Multiplanar Eddy Current Analysis of Interior Permanent Magnets in Synchronous Machines

Purpose – The purpose of this paper is to investigate torque ripple and magnetic force on the teeth in interior permanent magnet (IPM) machines over a wide range of speed operation for electrical power steering (EPS) applications. Design/methodology/approach – The flux-weakening capability of IPM machines has been analysed by finite element method considering the effect of cross-coupling between d- and q-axis current. The traditional method of analysing torque ripple is based on constant torque and flux-weakening region. However, the cross-coupling need to be considered when applying this technique to flux-weakening region. Meanwhile, the torque ripple with current amplitude and angle and with different speed in the flux-weakening region is also investigated. In addition, the magnetic force on the teeth due to the separated teeth with stator yoke is also investigated during the constant torque and flux-weakening region. Findings – The torque ripple and magnetic force on teeth in IPM machine are dependent on current and current angle. Both the lowest torque ripple and magnetic force on teeth exist over the whole torque-speed region. Research limitations/implications – The purely sinusoidal currents are applied in this analysis and the effects of harmonics in the current on torque ripple and magnetic force on teeth are not considered in this application. The 12-slot/10-pole IPM machine has been employed in this analysis, but this work can be continued to investigate different slot/pole number combinations. Originality/value – This paper has analysed the torque ripple and magnetic force on the teeth in IPM machines for EPS application over a wide range of operation speed, which are the main cause of vibration and acoustic noise. The variation of torque ripple with current amplitude and angle as well as speed in the flux-weakening region is also investigated. In addition, the magnetic force on the teeth is also investigated over the whole torque-speed region.

Performances of a dual three phase ferrite magnet assisted synchronous reluctance machine under different winding and inverter faults are investigated. The performances during fault are also compared with a rare earth based around the tooth wound interior permanent magnet (IPM) machine. A 30-slot/4-pole machine is investigated to present the performances under faults, whereas a 12-slot/8-pole machine is considered as an example of rare earth based IPM machine. It is shown that the permanent magnet assisted machine becomes unbalanced irrespective of the fault. The output torque under faults is substantially lower than the IPM machine even though the IPM machine may have higher braking torque. The performances are presented using 2D finite element analysis (FEA), and later, the simulation results are validated with experimental results.

This paper proposes an alternative interior permanent magnet machine (IPMM) design in which the rotor consists of stacks varied in the axial direction. The proposed design aims to reduce the amount of permanent magnet (PM) materials in conventional IPMMs. The PM width and the PM pole arc on the rotor surface for each rotor stack are both optimized to provide a resultant PM flux distribution in the air gap that contains fewer harmonics. Not only is the pulsating torque reduced significantly, the PM materials are also minimized since the PM portion making up the spatial PM flux harmonics is effectively removed. The results of the proposed design concept indicate a significant torque pulsation reduction in comparison with the base-line model 2007 Camry motor. Moreover, a trade-off is discovered between the average torque production and the PM utilization in an IPMM. The improvement made in the proposed designs proves that the PM materials can be used efficiently and the torque pulsation can be further minimized in IPMM designs.

In traction application of hybrid vehicles, a wide constant power speed range is a necessity for efficient utilization of the power source. Due to its higher efficiency and torque/size ratio, the interior permanent magnet (IPM) machine is gaining popularity in many automotive applications including traction. However, most of the commercially manufactured IPM machines have a limited constant power range. In this paper, a segmented magnet IPM machine has been analysed for its suitability in traction application. This type of machine can offer very wide constant power speed range. The performance of the proposed machine is compared with a prototype IPM machine built in the University of New South Wales (in 1997) and an IPM machine commonly available in market from Kollmorgen.

The magnet eddy current of multi-layered interior permanent magnet (IPM) machines is studied in the paper for the aircraft electric green taxiing systems. The armature reaction flux density distribution, eddy current density and harmonic spectrum at the end of permanent magnet are analysed. A method to reduce the magnet eddy current of multi-layered IPM machines is presented. That is to increase the distance between outer permanent magnet and rotor surface and the distance between two layers of permanent magnet so as to provide a larger core path for armature reactive flux. This method can effectively reduce the magnet eddy-current loss of the multi-layered IPM machines and improve the operation efficiency.

