Linear Flux-switching Permanent Magnet Research Articles

Comparative Analysis of Normal Force Characteristics and Dynamic Influence of Linear Flux-Switching Permanent Magnet Motor for Rail Transit

Comparative Analysis of Normal Force Characteristics and Dynamic Influence of Linear Flux-Switching Permanent Magnet Motor for Rail Transit

A Novel Fault Tolerance Structure of Arc Linear Flux Switching Permanent Magnet Motors Based on Redundant Winding

This paper presents a novel structure of the arc linear flux switching permanent magnet motor based on the redundant winding to inhibit the rises of the motor losses and temperature due to the open circuit fault tolerance. Firstly, the structural characteristic of the arc linear flux switching permanent magnet motor is introduced. Then, the fault tolerance current of single phase open circuit fault is calculated for different winding connection forms. The fault tolerance performances under different conditions are compared from a special view of motor temperature rises. Finally, a novel structure for fault tolerance enhancement is proposed, which can effectively improve the freedom degree of the fault tolerance current by using the redundant winding. This novel structure takes full advantage of the circumferential air gap between the arc stator. The calculation results show that the novel structure can allow the fault tolerance of open circuit fault has little influence on the motor copper losses and temperature rises while maintaining the on-load torque.

Design optimization of a novel linear transverse flux switching permanent magnet generator for direct drive wave energy conversion

Linear transverse flux permanent magnet machines (LTFPMs) are categorized as high force density topologies, which are suitable candidates for direct drive and low-speed applications. This paper introduces a novel LTFPM topology, which also proposes advantages of the flux-switching machines. This proposed linear transverse flux switching PM machine (LTFSPM) has two long passive translators located at the armature's top and bottom sides. The topology offers a high value of force density, and also, it is a cost-effective topology due to its double-sided passive translator. Furthermore, the PMs are fully utilized in the magnetic circuit, the end winding length is negligible, and the iron cores can be laminated easily. In this paper, the operation principle of the topology is explained and its magnetic circuit is discussed. To reduce the computational time of optimization procedure, a double-layer method is adopted, which provides high robustness, low computational time, and high precision. Results of the finite element method indicate that the proposed machine can be considered a potential candidate for linear motion applications especially direct drive wave energy conversion systems, which require high force density values.

Improved Primary/Secondary Pole Number Combinations for Dual-Armature Linear Switched Flux Permanent Magnet Machines

Due to additional armature windings on the secondary, dual-armature linear switched flux permanent magnet machines (DALSFPMMs) exhibit higher force densities than conventional LSFPMMs. Nevertheless, the existing DALSFPMMs suffer from larger secondary phase numbers because of the prime secondary pole numbers. This article proposes more optional primary/secondary pole number combinations with fewer phase numbers for DALSFPMMs. The machine topology is introduced first, followed by the analysis of phase numbers, which indicates the DALSFPMMs with 8/9 primary/secondary poles (8p/9s) and 9p/8s have fewer phase numbers and need fewer power electronic devices. Then, the operation principle of DALSFPMM is analyzed from the perspective of air-gap field. After that, the electromagnetic performances of four DALSFPMMs with 8p/9s, 9p/8s, 6p/7s, and 6p/5s are investigated by 2-D finite element method, showing the 8p/9s and 9p/8s machines have higher average thrust forces, lower thrust force ripples, and higher thrust force to permanent magnet (PM) volume ratios than the 6p/7s and 6p/5s counterparts. Finally, a prototype machine is manufactured for the experimental validation.

Development of a Thermal Analysis Tool for Linear Machines

The thermal design is one of the most important stages in the design process of electrical machines. Thanks to software packages, like Motor-CAD, rotating machine designers can predict the thermal operation of the machines with high precision. However, a Motor-CAD equivalent for linear machines does not exist. Thus, linear machine designers must develop specific thermal analysis tools when designing the machines. In this article, a generic thermal analysis tool for different kinds of linear machines is presented. The model has been designed in MATLAB Simulink. Hence, it should be easy to implement for most engineers. The article describes the configuration of the different elements of the tool. The calibration parameters and procedure, and typical values of the calibration variables, are also given in the document. Finally, in order to demonstrate the generic nature of the tool, the model is experimentally validated via DC thermal tests to a linear induction machine and a linear switched-flux permanent magnet machine. The results show that, despite being simple and easy to implement, the model can predict the thermal operation of different machines with high precision.

