High Slot Fill Factor Research Articles

Analysis and Optimization of the Winding Loss of Flat-Wire Motors

The flat-wire motor has the characteristics of small size, low noise, high slot fill factor and good thermal conductivity in the slot. It can significantly improve the power density of the motor and is widely used in electric vehicles. The skin effect and proximity effect of the flat wire under high-speed conditions lead to high loss. Based on the established finite element model of a two-dimensional flat-wire motor, this paper first studies the high-frequency loss of different winding layers and the conductor sizes of each layer. Secondly, the influence of the magnetic field on AC loss is reduced by optimizing the tooth-tip height and tooth-tip width. Finally, it is verified that the high-frequency loss is reduced by 16% with the optimized layers, conductor sizes and tooth-tip sizes under the drive condition of the CLTC-P (China Light-duty Test Cycle—Passenger).

Comparative Study of High-speed Permanent Magnet Synchronous Motors with In-line Slot Conductors and Equidirectional Toroidal Windings

The high-speed permanent magnet synchronous motor (HSPMSM) plays an important role in a wide range of engineering fields due to its high power density, high efficiency, and light weight. In this paper, a HSPMSM equipped with in-line slot conductors(I-LSC) is proposed and compared with one equipped with equidirectional toroidal winding (ETW). Firstly, the differences between them are revealed, including topology, back-electromotive force (EMF), slot fill factor, copper loss, and torque. Secondly, two-dimensional finite element method (2D-FEM) tools are used to obtain more precise performance such as air-gap field, back-EMF, torque characteristics, efficiency maps, and the unbalanced magnetic force (UMF). Considering the end-windings of copper loss of ETW and the end ring copper loss of I-LSC, the losses and efficiency of two motors are simulated by three-dimensional finite element method (3D-FEM). Finally, the simulation results validate the feasibility of the newly proposed winding and indicate that in-line slot conductors have superiority in power density due to the high slot fill factor.

Asymmetric Winding Structure for Concentrated Winding Permanent Magnet Motors to Achieve a Low Torque Ripple and High Slot Fill Factor

Asymmetric Winding Structure for Concentrated Winding Permanent Magnet Motors to Achieve a Low Torque Ripple and High Slot Fill Factor

AC Loss Analysis and Measurement of a Hybrid Transposed Hairpin Winding for EV Traction Machines

To address the problem of high-frequency AC loss of hairpin winding, a hybrid transposed hairpin winding (HTHW) scheme, which combines flat wire and litz wire, is proposed. The HTHW can effectively reduce the high-frequency AC loss, while maintaining a relatively high slot fill factor. In this paper, the AC loss generation mechanism under high-frequency excitation is firstly analyzed. Then, based on the field-circuit-coupled finite element method, the current density distribution and AC loss of hairpin winding with different transposed topologies are calculated and compared. Finally, an experimental platform enabling direct measurement of hairpin winding loss is built to verify the simulation. The simulation and experimental results show that the AC loss of the proposed HTHW is much lower than that of the traditional hairpin winding, for medium to high running frequency. In our case, the AC and DC resistance ratio of the presented HTHW is 2.12 at the frequency of 1200 Hz, contrasting that of the ratio of traditional hairpin winding, which is 10.2.

Asymmetric Winding Structure for Concentrated Winding Permanent Magnet Motors to Achieve a Low Torque Ripple and High Slot Fill Factor

Asymmetric Winding Structure for Concentrated Winding Permanent Magnet Motors to Achieve a Low Torque Ripple and High Slot Fill Factor

A Multi-Objective Design Optimization for a Permanent Magnet Synchronous Machine with Hairpin Winding Intended for Transport Applications

Nowadays, interest in electric propulsion is increasing due to the need to decarbonize society. Electric drives and their components play a key role in this electrification trend. The electrical machine, in particular, is seeing an ever-increasing development and extensive research is currently being dedicated to the improvement of its efficiency and torque/power density. Among the winding methods, hairpin technologies are gaining extensive attention due to their inherently high slot fill factor, good heat dissipation, strong rigidity, and short end-winding length. These features make hairpin windings a potential candidate for some traction applications which require high power and/or torque densities. However, they also have some drawbacks, such as high losses at high frequency operations due to skin and proximity effects. In this paper, a multi-objective design optimization is proposed aiming to provide a fast and useful tool to enhance the exploitation of the hairpin technology in electrical machines. Efficiency and volume power density are considered as main design objectives. Analytical and finite element evaluations are performed to support the proposed methodology.

