PM Rotor Research Articles

PMSM Drives and its Application: An Overview

Abstract: The Permanent magnet synchronous motor (PMSM) drive has emerged as one of the most preferred motor drives for industrial applications. Its distinguished advantages include high torque density, high efficiency, and vast speed range operation. This paper presents, First, details of PMSM drives and their components. Second, explain the modelling of PMSM. Third, discuss the needs of position sensors, their applications, and their performance with the required accuracy. They are finally concerned about extensive industrial applications and future sensorless and sensor-based PMSM drives research trends. Conclusion This paper reviews permanent magnet synchronous motor types and Permanent magnet materials used its advantage and disadvantage and the classification of PM rotor type. This paper briefly discusses the position sensor, its types, and application based on requirements. Based on comparative analysis of permanent magnet materials, briefly discuss sensors and classification of permanent magnet motor, recommendations are given on their practical application.

Optimal design of a yoke-less axial flux switching PM motor based on multi-objective PSO

PurposeIn this paper, an improved multiobjective particle swarm optimization (PSO) algorithm is proposed to optimize a three-phase, 12-slot, 19-pole, yokeless axial-field flux-switching permanent magnet (YASA-AFFSPM) motor.Design/methodology/approachBased on the structural characteristics of the YASA-AFFSPM, a mathematical model is established to calculate the main size of the YASA-AFFSPM motor. The split ratio, stator axial length, sandwiching pole angle, rotor pole angle, PM arc and number of conductors per slot are selected as optimization variables. Also, the efficiency, power factor, cogging torque and average torque are considered as the optimization objectives. The objectives are optimized by combining the improved multiobjective PSO algorithm with electromagnetic calculation.FindingsBased on the proposed algorithm, the investigated motor is optimized. The on-load efficiency, power factor and average torque of the motor performance have increased by 0.87%, 3.13% and 10.39%, respectively. Moreover, the cogging torque and slot fill factor have undergone decreases of 8.57% and 3.34%, respectively. Finally, the effectiveness of the algorithm is verified using experiment results.Originality/valueSo far, no comprehensive report has been observed on the optimization of the YASA-AFFSPM motor using evolutionary algorithms and the study of the effect of the motor parameters. Therefore, in this paper, the authors decided to investigate the effect of YASA-AFFSPM motor parameters and improve motor performance with the improved PSO method.

Modeling of Fault-tolerant Flux-switching Permanent-magnet Machines for Predicting Magnetic and Armature Reaction Fields

The paper develops accurate analytical subdomain models for predicting the magnetic and armature reaction fields in fault-tolerant flux-switching permanent-magnet machines. The entire region is divided into five subdomains, followed by rotor slots, air-gap, stator slots, PM, and external air-gap imported to account for flux leakage. The coil turns and the remanence of magnets are adjusted by keeping the magnetic and electrical loading on the motor constant. The distance between the centers of two adjacent stator slots varies due to the introduction of fault-tolerant teeth. According to the variable separation method, the general solution expression of each region can be determined by solving the partial differential systems of equations. The magnetic field distributions of subdomains are obtained by applying the continuity conditions between adjacent regions. Some analytical field expressions are represented as new forms under armature reaction field condition compared to those under no-load condition. Based on the developed analytical models, the flux density distribution and the electromagnetic performance can be calculated under no-load or armature reaction field condition separately. The finite element analysis is carried out to verify the validity of the proposed analytical model.

Levitation behaviours of an eccentric SC-PM system with multi-degree-of-freedom motion

The high temperature superconducting (HTS) magnetic levitation is actually a self-stable levitation with multi-degree-of-freedom (DoF). However, the research of HTS magnetic levitation focuses on the axial or radial levitation behaviour with single-DoF motion independently. This article mainly discusses the 3-D modelling and the levitation behaviours of an eccentric superconductor-permanent magnet (SC-PM) system with multi-DoF motion. Firstly, the Power-Law E − J relation is used to obtain the relationship of equivalent conductivity-electric field strength for the superconductor. Then, a 3-D finite element model (FEM) of SC-PM system is established and calculated in software MagNet. At the same time, the result of the simulation is verified by the experimental measurements. The axial levitation behaviour is analysed by establishing and solving the 3-D FEM in eccentric SC-PM system with different multi-DoF motions. The results show that the maximum axial levitation force decreases with the increase of the static eccentricity distance. When the PM rotor exhibits dynamic eccentricity, the axial levitation force presents periodic fluctuations of which the amplitude and period are related to the dynamic eccentric distance and speed.

