United States

I.Introduction&lt;br/&gt;Direct drive wave energy conversion (DDWEC) has attracted wide attention [1]. Various ways have been employed to further reduce the cost of wave energy conversion and promote the commercialization process, including the application of permanent magnets (PMs).&lt;br/&gt;PM generator has better electromagnetic performance for its high energy density [2,3]. The configuration of DDWEC proposed in this paper is combining the axial flux generator (AFG) and magnetic lead screw (MLS).&lt;br/&gt;However, the extensive use of PM will increase the manufacturing cost. For reducing the PM cost in DDWEC, a modified consequent-pole PM AFG (CPM-AFG) is proposed in this paper. By changing one side of PMs into iron-cores, which is called iron-pole, the volume of PM can be reduced.&lt;br/&gt;&lt;br/&gt;II.Generator Topology&lt;br/&gt;The whole configuration of the DDWEC system is that AFG located inside of the MLS is connected softly to the buoy when the screw and nut of MLS is connected directly to the buoy and rotor, respectively, as is shown in Fig. 1. Through MLS, the linear reciprocating motion of the wave can be transformed into the rotational motion of nut. When the buoy moves up and down, the rotor composed of modulation teeth in AFG rotate to generate energy. The rotor&#39;s angular velocity can be expressed as:&lt;br/&gt;&lt;i&gt;ω&lt;/i&gt;=&lt;i&gt;Gv=&lt;/i&gt;π&lt;i&gt;v&lt;/i&gt;/&lt;i&gt;τ&lt;/i&gt;&lt;br/&gt;where &lt;i&gt;G &lt;/i&gt;is defined as gear ratio of MLS, &lt;i&gt;v&lt;/i&gt; is screw&#39;s linear velocity and &lt;i&gt;τ&lt;/i&gt; is the pole width of MLS.&lt;br/&gt;Similar to magnetic gear, the pole pairs of armature windings &lt;i&gt;p&lt;/i&gt;&lt;sub&gt;aw&lt;/sub&gt;, the pole pairs of PM &lt;i&gt;p&lt;/i&gt;&lt;sub&gt;PM&lt;/sub&gt; and the iron pieces of rotor &lt;i&gt;N&lt;/i&gt;&lt;sub&gt;i&lt;/sub&gt; should satisfy:&lt;br/&gt;&lt;i&gt;N&lt;/i&gt;&lt;sub&gt;i&lt;/sub&gt;= &lt;i&gt;p&lt;/i&gt;&lt;sub&gt;aw&lt;/sub&gt; + &lt;i&gt;p&lt;/i&gt;&lt;sub&gt;PM&lt;/sub&gt;&lt;br/&gt;Fig. 1&lt;br/&gt;&lt;br/&gt;III.Results&lt;br/&gt;The simulation result shown in Fig. 2 indicates that although the volume of PM in the CPM-AFG is reduced by half, the flux linkage and torque are not reduced to half compared with the conventional surface-mounted PM axial flux generator (SPM-AFG). The amplitudes of SPM-AFG and CPM-AFG are 0.14Wb and 0.11Wb, respectively. The average electromagnetic torques of them are 23.2 Nm and 19.1 Nm, respectively.&lt;br/&gt;Fig. 2&lt;br/&gt;&lt;br/&gt;IV.Conclusion&lt;br/&gt;Simulation results shown that the proposed CPM-AFG is suitable for DDWEC which can reduce the consumption of PM, reduce the cost of manufacture and improves the utilization ratio of PM.

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2022 Joint MMM-INTERMAG

Axial Flux Generator with Consequent-Pole PM Stator for Direct Drive Wave Energy Conversion

