Stator Pole Research Articles

Design and Optimization of a Partitional Stator Flux-Modulated Memory Machine

In this article, a partitional stator flux-modulated memory machine (PS-FMMM) is proposed. Compared with a conventional variable-flux memory machine, it can significantly improve the torque density due to magnetic gear effect and PS, and can have good flux-regulating capability with AlNiCo magnets. First, the basic principle of the proposed PS-FMMM is introduced, and different combinations of stator poles and rotor poles are compared. Then, the torque-regulating characteristics of the proposed PS-FMMM under different magnetization levels of AlNiCo magnets are obtained. Finally, the pole-arc ratio of iron piece and parameters of AlNiCo magnets are optimized based on sensitivity analysis. Various finite-element analysis (FEA) simulation, optimization, and comparison studies of the proposed machine are performed. The results verified the effectiveness of the proposed structure.

Performance Analysis of a New Switched Reluctance Motor With Two Sets of Embedded Permanent Magnets

This article proposes an enhanced-torque switched reluctance motor with two sets of permanent magnets (PM-SRM) embedded inside the stator yoke and the end teeth of the neighboring modules. The PMs contribute to intensify the air-gap flux density and reduce the magnetic saturation in the stator poles. As a result, the output torque can be enhanced to a significant extent. The working principle of the proposed PM-SRM is clarified using its magnetic circuit model (MCM). The characteristics of the PM-SRM are obtained and compared with classical 12/8 and 6/5 SRMs and hybrid reluctance motors (HRMs) in terms of static and average torque and average torque per PMs volume. The steady-state performance of the PM-SRM in terms of current and torque waveforms is carried out, and the PM-SRM is compared with considered SRMs and HRMs in terms of output torque, power, and efficiency. All the comparisons demonstrate the out-performance of the proposed PM-SRM over other SRMs and HRMs. To validate the simulation results, a prototype of the PM-SRM is manufactured and the experimental results are obtained. Both the simulation and experimental results are indicative of the fact that the proposed PM-SRM can gain high torque and high PM utilization factor, simultaneously.

Acoustic Noise Mitigation of Switched Reluctance Machines with Windows on Stator and Rotor Poles

Switched reluctance machines (SRMs) have been studied by many researchers as an alternative to the other types of electrical machines for use in electric and hybrid vehicle applications. SRMs are fault tolerant and have wide speed operating range. However, they suffer from several disadvantages, including high vibration, acoustic noise, and torque ripple. In this article, the placement of rectangular windows in both the rotor and stator poles is proposed to reduce the vibration and acoustic noise of SRMs. An iterative optimization algorithm in a wide speed range of operation using finite-element analysis (FEA) tools provides the best position and dimension of window design parameters. Multiphysics FEA is also performed to predict the vibration and acoustic noise of the optimized design. The results of this study present that placing windows in both the stator and rotor of the SRMs can significantly reduce the acoustic noise compared with the baseline SRMs. Based on the simulation results, the optimum design has been constructed as a prototype and tested in a wide speed operating condition. The simulation and experimental test validation results prove the effectiveness of the proposed design in mitigating the acoustic noise and vibration.

Negative and Complex Reluctance in Injective Profile Section

Losses in magnetic circuits are closely related to reluctance. Dealing with coils, transformers, stator poles, rotors in motors, and electromagnets with iron slabs in electrical actuators may raise the question regarding the effect of the slope of section profiles on losses and performance. In this letter, with dc and ac sources, through injective section profiles, we obtain complex, negative, and quantified reluctances. The results suggest that the imaginary part of the reluctance can lead to reduced ferromagnetic materials losses. This means that imaginary reluctance is not always related to electrical conductivity and to power losses but also to the interaction of magnetic flux with the shape of the magnetic core. The imaginary reluctance can be used to increase active and reactive power and reduce magnetic losses. The negative reluctance was effective in reducing magnetic flux and magnetic flux density in a magnetic core.

