Interior Permanent Magnet Rotor Research Articles

Analysis, Design and Optimization of a High-Speed Interior Permanent Magnet Rotor

Analysis, Design and Optimization of a High-Speed Interior Permanent Magnet Rotor

Combined Electromagnetic and Mechanical Design Optimization of Interior Permanent Magnet Rotors for Electric Vehicle Drivetrains

In many high-speed electrical machines, centrifugal forces within the rotor can be first-order constraints on electromagnetic optimization. This can be particularly acute in interior permanent magnet (IPM) machines in which magnets are usually retained entirely by the rotor core with no additional mechanical containment. This study investigates the nature of the trade-off between mechanical and electromagnetic requirements within the context of an eight-pole, 100 kW IPM machine with a base speed of 4000 rpm and an extended speed range up to 12,000 rpm. A series of mechanical and electromagnetic models are used to estimate the level of shaft interference, mechanical stress in critical regions of the rotor and the impact of various features and dimensions within the machine on electromagnetic torque. A systematic exploration of the design space is undertaken for rotor diameters from 120 mm to 180 mm, with optimal designs in terms of torque per unit length established at each diameter while meeting the constraints imposed on mechanical stress. The final preferred design has a rotor of 165 mm and an axial length of 103 mm long with a fractional slot winding in a 30-slot stator. The overall machine has an active mass of 42.3 kg, which corresponds to ~2.4 kW/kg. This paper describes the optimization study in detail and draws on the results to explore the nature of the design trade-offs in such rotors and the impact of core properties.

A Methodology for Applying Skew in an Automotive Interior Permanent Magnet Rotor for Robust Electromagnetic and Noise, Vibration and Harshness Performance

Interior permanent magnet (IPM) motors in traction applications often employ discrete rotor skewing constructions to reduce torsional excitations and back-EMF harmonics. Although skewing is very effective in reducing cogging torque, the impact on torque ripple is not well understood and can vary significantly over the operating envelope of a motor. Skewing also leads to the creation of a non-zero axial force that may compromise the bearing life if not considered. This paper introduces a holistic methodology for analyzing the effect of skewing, aiming to minimize torsional excitations, axial forces and back-EMF harmonics whilst mitigating the impact on performance and costs. Firstly, analytical models are employed for calculating cogging torque, torque ripple and axial forces. Then, 2D and 3D finite element analysis are used to incorporate the influence of non-linear material behavior. A detailed structural model of the powertrain is employed to calculate the radiated noise and identify key areas allowing a motor designer to reduce noise, vibration and harshness (NVH). A meticulous selection process for the skewing angle, the number of skew stacks and the orientation of skew stacks is developed, giving particular attention to the effect of the selected pattern on NVH in both forward and reverse rotating directions.

Modelling and Analysis of Salient-Pole Rotor Interior Permanent Magnet Synchronous Motor for Oil and Gas Pump Applications

This paper presents the design and dynamic simulation of a line-start, three-phase Interior Permanent Magnet Synchronous Motor (IPMSM) intended for pump applications in the oil and gas industry. The problem addressed in this paper pertains to the replacement of an existing induction motor (IM) in an oil and gas pump station with a more efficient and controllable solution, the IPMSM since IMs are known to be less efficient and IPMSM is easier to control. The chosen motor type employs a traditional salient-pole rotor with cage windings, known for its line-start capability, making it a feasible choice for constant-speed and pump applications. The dynamic simulation of the proposed IPMSM is carried out using MATLAB/Simulink, focusing on fundamental harmonic analysis in direct-phase variables. The results demonstrate rapid startup to synchronous speed with minor deviations effectively dampened by the rotor's damper windings. Torque characteristics exhibit some pulsations caused by magneto-motive force (MMF) harmonics; a phenomenon captured by Finite Element Analysis (FEA). The performance results show that the proposed IPMSM with a salient-pole rotor is viable and a promising replacement for induction motors in oil and gas pump stations.

An improved subdomain method for air gap flux density of interior permanent magnet machines based on rotor reconstruction and flux equivalence

AbstractThe aim of this article is to develop a rotor reconstruction method for the V‐shaped interior permanent magnet (IPM) machine so that the subdomain method to analytically calculate the air‐gap flux density can be applied. With the proposed method, the V‐shaped IPM rotor with rectangular magnets, magnetic barriers, and saturated iron bridges can be transformed into a U‐shaped equivalent analytical model. The geometry and material parameters of the magnets in the equivalent U‐shaped model can be determined according to the flux equivalence in the air‐gap of the motor. Then using the subdomain method on the U‐shaped equivalent rotor, the static magnetic field problem can be solved and the flux density distribution in the air‐gap be obtained. The validity of this method and accuracy of the solution is verified by the finite element method with case studies. Compared with existing methods, the improved subdomain method has higher accuracy in calculating flux density including radial and tangential components. The presented rotor reconstruction method is not only limited to single‐layer V‐shaped rotor, it can also be applied to other IPM rotors with more complex structures. It is valuable in the design, optimisation of IPM motors, and even development of new rotor topology.

