Vernier Motor Research Articles

Output power improvement of a vernier motor using field winding configuration

In this paper, a field winding vernier (FWV) machine is proposed to get higher back electromotive force (EMF) than surface permanent magnet vernier (SPMV) machine. First, the magneto motive force (MMF) equation of FWV machine is derived to obtain the requisite field current to produce the same back EMF as SPMV machine. Using the derived equation, the surface current density is also estimated and compared with the maximum allowable current density to examine the possibility of improving the back EMF of the FWV machine and find the slot-pole combination that is advantageous for the FWV structure. Using the obtained information, three models of SPMV and FWV machines are designed, finite element analysis are performed, and it is verified that proposed FWV machine has the capability of producing higher back EMF than SPMV machine.

Model Predictive Current Control of Dual-Permanent-Magnet Vernier Motor based on Anti-Windup Controller

Dual-permanent-magnet vernier motor incorporates the merits of high torque density and low cost, suitable for low-speed high-torque applications. Due to integral saturation and high current ripples in dual-permanent-magnet vernier motor control system, a model predictive current control strategy based on Anti-Windup PI controller is proposed. Adaptive adjustment variable structure is adopted in integral segment of the controller, which can quickly eliminate integral saturation in system. Mode predictive current control based on dual vector is adopted in current interior loop of the system, double arbitrary voltage vector can be selected to operate simultaneously in each control cycle that extends selection range of voltage vector and adjustment range of amplitude, which can realize more accurate current control. Meanwhile, considering system delay, current delay compensation is added to predictive control. The simulation results showed that proposed control strategy can effectively restrain integral saturation, reduce current ripples, thus improving dynamic and steady state performance of the control system.

Power Factor Analysis of Dual-Stator Permanent Magnet Vernier Motor With Consideration on Turn-Number Assignment of Inner and Outer Stator Windings

Permanent magnet vernier motors (PMVMs) are extremely attractive in low-speed large-torque (LSLT) and direct-drive (DD) applications, due to high torque density and simple structure. However, they suffer from low power factor (PF). The existing research has shown that dual-stator PMVM (DS-PMVM) is an effective topology to improve the PF. This article focuses on the PF analysis of DS-PMVMs to maximize the PF. The analytical perspective is not trying to propose new topologies of DS-PMVMs but to consider the turn-number assignment of the inner and outer stator windings. In this article, both the analytical and the operational procedures are elaborated; by combining the 2-D finite element method (FEM) with the mathematical method, two DS-PMVMs are used to verify the theoretical analysis. The simulation results agree well with the results obtained by the theoretical analysis. The results also showed that 1) if the inductances of single-turn inner and outer stator windings are close or equal, the equal turn-number of inner and outer stator windings will make the PF of DS-PMVM maximum; otherwise, the PF will reach maximum with the unequal turn-number assignment and 2) the turn-number assignment can not only maximize the PF of DS-PMVMs but also meet the torque requirement.

Performance comparisons of alternative permanent‐magnet motor designs for personal mobility‐assistive device applications

Demands of appropriate personal mobility-assistive devices for those needed persons have been increased considerably in recent years, with their specific operational requirements, developments of adequate motors to different device parts are the main concerns. For applications onto those knee joint parts of the exoskeleton system, three types of permanent-magnet (PM) motors, namely the surface-mounted PM motor, the Vernier motor, and the flux-switching motor were designed. Based on the operational and physical constraints of the particular exoskeleton parts, optimisations of these PM motors were provided along with their thorough performance comparisons. From emulated finite-element analyses along with hardware experimental validations, by following the standard test settings, selection guidance for the suitable motor structures at different operational objectives will thus be supplied.

