Slot Opening Research Articles

Effect of Slot Opening Width on the Air-Gap Magnetic Field of a Direct Drive Permanent Magnet Motor

The direct drive permanent magnet motor (DDPMM) is a promising candidate for applications because of its high efficiency, high power density, and low maintenance costs. This study focused on the effect of slot opening width on the air-gap magnetic field of a DDPMM. An exact analytical model based on Fourier analysis was established to calculate the air-gap magnetic field. The analytical general solution of the air-gap magnetic field shows that the slot opening greatly affects the air-gap magnetic field distribution when the amount of the permanent magnet is constant. Then, the air-gap magnetic fields of the DDPMM with closed and open slots were compared at different positions. Furthermore, several finite-element models of motors composed of different numbers of unit motor were established based on the different slot opening widths to study the effect of slot opening width on the air-gap magnetic field. The results obtained using the finite element method verify that the slot opening width greatly affects the air-gap magnetic field.

General Analytical Magnetic Model for Partitioned-Stator Flux-Reversal Machines With Four Types of Magnetization Patterns

A partitioned stator-flux reversal (FR) permanent magnet machine (PS-FRPMM) is a new combination of a stator PM machine and a magnetically geared machine and has the specifications of both machines in terms of robust structure and torque density. In this paper, a comprehensive 2-D analytical model is developed for PS-FRPMM based on subdomain technique. The presented model has the capability to accurately and quickly investigate the effects of design parameters on the machine performance. The 2-D analytical model is evaluated on two case studies with 12 stator teeth and 10 rotor poles, and 18 stator teeth and 13 rotor poles, with four different magnetization patterns. The influences of various design parameters such as the rotor slot width, slot opening width, and the segment ratio of the PMs in the two-segment magnetization pattern have been investigated on the quantities, such as the instantaneous torque, torque ripple, unbalanced magnetic force (UMF), and electromotive force (EMF). For evaluating the presented analytical model, the 2-D finite element method (FEM) with and without saturation effects has been used. The comparative study between the analytical and numerical models shows good agreement. Finally, a 3-D FEM has been used, and the results of the 2-D analytical model and 3-D FEM are compared in terms of the accuracy and computational time. The results show that the presented model has lower computational time compared to the 2-D and 3-D FEM, while its accuracy is acceptable under different circumstances, such as saturation.

Slot loading effect on impedance and radiation performance of high‐gain patch antenna under TM 03 ‐mode operation

Based on antenna's impedance and radiation performance, the slot loading effect on the TM03-mode high-gain square patch antenna is investigated in this paper. Three different slot configurations are loaded to the patch along the central line, which can reduce the sidelobe in the E-plane. However, it is found that the H-plane beamwidth, impedance bandwidth and radiation Q factor become significantly different in these cases. At first, broader H-plane beamwidth, lower Q factor and wider impedance bandwidth can be obtained when only single slot is loaded in the center of the patch. In contrast, when two open slots are etched at two nonradiative edges of the patch, it will result in narrower H-plane beamwidth, higher Q factor and narrower impedance bandwidth. Moreover, better balanced performance can be achieved by simultaneously loading the central and sided slots. For validation, three kinds of antenna prototypes are designed, fabricated, and measured. The measured and simulated results agree well with each other, which demonstrate that different impedance and radiation performance can be freely adjusted and achieved by using different slot configurations.

A Wideband Differentially Fed Dual-Polarized Antenna With Wideband Harmonic Suppression

A wideband differentially fed dual-polarized antenna with wideband harmonic suppression is presented. The radiating structure is composed of open slots, stair-shaped strips, and a square patch. Eight open slots are etched on the four corners of the square patch to realize symmetrical radiation and low cross-polarization for orthogonal polarizations. Stair-shaped strips are not only used to excite the open slots, but also introduce the monopole resonance. In addition, patch resonance is excited on the center square patch. For matching these different resonances, shorted microstrip lines are utilized to achieve the wide impedance bandwidth. Moreover, compact stepped impedance resonators are elaborately introduced on the top of the patch to achieve wideband harmonic suppression without any increase of the antenna footprint. The proposed antenna is designed, fabricated, and measured to verify the design method. The measured results demonstrate that the proposed antenna has the impedance bandwidth of 1.70–2.81 GHz for S dd 11 S dd 11 higher than −2.2 dB, and the corresponding harmonic gain lower than −5.3 dBi. In addition, a stable gain of 7.2–7.9 dBi and beamwidth of 63°–71° are achieved for base station applications.

