Slot Combinations Research Articles

Design of Ladder-Slit Secondaries and Performance Improvement of Linear Induction Motors for Urban Rail Transit

In order to improve the performance of linear induction motors for urban rail transit, the ladder-slit secondary is designed, and the performance of linear induction motors with the ladder-slit and flat-solid secondary is calculated and compared. First, for the ladder-slit secondary, the slot combination, widths of the secondary conductor, and side bar are designed. Second, the finite-element model of the linear induction motor with the ladder-slit secondary is developed, and the influence of vertical forces on widths of secondary conductors is presented. Third, the eddy current and the transversal air-gap flux density are compared when the ladder-slit and flat-solid secondaries are applied, respectively. Finally, experiments are carried out by test lines to validate the calculated results of the force and efficiency. It shows that the ladder-slit secondary can reduce the edge effect and improve the performance.

Analysis of a Novel Double-Sided Yokeless Multitooth Linear Switched-Flux PM Motor

A novel double-sided yokeless multitooth linear switched-flux permanent magnet (DYMLSFPM) motor is proposed to improve the electromagnetic performance of conventional double-sided linear switched-flux PM (DLSFPM) motor in terms of force ripple and cogging force. Its feature of structure is the multitooth primary without yoke. First, an analytical method of permeance model is developed for determining the optimal combination of primary slots and secondary poles. For DYMLSFPM motor with six primary slots, there are four available different secondary poles 16/17/19/20, respectively. By comparing the results of four combinations, it shows that the DYMLSFPM motor with 19 secondary poles can have better thrust force performance, which is also verified by the finite-element analysis. After all these four structures are optimized first by single-variable optimization and then by global optimization with genetic algorithm for further analysis, 6-slots/19-poles (6s/19p) combination can have the second highest average thrust force and the lowest thrust ripple. Moreover, it requires significantly smaller volume of PMs and exhibits much lower cogging force than conventional 6s/7p DLSFPM motor. Finally, a prototype of 6s/19p DYMLSFPM motor is manufactured and tested to validate the predicted results.

Analysis of the Operation Principle for Rotor-Permanent-Magnet Flux-Switching Machines

This paper proposes a topology of special rotor-type permanent-magnet (PM) machine named rotor-PM flux-switching (RPM-FS) machine, which is evolved from stator-PM flux-switching (SPM-FS) topology and exhibits high power density, wide-range speed regulation, and good overload capability. The operation principle of RPM-FS machines is investigated based on the field modulation theory. It can be found that the torque is mainly contributed by the dominant harmonics in rotor-PM field and armature reaction field with the same order and rotating speed, i.e., 10, 14, and 34 pole pairs. In addition, a comprehensive comparison of modulation principles between the RPM-FS and SPM-FS machines is conducted from three perspectives, namely PM field, armature reaction field, and torque production mechanism. It is found that the modulation principle not only reveals the similarities of operation principle between two PM-FS machines, but also provides guidance for the combination of stator slots and rotor poles. Further, the electromagnetic torque produced by the dominant harmonics in two machines is verified by finite-element analysis and experiments.

Comparative Study of Three Different Radial Flux Ironless BLDC Motors

Three different radial flux ironless brushless dc (BLdc) motor types (motors without inner back-iron of the rotor, with inner back-iron of the rotor, and with dual-rotor) are investigated and compared in this paper. The magnetic field distribution, back electromagnetic force (EMF), axial end effect, and torque characteristics are investigated. First, the relationship between the magnetic field distribution and the motor size and pole pairs is investigated. It shows that the two parameters are not independent of each other and the magnetic field distribution is mainly related with the arc length of the permanent magnets. Second, the radial magnetic flux density in the coil regions of the three ironless BLdc motors is calculated and an evaluation factor is proposed to show the quality of the magnetic field distribution. Third, the influence of the winding configuration and the combination of slot and pole number on EMF is analyzed, and the corresponding evaluation factors are calculated and tabulated. Then, the axial end effect of the three ironless BLdc motors considering the fringe effect is investigated and compared. Next, the torque characteristics at full load and rated speed are studied for the three types of motors. Finally, the ironless BLdc motor without back-iron of the rotor is manufactured and tested. The experimental results are in good agreement with the finite-element method.