Analysis of alternating flux density harmonics inside the rotor of a 1 MW high-speed interior permanent magnet synchronous machine used for flywheel energy storage systems

With the popularization of renewable distributed energy generation in the power grid, flywheel energy storage systems (FESS) with fast response and high power density are gradually becoming popular for achieving fast frequency modulation. Generally, the rotor of high-speed permanent magnet synchronous machine (HSPMSM) used for FESS rotates in a vacuum to reduce air friction loss, which concurrently makes it difficult to dissipate heat in the rotor. For reducing rotor iron loss and preventing demagnetization of the PM due to high temperature, effective measures need to be applied. In this study, a 1 MW 10,500 r/min high-speed interior PMSM (HSIPMSM) is proposed for an FESS. As rotor iron loss is caused by alternating flux density harmonics (FDH) inside the rotor, the causes and characteristics of alternating FDHs are analyzed. Then, the finite element analysis (FEA) is combined with two-dimensional fast Fourier transform (2D-FFT) to obtain the alternating frequencies and amplitude variation trends of alternating FDHs in the designed rotor. The analytical results indicate that the amplitudes of alternating FDHs on the PM surface are effectively reduced due to bypass of the rotor core at the outside of the PM to alternating FDHs, which helps to restrain the rotor iron loss from the source. This provides a design idea for mitigating the high temperature of high-power high-speed PM rotors.

Design and optimization of yokeless magnetic gear with asymmetric Halbach permanent magnet array for electric vehicle powertrain

In this paper, a novel 3/27/24 (pole pairs of inner rotor permanent magnet [PM]s/modulator/outer rotor PMs) high torque density yokeless magnetic gear with asymmetric Halbach PM array is presented and optimized for electric vehicle powertrain. The key is to improve the torque performance by replacing the magnetic steel with the light nonmagnetic material as the rotor core and employing the embedded magnetic steel bar as well as trapezoidal PM structure to form a low magnetic resistance in the magnetic circuit. The proposed machine has significant performance improvements in two aspects. Firstly, it has high torque density and low iron loss with the yokeless structure. Secondly, it has a high anti-saturation capability and low torque ripple with the asymmetric Halbach PM array and the embedded magnetic steel bar. The proposed structure is optimized by the co-simulation of the finite-element method and C++ optimization software. For a clear evaluation, the proposed structure is compared with generalized solutions in terms of performance and cost. Comparison results indicate that the proposed solution has the highest output torque, torque density, and torque per PM weight among solutions, reaching 214.1 N·m, 58.2 N·m/kg, and 95.6 N·m/kg, which greatly enhances the performance of the magnetic gear.

Analysis and Design of Novel Axial Field Flux-Modulation Permanent Magnet Machines for Direct Drive Application

Axial field flux-modulation permanent magnet (AF-FMPM) machines have been developed for direct drive applications such as wind power generation, HEVs, and railway traction. However, the existing studies on AF-FMPM machines are limited to the PM rotor structure, and less research has been carried out on AF-FMPM machines with PM stator structure. This paper studies two axial field flux-modulation permanent magnet (AF-FMPM) machines, i.e., NS or NN type, which all consist of the same stator and rotor structures but the dual identical outer surface-mounted PM stators face each other in different position. A comprehensive theoretical analysis and global optimization of the AF-FMPM machine based on ANSYS Maxwell 3-D FEA is presented. The performance comparisons between the AF-FMPM machine (NS) and AF-FMPM machine (NN) are presented, including the influence of the critical structural dimensions on the machine performance, phase flux linkage, phase back EMF, cogging torque, and average torque performance. The results show that the phase back EMF and average torque of the AF-FMPM machine (NS) are more sinusoidal and higher than that of the AF-FMPM machine (NN). Furthermore, the NS type machine shows the non-saliency characteristics, while the NN type machine is the salient machine.