Electromagnetic Analysis and Performance Investigation of a Flux-Switching Permanent Magnet Machine

This paper aims to present a general and effective analytical approach to calculate the air gap flux density and the back electromotive force (EMF) of a flux-switching permanent magnet (FSPM) machine. The proposed analytical expression of the air gap flux density is based on an improved air gap permeance function considering the geometries of slotted stator core pieces and magnets between stator teeth as well as the salient rotor poles. The back EMF equation is accurately derived using the proposed air gap flux density equation expressed in terms of practical machine dimensions and thus it provides the key design factors as well as details of the back EMF production mechanism. To validate the proposed analytical expressions, they are applied to the case study of a 12-slot 10-pole FSPM machine, and the finite element analysis results confirm the analytical predictions. Besides, for the proposed analytical model, the effects of the machine’s geometries on back EMF characteristics are investigated. The investigation shows that the ratio of rotor slot opening to slot pitch has a significant effect on the back EMF, and its optimal value is suggested. The proposed equations also provide a mean to choose the slot and pole combinations to obtain a higher power density.

A Subdomain Model for Open-Circuit Field Prediction in Dual-Stator Consequent-Pole Permanent Magnet Machines

This paper proposes a subdomain model for open-circuit field prediction in dual-stator consequent-pole permanent magnet machines. The whole field domain is composed of four types of sub-domains, including magnets, air gaps, slot openings, and slots. The proposed model takes the effect of tooth-tips into account, which can accurately calculate the flux density in slots and cogging torque. The finite-element (FE) model is established, which validates that the proposed subdomain model can quickly and accurately predict the magnetic field distribution and cogging torque in dual-stator consequent-pole permanent magnet machines.

Study on Reducing the Maximum Perpendicular Magnetic Field of HTS Coils Used on Synchronous Generator Armatures

In this paper, a 30-kW permanent magnet superconducting synchronous generator is proposed for the marine application. The perpendicular magnetic field on the high temperature superconducting (HTS) coils will cause a large drop in critical current and create much more ac loss. The magnetic field consists of two parts, i.e., self-field created by the transport current and external field created by the rotor rotation. It can be reduced by decreasing the distance between the HTS coil and back iron, increasing the distance between the HTS coil and iron teeth or adding the slot wedges in the open slots. These are effective methods to improve HTS armatures’ critical current by reducing the perpendicular magnetic field on the HTS coil surface. Changing the turns ratio of HTS coils has little influence on reducing the maximum perpendicular magnetic field. However, it could decrease the number of flux lines passing through the HTS coil and reduce the total ac loss of the HTS coil.

Computationally Efficient Strand Eddy Current Loss Calculation in Electric Machines

