Stator Pole Arc Research Articles

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.

Braking Torque Due to Cross Magnetization in Unsaturated IPM BLDC Machines and Its Mitigation

Cross magnetization (CM) is an inevitable phenomenon in electrical machines. It is more prominent in interior permanent magnet (IPM) brushless dc (BLDC) machines. This is because PMs demagnetize in overloaded and saturated conditions. It leads to cross coupling between the direct and quadrature-axes quantities, and a decrease in the resultant air-gap flux-density distribution under saturated conditions. In this paper, it is shown that CM leads to braking torque even in unsaturated IPM BLDC machines. Furthermore, the effect of CM on flux linkage, electromotive force, and dynamic torque is presented. Its mitigation using suitable selection of slot–pole combination is presented. It is observed that odd slot–pole combinations are least affected, and even slot–pole combinations are severely affected by CM. Furthermore, it is found that the overlap area of rotor pole arc with the stator pole arc influences the severity of CM, more particularly in fractional slot–pole combination machines. To verify these claims, finite-element method is used for modeling and analyzing various slot–pole combinations of a spoke-type IPM BLDC motor. The results obtained from these simulations are validated with a fabricated reference prototype, which support the claims.

Optimization design of a doubly salient 8/6 SRM based on three computational intelligence methods

The aim of this paper is to optimize an 8/6 doubly salient switched reluctance machine using three computational intelligence methods, which include particle swarm optimization, a genetic algorithm, and differential evolution. Three cases are investigated where different parameters are considered like the stator pole arc, rotor pole arc, and ratios, which define the stator yoke and rotor thickness. The objective functions considered are the average torque and the torque-to-weight functions. The simulations are carried out using MATLAB and FEMM software. The optimal results found are compared with the initial design, and it is shown that high improvements are achieved.

Influence of Stator and Rotor Pole Arcs on Electromagnetic Torque of Variable Flux Reluctance Machines

The influence of stator and rotor pole arcs on electromagnetic torque of variable flux reluctance machines (VFRMs) having different stator and rotor pole combinations is investigated. Different from 6/4 stator/rotor pole switched reluctance machines, which usually employ equal stator pole arc and stator slot opening, unequal stator pole arc and slot opening can boost the torque density of the VFRM. Moreover, the optimal rotor pole arc to rotor pole pitch ratio in VFRMs is \(\sim ~1/3\) and the optimal stator pole arc is equal to or slightly smaller than the optimum rotor pole arc. For a 6-pole stator, the 4-, 5-, 7-, and 8-pole rotor VFRMs with the optimal stator and rotor pole arcs can increase the average torque by 1%, 4%, 30.7%, and 72.9% compared with those having equal stator pole arc and stator slot opening. In addition, the 6/7 stator/rotor pole VFRM exhibits the largest torque density. Prototype machines with optimal stator and rotor pole arcs are manufactured and measured to validate the analysis.

Design and Analysis of a Magnetless Double-Rotor Flux Switching Motor for Low Cost Application

This paper presents a novel magnetless double-rotor flux switching motor for low cost cooling fan application. By creatively incorporating concentrated toroidal windings into a double-rotor middle-stator structure, the proposed motor not only realizes the flux switching feature, but also shortens the end-windings to improve its operational efficiency. To achieve a better performance, the motor dimensions, especially the stator and rotor pole arcs, are optimized. Meanwhile, with the introduction of a stepped air-gap, the torque at any rotor position is boosted and problems with zero output torque at starting is successfully avoided. The final optimized motor is analyzed using finite element method, and its validity is confirmed by the simulation results.

Performance Improvement in the Axial Flux-Segmented Rotor-Switched Reluctance Motor

Axial flux-segmented rotor-switched reluctance motor (SSRM) topology could be a potential candidate for in-wheel electric vehicle application. This topology has the advantage of the increased active surface area for the torque production as compared to the radial flux SSRM for a given volume. To improve the performance of axial flux SSRM (AFSSRM), various stator slot/rotor segment combinations and winding polarities are studied. It is observed that the torque ripple is high for the designed three-phase, 12/8 pole AFSSRM. Therefore, the influence of the stator pole and rotor segment arc angles on the average torque and the torque ripple is studied. In addition, the adjacent rotor segments are displaced with respect to the stator, to reduce the torque dips in the phase commutation region. The proposed arrangement is analyzed using the quasi-3-D finite-element method-based simulation study and it is found that the torque ripple can be reduced by 38%. Furthermore, the low-frequency harmonic content in the torque output is analyzed and compared. The variation of the axial electromagnetic attractive force with displaced rotor segments is discussed. The effectiveness of the proposed technique is verified experimentally.