Design and Analysis of a Flux Reversal Machine With Evenly Distributed Permanent Magnets

In this paper, a flux reversal machine (FRM), which has a larger torque density and a smoother torque waveform than the conventional FRM, is introduced. The FRM has the same combinations of stator and rotor slots, winding pole pair, and permanent magnet (PM) usage as the conventional FRM, but has different PM arrangements, i.e., in the conventional FRM, a pair of PMs is mounted on the surface of each stator teeth while the PMs of the FRM introduced in this paper are evenly distributed along the inner surface of the stator. First, the origination from the conventional FRM to the proposed FRM is introduced. Then, the effects of the rotor slot number, split ratio, stator/rotor slot opening ratio, PM thickness, and pole arc on the average torque and cogging torque are investigated and analyzed, which give a reasonable prediction for maximum achievable power density and minimum possible cogging torque of the proposed FRM. Moreover, the proposed FRM is compared with a conventional FRM in terms of back electromotive force, rated torque, pulsating torque, power factor, and overload capabilities. Finally, a 12-stator-slot/17-rotor-slot FRM prototype is built to verify the theoretical analyses.

Effect of Pole–Slot Combination on Eddy-Current Formation in PMSM Rotor Assembly Including Retaining Plate Structure

The results of the 3-D finite-element method electromagnetic analysis of the constant speed variable output permanent magnet synchronous motor including the rotor retaining plate structure confirmed that the eddy current flow was induced in the rotor part. Eddy current flows from the permanent magnet to the rotor retaining plate, and it was found that there is induced voltage that generates eddy currents in the retaining plate from the aspect of eddy-current distribution. The eddy current flow from the permanent magnet to the retaining plate is related to the change in magnetic resistance during rotation and is also related to the effect of slot harmonics on the air-gap magnetic flux density. In this paper, the characteristics of the eddy current flow in the rotor assembly were investigated when the retaining plate is included for various slot combinations. The eddy-current generation according to the slot combination is analyzed and the cause of such tendency was investigated. Furthermore, from the pattern of eddy-current formation, it was noted that the aperiodic pole–slot combination models may have a larger eddy-current loss increase when combined with the retaining plate.

Loss and Air-gap Force Analysis of Cage Induction Motors With Non-skewed Asymmetrical Rotor Bars Based on FEM

Non-skewed asymmetrical rotors bars can be used to eliminate the slot harmonic fields and the resulting noise and vibration in cage induction motors. However, it is difficult to determine the spatial distribution of the asymmetrical rotor bars and the slot combinations, which can affect the loss and the air gap force significantly. With a 5.5 kW, 4-pole induction motor as an example, this paper studies the influence of the above factors on the loss and the air gap force by time-stepping finite element method, and the experiments are performed to validate the calculations.

Dynamic model of cage induction motor with number of rotor bars as parameter

A dynamic mathematical model, using number of rotor bars as parameter, is reached for cage induction motors through the use of coupled-circuits and the concept of winding functions. The exact MMFs waveforms are accounted for by the model which is derived in natural frames of reference. By knowing the initial motor parameters for a priori adopted number of stator slots and rotor bars model allows change of rotor bars number what results in new model parameters. During this process, the rated machine power, number of stator slots and stator winding scheme remain the same. Although presented model has a potentially broad application area it is primarily suitable for the analysis of the different stator/rotor slot combination on motor behaviour during the transients or in steady-state regime. The model is significant in its potential to provide analysis of dozen of different number of rotor bars in a few tens of minutes. Numerical example on cage rotor induction motor exemplifies this application, including three variants of number of rotor bars.