Evaluation and loss estimation of a high-speed permanent magnet synchronous machine with hairpin windings for high-volume fuel cell applications

High-speed machines offer several advantages, such as small sizes, avoidance of mechanical gears, and low maintenance, which has led to considerable research dedicated to them in the past decade. In recent times, rectangular wire windings with a hairpin structure have gained prominence in traction motors in the electromobility sector due to their high slot fill factor, simple production, and good thermal properties. Taking these advantages into consideration, this paper analyzes the possibility of using a high-speed permanent magnet synchronous machine (PMSM) with hairpin windings as an electric turbo compressor in fuel cell applications and outlines the critical design aspects.

Performance Analysis of Brushless Motors with Segmented Cores considering Manufacturing Constraints

Brushless servomotors are widely used in industry and in all domains that require precise and easy position/speed/torque control. To further improve the performance of these motors, the segmentation of the stator core is taken into account. This approach to core construction provides a high slot fill factor, compact design, and efficient use of materials. This paper aims to present that the manufacturing constraints and tolerances of this particular core construction can increase unwanted effects in brushless motors, like cogging torque, torque ripple and their influence regarding the back-EMF. Two models for a 12slots-10 pole configuration, one with segmented core and one with standard laminated core are compared and analysed using the FEA (Finite Element Analysis) method. The influence of the additional air gaps that occur in such constructions is investigated to provide an overview for the design of segmented motors. Various lengths for air gaps between the segments of the core are taken into consideration and non-uniform distribution of such gaps. The paper also provides further steps that must be taken in order to verify/validate the studied model’s impact on motor design.

High Efficiency PMSM With High Slot Fill Factor Coil for Heavy-Duty EV Traction Considering AC Resistance

Electric vehicle (EV) systems require a high energy-efficiency traction motor so that the motors for EV traction should achieve high efficiency and power density. Hence, a permanent magnet synchronous motor (PMSM) for EV traction using a maximum slot occupation (MSO) coil has been investigated in this study. By applying the MSO coil, high torque density was achieved, but an additional loss, which decreases the efficiency, was incurred through alternating current (AC) resistance. To reduce the AC resistance of the MSO coil, the following process was performed: First, by investigation using the analytical method, pole/slot numbers, current density and number of parallel circuits affecting the frequency, the shape and number of conductors were chosen as important variables. Resistances of the MSO coil with a stator core were analyzed according to the chosen variables above. From the results, MSO coil applied PMSM with proper pole/slot numbers, current density, and parallel circuits was determined to improve the efficiencies at the base and maximum speeds. To accurately estimate the efficiency of the determined model, loss evaluation methods were explained. Subsequently, the determined MSO coil applied model was compared with the conventional model having round wires, and the improvements were verified by load testing.

Comparative Thermal Analysis of IPMSMs With Integral-Slot Distributed-Winding (ISDW) and Fractional-Slot Concentrated-Winding (FSCW) for Electric Vehicle Application

Fractional-slot concentrated-winding (FSCW) interior permanent magnet synchronous motors (IPMSMs) have been attracting considerable attention due to their high power density, high efficiency, short end winding, high slot fill factor, low cogging torque, excellent flux-weakening, and fault tolerance capability. However, compared to integral-slot distributed-winding (ISDW) IPMSMs, the key challenge of using FSCW configurations is the significant rotor losses, particularly at high speed. To figure out the IPMSM with which winding configuration is more suitable for electric vehicle (EV) application, the thermal behaviors of four IPMSMs with ISDW, single-, double-, and four-layer FSCWs are comprehensively and comparatively investigated in this paper. First, electromagnetic design and loss analysis of the four IPMSMs are investigated to meet the EV traction motor requirements. Second, finite-element method is employed to investigate the thermal performance of the IPMSMs under different rotational speeds and torque overload capacities. Thirdly, experiments implemented on an ISDW prototype are carried out to validate the presented analysis method. Finally, some conclusions are drawn for a suitable winding configuration selection and the PM traction motor design.

