Single-layer Winding Research Articles

Трифазна двополюсна шаблонна одношарова обмотка асинхронного двигуна

Анотація. Асинхронні електродвигуни з короткозамкненим ротором є основою електроприводу робочих машин в промисловості та сільському господарстві. Покращення енергоефективності асинхронних електродвигунів – актуальна задача, одним із шляхів вирішення якої є використання модернізованої обмотки статора із застосуванням внутрішньої ємнісної компенсації реактивної потужності. Метою дослідження було удосконалення трифазної одношарової обмотки статора із повним кроком із забезпеченням покращення форми кривої магнітного поля у повітряному зазорі, підвищенням коефіцієнту корисної дії та коефіцієнту потужності машини. До використання запропоновано трифазну двополюсну шаблонну одношарову обмотку із повним кроком у якої кожна фазна обмотка статора виготовляється у вигляді двох напівобмоток, зсунутих у просторі на певний кут за напрямом обертання магнітного поля. До центральних точок фазних обмоток статора за певною схемою підключені електричні конденсатори, що дозволяє покращити форму кривої магнітного поля у повітряному зазорі, підвищити коефіцієнт корисної дії та коефіцієнт потужності машини. Магнітне поле асинхронного двигуна із запропонованою обмоткою статора має кращі характеристики, ніж у серійному двигуні, обраному за прототип. Зокрема крива магніторушійної сили обмотки статора уздовж довжини повітряного проміжку більш наближена до синусоїдальної, а значення обмотувальних коефіцієнтів для найбільш суттєвих 5-ї та 7-ї гармонік зменшені в 3,5… 4 рази у порівнянні з серійним двигуном-прототипом Ключові слова: обмотка, асинхронний двигун, крок обмотки, коефіцієнт розподілу, коефіцієнт вкорочення кроку, обмотковий коефіцієнт, конденсатор

A Low-Loss Inductor Structure and Design Guidelines for High-Frequency Applications

Operation in the high-frequency (HF) regime (3-30 MHz) has potential for miniaturizing power electronics, but designing small efficient inductors at HF can be challenging. At these frequencies, losses due to skin and proximity effects are difficult to reduce, and gaps needed to keep B fields low in the core add fringing field loss. We propose a low-loss inductor structure with step-by-step design guidelines for HF applications. The structure achieves low loss through double-sided conduction in its single-layer winding and through quasi-distributed gaps. An example ~15 μH inductor designed using the proposed design guidelines achieved an experimental quality factor of 720 at 3 MHz and 2A (peak) of ac current. The inductor also improved a high-current-swing power converter operated at 1-3 MHz; at 250 W, the inductor reduced converter losses by 19%, compared to a conventional inductor design. In some cases, litz wire may further improve the performance of the proposed structure. With litz wire, the example inductor had an improved quality factor of 980. Thus, the proposed inductor geometry and design guidelines are suitable for small highly efficient inductors at HF and can thereby help realize high-frequency miniaturization of power electronics. (This paper is accompanied by an example Python script for generating preliminary designs, available in the online supplementary material).

Conceptual Design of a 5 T 200 mm 1 T/s Ramping NbTi Synchrotron Magnet for Cancer Treatment

Recently, a collaborative research to develop an allsuperconducting synchrotron system for cancer treatment was embarked by a team led by Electronics and Telecommunications Research Institute in Korea. The system requires a 5 T dipole magnet with a uniform field region in cylindrical shape of 130 mm in diameter and 3000 mm in length, and operates at a ramping rate of 1 T/s. As the first step of the project, this paper presents a conceptual design of the magnet that consists of six single-layer cosine windings made of the NbTi Rutherford cable. Key design results include: (1) spatial field uniformity, ΔB/B <; 2 x 10 -4 within a target space of |r| <; 65 mm; (2) total ac loss of the entire coils, 297 J per cycle for a normal operation of 1 T → 5 T → 1 T at the 1 T/s ramping rate; (3) ac-loss-oriented cryogenic load of 23 W; (4) peak temperature of 4.9 K within the magnet during the consecutive normal operation; (5) enthalpy margin of 2.1 mJ/cm 3 with the current sharing temperature of 5.65 K; and (6) adiabatic temperature rise of 87 K upon a quench.