Analytical Prediction of 3-D Magnet Eddy Current Losses in Surface Mounted PM Machines Accounting Slotting Effect

This paper presents a novel analytical technique for predicting three-dimensional (3-D) magnet eddy current losses accounting the slotting effect of any pole–slot combinations for a surface mounted permanent magnet machine under any conditions of load. The slotting effect is incorporated from a subdomain model and the 3-D boundary conditions are imposed with the current vector potential to represent the 3-D eddy currents circulating in the magnets. The proposed model in polar coordinate system is demonstrated on a fractional slot rare-earth permanent magnet machine by analyzing its magnet losses as functions of axial and circumferential segmentations. The results have shown an excellent match with 3-D numerical calculations. The analytical prediction has also been validated by experimental tests. The interaction of the armature reaction field with the slotting harmonics is analyzed and their effect on eddy current loss in rotor magnets is established. The proposed technique is employed to evaluate the effect of slotting on magnet loss with increase in field weakening angle.

Improved chipless tag based on multifilters

AbstractIn this study, a novel compact chipless RFID transponder is presented. The coding information is based on spectral signature using three types of multiresonator: spiral, slot, and U‐shaped defected ground structure (DGS). Each resonator can be seen as a band‐stop filter which contributes to a particular resonance frequency. The previous spiral resonator based barcodes have only 1 bit information on each resonator which result in a large quantity of resonators relatively and a long microstrip line. In our design, the slot is cutting on the spiral resonator so more bits can be stored. The combination of slot and spiral resonators together provides an efficient decrease in resonator numbers. The DGS structure takes use of ground plane of the tag which further increases the capacity without expanding the size. The method of using these three types of resonators presents a clear improvement in miniaturizing the transponder which leads to a compact size of the tag. By applying frequency shift coding (FSC) coding technique, a coding density of 0.946 bit/cm2 is achieved. Improvement in two cross‐polarized transmitting and receiving antennas is also considered in the design. Corresponding experiments on realized prototypes are provided to validate the effectiveness of the proposed design.

Analysis and Detection of Inter-Turn Short-Circuit Fault Through Extended Self-Commissioning

This paper presents a comprehensive analysis of permanent magnet synchronous machine stator winding impedance variation in inter-turn short-circuit and eccentricity faults. The phase impedances are monitored through an extended self-commissioning procedure at the standstill mode before or after operation, and hence are agnostic to well-known issues caused by transients, load/speed level, or controller coefficient dependency. Moreover, the effect of stator iron core saturation on the electrical parameters is analyzed in depth. In order to distinguish the inter-turn shorts from the eccentricity fault which exhibits similar behaviors, a classification algorithm based on the saturation effect is introduced and analyzed on the machines with different pole–slot combinations. Both two-dimensional finite element analysis simulation and experimental test results are provided to show the efficacy of this analysis.

Influence of pole and slot combinations on vibration and noise in external rotor axial flux in‐wheel motors

This study provides a detailed finding of the influence of pole and slot combinations on vibration and noise in external rotor axial flux in-wheel motors (AFWMs). Firstly, electromagnetic force exerted on the surface of permanent magnet is discussed and a two-dimensional fast Fourier transformation is implemented to analyse its spatial distribution and frequency characteristics. Then, a multiphysics model is developed to predict the vibration and noise and figure out the main origin from the perspective of electromagnetism. The influence of pole and slot combinations on vibration and noise is also analysed via the proposed model. Finally, the effect of load on vibration and noise in AFWMs is further investigated. It turns out that zeroth spatial order of axial electromagnetic force is the main origin of vibration and noise in axial flux motors, which is quite different from radial flux motors. Moreover, AFWMs with larger lowest common multiple (LCM) of pole number (2 p ) and slot number ( Q s ) show lower noise level and for the motors that satisfy LCM(2 p,Q s ) ≠ 6 p , vibration and noise are greatly influenced by load. This study provides guidance for the design of low noise AFWMs.

