Vernier Machine Research Articles

A high-performance dual-stator permanent-magnet vernier machine for propulsion applications

A high-performance dual-stator permanent-magnet vernier machine for propulsion applications

Optimization of Non-uniform Flux Modulation Poles of a Dual-Stator Permanent Magnet Vernier Machine for Performance Improvement

Optimization of Non-uniform Flux Modulation Poles of a Dual-Stator Permanent Magnet Vernier Machine for Performance Improvement

Two-dimensional analytical model for five-phase fault-tolerant permanent-magnet vernier machines

PurposeThis study aims to extract an analytical model for five-phase fault-tolerant permanent-magnet vernier machines (FTPMVMs) based on the analytical solution of Maxwell’s equations, which has some advantages than the finite element model.Design/methodology/approachFTPMVMs enhance the torque density by combining the vernier characteristics and the fault-tolerant feature. The principle operation of FTPMVMs is discussed based on the magnetic field modulation due to both permanent magnets and armature current. The analytical solution of the magnetic vector potential in each sub-region is obtained based on the sub-domain technique.FindingsAccording to the calculated magnetic vector potential, the magnetic flux density, torque, self- and mutual inductance and back-electromotive force are calculated. The FEM is used to validate the results obtained from the proposed analytic model.Originality/valueTwo-dimensional analytical method is used to obtain the electromagnetic model of FTPMVMs.

Effect of Airgap Length on Electromagnetic Performance of Permanent Magnet Vernier Machines With Different Power Ratings

This article investigates the effect of airgap length on the electromagnetic performance of direct-drive surface mounted permanent magnet Vernier (SPM-V) machines with different power ratings. Using 3 kW machine as an example, its performance is comprehensively compared with a conventional SPM machine with the same airgap lengths using two-dimensional finite-element analysis. For each airgap length, the slot&#x002F;pole number combination for the SPM-V machine is investigated to achieve the optimal performance compared to the conventional SPM machine. In order to make the study more generic, the slot&#x002F;pole number and the airgap length variations are expressed as normalized pole pitch, i.e., <inline-formula><tex-math notation="LaTeX">$\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $</tex-math></inline-formula> (ratio of rotor pole pitch to electromagnetic airgap length). The results show that for 3 kW machines, <inline-formula><tex-math notation="LaTeX">$\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $</tex-math></inline-formula> &gt;2.2 is a good design criterion for the SPM-V machines to achieve higher average torque and efficiency than the conventional SPM machines. In addition, a reasonably good power factor (&gt;0.9 in this case) can be achieved. Although the power factor of SPM-V machines drops significantly at multi-MW power level, i.e., 3 and 10 MW, the criterion <inline-formula><tex-math notation="LaTeX">$\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $</tex-math></inline-formula> &gt;2.2 still results in achieving a performance closest to their optimal capability. However, when <inline-formula><tex-math notation="LaTeX">$\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $</tex-math></inline-formula> &gt;2.2, special consideration should be paid to avoid potential irreversible magnet demagnetization at multi-MW power levels.

Performance Analysis of Permanent Magnet Vernier Motor with Surface and Halbach Magnets

Background: Surface permanent magnet motors (SPMVM) and dual permanent magnet motors (DPMVM) have broad prospects in direct drive systems, but some problems occur with large magnetic leakage, large torque ripple and large amount of permanent magnets (PMs). Objective: In order to reduce the torque ripple and magnetic flux leakage of SPMVM and DPMVM, and improve the torque density, a dual permanent magnet vernier machine with Halbach PM array (DHPMVM) is proposed. Method: By air gap permeance method, flux density analysis of three kinds of motors was analyzed, and the main harmonics of SPMVM and DHPMVM are investigated with structure parameters. Electromagnetic characteristics of three motors such as no-load back, electromotive force (EMF), torque, and inductance are compared and analyzed by finite element method (FEM). Results: The study found that under the same size, winding distribution, electrical load and speed conditions, DHPMVM uses Halbach PM array and consequent pole structures to reduce magnetic flux leakage and torque ripple, increase torque density, PM utilization and torque per unit PM volume. Compared with SPMVM and DPMVM, the DHPMVM proposed in this paper has better electromagnetic performance. Conclusion: The DHPMVM topology is the better choice in terms of torque density, torque ripple, and magnet usage among the investigated topologies.