Investigation of Sinusoidal Shaped Rotor to Reduce Torque Ripple in Axial Flux Permanent Magnet Machine

Cogging torque is one of the main reasons for torque pulsation in AFPM machines that arises due to the force of attraction between stator slots and rotor poles thus adversely affecting the smoothness of output torque. In this paper a rotor shape for the axial flux internal rotor (AFIR) PM machine is proposed for cogging torque reduction and smoothing the output torque. In this research, the reduction in cogging torque is accomplished in two stages. In the first stage, a sinusoidal magnet shape is proposed having less cogging torque as compared to conventional and arced shaped magnet. In the second stage, the magnet overhang technique is used in the optimization process of the machine to further improve the performance characteristics. The optimization process comprises of a selection of variables, Latin hypercube sampling (LHS), model approximation by kriging method, and Genetic Algorithm (GA) to get optimum values of variables. Output results of proposed and optimized models are also compared to demonstrate that the optimized model has reduced torque ripples and improved average output torque. Models are simulated using 3D finite element analysis (FEA) for comparative analysis.

Electromagnetic Performance Analysis of 6-Slot/2-Pole High-Speed Permanent Magnet Motors With Coil-pitch of Two Slot-pitches

In this paper, a high-speed permanent magnet (HSPM) motor having 6-slot/2-pole (6s/2p) number combination and 2 coil-pitch windings are developed for domestic appliance application. Two HSPM motors with different layouts of 2 coil-pitch windings are optimized and their electromagnetic performances are evaluated. The best winding configuration is then identified for shorter motor axial length and larger torque density. Since 3-slot/2-pole (3s/2p) HSPM motors with non-overlapping windings have the same winding factor, a comparison between 3-slot and 6-slot motors is also conducted, particularly for torque density, losses, and unbalanced magnetic force (UMF). It shows that 6s/2p PM motors with 2 coil-pitch windings are suitable for high-speed application without UMF and less rotor PM loss. Finite element predicted electromagnetic performances are validated by experiments made on two prototype motors.

A Novel High Performance Magnetic Gear with Auxiliary Silicon Steel Sheet

Magnetic gear is a transmission device with novel structure. It uses the principle of magnetic field modulation to transmit torque. In view of the magnetic leakage of the magnetic gear in the process of rotation and cannot be eliminated, a magnetic gear model with auxiliary silicon steel sheet is proposed. Based on the conventional magnetic gear structure, the silicon steel sheet is placed outside the permanent magnet of the outer rotor. The magnetization mode of the outer rotor permanent magnet is tangential magnetization, and the spoke structure is adopted, and the inner rotor PMs is surface mounted and magnetized in the radial magnetization. The improved model is simulated by finite element method under three-dimensional conditions, and the electromagnetic performances of the model are optimized. Compared with the conventional magnetic gear model, the improved model has good performance, which improves the transmission capacity of output torque and reduces torque ripple. It is a great significance to improve the performance of magnetic gear.

A Modified Permanent Magnet-Assisted Synchronous Reluctance Motor Design for Torque Characteristics Improvement

A modified configuration for Permanent Magnet Assisted Synchronous Reluctance Motors (PMaSyRM) is studied in this paper. Conventionally, the PM materials are inserted in the flux barriers region of the rotor. Consequently, the PMs sizing parameters will be restricted to the available space that may limit the efficient use of PMs benefits. In this study, a portion of the rotor structure is replaced with an Interior PM (IPM) rotor so that an axially segmented integration of IPM and SyRM is obtained. Thus, the PMs design is performed specifically in the IPM segment independent of the SyRM scheme, while the SyRM segment remains PM-less. The main motivation of this concept is to improve the contribution of the PM material in the total torque as well as utilizing the special property of the proposed rotor configuration for pulsating torque reduction. A computationally cost-effective algorithm is proposed for the optimal design of IPM-SyRM motor by which a low-power design is carried out for a lightweight electric vehicle. The results for torque profile characteristics, PM volume, power-factor, and efficiency are compared with a conventional PMaSyRM that has been optimally designed as the reference case. Finally, a prototype is constructed to verify the theoretical analysis.

