Rotor Flux Barriers Research Articles

Torque Ripple Analysis of Synchronous Reluctance Motor with Different Rotor Topologies for Application with Dimensional Constraint

Synchronous reluctance machine (SynRM) is reemerging as a thermally robust and inexpensive actuator solution mainly due to the lack of permanent magnet. Added to that, the possibilities of having different rotor topologies make it very versatile where further optimization is possible depending on the objective, be it cost, ease of fabrication, power output, or torque quality. In an application where the outer dimension of the motor is strictly limited, this paper compares quantitatively and qualitatively the torque ripple of three SynRM machines of the same stator dimension equipped with different rotor topologies: segmented, tooth and flux barrier. Using an experimentally validated FE model, the torque ripple and the ripple’s harmonic content are compared at maximum load (stator current, IS = 50 A) and load angle (β = π/4). The machine adopting the flux-barrier rotor was shown to have the best torque quality (41% ripple), followed by tooth rotor (78% ripple) and finally segmented rotor (105% ripple). The harmonic contents are also presented and analyzed.

Open-Circuit Air-Gap Field Calculation of a New PM Machine Having a Combined SPM and Spoke-Type Magnets

This article presents the open-circuit analytical magnetic field distribution model for a new permanent magnets (PMs) rotor configuration designed to improve the utilization of rare earth magnets for flux density production. The air-gap flux density is determined with the superposition method according to the magnetomotive force (MMF) and the air-gap permeance model. Since the new rotor consists of two different rotor topologies, e.g., lateral and spoke magnets, their MMF functions are determined separately. The rotor flux barrier (FB) effect on the rotor MMF harmonics is included and studied closely. The investigations carried out on different rotor topologies show high positive impact of FBs on the third or the operating wave. Compared to the conventional rotor, the utilization of PMs for air-gap flux density production significantly is improved. To verify the analytic model, finite elements (FEs) are used and several simulation results are presented.

Analytical calculation of magnetic field components in synchronous reluctance machine accounting for rotor flux barriers using combined conformal mapping and magnetic equivalent circuit methods

Despite many efforts being devoted to simplify the analysis of Synchronous Reluctance Motors (SynRM), the use of analytical methods to calculate torque ripple in these machines remains an ongoing challenge. In this paper, the electromagnetic characteristics of a SynRM are obtained using the combined conformal mapping (CM) and magnetic equivalent circuit (MEC) method. The proposed combination makes it possible to take into account the effects of stator slots and rotor flux barriers (FBs) in modeling of the radial and tangential field components. This is accomplished by introducing virtual currents in the CM model to account for rotor potential drops due to the presence of FBs. These potential drops are calculated using the MEC model. Once specified, the field components are used to calculate the SynRM torque with three FBs. Finally, the accuracy of the proposed method is validated by comparison with finite element analysis results.

Design and Analysis of Normal Saliency IPM Spoke Motor

This article deals with the design of a normal saliency interior permanent magnet (PM) motor, also referred as flux-intensifying PM motor. A multibarrier rotor geometry is adopted and studied through an analytical model to obtain an almost sinusoidal airgap flux density waveform, so as to improve the performance and reduce the torque ripple. The developed analytical model is generic and applicable for any number of rotor flux barriers and for any number of poles. The motor performance improvement has been evaluated by finite-element analysis. Experimental validation has been carried out on a motor prototype.

Magnetic Field Analysis of SynRel and PMASynRel Machines With Hyperbolic Flux Barriers Using Conformal Mapping

Synchronous reluctance (SynRel) and permanent magnet (PM)-assisted SynRel (PMASynRel) machines with hyperbolic-shaped flux barriers are gaining more interest in commercialized products of known companies, because of their high saliency ratio. This article presents a faster approach for calculation of the air-gap flux density distribution and the electromagnetic torque of these machines than the finite-element method (FEM). The method is based on the conformal mapping (CM) techniques and magnetic equivalent circuit (MEC) solutions. A suitable CM is introduced to compute the magnetic reluctance of hyperbolic-shaped rotor flux barriers. The analytical method is then implemented on both SynRel and PMASynRel machines with the same stator structure as the Prius interior PM motor and five hyperbolic flux barriers per pole in their rotors. The accuracy of analytical results is assessed by the finite-element analysis (FEA).