Non-uniform air gap modeling and electromagnetic characteristics of a new six-phase doubly salient electro-magnetic generator

The voltage harmonics of the six-phase doubly salient electro-magnetic generator (DSEG) are large, and the electromagnetic isolation is poor due to the mutual inductance of the armature winding. An optimization scheme for the stator non-uniform air gap structure is proposed. By establishing a non-uniform air gap angle function model, the analytical expression of the induced electromotive force in the non-uniform air gap structure is derived. Using finite element and mathematical model to verify that the stator tip is changed from circular arc to linear structure can increase power and reduce voltage high harmonics, improve the power quality of the generator. Based on the equivalent magnetic circuit, the influence of the winding method of the excitation winding on the mutual inductance of the armature winding is studied. When the field winding is wound interval every two stator poles, the mutual inductance is small. The electromagnetic properties of the new six-phase electric excitation double salient pole are analyzed by two-dimensional finite element analysis. The rationality of the proposed motor structure is verified by experiments.

A novel doubly salient electro-magnetic generator with symmetrical phase magnetic circuits: Basic topology, analysis, and experimental verification

The field winding of conventional multiphase doubly salient electro-magnetic generator is wound across multiple stator poles. There is a problem that the flux paths of the respective phases are not completely symmetrical. A novel E-core stator was proposed, the basic topology of the multi-phase E-core doubly salient electro-magnetic generator (E-core DSEG) with symmetrical phase magnetic circuits is derived by using the electrical formulas. This establishes a theoretical basis for the design of multiphase E-core DSEG. Based on the finite element simulation software, the static characteristics of multi-phase E-core DSEG were analyzed, including magnetic field distribution no-load electromotive force, flux linkage, self-inductance of field winding, cogging torque and so on. Finally, a prototype of three phases 18/20-pole generator was made and tested. The rationality of theoretical analysis and generator topology was verified by simulation and experiment.

Уточнение моделей расчёта момента при проектировании явнополюсных индукторных двигателей

The article suggests a procedure for designing salient-pole inductor motors with developed tooth structures on the rotor and stator, which is supplemented by nonlinear calculation of a fragmentary magnetic circuit model with subsequently refining the saturation coefficient. The calculation is carried out using the semigraphical method before and after displacement of the rotor from the position of maximum air gap permeance by half the rotor tooth division with respect to teeth on the stator pole extension. Owing to introducing a weakly branched nonlinear magnetic circuit model into the design algorithm, in became possible to elaborate detail designs of motors for important electric drives of automatic systems, which confirmed their declared characteristics. It is noted that demagnetization of the magnetic circuit ferromagnetic areas, which is determined by calculation on the nonlinear model after turning the rotor by half the tooth division from the coaxial position, is the criterion of the correctly selected tooth area geometric parameters and electromagnetic loads.

A study on the shape between the stator poles of a homopolar magnetic bearing integrated with four C-shaped cores

There are two types magnetic bearings in general, heteropolar-type magnetic bearing (Heteropolar-type MB) and homopolar-type magnetic bearing (Homopolar-type MB). For each type of magnetic bearing, it has its own disadvantage. Heteropolar-Type MB cost low because of the low usage of the magnet, but high iron loss decides it is difficult to be cooling down. Homopolar-type MB has a low iron loss and can be cooling down easily, but cost is high because of high usage of magnet and has a complex structure. In this paper, our research group focused on the problem and proposed a new Homopolar-Type MB structure unifying four C-shaped cores, which can suppress the iron loss with a low usage of magnet and can be cooling down easily. What’s more, we also considerate the influences by the change of the structure and proposed the optimal one. The excellent characters of the new type Homopolar-Type MB will be shown by 3D-FEA.

Source of Acoustic Noise in a 12/16 External-Rotor Switched Reluctance Motor: Stator Tangential Vibration and Rotor Radial Vibration

Compared with internal-rotor switched reluctance motors (SRMs), external-rotor (ER) SRMs can show different vibration and acoustic noise behavior due to the differences in the designs, e.g. thinner rotor back iron to achieve smaller inertia, and longer stator pole height to improve the electromagnetic performance. This paper presents the considerations in the modeling and analysis of the acoustic noise sources of an ER SRM stator and rotor. The harmonic components of the stator tangential force density and rotor radial force density are analyzed and compared. The vibration modes, the vibration behavior, and acoustic noise of the stator and rotor are also compared. A 12/16 external-rotor SRM designed for a direct-drive E-bike application is used for the modeling, analysis, and experimental validation of vibration and acoustic noise. It is concluded that both the stator tangential vibration and the rotor radial vibration can be sources of the acoustic noise in an ER SRM.