Overview of the rectangular wire windings AC electrical machine

The rectangular wire winding AC electrical machine has drawn extensive attention due to their high slot fill factor, good heat dissipation, strong rigidity and short end-windings, which can be potential candidates for some traction application so as to enhance torque density, improve efficiency, decrease vibration and weaken noise, etc. In this paper, based on the complex process craft and the electromagnetic performance, a comprehensive and systematical overview on the rectangular wire windings AC electrical machine is introduced. According to the process craft, the different type of the rectangular wire windings, the different inserting direction of the rectangular wire windings and the insulation structure have been compared and analyzed. Furthermore, the detailed rectangular wire windings connection is researched and the general design guideline has been concluded. Especially, the performance of rectangular wire windings AC machine has been presented, with emphasis on the measure of improving the bigger AC copper losses at the high speed condition due to the distinguished proximity and skin effects. Finally, the future trend of the rectangular wire windings AC electrical machine is prospected.

Flux Modulation Principles of DC-Biased Sinusoidal Current Vernier Reluctance Machines

DC-biased sinusoidal current vernier reluctance machines (dc-biased VRMs) have a doubly salient structure, and their phase currents contain an alternating current (ac) component and a direct current (dc) component. Hence, their main features are one set of concentrated windings compared with variable flux reluctance machines, low vibration and noise due to smooth current, compared with switched reluctance machines, and robust rotor structure. Besides, its achievable high slot fill factor can improve the torque density further. In this paper, based on the flux modulation principles, the torque production mechanism of dc-biased VRMs is analyzed, and two slot combinations of 12/8 and 12/10 are proposed. First, the machine topology and inverter main circuit are illustrated. Second, the torque production mechanism is explained. Furthermore, the inductance characteristic, optimal current configuration for maximum torque and lowest torque ripple are analyzed theoretically and by the finite-element analysis. Finally, one prototype was designed and built, and the proposed analysis is validated by the experimental results.

Solar Plane Propulsion Motors With Precompressed Aluminum Stator Windings

This paper reports a propulsion motor for a solar-powered aircraft. The motor uses precompressed aluminum stator windings, with a fill factor of greater than 75%, in a permanent magnet synchronous machine. The motor performance is compared empirically to an identical machine with conventionally wound copper windings. It is shown that there are many advantages to using compressed aluminum windings in terms of weight reduction, thermal improvement, and lower cost, for the same loss and electromagnetic performance, provided a sufficiently high slot fill factor can be achieved. The design and manufacture of the compressed coils is also discussed. A modular stator arrangement is used, in the form of a solid coreback with keyed teeth to allow easy assembly of the compressed windings. It is noted that the electromagnetic performance of the machine is unaffected by the modular nature of the magnetic core. Two prototype motors, one wound with conventional copper and the other with precompressed aluminum windings, are constructed and tested.

Study of Multiphase Superconducting Wind Generators With Fractional-Slot Concentrated Windings