Performance Analysis of Synchronous Reluctance Motor with Limited Amount of Permanent Magnet

This paper analyzes the performance of a synchronous reluctance motor (SynRM) equipped with a limited amount of a permanent magnet (PM). This is conventionally implemented by inserting PMs in rotor flux barriers, and this is often called the PM-assisted SynRM (PMa-SynRM). However, common PMa-SynRMs could be vulnerable to irreversible demagnetization. Therefore, motor performance and PM demagnetization should be simultaneously considered, and this would require the PM to be properly arranged. In this paper, various rotor configurations are carefully studied and compared in order to maximize the motor performance, avoid irreversible demagnetization and achieve higher PM utilization. Moreover, the field weakening capability is investigated and improved by regulating armature excitation. A particular rotor type with flux intensification was found to possess higher PM utilization, lower demagnetization possibility with fairly high performance. Thus, suitable rotor configurations are recommended for certain applications.

Design methodologies for the output power maximisation of synchronous reluctance machines

Synchronous reluctance (SyR) machines can constitute a promising alternative to permanent magnet machines for low-cost applications. The recent literature reports some guidelines for choosing the proper number and position of the rotor flux barriers capable of enhancing the electromagnetic performance in low-speed applications. However, as the rotational speed increases, the electromagnetic and structural mutual interactions become relevant; therefore, an optimal design requires a proper trade-off between torque production and stress reduction, which can be difficultly predicted analytically. This work proposes an approach based on optimisation algorithms in order to find ‘non-conventional’ geometries able to improve the power density: genetic algorithms coupled to magneto-static finite elements analysis and structural analytical models, are adopted to co-design SyR machines with different numbers of stator slots and rotor barriers subjected to the same thermal constraints. This study investigates two design procedures aimed at maximising the output power of SyR machines by increasing the rotational speed. Both procedures allow determining the power limits for a given volume of active parts and a fixed amount of admissible losses; moreover, the second procedure automatically finds also the rotational speed which maximises the output power.

Design Criteria of Flux-Barriers in Synchronous Reluctance Machines

A criteria to design the rotor of multi flux-barrier synchronous reluctance (REL) machines is proposed. In particular, the focus will be on the proper design of flux-barriers geometry. An analytical model is adopted to compute the impact of the rotor flux-barriers on the torque, focusing on the torque ripple. Thanks to proper assumptions, the analytical model is simplified so as to highlight the main causes of torque ripple. Such an analytical model allows to derive the angles of the flux-barrier ends corresponding to the minimum torque ripple in a closed form. This result has never been presented in the past literature and it represents a useful tool as far as the motor design is concerned. Rotors with one, two, and three flux-barriers per rotor pole are taken into account. However, the advantageous analytical model can be extended to any number of flux-barriers per pole. Some examples referring to four-pole synchronous REL machines with different numbers of stator slots are investigated and illustrated. The results are compared with a full-featured analytical model and validated through finite element simulations.

Comparative analysis of salient pole and flux barrier rotor for synchronous reluctance machines including flux weakening range

Here, synchronous reluctance machine types related to electrical traction applications are investigated including flux weakening range. A flux barrier (FB) machine with a carbon fibre-reinforced plastic bandage and a salient pole machine are designed by finite element analysis and built up as prototype. Both rotors are implemented in a stator of an existing induction machine. A comparative analysis is presented using finite element simulation as well as experimental results. Measurements in the base speed range confirm the machine designs. An analysis of the flux weakening operation at high speeds show the possible limitations by increasing harmonics with the given single-layer winging. The implementation of a short pitched winding is an approach to improve harmonic behaviour of the salient pole (SP) machine at high rotational speeds.

Comparative Design and Analysis of New Type of Flux-Intensifying Interior Permanent Magnet Motors With Different <italic>Q</italic>-Axis Rotor Flux Barriers

In this paper, two new flux-intensifying interior permanent magnet (FI-IPM) motors owing the characteristic of Ld > Lq are proposed for extended operating speed range. The feasible approaches of realizing Ld > Lq are first discussed to emphasize rotor flux barrier design. According to the feasible approaches, interior flux barriers and surface flux barriers combined with different PM placements are adopted in these two motors. To verify the proposed approaches and the validity of motors, a comprehensive investigation and comparison between the two motors are carried out, including both electromagnetic performances and mechanical performances. By comparison, a prototype motor possessing lower torque ripple, lower magnetic saturation, wider speed range, and more robust mechanical property is manufactured and tested. The experiment results verify the characteristics of the proposed motors and the validity of the proposed approaches in FI-IPM motor design.

