the given magnetic and electrical constraints.

Design and Sensorless Control of a Novel Axial-Flux Permanent Magnet Machine for In-Wheel Applications

This paper proposes an axial-flux-modulation permanent magnet (PM) machine and its sensorless control strategy for in-wheel application in electrical vehicles. A Vernier structure is integrated with the axial-flux PM machine to include the magnetic gear effect and improve output torque. The sensorless control strategy of the proposed machine, including initial rotor position estimation and rotating position estimation, is proposed for flux-modulation motors in this paper. The initial rotor position estimation is based on the technique of rectangular pulse voltage injection and the rotating rotor position estimation is based on the sliding mode observer (SMO). The saturation effect on inductances, which is the theoretical basis of the rectangular pulse voltage injection, makes the stator parameter variation in different loads and affects the SMO estimation. To overcome this problem, a novel online parameter self-adjustment procedure for the SMO is introduced. The machine design and its sensorless control performance are verified by simulation and prototype experiments.

Comparison of Two Different IPM Traction Machines With Concentrated Winding

This paper investigates the capability and behaviors of two different tooth-concentrated winding topologies for traction electric machine applications. The well-known conventional 12-teeth/10-poles winding and also the new 18-teeth/10-poles winding with low-magnetomotive force (MMF) harmonic contents are investigated. Using these winding types, two permanent-magnet (PM) machines are designed and analyzed, and their performances have been compared. Considering the main machine parameters, such as the electromagnetic torque, losses, field-weakening capability, thermal behavior, and also the noise and vibrations characteristics, the obtained results show significant advantages for the new machine over the conventional design. For the new 18-teeth/10-poles PM machine design, a prototype machine is built and several measurements results for the electromagnetic torque and machine efficiency are given.

Double PM-Rotor, Toothed, Toroidal-Winding Wind Generator: A Comparison With Conventional Winding Direct-Drive PM Wind Generators Over a Wide Power Range

The double rotor, toothed, toroidal-winding permanent-magnet (PM) machine is not a well known concept and has received very limited attention in literature. In this study, the concept is proposed for use as a direct-drive wind generator. Due to the varying design requirements of wind generators over the different power ranges, the PM generator is optimized over the entire installed wind power range. For each power level, the optimum design is compared with optimum nonoverlap-winding and conventional overlap-winding PM machine designs. This also gives a much broader indication on the scaling of different wind generator technologies. Although the electromagnetic design, by means of finite-element analysis, of the generator is the main focus of the paper, some of the implementation issues are also discussed. An existing 15-kW double rotor PM wind generator is modified to include a toroidal-winding, which is used as a case study. Both simulated results and practical measurements in the laboratory for the 15-kW case study toroidal-winding PM generator are presented in this paper.

A 32 000 r/min Axial Flux Permanent Magnet Machine for Energy Storage With Mechanical Stress Analysis

This paper focuses on the design and analysis of a high-speed axial flux permanent magnet (PM) machine for an aerospace flywheel energy storage system. The design target is to experimentally verify the sinusoidal back electromotive force (EMF) considering the mechanical stress limitation of the machine at a speed of 32 000 r/min. Two machine models based on ferrite and SmCo PMs have been proposed. First, the back EMF analysis using a 3-D finite-element method is performed to determine the performance of the two models. Second, the mechanical stress analysis is performed to check the durability of the rotor strength. Finally, the selected model utilizing the ferrite PMs has been manufactured and tested at 32 000 r/min to validate its effectiveness at high-speed operation.

Global and local meta-models for the robust design of electrical machines

This paper presents an optimization framework for the robust design of electrical machines. During the run of a genetic algorithm, all evaluated solutions are kept in an archive, and are used to build different meta-models for the assessment of robustness. The proposed robust design algorithms are verified using analytical test functions and are shown to be efficient and accurate. They have also been applied to the robust design of a surface mount permanent magnet machine considering manufacturing imprecision and different optimal designs (robust and non-robust) are obtained.