Modeling of Flux Switching Motor with Selection of Pole Arcs for Maximum Torque Production

Flux Switching Motors (FSM) are gradually emerging in recent years due to their inherent simplicity, rugged construction and low cost power converter. The main focus of this paper is to optimize the design of 8/4 pole FSM by varying its pole arcs for the production of maximum torque. The sensitivity of the pole arcs on the performance of the FSM is performed by cyclically varying the stator and rotor pole arcs. A comprehensive program based on Genetic Algorithm (GA) technique is developed in MATLAB to compute the torque and the results are presented. Further the performance of the machine with the optimal combination of pole arcs is modeled and analyzed using two dimensional transient Finite Element analyses (FEA) for the production of maximum torque. The effectiveness of the results obtained from GA is validated using FEA.

Synthesis and analysis of a high‐performance low‐cost permanent magnet brushless DC motor

PurposeThe paper presents design development of a novel high‐performance low‐cost 6/4 pole permanent magnet brushless DC (PMBLDC) motor. The objective is to show how the cogging torque of this new design is minimised by determining the optimum stator pole arc length and the best shoe thickness.Design/methodology/approachAt the beginning a step‐by‐step design synthesis of a reference 6/4 pole PMBLDC motor with concentrated 3‐phase windings and asymmetric stator pole arcs is presented. It is followed by a full performance analysis of the reference motor. The FEM for electromagnetic field computation is employed. The characteristics of the motor are calculated and analysed. By simple variation of the stator pole geometry, two‐stage design optimisation for cogging torque minimisation is performed, and an optimised motor model is proposed. The comparative analyses of the reference and optimised motor models show the advantages of the proposed novel design.FindingsThe focus is to show the sensitivity of the cogging torque due to changes in the stator pole shoe design parameters, such as arc length and thickness, which are discretely changed inside the prescribed constraints, and the solution matrix is derived. It was found the optimised stator pole design, providing minimum cogging torque, has the original arc length 85° and pole shoe thickness 4 mm. Thus, the peak‐cogging torque from 0.294 Nm is reduced to respectable value 0.142 Nm.Originality/valueThe paper presents an original approach to synthesis of 6/4 PMBLDC new structured motor. A two‐step design procedure is introduced and optimised stator geometry is defined, minimising the cogging torque and, at the same time, improving the profile of back electromotive force (EMF) of the motor.

Evolutionary computation based multi-objective pole shape optimization of switched reluctance machine

This paper presents the application of elitist Non-dominated Sorting Genetic Algorithm version II (NSGA-II) to determine optimum pole shape design for performance enhancement of Switched Reluctance Machine (SRM). In SRM, torque output and torque ripple are sensitive to stator and rotor pole arcs and their selection is a vital part of SRM design process. The problem of determining optimal pole arc is formulated as a multi-objective optimization problem with the objective of maximizing average torque, minimizing torque ripple and copper loss. In order to account for the geometry as well as for the nonlinearity of material utilized, the Finite Element Method (FEM) is used to determine the performance of the machine. The proposed optimization technique is applied to determine optimal pole shape of an 8/6, four-phase, 5 HP, 1500rpm SRM. The results show the effectiveness of the proposed approach and confirm the application of NSGA-II as a promising tool for solving SRM design problems. The results obtained by NSGA-II are compared and validated with classical multi-objective approach based on weighted sum method using Differential Evolution (DE) algorithm.

