Interior Permanent Magnet Machine Research Articles

Numerical and Analytical Approaches to the Modeling of a Spoke Type IPM Machine With Enhanced Flux Weakening Capability

Interior permanent magnet (IPM) machines with spoke-type design are very attractive for several applications, including vehicle traction, which requires a good flux weakening performance to achieve high speed. For this purpose, a high demagnetizing current is usually injected to reduce the machine flux at high speed, with detrimental effect in terms of efficiency. This problem can be mitigated by equipping the rotor with a mechanical flux weakening device, which activates during high-speed operation by centrifugal force. This paper addresses the analytical modeling of this special kind of IPM motor through a simplified magnetic equivalent circuit (MEC) approach, which incorporates saturation and slotting effects as well as the flux weakening device operation. It is shown how the MEC model can effectively describe the IPM machine behavior despite its simplicity. Results are successfully validated by comparison both with finite element analysis, which requires much more computational resources, and with measurements from laboratory prototype testing.

Demagnetization Analysis of Interior Permanent Magnet Machines Under Integrated Charging Operation

Integrated battery charging (IBC)—multiplexing the motor windings as line inductors for charging electric vehicle battery packs—can improve the onboard charging capability without increasing the weight and cost. However, during the charging operation, currents flowing in the stator winding definitely generate a magnetic field, which may demagnetize the permanent magnets (PMs) in the PM traction motors. In this paper, the demagnetization effects of IBC current on magnets in interior PM machines are compressively investigated. In this paper, a recursive algorithm to update the PM magnetization states by using a parallelogram hysteresis model at different demagnetization levels is applied. The PM temperature is also considered for establishing this model. By coupling this algorithm to the finite element analysis, the demagnetization transit at different demagnetization levels can be assessed. By decomposing the flux density of each node within the magnets along its magnetization direction, irreversible demagnetization can be accurately evaluated. Impacts from both the pulsating and rotating demagnetization magnetic fields during the IBC operation are assessed and compared.

Six-Step Mode Control of IPMSM for Railway Vehicle Traction Eliminating the DC Offset in Input Current

In the six-step mode control of the interior permanent-magnet machine (IPMSM), inequality of the positive half-cycle length and the negative half-cycle length will bring about dc offset in the three-phase input current. This paper proposes a six-step mode control scheme of IPMSM for railway vehicle traction to eliminate the dc offset in input current. An approximately continuous rotor position signal is reconstructed in the field-programmable gate array chip. This position signal is used to generate the square drive signal for IPMSM in the flux-weaken region. Rotor position signal error of the resolver will also cause dc offset in the three-phase input current. A novel scheme using phase-locked loop to decrease the rotor position signal error is proposed. And using this scheme, the dc offset is eliminated from the three-phase input current. A seamless transition scheme from six-step mode control to space vector pulse width modulation (SVPWM) mode is proposed. The effectiveness of this six-step mode control scheme is proved by the experimental results.

Flux-Focusing Permanent Magnet Machines With Modular Consequent-Pole Rotor

In this paper, the modular consequent-pole (MCP) rotor is adopted in the fractional-slot interior permanent magnet (IPM) machine to utilize the strong flux-focusing effect and reduce the leakage flux. Hence, the torque density and utilization ratio of permanent magnet (PM) material can be improved. However, the unacceptable unbalanced magnetic force (UMF) may arise due to asymmetric airgap flux density produced by consequent-pole topology. Thus, a pole-shaping method based on three-sectional arcs is proposed to suppress it. Due to the relatively complex rotor structure, the multiobjective optimization combined finite-element method with genetic algorithm is performed in this paper. Furthermore, the electromagnetic performance of the IPM machine with MCP rotor (namely IPM-MCP machine), including the open-circuit airgap flux density, phase back EMF, torque, PM utilization ratio, efficiency, flux-weakening capability and UMF, are compared with the conventional surface-mounted PM (SPM), IPM, and consequent-pole IPM (IPM-CP) machines. It is demonstrated that the IPM-MCP machine obtains the largest output torque in these machines. Meanwhile, the IPM-MCP and IPM-CP machines respectively have >30% and >20% higher PM utilization ratio than the conventional SPM and IPM machines while they obtain similar torque ripple and efficiency. Moreover, the IPM-MCP machine can obtain much lower UMF than the IPM-CP machine due to the effective suppression of asymmetric airgap flux density. Finally, a 12-slot/10-pole IPM-MCP machine is fabricated to verify the analyses.