Comparative Study of Partitioned Stator Permanent Magnet Tubular Machines with Different Winding Configurations

In this study, partitioned stator permanent magnet (PS-PM) tubular machines having single- and double-layer windings layouts have been investigated. Two configurations of PS-PM tubular machines were considered, i.e. partitioned stator surface mounted permanent magnet (PS-SPM) and interior permanent magnet (PS-IPM) tubular machines. A comprehensive comparison has been carried out in order to investigate the impact of the winding layouts on such machines. It should be mentioned that the FE package that is used in this paper is (ANSYS Maxwell). It has been noted that irrespective of machines configurations, i.e. either PS-SPM or PS-IPM tubular machines, similar thrust force capability, higher average thrust force per magnet volume, lower thrust force ripple as well as cogging force and higher fault tolerance capability can be delivered by PS-PM tubular machines with single-layer winding compared to that with double-layer winding.

Power Converter Topologies and Control Strategies for DC-Biased Vernier Reluctance Machines

This paper investigates the two latest proposed drive system topologies for dc-biased vernier reluctance machines (VRMs), aims to find out the preferable drive system configuration, and explains the performance discrepancy between the two configurations. Different from the regular ac machines, the armature winding current waveforms of dc-biased VRMs are sinusoidal with dc bias. To provide the dc flow path, the two drive system topologies are associated with the machine, namely, an open winding converter with single-layer concentrated winding and a dual three-phase converter with double-layer concentrated winding. The two configurations are investigated and compared in terms of machine operation principle, power converter configuration, voltage utilization, system cost, and system efficiency. The theoretical analyses and experimental results validate that the two drive systems have their respective advantages.

Design of a Novel Parallel-Hybrid-Excited Dual-PM Machine Based on Armature Harmonics Diversity for Electric Vehicle Propulsion

A novel parallel-hybrid dual permanent magnet (PM) machine topology with both enhanced torque density and improved flux weakening capability is proposed for electric vehicle propulsion in this paper. The key is to artificially construct the harmonics diversity with a single-layer concentrated armature winding in the stator and thus simultaneously couple the armature field with the excitation field produced by slot PM, rotor PM, and stator dc source, respectively. Enhanced torque density is obtained in this new topology due to the symmetrical flux-modulation effect between dual PM sources. Moreover, benefiting from a parallel excitation characteristic of hybrid magnetic circuit, the demagnetization risk is significantly mitigated for slot PM source and thus an extended flux weakening range is obtained. In this paper, the proposed new topology and its design mechanism are investigated, along with its electromagnetic performance evaluated based on finite-element analysis. Further, some leading design parameters are analyzed and determined to provide a design guideline for the proposed new topology. Finally, a prototype is built and fully tested. Relevant experimental results agree well with the finite-element predication.

Novel 24‐slots14‐poles fractional‐slot concentrated winding topology with low‐space harmonics for electrical machine

This paper proposes a novel winding layout for the electric machines with fractional-slot concentrated windings (FSCW) using a stator shifting concept, with which all the non-working harmonics can be completely cancelled or significantly reduced and the non-overlapping winding can be kept. First, the basic winding layout with a 24-slot 14-pole machine to reduce the significant 1st sub-harmonic will be presented for machines with single-layer (SL) windings. From this, a novel double layer (DL) winding layout using the stator-shifting concept will be introduced. By adopting two SL winding sets with a 105° mechanical angle shift with respect to each other, it is not necessary to use overlapping windings. With this configuration, the 1st sub-harmonic will be completely cancelled and the parasitic 5th harmonic will be significantly reduced. Hence, the rotor losses, specifically magnet loss will be significantly reduced. Finally, two PM machines with different DL winding layout, namely, conventional 12-slot 14-pole and 24-slot 14-pole machine, will be designed and compared to validate the advantages of this winding topology.

Multilayer air gap winding designs for electric machines: theory, design, and characterisation

Here, the authors present a magnetic circuit design with a multilayer air gap winding. This design provides a new degree of freedom in the design process. The approach is based on a single layer air gap winding, which demonstrates the ability to scale, permitting application in small and large electric machines. A meandering structure with coils arranged parallel to the rotation axis are mounted in several layers on a slotless magnetic core. The authors consider a fixed ohmic power loss boundary condition to compare this approach with an existing validated machine design. Machine current is reduced with each winding layer, while self-inductance and induced voltage are increased. Since the air gap height is increased with every additional layer, the useable magnetic flux density decreases. Accordingly, an utilisable range in which optimal torque output is obtained can be described analytically. The authors provide comparison between a single-layer winding design, which achieves the global optimum torque, and a four-layer winding design, which gives a 16-fold increase in the phase self-inductance. Additional thermal simulations prove that the multilayer design give the same ohmic power losses as the single layer design, without having any thermal issues and hot spots.