Design and Optimization Analysis of Coreless Stator Axial-Flux Permanent Magnet In-Wheel Motor for Unmanned Ground Vehicle

In this article, a coreless stator axial-flux permanent magnet (CSAFPM) indirect drive (ID) in-wheel motor is proposed and researched taking into consideration the multiphysics constraints, including electromagnetic performance and mechanical strength for unmanned ground vehicles (UGVs). At first, two 12-slot-14-pole CSAFPM motors with different rotor structures are designed to meet the vehicle rim space and driving system demand. In addition, the rotor parameters are optimized to obtain higher torque density based on the response surface method (RSM) and finite element model (FEM). Meanwhile, the electromagnetic performance of optimized motors with different rotors is compared, including back electromotive force (EMF), output torque capability, and efficiency characteristics. The results indicate that the Halbach-array PM rotor has higher torque and efficiency than the spoke-type PM rotor. On that basis, the thermal stress and deformation of the stator support are analyzed and optimized, considering material property and temperature distribution. In addition, the stress of PM rotor, annular gear, and gear reducer are analyzed and optimized to achieve higher torque density. Finally, a 35-kW prototype is manufactured and tested to verify the performance of the design.

The effect of grain size on the internal oxidation of Sm2Co17-type permanent magnets

This work has examined the influence of grain size in sintered Sm2(Co,Fe,Cu,Zr)17-type permanent magnets on the growth of an internal oxidation zone (IOZ). Two magnets of similar composition but with average grain sizes of 46 μm and 170 μm respectively, were exposed to temperatures of 500 °C in air for times up to 1000 h. Overall, the smaller grained magnet showed a reduced growth rate of the IOZ (∼39.01 μm2h−1) compared to the larger grained magnet (∼48.95 μm2h−1) and a smaller irredeemable loss in Br (3.11%) after 1000 h. However, growth rate of the IOZ is shown to depend on the growth direction, in respect to the crystallographic c-axis of the matrix phase. The smaller grain size was shown to be most effective at retarding the growth of IOZ under surfaces parallel to the c-axis. It is proposed therefore, that a smaller grained sintered magnet may be the microstructure of choice for use in demanding, high temperature applications, where a protective coating is not always a possibility, such as a high-performance electrical machine with a surface mount PM rotor. Orientation of the exposed face must also be considered to minimise the resultant magnetic induction loss caused by oxidation.

Design and Analysis of Dual-Rotor Modular-Stator Hybrid-Excited Axial-Flux Permanent Magnet Vernier Machine

This paper proposes a new structure of the dual-rotor hybrid-excited axial-flux permanent magnet vernier machine (DR-HEAFPMVM) with the modular stator and the consequent-pole PM (CPM) rotor for low-speed, high torque density applications such as in-wheel electric vehicles. The tooth-wound non-overlapping armature windings and direct current (DC) excitation windings are, respectively, arranged in stator main-teeth and split-teeth to obtain the modulated and adjustable air-gap flux densities, resulting in high torque density and outstanding flux-weakening capability. First, the design considerations, operation principles, and air-gap flux density distributions of the proposed machine are elaborated based on the air-gap permeance function. Then, the influence of the pole ratios (PRs) and the DC excitation currents on the main electromagnetic performances of the DR-HEAFPMVM, such as the flux-weakening capability and back-electromotive force (back-EMF), on-load electromagnetic torque, loss distribution, and efficiencies, is investigated using the 3-D finite-element method (FEM). Results verify the feasibility of the flux adjustment of the DC excitation windings equipped in the split-tooth, and the design with a pole ratio of 8/1 tends to have higher torque density, higher machine efficiency, and considerable flux-weakening capability compared with the other two PRs.

