Permanent Magnet Brushless Machines Research Articles

Investigation of Five-Phase Flux-Switching Permanent Magnet Machines for EV and HEV Applications

As a member of stator permanent magnet (PM) brushless machines, flux-switching (FS) PM machine features outstanding advantages, e.g., robust rotor structure, easy temperature management, high torque density, etc. In this paper, the five-phase FSPM machines for electric vehicle (EV) and hybrid electric vehicle (HEV) applications are investigated. Firstly, the working principle of such machine is analyzed by air-gap field modulation theory. Then, the feasible slot/pole combination is discussed, considering flux leakage, back electro-magnetic force (EMF) quality and unbalanced magnetic force (UMF). Besides, in order to further choose the recommendable slot/pole combination, the torque performances are studied and compared by taking the 20-stators-slot FSPM machines as examples, such as rated torque, overload capability, flux weakening capability and fault tolerance capability. Further, in order to optimize the slot/pole combination which suffers from severe UMF, two different techniques for UMF reduction are proposed, including chamfering both in stator and rotor side. Finally, finite element analysis is employed to verify the analytical analyses. Meanwhile, a 20/18 prototyped machine is manufactured and tested. It is found that the experimental results verify the effectiveness of the analytical analyses.

Performance analysis of sandwich switched flux switching permanent magnet motor using modular rotor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

Design of 6 slots/10 poles modular rotor sandwich switched flux switching permanent magnet motor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

Analysis of Surface and Interior Permanent Magnet Motor Topologies for Active Electromagnetic Damping Applications

Many modern high-end vehicles exploit controllable damping solutions to enhance their adaptability to different road conditions and driving styles. Among these technologies, active dampers offer improved performance due to their four-quadrant operation in the torque–speed plane. In active electromagnetic dampers, brushless permanent magnet machines are used because of their high torque density. However, to the best of our knowledge, a process to set the previously reported; likewise, which rotor topology exhibits the best performance in such cases has not been validated. Consequently, the resulting actuator could exhibit suboptimal dynamical performance and power conversion efficiency. Although some design processes have been formulated in the past for semiactive controllers (the damping is modified using a variable resistive load), they are not suitable for active suspension control. Similarly, there are existing solutions to increase conversion efficiency using mechanical motion rectifiers; however, active forces cannot be exerted, limiting their applicability to semiactive actuators. Therefore, this paper presents a design methodology, using finite element method together with MATLAB/Simulink™, to set and test the parameters of AC brushless PM machines, intended for actively controlled suspensions. A novel approach to set the base speed, which takes advantage of field-weakening capability, is also presented. To test the proposed method, three machines with well-known rotor topologies were designed and evaluated as case studies, and the surface-mounted topology was found to be the most suitable for the analyzed task.

A review on analytical models of brushless permanent magnet machines

AbstractThis study provides an in‐depth investigation of the use of analytical and numerical methods in analyzing electrical machines. Although numerical models such as the finite‐element method (FEM) can handle complex geometries and saturation effects, they have significant computational burdens, are time‐consuming, and are inflexible when it comes to changing machine geometries or input values. Analytical models based on magnetic equivalent circuits (MEC) or solving Maxwell's equations can be faster and more flexible, but less accurate for complex machine structures. The paper focuses on the recent development of analytical models for brushless permanent‐magnet (PM) machines that have become increasingly popular in low and medium‐power applications. The literature review covers the recent developments in analytical models for PM machines with respect to various machine quantities such as magnetic flux density components, induced voltage, inductances, electromagnetic force/torque, efficiency, or unbalanced magnetic force (UMF). It outlines the advantages and disadvantages of different analytical models such as the zero‐dimensional (0‐D), one‐dimensional (1‐D), two‐dimensional (2‐D), and three‐dimensional (3‐D) analytical methods, as well as the Maxwell and basic mathematical analysis. Although the MEC models are faster than the numerical model, they are not as accurate for various structures of electrical machines including a great magnetic air gap. They also note that the analytical models based on the Maxwell equations are faster than the numerical ones and have the potential to obtain acceptable accuracy similar to the numerical models in electrical machines. Overall, this literature review provides valuable insights for researchers and engineers in selecting appropriate analytical models for PM machines. It highlights the trade‐offs between accuracy and computational efficiency when choosing between numerical and analytical models, and the flexibility of analytical models to address changes in machine geometries or input values. Additionally, this helps researchers save time in determining appropriate references regarding the analytical models of brushless PM machines.