Modeling and Parametric Design of Permanent-Magnet AC Machines Using Computationally Efficient Finite-Element Analysis

Computationally efficient finite-element analysis (FEA) (CE-FEA) fully exploits the symmetries of electric and magnetic circuits of sine-wave current-regulated synchronous machines and yields substantial savings of computational efforts. Motor performance is evaluated through Fourier analysis and a minimum number of magnetostatic solutions. The major steady-state performance indices (average torque, ripple and cogging torque, back-electromotive-force waveforms, and core losses) are satisfactorily estimated as compared with the results of detailed time-stepping (transient) FEA. In this paper, the CE-FEA method is presented and applied to a parametric design study for an interior-permanent-magnet machine. Significant reduction of simulation times is achieved (approximately two orders of magnitude), permitting a comprehensive search of large design spaces for optimization purposes. In this case study, the influence of three design variables, namely, stator tooth width, pole arc, and slot opening, on three performance indices, namely, average torque, efficiency, and full-load torque ripple, is examined, and design trends are derived. One hundred candidate designs are simulated in less than 20 minutes on a state-of-the-art workstation.

Single-Phase Hybrid Switched Reluctance Motor for Low-Power Low-Cost Applications

This paper presents a new single-phase, Hybrid Switched Reluctance (HSR) motor for low-cost, low-power, pump or fan drive systems. Its single-phase configuration allows use of a simple converter to reduce the system cost. Cheap ferrite magnets are used and arranged in a special flux concentration manner to increase effectively the torque density and efficiency of this machine. The efficiency of this machine is comparable to the efficiency of a traditional permanent magnet machine in the similar power range. The cogging torque, due to the existence of the permanent magnetic field, is beneficially used to reduce the torque ripple and enable self-starting of the machine. The starting torque of this machine is significantly improved by a slight extension of the stator pole-arc. A prototype machine and a complete drive system has been manufactured and tested. Results are given in this paper.

Particle Swarm Optimization Approach for Optimal Design of Switched Reluctance Machine

Problem statement: Switched Reluctance Motors (SRMs) are widely used in various applications due to their inherent simplicity and rugged construction In SRM, torque output and torque ripple are sensitive to stator and rotor pole arcs and their selection is a vital part of SRM design process. In this study Particle Swarm Optimization technique is proposed for determining optimum pole arc of SRM. Approach: The problem of determining optimum pole arc is formulated as a multiobjective optimization problem with the objective of maximizing average torque and minimizing torque ripple. A comprehensive program based on analytical model is developed in Matlab to compute the value of inductance and average torque. Results: The optimization procedure is tested on 8/6, four-phase, 5 HP, 1500 rpm SRM. The results are compared and investigated with those obtained from Genetic Algorithm (GA) technique and Finite Element Analysis(FEA) simulation. Conclusion: The results demonstrate that the proposed method is effective and outperforms GA in terms of solution quality, accuracy, constraint handling.

복지형 NEV용 외전형 In-Wheel SRM 설계

Outer rotor type in-wheel switched reluctance motor for Welfare neighborhood electric vehicle is researched. In-wheel system is to drive the electric vehicle without mechanical transmission, shaft, differential gears or other mechanical system. To calculate drive power for each wheels, the elder's and disable's safety driving conditions are considered. The designed outer rotor SRM has a 6-stator and 8-rotor pole. The determined dimensions as well as the stator and rotor pole arc are simulated and tested with CAD and finite element analysis to verify the performance of the proposed motor.

Multi-Objective Optimization Design of In-Wheel Switched Reluctance Motors in Electric Vehicles

The method of the optimization design with multi-objectives for switched reluctance motors (SRMs) in electric vehicles (EVs) is proposed in this paper. It is desired that electric motors for EVs have high torque, high efficiency, and high torque density. Thus, the developed optimization function is selected as the correct compromise between the maximum average torque, maximum average torque per copper loss, and maximum average torque per motor lamination volume, by using three weight factors and three base values. The stator and rotor pole arc angles are selected as the optimized variables. Furthermore, the authors also discuss the design requirements and some constraints on the optimization design. The results of the optimization design show that the proposed method meets the requirements of EVs on electric motors well. A prototype of the optimally designed in-wheel SRM for EVs has been manufactured. This paper provides a valuable method to implement the optimal design of SRMs for EVs.

