Rotor Teeth Research Articles

Improved air gap permeance modelling for single-slice magnetic equivalent circuits of skewed induction motors

PurposeWhen rotor and stator teeth are close, the connecting air gap flux tube's cross-sectional area exceeds the tooth overlap area. This flux fringing effect is disregarded in the air gap permeance calculation of single-slice magnetic equivalent circuits (MECs) of electric motors with skewed rotors. This paper aims to extend an air gap permeance calculation method incorporating flux fringing for unskewed rotors to skewed and radially eccentric rotors.Design/methodology/approachAssuming axial independence, the unskewed air gap permeance is rotated according to the skew and integrated along the axial dimension, resulting in a first method. The integral is approximated analytically, resulting in a second method. Results are compared to a commonly used reference method and validated using a non-linear finite element method (FEM) simulation.FindingsThe proposed methods provide better alignment with the FEM validation compared to the reference method for skewed rotors and common rotor eccentricity, i.e. below 50% of the air gap length. The analytical method is shown to be competitive with the reference method regarding computational time cost.Originality/valueTwo novel air gap permeance methods are proposed for single-slice MECs with skewed rotors. Their characteristics are discussed and validated.

A novel boost power converter suitable for bearingless switched reluctance motor with wider rotor teeth

Abstract Aiming at the problem that the excitation current build-up speed of the bearingless switched reluctance motor with wider rotor teeth (BSRMWR) is too slow during commutation, this paper proposes a simple structured boost power converter. When the motor is commutation, it uses the winding demagnetization energy to quickly establish the excitation current for the latter phase winding and realizes the low torque ripple operation of the motor on the basis of ensuring the stable levitation of the motor. The topology and working status of the novel power converter are analyzed. On this basis, a 12/8 pole single-winding BSRMWR driving system based on the novel boost power converter is constructed. Through Matlab/Simulink simulation, the feasibility and effectiveness of the novel power converter are verified.

Investigation of torque and sensitivity analysis of a two-phase hybrid stepper motor

Abstract Stepper motors are extensively used in various automated systems, notably hybrid stepper motors (HSMs), renowned for their high torque density. Optimizing and improving their performance and torque density is highly beneficial. The first step in motor optimization is to perform a sensitivity analysis to identify the parameters most significantly affecting motor performance and torque density. Using Ansys Maxwell, a finite element method (FEM) software, we modeled and analyzed a commercially available HSM. After validating the computer model’s accuracy, we investigated the motor’s sensitivity to various parameters and discussed their effects on performance. Our findings highlight the significance of parameters such as air gap, magnet diameter, wire-turn numbers in the coils, and the shapes of the rotor and stator teeth in influencing HSM sensitivity—conversely, factors like magnet height and stator pole thickness exhibit negligible impact on motor performance.

Iron loss calculation model of high‐voltage multi‐pole asynchronous motors considering high harmonic flux density

AbstractA variable coefficient segmented iron loss calculation model is proposed for high‐voltage multi‐pole asynchronous motors, which fully considers the influence of high‐order harmonic magnetic density on such motors. This model introduces additional hysteresis loss, improved eddy current loss coefficients, and rotation magnetisation coefficients to account for changes in losses due to small hysteresis loops and skin effect, as well as rotation magnetisation losses. A 710 kW 10‐pole asynchronous motor is used as the research object. A full‐domain iron loss calculation model considering stator and rotor tooth top surface losses is developed. The model can be used to accurately calculate the overall and local harmonic iron losses in the stator and rotor cores of high‐voltage multi‐pole asynchronous motors. And quantitatively analyse the distribution pattern of any harmonic iron loss at any location in the motor core. It realises the refinement calculation and analysis of iron losses in the whole domain of high‐voltage multi‐pole asynchronous motor. Finally, no‐load and load tests were conducted on the 710 kW 10‐pole asynchronous motor. The iron losses of the 710 kW 10‐pole asynchronous motor at no load and load are calculated using the above mentioned model and the classical trinomial constant factor model. The results are compared with the measured iron loss values. It is proved that the iron loss model is more accurate in calculating the iron loss of high‐voltage multi‐pole asynchronous motor. The result helps researchers to calculate the iron loss distribution of high voltage motors more accurately. Thus, the design and operating parameters of the motor can be optimised to improve the efficiency and performance of the motor. It provides the necessary technical support and key basis for the reduction of loss and energy saving of high‐voltage motors and the optimisation of their core structure.

