Stator Pole Research Articles

Design and analysis of a three‐phase brushless flux switching generator for aircraft ground power units

This study proposes a new three-phase dual-rotor middle-stator brushless flux switching generator for 400Hz diesel-driven aircraft ground power units. For the proposed machine, both field and armature windings are hosted in the stator in such a way that not only fulfils brushless structure, but also realises the flux switching function. Moreover, both windings have non-overlapping concentrated windings to shorten the end-windings and reduce the copper losses. In the meantime, the rotor has only slots without any active parts. First, the machine detailed design is provided, and its performance is analysed using finite element method. Also, a selection topology of both stator and rotor pole arcs is carried out, targeting maximum generated electromotive force, minimum harmonic content, and minimum cogging torque. Then, a prototype is implemented and experimented to confirm the feasibility of the proposed machine.

A Split-Field-Windings Doubly Salient Brushless DC Generator With Reduced Excitation Capacity for Hybrid Electric Vehicles

This paper proposes a split-field-windings doubly salient brushless dc generator (SDSBLDCG) to reduce excitation capacity. The series field winding connected at the dc side of the associated rectifier provides part of the field magnetomotive force. A split factor is introduced to indicate different combinations of the field windings based on the same slot fill and current density. Then, the influence of split factor on the generator performance is investigated by finite-element analysis. The dynamic characteristics of the SDSBLDCG system are also analyzed to evaluate the adoptable split factor. A 43 kW prototype SDSBLDCG with 24 stator poles and 16 rotor poles having optimized split factor, as well as its generator control unit, is designed and developed for the medium-duty hybrid electric bus. The capacity of the field current regulator is reduced by 45% compared with that of the conventional doubly salient brushless dc generator. The utility of the controller and the dynamic performance of the system are also verified. Both simulated and measured data show that the proposed SDSBLDCG is a promising candidate for the on-board generator system, particularly in medium- and heavy-duty hybrid electric vehicles.

Comparative Study of Transversal-Flux Permanent-Magnetic Linear Oscillatory Machines for Compressor

Traditional moving-magnet transversal-flux linear oscillatory machines (MTLOM) suffer from high fabrication difficulty and cost, low robustness and reliability, and low material utilization ratio, etc. In this paper, a novel stator-magnet moving-iron transversal-flux linear machine (SMTLOM) is proposed, with magnets inserted into the stator yoke (rather than mounted on stator poles) and mover composed of iron core only. First, the topology of proposed SMTLOM is described, as well as its operation principle. Then, the comparison rules are built to make fair comparison between the conventional MTLOM and the novel SMTLOM, from the perspective of practical application, including the same maximum size limitation, output thrust, and thermal source. By using a three-dimensional finite-element analysis (3-D FEA), comparisons of some key performance indexes, such as back electromotive force, thrust per coil length, thrust per magnets volume, thrust per machine volume, temperature distribution, material cost and structure reliability, etc., are made between these two types of machines. The results from 3-D FEA demonstrate that the novel SMTLOM has enjoyed merits of lower fabrication cost and weight, much higher reliability, thrust density, material utilization ratio, etc., which indicate that the novel SMTLOM is more suitable for driving compressor and easier for mass production.

Two-Speed Line Start Permanent Magnet Synchronous Motor With Dual Magnetic Polarity

This paper presents a design of a line start permanent magnet (PM) synchronous motor capable of operating in two different synchronous speeds without requiring a drive unit. The proposed design is based on variable pole numbers for the stator and the rotor. In general, the two-speed operation is realized by the combination of electromagnetic torque and reluctance torque, which enables the motor to operate as a synchronous PM motor at high speed and a synchronous reluctance motor at low speed. However, the proposed design enables the motor to operate as a PM motor at both low- and high-speed regions. The stator winding consists of two independent windings to switch the operating pole count for low- and high-speed applications. For the motor to operate in two different operating speeds, the rotor must be capable of creating two different magnetic polarities (pole numbers) to adapt itself to the operating stator pole number. For this purpose, PMs are specially arranged such that the magnetic flux density has a distribution similar to the resultant flux of two rotors with different magnetic pole numbers. This forms a rotor with dual magnetic polarity and enables the motor to operate as a synchronous PM motor at two operating speeds. The finite element analysis simulation results confirm the effectiveness of the proposed design in both steady-state and transient regime. To further validate the proposed solution, the performance of the motor has been verified by experimental measurements on the motor prototype.