– The paper presents a systematic comparison of four topologies of the interior permanent magnet machine (IPMM) designed for low speed applications. This comparative study investigates the suitability of the concentrated winding and distributed winding in the stator and the flat-shaped or V-shaped magnets in the rotor poles. The paper also studies the inductance characteristics of the designs using finite element analysis. Various steps taken to minimize the cogging torque and torque ripple in the studied machines were also discussed in details. Keywords : AC standstill saliency test, Cogging torque, Concentrated winding, Distributed winding, Direct-drive, Interior Permanent Magnet Machine, PM machine, Torque ripple 1. Introduction I n direct drive wind turbine systems, intermediate gear boxes are eliminated to increase the efficiency and reliability of the whole system, as well as reducing maintenances down-time. The generator used in such systems needs to have a low rated speed. This demand for an increase in the number of pole pairs of the generator. A review done in [1], [2] on direct-drive wind turbines suggests that permanent magnet (PM) machines are the most favorable for direct-drive wind turbine. While the most common type of PM machines used in the wind industry is the radial flux surface mounted magnet (SPM) type, an interior PM synchronous machine (IPMSM) offers a number of advantages over the SPM type. The most commonly cited advantages are: the presence of reluctance torque ( ) as shown in (1) in an IPM machine is beneficial in achieving a higher torque with lower magnet volumes and IPMSM has a mechanically and magnetically robust rotor. It should be noted that the presence of saliency in the IPSM results in the reluctance torque and also contributes toward the constant power speed range. A recent study carried out in [3] found that the use of an IPM machine in a small scale direct drive wind turbine can provide quicker return of investment compared to a SPM machine, especially in sites where average wind speed is low. According to [3] the return of investment can be achieved by taking advantage of provision for a constant power speed range available in IPMMs. But cogging torque in an IPMM is generally greater compared to a SPM machine due to the greater variation of reluctance between the stator and rotor [4]. This makes reduction of the cogging torque crucial in a low speed IPM machines [5]. The IPMSM with radially magnetized V-shaped (V-S) magnets has a better flux concentration and higher saliency ratio than its counter-part flat-shaped (F-S) magnet designs which makes it more attractive for traction drives [6]. The torque components of an IPM machine is (1) where, = magnet alignment torque, = cogging torque, and reluctance torque. The majority of IPM machines are designed with distributed windings (DW). Recently, the concentrated winding (CW) for the IPMSM is getting attention from the research community due to its high slot-fill factor, high tolerance to phase fault, simplified manufacturing process, non-overlapping coils resulting in shorter end-windings and reduced copper usage. In spite of having these advantages, the CW was not widely used in the past due to its characteristics in producing EMF and MMF waveforms with unacceptably high total harmonic distortion. However, in recent years, it has been shown that through appropriate choice of slot and pole combinations [7], the CW stator has the ability to produce sinusoidal EMF waveform with high a winding factor, and smooth average torque. In this paper, four design topologies of IPMSM were considered for investigation which includes (a) conventional distributed winding in the stator and flat-shaped IPM structure in the rotor( DW FS-IPMM), (b) distributed winding in the stator and V-shaped IPM structure in the rotor (DW VS-IPMM), (c) concentrated winding in the stator and flat-shaped IPM structure in the rotor (CW FS-IPMM), (d) concentrated winding in the stator and V-shaped IPM structure in the rotor(CW VS-IPMM). Fig. 1 shows the cross-section of the four topologies and no-load flux distribution. The objective of this paper is to present a detailed comparison of the major performance characteristics of all the four topologies illustrated in Fig.1. The selection process of the major dimensions and winding structure of the proposed IPMM is described in Section 2. Section 3 presents the cogging torque and torque ripple minimization of all the four investigated designs.

Influence of two- and three-dimensional simulations on bubble behavior in gas–solid fluidized beds with and without immersed horizontal tubes

In spite of the importance of a detailed description of the filamentary current constriction of the IGBT during the turn-off operation that could lead to the device’s failure, there are to date no quantitative 3D simulation results of the filament growth and dynamic that can be compared with experimental results. In this paper we present 3D numerical simulations on the failure mode in the Unclamped Inductance Switching (UIS) test operation, extended to the full device area, which will be usefully compared with detailed experimental results on a large number of trench IGBT test samples. For the first time extended 3D dynamic electrothermal simulations of the whole die are made, to take into account both the electric and thermal effects of the filamentary conduction in avalanche mode. The onset of a filament growth condition for a current level just above the turnover voltage evaluated by the 3D simulations, and the area of the filament, obtained for the first time, are well in agreement with the quantitative data extracted by the experimental evaluations. Moreover, the thermal heating due to the filament formation is found to be quite independent from the current level, because it depends on the current density in the filament, rather than on the injected current. The delay time between the filament formation and the final failure time seen in the experimental results is verified to be due to the movement of the filament all around the chip surface in search of a cooler spot. The movement of the filament along the whole die area is verified for the first time by full area 3D electrothermal dynamic simulations, with times in agreement with the experimental delay between filament formation and final failure seen in all the failure reports.

