Interior Permanent Magnet Machine Research Articles

Design and Comparison of High-Speed Induction Machine and High-Speed Interior Permanent Magnet Machine

Designing high-speed machines is a complicated process that needs thorough investigation due to their various applications in the industry. The choice of selecting between Induction Machines (IMs) and Permanent magnet Machines (PMs) depends on the required robustness, efficiency, and cost. In this paper, an IM and Interior Permanent magnet Machine (IPM) with similar output power (10kW), rotational speed (30,000rpm), and input voltage (380V) with Fractional-Slot Concentrated Winding (FSCW) are designed, optimized, and analyzed. The comparison is based on design challenges, cost, and efficiency. A genetic Algorithm is used to optimize the proposed machines and finite element analysis (Maxwell) is employed to support the result.

Analytical method to compute bridge stresses in V‐shape IPMs

V-shape interior permanent-magnet machines (IPMs) have been widely utilised in the industry due to their high-power density, high efficiency, and low manufacturing cost. There has been growing interest in applying multi-objective optimisation to the design of electric machines. In the context of V-shape IPM designs, it is important to include stress analysis in the optimisation design analysis as the steel bridges in the IPM rotor are structural weak points, where high stresses develop. However, traditional finite element analysis (FEA) that is normally used to compute bridge stresses becomes cumbersome due to its high computational cost. In this study, a computationally efficient analytical method is proposed to compute the mechanical stresses developed within the steel bridges in a V-shape IPM. The proposed method is shown to yield accurate predictions compared with FEA while reducing computational cost. A design study is conducted that demonstrates that the machine performance can be improved by incorporating the proposed structural analysis in a multi-objective optimisation-based-design environment.

Performance Testing and Analysis of Synchronous Reluctance Motor Utilizing Dual-Phase Magnetic Material

While interior permanent magnet (IPM) machines have been considered state of the art for traction motors, synchronous reluctance (SynRel) motors with advanced materials can provide a competitive alternative. IPM machines typically utilize neodymium iron boron permanent magnets, which pose an issue in terms of price, sustainability, demagnetization at higher operating temperatures, and uncontrolled generation. On the other hand, SynRel machines do not contain any magnets and are free from these issues. However, the absence of magnets as well as the presence of bridges and centerposts limit the flux-weakening capability of a SynRel machine, and limit the achievable constant power speed ratio without having to significantly oversize the machine and/or the power converter. In this paper, a new material referred to as the dual-phase magnetic material, where nonmagnetic regions can be selectively introduced within each lamination, will be evaluated for SynRel designs. The dual-phase feature of this material enables nonmagnetic bridges and posts, eliminating one of the key limitations of the SynRel designs in terms of torque density and flux weakening. This paper will present the design, analysis, and test results of an advanced proof-of-concept SynRel design utilizing dual-phase material with traction applications as the ultimate target application.

Electromagnetic Performance Analysis of Interior PM Machines for Electric Vehicle Applications

An interior permanent magnet (IPM) machine with ∇ + U shape rotor topology is proposed and its electromagnetic performance with typical V shape and ∇ shape for electric vehicle (EV) applications are compared. The pole-arc to pole-pitch ratios are optimized to maximize the fundamental air-gap flux density and minimize its total harmonic distortion (THD) of all the three IPM machines by the finite element (FE) method. It can be obtained that ∇ + U shape rotor topology has the lowest THD of the air-gap flux density. The back electromotive force and its THD orders, cogging torque, torque density, torque ripple, d - and q -axis inductances, saliency ratio, and iron loss of three machines are analyzed and compared. It is demonstrated that the ∇ shape IPM machines have the highest average torque, and the torque ripples of the V shape and ∇ shape machines are almost the same. The ∇ + U shape IPM machine has the lowest torque ripple and iron loss with only a little reduction of average torque. Finally, the ∇ + U shape IPM machine is prototyped to verify the results of the FE analysis.

Effects of Multi-Axial Mechanical Stress on Loss Characteristics of Electrical Steel Sheets and Interior Permanent Magnet Machines

In this paper, we investigate the effects of multi-axial mechanical stress on eddy current and hysteresis losses in electrical steel sheets used for rotating machines. First, the variation of these losses with the multi-axial stress is confirmed by material experiments. From the results, appropriate and useful mechanical-electromagnetic modeling for loss analysis of rotating machines is discussed. Finally, the proposed modeling is applied to the combined electromagnetic field and stress analyses of an interior permanent magnet machine to reveal the effects of multi-axial stress on the rotor core loss, which is directly related to the thermal demagnetization of permanent magnets. It is clarified that both the hysteresis loss and the eddy current loss including excess loss depend on the multi-axial stress. As a consequence, the rotor core loss of interior permanent magnet machine increases by the stress caused by centrifugal force.