Design and Performance Comparison of Novel Flux-Concentrating IPM Machines for Power Generation System Application of Extended-Range Electric Vehicle

A new spoke-type interior permanent magnet (IPM) machine with enhanced flux-concentrating capability and high saliency ratio rotor is proposed for the extended-range electric vehicles traction applications. The evolution of the proposed flux-concentrating rotor structure from the spoke-type IPM rotor is illustrated to achieve a higher saliency ratio and higher air-gap flux density. Two IPM motors with the same magnets volume are developed and compared with the proposed IPM machine. The rotor configurations are optimized by the multiobjective genetic algorithm to maximize the torque/power and minimize the cogging torque, as well as increasing the saliency ratio. Furthermore, the major electromagnetic performance of the three machines are analyzed and compared by the finite-element analysis (FEA), including the air-gap flux density, cogging torque, saliency ratio, torque-current curves, and field-weakening capability. The results show that the IPM machine with high saliency ratio rotor can achieve higher torque/power, maximum torque per ampere capability, and flux-weakening ability. Finally, a-rated 60-kW PM motor with the proposed rotor is manufactured and experimented to verify the results of the FEA.

Design and Optimization of an Asymmetric Rotor IPM Motor with High Demagnetization Prevention Capability and Robust Torque Performance

In this paper, an asymmetric rotor interior permanent magnet (ARIPM) motor with high demagnetization prevention capability and robust torque performance is proposed. The key contribution of this paper lies in two aspects. On the one hand, a novel asymmetric rotor with a shifted magnet axis is proposed to improve the demagnetization prevention capability and torque density. In order to obtain a proper asymmetric rotor topology of the ARIPM motor, the multi-physical performances, especially the PM demagnetization characteristics of five types of PM arrangements, are analyzed. Furthermore, an asymmetric rotor with V- and VV-type PM arrangement is preliminarily designed, considering the multi-physical performance balance and the potentially high anti-demagnetization ability. On the other hand, it is found that the asymmetric rotor structure can not only improve the nominal value of motor performance but also can enhance the resistance to the influence of manufacturing uncertainties. Therefore, multi-objective optimization of the ARIPM motor with rotor notch design is carried out to obtain an optimal motor structure with both high nominal value and robustness of motor performances. By comparing the simulation results with those of a benchmark motor, the superiority and validity of the proposed ARIPM motor are confirmed. Experimental tests will be carried out in the future to further verify the effectiveness of the proposed motor.

A New Flux-Concentrating Rotor of Permanent Magnet Motor for Electric Vehicle Application

This article presents a new interior permanent magnet (IPM) rotor structure/ assembly, which inherits from the Halbach magnet configuration and spoke-type IPM rotor to achieve a high saliency ratio and high torque/ power density. With this rotor structure, the torque density and power density are improved obviously, while the rotor inner diameter can be maximized to reduce core material and increases internal space in the rotor. Accordingly, the electromagnetic performance of three motors consists of a unified stator but different rotors, namely flux-concentrating rotor, Halbach array permanent magnet (PM) rotor and spoke-type IPM rotor is compared by finite element analysis. Nevertheless, due to the segmented structure of flux-concentrating PM rotor without magnetic bridges, the mechanical challenges are analyzed in detail for electric vehicle application to hold the pole pieces validate the structural feasibility at 7200 r/min. Finally, a 72-slot/ 16-pole fractional-slot PM motor with new flux-concentrating rotor is manufactured and tested to verify its performance and feasibility. It can be concluded that the new rotor is superior to the spoke-type IPM and Halbach array PM rotor in terms of torque density and PM utilization.

A Novel Spoke-Type IPM Rotor With Hybrid Radial and Axial Flux Concentration for Reduction of Interpolar Leakage Flux

Axial leakage magnetic flux is generated in the spoke-type interior permanent magnet synchronous motor (IPMSM) because of the flux-concentrating rotor structure, which degrades the performance of the motor. In this article, a traditional spoke-type interior permanent magnet (IPM) motor is fabricated and tested first. Then a novel spoke-type IPM rotor with hybrid radial and axial flux-concentrating capability is proposed to reduce the interpolar leakage flux and improve the torque performance. Furthermore, the radially magnetized PMs are installed in the inner circumference of the rotor, which can reduce the rotor-interior flux leakage. Finally, the superiority of the two proposed structures is verified through three-dimensional finite-element analysis (3-D FEA).