There have been remarkable advances in semiconductor industry but the miniaturization of magnetic devices is progressed very slowly. So many studies are carried out overcoming the gap. To develop small size devices, proper design and property simulation of the devices are requested to spare the efforts before fabrication processes. However, there is a few of simulation studies have been reported. In this work, we fabricated thin film toroidal inductors using permalloy as a core material and measured the properties to estimate 2D and 3D simulation in the magnetic devices. The 3D simulation shows more agreeable results than the 2D simulation. On the other hand, when we changed core materials, the inductor using Fe-Hf-C-N nanocrystalline alloys as core material shows the better properties than using permalloy and Fe-Zr-C-N alloys.

We used ultrasonic shear waves for nondestructive defect detection in a billet using transmitted waves. We utilized the deviation the time-of-flight (TOF) obtained by cross-correlation of transmitted waves of a defect-free reference plane and that of a measurement plane containing a defect. We compared the performance of longitudinal waves and shear waves at different wavelengths in detecting the diameter of a circular defect in two-dimensional (2D) simulation and the TOF for a cylindrical defect while changing the vibration direction of shear waves in three-dimensional (3D) simulation. Shear waves detected defects better than longitudinal waves in the 2D simulation, especially at wavelengths of 1.4–2.4 mm. In the 3D simulation, the maximum TOF was larger when the vibration direction was perpendicular to the defect’s major axis than when it was parallel in the measurement using shear waves. This suggests a defect’s shape can be estimated by measurement using shear waves.

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.

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.

This paper investigates the challenges of including saliency ratio as an objective function in the design optimization of interior permanent magnet (IPM) machines. The saliency ratio is the ratio between q- and d-axis inductances. Improvement of the reluctance torque component and self-sensing capabilities are directly related to the saliency ratio of the IPM machine. Thus, the maximization of the saliency ratio could be a design objective in the multi-objective design optimization process. The paper shows that assumptions made in conventional methods reduce the accuracy of estimated inductances which deviate the optimization process to a local optimum design. On the other hand, improved accuracy in the method to determine the IPM machine's inductances significantly increases the computational costs in the design optimization process. Motivated by the above challenges, this paper proposes a method to estimate the saliency ratio using magnetic energy in the design optimization of IPM machines. The energy method simultaneously increases the accuracy of inductance calculation and decreases the computational costs. The method considers the saturation of iron cores, cross-magnetization effects and the variation of inductances with respect to rotor positions. A procedure to implement the energy method in a multi-objective optimization algorithm is presented. The saliency ratio optimization using the conventional and the energy method are compared to the experimentally measured values to demonstrate the effectiveness of the proposed approach. A fractional-slot concentrated-wound (FSCW) IPM machine was considered for this study.

The interior permanent magnet (IPM) machine is considered to be the one of the most efficient electrical machine. The high efficiency along with good performance characteristic makes them suitable for drive with wide speed range. The conventional IPM machine has almost nil or very little field weakening range. Many attempts have been made to improve the range by modification of rotor configuration. In this paper, different types of rotor configuration of IPM machine that is suitable for flux weakening operation has been reviewed. A new rotor design of segmented magnet has been studied by finite element (FE) analysis. The result of FE model of segmented magnet rotor and a conventional rotor of IPM machine has been compared and discussed. In the new design an improved flux weakening aspect has been noticed. Since the new design does not need any special construction effort, it could be a better solution for IPM rotor configuration suitable for field weakening operation.

The cogging torque is usually very sensitive to the manufacturing tolerances during machine mass production, and this paper investigates the different sensitivities between interior permanent magnet (IPM) machines with different slot/pole number combinations. Exemplified by two typical combinations, i.e., 12-slot/8-pole and 12-slot/10-pole designs, the fundamental performance is first analyzed under ideal conditions. Then, with the tolerances of permanent magnet diversity and tooth bulges considered, the most sensitive cases are identified for the two machines, based on which the ultimate values of additional cogging torques are obtained and compared. In order to verify the different sensitivities, the field spatial harmonics in the two machines with and without considering the tolerances are further analyzed, from which the different origins of additional cogging torque components can be obtained. Finally, the IPM prototypes with and without amplified tolerances are fabricated and tested to verify the analyses.