Coil- and phase-flux-linkage characteristics of dual excited permanent magnet machijnes equipped with different winding configurations

The flux-linkage characteristics of dual excited permanent magnet (PM) machines equipped with concentrated windings of single- and double-layer types is investigated in this paper. This includes precise comparison of the coil and phase flux-linkage waveforms of the machines having different stator and rotor pole topologies. It is observed that, the developed machine having double layer-wound configuration have unipolar coil flux linkage waveforms, although with a resultant bipolar phase flux-linkage waveforms on summation, while their corresponding single layer-wound counterparts are characterised by both bipolar coil and phase flux-linkage waveforms. Also, the opposite coils of the machines having single-layer windings as well as even rotor pole topology produces coil flux-linkage waveforms whose shape and magnitude are identical and same; thus, resulting to more phase harmonics unlike their counterparts that are equipped with odd rotor poles and single-layer winding configuration whose coil waveforms are shifted, thereby resulting to effective cancellation of harmonics in the resultant phase waveforms. In general, the single-layer-wound machines exhibit higher peak-to-peak and fundamental flux-linkage values than their double-layer-wound equivalents. Keywords : Dual excitation, flux-linkage, single- and double-layer windings, rotor and stator pole combinations.

Experimental Validation of a Thermal Model for High-Speed Switched Reluctance Machines for Traction Applications

This paper presents the experimental validation of a novel cooling concept applied to a high-speed switched reluctance machine topology for traction applications. By circulating the coolant between the coils and the stator poles, the winding and the stator iron are virtually thermally decoupled. A number of test motorettes are used to demonstrate the potential of the cooling concept at current density values up to 27 A/mm2 continuously. The measurements are also used to validate a thermal model of the machine, and further improvements of both the model and the experimental setup are proposed.

Flux measurement and conditioning system for heteropolar active magnetic bearing using Kapton-foil Hall sensors

Abstract This paper addresses the problem of measuring the electromagnetic flux in the air gap of the active magnetic bearing (AMB) without mechanical structure modifications. The designed and fabricated flux measurement and conditioning system based on the ultra-thin flexible Kapton-foil Hall sensors (developed by IFW Dresden Institute for Integrative Nanosciences) and signal amplifiers are presented. The flexible sensors are directly mounted on the curved surfaces of stator poles of the AMB and measure flux density in the AMB air gap. Then, the measurement itself and the conditioning system are verified in different measuring conditions of the heteropolar radial AMB with the air gap width of 0.4 mm. The measurement results were used in identifying crucial rotor flux-AMB system parameters. The proposed direct flux measurement system is successfully verified in the designed test rig in the presence of rotor position disturbances or coil current oscillation. The advantages and drawbacks of the presented measurement setup are discussed.

Evolutionary Algorithms for Optimization of 4/4 Single Phase Switched Reluctance Machine

This paper presents the application of two classes of Evolutionary Algorithms (EA) to determine optimum design of Single-Phase Switched Reluctance Machine (SPSRM). The EA used is Genetic Algorithms (GA) and Differencial Evolution (DE). Due to sensitivity of the output torque to the stator and rotor pole arcs, these are selected as design variables for a multi-objective optimization with the objective of maximizing average torque and torque density, and minimizing copper loss. The proposed optimization is tested on a 4/4 1,25 kW SPSRM, and the results of both algorithms are compared. The performance of the optimized motor are compared to the initial motor through the finite element analysis. The results show improvement in both efficiency and output torque.