A Virtual Prototyping Approach for Development of PMSM on Real-Time Platforms: A Case Study on Temperature Sensitivity

This paper presents a comprehensive evaluation of system interactions in a battery electric vehicle caused by temperature sensitivity of permanent magnet synchronous machines (PMSM). An analytical model of a PMSM considering iron losses and thermal impact is implemented on a field programmable gate array suitable for hardware-in-the-loop testing. By the presented virtual prototyping approach, different machine characteristics defined by the design are used to parameterize the analytical model. The investigated temperature effect is understood as an interacting influence between machine characteristics and control, which are investigated in terms of torque generation, voltage utilization and efficiency under closed-loop condition in a vehicle environment. In particular, using a surface permanent magnet rotor and an interior permanent magnet rotor, the performance of both machine designs is analyzed by varying temperature-adjusted feedforward control strategies on the basis of a driving cycle from a racetrack. The comparison shows that the machine design with surface-mounted magnets is associated with higher temperature sensitivity. In this case, the temperature consideration in the feedforward control provides a 14,% loss reduction in closed-loop vehicle test operation. It can be summarized that the electromagnetic torque is less sensitive to a temperature variation with increasing reluctance. The presented development approach demonstrates the impact of interactions in electric powertrains without the need of real prototypes.

A Novel Asymmetric Interior Permanent Magnet Synchronous Machine

This article proposes a novel asymmetric interior permanent magnet (AIPM) rotor topology that has a mixed V-shape and spoke-type PM configuration, designated as a 1.5-layer PM structure, and asymmetric arrangement of V-shape PMs and asymmetric flux barriers. The AIPM rotor topology is employed for IPM synchronous machines to utilize the magnetic-field-shifting (MFS) effect for increasing average torque by reducing the current angle difference between peak PM and reluctance torque components. Three machines, i.e., the proposed 1.5-layer AIPM, a symmetrical 1.5-layer IPM-I, and a conventional V-shape benchmark IPM-II are designed and optimized using the same stator, rotor diameter, and total PM usage by global parametric optimization considering the mechanical stress. The effect of asymmetric features of the 1.5-layer AIPM rotor design, i.e., asymmetry of V-shape cavity as well as position and dimensions of flux barrier, on maximum torque and open-circuit air-gap field are investigated. The electromagnetic performances of three machines are compared. It confirms that the proposed AIPM machine has the highest maximum torque and the smallest cogging torque simultaneously. It is also revealed that the torque enhancement is achieved by both the 1.5-layer structure and MFS effect. Finally, a prototype of an AIPM machine is manufactured and tested to validate the analyses.

Optimal Design of 9-Phase Permanent Magnet Synchronous Generator With Low Voltage Change Rate for Diesel Railway Vehicles

Due to the unchangeable air-gap flux density, the voltage output by permanent magnet synchronous generator (PMSG) will have a variation when the load changes. In order to reduce the voltage variation when PMSGs provide power for the rectifier load in diesel railway vehicles, an optimal method is presented to design a 9-phase PMSG. This optimal method not only ensures the open-circuit voltage of the generator equals the rated voltage of the load, but also it guarantees the PMSG has a low voltage change rate at the same time. In this paper, the saliency ratio range and the relationship between resistance of load and the induction of <i>d</i>-axis are derived according to the two-axis theory, when the PMSG has the negative or zero voltage change rate. Then based on the result of the derivation, by adding the I-shaped permanent magnet (PM) to the <i>d</i>-axis magnetic circuit of V-shaped interior PM rotor, a V-I-shaped PMSG is formed. After that, the Kriging method and the finite-element method (FEM) are used to establish a multi-objective function model. By calculating the minimum value of the multi-objective function, the construct dimension of the I-shaped PM is obtained. After the optimal design results are verified by the FEM, a 520 kVA 9-phase PMSG is manufactured to validate the effectiveness of the proposed methods.

Comparison Study of Permanent Magnet Synchronous Machines With Consequent Pole and HUPM Rotor

The consequent permanent magnet (CPM) pole rotor and harmonic utilization permanent magnet (HUPM) rotor are promising candidates for electric machines with less rare earth materials. Therefore, this article focuses on the analysis and comparison of these rotor types in terms of air-gap flux density characteristics, magnet utilization, and torque density. In the first part, an analytical approach is used to investigate the magneto motive force (MMF) distribution of the rotor and air-gap flux density characteristics. In the second part, finite-element methods (FEMs) are used to compare both rotor topologies with a conventional interior permanent magnet (PM) and spoke PM rotor. The results show that CPM and HUPM rotors can reduce the volume of PMs compared with the conventional configurations. However, with the HUPM rotor, a higher torque density and magnet utilization ratio can be achieved at the same time.