Design and Analysis of a High Torque Density Hybrid Permanent Magnet Excited Vernier Machine

Permanent magnet (PM) excited vernier machines capable of high torque density have good potential for electric vehicles while requiring high rare earth PM consumption. To achieve a high torque density at a reasonable material cost, hybrid PM excited vernier machines incorporating both expensive rare earth and low-cost ferrite magnets are investigated in this paper. Various combinations of PM arrangements for the hybrid permanent magnet excited vernier machine are investigated to acquire low cost and superior torque density. The best solution obtained is that the PM on the stator adopts rare earth material while the rotor uses ferrite. Furthermore, the PMs on the stator are arranged in an iron-cored Halbach array, which can reduce leakage flux and enhance flux density effectively and the ferrite PMs are used in the rotor, therefore, high-temperature demagnetization is avoided. Then, the reluctance torque and the cogging torque can offset each other effectively, which is beneficial to reducing the torque ripple and smoothing the electromagnetic torque. Finally, a prototype is manufactured and tested to verify the correctness of the theoretical analysis.

Design, Analysis, and Optimization of Permanent Magnet Vernier Machines Considering Rotor Losses

The purpose of this paper is the design, analysis, and optimization of a new structure of a permanent magnet vernier machine (PMVM) with a high torque density and low rotor losses. First, the modulation principle and topology of this PMVM is introduced. Then, its average torque and rotor loss are enhanced and reduced by optimizing the flux modulation poles distribution. For the sake of further reducing the rotor losses on the premise of maintaining the torque density, the contribution of the air gap flux density harmonics to the rotor loss is analyzed. Then, a new topological structure of a rotor with a flux barrier is introduced to reduce the rotor losses due to the decrease of each harmful harmonic. Through the analysis of the structure of the PMVM with the flux barrier, the influence of the parameters on the performance is built. After that, a multi-objective optimization algorithm is used to optimize the PMVM so as to obtain the optimal performance. Moreover, the electromagnetic performance comparison between the newly proposed machine and the original one is presented to indicate that lower rotor losses can be obtained by the proposed machine when the torque is ensured. Finally, a prototype of proposed PMVM is built and further tested to verify the validities of the theoretical and finite-element analyses.

Design and Analysis of Dual-Rotor Modular-Stator Hybrid-Excited Axial-Flux Permanent Magnet Vernier Machine

This paper proposes a new structure of the dual-rotor hybrid-excited axial-flux permanent magnet vernier machine (DR-HEAFPMVM) with the modular stator and the consequent-pole PM (CPM) rotor for low-speed, high torque density applications such as in-wheel electric vehicles. The tooth-wound non-overlapping armature windings and direct current (DC) excitation windings are, respectively, arranged in stator main-teeth and split-teeth to obtain the modulated and adjustable air-gap flux densities, resulting in high torque density and outstanding flux-weakening capability. First, the design considerations, operation principles, and air-gap flux density distributions of the proposed machine are elaborated based on the air-gap permeance function. Then, the influence of the pole ratios (PRs) and the DC excitation currents on the main electromagnetic performances of the DR-HEAFPMVM, such as the flux-weakening capability and back-electromotive force (back-EMF), on-load electromagnetic torque, loss distribution, and efficiencies, is investigated using the 3-D finite-element method (FEM). Results verify the feasibility of the flux adjustment of the DC excitation windings equipped in the split-tooth, and the design with a pole ratio of 8/1 tends to have higher torque density, higher machine efficiency, and considerable flux-weakening capability compared with the other two PRs.

Analysis of Rotor Losses in Permanent Magnet Vernier Machines

This article investigates rotor losses in permanent magnet Vernier machines. By analyzing air-gap field, the harmonic distribution and frequency of modulated open-circuit flux density and armature reaction flux density are obtained. Then, rotor losses production principle is revealed and the influence of each harmonic on the loss is analyzed. Meanwhile, the influence of each harmonic on torque is also studied. It is found that some harmonics have no contribution to torque but produce additional losses. On this basis, a new rotor structure is proposed to suppress the rotor losses. Comparison results indicate that by suppressing nonworking harmonics, the rotor losses can be reduced effectively without affecting the effective torque. Finally, the theoretical and finite-element analysis results are verified by prototype tests.

Multicriteria Optimal Latin Hypercube Design-Based Surrogate-Assisted Design Optimization for a Permanent-Magnet Vernier Machine

This article proposes an efficient surrogate-assisted design optimization method based on a multicriteria optimal Latin hypercube design (LHD) for multi-objective optimization of a surface-mounted permanent-magnet vernier machine (SPMVM). An improved iterated local search (ILS) method is proposed to optimize the spatial distribution uniformity and orthogonality of LHDs so that the data feature over the wide ranges of optimization variables can be captured more efficiently. Using the optimal LHD, a highly generalizable surrogate model can be trained with fewer samples, thus greatly reducing the required number of finite element analysis (FEA) cases and improving the optimization efficiency. A prototype corresponding to the optimal design is built and measured to validate the proposed method.