Magnetic Field Analysis and Development of Disk Axial–Radial Hybrid Excitation Generator for Range Extenders in Extended-Range Electric Vehicles

Magnetic Field Analysis and Development of Disk Axial–Radial Hybrid Excitation Generator for Range Extenders in Extended-Range Electric Vehicles

Cogging Torque Reduction of Axial-Modular Flux Switching Permanent Magnet Machine by Module Combination Technique

Flux switching permanent magnet machine exhibits high cogging torque due to the doubly salient topology and high air gap flux density. This paper proposes a new axial-modular flux switching permanent magnet (AM-FSPM) machine, which has an improved torque capability and the potential of cogging torque suppression by module combination technique. The cogging torque analytical expression of the machine with axial-modular topology is derived based on a magnetomotive force-permeance model. Then, the AM-FSPM machines are divided into two types by the combinations of stator-slot and rotor-pole, named fundamental harmonic offset naturally and fundamental harmonic offset manually. In addition, four approaches are investigated to reduce cogging torque by changing modular magnetomotive force and changing modular permeance. It can be concluded that the modular rotor tooth combination method has the most attractive torque performances among the four methods. Finally, the effectiveness of the proposed approaches is verified by the 3D finite element analysis and experimental results.

A pole-changing flux reversal permanent magnet motor

In this paper, a pole-changing (PC) flux reversal permanent magnet (FRPM) motor is proposed for obtaining a wide speed range. According to the general air-gap field modulation theory, the permanent magnet (PM) magnetic field is modulated into a series of harmonics with different pole numbers by rotor teeth. By introducing an especial PM arrangement, two groups of working harmonics with different pole-pair numbers are generated in the proposed 12-7 PC-FRPM motor due to the modulation of rotor teeth. Based on the calculated slot pitch angles of these harmonics, two winding connections can be obtained for PC operation to achieve two operating modes. The electromagnetic performance of PC-FRPM motor before and after PC are analyzed using finite element analysis and verified by the experimental test results.

Performance Enhancement of Flux Switching Motor for Electric Vehicle Applications: An Overview

As the reduction of greenhouse gas emissions becomes crucial, electric vehicles (EVs) are expected to enter the market extensively in the coming years. The efficiency of the electrical motor used in EVs plays a significant role in their overall performance. This paper explores the flux switching motor (FSM) and its applications in EVs. The FSM is compared to other electrical motors, highlighting its potential as a suitable choice for EV traction. Various configurations and techniques are reviewed to enhance the performance of FSMs, including magnetic materials, torque ripple alleviation, and magnetic flux weakening. The advantages and disadvantages of these methods are discussed, providing valuable insights for designing FSMs for EVs. Generally, EV traction requires high torque density and high power density electrical motor. To achieve these goals, high electric and magnetic loading must be considered in design stage of the motor. Application of the FSM may be one of the appropriate option. For many reasons, three-phase FSM is preferred. Considering the base speed of machine in the EV and high electric loading, the FSM with 12 stator teeth and 10 rotor teeth may be the most appropriate choice in which the stator core is oriented and rotor core is nonoriented iron. To enhance the torque density and applied flux weakening method, combination of Nd and Al–Ni–Co magnets is preferred.

A modified approach for efficient cogging torque suppression in a flux switching permanent magnet generator used in micro‐scale wind turbines

AbstractIn recent years, Flux Switching Permanent Magnet (FSPM) machines have attracted notable attention in direct drive, low speed, and high torque density applications such as wind turbines. However, their relatively high cogging torque has been identified as a significant challenge for such applications primarily because of its effects on both starting and running performance of the wind turbines. The authors, therefore, aim to present a modified approach that can improve the cogging torque issue and eliminate the weaknesses of the previously introduced designs. To reach this goal, first, an operating point is chosen for the studied machine regarding the available small‐scale turbines in the market. Then, the potential benefits of combining different cogging torque reduction schemes are investigated thorough the proposed method. This is intended to be done on the rotor teeth without imposing any complications or extra costs. The results show that a simultaneous improvement in the cogging torque and the energy conversion capability of the machine could be achieved through this cost‐effective approach. To end with, the sensitivity of the best cases to the expected manufacturing tolerances is investigated. All analyses are performed via two‐dimensional finite‐element (2D‐FE) models, the accuracy of which has been pre‐certified through experimental measurement.