Superconducting (SC) generator offers a promising candidate for offshore direct-drive wind generators with power of 10 MW or higher. Since copper losses commonly dominate in the SC direct-drive wind generators with SC field windings and copper armature windings, an important way to increase the generator efficiency is to improve the armature winding design. Compared to traditional overlapping windings, fractional-slot concentrated windings (FSCW) have shorter end connection and higher slot fill factor, which has a great contribution to copper loss reduction. However, high content of magnetic motive force (MMF) harmonics is a big challenge for applying FSCW in SC generators. The asynchronous MMF harmonics may cause high eddy-current losses in the rotor assembly, resulting in efficiency reduction and more refrigeration burden. A novel multiphase FSCW with fewer MMF harmonics for SC generators is presented in this paper, followed by an MMF harmonic analysis through winding function method. Comparison with three-phase and traditional dual three-phase FSCW is performed. Characteristics of the generators are compared, in terms of back electromotive-force, electromagnetic torque, and rotor eddy-current losses by using finite element analysis. The advantages of the proposed FSCW are verified. Further, it is observed that the alternating components of the flux density at SC coil area is attenuated significantly by the proposed topology, indicating that the AC losses of the SC coils may be substantially reduced. The feasibility of applying FSCW topology in the design of SC wind generator is enhanced through the study.

Preliminary Design Analysis of Low Speed Interior Permanent Magnet Machine with Distributed and Concentrated Windings

Abstract – 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.

Novel Motor that Has a High Winding Factor and a High Slot Fill Factor

Novel Motor that Has a High Winding Factor and a High Slot Fill Factor

Rotor End Losses in Multiphase Fractional-Slot Concentrated-Winding Permanent Magnet Synchronous Machines

Fractional-slot concentrated windings (FSCW) have been gaining a lot of interest in permanent magnet (PM) synchronous machines. This is due to the advantages they provide including shorter nonoverlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power versus speed range, and fault tolerance. This paper focuses on eddy-current losses in the rotor clamping rings. Additionally, the loss in the nonmagnetic shaft with the option of i) metallic, ii) nonmetallic, and iii) metallic with shielding laminations clamping rings is analyzed. The study is based on finite element analysis (FEA). Desirable slot/pole combinations for different number of phases with both single- and double-layer windings are investigated. Experimental results for a three-phase 12 slot/10 pole design are presented to confirm that the losses in the rotor clamping rings can be very significant in case of FSCW machines and should not be overlooked during the design phase.

End Effects in Multiphase Fractional Slot Concentrated-Winding Surface Permanent Magnet Synchronous Machines

Fractional-slot concentrated windings have been gaining a lot of interest in permanent magnet synchronous machines. This is due to the advantages they provide, including shorter nonoverlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power versus speed range, and fault tolerance. This paper investigates the end effects in this type of machines. The study focuses on eddy-current losses in the frame, end shields, and clamping rings (magnetic/nonmagnetic). Desirable slot/pole combinations for different number of phases are investigated including both the single- and the double-layer windings. Suggestions for clearances between end windings and the support structure are given.

Fractional-Slot Concentrated-Windings Synchronous Permanent Magnet Machines: Opportunities and Challenges

Fractional-slot concentrated-winding (FSCW) synchronous permanent magnet (PM) machines have been gaining interest over the last few years. This is mainly due to the several advantages that this type of windings provides. These include high-power density, high efficiency, short end turns, high slot fill factor particularly when coupled with segmented stator structures, low cogging torque, flux-weakening capability, and fault tolerance. This paper is going to provide a thorough analysis of FSCW synchronous PM machines in terms of opportunities and challenges. This paper will cover the theory and design of FSCW synchronous PM machines, achieving high-power density, flux-weakening capability, comparison of single- versus double-layer windings, fault-tolerance rotor losses, parasitic effects, comparison of interior versus surface PM machines, and various types of machines. This paper will also provide a summary of the commercial applications that involve FSCW synchronous PM machines.

A new two-phase homopolar switched reluctance motor for electric vehicle applications

This paper presents a novel 2-phase homopolar switched reluctance motor (SRM), whose design successfully avoids dead-zone problems that afflict low cost 1- and/or 2-phase SRMs. Unlike conventional radial-winding-radial-gap motors, the proposed SRM has an interior stator that is of the pancake type with axial winding. Such a design allows for a high slot-fill factor and is suitable for implementation as a flat pancake-shaped stator. An efficient, compact prototype was produced with TMS320F240 DSP driving control unit. Experimental results indicate that the present SRM design has the potential to be used for electric bicycles and scooters.