Winding Scheme With Fractional Layer for Differential-Mode Toroidal Inductor

This paper studies how an outer fractional winding can impact the equivalent parallel capacitance (EPC) of a differential-mode inductor, which is a critical passive component in a power electronic converter to combat with electromagnetic noises, and proposes a winding scheme that can reduce EPC and increase inductance, achieving both high-frequency filtering performance and high density. To perform these studies, a comprehensive layer capacitance model based on energy equivalence principle is established, which decouples EPC contribution among three elements, i.e., outer fraction layer, layer-to-layer, and layer-to-core, thus enabling the impact evaluation of different winding elements and schemes. Experimental comparison results have validated the accuracy of this EPC model and excellent performance of the proposed winding scheme with EPC reduction by 4×. It reveals that contrary to previous understanding, the inverse winding, in fact, is more effective for EPC reduction than the direct winding in most of the partial layer scenarios, and that by using this scheme with the outer fraction layer, 45% higher inductance and slightly less EPC can be achieved, compared to the single-layer winding design.

Comparative Analysis of Variable Flux Reluctance Machines With Double- and Single-Layer Concentrated Armature Windings

In this paper, the variable flux reluctance machines (VFRMs) with double- and single-layer concentrated armature windings are comparatively analyzed. First, the single-layer winding is found to have an identical winding factor as a double-layer winding, but significantly larger peak value of magneto-motive force, which will result in severe local saturation in cores of VFRMs with single-layer winding. Then, based on the magnetic gearing effect and finite-element analysis, the electromagnetic performances of VFRMs with both winding types are compared. The VFRMs with single-layer winding are proved to be always lower in average torque, higher in torque ripple, larger in iron loss, and lower in efficiency than those with double-layer winding. Nevertheless, better fault-tolerance capability is achieved for a single-layer winding due to its physical separation between phases and larger phase self-inductance. Overall, the double-layer armature winding is the preferable choice for the VFRMs. Finally, a 6-stator-slot/4-rotor-pole VFRM with both double- and single-layer windings is prototyped for verification.

Design Optimization and Performance Investigation of Linear Doubly Salient Slot Permanent Magnet Machines

Novel linear doubly salient slot permanent magnet machines (LDSSPMMs) are investigated in this paper. First, the machine topology and operation principle are introduced, and the choices of feasible slot/pole combinations and winding configurations for three armature phases are discussed. Then, the 12 slots and 10/11/13/14 poles LDSSPMMs with double-layer (DL)/single-layer windings are globally optimized using genetic algorithm. The electromagnetic performances including flux linkage, back electromotive force (back EMF), detent force, and static force-current characteristics are comparatively studied using two-dimensional (2-D) finite-element analysis (FEA). It shows that 12 slots/13 poles (12s/13p) and DL winding are the optimal choices to provide higher thrust force as well as lower force ripple. Moreover, the risk of local irreversible demagnetization of PMs is analyzed, which only occurs at very limited corners of the PMs and can be eliminated by PM shaping. Furthermore, the electromagnetic performances between linear variable flux reluctance machines (LVFRMs), linear hybrid-excited slot PM machines, linear primary yoke PM machines, and LDSSPMMs are comparatively studied. It shows that LDSSPMM can provide much higher thrust force than LVFRM at the same copper loss. With the increase of copper loss, LDSSPMM exhibits better thrust force capability than other machines. Finally, a prototype of 12s/13p DL-LDSSPMM is manufactured and tested to validate the 2-D FEA predicted results.

Consequent Pole Permanent Magnet Vernier Machine With Asymmetric Air-Gap Field Distribution

In recent years, permanent magnet vernier (PMV) machines have been attracting more and more attention due to the inherently exhibited advantages such as high torque density and simple mechanical structure. In this paper, a consequent pole (CP) PMV machine with single-layer concentrated winding is proposed. The novelty is that the asymmetric air-gap field distribution is introduced to improve its working harmonics and to reduce the PM consumption. By employing a CP structure, the flux density amplitude can be enhanced. Moreover, due to uneven distribution of modulator poles on the armature teeth and fault tolerant teeth, the number of periods of modulator poles is only half of that of the stator teeth. Then, significant improvement in flux density working harmonics can be achieved. Furthermore, the superior electromagnetic decoupling capability can be achieved by introducing the fault-tolerant teeth. The relevant electromagnetic performance such as flux density, back electromotive forces, cogging torque and on-load torque have been calculated by using finite-element analyses, which have also been validated by experiments.

