Fractional Number Of Slots Research Articles

The Application of Magnet Structures to Reduce the Cogging Torque Associated with Fractional Slot Number in Permanent Magnet Generators

This study proposes the application of a magnet structure to minimize the cogging torque (CT) and unstable pull in endless magnet generators. The investigation was conducted using an integral slot number of 24 slots and 10 poles, as well as a fractional slot number of 18 slots and 8 poles. The purpose of combining the multi-slot mechanism with pole arc optimization at the magnet edge was to underestimate the peak CT through a reduction in the quantity of tangential flux density. However, the results indicate that CT did not decrease significantly using this method, and this led to the optimization of the edge shape in the magnet structure through the introduction of the surface response method. The combination method’s goal was to ensure a significant reduction in both the integral and fractional slot numbers of the permanent magnet generator. The results show that the CT in the structure with an integral slot number of 24 slots and 10 poles decreased to around 99.4% compared with the baseline structure, while the CT in the structure with a fractional slot number of 18 slots and 8 poles was minimized to 98.8%. This led to the conclusion that the techniques could be combined in structure with any number of integral and fractional slots to reduce CT.

Analysis The Effect Of Magnet Structure On The Unbalance Magnetic Pull Of Fractional Slot Number Type In Permanent Magnet Machine

Within this study, the effect of magnet structure on the unbalanced magnetic draw (UMP) of fractional slot number permanent magnet machines (PMMs) was methodically investigated. The literature revealed that fractional slot number PMMs use a variety of magnet structure configurations, including radial, parallel, and hybrid arrangements. Different magnet configurations were discovered to affect the distribution of magnetic flux density, thereby impacting UMP concentrations. The effect of various magnet geometries, including arc, rectangular, and trapezoidal, on UMP was examined. Moreover, the selection of magnet materials, such as ferrite, neodymium-iron-boron, and samarium-cobalt, influenced the magnetic field distribution and UMP characteristics. Due to their particular slot and pole combinations, fractional slot number PMMs were found to be more susceptible to UMP than other PMM varieties. Unbalanced forces caused by UMP resulted in unwanted vibrations, increased noise levels, and possible machine durability issues. Numerous factors influence UMP in fractional slot number PMMs, including the number of slots and poles, the length of the stator-rotor air gap, the magnet pole breadth, and the magnet thickness. The level of UMP was affected by the interaction of these factors with magnet structure configurations.

To the analysis of magnetoelectric valve motors with integer and fractional number of slots per pole andphase

To the analysis of magnetoelectric valve motors with integer and fractional number of slots per pole andphase

The Effect of Magnet Structure on the Cogging Torque Reduction in a Permanent Magnet Generator

The cogging torque would still be a constant part of permanent magnet-electric machines. This happens because of the construction in which permanent magnets are attached to the rotor, and a slot is present at the core of the stator. The contact between the two, related to the distance between the magnetic surface and the stator slot, makes it challenging to eliminate the cogging torque. This study aims to maximize cogging torque by reducing it with a new method. The proposed method is a mixture of two techniques that indicate significant promise. This invention mixes two techniques to improve the final results. The first process is called magnetic edge shaping, and the second technique is called a dummy slot on the stator. A fractional slot number (FSN) type with 24 slots and 18 poles is the permanent magnet machine used for this investigation. This work is assisted by software version 4.2 of the Finite Element Magnetic Method (FEMM), which will simulate the original and the proposed design. The proposed method proved to be effective in minimizing the peak value of the cogging torque, as shown by the simulation results of 98% of the initial design. Combining the two techniques may reduce the tangential value of the flux so that the flux leading to the slot is lower than the initial design.

Novel of Cogging Torque Reduction Technique for Permanent Magnet Generator by Compounding of Magnet Edge Shaping and Dummy Slotting in Stator Core

This paper dealt with the investigation and implementation of the cogging torque reduction technique in permanent magnet generators with a fractional slot stator/rotor combination of 24 slot/18 pole structure. A novel of cogging torque technique in a permanent magnet generator was developed and proposed in the paper. In the study, the cogging torque reduction technique was based on the compounding of two cogging torque reduction techniques, i.e., the magnet edge shaping with dummy slotting in the stator core of the fractional slot number. By employing the CT reduction technique proposed, effects on the decreasing of tangential flux density in the air gap of the permanent magnet generator, while the normal flux density almost remained constant. The tangential flux density is one important parameter regarding the peak of cogging torque in permanent magnet generator or other electrical machine structure. The normal and tangential flux have been analyzed. The cogging torque of the permanent magnet generator was analyzed and presented in the paper. By compounding both cogging torque reduction techniques, i.e., magnet edge shaping and dummy slotting in stator teeth have been expected to achieve the cogging torque reduction. The electromagnetic performance of the permanent magnet generator was performed using a finite element analysis of FEMM 4.2. It has been proved that by combining of magnet edge shaping and dummy slotting in stator teeth can reduce the cogging torque of permanent magnet generator significantly. It has been found that the cogging torque reduction for the proposed structure around 98.08 % compared with the initial structure.