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

I.Introduction Direct drive wave energy conversion (DDWEC) has attracted wide attention [1]. Various ways have been employed to further reduce the cost of wave energy conversion and promote the commercialization process, including the application of permanent magnets (PMs). PM generator has better electromagnetic performance for its high energy density [2,3]. The configuration of DDWEC proposed in this paper is combining the axial flux generator (AFG) and magnetic lead screw (MLS). However, the extensive use of PM will increase the manufacturing cost. For reducing the PM cost in DDWEC, a modified consequent-pole PM AFG (CPM-AFG) is proposed in this paper. By changing one side of PMs into iron-cores, which is called iron-pole, the volume of PM can be reduced. II.Generator Topology The whole configuration of the DDWEC system is that AFG located inside of the MLS is connected softly to the buoy when the screw and nut of MLS is connected directly to the buoy and rotor, respectively, as is shown in Fig. 1. Through MLS, the linear reciprocating motion of the wave can be transformed into the rotational motion of nut. When the buoy moves up and down, the rotor composed of modulation teeth in AFG rotate to generate energy. The rotor's angular velocity can be expressed as: ω=Gv=πv/τ where G is defined as gear ratio of MLS, v is screw's linear velocity and τ is the pole width of MLS. Similar to magnetic gear, the pole pairs of armature windings paw, the pole pairs of PM pPM and the iron pieces of rotor Ni should satisfy: Ni= paw + pPM Fig. 1 III.Results The simulation result shown in Fig. 2 indicates that although the volume of PM in the CPM-AFG is reduced by half, the flux linkage and torque are not reduced to half compared with the conventional surface-mounted PM axial flux generator (SPM-AFG). The amplitudes of SPM-AFG and CPM-AFG are 0.14Wb and 0.11Wb, respectively. The average electromagnetic torques of them are 23.2 Nm and 19.1 Nm, respectively. Fig. 2 IV.Conclusion Simulation results shown that the proposed CPM-AFG is suitable for DDWEC which can reduce the consumption of PM, reduce the cost of manufacture and improves the utilization ratio of PM.

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poster

1.Introduction Magnetorheological fluid (MRF) is a material whose viscous and plastic rheological property can be changed sharply under an external magnetic field [1]. The brake based on MRF characteristics has the advantages of simple structure, fast response and convenient control compared with traditional brakes [2-3]. However, the current studies on MRF brake mostly use an independent structure [4-5] connecting in series with motor to form joint module,which has the defect of large axial length. It greatly limits the space of joint modules. In this paper, an axial flux permanent magnet motor (AFPMM) with MRF brake structure is proposed to obtain the small axial size and fast braking response. 2.Machine topology Fig.1(a) shows the top view of an AFPMM with MRF brake structure (no rotating seal cap for easy viewing), which has two working modes: rotation and brake mode. Fig.1(b) shows the front cutaway view of the proposed machine. Fig.1(c) shows 2D radial flux circuit of MRF brake structure. When the MRF is magnetized and thus the viscous force of MRF is rapidly increased, the large shear stress is produced to brake the AFPMM. 3.FE analysis In this paper, the speed and the maximum current density of the AFPMM are set to 1200 r/min and 8A/mm2 respectively. Fig.2(a) shows the variation of motor torque under different axial excitation currents. Fig.2(b) shows radial component distribution of magnetic flux density in MRF along axial direction under two working modes. It can be found that the axial flux in rotation mode does not magnetize the MRF to produce brake torque. Based on Bingham model, the brake torque formula of MRF is shown in Fig.2(c). Fig.2(d) shows the variation of MRF brake torque under different radial excitation currents. It can be seen that the brake torque under the brake mode is enough to get an effective braking.

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An Axial Flux Permanent Magnet Motor with Magnetorheological Fluid Brake Structure

An Axial Flux Permanent Magnet Motor with Magnetorheological Fluid Brake Structure

The dual three-phase permanent magnet synchronous motors (DTP-PMSMs) possess two sets of three-phase winding exhibiting the high capability in fault-tolerant operations [1]. The open-phase fault is one typical fault and various research has been conducted on open-phase fault modeling and control of the DTP-PMSMs [2], [3]. Recently, a dynamic fault modeling and control for six-phase PMSMs based on multireference frame has been proposed [4]. In this paper, other than using the multireference frame, the fault modeling is based on the existing vector space decomposition (VSD) for DTP-PMSMs, and the open-phase fault is regarded as a combination of positive and negative sequence components. Therefore, the number of current regulators is reduced and dynamic performance is improved. By using VSD, currents of the dual three-phase winding are projected into three orthogonal subspaces, namely αβ plane (torque-producing plane) and xy plane (non–torque–producing plane).Fig. 1(b) shows the current waveforms under open-phase fault, which can be represented by positive sequence currents (healthy operation) and negative sequence currents. The positive sequence currents are projected to αβ plane and the negative sequence currents are projected to xy plane. As shown in Fig. 2(a), in the αβ plane, the projected faulty currents are the dc currents as the projected positive sequence currents, and while in the xy plane, the projected faulty currents are the ac currents with the same dc components as the projected negative sequence currents. Since the torque only generated in the αβ plane, the torque generated under open-phase fault is stable as that under healthy operation. Fig. 2(b) compares the torque waveforms under the proposed fault modeling in this paper and the modeling based on a multireference frame. Since the harmonic components can be suppressed using VSD, the torque ripple is about 10% lower by using the proposed method. The detailed modeling and experimental verification will be presented in the full paper.

