Vernier Machine Research Articles

Design and Multi-Mode Operation of Double-Stator Toroidal-Winding PM Vernier Machine for Wind-Photovoltaic Hybrid Generation System

This paper proposes the design and multi-mode operation of a new double-stator toroidal-winding permanent-magnet vernier (DSTW-PMV) machine, which is for the wind-photovoltaic (W-PV) hybrid generation system. In the W-PV system, the wind and PV power are complementary with each other for power variation reduction. Through the multi-mode operation, the output voltage of the machine can be stabilized with high continuity under different rotational speeds to solve the inherently indeterminate wind speed problem and further improve the power smoothness of the whole W-PV system. First, the machine optimization is carried out to obtain the optimal pole-pair combination and geometrical topology for the proposed machine. Second, based on the optimal topology, the multi-mode operation principle of the output voltage adjustment is illustrated. By utilizing the diversities of the toroidal winding configurations and terminal connection strategies, the proposed machine accommodates 54 operating modes with different output voltages under rated speed. Accordingly, under the rated output voltage, the machine speed can be extended to three rated speed with high continuity. Furthermore, some modes generate the rated output voltage with identical speed, which contributes to the high redundancy and high operating efficiency. Hence, with the multi-mode operation and the auxiliary of the PV power, the whole power generation system accommodates the higher flexibility, stability, reliability, and efficiency.

Quantitative Comparison of Distinct Dual-Stator Permanent Magnet Vernier Machines for Direct-Drive Applications

This paper proposes dual-stator permanent magnet Vernier (DS-PMV) machines for direct-drive applications. Also, the quantitative comparison of DS-PMV machines is carried out in terms of no-load performance and output torque characteristic. First, the operation principle is elaborated. Then, the theoretical expressions of air-gap magnetic fields are derived through the magnetic circuit approach. Moreover, the basic machine performances with different pole-slot configurations are quantitatively compared. The corresponding demonstration results are given, which verify that the designs without auxiliary teeth tend to have lower amplitudes of back electromotive force (EMF) harmonics, higher rated average torque, and lower torque ripple.

Development of low translator mass linear Vernier machine for wave energy power take off

This article proposes a new topology of double-sided linear Vernier permanent magnet (LVPM) machine with segmented translator structure. A combination of a typical Halbach array consists of two horizontally magnetised permanent magnets (PMs) sandwiched between a salient iron tooth and adjacent vertically magnetised PM pole with the aim of improving its electromagnetic performance. The coreless partitioned translator contributes to a significant reduction in mass and the associated cost. With the aid of finite element analysis (FEA), two LVPM machines with the same PM, and stator volume have been investigated, analysed, and compared. The results imply that the proposed LVPM is capable of producing higher force density, while it exhibits lower cogging force and force ripple compared to its counterpart.

Torque Component Quantification and Design Guideline for Dual Permanent Magnet Vernier Machine

A quantitative analysis and design guideline for dual-permanent-magnet Vernier machine (DPMVM) are presented in this paper. First, by winding factor analysis for dominant air-gap harmonics, torque components excited by stator PMs and rotor PMs are quantified, which reveals that, in DPMVM, the rotor PMs essentially have higher torque generation ability than stator PMs, due to the effective utilization of fundamental PM harmonic without flux modulation. Furthermore, mutual influence between dual PM sources is analyzed. It is revealed torque contribution of stator PMs is unilaterally affected by design parameters of rotor PMs. Finally, a design guideline is provided for DPMVM, considering the design priorities of dual-PM sources. Finite element simulation and prototype experiments prove the validity of the theoretical analysis.

Influence of Armature Windings Pole Numbers on Performances of Linear Permanent-Magnet Vernier Machines

Linear permanent-magnet vernier (LPMV) machine has attracted more and more attention for several advantages including high power density and low cost. Both magnets and windings are located on the short mover, while the long stator is only consisting of iron, which is very suitable for long stroke applications. This paper investigates the influence of armature windings pole-pair numbers on the electromagnetic performances of LPMV machine by using an analytical method based on the finite element. The aim of this paper is to make a comprehensive comparative study of the machine with different armature windings pole-pair numbers while keeping slot number as a constant, select the topology of high performances and recommend suitable application areas. The performances of machines with the armature windings pole-pair numbers $P_{\mathrm {w}}= 1$ , 3, 6 are analyzed in detail. Finally, a new modular LPMV machine with $P_{\mathrm {w}} = 6$ , which possess higher thrust force, lower thrust force ripple, and high fault-tolerant capability, is prototyped and experiments are conducted for validation.