Study of The Effect of Height and Length of Slotting in Magnet Edge on the Cogging Torque Reduction of Fractional Slot Number in Permanent Magnet Machine

Cogging torque generated in permanent magnet machine effects to some undesirable vibration and noises. In order to minimize the cogging torque in permanent magnet is the most important issues recently. This paper investigated the influence of the value of height and length of slotting in magnet edge on the cogging torque reduction. For purpose of study the structure of 24 slot/10 pole of permanent magnet machines have been chosen. The 2-D finite element based on FEMM 4.2 software was implemented to compute the permanent magnet machine performance. Simulation results showed that by optimising the height and length of slotting in magnet edge can reduce the cogging torque of permanent magnet machine significantly. The most effective way by employing a-two step slotting with 2.5 mm of height and 0.7 mm of length of the slotting in magnet in the first step of slotting. In the second step of in magnet edge, the length of slotting has been assigned as much as 2.3 mm and the height of slotting was 0.588635 mm. By employing the FEMM, three of different magnet structures of permanent magnet machine were analysed. It was found that the cogging torque of permanent magnet machine proposed magnet structure as much as 99.7 % compared with the initial structure of the permanent magnet machine.

Improvement of Cogging Torque Reduction by Combining the Magnet Edge Shaping and Dummy Slot in Stator Core of Fractional Slot Number in Permanent Magnet Machine

A new technique in reducing the cogging torque by combining the magnet edge shaping and dummy slot in stator core of fractional slot number in permanent magnet machine was studied in this paper. The cogging torque is the most issue in permanent magnet application, since it effects to reduce the machine performance. A permanent magnet machine of fractional slot number with 24 slot/20 pole was presented in the paper. Firstly, the permanent magnet machine with conventional both of magnet structure and stator structure has been investigated as the basic reference of initial structure. Secondly, the magnet edge shaping with conventional stator core was investigated. Thirdly, in proposed structure, the combination of magnet edge shaping with dummy slot in stator was employed. The three different structures of the permanent magnet machine then analysed and compared. By implementation of magnet edge shaping combined with dummy slot in stator core has increased the interaction between magnet and stator core. This leads to increase the cogging torque frequency and reduce the peak value the cogging torque of the machine. Using the FEMM, the cogging torque value of the permanent magnet machine was analysed and computed. It was found that cogging torque reduction of the proposed structure as much as 99.47 % compared with the initial structure.

3-D Numerical Hybrid Method for PM Eddy-Current Losses Calculation: Application to Axial-Flux PMSMs

This paper describes a 3-D numerical hybrid method (NHM) of the permanent-magnet (PM) eddy-current losses in axial-flux PM synchronous machines (PMSMs). The PM magnetic flux density is determined using the multi-static 3-D finite-element method (FEM) at resistance-limited (i.e., without eddy-current reaction field). Based on the predicted flux density distribution, the eddy-currents induced in the PMs and the 3-D PM eddy-current losses are calculated by 3-D finite-difference method (FDM) considering a large mesh. Therefore, this 3-D NHM is based on a coupling between the multi-static 3-D FEM and the 3-D FDM. Two 24-slots/16-poles (i.e., fractional-slot number) axial-flux PMSMs having a non-overlapping winding (all teeth wound type) with stator double-sided structure are studied: 1) surface-PM (SPM) and 2) interior-PM (IPM) To evaluate the reliability of the proposed technique, the 3-D PM eddy-current losses are determined and compared with transient 3-D FEM (i.e., magneto-dynamical 3-D FEM). The same nonlinear properties of the laminations have been applied for multi-static/transient 3-D FEM. The computation time can be divided by 25 with a difference less than 12%.

The Comparative Analysis of Permanent Magnet Electric Machines with Integer and Fractional Number of Slots per Pole and Phase

The comparison of permanent magnet motors with integer and fractional number of slots per pole and phase was made. The torque developed by the motor and the torque ripples level were chosen as the major criterions. The comparison was made according to the results of equations of numerical calculation of magnetic field in active motors volumes using the finite element analysis. The recommendations on the choice of the most suitable option are given.