Design and Optimization of a Pole Changing Flux Switching Permanent Magnet Motor

A flux switching permanent magnet (FSPM) motor is designed and optimized in this paper to achieve high torque density and expanded speed regulation range from a design viewpoint of pole-changing (PC). Based on the field modulation theory, the PM field in the FSPM motor is modulated by the stator and rotor teeth, generating rich harmonics with different pole-pair numbers in the air-gap flux density. By adopting an appropriate slot pole combination, working harmonics with different slot pitch angles are obtained to establish a basis of the PC-FSPM motor. Then, different working harmonics can be used to achieve different energy conversions with different winding configurations, so the PC operation can be performed to realize the high torque and wide speed regulation range by switching the working modes. Based on the field modulation theory, the operation principle of conventional and PC-FSPM motors are analyzed and compared. Then, according to the design principle of the PC-FSPM motor, a 24/22-pole PC-FSPM motor with the E-core is designed and optimized by a multi-level optimization method. Finally, the electromagnetic performances are analyzed by finite element analysis and the test results of the prototype have verified the feasibility of the motor.

Comparative Analysis of Novel Asymmetric Consequent-Pole and Conventional Flux Reversal Permanent Magnet Machines

Torque density is a critical performance index for flux reversal permanent magnet (FRPM) machines. In this paper, a novel asymmetric consequent-pole (ACP) FRPM machine with alternate teeth wound is proposed. Different from the conventional consequent-pole FRPM machine with uniform “Fe/N-Fe/N-Fe/N” structure, the proposed ACP FRPM machine adopts “Fe/N/Fe-N-Fe/N/Fe” topology. With the novel topology, torque capability of the proposed machine is significantly improved due to the newly produced lower working harmonics of air-gap flux density. The operating principle of the proposed ACP FRPM machine is analyzed based on the magnetomotive force (MMF)-permeance model with variable winding factors and validated by finite element analysis (FEA). The effects of geometric parameters such as magnet, main tooth-tip and rotor tooth width on average torque and torque ripple are also investigated. Finally, a prototype has been manufactured to validate the theoretical results. With experimental test results, it is demonstrated that the proposed topology can achieve 109.1% higher back EMF and 55.7% higher torque density despite the stator current is reduced by 25.4% compared with the conventional consequent-pole FRPM machines.

A 2D hybrid analytical electromagnetic model of the dual‐stator axial‐field flux‐switching permanent magnet motor

AbstractThe two‐dimensional (2D) analytical model for the calculation of the components of the flux density distribution in the air gap in a dual‐stator axial‐field flux‐switching permanent magnet (PM) motor (DSAFFSPM) is presented. The novelties of this study are deriving a 2D hybrid analytical model and replacing the rotor teeth with some surface currents for the calculation of air‐gap magnetic flux density for the first time in the DSAFFSPM motor. The 2D analytical model for DSAFFSPMs is more challenging due to the doubly salient structure and inner PM of the stator. 1D analytical interior PMs are first transferred to the bore of the stator body using the magnetic equivalent circuit model (MEC). Next, the effects of the rotor teeth are taken into consideration by injecting virtual surface currents for 2D analytical model. Applying boundary conditions and solving the Laplace/Poisson equations, the vertical and tangential flux components of the flux density distribution in the air‐gap DSAFFSPM motor are computed. The verification of the proposed method and the obtained results are validated by the 3D finite element method.

A Brushless Hybrid Excited Motor Based on Field Modulation Theory

This paper proposes a novel brushless hybrid excited (HE) motor, in which both armature and field windings are located on the stator, and PMs are housed on the rotor. The key difference is that a special consequent-pole rotor structure is adopted, in which each two PMs is separated by a rotor tooth. So, when DC current is fed into the field winding, the produced stationary wound field can be modulated by the rotor teeth to generate rotary wound field harmonics. Thus, an effective HE operation can be achieved due to the interaction between the synchronous rotating PM field and the wound field harmonics. The motor configuration is introduced firstly. Then the operating principle is discussed by the magnetic field modulation theory. By finite element analysis, the electromagnetic performances are calculated and analyzed. The results verify the validity of theoretical analysis.