Design and Analysis of Outer Rotor Permanent-Magnet Vernier Machines with Overhang Structure for In-Wheel Direct-Drive Application

This paper presents a novel outer rotor permanent-magnet vernier machine (PMVM) for in-wheel direct-drive application. The overhang structures of the rotor and flux modulation pole (FMP) are introduced. The soft magnetic composite (SMC) was adopted in the FMP overhang to allow more axial flux. The 3-D finite element analysis (FEA) was carried out to prove that the proposed machine can effectively utilize the end winding space to enhance the air-gap flux density. Hence the PMVM can offer 27.3% and 14.5% higher torque density than the conventional machine with no overhang structure and the machine with only rotor overhang structure, respectively. Nevertheless, the efficiency of the proposed machine is slightly lower than the conventional ones due to the extra losses from the overhang structures.

Design Optimization of a Spoke-Type Permanent-Magnet Vernier Machine for Torque Density and Power Factor Improvement

Permanent-magnet vernier machine has an excellent potential for electric vehicles due to its desirable features of a simple mechanical structure and high torque density, whereas the poor power factor is its main drawback. In this paper, a spoke-type permanent-magnet vernier machine is designed and optimized for torque density and power factor improvement. First, the machine structure, operation principle, and sizing equation are introduced. Then, the machine is optimized by a multi-objective genetic algorithm. To enhance the optimization efficiency and accuracy, multi-level, sensitivity analysis, and approximate model technologies are employed in the optimization. It is shown that the improved torque density and power factor are achieved in the optimized machine as compared to the initial one. Finally, a prototype machine is built, and the experiments on the prototype machine are carried out to verify the design optimization.

Optimal design of dual stator spoke type vernier machine considering armature winding placement

This work was supported in part by the BK21PLUS Program through the National Research Foundation of Korea within the Ministry of Education, and in part by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science) (No.NRF-2017R1A2B4007697).

A dual consequent pole variable flux Vernier machine for wide speed range

A dual consequent pole variable flux Vernier machine for wide speed range

Design and Analysis of Surface-Mounted PM Vernier Machines Considering Harmonic Characteristics of Winding MMF

This paper proposes a design method for the flux modulation poles (FMPs) formed on the stator of surface-mounted permanent magnet vernier machines (SPMVM) considering the winding configurations. In three types of the SPMVM with the different winding configurations, the FMP shapes to maximize the output torque are optimized by employing the analytical equations for the magneto-motive force (MMF) due to the windings, permeance, and flux density in the air-gap. Then, the validity of the optimal shapes for the FMPs is verified by the finite element analysis. It is found that the optimal FMP shapes are designed differently in the three types of the SPMVM and increase the output torque by different ratios according to the winding configurations. In addition, the experimental results for the prototype show that the proposed method can optimally design the FMP shape by analyzing mathematically the effects of the winding configuration and the FMP shape on the output torque of the SPMVM.

A New Perspective on the PM Vernier Machine Mechanism

Permanent magnet vernier (PMV) machines have attracted more and more attention for their merits of high torque density and simple structure. Also, the principle of electromechanical energy conversion is the most common way to investigate the PMV machine by calculating back electromotive force and electromagnetic torque. In this paper, a new perspective on the mechanism of PMV machines based on the Maxwell stress tensor method is presented to deepen the insight into the reason why the force on the rotor of a PMV machine is larger than that of an surface permanent magnet (SPM) machine. Based on the finite element analysis (FEA) method, three machines with exactly the same rotor are analyzed and compared, namely 24-slot/20-pole SPM, 12-slot/20-pole surface PMV, and 6-slot/20-pole split-tooth PMV machines. The radial and tangential flux densities and force distributions along the airgap are illustrated. The influence of pole ratio on the performance of PMV machines is also investigated. It is shown that the improvement of tangential flux density in the PMV machine plays a primary role in the higher torque density, which shows a promising way to improve the torque density of machines.

