X. Ge

A Novel Design of Rotor Contour for Variable Reluctance Resolver by Injecting Auxiliary Air-Gap Permeance Harmonics

This paper proposes a novel rotor contour design for variable reluctance (VR) resolvers by injecting auxiliary air-gap permeance harmonics. Based on the resolver model with nonoverlapping tooth-coil windings, the influence of air-gap length function is first investigated by finite element (FE) method, and the detection accuracy of designs with higher values of fundamental wave factor may deteriorate due to the increasing third order of output voltage harmonics. Further, the origins of the third harmonics are investigated by analytical derivation and FE analyses of output voltages. Furthermore, it is proved that the voltage harmonics and the detection accuracy are significantly improved by injecting auxiliary air-gap permeance harmonics in the design of rotor contour. In addition, the proposed design can also be employed to eliminate voltage tooth harmonics in a conventional VR resolver topology. Finally, VR resolver prototypes with the conventional and the proposed rotors are fabricated and tested respectively to verify the analyses.

A Novel Variable Reluctance Resolver with Nonoverlapping Tooth–Coil Windings

A novel variable reluctance (VR) resolver with nonoverlapping tooth-coil windings is proposed in this paper. It significantly simplifies the manufacturing process of multilayer windings in conventional products. Finite element (FE) analysis is used to illustrate the basic operating principle, followed by analytical derivation of main parameters and optimization of major dimensions, including air-gap length and slot opening width. Based on winding distributions and FE results, it is shown that identical stator and winding can be employed for a resolver with three different numbers of rotor poles. Further, other stator slot/rotor pole combinations based on the nonoverlapping tooth-coil windings are generalized. In addition, the influence of eccentricity and end-winding leakage on the proposed topology is investigated. Finally, a prototype is fabricated and tested to verify the analysis, including main parameters and electrical angle error.

A Novel Variable Reluctance Resolver for HEV/EV Applications

In order to simplify the manufacturing process of variable reluctance (VR) resolvers for hybrid electric vehicle/electric vehicle (HEV/EV) applications, a novel VR resolver with nonoverlapping tooth-coil windings is proposed in this paper. A comparison of the winding configurations is first carried out between the existing and the proposed designs, followed by the description of the operating principle. Furthermore, the influence of actual application conditions is investigated by finite-element (FE) analyses, including operating speed and assembling eccentricity. In addition, identical stator and windings of the novel design can be employed in three resolvers of different rotor saliencies. The voltage difference among the three rotor combinations, as well as the detecting accuracy, is further investigated. Finally, prototypes are fabricated and tested to verify the analyses.

Analysis of Windings in Variable Reluctance Resolver

In this paper, the relationship between the numbers of stator slots, winding polarities, and rotor poles for variable reluctance resolvers is derived and verified, which makes it possible for the same stator and winding to be shared by the rotors with different poles. Based on the established relationship, a simple factor is introduced to evaluate the level of voltage harmonics as an index for choosing appropriate stator slot and rotor pole combinations. With due account for easy manufacturing, alternate windings are proposed without apparent deterioration in voltage harmonics of a resolver. In particular, alternate windings with nonoverlapping uniform coils are proved to be possible for output windings in some stator slot and rotor pole combinations, which further simplify the manufacture process. Finite element method is adopted to verify the proposed design, together with experiments on the prototypes.

Analytical On-Load Subdomain Field Model of Permanent-Magnet Vernier Machines

Permanent-magnet vernier machine (PMVM) is a relatively new type of PM machines. An analytical subdomain model accounting for tooth-tips and flux modulation poles is developed to accurately predict on-load field distributions in PMVMs. Based on two-dimensional (2-D) polar coordinate and magnetic vector potential, this method solves the Maxwells equations in slot, air-gap, flux modulation pole slot (FMPS), and PM regions. Consequently, the electromagnetic performance such as cogging torque, back-electromotive force (EMF), electromagnetic torque, power factor, and magnet loss are calculated. In addition, the model can also be used for the evaluation of demagnetization withstand capability. The finite-element analysis (FEA) and experimental results validate the accuracy of the developed analytical model.