Design and Analysis for Torque Ripple Reduction in Synchronous Reluctance Machine

The rotor of transversally laminated synchronous reluctance motor is constructed with multi-flux barriers by stamping the laminated steel sheets and the machine is short for TLR-SynRM. It has obvious advantages of smooth rotor surface, and the lower copper loss, et al. [1]. Nevertheless, TLR-SynRM has the drawback of high torque ripple, and one of the main reasons is the non-sinusoidal distribution of the air-gap flux density caused by the spatial harmonics of stator magnetic potential and flux-barrier rotor configuration. In [2], it has been carried out the genetic algorithm (GA) optimizations to improve the angles of the flux-barrier ends to reduce the torque ripple. In this paper, it proposes the step-shaped gradient flux barriers in TLR-SynRM for torque ripple reduction.A method is presented to compute the reluctances of each layer of flux barriers through conformal mapping method. Based on this calculation, it is shown how the air-gap flux density distribution of TLR-SynRM can be analytically computed through magnetic equivalent circuit (MEC) method. Combining with the two methods, the flux-barrier parameters for torque ripple reduction can be improved and the final improved flux-barrier parameters are obtained.

Optimal Torque Ripple Reduction Technique for Outer Rotor Permanent Magnet Synchronous Reluctance Motors

Torque ripple reduction has been one of the main considerations in the optimal design of traction motors, such as permanent magnet assisted synchronous reluctance motors. Several design techniques including optimal slot/pole combination, stator slot and rotor magnet skewing, and shape optimization of rotor flux barriers have been studied intensively to reduce the torque pulsations in the internal rotor reluctance motors. However, internal rotor reluctance motors involve power train complexity and space constraints in the traction application. On the other hand, outer rotor motors can be designed optimally to eliminate these drawbacks and in addition, produce higher power density. In such outer rotor reluctance motor designs, torque ripple plays crucial role as the in-wheel motor is under duress of consistent rotational forces. Furthermore, optimization of outer rotor in-wheel motors needs to be thoroughly investigated to reduce the torque ripple and to generate higher torque density. In this paper, a rotor shape optimization based on design of notches and rotor flux barrier is presented. Detailed optimization process in adjunct to analytical and simulation results comparison is presented. Finally, optimal designs are fabricated and tests are conducted on the 3.7-kW prototypes to validate the proposed design-optimization theory.

Synchronous Reluctance Machine Optimization for High-Speed Applications

The synchronous reluctance machines with transversally laminated rotor and multi flux barriers per pole reach a high torque density, so that they are proposed as a valid alternative to permanent magnet machines. Such machines have been analyzed for different applications, mainly home appliance, industrial tool, traction, up to low-speed high-power generators. On the contrary, the use of synchronous reluctance machines for high-speed applications remains almost unexplored yet. The aim of this paper is to investigate the potential of a high-speed synchronous reluctance machine. An optimization is carried out so as to maximize the machine performance (high power, proper power factor, low vibration) at a given speed. The machine size is fixed and the focus is on the rotor geometry, with the purpose of maximizing the electromagnetic torque, according to the necessary thickness of the ribs. It is shown that, even if the ribs are thick, it is possible to reach a proper torque density. It is shown that different solutions exist, which allow to reach high torque and minimum torque ripple. However, the optimal solutions are quite sensitive to the geometrical variations, so that a particular care is required in the manufacturing of the machine. Finally, the power limit of the synchronous reluctance motor with barrier rotor is found.

A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges

In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force is shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics depending on additional DC control coil currents are shown.

Effect of Acoustic Noise on Optimal SynRM Design Regions

This paper investigates the rotor design optimization of synchronous reluctance machines (SynRMs) by using electromagnetic and structural finite-element simulations. Three conflicting objectives, i.e., average torque, torque ripple, and sound pressure level, were considered using a surrogate-based multi-objective approach. While the stator is fixed, the rotor flux barriers of a 33-slot 8-pole SynRM were geometrically varied to extract optimal design regions. These regions or constraints help decrease the computational time during the sampling procedure of a multiple-barrier design. Different numbers of flux barriers were studied and related to each other. Adding the sound pressure level was observed to affect previous results by spreading the Pareto front solutions across the design space.