A Simple and Efficient Tool for Design Analysis of Synchronous Reluctance Motor

We present an efficient tool for design analysis of a synchronous reluctance motor (SynRM). We use winding function analysis (WFA) instead of finite-element analysis (FEA). With WFA, parameter sensitivity can be analyzed and the effects of parameters on the machine design can be evaluated very rapidly (under linear condition). We investigated the effect of rotor skewing, stator winding chording, pole arc, and interpolar air-gap length on average torque and torque ripple. We compare the results obtained by WFA with those obtained by 2-D FEA. We show that the two methods give approximately the same results but WFA requires less computation time.

Switched Reluctance Motor Design Using Neural-Network Method With Static Finite-Element Simulation

The paper describes a neural network method for optimal design of a switched reluctance motor (SRM). The approach maximizes average torque while minimizing torque ripple, considering mainly the stator and rotor geometry parameters. Before optimization takes place, an experimental validation of the SRM model, based on the finite-element method, is performed. The validation predicts average torque and torque ripple characteristics for several motor configurations while stator and rotor pole arcs are varied. The numerical results are highly nonlinear, and a function approximation of the data is therefore difficult to implement. We therefore interpolate the data by using a neural network based on a generalized radial basis function. The computed results allow us to search for optimum motor parameters. The optimum design was confirmed by numerical field solutions.

Starting the Single-Phase Switched Reluctance Motor Using Rotor Shorting Rings

This article presents a technique that uses rotor shorting rings to start the single-phase switched reluctance (SR) machine, from any rotor position, in a specified direction. It also outlines how the shorting rings enable starting of the machine. Transient finite-element analysis is used to illustrate the torque-producing mechanism from the aligned position using the rotor-mounted shorting rings. It is also used to determine the optimal stator and rotor pole arcs and shorting ring design for a 200-W prototype machine. An SR drive system incorporating rotor shorting rings is evaluated, and experimental results show the effectiveness of the technique

Geometric design of pole arcs considering electric parameters in switched reluctance motor

This paper presents a design scheme to minimize torque ripple in 6/4 Switched Reluctance Motor (SRM) using transient Finite Element Analysis (FEA) in which the magnetic field is combined with a driving circuit. Pole arcs and switching angles are major design factors. If these design factors are considered independently, the enhancement of SRM performance is restricted. Therefore this paper proposes not only optimal combination of stator pole arc and rotor pole arc but also the turn-on and turn-off angles as a function of pole arcs. Especially, turn-on and turn-off angle are formulated from a voltage equation and feasible design ranges are suggested with variable speed.

Optimum pole arcs for a switched reluctance motor for higher torque with reduced ripple

In this paper, the results of a two-dimensional (2-D) finite element (FE) analysis carried out on a 8/6 switched reluctance motor with a view to arrive at the optimum pole arcs for the stator and rotor teeth are presented. The authors have put forward a new method for calculating the average torque for comparison of static torque profiles to identify the optimum one. In this new method, 15/spl deg/ of the static torque profile, where the developed torque is nearly constant is considered for calculating the average torque. Operating the motor in this range instead of the first quarter cycle of the static torque profile will ensure higher average torque with minimum ripple. This average torque is considered as the parameter for comparison of different torque profiles of various pole arcs for the stator and rotor. It is observed that the geometry with the existing stator pole arc of 20.2/spl deg/ and a changed rotor pole arc of 30/spl deg/, instead of the existing 23.5/spl deg/ will be the optimum for this motor, as it gives the highest average torque with the minimum ripple.

Linear analysis of two-, three- and four-phase switched reluctance machines with variable pitched winding configurations

The results from a generalised linear analysis of switched reluctance machines with various winding and phase configurations are presented. The generalised analysis is used to analyse ten 4/2, 6/4, and 8/6 pole machines with various stator coil pitches and excitation patterns. Twenty six combinations are analysed with a fixed frame size. The optimum stator and rotor pole arc combinations for maximum torque per unit current production are determined. An iterative procedure is then used to determine the optimum rotor diameter, given the frame size, permissible total copper loss and flux density. The restrictions on copper loss and flux density provide a reasonable comparison between the average torque developed by each machine. The technique is linear, therefore it does not incorporate saturation and pole flux fringing effects. The analysis highlights that the optimised machine geometry is a function of the current excitation pattern and coil pitch employed.