Research On Enhanced Harmonic Effect of a Dual-PM-Excited Flux-Modulated Motor

In this paper, an improved design for a dual-permanent-magnet-excited (DPME) motor is proposed, where the harmonic characteristics are newly introduced into the design process to enhance the harmonic effect. Based on the role that harmonics play in the torque generation process, not only the amplitude characteristics of harmonics are considered, but also the phase characteristics of harmonics are introduced, which is the key to improve PM utilization. In addition, the harmonics excited by stator PM (SPM) source or rotor PM (RPM) source are considered separately due to the unique dual-PM source characteristic of the DPME motor, which can further enhance the amplitude and phase characteristics of harmonics and then improve the PM utilization. Firstly, the dominant harmonics excited by SPM or RPM are picked out with the analysis of amplitude characteristics. Then, by taking into account the phase characteristics, the effective harmonics excited by SPM or RPM are selected within the dominant harmonics and serve as design objectives. After that, a collaborative design can be realized with the parameters and the two harmonic characteristics of effective harmonics. Finally, the electromagnetic performances are investigated by the Finite Element Analysis (FEA), and the results verify the effectiveness of the design considering harmonic characteristics of dual-PM sources.

A Novel Asymmetric-Magnetic-Pole Interior PM Machine With Magnet-Axis-Shifting Effect

This article proposes a novel asymmetric-magnetic-pole interior permanent magnet (AMP-IPM) machine, which is geometrically characterized by a combination of dual-layer reluctance and flat-type PM rotor structures. The design concept of “asymmetric-magnetic-pole” is introduced to achieve a magnet-axis-shifting effect, namely, the magnet <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis is shifted to make PM and reluctance torque components approximately maximize at similar current angles. Consequently, the resultant torque can be further improved without increasing magnet usage. The machine topology is first introduced. The electromagnetic characteristics of the proposed AMP-IPM machine are then investigated and compared with those of the benchmark conventional IPM machine with symmetrical magnetic poles, with similar sizing and PM usage. Finally, an AMP-IPM machine prototype is manufactured and tested, which confirms the feasibility of the proposed AMP design for the torque performance improvement.

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.

A Novel Spoke-Type Asymmetric Rotor Interior Permanent Magnet Machine

This article proposes a novel spoke-type asymmetric interior permanent magnet (AIPM) rotor topology that employs an additional asymmetric flux barrier in each pole of interior permanent magnet (IPM) synchronous machines for torque density enhancement and torque pulsating suppression without introducing any extra cost. The proposed AIPM-I machine, an existing spoke-type AIPM-II machine with asymmetric rotor profile, and a conventional spoke-type IPM machine are designed and optimized with the same 12-slot/8-pole stator with nonoverlapping windings as well as the same rotor diameter and PM dimensions. The effect of asymmetric flux barrier dimensions on the proposed AIPM-I machine is investigated with particular emphasis on torque characteristics. The electromagnetic performance and rotor mechanical strength of final optimal designs of three machines are compared. It confirms that the proposed AIPM-I machine can achieve significant torque enhancement and torque ripple reduction across the wide current range while also showing significantly smaller cogging torque at open-circuit condition, compared with both existing AIPM-II and conventional IPM machines. Finally, a prototype of the proposed AIPM-I machine has been manufactured and measured for validation.

Comparative study of rotor PM transverse flux machine and stator PM transverse flux machine with SMC cores

Comparative study of rotor PM transverse flux machine and stator PM transverse flux machine with SMC cores

Novel Magnetic-Field-Shifting Techniques in Asymmetric Rotor Pole Interior PM Machines With Enhanced Torque Density

This article overviews novel magnetic-field-shifting techniques for enhancing the torque in a new class of asymmetric rotor pole interior permanent magnet (AIPM) machines. The principle for torque enhancement is introduced first. AIPM topologies are then categorized in terms of asymmetries and symmetries of PM configuration and rotor core geometry. Subsequently, the merits and demerits of various AIPM rotor topologies in each category are analyzed and compared. Finally, the torque capabilities of selected AIPM machines are compared.