Optimal pole width ratio for high force density linear switched reluctance motors

The double salient structure significantly reduces the forces in a linear switched reluctance motor (LSRM). The structure is then optimized for high force densities. The pole width is the key parameter in the double salient structure with this paper focusing on the optimal pole width ratio for a high force density LSRM using qualitative and quantitative analyses and experimental measurements. The qualitative analysis based on a linear flux linkage model shows a maximum average force for various translator and stator pole widths. Then, a finite element analysis (FEA) based parametric modeling method is used to validate the results and to calculate the optimal pole width range. Force measurements then agree well with the FEA results. They both show that the optimal stator pole width ratio is 0.4 to 0.45 and the optimal translator pole width ratio is 0.45 to 0.5 for a high force density in the LSRM. The optimal width ratio does not change with the air gap or slot depth. 摘要 双凸极作为直线开关磁阻电机 (LSRM) 的特征结构对于电机的出力性能有着较大的影响。由于极宽是双凸极结构的关键尺寸, 因此该文从理论定性分析、有限元定量分析和实验测量3个方面探究了提升LSRM力密度的最佳定动子极宽比。利用磁链线性模型定性地分析了定动子极宽如何影响电机平均输出力, 从机理上揭示了定子和动子极宽分别存在使得平均输出力最大的极值点。利用参数化建模方法建立了有限元分析模型, 定量地验证了理论分析的推断并给出了最大平均输出力所对应的最佳定动子极宽比范围。通过实验测量了不同定动子极宽的力曲线, 实验测量结果和有限元计算结果相一致, 从而验证了有限元分析的准确性。有限元分析和实验结果表明：对于提升LSRM力密度的最佳定子极宽比范围为0.4~0.45, 最佳动子极宽比范围为0.45~0.5, 且最佳定动子极宽比范围基本不受气隙、槽深的影响。

Investigation of a Switched Reluctance Generator Using the Voltage Pulse Width Modulation Method

An analytical modeling method of the current for a Switched Reluctance Generator (SRG) using voltage Pulse Width Modulation (PWM) control is proposed. The current equation is achieved from the inductance model in combination with the voltage equation. The proposed inductance model is divided into four regions which depend on the pole arcs of the rotor and stator and the inductance at aligned and unaligned positions. A method to obtain a PWM duty cycle and the optimal turn-on and turn-off angles of the SRG undervoltage PWM control is presented. An SRG with 8 stator poles and 6 rotor poles was setup to validate the proposed method. The PWM duty cycle and optimal control variables based on the proposed method were used to control the SRG. The results indicated that the SRG could generate the optimum phase current over a wide speed range.

High-speed switched reluctance machine: natural frequency calculation and acoustic noise prediction

In this study, an analytical model is proposed for natural frequency calculation and acoustic noise prediction for high speed switched reluctance machines. The developed natural frequency model results are compared with the mechanical finite element analysis results in terms of 6 different mode shapes that cause the majority of the acoustic noise in switched reluctance machines. The results show that the analytical results are consistent with the numerical method results with minimum 90% matching. Based on the natural frequency calculation model, a new acoustic noise prediction method is developed that only needs a radial force waveform as an input emerging on stator pole surfaces. The comparison of the developed and the numerical results clearly indicates that the acoustic noise level of the switched reluctance machine can be effectively found during the design process without using time-consuming numerical methods.

Simultaneous Optimization of Geometry and Firing Angles for In-Wheel Switched Reluctance Motor Drive

Interests in using rare-earth free motors such as switched reluctance motors (SRMs) for electric and hybrid electric vehicles continue to gain popularity, owing to their low cost and robustness. Optimal design of an SRM, to meet specific characteristics for an application, should involve simultaneous optimization of the motor geometry and control in order to achieve the highest performance with the lowest cost. This paper presents a constrained multiobjective optimization framework for design and control of an SRM based on a nondominated sorting genetic algorithm II. The proposed methodology optimizes SRM operation for high volume traction applications by considering multiple criteria including efficiency, average torque, and torque ripple. Several constraints are defined by the considered application, such as the motor stack length, outer diameter, minimum operating power, minimum desired efficiency, rated speed, rated current, and supply voltage. The outcome of this optimization includes an optimal geometry, outlining variables such as air gap length, rotor inner diameter, stator pole arc angle, rotor pole arc angle, rotor back iron, stator pole height, and stator inner diameter as well as optimal turn-on and turn-off firing angles. Then the machine is manufactured according to the obtained optimal specifications. Comprehensive finite-element analysis and experimental results are provided to validate the theoretical findings.