Analytical Computation for AC Resistance and Reactance of Electric Machine Windings in Ferromagnetic Slots

Under the effects of alternating current (AC), the resistance and reactance of electric machine windings are different from their static state. As electric machine windings usually comprise many conductors, it makes the modeling and analysis very cumbersome using the finite element method. This paper presents an analytical method for computing AC resistance and reactance of electric machine windings placed in ferromagnetic slots, which is more convenient and efficient, and could be extended to the slots with different complex structures. First, the slot is divided into a number of layers based on the concept of discretization. Then, the magnetic field governing equation is established, and the distributions of magnetic field intensity and the current density of conductors under AC conditions are solved. By Poynting's theorem, the complex power flowing into the conductors is calculated, and then the effective resistance and reactance of the windings are obtained. Finally, the deduced analytical solutions are compared with the finite element method, and the results show that they have a good agreement for both single-layer winding and the double-layer windings with current phase difference. The presented analytical model is useful for understanding the AC effects and optimization of electric machine windings placed in ferromagnetic slots.

Design and Optimization of a Novel Slot-PM-Assisted Variable Flux Reluctance Generator for Hybrid Electric Vehicles

This paper proposes a new slot-permanent-magnet (PM)-assisted variable flux reluctance generator (VFRG) for the hybrid electric vehicles. Compared with the existing dc-excited VFRG, auxiliary PMs are introduced into stator slots, which can fully utilize the redundant harmonics excited by single-layer concentrated armature winding and boost power density significantly. In this paper, the generator structure, operation principle as well as the winding restriction are discussed. Different slot pole combinations are fully compared in terms of both no-load and on-load characteristics. Some important design parameters are redefined for this slot-PM-assisted topology based on a sensitivity analysis. To release cost burden, both rare-earth-magnet and ferrite-magnet-assisted designs are considered into optimization. The feasibility of this new topology is verified by using finite element analysis and prototype testing.

Two-Dimensional Exact Subdomain Technique of Switched Reluctance Machines with Sinusoidal Current Excitation

This paper presents a two-dimensional (2D) exact subdomain technique in polar coordinates considering the iron relative permeability in 6/4 switched reluctance machines (SRM) supplied by sinusoidal waveform of current (aka, variable flux reluctance machines). In non-periodic regions (e.g., rotor and/or stator slots/teeth), magnetostatic Maxwell’s equations are solved considering non-homogeneous Neumann boundary conditions (BCs). The general solutions of magnetic vector potential in all subdomains are obtained by applying the interface conditions (ICs) in both directions (i.e., r- and θ-edges ICs). The global saturation effect is taken into account, with a constant magnetic permeability corresponding to the linear zone of the nonlinear B(H) curve. In this investigation, the magnetic flux density distribution inside the electrical machine, the static/dynamic electromagnetic torques, the magnetic flux linkage, the self-/mutual inductances, the magnetic pressures, and the unbalanced magnetic forces (UMFs) have been calculated for 6/4 SRM with two various non-overlapping (or concentrated) windings. One of the case studies is a M1 with a non-overlapping all teeth wound winding (double-layer winding with left and right layer) and the other is a M2 with a non-overlapping alternate teeth wound winding (single-layer winding). It is important to note that the developed semi-analytical model based on the 2D exact subdomain technique is also valid for any number of slot/pole combinations and for non-overlapping teeth wound windings with a single/double layer. Finally, the semi-analytical results have been performed for different values of iron core relative permeability (viz., 100 and 800), and compared with those obtained by the 2D finite-element method (FEM). The comparisons with FEM show good results for the proposed approach.

Stator Slitting of 12-Slot 10-Pole Concentrated Winding Motors

This paper proposes a design method of stator cores to modify the component ratio of space harmonics in the magnetic field due to stator windings for 12-slot 10-pole concentrated winding motors. The method inserts slit-like magnetic flux barriers in stator wound teeth. In fractional-slot concentrated winding motors, the magnetic field due to stator windings includes dominant space harmonics with a specific space harmonic that produces drive torque. These space harmonics give rise to undesirable effects that increase iron loss in cores and eddy-current loss in magnets. For 12-slot 10-pole motors with single-layer windings, the proposed method increases the driving space harmonic and decreases dominant detrimental space harmonics. This modification of the space harmonics leads to torque enhancement and efficiency improvement. The efficacy of the proposed method is determined by deriving the winding factor, estimating magnetic flux distribution and motor performance through a finite element method analysis, and demonstrating the actual motor performance of a prototype.