An Analytical Study on Iron Pole Shape Optimization in High-Speed Interior Permanent Magnet Machines

Interior permanent magnet (IPM) motors are of extensive interest in high-speed applications, where high efficiency, high power density and robustness for these motors are a challenge. However, the noise and vibration caused due to cogging torque, electromagnetic torque ripple and reluctance torque ripple can greatly affect the machine performance. The main contribution of this paper is to develop a hyperbolic form analytical expression for optimal rotor iron pole curve in IPM motors to mitigate pulsating torque components. The analytical method is based on the resolution of Laplace equation in air gap sub-domain in polar coordinate by using the sub-domain method. The proposed method is applied to the performance computation of a prototype IPM machine, i.e., a three-phase 18S-8P motor. The analytical results are validated through FEA method and experimental tests.

Magnetic Equivalent Circuit Model Considering the Overhang Structure of an Interior Permanent-Magnet Machine

Overhang is a useful structure for increasing the torque and power densities of permanent-magnet (PM) machines without expansion of the machine space. A 3-D finite-element method (FEM) is needed to evaluate the performances of PM machines with an overhang structure because the overhang structure results in non-uniform magnetic flux distributions in the axial direction. However, it is computationally expensive, especially in the early design stage. In this paper, we propose a magnetic equivalent circuit (MEC) model considering the overhang effects of interior PM (IPM) machines. With the proposed MEC, the performances of IPM machines with an overhang structure were precisely calculated and the computational time was significantly reduced. The proposed MEC was verified by the 3-D FEM.

Analysis of Current Signals in a Partially Demagnetized Vector Controlled Interior Permanent Magnet Generator

Abstract This manuscript analyzes the operation of an interior permanent magnet (IPM) machine working as a permanent magnet synchronous generator (PMSG). The partial demagnetization operation is analyzed. To obtain more accurate voltages and currents of the machine, finite element analysis (FEA) is used in co-simulation with the full converter and the converter’s control algorithm. Direct field oriented control (DFOC) shows robustness by maintaining the speed even with a 25% demagnetized PMSG. Also, an analysis of the rotating reference frame DQ signals is done to asses demagnetization.

Optimal design of rotor geometry in interior permanent magnet machine

Optimal design of rotor geometry in interior permanent magnet machine

A New Hybrid Method for Magnetic Field Calculation in IPMSM Accounting for Any Rotor Configuration

In this paper, a new hybrid model is proposed for the prediction of air gap magnetic field distribution (MFD) in interior permanent magnet machines with any rotor configuration. The slotless magnetic field is first predicted by finite-element method (FEM) with automatic scripting in MATLAB to consider saturation in the rotor iron. Afterward, the conformal mapping viz., Schwarz–Christoffel mapping is introduced to take the slotting effect into account. Consequently, the MFD could be calculated. The back electromagnetic forces, cogging torque, and output torque are obtained accordingly. Then a subdomain model is developed to consider the armature reaction. The results show that the proposed hybrid approach agrees well with the FEM. The model is further verified by experiments. The main contribution of this paper is to reduce the computation time remarkably while maintaining the calculation accuracy.

Inductance Testing for IPM Synchronous Machines According to the New IEEE Std 1812 and Typical Laboratory Practices

Equivalent circuit parameters serve as the basis for performance estimation and implementation of power electronic drives controls and therefore their accurate evaluation is very important. Specified in the newly approved IEEE Std 1812, a short-circuit test can be employed, in combination with an open-circuit measurement, in order to determine the back emf and the synchronous inductance. In the case of interior permanent magnet (IPM) machines, this approach can be used only to determine the d -axis inductance and additional and separate measurements are required for the q -axis inductance. In this respect, various methods, inclusive of dc step response tests, on-load tests, and a widely used test in industry, which involves locked-rotor measurements at variable voltage and constant frequency supply, are studied in detail, based on two-dimensional finite element analysis. Locked-rotor methods based on dc current supply and static torque versus rotor position measurements are introduced for determining the q -axis inductance in combination with the standardized open-circuit and short-circuit tests. A critical study of the inductances determined from different tests is conducted, and experimental results on an IPM motor design with non-sinusoidal back emf, relatively high torque ripple, and low leakage are presented.

