Flux-modulated Permanent Magnet Research Articles

Electromagnetic Characteristics of a Flux-Modulated Permanent Magnet Linear Machine With Sandwich Armature for Free-Piston Energy Converter System

The linear machine is the key part of free-piston energy converter system, and its electromagnetic characteristics directly determine system performance. This paper proposes a novel flux-modulated permanent magnet (PM) linear machine with sandwich armature for free-piston energy converter system. The sandwich armature is composed of modulated layer, air-core winding layer and iron core. It integrates electromagnetic advantages of a flux-modulated and slotless machine, so it can achieve good comprehensive performance by appropriate design of sandwich armature. Firstly, an accurate subdomain model is established to analyze magnetic field characteristics of proposed machine, and then the suitable pole/slot combinations are determined. Subsequently, machine performance such as thrust force and efficiency are discussed based on design dimensional constraints. Finally, structural optimization of cylinder armature is developed for eddy-current loss suppression, and then experiments on prototype are carried out. The performance comparisons with flux-modulated and slotless machines show that the proposed prototype has high peak thrust, small electromechanical time constant, and strong design flexibility. Hence it is a preferred solution for free-piston energy converter system.

Indirect Method to Measure of Initial Mover Position in Flux-Modulated Linear Actuator for Five-Axis Gantry Robot Using Low-Cost Current Sensors and Considering End Effect

An initial mover position (IMP) detection algorithm for a dual-saliency flux-modulated permanent magnet linear synchronous motor (DS FM-PMLSM) for a five-axis gantry robot has been proposed in this proposed work. The proposed IMP algorithm uses the saliency of the proposed machine, which results in the inductance variation and checks the change in the inductance by providing sequential current profiles. The effect of the end region at the entry and exit are included to check the robustness of the proposed IMP. A design platform using MATLAB and Altair-Flux has been developed to simulate the proposed IMP algorithm for different positions of the mover. Based on the simulation model, a test setup is developed using a low-cost sensor and six-step inverter and tested the validity of the proposed IMP algorithm for the DS FM-PMLSM.

Analysis and Design of Novel Axial Field Flux-Modulation Permanent Magnet Machines for Direct Drive Application

Axial field flux-modulation permanent magnet (AF-FMPM) machines have been developed for direct drive applications such as wind power generation, HEVs, and railway traction. However, the existing studies on AF-FMPM machines are limited to the PM rotor structure, and less research has been carried out on AF-FMPM machines with PM stator structure. This paper studies two axial field flux-modulation permanent magnet (AF-FMPM) machines, i.e., NS or NN type, which all consist of the same stator and rotor structures but the dual identical outer surface-mounted PM stators face each other in different position. A comprehensive theoretical analysis and global optimization of the AF-FMPM machine based on ANSYS Maxwell 3-D FEA is presented. The performance comparisons between the AF-FMPM machine (NS) and AF-FMPM machine (NN) are presented, including the influence of the critical structural dimensions on the machine performance, phase flux linkage, phase back EMF, cogging torque, and average torque performance. The results show that the phase back EMF and average torque of the AF-FMPM machine (NS) are more sinusoidal and higher than that of the AF-FMPM machine (NN). Furthermore, the NS type machine shows the non-saliency characteristics, while the NN type machine is the salient machine.

Comparative Analysis of Double Flux Modulation Permanent Magnet Machines With Different Stator PM Arrangements

In this article, two double flux modulation permanent-magnet machines (DFMPMs) with PMs on both stator and rotor are introduced. The two DFMPMs share a similar operation principle. However, due to the different stator-PM arrangements, the two DFMPMs show different performances. In order to analyze their performance characteristics, their analytical models are built and verified by finite element analysis (FEA). Moreover, to quantitatively compare their electromagnetic performances more accurately, the two DFMPM topologies are optimized, respectively, and compared in terms of back-EMF, cogging torque,rated torque, torque ripple, power factor, and efficiency. Finally, the DFMPM topology with relatively better performances is built and tested. The experimental results match well with the FEA simulations.

Research on Power Factor Characteristic for a Flux-Modulated Permanent Magnet Motor From Perspective of Magnetic Source Topologies Effect

In this paper, the power factor (PF) characteristic for a flux-modulated permanent magnet (FMPM) motor has been analyzed and investigated. To obtain high PF FMPM motor, the magnetic source topologies effect is analyzed based on flux-modulated principle. Firstly, the PF calculation method of the FMPM motor is derived, and some key parameters affecting the PF are analyzed theoretically. Secondly, compared and analyzed the PF from perspective of magnetic source topologies (MSTs) effect, the initial model is determined. And some key parameters are designed and the FMPM performances are evaluated. Finally, research results show that a FMPM motor with surface-embedded PM topology and 18-slot 28-pole has high PF and torque capacity. Moreover, this paper provides guidance for the same design to gain high PF from perspective of magnetic source topologies effect.