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Fig. 1 (a) Vector space decomposition. (b) Dual three-phase current waveforms under open-phase fault.

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Fig. 2. (a) Current waveforms in different planes using VSD. (b) Torque waveforms comparison.

Open-phase fault modeling for dual three-phase PMSM using vector space decomposition and negative sequence components

Due to its excellent performances like high efficiency and high power factor[1], line-start permanent magnet (LSPM) machine is widely used in long-time operated applications, i.e., textile, pump, fan [1]. LSPM machine with squirrel cage doesn’t need inverter to start, thus it has advantages of lower cost and smaller volume[2]. However, The rotor of LSPM machine just combine one interior permanent magnet (IPM) rotor and one induction rotor together into a whole rotor, thus the two rotor would compete the limited space when designing the rotor. Also, the aluminum-bar induction winding in the rotor only works in starting process, and it will occupy the limited magnet path of the rotor, which would be the extra burden to the machine because aluminum has permeability similar as air. Hence, a novel steel-bar starting cage line-start permanent magnet machine is proposed to solve this paradox. Low carbon steel 1010[3] is selected as rotor cage material to allow magnet flux pass through at steady state. Steel 1010 has high permeability but lower conductivity compared with aluminum and copper, the proposed machine shown in Fig.1 shows that steel-bar rotor could still start easily without the help of inverter, and has better performance at steady state as is shown in Fig.2. The spoke type insulation layers of the steel-bar is meant to reduce the core loss, but simulation results show that the starting process is also shorten. Besides, the torque ripple at steady state is also lower with the help of insulation layers. A LSPM machine with aluminum-bar cage is also designed to compare in Fig.2. The steel-bar is of larger cross area because steel-bar doesn't occupy magnetic path, which is a main advantage of steel bar. However, steel-bar is like closed opening slot when induced current flows through, so the steel-bar should be saturated before it produces flux to airgap, which is why steel-bar rotor has lower starting torque. But for pump load which requires low torque at low speed, proposed machine shows dominant advantages.

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Fig.1 Proposed Steel-Bar Starting Cage Line-start PM Machine with Spoke Type Insulation Layers

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Fig.2 Torque and Torque Ripple vs Current Angle Curve of Proposed Machine and Traditional Aluminum-Bar Machine

Novel Steel-Bar Starting Cage Line-Start Permanent Magnet Machine with Spoke Type Insulation Layers

Abstract—This paper focuses on the force ripple minimization of consequent pole permanent magnet linear synchronous motor (CP-PMLSM). By using arc teeth without tooth shoe, CP-PMLSM is investigated in detail by extensive finite element analysis (FEA). With Taguchi parameters method, the geometry of end teeth and auxiliary teeth is optimized to reduce the force ripple, and the optimal combination of parameters can be obtained. the contrasting result between the initial and the optimized PMLSM shows that the force ripple is suppressed to a quite low value in all load conditions by the aforesaid procedure. Keywords—Force ripple, finite element analysis, consequent pole, permanent magnet linear synchronous motor (PMLSM). I. Introduction Recently, Permanent Magnet Synchronous Linear Motors (PMSLMs) have been widely used in industry applications owing to their outstanding performance. However, as the magnetic circuit is disconnected at the end of the primary core, the distorted magnetic field makes the motor high force ripple. The addition of the auxiliary teeth and teeth notching are employed to reduce the detent force[1]. The geometry of end-teeth is optimized to reduce the force ripple in all load conditions [2]. High-order harmonic components can be suppressed by the optimal skewed PM design, and a discrete-time linearization observer is utilized to compensate low-order harmonic ones [3]. In this paper, arc teeth without tooth shoe is optimized to reduce the force ripple by extensive finite element analysis (FEA). The dimensions of end teeth and auxiliary teeth is optimized by Taguchi method to obtain the optimal combination of parameters. The contrasting result shows that the force ripple is suppressed to a quite low value in all load conditions by the aforesaid procedure. II.Electromagnetic Performance Evaluation The simulation results of flux density, back-EMF, and electromagnetic torque are analyzed by the finite element analysis (FEA). The load flux distribution is shown in Fig. 2. The Comparison of force wave and back-EMF in no-load and load between the initial and the optimized is shown in Fig. 3. The back-EMF and electromagnetic torque with various excitation modes are shown in Fig. 3.