Performance Evaluation of Stator/Rotor-PM Flux-Switching Machines and Interior Rotor-PM Machine for Hybrid Electric Vehicles

A three-phase interior permanent magnet (IPM) machine with 18-stator-slots/12-rotor-poles and concentrated armature winding is commercially employed as a 10 kW integrated-starter-generator in a commercial hybrid electric vehicle. For comprehensive and fair evaluation, a pair of flux-switching permanent magnet (FSPM) brushless machines, namely one stator permanent magnet flux-switching (SPM-FS) machine, and one rotor permanent magnet flux-switching (RPM-FS) machine, are designed and compared under the same DC-link voltage and armature current density. Firstly, a SPM-FS machine is designed and compared with an IPM machine under the same torque requirement, and the performance indicates that they exhibit similar torque density; however, the former suffers from magnetic saturation and low utilization of permanent magnets (PMs). Thus, to eliminate significant stator iron saturation and improve the ratio of torque per PM mass, an RPM-machine is designed with the same overall volume of the IPM machine, where the PMs are moved from stator to rotor and a multi-objective optimization algorithm is applied in the machine optimization. Then, the electromagnetic performance of the three machines, considering end-effect, is compared, including air-gap flux density, torque ripple, overload capacity and flux-weakening ability. The predicted results indicate that the RPM-FS machine exhibits the best performance as a promising candidate for hybrid electric vehicles. Experimental results of both the IPM and SPM-FS machines are provided for validation.

Investigation of Bessel Functions in Analytical Modeling of Rotor Eddy Current Losses in PM Machine Rotor With Copper Shield

In high-speed surface-mounted permanent magnet (SPM) brushless machines, time- and space-harmonic excitations can induce significant eddy currents flowing in the rotor conductive parts. An effective measure to suppress the eddy currents is to employ a copper shield between the magnets and the retaining sleeve. In this article, a Fourier-based analytical model is proposed to evaluate the rotor eddy current losses. The model is set up in the cylindrical coordinate system and is able to compute the eddy current fields and losses in all rotor domains, that is, the sleeve, shield, magnets, and shaft. Although it is generally believed that both ordinary Bessel functions (OBFs) and modified Bessel functions (MBFs) are workable for solving the magnetic vector potential, it is argued in this article that only the MBF-based models are numerically stable when the high-conductivity domain (e.g., the copper shield) exists, while the OBF-based models may result in irrational results. Both the OBF- and MBF-based analytical models for a prototype motor are established and comparatively studied, with verification of the finite-element (FE) method. Moreover, the cause of losing analysis accuracy in the OBF-based models is revealed.

Concept and Implementation of Embedded Magnetic Encoder in Flux-Switching Permanent-Magnet Machines

Rotor angle is essential in permanent-magnet (PM) brushless machines. Recently, an embedded magnetic encoder (EME) scheme, consisted of linear Hall sensors installing inside of the PM machines, has been proposed to sense the flux density and consequently provides rotor position. Compared with traditional optical encoder and resolver, the linear Hall sensor prevails over in both space and cost. The aforementioned scheme is employed successfully in rotor-PM machines, where a PM-excited field rotates at the synchronous speed. In this article, the feasibility of EME in stator-PM flux-switching machine is validated, where PMs are located in stator, resulting in a stationary PM field. The stator slots are selected as installation position of linear Hall sensors to avoid changing the existing structure of machines. The variation of linear Hall signal is due to the changing reluctance of rotor rather than rotating PMs. Then, a decoding algorithm is designed based on an add-up operation, a complex coefficient filter, and a synchronous reference frame phase-locked loop. Finally, experiments on a prototype machine are conducted to validate the effectiveness of EME scheme under both speed-varying and load-varying conditions.

Exact Multiphysics Modeling and Experimental Validation of Spoke-Type Permanent Magnet Brushless Machines

Multiphysics modeling and analysis are classic but vital problems for permanent magnet brushless (PMBL) machine design. Bulk of studies give analysis but lack modeling guidelines, comparisons, and rational validations. Accordingly, the principal objective of this article is to systematically investigate the accuracy and rationality among five proposed multiphysics models. Also, it will offer guidelines of modeling and progressive validation for in-depth PMBL machine design optimization from multidisciplinary aspects of electromagnetic, mechanical, vibration, and control. A combined mathematical modeling, finite element analysis, cosimulation, experimental coupling methodological approach is carried out. As a critical phenomenon, electromechanical vibration necessitates theoretical analysis of modified excitation forces considering inverter-side harmonics. Based on a typical spoke-type PMBL machine prototype and tests, the performances under different operation modes are verified, which serve as the prerequisite of vibration prediction. Finally, parallel comparisons between multiphysics simulation and experimental results verify the accuracy and rationality of proposed models, and a balance between model complexity and accuracy is thus presented.