Investigation of Optimal Split Ratio in Brushless Dual-Rotor Flux-Switching Permanent Magnet Machine Considering Power Allocation

This paper investigates an optimal split ratio for a brushless dual-rotor flux-switching permanent magnet (BDR-FSPM) machine. Based on the design theory of conventional FSPM machine, the split ratio of the BDR-FSPM machine is deduced and redefined. And the crucial factors which have close relationship with the split ratio are determined, consisting of power split ratio, magnetic loading, PM pole width, and stator pole width. To conveniently explore the optimal split ratio, the response surface method is purposely utilized for conducting optimization, where the magnetic loading and output torque are chosen to be the objectives. In addition, considering the application requirement of hybrid electric vehicles, the concept of power allocation is proposed and integrated into the optimization process of split ratio. Then based on the optimal split ratio, the machine performances are analyzed in detail, including air gap flux density, back-electromotive force (EMF), coupled-EMF, and torque performances. Finally, a prototyped BDR-FSPM machine is manufactured and tested to verify the validity of the proposed split ratio optimization and machine design approach.

Fast design method of variable flux reluctance machines

In this paper, a fast design method is developed based on a combination of analytical and finite element (FE) methods for variable flux reluctance machines (VFRMs). Firstly, the feasibility of using analytical method in optimization under unsaturated condition is confirmed. Then, by applying the FE method, the influence of magnetic saturation is considered. Compared with the unsaturated case, the optimal split ratio for magnetically saturated case is increased by 1~1.2 times, the optimal rotor pole arc ratio varies within 0.33~0.44, and the stator pole arc ratio remains the same. Based on this, the optimal structural parameters can be initially set by analytical method and then refined by the FE method. Due to the fast speed of analytical method, less variable counts and narrowed variation ranges, the proposed method is significantly faster than the conventional pure FE based global optimization. Finally, the proposed method is used for optimizing the 6-stator-slots VFRMs having different numbers of rotor poles. The 6-stator-slot/7-rotor-pole (6s/7r) VFRM is found to have the highest torque density. It is prototyped and tested to verify the analyses.

Design studies of inner and outer embedded Permanent Magnet for hybrid electric vehicles

Hybrid vehicles require high torque for propel, hence permanent Magnet machines are highly suiting for the improvement in the torque density. The paper focus on designing built-in interior permanent magnet (IPM) synchronous machine for hybrid electric drive. With the permanent magnet switched from rotor to stator and the characteristics over a wide range of speed operation is studied. The results obtained though performance analysis shows that at 130 rpm high torque with power peaking at around 900 rpm. Both the inner and outer machine are studied using numerical study tool for performance analysis for the application mentioned above. The inner magnet rotor design has provide a better magnetic flux flow due to the larger flux linkage between the permanent magnet and stator pole. Both type of machines are evaluated for torque where the machine with inner magnet provide a higher torque density of 4.94% as compared to the outer magnet machines.

Analysis and Experiment of Eddy Current Loss in Radial Magnetic Bearings with Solid Rotor

In order to reduce power losses for the aerospace applications, this paper analyzes the eddy current losses produced by high-speed rotating solid rotor core magnetic bearings of magnetically suspended control & sensitive gyroscope (MSCSG). An analytical model of the eddy current loss of a solid rotor radial magnetic bearing (RMB) is presented. Considering the difference between NNNN and NSNS magnetic circuits of RMB, the magnetic field expressions of stator magnetic poles are listed. The magnetic field of stator poles is replaced by Fourier series expansion. According to the magnetic field distribution around the magnetic pole surface and the boundary conditions of the rotor surface, the mathematical expression of eddy current loss is obtained. The measurement method of rotational power loss in radial magnetic bearing is proposed, and the results of the theoretical analysis are verified by experiments in the prototype MSCSG. The experimental results show the correctness of calculation results. Eddy current loss models and test methods provide theoretical support for analyzing eddy current losses in solid rotors and reducing power consumption.