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Force Ripple Minimization Design for Consequent Pole Permanent Magnet Linear Synchronous Motor

I. INTRODUCTION Transverse flux permanent magnet (TFPM) machine owns the characteristics of large torque and high efficiency[1]. Many new TFPM structures such as double C-hoop stator and double Ω-hoop stator machines have been proposed[2][3]. Accordingly, the new structure of back-to-back Ω-type stator TFPMLM is proposed to improve the stator space utilization based on the above mentioned previous machines. Owning to the better utilized stator space and the mutual decoupled electrical and magnetic loads the machine achieves better performances on higher peak force and thrust-weight ratio which is suitable for the application of urban rail transit. II. STRUCTURE OF Back-to-back Ω STATOR TFPMLM The distinguishing feature of the proposed machine is that one pair stator hoops share the same winding to achieve more compact space utilization. Fig. 1(a) shows the schematic diagram of the fabricated prototype, which has pairs of back-to-back Ω-type stator hoops and a mover composited by cores and PMs. The stator hoops fixed in the non-ferromagnetic stationary pedestal and the mover cores and flux-concentrated PMs are screwed independently onto two non-ferromagnetic mover brackets. A linear guide rail contacts the stationary pedestal and the mover bracket. The sliding rail is lapped on head-end of the pedestal while the slide block is screwed onto the bracket. The armature winding binding each stator hoop pairs to form two half magnetic circuits twining round the stator hoops and the mover cores which are laminated by facile silicon-steel. III. FEM ANALYSIS AND TEST RESULT Fig. 1 (b) shows the 3D-FEM magnetic field distributions with maximum flux density of 0.7T. Fig. 2 (a) shows the flux density with optimum value as 0.6 around to achieve the best performance. The flux linkage and the measured back-EMF waveforms with amplitudes of 70mWb and 30V respectively at rated moving speed of 1.5m/s are shown in Fig. 2 (b). The positioning force is obtained and optimized also to verify the analyses and feasibility of the structure design. A prototype with 120N peak force is fabricated and some experiments are conducted.

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Fig. 1 The schematic diagram and the magnetic field distributions.

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Fig. 2 Flux linkage and measured back-EMF waveforms.

Back-to-back Ω Stator Transverse Flux Permanent Magnet Linear Machine

With the development of drive system, the linear-rotary (LR) actuators have been applied in robotics due to its multiple freedom degree characteristic [1]. Rare-earth permanent magnet (PM) materials, such as NdFeB, have high remanence density and coercivity, which can provide high energy density. Hence, the LR PM actuator has been widely used in the drive systems due to simple structure and small volume. In this paper, a LR PM actuator which involves linear, rotary and spiral motions is proposed for the application of multiple freedom degree robotics. The proposed actuator is composed of unique single stator with two sets of independent windings and consequent-pole staggered (CPS) PM mover, as shown in Fig. 1. The novelty is that one CPS PM mover is specially designed to generate radial and axial magnetic field, and to reduce PM consumption. Combined with it, two sets of independent orthogonal non-overlapping concentrated armature windings are employed to generate enough torque, thrust force and to achieve the decoupling operation of linear and rotary motions. The CPS mover is composed of several step-staggered parts. The magnetized direction of PMs in the adjacent step-staggered parts is opposite. The staggered degree of adjacent parts is π/Pr, where Pr is PMs pole pairs along the circumferential direction. Thus, the even-order harmonics of no-load back-electromotive force are eliminated by the CPS mover, which greatly reduce the torque ripple. To reduce the axial leakage flux, there is axial flux barrier between the step-staggered parts. Furthermore, the fault-tolerance (FT) teeth and armature teeth are alternately arranged on the stator to enhance FT performance. The electromagnetic performance of the proposed machine is predicted by finite-element method. Fig. 2 shows the output characteristic of proposed actuator. The average values of torque and thrust force are 6Nm and 158N, respectively. The torque ripple and thrust force ripple are 0.97% and 33%, respectively. More details and optimization will be discussed in the full paper.