ANALYZING A THREE HUNDRED TEETH BI-PHASE HYBRID STEPPER MOTOR WITH DIFFERENT NUMBERS OF POLE PAIRS

The paper presents numerical models of a bi-phase, 0.3° full step hybrid stepper motor (HSM), with 16, 24, 32, 40, and, respectively, 48 poles in the stator. For the motor to move with a constant step angle, the stator and the rotor teeth must be shifted against each other with an angle of zero, 90, 180, and 270 electric degrees for each four consecutive stator poles. Due to this, bi-phase steppers with the number of poles in the stator different than eight are hardly seen. Therefore, to allow the construction of HSMs with different numbers of poles, some of the stator poles must be shifted from their symmetrical position. The five topologies' HSM detent and holding torque characteristics and their geometrical and constructive differences are presented. The Finite Element Method (FEM) based models are developed using the professional software COMSOL Multiphysics.

Influence of geometrical and operational parameters on tooth wear in the working mechanism of a satellite motor

This article describes the phenomena affecting the wear of the rotor of the working mechanism in a hydraulic satellite motor. The basic geometrical relationships that allow the calculation of the coordinates of the points of contact between the satellite and the rotor and the curvature are presented. A method for calculating the number of contacts of the satellite teeth with the rotor teeth and of the satellite teeth with the curvature teeth during one revolution of the rotor is proposed. A method of calculating the forces acting at the points of contact of the satellite with the rotor and the curvature is also proposed, as well as a method of calculating the stress in the tooth contact of the interacting components of the mechanism. The results of calculations of forces and stresses in tooth contact in a satellite mechanism consisting of a four-hump rotor and a six-hump curvature are presented. It is shown that the two chambers around the satellite are in the same phase in a certain range of the rotation angle of the rotor, i.e. in the emptying phase or in the filling phase. This results in the value of the force acting on the satellite resulting from the pressure difference being zero. It has also been shown that the most important parameters affecting tooth wear are the pressure difference in the working chambers of the satellite mechanism and the rotor speed.

Comparative analysis of various materials for linear switched reluctance motor applied in railways

Linear switched reluctance motors (LSRM) are a very important and one of the most researched motors for applications in railways due to its robust structure, superior efficiency, lower mass production cost and superior tolerance towards faults. The study of electromagnetic properties plays a pertinent role in the selection of materials for linear switched reluctance motor. In this work a Finite element method (FEM) based tool is used for visualizing the electromagnetic field (magnetic flux) within the LSRM. The ANSYS maxwell software is used for obtaining the magnetic flux density variation in various materials. Based on the electromagnetic analysis of different materials obtained using the ANSYS software, the selection of material suitable for design of motor for implementation in railways application is made. The electromagnetic analysis between the stator and the translator is investigated and based upon this the selection of material is made. The magnetic flux between the stator and rotor teeth are analyzed during both the instants of alignment and unalignment. Various materials namely Cobalt, Steel 1008 and Samarium Cobalt (SmCo4) are tested and analyzed using the FEM based ANSYS software.

Numerical-field analysis of active and reactive winding parameters and mechanical characteristics of a squirrel-cage induction motor