Influence of stator and rotor geometric parameters on rotor bar current waveform and performance of IMs

In this study, the influence of the stator and rotor geometric parameters on the rotor bar current waveform and performance characteristics of a squirrel-cage induction machine (IM), based on a slot/pole number combination (48-stator slot/8-pole/52-rotor slot), with the same winding layout, stator outer diameter, stack length, stator current, and rated speed as the Toyota Prius 2010 interior permanent magnet machine, is investigated. In order to reveal the individual influence of each parameter, parametric analyses have been conducted for each geometric parameter, and the corresponding variations of torque, torque ripple, power losses, and efficiency are numerically studied. It has been shown that in addition to rotor slot width, rotor slot depth, and stator slot width, corresponding to rotor tooth width, rotor tooth height, and stator tooth width, respectively, have a significant effect on the bar current waveform and performance characteristics while the slot opening widths have the least effect.

Phase voltage distortion of IPM and SPM machines with distributed windings in field weakening region

This study investigates the field-weakening capability of interior permanent magnet (IPM) and surface-mounted permanent magnet (SPM) machines with distributed windings by considering phase voltage distortion in field-weakening region. For analysis and comparison, the Nissan Leaf vehicle traction machine is studied as a reference benchmark machine and then a comparable SPM machine is designed within the main constraints of the benchmark machine. A finite element analysis model of the benchmark machine is developed and validated by published experimental measurement. Sinusoidal phase current is desired to enhance machine torque performance and power electronic converters employing vector control method are commonly used for traction machine supply. However, the machine terminal phase voltage distortion may introduce additional difficulties for machine control. Therefore, firstly, phase voltage distortions of IPM and SPM machines with distributed windings are compared and the mechanisms are discussed. Due to the voltage distortion, the peak value of phase voltage may be higher than the fundamental one. Therefore, the influences of IPM and SPM topologies on machine traction characteristics are investigated. The study indicates that SPM machines with distributed windings can be designed to achieve comparable torque and power performance and better field-weakening capability compared to IPM machines.

Rapid sizing concept of interior permanent magnet machine for traction applications

This study presents a rapid sizing technique for interior permanent magnet (IPM) machine in traction application considering saturation effects. It is demonstrated that with limited computing resources, sizing, parameters considering saturation effects, and efficiency maps (loss maps) of an IPM machine can be generated within seconds with acceptable accuracy in comparison with finite element study and measurements. Thus, the proposed rapid sizing method is highly essential at the preliminary design stage of electric vehicle powertrains.

Improvement torque performances of interior permanent-magnet machines

Due to their excellent efficiency, power density and constant power speed region, interior permanent-magnet (IPM) machines are very suitable for electric vehicles (EVs). This paper proposed a new IPM rotor topology, which can offer high reluctance torque, wide constant power speed range and excellent overload capability. Besides, five rotor topologies with integral-slot distributed-windings IPM machines, including four existing IPM topologies and the proposed IPM topology, are designed optimally. Their characteristics, which include d-q axis inductances, saliency ratios, electromagnetic torques, corresponding torque ripples, back-electromotive forces (EMFs), overload capabilities and flux weakening performances are evaluated quantitatively. Finally, a three phase 48s8p hybrid rotor PM machine is built to verify the performances of the proposed IPM machine. This work provides some general concepts for machine developers who are willing to build IPM machines for high-performance EV applications.

Fast and Accurate Model of Interior Permanent-Magnet Machine for Dynamic Characterization

A high-fidelity two-axis model of an interior permanent-magnet synchronous machine (IPM) presents a convenient way for the characterization and validation of motor dynamic performance during the design stage. In order to consider a nonlinear IPM nature, the model is parameterized with a standard dataset calculated beforehand by finite-element analysis. From two possible model implementations, the current model (CM) seems to be preferable to the flux-linkage model (FLM). A particular reason for this state of affairs is the rather complex and time-demanding parameterization of FLM in comparison with CM. For this reason, a procedure for the fast and reliable parameterization of FLM is presented. The proposed procedure is significantly faster than comparable methods, hence providing considerable improvement in terms of computational time. Additionally, the execution time of FLM was demonstrated to be up to 20% shorter in comparison to CM. Therefore, the FLM should be used in computationally intensive simulation scenarios that have a significant number of iterations, or excessive real-time time span.