Analysis and Experimental Tests of the Sensorless Capability of a Fractional-Slot Inset PM Motor

The sensorless techniques based on high-frequency signal injection to determine the rotor position is applied to an inset permanent-magnet (PM) motor, whose rotor is characterized by small iron teeth between each couple of PMs. Although these rotor teeth, which are centered along the $q$ -axis, do not significantly contribute to torque production, they yield appropriate rotor saliency to be exploited for the rotor position sensorless detection. The inset PM motor considered in this paper is characterized by a fractional-slot stator, i.e., by a fractional number of slots per pole and per phase. Such a solution is commonly used when a surface-mounted PM machine is considered since it exhibits a higher torque density. A 12-slot 8-pole inset PM motor is investigated as far as its self-sensing capability. Both finite-element analysis and experimental measurements are presented, showing satisfactory agreement. It is shown that the prototype of the inset PM motor available in the laboratory exhibits a good capability to be controlled by sensorless techniques. However, a negative effect is recognized by a nonnegligible ripple of torque and flux linkages. They affect the dynamic performance of the PM motor drive.

FEM Analysis of Brushless DC Servomotor with Fractional Number of Slots per Pole

The authors present in this paper the analysis with Finite Element Method (FEM) of the magnetic circuit for a Brushless DC servomotor with fractional number of slots/pole (9 slots and ...

Rotor design strategy of interior permanent magnet synchronous motor for fuel cell electric vehicle

Thispaper proposes arotor-designstrategyofinteriorpermanent magnet synchronous machine (IPMSM)considering various design constraints for a fuel-cell electric vehicle. The conventional process in the rotor design only considers the magnitude of the iron loss or the magnet loss while neglecting the loss distributions in the rotor core. This approach results in a design where losses are accumulated on a localized region in the rotor core, especially in the case of IPMSM with a fractional number of slots per pole. This can cause significant irreversible demagnetization of the permanent magnets since the rotor core usually suffers from poor heat transfer. The proposed strategy targets this problem by focusing on the loss distributions according to driving condition. In addition, it offers a parallel approach where mechanical stress analysis is combined with the rotor design process in order to guarantee mechanical strength by centrifugal force at maximum speed. The validity of proposed method was verified by comparing simulation result using the finite element method with experimental data.

Magnetomotive force of stator multiphase windings with fractional number of slots Q per pole and phase

A method for investigating the magnetomotive force (MMF) of a stator multiphase winding with arbitrary number of slots Q (including the case when Q < 1) is presented. The structure of the synchronous generator is improved using the six-phase stator windings with fractional number of slots Q per pole and phase and, as a result, the lower space and time harmonics cannot appear in the MMF curve.

Analysis of Radial Force on a Permanent Magnet Synchronous Motor Caused by Dimensional Variation

Main reasons for causing vibration in a permanent magnet synchronous motor (PMSM) are torque ripple and radial force harmonics, and hence, both of them are undesirable in high-precision machine tools and accurate motion-control actuators. Recent research on radial force is the prediction of major vibration frequencies and modes in terms of motor design such as different winding types and a fractional slot number per pole in the stator. Also, proper phase current has been investigated for minimizing radial force harmonics. During the previous studies, all the motors are assumed to be ideally built up in terms of mechanical dimensions, but it is impossible due to dimensional variation within or outside tolerance in production. Therefore, in this paper, the effect of several key factors on radial force is examined and compared regarding manufacturing imperfection.

Modular Three-Phase Permanent-Magnet Brushless Machines for In-Wheel Applications

This paper describes the merits of a recently developed form of a three-phase permanent-magnet (PM) brushless AC machine in which the concentrated coils of each stator phase are wound either on adjacent teeth or on alternate teeth. Such a machine is often referred to as modular and offers a number of significant advantages over conventional PM brushless machines. For example, it results in a smaller number of slots for a given number of poles, which is a distinct manufacturing advantage, and yields a fractional number of slots per pole, which is conducive to low cogging torque. It also enables a significant increase in the achievable machine inductance to facilitate constant power operation over a wide speed range by flux weakening. However, the torque in modular machines is developed by the interaction of a high-order stator space harmonic MMF with the PMs, since the fundamental stator MMF has fewer poles than the PM rotor. Hence, significant eddy currents may be induced in the rotor by the fundamental and low-order space harmonic MMFs. The eddy-current loss can, however, be reduced by segmenting the magnets. Given that modular machines combine the high specific power and efficiency of conventional PM brushless machines with a high machine inductance, to enable a wide speed range, constant power operation, their potential for low manufacturing cost, and the fact that they have inherently low cogging torque, they are eminently suitable for in-wheel traction applications.