Design Optimization of a HTS-Modulated PM Wind Generator

The flux-modulated machine based on air-gap magnetic flux modulation theory has become a focus in low speed and high torque density applications. In this paper, the optimal design of a large scale flux modulation (FM) permanent magnet (PM) generator with high temperature superconducting (HTS) bucks for wind energy conversion systems is presented. Firstly, the working performances of the generator with and without HTS bucks sandwiched between iron segments are analyzed and compared through finite element analyses (FEA). The FM effect enhancement by employing the HTS bucks is proved through the comparisons. Secondly, the sensitivities of the generator structural parameters on the back electromotive force (EMF) and the cogging torque amplitude are analyzed by Taguchi method to decide the optimization variables and their variation ranges. Thirdly, the structural parameters determined by the sensitivity analyses are optimized through the coupling of genetic algorithm (GA) and FEA to maximum the generator output power capacity. The calculation burden during optimization is reduced with a reduction on the optimization variable number through the Taguchi method based sensitivity analyses. Finally, the electromagnetic characteristics of the FMPM generator with optimized structural sizes are numerically investigated.

Design and analysis of different cooling schemes of a flux‐modulated permanent magnet in‐wheel motor for electric vehicle applications

The flux-modulated permanent magnet (FMPM) in-wheel motor has provided a promising solution to drive electric vehicles (EVs) because of its salient features such as tight structure, high power (torque) density, and high transmission efficiency. But it easily causes excessive temperature rise and limits the torque output due to the poor heat dissipation capacity inside the in-wheel cavity. In this regard, a 3D fluidic-thermal coupled model integrating computational fluid dynamics and numerical heat transfer is proposed and validated by experimental results on a 2.1 kW, 1800 rpm PM motor prototype. The temperature rise distribution of a 22.6 kW, 600 rpm FMPM in-wheel motor under an existing natural cooling structure is then numerically investigated. It is revealed that it is difficult to satisfy the thermal requirements of the motor using only natural cooling approach. Consequently, a self-ventilated cooling system and a non-contact lead-in (NCLI) system are used to maintain the temperature rise. In addition, to further improve the heat dissipation capacity, the NCLI structure is modified with water cooling channels separated by orifice plates to limit the excessive motor temperature rise. The motor temperature rises under different cooling schemes are analyzed to verify the effectiveness of the proposed cooling structures.

Flux-Modulated Permanent Magnet Machines: Challenges and Opportunities

High torque density is a desirable feature of electrical machines used in traction applications, such as electric vehicle (EV)/hybrid electric vehicle (HEV) propulsion, wind turbines, more electric aircrafts, etc. The flux-modulated permanent magnet (FMPM) machine is considered as one of the most promising candidates to achieve high torque density. The incorporated gearing effect is ideal in reducing the rotating speed and amplifying the output torque of the FMPM machines. This paper aims at a comprehensive review of the topology evolution of the FMPM machines. Based on different structures, the FMPM machines are grouped into four categories: surface-type FMPM machines, spoke-type FMPM machines, partitioned stator FMPM machines, and bidirectional FMPM machines. The operating principles, advantages, drawbacks, and major applications of the FMPM machines are discussed in detail. In the end, the current state of the art, opportunities, challenges, and future trends of the FMPM machines are discussed. Therefore, this paper offers a systematic guidance on the selection and design of the FMPM machines.

Airgap-Harmonic-Based Multilevel Design and Optimization of a Double-Stator Flux-Modulated Permanent-Magnet Motor

In this article, based on flux modulation theory, an airgap-harmonic-based multilevel optimization design approach is proposed for a double-stator flux-modulated permanent-magnet (DS-FMPM) motor. The proposed DS-FMPM motor is purposefully designed, so as to realize the design requirements of driving cycle. In the proposed optimization approach, based on three fundamental elements of general flux modulation theory, motor optimization design is carried out from three levels. Furthermore, a response surface method, sensitivity analysis, and a genetic algorithm are purposely employed in different levels to obtain optimal motor design. In addition, electromagnetic performances of a DS-FMPM motor are demonstrated in detail. Finally, a prototype motor is manufactured and tested. Both simulation and experimental results verify the feasibility of the DS-FMPM motor and the effectiveness of the proposed airgap-harmonic-based multilevel optimization design approach.

Design and Analysis of a Multi-Flux-Modulated Permanent Magnet Motor

In this paper, a new multiple flux-modulated permanent magnet (M-FMPM) motor is proposed, where three flux modulations and two modulation forms are implemented to enhance the torque density. Firstly, a new topology of the motor and the corresponding multi-flux-modulation theory are presented. And thus the flux modulation forms can be enriched and the torque performance can also be further effectively improved. Then, according to the proposed geometric model, the shape of PM is artfully designed to obtain the desirable torque performance. Based on the finite element method (FEM), the magnetic distributions, airgap harmonic group are analyzed, and torque capability are compared between the forms of multi-flux-modulation (MFM) and single-flux-modulation (SFM). Finally, both the theoretical analysis and finite element analysis results verify the effectiveness of the proposed multi-flux-modulation theory and the M-FMPM motor.