Linear Vernier actuator with two movers

Background: Linear motion devices for industrial machines and robots are expected to realize their high efficiency drive and simple structure. Usually, a feed screw mechanism composed of a rotary motor and a ball-screw or slide-screw is employed. However, it has some problems such as the decrease of the drive efficiency, flexibility against external forces, noise, etc. Various linear actuators and motors have been developed utilizing the feature of a direct drive.
 Aim: In this paper, we propose a novel linear actuator which 2 movers can be independently controlled using 3-phase and 6-phase superimposed currents for decreasing the size and weight of the system. The proposed linear actuator is driven by the operating principle of a vernier motor which is expected to achieve a high thrust force density per permanent magnet volume.
 Methods: The operating principle and the static thrust force characteristics of the proposed linear actuator are verified by an electromagnetic field analysis using 3-D finite element method, and the back electromotive force characteristics are also analyzed. In addition, the dynamic characteristics under position feedback control are analyzed. The control system uses a vector control using PID controller, and the control input is given by the 3-phase and 6-phase superimposed currents.
 Results: The static force characteristics were investigated. From the analyzed results, the force interference between the two movers was small. Moreover, the interference of the back electromotive force of the 3-phase and 6-phase movers were not observed. The movers could be independently driven under position feedback control using 3-phase and 6-phase superimposed currents. The dynamic characteristics analyses showed that the mover well followed a target position. From a step response, the time constant and the response of the position feedback system were investigated.
 Conclusion: This paper presents a linear vernier actuator with two movers. The basic structure and operating principle of the actuator were described. Moreover, the static characteristics and the dynamic characteristics under position feedback control were analyzed. It was found that the movers can be independently driven.

Comparison and analysis of permanent magnet vernier motors for low‐noise in‐wheel motor application

In this study, the permanent magnet vernier motors (PMVMs) with different external rotor topologies are investigated and compared to obtain the optimal topology, which can reduce the vibroacoustic noise and keep the excellent output performance. Firstly, the unipolar and bipolar PMVM motors with V-shape magnets are designed based on the torque and cost of the consequent-pole PMVM (CPMVM), which have the reduced unbalanced magnetic force (UMF). Then to evaluate the performances of PMVMs comprehensively, the characteristics including flux density, back-electromotive force, torque, the electromagnetic force and acoustic noise etc., are quantitatively investigated and compared by the finite element analysis (FEA). Finally, the modal parameters and acoustics noise spectrum of CPMVM are tested and compared with the noise FEA results, which verify the V-shape magnet PMVMs can reduce the UMF and low-frequency noise level by maintaining the output performance.

Performance Evaluation of Vernier Motor with a Consequent Pole Rotor

Performance Evaluation of Vernier Motor with a Consequent Pole Rotor

Power factor improvement of permanent‐magnet linear vernier motor by using dual‐inverter with hybrid discontinuous PWM

A permanent-magnet linear vernier (PMLV) motor has the advantages of large force and low cost, but it suffers from a low-power factor. This study proposes an instantaneous power control algorithm by using a dual-inverter open-winding (OW) configuration to equivalently improve the PMLV motor power factor. In the proposed algorithm, the active and reactive powers for the motor operation are supplied by the main and compensation inverters, respectively. Therefore, the main inverter dc-link voltage is fully utilised to generate the active power, which is equivalent to the improvement of the motor power factor. Furthermore, a hybrid discontinuous pulse width modulation (HDPWM) scheme is proposed, which takes into consideration the power factor characteristics of the dual-inverter. Compared to the existing OW modulation ones, the proposed HDPWM technique can greatly reduce the dual-inverter loss. The experimental results are carried out to verify the proposed control strategy.

Calculation of PM Vernier Motors Using an Improved Air-Gap Permeance Function

This paper proposes a more convenient and more accurate air-gap permeance function for the calculation of the air-gap flux density of flux modulation machines with permanent magnets (PMs). First, we review the previous air-gap permeance obtained from the approximated linear model and explain the problem that the accuracy of calculation becomes worse as the magnet thickness becomes larger. To solve this problem, we introduce an equivalent model that reflects the actual cylindrical structure of the machine with slots and, then, derives the air-gap function that is easy to be converted into the Fourier series, and finally propose the new air-gap permeance function. Using the proposed permeance function, the working harmonic components in the air-gap flux density of the surface magnet vernier motor are easily predicted, and then additional characteristics as well as flux density are compared with the finite-element simulation results to check the validity of the proposed method.