Harmonic analysis of MMF of three-phase fractional symmetric windings of the electric machines

Harmonic analysis of the magnetic motive force (MMF) of m′ = 3 and m′ = 6 zone symmetric electric winding machines with a fractional number of slots per pole and phase q = z/(m′p) = N/d is carried out. A software program is developed for values of d = 2–50 not divisible by m = 3, illustrated by examples of harmonic analysis of double layer windings when d = 2, 4. We present new diagrams that make it possible to exclude the subharmonic v = 1/2 from the MMF; they are optimized according to the condition of the differential scattering minimum

Design considerations for fractional-slot winding configurations of synchronous machines

This paper presents some design considerations for synchronous machines characterized by a fractional number of slots per pole per phase. The main advantage of this configuration is a smooth torque, which is due to the elimination of periodicity between slots and poles. A second advantage is a higher fault-tolerant capability, making the machine able to work even in faulty conditions. However, the fractional-slot configuration presents a high content of MMF harmonics that may cause an unbalanced saturation and thus an unbearable torque ripple. A method to design fractional-slot machines is illustrated in this paper, including double-layer and single-layer windings. The analytical computation is extended to determine the harmonics of MMF distribution. Their effect is highlighted in isotropic as well as anisotropic machines. Finally, some considerations are reported to avoid unsuitable configurations

Synthesis of cogging-torque waveform from analysis of a single stator slot

A simple analytical technique is proposed to synthesize the cogging-torque waveform of a permanent-magnet brushless machine from the cogging torque, which is associated with a single stator slot. An analytical expression is derived, which reveals the relationship between the two. It is then applied to two motors, which have a fractional number of slots per pole. It is shown that the resultant cogging-torque waveform can be synthesized to a high accuracy, as confirmed by both finite-element analysis and measurements. It is also shown that not all the cogging-torque harmonics that exist in the cogging-torque waveform due to a single slot will be present in the resultant cogging torque, and that the most significant components can be identified analytically.

Eddy-current loss in the rotor magnets of permanent-magnet brushless machines having a fractional number of slots per pole

We develop an analytical model for predicting the eddy-current loss in the rotor magnets of permanent-magnet brushless machines that have a fractional number of slots per pole, when either all the teeth or only alternate teeth are wound, and in which the unwound teeth may be narrower than the wound teeth. The model enables the magnetic field distribution in the air gap and magnet regions to be determined, by neglecting the eddy-current redistribution effect and assuming that the eddy currents are resistance limited. It can account for space-harmonic magnetomotive forces (MMFs) resulting from the winding distribution and time-harmonic MMFs due to nonsinusoidal phase currents, as well as for the effect of curvature and circumferential segmentation of the magnets. We have validated the model by finite-element analysis, and used it to investigate the eddy-current loss in the magnets of three surface-mounted magnet brushless motors that have similar slot and pole numbers, and employ identical rotors but different stators, when they are operated in brushless ac (BLAC) and dc (BLDC) modes. We show that the stator winding configuration, as well as the operational mode, significantly influence the resultant eddy-current loss.

Simulation of wave-energy converter with octagonal linear generator

To extract electrical energy from sea waves in a commercially and technologically acceptable manner, a number of issues have to be solved. Electricity generation by means of direct conversion of the oscillating gravitational potential energy of a floating buoy can be anticipated, provided a proper design of a generator could be made. This paper deals with the simulation of a novel design for a linear generator aimed for the extraction of energy from ocean waves. The ocean waves are modeled by 4-m-height sinusoidal waves with a characteristic period of 7 s. A wide range of the geometrical sizes, permanent magnets, stator winding, and spring forces acting on the buoy are possible. This paper presents simulations of octagonal three-phase linear generators in the 100-kW power range. The beneficial effects of a stator of octagonal shape are briefly investigated, but not studied in depth. The main emphases in the present study have been to decrease power fluctuations and suppress voltage harmonics. In conventional rotating machines, well-known measures are to use a fractional number of slots per pole and phase, and an additional method is to make the pole edges smoother. These methods are here simulated for the first time on a linear machine aimed for ocean wave-energy conversion and a substantial reduction in power fluctuations and voltage harmonics are predicted.