A Novel Doubly-Fed Flux-Switching Permanent Magnet Machine With Armature Windings Wound on Both Stator Poles and Rotor Teeth

In this article, a novel doubly-fed flux-switching permanent magnet (DF-FSPM) machine is proposed, whose armature windings are wound on both stator poles and rotor teeth. Different from the conventional FSPM machine in which the armature windings are only located in the stator, the rotor slot area is fully utilized in the DF-FSPM machine to improve the electrical loadings and, thus, the torque density. Moreover, it has the potential of fault-tolerant operation, since it comprises two sets of armature windings, which can work individually. The topology and the operating principle of the machine are introduced with reference to a 12-stator-pole/10-rotor-tooth DF-FSPM machine. The electromagnetic performances of the optimized DF-FSPM machine and its FSPM counterpart machine are compared, including the induced voltage, inductances, torque capability, flux weakening capability, efficiency, and power factor. It shows that the DF-FSPM machine can exhibit about 46.5% higher torque density than the FSPM machine, while its torque production per magnet volume is also improved by about 39.6%. In addition, the efficiency and power factor of the DF-FSPM machine are higher than those of the FSPM machine. Finally, experimental validation is conducted on a prototype machine.

Compensation analysis of longitudinal end effect in three‐phase switched reluctance linear machines

The longitudinal end effect of switched reluctance linear machine (SRLM) makes the electromagnetic characteristics of different phases unbalanced, especially in magnetic flux distributions. These discrepancies unbalance phase currents and aggravate the force ripple of SRLM, which are verified on a double-sided SRLM. This study aims to analyse the influence of the longitudinal end effect on SRLMs and to investigate simple but practical compensation methods for the performance improvement of linear machines. Through magnetic circuit analysis, a new compensation method which is widening stator end poles is proposed for the first time. Three-dimensional finite element analysis (3D FEA) shows that this new method can decrease the force factor by about 93.9%, while the previously used method which is adding auxiliary stator poles can decrease the force ripple factor by only about 27.5%. In addition, the proposed method needs less extra space than the previous method. Hence, the new compensation method is more practical and more efficient. Furthermore, the theoretical value of optimal width of stator end poles is expressed, and its effectiveness is confirmed by sensitivity analysis.

Development of a Three-Phase Dual-Rotor Magnetless Flux Switching Generator for Low Power Wind Turbines

This article presents a new three-phase flux switching generator (FSG), which is mainly designed for variable-speed low power wind turbines. The magnetless structure of this generator not only reduces the machine cost but also increases the flux controllability. In order to shorten the field and armature end-windings, non-overlapped concentrated windings have been ingeniously incorporated into the dual-rotor middle-stator structure. A parametric study of both stator and rotor pole arcs is carried out, targeting maximum generated EMF, and minimum cogging torque. Using finite element method, the performance of the final design is analysed. Through the ac–dc rectification, the generated EMF is rectified to give out the dc output voltage, which can be regulated by controlling dc excitation current, and accordingly, the machine can behave as a constant-output dc generator under different conditions of rotor speeds and load currents. Finally, a prototype has been manufactured and experimented to prove its validity for dc microgrids integrated with wind generation systems.

Comparison and Design Optimization of a Five-Phase Flux-Switching PM Machine for In-Wheel Traction Applications

A comparative study of five-phase outer-rotor flux-switching permanent magnet (FSPM) machines with different topologies for in-wheel traction applications is presented in this paper. Those topologies include double-layer winding, single-layer winding, C-core, and E-core configurations. The electromagnetic performance in the low-speed region, the flux-weakening capability in the high-speed region, and the fault-tolerance capability are all investigated in detail. The results indicate that the E-core FSPM machine has performance advantages. Furthermore, two kinds of E-core FSPM machines with different stator and rotor pole combinations are optimized, respectively. In order to reduce the computational burden during the large-scale optimization process, a mathematical technique is developed based on the concept of computationally efficient finite-element analysis. While a differential evolution algorithm serves as a global search engine to target optimized designs. Subsequently, multiobjective tradeoffs are presented based on a Pareto-set for 20 000 candidate designs. Finally, an optimal design is prototyped, and some experimental results are given to confirm the validity of the simulation results in this paper.