Recent advances in variable flux memory machines for traction applications: A review

This paper overviews the recent advances in variable flux memory machines (VFMMs) for traction applications with particular reference to newly emerged machine topologies and related control strategies. Due to the use of flux memorable low coercive force (LCF) magnets, the air-gap flux of VFMM can be flexibly varied via a magnetizing current pulse. Thus, the copper loss associated with the flux weakening current and high-speed iron loss can be significantly reduced, and hence high efficiency can be achieved over a wide speed and torque/power operation. These merits make VFMM potentially attractive for electric vehicle (EV) applications. Various novel VFMMs are reviewed with particular reference to their topologies, working principle, characteristics and related control techniques. In order to tackle the drawbacks in the existing VFMMs, some new designs are introduced for performance improvement. Then, the electromagnetic characteristics of an exemplified EV-scaled switched flux memory machine and various benchmark traction machine choices, such as induction machine, synchronous reluctance machines, as well as commercially available Prius 2010 interior permanent magnet (IPM) machine are compared. Finally, the key challenges and development trends of VFMM are highlighted, respectively.

Incorporating Control Strategies Into the Optimization of Synchronous AC Machines: A Comparison of Methodologies

This paper presents a comparison of methodologies to incorporate control parameters into the design optimization of synchronous ac machines. A metric is used to quantify the conflict level between the average torque and torque ripple for an interior permanent magnet machine and a synchronous reluctance machine. Using 2-D finite-element analysis simulations, the results demonstrate that the traditional approach of lumping the control and design variables together can lead to poor designs, especially when the conflict is high.

Maximum-Torque-per-Ampere and Magnetization-State Control of a Variable-Flux Permanent Magnet Machine

The variable-flux flux-intensifying interior permanent magnet machine exhibits high efficiency with variable permanent magnet flux properties. Control algorithms for a single magnetization state and during transition between different magnetization states are developed. Maximum-torque-per-ampere control is implemented for loss reduction. However, the proposed prototype machine exhibits sophisticated nonlinear inductance properties, which have a significant impact on precise maximum-torque-per-ampere control. This paper proposes an artificial-neural-network-based maximum-torque-per-ampere control scheme. The well-constructed neural network exhibits an excellent capability in nonlinearity simulations and is suitable for maximum-torque-per-ampere current command generation. In addition, the magnetization state should be manipulated properly according to the machine's working condition. A novel magnetization-state control system that generates magnetization-state switch signals by calculating the dc-link voltage margin ratio is proposed. The combination of the neural-network-based maximum-torque-per-ampere control and the magnetization-state control constitutes the proposed control system. The entire control system is validated experimentally.

Improved equivalent magnetic network modeling for analyzing working points of PMs in interior permanent magnet machine

As is well known, the armature current will be ahead of the back electromotive force (back-EMF) under load condition of the interior permanent magnet (PM) machine. This kind of advanced armature current will produce a demagnetizing field, which may make irreversible demagnetization appeared in PMs easily. To estimate the working points of PMs more accurately and take demagnetization under consideration in the early design stage of a machine, an improved equivalent magnetic network model is established in this paper. Each PM under each magnetic pole is segmented, and the networks in the rotor pole shoe are refined, which makes a more precise model of the flux path in the rotor pole shoe possible. The working point of each PM under each magnetic pole can be calculated accurately by the established improved equivalent magnetic network model. Meanwhile, the calculated results are compared with those calculated by FEM. And the effects of d-axis component and q-axis component of armature current, air–gap length and flux barrier size on working points of PMs are analyzed by the improved equivalent magnetic network model.