A novel bearingless interior permanent magnet slice motor for pump*

A 2 pole bearingless interior permanent magnet (IPM) motor with slice rotor configuration is presented in this paper. A novel IPM rotor is designed considering various specifications such as force constant, torque constant and cogging torque. Cogging torque and resulting vibrations affects the motor and levitation operation significantly. Since the cogging torque is a result of the motor geometry, finite element (FE) simulation is used to simulate various rotor geometries to find the desired rotor configuration. FE simulations are also used to obtain other parameters like force and torque constant, and magnetic stiffness for designing control. The final design is fabricated and tested for closed loop levitation control and speed control. The simulation results and experimental control system performance is shown and explained in the paper.

The Analytical Comparative Analysis of Electromagnetic Characteristics of Four Typical Radial Flux Permanent Magnet Eddy Current Couplers

The analytical model of a permanent magnet eddy current coupler (PMECC) is mainly used for evaluation of its characteristics and the initial optimization of design. Based on the equivalent magnetic circuit method, this paper carries out analytical modeling for four typical PMECCs composed of surface-mounted and interior permanent magnet, slotted and non-slotted conductor rotors, which provides a theoretical basis for the subsequent research in this paper. The basic electromagnetic characteristics of the PMECCs are investigated by the established analytical model. Simultaneously, the analytical results about permeance, flux density, torque and power are verified by FEA simulation. The analysis results show that the slotted CR will obtain a much higher power density, and the iron loss mainly exists in the CRs. In addition, the analytical and FEA results agree well, which proves the reliability of the proposed, nearly unified analytical model.

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 Asymmetric Rotor Interior Permanent Magnet Machine With Hybrid-Layer Permanent Magnets

This article proposes a novel asymmetric interior permanent magnet (AIPM) rotor topology for torque enhancement and torque ripple reduction in IPM synchronous machines. The AIPM rotor structure is featured by a hybrid-layer permanent magnet configuration, i.e., for each pole, a part of PM configuration has one-layer while the other part has two layers. It allows the magnetic-field-shifting (MFS) effect to be utilized by reducing the current angle difference between maximum PM and reluctance torque components, thereby effectively increasing the maximum resultant torque. The proposed AIPM machine and a conventional V-shape IPM machine are designed and globally parametric optimized with the same 24-slot/4-pole stator, rotor diameter, and PM usage. The influence of key rotor geometric parameters of the AIPM machine on torque and open-circuit air-gap magnetic field characteristics are investigated. The comparison of electromagnetic performance confirms that significant torque enhancement and torque ripple reduction in the AIPM machine compared with the conventional V-shape IPM machine and reveals the MFS effect is essential for torque increase. Finally, an AIPM machine is manufactured and tested for validation.

Design and implementation of a novel interior permanent magnet bearingless slice motor.

In this paper, we present a bearingless motor with a novel segmented dipole interior permanent magnet (IPM) slice rotor. The segmented dipole IPM rotor contains a unique pattern of interior permanent magnets arranged to generate a dipole air gap flux pattern. The magnets are encapsulated within an electrical steel rotor structure. The stator contains a three-phase, four-pole winding for suspension and a three-phase, two-pole winding for rotation. We present analyses of several candidate rotor designs. The analyses indicate that the segmented dipole IPM rotor achieves a reduced trade-off between force and torque capacity and relatively symmetric force dynamics as compared to prior art designs and alternate topologies. Symmetric and decoupled force dynamics allow a simple force decoupling algorithm to be used. We designed, constructed, and tested a prototype system. We experimentally demonstrate that the prototype system can achieve stable levitation and open-loop rotation.

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.

Analytical Design of Sculpted Rotor Interior Permanent Magnet Machines

A computationally efficient design of interior permanent magnet (IPM) motor rotor features is investigated utilizing analytical methods. Over the broad operating range of IPM machines, interactions of MMF sources, permeances, and currents result in torque harmonics. The placement of traditional rotor features along with sculpt features are utilized to minimize torque ripple and maximize average torque. We extend the winding function theory to include the IPM rotor’s primary and secondary reluctance paths and the non-homogeneous airgap of the rotor sculpt features. A new analytical winding function model of the single-V IPM machine is introduced, which considers the sculpted rotor and how this model can be used in the design approach of machines. Results are validated with finite elements. Rotor feature trends are established and utilized to increase design intuition and reduce dependency upon the lengthy design of experiment optimization processes.