A Computationally Efficient PM Power Loss Mapping for Brushless AC PM Machines With Surface-Mounted PM Rotor Construction

This paper describes a computationally efficient approach for mapping rotor power loss in permanent magnet (PM) machines. The PM loss mapping methodology discussed here utilizes a small number of time-step finite-element analyses (FEAs) to determine the parameters of a functional representation of loss variation with speed (frequency) and stator current and is intended for a rapid evaluation of machine performance over the entire torque–speed envelope. The research focus is placed on field-oriented-controlled brushless AC PM machines with surface-mounted PM rotor construction, although the method could be adapted for other rotor formats. The loss mapping procedure accounts for the axial segmentation of the PM array through the use of an equivalent electrical resistivity of the segmented PM array, which is obtained from three-dimensional (3-D) FEA. The PM loss can be accurately mapped across the full operational envelope, including the field-weakened mode, through a single 3-D and four two-dimensional time-step FEAs. The proposed methodology is validated on an 18-slot 16-pole surface-mounted brushless AC PM machine design. The loss mapping procedure results closely agree with the computationally demanding alternative of direct 3-D finite-element prediction of the PM power loss undertaken at each of the machine's operating points.

A General Framework Based on a Hybrid Analytical Model for the Analysis and Design of Permanent Magnet Machines

In highly concurrential markets the time to market is reduced, which implies a need of design tools having relatively high accuracy to computation time ratio. It is to address this problematic that the presented modelling approach has been developed. A general framework for the analysis and design of electromagnetic devices is presented. This framework is based on a new hybrid analytical model (HAM) [1]-[4]. The HAM can be applied to different electric machines types (synchronous and asynchronous) and structures (rotating with radial field or axial field, linear flat or tubular structures, or multi-degree-of-freedom structures). It is based on a direct coupling of analytical solution of Maxwell's equations (AM) with reluctance networks (RN). This new technique allows to combine advantages of both methods and should help reduce computation time as compared to finite elements method [3]. This modeling approach is relatively simple and allows the accurate prediction of performances of electromagnetic devices.

A New Robust Dominance Criterion for Multiobjective Optimization

This paper discusses robust design issues in the multiobjective design of electromagnetic devices. A Pareto front of the worst cases of the solution due to the perturbation of the design variables is used to describe the robustness of a design. A robust dominance (r-dominance) relationship between two solutions of a multiobjective problem is defined. To reduce the computational cost of evaluating the robustness, a local response surface model is built on the uncertainty set. This robust multiobjective design scheme was applied to the design of an interior permanent magnet machine, where a tradeoff exists between the average torque and the torque ripple as the rotor angle is varied. The results show that the proposed r-dominance, when embedded in a multiobjective optimization search method, is able to find robust solutions to multiobjective design problems.

Investigation and Design of a High-Power Flux-Switching Permanent Magnet Machine for Hybrid Electric Vehicles

Flux-switching permanent magnet (FSPM) machines exhibit high torque density, high efficiency, and robust rotor structure. In this paper, a prototype of a high-power three-phase 12-stator-slot/10-rotor-pole FSPM motor used for hybrid electric vehicles (HEVs) is designed by finite-element analysis (FEA). First, the initial FEA model is improved by gradually taking into account lamination ${B}$ – ${H}$ curves due to different electrical frequencies, operation temperatures, 3-D end effect, and rotor eccentric. Thereafter, a modular manufacture method of the FSPM motor is discussed with the improved FEA model and validated by experimental measurements. Then, the measured overload capability of the FSPM motor is compared with that of an interior permanent magnet (IPM) motor used in Honda Civic, and the results indicate that the IPM motor exhibits significantly stronger overload capability, which is analyzed in depth from soft-iron materials, cooling conditions, and and so on. Finally, both the merits and demerits of FSPM motor employed for low-voltage and high-current HEV applications are highlighted.