Design of Vernier Motor Considering PM Irreversible Demagnetization for Abnormal Operating Condition

This study investigates the design of a flux modulation pole (FMP)-type vernier motor considering irreversible demagnetization in a permanent magnet (PM). The FMP-type vernier motor, which has a distinct configuration compared to the conventional vernier motor, is taken into account because the PM placed at its stator is vulnerable to irreversible demagnetization. The demagnetization ratio of the PM is analyzed and compared using two different types of flux barrier, namely the bar- and delta-type barriers with varying design parameters. To guarantee reliability of the motor performance, both normal and abnormal operating conditions are considered for each type of flux barrier. Finally, selected models are compared to the base FMP-type vernier motor model in terms of demagnetization ratio and output torque.

Analytical investigation of air-gap flux density distribution of a PM vernier motor

Analytical investigation of air-gap flux density distribution of a PM vernier motor

Sensorless Control of a Linear Permanent-Magnet Motor Based on an Improved Disturbance Observer

Linear permanent-magnet (PM) motors incorporate the merits of high efficiency, simple mechanism, and low cost, which have a bright future in urban rail transit. However, the position sensor costs are huge, which is the main barrier against a wider implementation. In this paper, a type of modified disturbance observer is newly proposed to improve the precision. Two disturbance observers are utilized to estimate the back electromotive force. Then, position information is detected by a phase-locked loop. Finally, the linear PM motor runs with the feedback of estimated position and speed instead of position encoder measuring. The algorithm avoids designing filters and injecting signals. Experimental results based on a linear primary PM vernier motor demonstrate the accuracy and dynamic performance. The comparisons in the aspect of the robustness to measurement errors certify that the modified disturbance observer is superior to the conventional disturbance observer.

A V-Shaped PM Vernier Motor With Enhanced Flux-Modulated Effect and Low Torque Ripple

This paper proposes a new V-shaped permanent magnet vernier (V-PMV) motor for potential applications in direct-drive system. By utilizing the V-shaped PM topology and suitable pole–slot ratio, not only the flux leakage can be reduced effectively which is inevitable in traditional surface-mounted and spoke-type vernier permanent magnet (VPM) motor, but also the utilization of air-gap magnetic field harmonics can be improved. Moreover, dummy slots are employed on the inner edge of rotor, so that the torque ripple can be reduced. To fairly estimate electromagnetic performances of the proposed V-PMV motor, an existing flux-concentrating VPM motor is selected purposely and designed with the same size for comparative analysis by using the finite-element method. The simulation results indicate that the V-PMV motor can offer the advantages of high PM utilization, and low cogging torque and torque ripple.

Unity Power Factor Fault-Tolerant Control of Linear Permanent-Magnet Vernier Motor Fed by a Floating Bridge Multilevel Inverter With Switch Fault

The characteristics in power factor and reliability of the linear permanent-magnet vernier (LPMV) motor determine the applications. In order to ensure its continued operation, a novel fault-tolerant scheme is proposed for the breakdown of one certain bridge arm based on a floating capacitor bridge dual-inverter structure driving an open-winding LPMV motor. The dual-inverter structure consists of two voltage source inverters. Namely, one is connected to a dc power named as main inverter, and the other is linked to a floating capacitor called capacitor inverter. In order to solve the voltage limit problem, a unity power factor strategy is developed in this fault-tolerant control, in which the main inverter is just in charge of active component, and all of the reactive power is compensated by capacitor inverter. Simulated and experimental results validate the proposed control strategy.