Annular Slot-Based Miniaturized Frequency-Agile MIMO Antenna System

In this letter, a miniaturized annular slot-based multiple-input–multiple-output (MIMO) antenna system is presented. The proposed frequency-agile antenna exhibits wide tuning range operation by covering several well known wireless standards including GSM1800/LTE/UMTS/WLAN along with several others. The resonance frequency varies from 1.8 to 2.45 GHz. The structure of each antenna element consists of a combination of annular and circular slots, and the antenna is made reconfigurable using a varactor diode within its annular slot. Only one varactor diode is used in achieving this wide tuning band of operation. The four-element MIMO antenna system is realized on a $\text{60} \times \text{120}\times \text{0.76}$ -mm $^3$ RO4350 substrate. The proposed design is suitable for wireless handheld devices and mobile terminals as well as cognitive radio front ends. The measured results show maximum gain of 2.43 dBi and maximum efficiency ( $\eta$ ) of 73%. The envelope correlation coefficient did not exceed 0.186 across the complete operating bands.

Design and research of modular permanent‐magnet DC generator based on magnetic integrated transformer for offshore wind farms

Traditional topologies of all-DC offshore wind farm raised the voltage by making multiple generators connected in series, which would cause problems of additional enforcement insulation and complex power distribution and voltage control when situations of unbalanced wind speed and potential faults were encountered. A modular permanent-magnet DC wind generator topology based on the magnetic integrated transformer (MIT) for the offshore wind farm was proposed in this study. The combination of fractional slot concentrated winding direct-drive permanent-magnet synchronous generator and MIT directly produced high-voltage direct current at the end of a generator, which was of strong fault tolerance. Mathematical models of the generator, power electronic converters, and MIT were established. Both power factor correction control strategies of generator winding currents and voltage stability control strategy of generator inner low-voltage direct current bus were designed. Simulation results demonstrated that the designed generator can achieve smooth transitions during start, variable wind speed and fault processes, and realise the maximum power point tracking, which verify the rationality and feasibility of the proposed topology and strategy, and can provide a useful technical reference for the future all-DC offshore wind farms.

Dual rotor flux switching permanent magnet machines with phase-group concentrated-coil windings for high performance

This paper proposes a novel dual rotor radial field flux switching permanent magnet machine (FSPMM) with phase- group concentrated-coil (PGCC) windings and two misaligned rotors to obtain high performance, including high torque density and low cogging torque, as well as low torque ripple. The proposed FSPMM features a new combination of stator slots and rotor poles, which is determined by the winding configurations. The PGCC windings are adopted to obtain a unity displacement winding factor, and enhance the flux focusing effects together with the use of spoke-type PM constructions. The unaligned arrangement of two rotors will help to not only achieve further flux magnification by an alternate operating principle for PM flux concentration, but also suppress the cogging torque. To highlight the advantages of the proposed FSPMM, two conventional FSPMMs with typical machine configurations having concentrated windings are adopted for performance comparison based on a finite element method (FEM) using JMAG-Designer.

Predicting Negative Emotions Based on Mobile Phone Usage Patterns: An Exploratory Study.

BackgroundPrompt recognition and intervention of negative emotions is crucial for patients with depression. Mobile phones and mobile apps are suitable technologies that can be used to recognize negative emotions and intervene if necessary.ObjectiveMobile phone usage patterns can be associated with concurrent emotional states. The objective of this study is to adapt machine-learning methods to analyze such patterns for the prediction of negative emotion.MethodsWe developed an Android-based app to capture emotional states and mobile phone usage patterns, which included call logs (and use of apps). Visual analog scales (VASs) were used to report negative emotions in dimensions of depression, anxiety, and stress. In the system-training phase, participants were requested to tag their emotions for 14 consecutive days. Five feature-selection methods were used to determine individual usage patterns and four machine-learning methods were tested. Finally, rank product scoring was used to select the best combination to construct the prediction model. In the system evaluation phase, participants were then requested to verify the predicted negative emotions for at least 5 days.ResultsOut of 40 enrolled healthy participants, we analyzed data from 28 participants, including 30% (9/28) women with a mean (SD) age of 29.2 (5.1) years with sufficient emotion tags. The combination of time slots of 2 hours, greedy forward selection, and Naïve Bayes method was chosen for the prediction model. We further validated the personalized models in 18 participants who performed at least 5 days of model evaluation. Overall, the predictive accuracy for negative emotions was 86.17%.ConclusionWe developed a system capable of predicting negative emotions based on mobile phone usage patterns. This system has potential for ecological momentary intervention (EMI) for depressive disorders by automatically recognizing negative emotions and providing people with preventive treatments before it escalates to clinical depression.