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Fig. 1 Structure of proposed LR PM actuator.

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Fig. 2 Output characteristic of proposed LR PM actuator.

Design and Analysis of a Linear-Rotary PM Actuator with Consequent-Pole Staggered Mover

I. Introduction Single-phase permanent magnet linear oscillating actuators (SP-PMLOA) have widely used in the application field of short-stroke and high frequency linear reciprocating, because of simple mechanical structure, without the rotary-to-linear conversion, low maintenance costs and fast dynamic response. In the design of SP-PMLOA, the detent force was seldom paid attention by scholars. Due to the unique assembly structure and the operation mode of the LOA, the detent force, which changes linearly in the stroke, can be equivalent to a magnetic resistance spring, and its effect on the electromagnetic performance can be ignored. However, the consequence of ignoring the detent force is that the power density of the SP-PMLOA becomes very low or the axial length of the SP-PMLOA is increased. Therefore, the principle of end force generation is introduced, and a new method to reduce end force and alveolar force is proposed in this paper. II. Analyze the Detent Force Generally, the detent force is the superposition of end force and cogging force, both of which are caused by the interaction between the permanent magnets in the mover and the stator core. Therefore, according to the principle of cogging force and end force generation, when the cogging force gradually increases, end force gradually decreases. The cogging force and the end force can be offset by changing the position of the permanent magnet. III. Results Fig.1 shows the structure of the novel SP-PMLOA, which adopts double-sided stators and one active mover. Three permanent magnets are arranged on the non-magnetizing back iron. The thickness of the middle permanent magnet is larger than that of the permanent magnets on both sides, which can effectively reduce the detent force. The detent force comparison of three models is shown in Fig.3. as can be seen, the maximum detent force of the improved model is slightly greater than that of one PM model, but smaller than that of the traditional three PMs model. IV. Conclusion In this paper, the detent force generation principle of SP-PMLOA has been analyzed. it has been validated that the proposed model can effectively reduce detent force and the amount of PMs used.

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Electromagnetic Design of Single-Phase Permanent Magnet Linear Oscillation Actuator Considering Detent Force Minimum

Electromagnetic Design of Single-Phase Permanent Magnet Linear Oscillation Actuator Considering Detent Force Minimum

Abstract — The magnetic lead screw (MLS) is a new linear actuator with a high force density that enables contactless energy transfer. Improving the force density and reducing the installation error of the approximate helical type permanent magnets (PM) are the key challenges to realize the MLS. In this paper, based on the study of several existing PMs shapes and magnetization methods for MLS, a new MLS based on a combination of PM structures and magnetization directions is proposed. it not only reduces the mounting error by approaching the helical pole in a simpler way, but also increases the force density of the MLS. The results show that in addition to the air gap and the sizes of the PM having a significant effect on the force density, the effect of backiron saturation on it also needs to be considered. Finally, the performance of the proposed structure is compared with several existing structures and it is concluded that the force density is increased by nearly 60% for the same MLS volume and amount of PMs. Index Terms — MLS, magnetization direction, structure, PM, force density. The three common structures of MLS are shown in Fig. 1. (a) is the traditional model of radial magnetization for PMs, (b) is the halbach model of PMs with halbach magnetization, (c) is the salient model of radial magnetization for PMs. (d) is the proposed model, which adopts halbach magnetization, the salient pole shape adopts the radial magnetization, and the rectangular shape adopts the axial magnetization, and the salient pole PM can fix the rectangular PM, which is easy to install. The operation principle and others will be detailed in the full text. The structure proposed in this paper is shown in Fig. 1(d), and the detailed design process will be described in the full text. At present, there are two kinds of processing and installation structures to simulate helical PM as shown in Fig. 2: half skew ring and discrete. This paper also makes a comparison of these two PM structures, so that a PM structure with simple processing and installation and high force density are given. Finally, the comparison of these structures is detailed in the full text.