Transient Analysis and Verification of a Magnetic Gear Integrated Permanent Magnet Brushless Machine With Halbach Arrays

The magnetic gear integrated permanent magnet brushless machine (MG-IPMBM) is a kind of compact structure with high torque density and complex electromagnetic energy transfer. In order to analyze the transient characteristics of the machine, an analysis method of field circuit coupling is proposed. Both magnetic gear (MG) and permanent magnet motor are magnetized by Halbach array. Combining the analytical model of the MG magnetic field with MATLAB motor simulation module, a joint simulation model of field circuit coupling double closed-loop control system based on the Simulink-analytical method is established. The electromechanical transient response characteristics of machine under load starting, load mutation, and overload self-protection are analyzed. The simulation results show that the output speed and torque of machine can accurately follow the given value, and its unique overload self-protection ability greatly improves the safety of machine operation. In addition, a prototype is made and an experimental platform is built. The experimental results show that the output torque follows quickly, the torque ripple is small, and transient performance of the machine is good.

Analytical Model of the Slotless Double-Sided Axial Flux Permanent-Magnet Brushless Machines

Analytical approaches, if possible, are suggested for saving the simulation time in the design stage of the electrical machines. This benefit is highlighted when the optimization issues including too many iterations are desired. Hence, this paper presents a 2-D analytical model for magnetic field distribution based on the sub-domain method in a slotless double-sided axial flux permanent-magnet (PM) brushless machines (AFPMBMs) with internal-rotor-external-stators. According to this method, the machine cross-section is divided into the appropriate number of sub-regions and the related partial differential equations (PDEs) extracted from Maxwell equations are formed for magnetic vector potential in each sub-region. Applying curl on the obtained results leads to calculating the magnetic flux density components in each sub-region. Based on the superposition theorem, the analytical procedure is utilized in the two separate steps where in the first step the magnetic flux is originated by only PMs with various magnetization patterns (i.e., parallel, ideal Halbach, 2-segment Halbach and bar magnet in shifting magnetization patterns) and the armature currents are zero. In the second step, all PMs are inactivated and only armature currents affect the magnetic flux distribution. Finally, the obtained analytical results are compared with those of the Finite element method (FEM) to confirm the accuracy of the proposed analytical model. The extracted results reveal the benefit of the analytical model for replacing instead of the FEM to predict the magnetic flux density component in the presented AFPMBMs in a shorter time.

An Induction Machine Design With Parameter Optimization for a 120-kW Electric Vehicle

Electric traction machines have been applied to both industrial variable-speed applications and electric vehicles. The induction machine (IM) is a potential candidate for traction machines due to the established industrial base. However, most of the existing studies on traction IM design rely on optimization algorithms or iterative calculation programs that subsequently give no clear understanding of the design requirements for field-weakening or extended speed operation. Hence, published procedures to guide IM design for traction applications are somewhat ad hoc to date. This article identifies the key IM design parameters required to achieve a traction characteristic within power supply constraints. As an example, a 120-kW electric vehicle traction machine is studied as a benchmark machine and then the proposed design procedure is employed to redesign the machine to improve its extended speed performance. Improvements in terms of efficiency and field-weakening capability are presented. The experimental results from the benchmark machine are used for validation of the subsequent simulation studies reported in this article. Finally, the identified parameters are shown to be similar with brushless permanent magnet machines. Thus, a generalized machine design philosophy can be concluded.

Analytical Modeling and Optimization of Dual-Layer Segmented Halbach Permanent-Magnet Machines

In this article, two kinds of dual-layer segmented Halbach arrays have been proposed for permanent-magnet (PM) brushless machines. The analytical expressions of magnetic fields due to the inner-/outer-layer Halbach magnets have been separately obtained. For the maximal flux density in the air gap, the optimal magnet segment radian ratios or magnetization angles for each dual-layer Halbach array have been analytically determined separately. The induced back electromotive force and electromagnetic torque have been analytically obtained. The prediction results show that the optimized electromagnetic performances for each double-layer segmented Halbach array with different slot and pole combinations are better than those for the corresponding single-layer one. The proposed analytical model can also be applied for optimizing the multi-layer segmented Halbach array. The analytical prediction results of a PM machine with the double-layer segmented Halbach array have been compared with those obtained by a finite-element method.

Study on Rotor Eddy Current Losses in High-speed Permanent Magnet Brushless Machines for Aircraft Applications

To improve the power density of aviation electric drive system, the high-speed permanent magnet machines has more and more popular in the air compressor, radial compressor, and electro-hydrostatic actuator applications. Two methods have studied to reduce the rotor eddy current losses in high-speed permanent magnet machines in this paper. Firstly, rotor eddy current losses at different stator slot openings are investigated, the stator core loss are considered simultaneously. Secondly, to reduce the magnet eddy current loss in carbon fiber retaining sleeve, the copper shield is added between permanent and carbon fiber, and the rotor eddy current losses at different copper shield width are studied.