Design and Optimization of a Flux-Modulated Permanent Magnet Motor Based on an Airgap-Harmonic-Orientated Design Methodology

In this article, an airgap-harmonic-orientated design method is proposed, where the airgap harmonics are newly acted as the effective bridge between the three key elements of permanent magnet sources, modulators, or armature windings and the motor performances. In the proposed design method, the airgap harmonics play couple roles of design objectives and variables, which are not only served as the design variables for the motor performances, but also considered as the objectives for design parameters. For extensive investigation, a V-shape flux-modulated permanent-magnet (V-FMPM) motor is selected as a design example, which has a potential application for the electrical vehicles. In the optimization process, the sensitivity analysis of different airgap harmonics on the torque performance is conducted to select the leading airgap harmonics. Meanwhile, the sensitivity degrees of the design parameters on the leading harmonics are calculated to pick out the sensitive design parameters. Then, the performances of the V-FMPM motor are evaluated for validating airgap-harmonic-orientated design method. Finally, a prototype motor is built and tested. Both the theoretical analysis and experimental results verify the effectiveness and reasonability of the proposed design method and the V-FMPM motor.

Design and Analysis of Double-Air-Gap Flux-Modulated Permanent Magnet Motor Considering Leading Working Harmonics

In nature, to flux-modulated permanent magnet (FMPM) motors, the electromagnetic energy transmission is realized by abundant harmonics in the air-gap field. It means that, under the flux modulation effect, the harmonics in FMPM motors play an important role for motor performances. In this paper, by incorporating the concept of harmonics design into motor design process, a double-air-gap FMPM motor considering leading working harmonics is proposed and studied for potential applications of electric vehicles or electric tractors. First, the leading working harmonics are distinguished and chosen conveniently by evaluating the contributions of diverse harmonics to PM flux linkage. Then, a correlation design between the harmonic characteristics and geometric parameters is implemented based on the selected leading harmonics. In addition, the motor performances are evaluated by using the finite-element method, consisting of the air-gap harmonic analysis, no-load back-electromotive force, and torque performances. Finally, the theoretical analysis and computational results verify the effectiveness of the proposed motor.

Improvement of Power Factor in a Double-Side Linear Flux-Modulation Permanent-Magnet Motor for Long Stroke Applications

Cost-effective and high-performance linear motors attract more and more attention for many applications. This paper proposes a novel double-side linear flux-modulation permanent-magnet (DS-LFMPM) motor with low cost, high thrust force density, and high power factor. The novelty of the proposed DS-LFMPM motor is to improve power factor by using double-side topology. Its topology is presented, and its operation principle is investigated. From the harmonic spectrums of the flux density in the air gap before and after the modulation of the mover teeth and the stator teeth, it can be concluded that the proposed motor has good flux-modulation effect. Also, the expression of the orders of the harmonic spectrums is given. The design process of sizes and structure is particularly explained. The electromagnetic performances are predicted by using the finite-element method and the proposed motor is prototyped for verification. The results show that the proposed DS-LFMPM motor can produce high thrust force density and high power factor.

A Quantitative Comparison Analysis of Flux Modulation Permanent Magnet Machines with Four Topologies

This paper presents flux modulation permanent magnet machines with four topologies, which have incorporated the magnetic gear structure and a stator within one machine. Four types of flux modulation permanent magnet machines are compared quantitatively. According to the location of the four structures, the four proposed machines are referred as motor I, motor II, motor III, and motor IV. This paper focuses on the performance comparative analysis of the four proposed machines by using finite element method (FEM). The output electromagnetic torque, induced voltage, cogging torque and efficiency of the four proposed machines have been investigated.

A Novel Dual-Rotor Bidirectional Flux-Modulation PM Generator for Stand-Alone DC Power Supply

A novel bidirectional flux-modulation permanent magnet (BFMPM) machine for stand-alone dc wind power generation is proposed in this paper. The key is to control the inner rotor position with a small servo motor, and with the bidirectional flux-modulation effect, the resultant induced voltages in two sets of stator windings can be adjusted accordingly. Consequently, in a wide wind speed range, the various-speed constant-amplitude-voltage operation is realized. The novel structure has two major merits. First, it has high reliability without the maintenance problems caused by mechanical gearboxes, slip ring assembly, and brushes. Second, the proposed system requires a low-cost uncontrolled diode rectifier, which enhances the reliability and reduces the cost of the system. The analytical model and operation principle of the BFMPM machine are illustrated and the simulation results using a finite-element method is presented. A prototype is optimized and fabricated. The experimental results agree well with the simulation results and verify the correctness of the analytical model and the effectiveness of the proposed structure. Therefore, the novel structure offers a potential solution to provide a stable dc power for the standalone condition, such as remote area and offshore island.