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

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

Separately Excited Synchronous Motor With Rotary Transformer for Hybrid Vehicle Application

The cost of rare earth (RE) permanent magnet along with the associated supply volatility have intensified the interests for machine topologies, which eliminate or reduce the RE magnets usage. This paper presents one such design solution, the separately excited synchronous motor (SESM) that eliminates RE magnets, but does not sacrifice the peak torque and power of the motor. The major drawback of such motors is the necessity of brushes to supply the field current. This is especially a challenge for hybrid or electric vehicle applications where the machine is actively cooled with oil inside the transmission. Sealing the brushes from the oil is challenging and would limit the application of such a motor inside a transmission. To overcome this problem, a contactless rotary transformer is designed and implemented for the rotor field excitation. The designed motor is built and tested. The test data show that the designed motor outperforms an equivalent interior permanent magnet (IPM) motor, which is optimized for a hybrid application for both peak torque and power. Better drive system efficiency is measured at high speed compared with the IPM machine, while the latter outperforms (for efficiency) the SESM at low- and medium-speed range.

Magnet Shape Optimization of Two-Layer Spoke-Type Axial Flux Interior Permanent Magnet Machines

In this paper, the two-layer spoke-type (TLST) axial flux interior permanent magnet (AFIPM) machine is proposed. Simple flux barriers are added to optimize the air gap flux density, in which way there is no need to change the surface of the rotor. The optimization principle is revealed and the advantages of the TLST AFIPM machine compared with the spoke-type (ST) AFIPM machine are clarified. An optimization design process based on magnetic equivalent circuit combined with idealized and improved air gap flux density waveform is proposed, in which way the calculation time is saved by avoiding an excess of finite element method (FEM) simulations. Finally, 3D FEM simulation is adopted to verify the optimization results.

Magnetic Field Analysis of Multi-Flux-Barrier Interior Permanent-Magnet Motors Through Conformal Mapping

An extended analytical method for predicting the open-circuit air-gap field distribution in interior permanent magnet (IPM) machines equipped with multilayer Permanent Magnets (PMs) is proposed in this paper. This presented method is based on the conformal mapping technique. The mapping is used to calculate the relative permeances, which consider the effect of stator slots and rotor saliency on the magnetic field distribution. The open-circuit air-gap field distribution in a multi-flux-barrier IPM can be predicted through the superposition principle. The analytical solution is implemented on: an eight-pole, 50 kW IPM motor used in 2004 Toyota Prius hybrid electric vehicle and four IPMs with two, three, four, and five flux barriers per pole. To verify this extended method, the results are compared with those obtained from the finite-element analysis.

Analysis of Low-Speed IPMMs With Distributed and Fractional Slot Concentrated Windings for Wind Energy Applications

This paper introduces an alternative pathway to designing an efficient interior permanent magnet machine (IPMM) for direct–drive (D-D) wind energy applications. It analyzes the design optimization methodology in great detail, employing multiple experimental verifications to acutely pinpoint the most desirable and feasible format. The focal objectives of minimizing cogging torque, torque ripple, and maximizing efficiency were among the priority design goals and obtained through design optimization. It is demonstrated in the process that both the torque ripple and the cogging torque can be reduced to less than 5% by adjusting the slot and pole dimensions, without any other alterations in rotor pole shaping or skewing. This paper leads the way, pioneering experimental substantiation of theory, by varying existing geometrical parameters, winding, and pole design of a basic IPMM to come up with a highly efficient wind turbine generator with negligible cogging torque and torque ripple. The electromagnetic is at the heart of this paper’s design goals, as parameter optimization is essential for a wind turbine application. The winding layout is brought under scrutiny and both the distributed and concentrated wound IPMMs are compared to further adopt the design optimization. The superiority of the concentrated-wound design is demonstrated, and consequently a prototype machine is constructed based on the proposed design for experimental verification. The results from the experiment verify the feasibility of the proposed design for D-D wind turbine applications.

Detailed Analytical Modeling of Fractional-Slot Concentrated-Wound Interior Permanent Magnet Machines for Prediction of Torque Ripple

Electromagnetic torque in interior permanent magnet machines is a function of their inductances and permanent magnet (PM) flux linkages, which are assumed sinusoidal in the standard dq model of the machine. This assumption is flawed when a fractional-slot concentrated-wound stator is utilized, because its nonsinusoidal winding function leads to harmonics in the machine parameters. In order to address this deficiency, the nonsinusoidal machine parameters are modeled in this paper, based on which, a modified extended dq model is proposed. The harmonics in the machine parameters are included in the proposed modified extended dq model and their effects on the machine operational characteristics are accounted for. Detailed equations for the average torque and torque ripple are then derived based on the proposed modified extended dq model. Experimental tests are also described for the measurement of the proposed modified extended dq model parameters. The estimated torque and torque ripple by the proposed model are validated through experimental tests on a prototype fractional-slot concentrated-wound interior permanent magnet machine.