A fast finite element (FE) based method for the calculation of eddy current losses in the stator windings of randomly wound electric machines is presented in this paper. The method is particularly suitable for implementation in large-scale design optimization algorithms where a qualitative characterization of such losses at higher speeds is most beneficial for identification of the design solutions that exhibit the lowest overall losses including the ac losses in the stator windings. Unlike the common practice of assuming a constant slot fill factor s <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> for all the design variations, the maximum s <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> in the developed method is determined based on the individual slot structure/dimensions and strand wire specifications. Furthermore, in lieu of detailed modeling of the conductor strands in the initial FE model, which significantly adds to the complexity of the problem, an alternative rectangular coil modeling subject to a subsequent flux mapping technique for determination of the impinging flux on each individual strand is pursued. Rather than pursuing the precise estimation of ac conductor losses, the research focus of this paper is placed on the development of a computationally efficient technique for the derivation of strand eddy current losses applicable in design optimization, especially where both the electromagnetic and thermal machine behavior are accounted for. A fractional-slot concentrated winding permanent magnet synchronous machine is used for the purpose of this study due to the higher slot leakage flux and slot opening fringing flux of such machines, which are the major contributors to strand eddy current losses in the windings. The analysis is supplemented with an investigation on the influence of the electrical loading on ac winding loss effects for this machine design, a subject that has received less attention in the literature. Experimental ac loss measurements on a 12-slot 10-pole stator assembly will be discussed to verify the existing trends in the simulation results.

Weryfikacja możliwości redukcji emisji amoniaku dla różnych praktyk aplikacji gnojowicy w Polsce

Rolnictwo polskie zobowiązane jest do redukcji emisji amoniaku (NH3), w stosunku do 2005 r., o 1% corocznie w latach 2020-29 oraz o 17% corocznie od 2030 r. Znaczącym źródłem emisji jest stosowanie gnojowicy. W Polsce aplikuje się ją głównie rozbryzgowo na powierzchnię pola i przyoruje po 4-24 godzinach od aplikacji. W pracy zastosowano model ALFAM2 do scharakteryzowania emisji NH3 z rozbryzgowego stosowania gnojowicy w zależności od specyficznych dla Polski: dawek gnojowicy, jej suchej masy, temperatury powietrza, prędkości wiatru, opadów oraz pH gnojowicy. W stosunku do emisji NH3 z gnojowicy stosowanej na powierzchnię pola oszacowano emisje powstające przy aplikacji gnojowicy za pomocą wężów wleczonych, wężów z redlicami oraz aplikacji do otwartych szczelin, płytko doglebowo i głęboko doglebowo. Na podstawie uzyskanych wyników oszacowano wielkości redukcji emisji dla podstawowych praktyk jej aplikacji.

Investigation of a Modular Linear Doubly Salient Machine With Dual-PM in Primary Yoke and Slot Openings

A modular linear doubly salient machine with dual-PM in the primary yoke and slot openings is proposed in this paper. First, the machine topology is introduced, where the PMs are employed in both the primary yoke and slot openings. The magnetic fluxes excited by the PMs in the slot openings pass through the air gap and link the secondary, not short-circuited by the primary teeth. Hence, the magnetic fluxes excited by both PMs can be concentrated and enhanced in the air gap. Then, the operation principle is investigated based on the permeance model, which shows that it obeys the flux modulation principle. The electromagnetic performances are analyzed in detail using FEM, which shows that the force density and overload capability can be significantly improved with the slot PMs. Finally, the 2-D finite-element (FE) predicted results are validated by the 3-D FE results that considering the transverse end effect.

Subdomain model for predicting armature reaction field of dual-stator consequent-pole PM machines accounting for tooth-tips

This paper presents an exact analytical subdomain model of dual-stator consequent-pole permanent-magnet (DSCPPM) machines accounting for tooth-tips, which can accurately predict the armature reaction field distribution in DSCPPM machines. In the proposed subdomain model, the field domain is composed of four types of sub-regions, viz. magnets, outer/inner air gaps, slots and slot openings. The analytical expressions of vector potential in each sub-region are determined by boundary and interface conditions. In comparison to the analytically predicted results, the corresponding flux density field distributions computed by finite element (FE) method are analyzed, which confirms the excellent accuracy of the developed subdomain model.