A Novel Magnet-Axis-Shifted Hybrid Permanent Magnet Machine for Electric Vehicle Applications

This paper proposes a novel magnet-axis-shifted hybrid permanent magnet (MAS-HPM) machine, which features an asymmetrical magnet arrangement, i.e., low-cost ferrite and high-performance NdFeB magnets, are placed in the two sides of a “▽”-shaped rotor pole. The proposed magnet-axis-shift (MAS) effect can effectively reduce the difference between the optimum current angles for maximizing permanent magnet (PM) and reluctance torques, and hence the torque capability of the machine can be further improved. The topology and operating principle of the proposed MAS-HPM machine are introduced and are compared with the BMW i3 interior permanent magnet (IPM) machine as a benchmark. The electromagnetic characteristics of the two machines are investigated and compared by finite element analysis (FEA), which confirms the effectiveness of the proposed MAS design concept for torque improvement.

Separation and comparison of average torque in five‐phase IPM machines with distributed and fractional slot concentrated windings

This study proposes a method to separate average permanent magnet (PM) torque and average reluctance torque of five-phase interior permanent magnet (IPM) machine based on transient finite element method (FEM). The key of this method is to count total torque as four torque components by considering the saturation and cross-magnetisation between d – q axes, and every torque components are calculated from d–q axes parameters directly. The parameters in d–q axes reference frame are transformed from ABCDE reference frame via five-phase Park transformation. Comparing with the existing methods, the proposed method maintains the same accuracy while time saving because d–q axes parameters can be obtained directly by one-time FEM simulation. Meanwhile, the proposed method is adopted to separate the PM torque and reluctance torque from two five-phase IPM machines with fractional-slot concentrated winding (FSCW) and integral-slot distributed winding (ISDW). Finally, the FEM and experimental results show that the IPM machine with FSCW produces lower reluctance torque ratio than that of IPM machine with ISDW. Besides, the results demonstrate that the flux-weakening performance connects with characteristic current (Ψ PM d / Ldd ) strongly.

Electromagnetic Performance Comparison of Multi-Layered Interior Permanent Magnet Machines for EV Traction Applications

Electromagnetic performance of three multi-layered interior permanent magnet (IPM) machines are investigated and compared for electric vehicle applications in this paper. The rotor structure, air-gap field distribution, torque density, torque ripple, core loss, magnet eddy-current loss, and output power are studied with finite-element analysis. It is demonstrated that the two-layered rotor structure with magnets buried deeply has the lower torque density and magnet eddy-current loss due to the utilization of magnets and the block effects of the armature-reaction flux is lower. The three-layered IPM machine has the lower torque ripple and core loss than two-layered IPM machines because the harmonics of air-gap density are reduce by the increase of magnet layers. Finally, an IPM machine with three-layered magnets rotor is prototyped to verify the analysis.

An Investigation Into the Effect of PM Arrangements on PMa-SynRM Performance

The paper aims to provide a guideline for rotor design of permanent magnet (PM) assisted synchronous reluctance machine (PMa-SynRM). Unlike interior PM machines, the PMa-SynRM is essentially an SynRM with dominant reluctance torque. The PMa-SynRM is often designed by directly embedding magnets into an SynRM rotor to improve the performance. However, how the PMs can be arranged in the rotor to enhance motor performance has not been fully discussed. This paper investigates the influence of several key factors concerning the PM arrangements, including number of PM layers, inserted positions, and PM sizes. The torque, flux linkages, power factor, and motor performance are comprehensively evaluated. Based on the analysis, a brief guideline is suggested for PMa-SynRM rotor design. Finite element analysis is used for evaluation and experiments are conducted to validate the analysis.

Reduction of Stator Core Loss in Interior PM Machines for Electric Vehicle Applications

Stator core loss of four interior permanent magnet (IPM) machines is studied for electric vehicle applications in this paper. The no-load air-gap density, core loss density, core loss harmonics, and the segregation of hysteresis and eddy current losses are investigated with finite-element analysis. The results show that the rotor surface shaping of a single-layered IPM machine and increasing the rotor magnet layers can reduce the stator core loss due to the harmonics of the rotor magnetomotive force. The stator core loss reduction effectiveness of rotor surface shaping is similar to a two-layered magnet configuration, but the reduction effectiveness is less than that the magnet layers increased to three numbers. An IPM machine with three-layered magnets rotor is prototyped to verify the analysis.