Permanent Magnet Vernier Machines for Direct-Drive Offshore Wind Power: Benefits and Challenges

Permanent magnet Vernier (PM-V) machines, at low power levels (few kWs), have shown a great potential to improve the torque density of existing direct-drive PM machines without much compromising on efficiency or making the machine structure more complicated. An improved torque density is very desirable for offshore wind power applications where the size of the direct-drive machine is an increasing concern. However, the relatively poor power factors of the PM-V machines will increase the power converter rating and hence cost. The objective of this paper is to review the benefits and challenges of PM-V machines for direct-drive offshore wind power applications. The review has been presented considering the system-level (direct-drive generator + converter) performance comparison between the surface-mounted permanent magnet Vernier (SPM-V) machines and the conventional SPM machines. It includes the indepth discussion on the challenges facing the PM-V machines when they are scaled up for multi-MW offshore wind power application. Other PM-V topologies discussed in literature have also been reviewed to asses their suitability for offshore wind power application.

Novel Self-Excited Brush-Less Wound Field Vernier Machine Topology

To realize the brush-less operation for wound field vernier machines (WFVMs), a novel self-excited topology is proposed in this paper which involves a four-pole main armature winding and a two-pole excitation winding connected in series using an uncontrolled rectifier. Upon supplying current from a single current-controlled voltage source inverter (VSI), this procedure results in four-pole and two-pole magnetomotive force (MMF) components in the airgap. The four-pole MMF produces the main stator field while the two-pole MMF component develops a sub-harmonic field in the airgap. The rotor is altered to house a forty-four-pole rotor field and two-pole harmonic windings. The two-pole harmonic field is employed to induce a current in the harmonic winding, which is rectified by means of a full-bridge diode rectifier to energize the rotor field winding and realize brush-less operation for WFVM. Two-dimensional finite element analysis (2-D FEA) is implemented in JMAG-Designer to confirm the operation of the proposed WFVM topology and attain the electromagnetic performance for a four-pole, twenty-four-slot outer-rotor vernier machine.

Design and Analysis of Single Inverter-Fed Brushless Wound Rotor Vernier Machine

In this paper, a brushless wound rotor vernier machine (Bl-WRVM) with a single inverter configuration is proposed to achieve the brushless operation. In the proposed topology, a single inverter is connected with series-connected ABC and XYZ windings through which the current flow produces the magnetomotive force with fundamental and sub-harmonic components, respectively. The XYZ windings have similar pole pairs to the excitation windings, whereas its number of poles is different from the ABC winding. A 24-slot stator, 4-pole armature ABC winding, 2 Pole armature XYZ and excitation windings, and 44-pole field winding for the outer rotor is designed and 2D finite element analysis is carried out to determine the performance of the machine. The proposed topology makes the Bl-WRVM cost-effective by applying only a single inverter as compared to a dual-inverter Bl-WRVM and it improves its torque quality.

Effect of End-Winding on Electromagnetic Performance of Fractional Slot and Vernier PM Machines With Different Slot/Pole Number Combinations and Winding Configurations

In this paper, the effects of end-winding on electromagnetic performance of surface mounted permanent magnet machines (SPMMs) (including vernier machines) with different slot/pole number combinations and winding configurations are analyzed and compared. By using genetic algorithm based on finite element analysis, SPMMs with different coil pitches are optimized for maximum average torque under fixed copper loss or fixed copper and iron losses, with/without considering the influence of end-winding. The effects of coil pitch and stack length on torque and torque density are investigated, and the optimal coil pitch for each slot/pole number combination is obtained. The efficiencies, inductances, and power factors of optimized SPMMs are also compared. The torques of optimized SPMMs considering iron loss decrease, especially at high speed and larger rotor pole number. It is found that the end-winding has significant effect on torque, torque density, winding inductance, and power factor etc. Compared with the fractional slot concentrated winding SPMMs with the same lamination stack length but slot number higher than pole number, the integer-slot distributed winding SPMMs with pole number higher than slot number have higher torques due to field modulation effect, but lower torque densities due to longer axial end-winding lengths.