Analysis of a New Dual-Stator Vernier Machine With Hybrid Magnet Flux-Reversal Arrangement

This paper proposes a new hybrid magnet (HM) dual-stator vernier machine (DSVM) with flux-reversal (FR) magnet arrangement, in which NdFeB and ferrite magnets are reversely mounted on tooth tips of outer and inner stators, respectively. The hybrid dual excitation topology enhances the magnetic fields of inner and outer air-gaps, which are modulated by the rotor composed of iron poles. The proposed topology, operating principle, and design consideration are described. The merits of the proposed HM-FRDSVM are verified when compared to the same FRDSVMs with dual NdFeB magnet excitation and with dual ferrite magnet excitation and the conventional dual stator synchronous permanent magnet machine. The two-dimensional finite element analysis results show that the proposed machine has high torque cost performance with low torque ripple and low cogging torque that are desirable for large telescope drive application.

A Rare-Earth Free Magnetically Geared Generator for Direct-Drive Wind Turbines

A novel Vernier type magnetically geared direct-drive generator for large wind turbines is introduced in this paper. Conventional Vernier-type machines and most of the direct-drive wind turbine generators use excessive amount of permanent magnet, which increases the overall cost and makes the manufacturing process challenging. In this paper, an electrically excited (PM_less) claw-pole type Vernier machine is presented. This new topology has the potential of reducing mass and cost of the generator, and can make the construction easy in manufacturing and handling. Analytical designs are verified using 3D finite-element simulations and several designs are evaluated to find the optimum design for a 7.5 MW, 12 rpm wind turbine application. It is shown, that the required torque can be achieved with an outer diameter of 7.5 m, and with a mass of 172 t (including the structural mass). The proposed generator is compared with commercial direct-drive generators, and it is found that the proposed generator has the highest torque density with 34.7 kNm/t.

Permanent magnet vernier machine: a review

Permanent magnet vernier machines (PMVMs) gained a lot of interest over the past couple of decades. This is mainly due to their high torque density enabled by the magnetic gearing effect. This study will provide a thorough review of recent advances in PMVMs. This review will cover the principle of operation and nature of magnetic gearing in PMVMs, and a better understanding of novel PMVM topologies using different winding configuration as well as different modulation poles and rotor structures. Detailed discussions on the choice of gear ratio, slot–pole combinations, design optimisation and role of advanced materials in PMVMs will be presented. This will provide an update on the current state-of-the art as well as future areas of research. Furthermore, the power factor issue, fault tolerance as well as cost reduction will be discussed highlighting the gap between the current state-of-the art and what is needed in practical applications.

Consequent Pole Permanent Magnet Vernier Machine With Asymmetric Air-Gap Field Distribution

In recent years, permanent magnet vernier (PMV) machines have been attracting more and more attention due to the inherently exhibited advantages such as high torque density and simple mechanical structure. In this paper, a consequent pole (CP) PMV machine with single-layer concentrated winding is proposed. The novelty is that the asymmetric air-gap field distribution is introduced to improve its working harmonics and to reduce the PM consumption. By employing a CP structure, the flux density amplitude can be enhanced. Moreover, due to uneven distribution of modulator poles on the armature teeth and fault tolerant teeth, the number of periods of modulator poles is only half of that of the stator teeth. Then, significant improvement in flux density working harmonics can be achieved. Furthermore, the superior electromagnetic decoupling capability can be achieved by introducing the fault-tolerant teeth. The relevant electromagnetic performance such as flux density, back electromotive forces, cogging torque and on-load torque have been calculated by using finite-element analyses, which have also been validated by experiments.

Low-Cost Dual-Mechanical-Port Dual-Excitation Machine for Washing Machine Application

This paper proposes a low-cost dual-mechanical-port dual-excitation machine for washing machine application. The proposed machine artfully combines two machines (vernier and permanent magnet synchronous machine (PMSM)). An outer vernier rotor is used for the low-speed washing operations, and an inner PMSM rotor is used for the high-speed drying operations of the washing machine. The proposed machine is compared with a similar recently presented machine to verify its cost-effectiveness. Comparison using the finite element analysis (FEA) shows that the ferrite magnets used in the proposed topology are more cost-effective. Furthermore, compared to the existing machine, the power factor of the proposed machine is high during the drying operation; hence, a lower rating inverter is sufficient to drive the machine, which further reduces the overall cost. In addition, the proposed machine provides similar efficiencies as the existing machine for both washing and drying operations.