An Investigation of Zeroth-Order Radial Magnetic Forces in Low-Speed Surface-Mounted Permanent Magnet Machines

Zeroth mode of vibration is investigated in low-speed high-torque surface-mounted permanent magnet (PM) machines with non-overlapping concentrated windings. Magnetic field distribution in the air gap is computed using time-stepping finite-element analysis, and Maxwell stress tensor is then employed to calculate the radial force density. Based on the time variation of the mean value of the radial force density spatial distribution, the zeroth-order radial forces are studied. Simple structural equations are used to compare the stator deformations for the machines under investigation. Contribution of the zeroth mode to produce vibration is analyzed and compared with the lowest non-zero mode. The influence of pole and slot combinations and the effect of rectifier load are discussed. This paper is carried out to investigate whether or not the zeroth-order radial forces can be of importance in the presented surface-mounted PM machines that are not connected to pulsewidth modulation (PWM) converters.

Influence on Vibration and Noise of Squirrel-Cage Induction Machine With Double Skewed Rotor for Different Slot Combinations

Quiet induction motors are in great demand at industrial manufacture and social activities. A double skewed rotor structure can effectively reduce an electromagnetic noise by eliminating odd-order radial electromagnetic force and weakening even-order radial electromagnetic force, which are generated by a harmonic field. In this paper, orders of electromagnetic force for different slot combinations are analyzed. The natural frequency of stator is calculated by a modal analysis. Spatial and temporal variation characteristics of radial electromagnetic stress wave of the motor are calculated by a finite-element method, and analyzed in space and time domains by the 2-D Fourier analysis. The induction motor is quiet when both the vibration mode and the frequency of electromagnetic force wave keep away from the resource mode and the natural frequency of stator core. The quietest induction motor is found by means of the comparison with four different slot combinations.

Design and Analysis of an In-Wheel Motor With Hybrid Pole–Slot Combinations

In-wheel motors provide propulsion power for a vehicle on a wide-speed-range basis. Day-to-day driving patterns indicate a particular need for high torque, such as when accelerating from a very low speed or when climbing a hill. Therefore, an in-wheel motor needs to provide not only sufficient power but also high torque, depending on different driving situations. However, high torque and high power frequently represent two separate goals in the motor design that may not be coherent. This paper proposes an innovative motor with a hybrid pole–slot combination that can provide the decoupling of torque and power characteristics at different speed ranges and, therefore, extend the motor’s capability. A feasibility study of the motor was conducted using the finite-element analysis.

PROPER SELECTION OF NUMBER OF SLOTS AND POLES IN FRACTIONAL SLOT PERMANENT MAGNET MACHINES: LOSS REDUCTION APPROACH

Spatial harmonics of magneto motive force induces electrical current in conductive parts of rotor which causes losses in rotor. These losses in fractional slot machines due to high content of spatial harmonic are high. This article aims at introducing a method for rotor losses comparison in different combination of slot per pole in fractional slot and integral slot machines. In order to do that, first a method for winding design and then a method for analytical calculation of losses will be provided. Next a rotor loss index will be introduced by which comparison of different combination of slot per pole is achieved. This index enables one to choose the slot per pole combination that the minimum losses. Finally using the obtained information, two motor with different slot per poles combination were designed and built. The two motor losses were also comparing.