Extended End-Winding Cooling Insert for High Power Density Electric Machines With Concentrated Windings

Concentrated windings are favourable in electric motors with a high torque density because of the achievable high winding filling factor and their short end-windings. Nevertheless, the performance of the cooling system has the biggest impact on the reachable torque density limits. This article introduces a thermally conductive insert piece that encloses the stator end-windings with extensions in the stator slots. This results in an extended contact surface between the stator windings and the machine housing, which is advantageous for the conductive heat transfer. The introduced indirect cooling concept is compatible with traditional cooling techniques such as forced air and water jacket cooling. The concept is illustrated with 3D thermal finite element simulations, including the anisotropic thermal material properties, as well as ad hoc measurements on a stator pole unit mock-up of a 6-4 switched reluctance machine. Where the stator with reference cooling system was only able to handle a continuous current density of 19.0 A/mm $^2$ , 26.5 A/mm $^2$ could be obtained in the winding of the stator with the extended end-winding cooling inserts.

Torque Calculation of Permanent Magnet Spherical Motor Based on Virtual Work Method

A double-layer permanent magnet spherical motor (PMSM) with same spatial distribution of stator poles and rotor poles is designed based on spherical harmonic theory in this article. The stator coils are equivalent to permanent magnets to simplify the calculation, and the torque model based on virtual work method is derived. First, the torque model of single pair of poles is derived on the premise of considering the fundamental component of the magnetic field. Then, the relative positions of stator poles and rotor poles, the direction angles of torque components are discussed. Finally, the torque model is obtained by space vector theory and superposition theorem. Moreover, the simulation and experiment are implemented to verify the feasibility and correctness of the proposed torque model. The obtained torque model in this article has similar expression with that of traditional motor, which lays a theoretical foundation for the structure optimization and control strategy of PMSM.

Influence of inner/outer stator pole ratio and relative position on electromagnetic performance of partitioned stator switched flux permanent magnet machines

Based on the 6-pole outer stator (armature winding-stator), the influence of inner (permanent magnet-stator)/outer stator pole ratio n (n=NIS/NOS), stator relative positions and rotor pole number combinations on electromagnetic performance of partitioned stator switched flux permanent magnet (PM) machines (PS-SFPMMs) is investigated in this paper. Since the armature windings and PMs are located in two separated stators and PMs are stationary, PS-SFPMMs have high fault tolerance capabilities. To maximize the torque performance, the PM of inner stator pole should be aligned with outer stator pole when n is odd while the iron rib of inner stator pole should be aligned with outer stator pole when n is even. No matter what n is selected, the rotor pole number NR can be any integers except the phase number and its multiples. The analysis results indicate that the optimal NR is closed to (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IS</sub> +N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OS</sub> )/2 and it is odd when n is odd while it is even when n is even. Meanwhile, symmetrical phase back-EMF waveform will be obtained when the ratio of Min(N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OS</sub> , N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IS</sub> ) to the greatest common divisor of Min(NOS, NIS) and NR is even. Based on the optimal rotor pole numbers for 6-pole outer stator with different n and corresponding optimal relative position together with same rated copper loss, the average torque is improved by 18.4%, 25.1% and 25.7% respectively in PS-SFPMMs with n equal to 2, 3 and 4 when compared with PS-SFPMM with n equal to 1. The analyses are validated by experiment results of the prototype machine.

A Novel Hybrid Excited Doubly Salient Machine With Asymmetric Stator Poles

A novel hybrid excited asymmetric stator pole doubly salient machine (HEASPDSM) is proposed in this paper. The new topologies and operational principle are first investigated by using a simplified equivalent magnetic circuit model. The harmonic components of air-gap flux density are then analyzed. The influence of key structural parameters of the proposed machine on the flux regulation ability and torque is studied. A full comparison on main electromagnetic performance indexes of the proposed 12/7 (stator/rotor poles) HEASPDSPM and several traditional doubly salient machines is presented. A prototype is fabricated and tested to validate the theoretical analysis. The results well demonstrate that the HEASPDSPM possesses various merits, such as strong flux regulation capability, high torque density, low cogging torque, and low torque ripple.