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

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

Field-Weakening Capability of Interior Permanent-Magnet Machines With Salient Pole Shoe Rotors

Brushless permanent-magnet (BLPM) machines, with inherent advantages of high-power density and high efficiency, have been widely employed to achieve traction characteristics for traction applications. Generally, traction characteristics require high torque at low speed and wide field-weakening region keeping constant power. However, both conventional interior permanent-magnet (IPM) and surface-mounted permanent-magnet (SPM) machines suffer from high-speed issues in the field-weakening region. A different BLPM machine topology, the pole shoe topology, is proposed in this paper. Although the pole shoe machine is common in industrial variable speed drives employing constant torque regimes, it has not been previously considered for machines designed for a wide field-weakening region. For analysis and comparison, a conventional IPM machine, which is employed as the Nissan Leaf vehicle traction machine, is studied as a reference benchmark machine. Experimental results from this machine are used to validate the analysis presented in this paper. The design results show that the proposed pole shoe machine achieves better field-weakening performance, compared with the conventional IPM and SPM machine topologies.

Iron Saturation Impact on High-Frequency Sensorless Control of Synchronous Permanent-Magnet Motor

An increasing interest for permanent-magnet (PM) synchronous machines equipped with fractional-slot concentrated winding is observed. Among others, the surface-mounted PM (SPM) machines are widely used by motor manufacturers. The spoke-type interior PM (IPM) machines are also particularly attractive. Nowadays, PM machines are often selected for variable-speed applications without precise positioning requirements, taking the advantage of sensorless control algorithms. However, the capability to detect the electrical rotor position without sensor also at zero speed (by means of techniques based on high-frequency signal injection) is an enhancing feature that requires a proper machine design. The aim of this paper is to evaluate the impact of both rotor and stator modifications, taking a commercial motor as a reference geometry. The analysis of both SPM and IPM rotor structures, as well as stator tooth geometry variations, pointed out how the machine geometry greatly affects the sensorless capability due the injection of a high-frequency voltage. Finite-elements simulations have been validated by experimental tests on two IPM motors manufactured with a different stator design.

Interior permanent magnet motor‐based isolated on‐board integrated battery charger for electric vehicles

This study proposes an isolated on-board integrated battery charger using an interior permanent magnet (IPM) machine with a nine-slot/eight-pole combination or its multiples, and equipped with a non-overlapped fractional slot concentrated winding. The proposed winding layout comprises three three-phase winding sets that are connected in such a way as to provide six motor terminals. Hence, a six-phase or two three-phase converters will be required for propulsion. Under motoring mode, the machine can be effectively regarded as a six-phase machine, which provides a high fault-tolerant capability, and allows for a `limp home' mode of operation. Additionally, all magneto motive force subharmonics are eliminated, which significantly reduces the induced rotor eddy current losses, when compared with a conventional three-phase motor having the same slot/pole combination. In battery charging mode, the winding is reconfigured, so that the machine is considered as a three-phase to six-phase rotating transformer. A 40 kW IPM machine is designed and simulated under different modes of operation using two-dimensional finite element analysis to validate the proposed concept. A small-scale prototype machine is also used for experimental validation.

Analysis and design of electrical machines with material uncertainties in iron and permanent magnet

PurposeManufacturing processes, such as laminations, may introduce uncertainties in the magnetic properties of materials used in electrical machines. This issue, together with magnetization errors, can cause serious deterioration in the performance of the machines. Hence, stochastic material models are required for the study of the influences of the material uncertainties. The purpose of this paper is to present a methodology to study the impact of magnetization pattern uncertainties in permanent magnet electric machines.Design/methodology/approachThe impacts of material uncertainties on the performances of an interior permanent magnet (IPM) machine were analyzed using two different robustness metrics (worst-case analysis and statistical study). In addition, two different robust design formulations were applied to robust multi-objective machine design problems.FindingsThe computational analyses show that material uncertainties may result in deviations of the machine performances and cause nominal solutions to become non-robust.Originality/valueIn this paper, the authors present stochastic models for the quantification of uncertainties in both ferromagnetic and permanent magnet materials. A robust multi-objective evolutionary algorithm is demonstrated and successfully applied to the robust design optimization of an IPM machine considering manufacturing errors and operational condition changes.