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Proposed model

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Performance comparison of four models

Design optimization and Analysis of a Novel High Force Density Magnetic Lead Screw with Discretized PMs and Different Magnetized Directions

I. INTRODUCTION In recent years, novel primary-excited PMLMs (PE-PMLMs) attract more and more attention with the merits of high thrust force density and low cost in long stroke application [1]. Different from the conventional PMLMs, PE-PMLMs integrate both the armature winding and PMs in the short primary, while the long secondary only consists of salient iron core [2]-[4]. The total cost can be greatly reduced thanks to this simple structure. However, PE-PMLMs still suffers from several key issues: 1) Severe saturation problem in the primary core. 2) Low overload capability due to the saturation problem. 3) Low mechanical reliability due to the influence of normal force on the primary. To solve these drawbacks in PE-PMLMs, this paper proposes a double-sided flux concentrated permanent magnet linear machines (DS-FCPMLMs) with saturation relieving effect. The utilized dual PMs in the primary yoke and slot opening can significantly improve the force density while relieving the saturation. II. TOPOLOGY AND PERFORMANCES Fig. 1(a) shows the topology of DS-FCPMLMs. Cross-shaped modular primary segments can be used to reduce the cost and enhance the extendibility of primary. Each primary module consists of one cross-shaped primary tooth and two coils. Then, PMs are employed in both the primary yoke and slot opening between two modules. The basic operation principle of this machine is shown in Fig. 1(b). The PM flux switches among four coils of the same phase at different secondary position. Hence, sinusoidal bipolar phase flux linkage can be obtained. Fig. 2 shows the electromagnetic performances of DS-FCPMLMs compared with DS-BFPMLMs that only has yoke PMs. Due to the flux concentrated effect, the back-EMF of DS-FCPMLMs can be enhanced by 48% compared with DS-BFPMLMs. Besides, DS-FCPMLMs can provide the average force of 338 N, which is increased by 52% compared with DS-BFPMLMs. Moreover, the magnetic saturation can be relieved in DS-FCPMLMs with the effect of slot PMs. Therefore, the proposed DS-FCPMLMs have the potential to provide direct drive propulsion for long stroke application.

![](https://assets.underline.io/uploads/markdown_image/1/image/c05017834f7742c799e6a24cbb87122e.jpg)

Fig. 1. The topology and operation principle of DS-FCPMLMs.

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Fig. 2. The electromagnetic performances of DS-FCPMLMs.

Design and Analysis of Novel Double-sided Flux Concentrated Permanent Magnet Linear Machines with Saturation Relieving Effect

Introduction Transverse flux tubular linear machine (TF-TLM) has merits of high torque density and low side force and is suitable for wave energy conversion (WEC) application. However, excited by permanent magnets (PM), it is hard for TF-TLM to adjust the air gap magnetic field and keep the terminal voltage constant at different operation speed [1]. In this paper, a hybrid-excitation transverse-flux tubular linear machine (HE-TF-TLM) excited by consequent-pole permanent magnet (CP-PM) and DC windings in parallel is proposed. The 3D FEA results have proved that the voltage regulation ratio of HE-TF-LM reaches 87.36%, and thrust density of the machine is not compromised, which is calculated as 155kN/m3. Operation Principle Fig.1 (a1), (b1) (c1) illustrate the flux distribution of the generator of Phase A under condition of idc=0A, 6A and -6A respectively. Fig.1 (a2), (b2) and (c2) presents the magnetic field distribution via 3D FEA calculation. After applying DC current idc&gt;0A, due to the large reluctance of PM, φDCa travels through A2 and A6 to form the magnetic route. Therefore, flux linkages in A2 and A6 are enhanced by φDCa and φPMa together. After applying DC current idc&lt;0A, flux linkages in A2 and A6 are cancelled by φDCa and φPMa. However, as φDCa and φPMa join together in the field teeth, the saturation in the field teeth is inevitable under this condition. Results Analysis Fig.2 (a) presents the no-load back emf under different DC excitation (idc=0A, 6 A, -6A, Ndc=55). The 3D FEA results reveal that the back emf can be altered from 96mV/turn to 253mV/turn at unit speed. And the voltage regulation reaches 87.36%. Fig.2 (b) calculates the induced voltage under different working speed (0.5m/s, 1m/s and 2m/s). It is perceived that by altering the excitation current, the output voltage of the generator can keep constant. Fig.2 (c) presents the output thrust force of the machine under different DC excitations (idc=0A, 6 A, -6A). According to the FEA results, output thrust force reaches 279.14N, and the thrust density of the proposed machine can be effectively improved to 155 kN/m3 at rated excitation (idc=6A). Meanwhile, the output thrust force can be effectively changed by altering DC current.

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