Optimal Number of Magnet Pieces of Flux Reversal Permanent Magnet Machines

This paper aims to comprehensively analyze the influence of number of permanent magnet (PM) pieces on electromagnetic performance of flux reversal permanent magnet (FRPM) machines. First, the unified analytical model of FRPM machines having different numbers of PM pieces is established, from which the optimal number of PM pieces and the corresponding rotor pole number can be identified. It shows that by employing the optimal number of PM pieces instead of the conventional two on each stator tooth, additional back-EMF component can be generated which is beneficial to boost the machine performance. Then, the influence of critical design parameters including stator slot opening ratio, split ratio, and stator slot number is investigated, providing a guidance to the design of FRPM machines aiming at maximum output torque. In addition, both finite element analyses and experimental tests are conducted to verify the analytical analyses. For 6-slot-stator FRPM machines, experimental results show that more than 40% higher output torque can be achieved in the machine with optimal number of PM pieces when compared to the conventional one.

Optimization of surface-mounted permanent magnet brushless AC motor using analytical model and differential evolution algorithm

Abstract This paper discusses the optimization of surface-mounted permanent magnet brushless AC (PMBLAC) motor using Analytical Sub-domain model with Differential Evolution Algorithm (ASDEA). Only two regions were considered in this analytical sub-domain model, ie magnet and airgap regions, with assistance of Complex Relative Permeance Function (CRPF) to account for the stator slotting effect. Five machine parameters were chosen to be optimized, namely the magnet arc-pole-pitch ratio, slot opening width, magnet thickness, airgap length and stator inner radius. The optimization process has four objectives, ie minimum torque ripple, low cogging torque, high efficiency, and high output torque. The results from the optimized ASDEA were compared with the Analytical Sub-domain Genetic Algorithm (ASGA) and further validated against 2-D finite element model (FEM). Results show a good agreement between analytically optimized models and finite element model. The ASDEA has faster computational time compared to ASGA, and this provides benefit in terms of reducing the machine design parameterization time and less redundancy work required to achieve motor design specifications.

Idioms, collocations, and structure

Phrasal idioms have been used as evidence in syntactic theorizing for decades. A common assumption, occasionally made explicit (e.g., Larson 2017), is that non-literal phrasal idioms differ significantly from completely literal collocations in the kinds of syntactic structures they can be built from. I show with a detailed empirical study that this is false. In fact, the syntactic constraints on idioms and collocations are identical. In particular, patterns that are missing from one are missing from the other, most strikingly ditransitives with a fixed first object and open second object (*throw the wolves X). Idioms and collocations should therefore be treated the same, as a broad class of conventionalized expressions. I propose a new analysis of the syntactic forms that conventionalized expressions can take. Unlike most previous analyses, I take the open slots to be part of the expression, and the task then becomes to explain the distribution of the open slots. A structural constraint on open slots accounts for the missing ditransitive pattern. It also explains why expressions with a fixed subject but open object are rare, but also why certain examples of this pattern do exist in English and in other languages.

Cogging Torque Reduction and Offset of Dual-Rotor Interior Permanent Magnet Motor in Electric Vehicle Traction Platforms

Recently, various methods have been proposed to increase the output power density of a driving motor applied to an electric vehicle. One such method is to design a structure with two motor rotors. High output density can be obtained by applying the dual rotor to the motor. However, this increases the cogging torque, which can cause high noise and vibration. In this paper, we proposed a method for reducing the cogging torque by adjusting the angle between the magnet and the dual rotor, as well as a novel method for reducing the cogging torque by angular adjustment of the slot opening based on electromagnetic field analysis. In addition, the design was implemented by applying a split core to increase the ease of manufacturing and the dot rate in the motor. We believe that high cogging torque, which is a disadvantage of dual rotor motors, can be lowered by the methods proposed in this paper. The results of this study are expected to be applicable to electric vehicles that require high output power density.

Biomechanical in vitro evaluation of a ready-to-use calcium phosphate cement implanted to augment intramedullary nail fixation of a three-part humeral head fracture model.