Introduction. The active and reactive (inductive) winding resistances of three-phase asynchronous motors (IM) are investigated. These important parameters are determined during design and are the basis for calculating a number of energy parameters and characteristics. Problem. In the classical design of IM, the winding resistances are determined with insufficient accuracy due to a number of assumptions and conventions. Especially it concerns the operation of IM with increased slip and it affects the accuracy of realization of its design data, starting parameters and characteristics. Goal. The paper aims to further develop the IM design system by numerical-field computational analysis of active and reactive resistances of the IM windings in the whole range of changes in its slip and calculation of the mechanical characteristic of IM to confirm the adequacy of the calculations of these resistances. Methodology. Resistances of the IM windings are determined by numerous calculations of the magnetic fields of dispersion with the FEMM program within stator and rotor teeth steps, and with current displacement in a squirrel-cage rotor core. Everything is done in the slip range when operating from start-up to idle with changing currents in the slots and the corresponding magnetic saturation of the core teeth. A Lua script has been created for the calculations, controlling the FEMM program and providing automation of all calculations. Results. The numerical-field method shows that the classical design method gives very large errors in determining the magnetic conductivities of IM slot dispersion, as well as current displacement in the bars of the squirrel-cage rotor winding. This is especially evident with increased slips in the start-up mode. Originality. Numerical estimates of the differences between the classical and numerical-field methods are given and the origin of errors is analyzed: the strong saturation of the teeth of the stator and rotor cores. This leads to a significant decrease in the magnetic conductivities of slot dispersion and the practical absence of current displacement in the rotor bars, on which the main emphasis was previously made. The obtained results made it possible to calculate the mechanical characteristic of the IM according to a transparent formula without the use of correction coefficients and reference graphical functions. Practical value. The provided technique of numerical-field analysis and the obtained results of the calculation of active and reactive winding resistances and mechanical characteristic are recommended as a basis for the improvement of the IM design system.

New design and optimization of an in-wheel permanent magnet motor with tangentially magnetized magnets and unequal stator teeth

Abstract Permanent magnet synchronous machines (PMSM) are competitive motors for in-wheel traction systems of electric vehicles. A new tangentially magnetized permanent magnets machine with outer rotor and unequal stator teeth for in-wheel motor application is proposed in this paper. The analytical calculations of the proposed topology are presented by determining the magnetic flux densities and the iron losses in all parts of the machine. The machine design is optimized using three state-of-the-art multiobjective algorithms which are AbYSS, MOCell and NMOPSO algorithms. Moreover, the optimization procedure is carried out according to three objectives: the maximization of the machine efficiency and the minimization of the mass and ripple torque. The optimization results showed that all the algorithms can find a set of optimal solutions and that the NMPSO algorithm outperforms the other two techniques. The finite element method (FEM) is used to investigate the optimization results. It is observed some magnetic saturation in the rotor yoke and the magnet’s extremes. The value of the induction in these machine regions is about 1.9 T. The comparison between the FEM and optimization results proved the rationality of the proposed optimization procedure.

A Novel Flux-Reversal Bearingless Slice Motor Controlled by Rotor Angle Independent Suspension Current

A novel flux-reversal bearingless slice motor with rotor angle independent suspension current (DC-FRBLM) is proposed in this article. The rotor is simple and robust with neither a permanent magnet (PM) nor field windings. And the suspension currents can be controlled independently from the rotor angle. As a result, the merits of fault tolerance, high structure compactness, simple control, and low manufacturing difficulty can be realized. The topology and circuit of the proposed DC-FRBLM are introduced first. The combination requirement of stator slot and rotor tooth number is investigated. Simultaneously, the suspension principle is analyzed theoretically by studying the airgap harmonics of the PM field and armature field. Then, three DC-FRBLMs with different stator slot numbers are analyzed based on finite element analysis. The suspension principle is verified by the airgap field FFT results. The effects of some key design parameters are investigated in order to improve torque/suspension performance. Finally, a DC-FRBLM prototype is manufactured and tested to confirm the theoretical analysis. The experimental results show the proposed prototype can be steadily suspended with rotor angle independent suspension current.

Contribution to Improve Magnetic Performance and Torque Ripple Reduction of the Low-Speed DSPM Machine

This article deals with the performance improvement of a toothed pole variable reluctance machine excited by permanent magnets housed in the stator yoke. The objective was to reduce the electromagnetic torque ripples caused by the structure geometry and by the supply technique. The machine was designed to meet the specifications of a small wind energy conversion system. The proposed solution improved the electromagnetic design of the new structure in order to minimize the variation of the reluctance. This improvement was obtained by action on the geometry of the structure (the location of the permanent magnets), by action on the stator and rotor tooth pitch, and by the application of an indirect control strategy called torque sharing function. The PSO optimization algorithm was applied in the first part for the optimization of the machine’s global parameters to maximize torque density and then, in the second part, for the research of the optimum tooth pitch parameters to minimize torque ripple. Static and dynamic performances were obtained using 2D-FEM and MATLAB/Simulink software. The results reveal that by action on the stator/rotor tooth pitch, the ripple torque was reduced by about 53%, and by approximately 76% with the used command technique.