Quantitative Analysis of Contribution of Air-Gap Field Harmonics to Torque Production in Three-Phase 12-Slot/8-Pole Doubly Salient Synchronous Reluctance Machines

This paper adopts simple analytical modeling to investigate the contribution of air-gap field harmonics to the torque production in some three-phase, 12-slot/8-pole doubly salient synchronous reluctance machines (DSRMs) with both conventional and mutually coupled winding configurations. The air-gap flux density has been calculated based on the analytically obtained magnetomotive force and doubly salient air-gap permeance for both the double-layer and single-layer DSRMs with different winding configurations. Then, the contribution of different air-gap field harmonics to average torque and torque ripple can be investigated and validated by direct finite-element analyses. It has been found that in the DSRMs, the 10th-order harmonic in the double-layer conventional winding (DLC), the 4th-order harmonic in the double-layer mutually coupled winding (DLMC), the 7th-order harmonic in the single-layer conventional winding (SLC), and the 10th-order harmonic in the single-layer mutually coupled winding (SLMC) have the highest contribution to positive average torque and with positive influence on torque ripple reduction. However, the 2nd-order harmonic in the DLC, the 8th-order harmonic in the DLMC, the 5th-order harmonic in the SLC, and the 2nd-order harmonic in the SLMC machines mainly reduce the average torque.

Novel Modular Switched Reluctance Machines for Performance Improvement

Compared to nonmodular machines, modular topologies become increasingly attractive due to their simplified manufacture process, better fault-tolerant capability, and potentially reduced material consumption. In order to maintain or even enhance the machine performance while achieving high fault-tolerant capability, novel modular, single-layer winding switched reluctance machines (SRMs) with different pole numbers are proposed, which are supplied by rectangular wave current with different conduction angles. The influences of the pole number and flux gap width between E-core segmented stators on the electromagnetic performance have been investigated in terms of self- and mutual inductances, electromagnetic torque, copper loss, iron loss, and radial force. It has been found that the modular structures with higher rotor pole numbers than stator slot numbers (12-slot/14-pole and 12-slot/16-pole SRMs) can maintain and even improve the average torque due to the nature of self and mutual inductances. In addition, the torque ripples for modular machines are significantly reduced (below 50%), so do the iron loss and radial force, leading to higher efficiency albeit with potentially lower vibration and acoustic noise. Two prototypes with 12-slot/8-pole and 12-slot/14-pole combinations have been built with both nonmodular and modular structures to validate the predictions in terms of inductances and static torques.

Problems and Possible Ways of Achieving the Design Strength of Quasi-Force-Free Windings

Calculations using the base model with a continuous current distribution have shown that in a simple single-layer winding with current, directed at an angle to the axis of the magnet, about 45°, mechanical stresses are several times smaller than the magnetic pressure of generated field. Experiments confirmed the sharp reduction of the winding deformation with the use of the azimuthal field for sustaining the winding balance. A real multiturn winding is weakened by the insulating gaps between the turns and is exposed to cross-component induction. The 3-D calculations have shown that the stresses in windings may be close to the calculated ones for the base model if the gaps are filled with a dielectric with high enough density modulus and because of the use of screens for field correction.

An Improved Torque Density Synchronous Reluctance Machine With a Combined Star–Delta Winding Layout

This paper investigates the performance of synchronous reluctance motors when the stator is equipped with a combined star–delta winding layout. The conventional star winding is used as a benchmark in this study to compare different possible single-layer winding layouts. Among these different winding layouts, those which maximize the fundamental magneto-motive force component are selected. A simple mathematical formula is then derived to calculate the equivalent winding factor for different shares between star and delta subwindings. It has been proved that for the same copper volume and line current magnitude, the star–delta connection can offer an enhancement in the torque density of approximately 5.2% over the conventional star case under rated conditions. However, this gain is affected by the employed number of poles and stator slots. On the other hand, the effect of the winding layout on either power factor or core loss can be merely neglected over a wide range of speeds and currents. Nevertheless, the machine efficiency under a combined star–delta connection is relatively improved under light loading as a result to the machine torque/current ratio enhancement. The theoretical findings are experimentally validated using two identical 5.5 kW prototype machines, having star and combined star–delta winding connections.