The aim of this study was the dynamic biomechanical evaluation of a ready-to-use oil-based calcium phosphate cement paste implanted to augment intramedullary nail fixation of a three-part humeral head fracture model. Fractures in the osteoporotic bone are often fractures of the proximal humerus. Secondary fracture displacements due to cut-out in osteoporotic bone have been observed in up to 13% of cases. Procedures have been developed to augment fracture fixation with polymethylmethacrylate to increase stability, but there are still unsolved challenges relating to its material-specific properties. Calcium phosphate cement could be a biological alternative in the augmentation of osteoporotic fractures because of its more favourable material properties. Fracture fixation was performed on eight pairs of human cadaveric bones to stabilize a standardized three-part humeral head fracture model by implantation of the Targon® PH (Braun-Aesculap AG, Tuttlingen, Germany) intramedullary nail and insertion of three head screws and two bicortical shaft screws. The procedure was randomized, and one bone of each pair received calcium phosphate cement augmentation. Custom-made cannulated screws with an open lateral slot facilitated augmentation, making it possible to cement the threaded portion of the screw (1-mL calcium phosphate cement/screw). After the calcium phosphate cement had hardened, the humeri were subjected to dynamic axial loading. Load was progressively increased, monitored by ultrasound-based motion analysis, and total deformation was recorded. Load testing continued until implant failure. The augmented group withstood significantly more cycles before implant failure. The average initial stiffness showed a significant difference between the two study groups. Ultrasonic sensor technology was used to measure angular displacement during testing and a significant difference was found. Calcium phosphate cement offers a potential alternative to implant augmentation in the treatment of osteoporotic humeral head fractures. Future studies are required to confirm these observations clinically in vivo.

Large eddy simulation of the backdraft dynamics in compartments with different opening geometries

Large eddy simulation (LES) was performed to investigate backdraft in reduced-scale compartments using the fire dynamics simulator. Mixing-controlled fast chemistry combustion model was adopted in the LES predictions of the backdraft phenomenon. The effect of the opening geometry of the compartment on the critical fuel percentage required for backdraft occurrence was numerically investigated by considering compartments with a door or a slot opening. The LES with the mixing-controlled fast chemistry combustion model provided reasonable results for the gravity current and backdraft development process in the reduced-scale compartments. The predicted results of the critical fuel percentage for backdraft occurrence were in good agreement with those obtained by previous experiments on door and slot opening geometries. The LES also predicted the trend in peak pressure with increasing fuel concentration inside the compartment reasonably well. The oxygen concentration of the entrained airflow inside the compartment affected the peak pressure during backdraft development. The peak pressures for the compartment with a slot opening were higher than those for a compartment with a door opening at the same fuel concentration. The difference in the peak pressures between the two compartment geometries was attributed to the difference in the entrained oxygen concentration caused by different ignition times.

Influence of Stator and Rotor Pole Number Combinations on the Electromagnetic Performance of Stator Slot-Opening PM Hybrid-Excited Machine

A new type of three-phase stator hybrid excited machine with permanent magnets (PMs) located at the slot openings of field winding slots is presented in this paper. It has the advantage of good flux regulation capability due to the field excitation. The machines with different stator/rotor pole combinations, i.e., 6-stator pole and 7-/8-/10-/11-/13-/14-rotor poles, have been comparatively investigated in terms of the open-circuit and on-load characteristics, as well as the influence of dc current and the unbalanced magnetic forces. The 2-D finite element analysis (FEA) has been employed for analysis and optimization of the machines together with experimental validation.

Comparison of optimal slot/pole number combinations in fractional slot permanent magnet synchronous machines having similar slot and pole numbers

Here, the selection of optimal slot/pole (Ns-slot/pr-pole) number combination between the pairs of fractional slot concentrated winding (FSCW) permanent magnet synchronous machines (PMSMs) with Ns = 2pr ± 1 or Ns = 2pr ± 2 will be analysed by a modified winding function accounting for slot opening and validated by finite element method. The results show that for FSCW PMSMs with Ns = 2pr ± 1 or Ns = 2pr ± 2, the higher pole machine will have larger winding factor and hence better torque performance than the lower pole one. Moreover, it also reveals that this torque advantage is more evident in the external rotor machine than that in internal rotor machine.

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.