INFLUENCE OF STATOR EMBRACE ON TORQUE OF IN-WHEEL SWITCHED RELUCTANCE MOTOR

In this paper, influence of stator pole embrace on torque of In-Wheel Switched Reluctance Motor (IW-SRM) is investigated by numerical modeling based on Finite Element Method (FEM). For this reason, 3D numerical model of IW-SRM is built by using Ansys Maxwell Software Package. IW-SRM is analyzed and output torque and magnetic flux density of the IW-SRM are calculated. The analysis of IW-SRM is realized for different stator pole embraces and the results of the output torque and magnetic flux density of IW-SRM taken for various stator pole embraces are compared with each other. As seen from the results, when the value of stator pole embrace reduces, the output torque of IW-SRM increases. As a result in this study, the effects of different stator pole embraces are examined on the output torque of IW-SRM.

Investigation on a Multimode Switched Reluctance Motor: Design, Optimization, Electromagnetic Analysis, and Experiment

A switched reluctance motor (SRM) with 12/10 poles is investigated in this paper. Compared with the conventional SRMs with single mode, the machine is not only able to be worked as a six-phase motor but also could be used as a three-phase motor, which is thus named multimode SRM (MMSRM). The primary dimensions of the stator and rotor cores are calculated by considering it as a six-phase SRM with long magnetic paths, and the performances of three-phase mode with short magnetic paths are used to test the parameters. The arcs of stator and rotor pole are treated as the optimization objects to minimize torque ripple and copper loss per torque and maximize torque per ampere of the MMSRM. A function is selected to solve the multiobjective problem and the final values of arcs of stator and rotor pole are determined based on the results of finite-element method. The effects of arcs of stator and rotor pole on electromagnetic performances of MMSRM are discussed independently, and a prototype is manufactured to test the simulations. A good agreement between the simulated and measured results verifies the validity of the analytical method and results.

Analytical method for the prediction of natural frequencies of switched reluctance motor based on electromechanical analogy method

PurposeAn improved analytical method for calculating the natural frequencies of a switched reluctance motor (SRM) stator is proposed in this paper. The method is different from traditional analytical methods, which only consider the influence of mass of the stator poles and windings on the natural frequencies of the SRM stator. This paper aims to consider the influence of stiffness and mass of the stator poles and windings simultaneously and reasonably.Design/methodology/approachAn innovated analytical method based on the electromechanical analogy method is presented. In the proposed analytical formulae for calculating the natural frequencies, the influence of the windings on natural frequencies is considered by using the springs to simulate the flexible connection between the stator core and windings, and the stator poles are treated as both additional mass and additional equivalent stiffness. Both three-dimensional (3D) finite-element analysis (FEA) and experimental modal analysis results validate the improved method.FindingsThe influence of the mass and stiffness of stator winding is considered by using the springs to simulate the flexible connection between the stator core and windings, and the stator poles are treated as both additional mass and additional equivalent stiffness. The traditional analytical method only considers the influence of mass. Therefore, the calculation results are comparatively lower than 3D FEA results and may lead to a large error. The 3D FEA and experimental modal analysis confirm that the proposed method has good precision for low-order natural frequency calculation of SRMs.Originality/valueAn improved analytical method for calculating the natural frequencies of an SRM stator is proposed. Unlike the traditional analytical method, the proposed method can consider the influence of stiffness and mass of the stator poles and windings. This method is valuable for designers to predict the natural frequencies accurately.

Design of a New Enhanced Torque In-Wheel Switched Reluctance Motor With Divided Teeth for Electric Vehicles

This paper presents a new switched reluctance motor (SRM) with wide speed range for the application of electric vehicles. It has an in-wheel structure for direct drive and multiple teeth per stator pole to enhance output torque. Also, the number of rotor poles is more than that of stator teeth. A 6/16 three-phase in-wheel SRM with the concepts of multi-teeth per stator pole and more rotor poles than stator teeth has been proposed for analysis. The torque performance of the topology with multi-teeth per stator pole is proven by theoretical analysis. Moreover, a new design formula is introduced for a novel combination of stator and rotor poles. The parameters of the motor are optimized by genetic algorithm method for the maximum torque output. Then the torque performance is computed by finite-element method (FEM) and compared with its counterparts, including three-phase 6/8 and 6/10 SRMs. The FEM results exhibit higher torque density for the proposed topology.