Winding Switching and Turn Switching in Permanent Magnet Vernier Machines for Wide Speed Range Operation and High Efficiency

This paper proposes to turn to switch along with winding switching for high-efficiency of permanent magnet vernier machines (PMVM) during wide speed range operation for electric vehicles application. For winding switching, the three-phase winding of the machine is divided into two sets of windings, namely, winding set A, B, C and winding set X, Y, Z. For turn switching, the number of turns for one set of winding is changed. With the different number of turns for winding set X, Y, Z, the efficiency of the machine can be significantly improved. Initially, the basic electromagnetic characteristics, such as the flux linkage, back electromotive force (EMF), torque, and phase voltages of the machine are investigated using winding switching and turn switching. Then, the output power, torque-speed curve, core losses, efficiency, and power factor of the machine are analyzed in detail using a different number of turns. In addition, the transient effects of winding switching and turn switching have been analyzed. Finally, a control strategy is proposed which combines turn switching and winding switching to ensure high-efficiency of PMVMs during wide speed range operation. A PMVM is designed and driven in accordance with the proposed control strategy (PCS) to show the characteristics of PCS. The PMVM driven with PCS is compared to a recently presented PMVM. The recently presented PMVM is driven by a different control strategy and is analyzed with two different kinds of steel laminations that are general steel (50TW470) and special steel (20JHF1300).

Investigation of Spoke Array Permanent Magnet Vernier Machine With Alternate Flux Bridges

In recent years, permanent magnet vernier (PMV) machines are attracting more and more attentions owing to their high torque density feature, which is mainly benefited from its special operation principle called flux modulation effect. Nevertheless, It is found that its working flux density is low, viz., ∼0.3T for modulated flux density in the surface mounted PMV machines. Hence, there is a really large space to further improve the torque density of PMV machine. The spoke array magnet is widely used in the regular PM machine to improve working flux density. However, the flux barrier effect of spoke array magnet for the PMV machine has been proved, and a large torque reduction would be introduced in the high pole ratio spoke array PMV machine. In this paper, a novel spoke array PMV machine is proposed to improve working flux density and the torque density of PMV machines. The alternate magnetic bridges are added in the rotor core to connect iron pieces with same polarity and provide magnetic circuit for the low-pole number working magnetic field, hence the no-load back EMF and output torque of the proposed machine can be significantly improved. Moreover, analytical airgap flux density distribution based on equivalent magnetic circuit is presented to reveal the mechanism of working flux density improvement, and finite element analysis is used to investigate the performance features and structure parameter influence on the key performances, viz., back EMF and torque, of the proposed machine. Finally, a 25 N·m prototype has been built and tested to validate these analyses.

Analysis of Thrust Performance of a Dual-Mover Linear Vernier Machine With Horizontal-Magnetized PM Arrays

Recently, a novel dual-mover linear vernier machine with horizontal-magnetized permanent magnet arrays has already been proposed to improve the thrust and power factor (PF). According to published papers, the thrust and the PF of the novel LVM can be increased by more than 30% and can be improved up to 0.7, respectively, compared to a conventional LVM. However, by now, the analysis of this kind of machine is merely based on the finite element method (FEM). Consequently, this paper will focus on the analytical analysis of thrust performance. Average force, force ripple, slot cogging force, as well as end cogging force are taken into consideration. The effectiveness of the analytical calculations is validated by FEM. By using the derived expressions, it is possible to predict the thrust performance and optimize the machines efficiently.

High-Efficiency Dual Output Stator-PM Machine for the Two-Mode Operation of Washing Machines

This paper proposes the novel topology of a high-efficiency dual output stator-permanent magnet (PM) machine (DOSPMM) for two different washing machine operating speeds. The proposed machine consists of two machines integrated into a single machine: Machine I is an outer rotor type Vernier machine with low speed and high torque for washing mode operations. Machine II is an inner rotor type flux-reversal PM (FRPM) machine with high speed and low torque for dehydrating mode operations. Each machine was designed to be highly efficient for the assigned operating mode. Both machines also possess robust rotors due to stator positioned PMs. To demonstrate the superiority of the proposed machine, performance comparisons with conventional machines for general washing machine applications were performed via finite-element method (FEM) analysis. A prototype of the proposed machine was built and experimental results of the prototype machine were presented for a validation of the work.