Speed Regulation System of a Flux-Modulated Permanent-Magnet In-Wheel Motor Based on Sliding Mode Control and Adaptive Notch Filter

This paper presents a new nonlinear algorithm of speed regulation system for a flux-modulated permanent magnet in-wheel (FMPMW) motor. To improve the robustness and static performance of speed regulation system, sliding mode control with a sigmoid function is adopted. Compared with PI controller, the proposed algorithm can improve the robustness and minimize the torque ripple of the system. In addition, an adaptive notch filter is proposed to restrain the fifth and seventh current harmonics, which the static performance of control system can be further improved. Based on a 2-kW FMPMW prototype motor, the simulation and experimental results verify the good robustness and static performance of the proposed algorithm.

A Novel Double Stator Flux Modulation Machine With Low-Temperature Superconducting Windings

Flux modulation permanent magnet machines (FMPMMs) exhibit many superiorities over regular permanent magnet machines (PMMs), such as simple and robust configuration, high torque density, and efficiency; thus they are promising candidates for the motors in wind turbine powertrains, electric vehicles, and ship propulsion systems. However, since the PM flux linkage is almost constant, the flux-weakening capability of FMPMMs is usually inferior to that of the wound field machines (WFMs). Moreover, the power factors of FMPMMs are also lower. In order to incorporate the merits of FMPMMs and WFMs, this paper proposes a double-stator flux modulation machine with low-temperature superconducting field windings, which can exhibit higher torque density, stronger flux weakening capability, and larger power factor than the conventional FMPMMs. The configurations and working mechanism of the proposed machine are introduced, and its key performances are comparatively analyzed to a regular FMPMM based on a finite-element algorithm.

Design of a novel dual flux modulation machine with consequent-pole spoke-array permanent magnets in both stator and rotor

In this paper, a novel dual flux modulation (DFM) machine with consequent-pole spoke-array permanent magnets (PMs) in both stator and rotor is proposed to achieve a larger torque density than regular flux modulation machines. The stator has two portions of PMs, one is set next to the stator slot with circumferential magnetization, and the other is inserted between the stator yoke and flux bridge with radial magnetization. The rotor has consequent-pole spoke-array PMs and alternative flux bridges. The proposed DFMPM machine can be regarded as the combination of the flux switching PM (FSPM) machine and vernier PM (VPM) machine. First, the structure and operational principle are introduced. Then, the proposed 12-stator-slot/10-rotor-tooth dual flux modulation permanent magnet (DFMPM) machine is compared with the FSPM machine and VPM machine in terms of flux lines distribution, back-electromotive force (EMF), cogging torque and average torque. Finally, the four proposed DFMPM machines are optimized for maximum average torque and minimum ripple torque considering the effects of split ratio, slot opening ratio, PM depth, PM angle and iron angle.

A Novel Contra-Rotating Power Split Transmission System for Wind Power Generation and Its Dual MPPT Control Strategy

This paper proposes a new brushless contra-rotating power split transmission (CR-PST) system for the direct-drive wind power generation. The core element of this system is a doubly fed dual-rotor flux-modulation permanent magnet machine, which has two contra-rotating rotors connected with two wind blades to absorb the wind energy, and two sets of stator windings to realize torque split between the two shafts. This proposed CR-PST system has compact structure and bidirectional flux-modulation design, as well as increased wind power conversion efficiency. Compared with the conventional wind turbine system, which can only work with single maximum power point tracking (MPPT) control strategy, the proposed CR-PST system can collect increased wind energy with dual MPPT method for the given wind speed. Time-stepping finite-element method is used to analyze the steady and dynamic performance of the proposed system and the control strategy is verified by experiments and simulation results.

Performance Comparison of Surface and Spoke-Type Flux-Modulation Machines With Different Pole Ratios

In this paper, performance comparison between surface and spoke-type flux modulation (FM) permanent magnet (PM) machines is presented. Generally, spoke-array magnet arrangement is capable of increasing the torque density of PM machines due to its flux-focusing effect. Nevertheless, a flux-barrier effect is found when this magnet topology is applied in FM machines, which may offset the advantage in torque capability when the pole ratio is high. By flux distribution comparison of these two-machine topologies, the flux-barrier effect is visually explained. Through numerical FEA, this effect is further investigated in spoke-type vernier PM machines with a series of pole ratios. Finally, compared with surface-type FM machines, considerable reduction in modulated magnetic field as well as output torque capability is verified in high pole ratio, spoke-type FM machines.