Comparison of stator‐ and rotor‐surface‐mounted PM brushless machines

Flux-reversal permanent magnet (PM) machines can be considered as stator-surface-mounted PM (SSPM) machines, where normally a pair of magnets with reversal magnetization polarities is mounted on the surface of each stator tooth. Hence, the SSPM machines and the conventional rotor surface-mounted PM (RSPM) machines are rather similar since both machines house the PMs in the air-gap, and the only difference is the location of magnets in the stator side and rotor side, respectively. In this study, a comparative study between SSPM and RSPM machines is conducted to investigate the difference including topology, operation principle and performance. First of all, the topology of both machines is compared. Then, the operation principle in both machines is analysed based on the air-gap field modulation theory. Correspondingly, the characteristics of flux density harmonics either due to PMs or armature reaction are obtained. Therefore, the harmonics that make contribution to back-electromotive force and rated torque are quantified. Besides, other electromagnetic performances, e.g. overload capability, flux weakening ability and loss distribution are also evaluated. Finally, a 12/14 prototyped SSPM machine is manufactured and tested to verify analytical and finite element method-based prediction.

Magnetic field analysis and optimisation of permanent magnet machineswith novel two‐segment Halbach array

An analytical technique for predicting and optimising the open-circuit magnetic field in brushless surface-mounted permanent magnet (PM) machines with novel two-segment Halbach array has been presented. For the maximum fundamental air-gap flux density, the optimal magnetisation angle has been analytically derived. The effect of the rotor core on the fundamental air-gap flux density in the machine has been investigated. In addition, the proposed analytical technique can also predict the induced back-electromotive force and the electromagnetic torque. The analytical results show that the electromagnetic performance can be significantly improved for the proposed two-segment Halbach array compared with the conventional two-segment Halbach array. Predicted results have been validated by the finite-element analyses for 9-slot/8-pole slotless/slotted brushless PM machines.

High-Performance Ferrite Permanent Magnet Brushless Machines

The performance of a brushless permanent magnet machine topology equipped with axially and circumferentially magnetized ferrite permanent magnets is presented. Simulation studies show that for smaller ratios of axial length to active length, air-gap flux densities in excess of 1 T can be achieved, resulting in significant improvements in torque production and efficiency. A prototype machine is manufactured, and test results confirm the predictions of the EMF and the static torque.

Inductance analytical calculations of brushless surface-mounted permanent-magnet machines based on energy method

PurposeThis paper aims to show the proposed energy method for inductance calculation is valid for any number of poles, phases and any winding layout.Design/methodology/approachA two-dimensional (2-D) analytical energy-based approach is presented to calculate self-inductances and mutual inductances of brushless surface-mounted permanent-magnet machines.FindingsThe proposed calculation procedure is valid for brushless permanent-magnet machines with slotted or slotless stator structure. Comparisons between energy method and flux linkage method are presented based on simulation and experimental results. It shows that the energy method has an excellent agreement with the result obtained from finite element method (FEM) and experimental study.Originality/valueThis paper compares energy-based method with flux linkage method and FEM for inductance calculations in slotless and slotted permanent-magnet motors. The relations for inductance calculation are presented which are obtained based on 2-D analytical representation of magnetic field.

Design and Analysis of Halbach Ironless Flywheel BLDC Motor/Generators

Halbach array-based permanent magnet (PM) brushless machines exhibit attractive features when compared with conventional PM brushless machines with normal segmented magnets, including the flux-concentration effect, essentially sinusoidal air-gap flux density due to PMs, and negligible cogging torque. However, as for a motor/generator used in flywheel, an external rotor composed of Halbach array and rotor back-iron is necessary to increase the inertia of flywheel system, which is different from the conventional external-rotor machines. In this paper, a Halbach array PM motor is studied compared with the radial magnet array. The relationship between the air-gap field distribution and the magnet array is discussed. Finally, the eddy current loss in PMs of the external-rotor ironless brushless dc motor is analyzed between the Halbach PM motor and the conventional PM motor.

Multimode Optimization Research on a Multiport Magnetic Planetary Gear Permanent Magnet Machine for Hybrid Electric Vehicles

In this paper, by incorporating the new concept of the noncontact magnetic planetary gear into a permanent magnet brushless machine, a new multiport magnetic-planetary-gear permanent magnet machine is proposed. To achieve flexible combination and split of the power and torque among different electrical or mechanical ports in the machine, a multiobjective optimization design method considering multioperational modes is proposed and investigated. To obtain high optimization design efficiency, the whole optimization is divided into three steps based on various driving modes. In each step, the multobjective genetic algorithm, response surface method, and direct screening method are utilized, respectively. Moreover, the basic no-load characteristics and torque performances of the proposed machine are also studied. Finally, a prototype machine based on the optimized structure dimensions is manufactured and tested. Both the theoretical and experimental analysis verifies the effectiveness of the investigated machine and the proposed method.