Design and Analysis of a Novel Modular-Stator Tubular Permanent-Magnet Vernier Motor

This paper proposes a new modular-stator tubular permanent-magnet (PM) Vernier motor. The proposed motor offers a good fault-tolerant capability and an improved force performance, suitable for the electromagnetic active vehicle suspension. The proposed motor artfully integrates PM Vernier motors and tubular motors together, offering a zero-net radial force between the armature and mover, and the robust mover structure and high thrust force. Meanwhile, the modular complementary stator structure is designed to decouple the adjacent phase windings, hence offering the desired fault-tolerant capability. Moreover, the PMs with two magnetized directions are adopted, namely radially and axially. One is used to produce the main flux, while another can reduce fringing leakage flux, hence increasing the thrust force. The electromagnetic performances are analyzed by using the finite-element method, verifying the effectiveness of the theoretical analysis.

A Superconducting Vernier Motor for Electric Ship Propulsion

A megawatts (MW)-class direct-drive vernier motor for electric ship propulsion is proposed in this paper. The proposed vernier motor adopts the homopolar structure and utilizes the high-temperature superconducting wire for electrical excitation. The stator houses the superconducting field winding and the copper armature winding. The rotor consists of an iron core without excitation sources. Thus, no cryo-moving components are required. A dual-body Dewar for cooling the pancake high-temperature superconducting field winding is proposed. The motor performance is analyzed and evaluated using three-dimensional finite-element analysis. Both the brushless ac and brushless dc operation modes for the proposed motor are assessed and compared.

Study of Relationship Magnetic Poles and Motor Winding Poles of PM Type Bearingless Vernier Motor

Study of Relationship Magnetic Poles and Motor Winding Poles of PM Type Bearingless Vernier Motor

A Concept of General Flux-Modulated Electric Machines Based on a Unified Theory and Its Application to Developing a Novel Doubly-Fed Dual-Stator Motor

A concept of general flux-modulated electric machines is introduced in this paper, which is based on a proposed unified theory for such types of machines. It can explain the operating principles of a basic flux-modulated motor, a flux-switching motor, a vernier motor, and a dual-permanent-magnet (PM)-excited motor with PMs on both rotor and stator. Based on the proposed theory, a novel doubly-fed dual-stator (DFDS) motor is presented. Finite-element method of magnetic field with mechanical motion coupled computation is employed to evaluate the performances of the machines. Its design method using an optimization algorithm is also presented. Experiment results of a prototype are presented to showcase the performance of the proposed novel DFDS motor.

Design of a PM Vernier Machine with Consideration for Modulation Flux and Comparison with Conventional PM motors

This study deals with the core design of a PM vernier machine considering modulation flux effects, and the comparative investigation on volume and performance characteristics of the vernier over conventional PM machines are addressed. To these ends, for a PM vernier machine in operation at the base-speed, the flux density equations for teeth and yokes considering the flux modulation effects are derived, where the air gap harmonic permeance function is used. Using the derived equations, a PM vernier motor with specified yoke flux densities is designed. To identify the predicted flux yoke densities, the flux distribution and iron losses in core parts are analyzed through time-step finite element (FE) simulations. Through Fourier series expansion of the air gap flux waves obtained by FE analysis at several specified times, the harmonic components constituting the flux waves are investigated and their speeds are also evaluated in numerical ways. Finally, to estimate the competitiveness of vernier machines versus conventional machines, the designed PM vernier motor is compared against two different conventional PM motors designed through the same design procedures in various aspects such as volume, torque capacity, efficiency, and power factor, in which, in particular, the core losses are included in efficiency calculation.

Characteristic Analysis of Surface Permanent-Magnet Vernier Motor According to Pole Ratio and Winding Pole Number

This paper aims to analyze the characteristics of a surface permanent-magnet Vernier motor (SPMVM) according to the pole ratio among the rotor magnet pole pairs, stator teeth, and winding pole number. The SPMVM has the same operational principle as a magnetic gear, and it is operated using the space harmonics of the air-gap flux density due to the magnetomotive force and air-gap permeance. In this paper, first, the design parameters of the SPMVM are specified based on an analytical calculation of the air-gap magnetic flux density. Moreover, various combinations of the rotor magnet pole pairs and stator teeth number are made and compared according to the operational principle of a Vernier motor using a 2-D finite-element method.