Influence of manufacturing tolerances on cogging torque in interior permanent magnet machines with eccentric and sinusoidal rotor contours

The rotor shaping methods are frequently used to reduce the cogging torque in interior permanent magnet (IPM) machines. This paper investigates the influence of manufacturing tolerances on cogging torque in IPM machines with eccentric and sinusoidal rotor contours. First, two 12-slot/8-pole IPM machine models are established and the fundamental performance under ideal conditions is presented. Then, based on the most sensitive distributions of non-ideal PMs and assembly tooth-bulges, additional cogging torque components are calculated respectively, together with a comparative study to identify the different sensitivities between the two rotor contour designs. For verification, the field spatial harmonics with and without considering the tolerances are further analyzed, followed by tests on the prototypes with and without amplified tolerances.

Comparison of Partitioned Stator Switched Flux Permanent Magnet Machines Having Single- or Double-Layer Windings

A novel type of partitioned stator switched flux permanent magnet (PS-SFPM) machine with either single-layer or double-layer windings is developed in this paper. The proposed PS-SFPM machines have two stators, which separately accommodate the armature windings and the PMs, and between which is the rotor made of iron pieces, while the number of stator poles with PMs may be equal or half of that with armature windings. All the machines are optimized under fixed copper loss for maximum average torque by genetic algorithm. Their electromagnetic performances are compared, such as open-circuit flux-linkages and back-electromotive forces (EMFs), cogging torque, static torque waveforms, average torque against current, PM utilization ratio, and flux-weakening performances. The results show that due to more PM usage and higher open-circuit back-EMF, the PS-SFPM machines having the number of stator poles with PMs the same as that with armature windings exhibit higher average torque, irrespective of the winding topologies, either single-layer or double-layer windings. However, the single-layer winding PS-SFPM machines having the number of stator poles with PMs half of that with armature windings have the best PM usage and the highest ratio of average torque to PM volume, as well as good flux-weakening capability. A prototype machine is manufactured and tested to validate the analyses.

Comparison of electrically excited and interior permanent magnet machines for hybrid electric vehicle application

This paper comprehensively compares electrically excited (EE) and interior permanent magnet (IPM) machines for a hybrid electric vehicle application based on 2010 Toyota Prius system. An EE machine is globally optimized when it has the same machine size and total copper loss with the IPM machine. Efficiency maps of both machines are obtained and compared with iron losses calculated by finite element analyses. It shows that the EE machine can be a low cost alternative to the IPM machine with slightly lower efficiency and maximum torque. Due its adjustable excitation, the EE machine is able to achieve a wider constant power speed range than the IPM machine. However, the efficiency of the EE machine is not better than the IPM machine in the high speed region, since flux weakening control via armature windings is still necessary.

Optimal Step-Skew Methods for Cogging Torque Reduction Accounting for Three-Dimensional Effect of Interior Permanent Magnet Machines

This paper proposes optimal step-skew methods for cogging torque reduction in interior permanent magnet (IPM) machines. First, a vector diagram method is employed to analyze the principle of a conventional three-step-skewed rotor, followed by two-dimensional (2-D) finite element (FE) validation. However, a considerable component of the cogging torque still exists according to 3-D FE analysis. End leakage flux and interaction between adjacent rotor steps are then investigated. To further reduce the residual cogging torque component, two improved step-skew methods are proposed—first, a rotor with optimal step-skew angles and, second, a rotor with optimal step lengths. Furthermore, the influence of manufacturing tolerance with axial placement of the rotor steps is investigated and leads to further corrections of the proposed methods, followed by analyses on other IPM machines having different stator slot/rotor pole combinations. Finally, prototypes are fabricated and tested to verify the foregoing analyses.

Electromagnetic performance of switched flux PM machines with two separate stators

Purpose – The purpose of this paper is to propose a novel type of switched flux PM machines with two separate stators. Design/methodology/approach – 2D-FEA is employed to analyze the electromagnetic performance of the proposed machines. Moreover, the results are validated by experiments. Findings – The proposed machine has higher torque density, less unbalanced magnetic force on the modulating steel piece and uses less PM volume. Originality/value – The proposed machine is a low-cost novel topology with different rotor pole combinations.