On the Design and Construction Assessments of a Permanent-Magnet-Assisted Synchronous Reluctance Motor

By appropriately inserting ferrite magnets into the rotor of a synchronous reluctance motor (SynRM), the machine operational power factors and torque outputs can be improved. With specific rotor structures to accommodate those ferrites, many of these permanent-magnet-assisted SynRMs (PMA-SynRMs) have been proposed to comply the expected operational objectives. For construction convenience, the ferrites that being inserted into the flux barriers of these PMA-SynRMs are generally in rectangular shapes; hence, some adjustments on the rotor flux barriers and additional bridges are required. Such changes will inevitably affect the performance of the original SynRMs with optimized rotor structures, and these tradeoffs are thus to be recovered by parts of those adopted ferrites. This paper will provide an evaluation index that can characterize the performance of PMA-SynRMs with different volume compositions of the ferrites, along with the impact assessments of the SynRMs with modified flux barriers such that those ferrites can be properly allocated. Based on the designs obtained from thorough 3-D finite-element analyses, a 3-hp PMA-SynRM will be constructed and the related experimental measurements will also be supported to validate the design adequacies.

Cogging torque reduction of Interior Permanent Magnet Synchronous Motor (IPMSM)

In this paper using combination of two separated ideas the torque ripple of Interior Permanent Magnet Synchronous Motor (IPMSM) is reduced. These two ideas are rotor PM segmented and modifying the rotor structure based on pole-arc ratio of flux barrier optimization. In addition the torque ripple due to the reluctance torque component decreased too. Analysis and simulation results including saturation have been performed using analytical method and Finite Element Method (FEM). The rotor flux barrier configuration of the proposed design is carried out by Response Surface Method (RSM) as optimization technique which is verified by FEM

Performance Improvement of Ferrite-Assisted Synchronous Reluctance Machines Using Asymmetrical Rotor Configurations

Recently, the demand for developing high performance electric machines which are free of rare earth magnets are becoming more and more attractive since the raw materials in the rare earth magnets suffer the challenge of increased price and limited supply [1]. In particular, the ferrite-assisted synchronous reluctance machines (FA SynRMs) are regarded as one competitive candidate which incorporate the advantages of the permanent magnet synchronous machines (PMSMs) and synchronous reluctance machines (SynRMs) [2]-[3]. However, all the reported research for FA SynRMs is performed on a fact that the magnets are inserted in the central rotor flux barriers. Thus the rotor shape maintains circumferential symmetry such that the magnetic torque and the reluctance torque obtained from an d-q rotor frame equivalent circuit reach the maximum value at different current phase angles theoretically by 45° (elec.) with each other. Hence, only a portion of each torque component is effectively utilized. Nevertheless, the situation can be improved by taking advantage of the design concept in [4], in which the maximum values of torque components can meet near or at the same current phase angle by flux barrier design in a V-type IPM machine.

Selection of PM Flux Linkage for Maximum Low-Speed Torque Rating in a PM-Assisted Synchronous Reluctance Machine

In recent years, there is an increasing interest in adopting synchronous reluctance machines for several applications. This is due to two main factors. The first is the increasing and highly variable cost of rare-earth permanent-magnet (PM), such as NdFeB and SmCo. The second is the requirement for more efficient machines with respect to induction machines in general applications. However, a drawback of the synchronous reluctance machine is the low power factor. Such a drawback is compensated by assisting the machine by means of a proper volume of PM material, generally ferrite, which is introduced in the rotor flux barriers. The PM flux saturates the rotor iron bridges, increases the power factor of the machine (which corresponds to a decrease of the volt-ampere ratings of the inverter), and adds a PM flux torque component. This paper investigates how to select the amount of ferrite magnet in a PM-assisted reluctance machine, adopting a model that considers the machine operation at low speed with both a current and a flux linkage limit. It is shown that, by means of the aforementioned analysis, the machine performance at low speed can be improved by means of a proper choice of the PM flux linkage.

Asymmetric Flux Barrier and Skew Design Optimization of Reluctance Synchronous Machines

In this paper, an investigation into an alternative topology for reluctance synchronous machine rotor flux barriers is presented. The investigated topology employs a high number of flux barrier variables with an alternative asymmetric rotor structure. The focus in this paper is on maximizing average torque and minimizing torque ripple, using finite element-based design optimization, in order to study the possibility of achieving acceptably low torque ripple. A subsequent investigation into the effect of rotor skew on the proposed optimized design to reduce torque ripple even further is also conducted, as well as the manufacturing and testing of the proposed flux barrier prototype.