Analysis of torque ripple and fault-tolerant capability for a 16/10 segmented switched reluctance motor in HEV applications

PurposeThe torque ripple and fault-tolerant capability are the two main problems for the switched reluctance motors (SRMs) in applications. The purpose of this paper, therefore, is to propose a novel 16/10 segmented SRM (SSRM) to reduce the torque ripple and improve the fault-tolerant capability in this work.Design/methodology/approachThe stator of the proposed SSRM is composed of exciting and auxiliary stator poles, while the rotor consists of a series of discrete segments. The fault-tolerant and torque ripple characteristics of the proposed SSRM are studied by the finite element analysis (FEA) method. Meanwhile, the characteristics of the SSRM are compared with those of a conventional SRM with 8/6 stator/rotor poles. Finally, FEA and experimental results are provided to validate the static and dynamic characteristics of the proposed SSRM.FindingsIt is found that the proposed novel 16/10 SSRM for the application in the belt-driven starter generator (BSG) possesses these functions: less mutual inductance and high fault-tolerant capability. It is also found that the proposed SSRM provides lower torque ripple and higher output torque. Finally, the experimental results validate that the proposed SSRM runs with lower torque ripple, better output torque and fault-tolerant characteristics, making it an ideal candidate for the BSG and similar systems.Originality/valueThis paper presents the analysis of torque ripple and fault-tolerant capability for a 16/10 segmented switched reluctance motor in hybrid electric vehicles. Using FEA simulation and building a test bench to verify the proposed SSRM’s superiority in both torque ripple and fault-tolerant capability.

Optimal Stator Design of Doubly Salient Permanent Magnet Generator for Enhancing the Electromagnetic Performance

An optimal stator design technique of a three-phase doubly salient permanent magnet generator (DSPMG) for improving the output power is proposed. The stator configuration was optimally designed by adjusting the stator pole depth and stator pole arc. The trapezoid outer stator tip was also designed. Then, the output characteristics of the designed DSPMG including the flux linkage, electromotive force (EMF), harmonic, cogging torque, efficiency, magnetic flux distribution and voltage regulation were characterized by using the finite element method. Results were compared to the original structure in the literature. It was found that the flux linkage, EMF, cogging torque, and efficiency of the proposed DSPMG were significantly improved after the stator pole depth and stator pole arc were suitably modified. Further details of optimal stator pole depth and stator pole arc are presented. The EMF produced by the optimal proposed structure was 47% higher than that of the conventional structure, while 56% cogging torque improvement and 20% increased efficiency were achieved. The EMF generated by the proposed structure was classified in the high-range scale compared to the other existing models. The symmetrical magnetic flux distribution of all structures was indicated. The voltage regulation of the modified structure was also significantly improved from the conventional model. The proposed design technique can be utilized to maximize the electromagnetic performance of this particular generator type.

Performance improvement of asymmetrical-pole partitioned stator permanent magnet generator by optimizing stator teeth number

The partitioned stator doubly salient permanent magnet generator (PS-DSPG) with asymmetrical-pole configuration has been widely applied for producing electrical power due to their high reliability, high flux linkage and high electromagnetic force (EMF). Therefore, we aim to improve the performance of this generator an asymmetrical-pole structure technique applied to outer stator pole. The phase flux linkage and phase EMF were characterized by finite element method. It was verified that the flux linkage and EMF were increased when increasing the number of outer stator. Especially, the 30/8/14-pole (outer stator/rotor/PM-pole) of PS-DSPG structure with asymmetrical-pole technique produced high symmetric EMF waveform. the arc variation of rotor iron piece of all proposed structures was investigated. It was found that the 30/8/14-pole of the proposed asymmetrical-pole PS-DSPG structure provides EMF about 61.29% higher than the conventional structure at expanded rotor arc of 140%. Hence, the 30/8/14-pole asymmetrical-pole PS-DSPG structure can be utilized for electrical generation in low-speed applications.