Experimental Verification of Dual Airgap PMVM Having Yokeless Rotor for Extended Speed Application

Permanent magnet vernier machines (PMVM) are recently proven to be a good candidate for extended-speed operation in the constant power region. In this paper, a dual-airgap PMVM having a yokeless rotor has been presented for extended-speed operation. The PMVM model is designed with two stators and a sandwiched rotor without an iron yoke. To achieve the extended speed operation, the yokeless structure of dual airgap PMVM benefits from the increased inductance which makes it possible to operate at higher speeds. For this purpose, the prototype of this machine is built, and experimental testing is performed to verify its performance in a constant power region. Electromagnetic performance such as back EMF and output torque at high speeds are analyzed. The experimental results are compared with those obtained using finite element analysis which confirms the ability of dual airgap PMVM having a yokeless rotor to perform well at higher speeds in a constant power region.

Split Pole Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Opening and Consequent Pole Rotor

Due to simpler mechanical structure and magnetic gearing effects, Permanent Magnet Vernier Machines (PMVMs) attract researcher interest because of their higher torque density for direct drive applications. However, regular PMVMs utilize more rare earth Permanent Magnet (PM), which increases machine cost and weight. Moreover, the PMs are mounted on the rotor surface, which enhances flux leakage and flux circulation, which degrade electromagnetic performance that ultimately decreases average torque, torque density, power density and efficiency. A new Split Pole PMVM (SP-PMVM) with Halbach PM arrangement in the stator slot opening and consequent pole rotor is proposed to overcome the issues above. The proposed SP-PMVM enhanced flux modulation phenomena to improve electromagnetic performance. Comparing the proposed machine with the existing designs reveals that the proposed design reduces the PM utilization by 22.2% and improves the flux linkage by 41.3% due to suppression of leakage flux and flux circulation. Moreover, the average torque is boosted by 42.35%. Furthermore, torque and power densities are increased by 83.01% and 44.84%, respectively. In addition, in comparison with the existing conventional design, the efficiency of the proposed model is enhanced by 25.01% at the cost of 19.75% cogging torque.

Modeling and detection of demagnetization fault in permanent magnet vernier machine using flexible magnetic equivalent circuit method

In this paper, an analytical model is proposed for evaluating electromagnetic performances of permanent magnet vernier machines (PMVMs) under healthy and faulty conditions. The proposed model employs flexible magnetic equivalent circuit (MEC) method, which its accuracy can be selected by tunable parameters. The model is capable of considering the influence of saturation effect, skewed slots, slot leakage fluxes, and various winding arrangements for the machines with desired properties. First, the proposed model is used to predict the no-load performance of machine at healthy condition. Then, the machine loading behaviors under healthy and demagnetization fault conditions are analyzed by the MEC model. Moreover, the results of the proposed model are compared and validated with those of 2-D finite element method (FEM) and 3-D FEM. Eventually, a specific pattern is extracted from the stator current spectrum to detect the demagnetization fault.

Single stator‐single rotor permanent magnet Vernier machine topologies for direct‐drive applications: Review and case study

Stator and rotor structures, arrangement of permanent magnets (PMs), and type of coils of PM Vernier machines are reviewed and classified. Then, electromagnetic performance and the energy conversion process in the machine are described. Determination of magnetic field distribution and air-gap permeance of the machine is very complicated than that of other PM machines. Impacts of variations of dimensions in the machine such as the number of modulators on the modulus width and the rotor PMs thickness on the load characteristics (cogging torque, back-EMF, and power factor) are investigated. In addition, principles of flux modulation machines operation are presented and the shape and dimensions of the modulators are optimized. The two-phase and four-phase winding types are used to improve the output power of the machine. Finally, a 150 W PM Vernier generator is designed and prototyped to feed the road speed camera.

Modelling and analysis of permanent magnet vernier machine using flexible magnetic equivalent circuit method

This paper develops a new model with adjustable accuracy to evaluate performance of permanent magnet Vernier machine (PMVM) based on flexible magnetic equivalent circuit (MEC) method. The desired machine parameters such as number of flux modulation poles (FMPs), winding pole-pairs, and geometrical dimensions can be chosen in the presented model. By utilizing nonlinear core magnetization curve, saturation effect is taken into account. There are two main contributions in this study. First, the flexible MEC model is developed to predict the machine performance accurately. The second contribution is that the developed model can be used to evaluate the performance of the machine under no-load and loading conditions at the same time. The results of MEC model under no-load and loading conditions are compared with 2D-finite element method (FEM) and 3D-FEM in terms of accuracy and simulation time. The results indicate acceptable accuracy and suitable processing time of the proposed MEC model.

Featured Cover

The cover image is based on the Review Article Single stator-single rotor permanent magnet Vernier machine topologies for direct-drive applications: Review and case study by Jawad Faiz et al., https://doi.org/10.1002/2050-7038.13240.