Comparison Between Dual-Armature Linear Switched Flux Permanent Magnet Machine and Linear Surface-Mounted Permanent Magnet Machine Considering Thermal Conditions

It has been proved that dual-armature permanent magnet (PM) machines have higher power density than conventional PM machines under the same copper loss. However, the thermal conditions of these machines are different. This paper makes a fair comparison between a dual-armature linear switched flux PM machine (DALSFPMM) and a linear surface-mounted PM machine (LSPMM) by considering both electromagnetic performances and thermal conditions. First, the topologies of two machines and platform are introduced. Then, the 2D and 3D finite element (FE) models are employed for the electromagnetic and thermal analyses, respectively. During the machine optimization, the thermal analysis is used to determine the copper loss under the fixed machine dimensions, while the electromagnetic analysis is used to optimize the machine dimensions under the fixed copper loss. After iterations, two machines are optimized and their performances are compared. Under the limitations of 80 °C maximum PM temperature and 120 °C maximum winding temperature, the DALSFPMM can exhibit 38% higher thrust force density for the continuous duty and up to 43% higher thrust force density for the short-time duty. Finally, a prototype machine of DALSFPMM is tested to validate the analyses.

Research on Detent Force Characteristics of a Linear Flux-Switching Permanent-Magnet Motor

Linear flux-switching permanent-magnet (LFSPM) motors have been proposed for electromagnetic launch system (EMLS). Benefiting from the permanent magnet (PM) settled on the long double-sided primary and the yokeless secondary, the proposed structure has the advantage of high thrust force density and simple structure compared with the traditional linear permanent-magnet synchronous motor (LPMSM) and linear induction motor (LIM), which makes it more suitable for the EMLS. However, it suffers from the deficiency of relatively high detent force due to the permanent magnets (PMs) settled on the primary, which will also exert an influence on the thrust ripple. Different from the traditional rotary motor, the linear motor also suffers from the end force caused by the end effect. So, a new structure of secondary, which is called symmetric unequally spaced (SUS) secondary in this paper, is proposed to improve the electromagnetic performance from the point of the detent force and thrust ripple for the motor. The thrust ripple and detent force are effectively declined by applying the proposed method without the sacrifice of the average thrust force. The validity of the method is verified by finite element analysis (FEA). A prototype with SUS secondary is manufactured to verify the simulation result.

Investigation On High Temperature Superconducting Linear Flux-Switching Motors With Different Mover and Stator Pole Pitch Ratios For Urban Railway Transit System

Linear Induction Motors (LIMs) are popular as driving motors in urban railway transit systems due to their simple and robust stator structures. However, the efficiency and power factor of LIM are lowered because of its eddy effect. As a promising alternative, Linear Flux Switching Permanent Magnet (LFSPM) motor offers high electromagnetic performance while keeping its stator simple. Despite these merits, the adoption of Permanent Magnets (PMs) of LFSPM motors influences their flux-weakening ability, thus leading to narrow speed range. To solve this problem, it is feasible to use High Temperature Superconducting (HTS) coils to replace PMs, forming HTS Linear Flix Switching Motor (HTS-LFSM). Among various parameters that influence the performance of HTS-LFSM, ratio of primary and secondary pole pitches is a leading parameter. Aim at investigating the relationship between pole pitch ratios and electromagnetic performance, different typical pole pitch ratios are compared against each other based on several common principles. The merits and drawbacks are analyzed with the help of Finite Element Method (FEM), and some conclusions are drawn.

A Novel Double-Sided High Temperature Superconducting Linear Modular Flux-Switching Motor

Double-Sided Linear Flux-Switching Permanent Magnet (DSLFSPM) motor has the merits of high efficiency, high power factor and low-cost stator structure. But the speed range of DSLFSPM is limited due to its adoption of permanent magnets. Double-Sided High Temperature Superconducting Linear Flux-Switching Motor (DSHTS-LFSM) adopts HTS coils to replace the permanent magnets, thus obtaining better power density and wider speed range. However, when the magnetic field gets much stronger, the iron core is easily saturated and flux leakage gets serious, which threatens the reliability of HTS coils and lowers the utilization of iron core. To solve this problem, a novel Double-Sided High Temperature Superconducting Linear Modular Flux-Switching Motor (DSHTS-LMFSM) is proposed. The armature windings are designed different from existing DSHTS-LFSMs to reduce flux leakage. Furthermore, by sealing the HTS coils together in a Dewar away from armature windings, the reliability is improved. In this paper, the structure and working principle of the proposed DSHTS-LMFSM is explained. The electromagnetic performance of it is calculated using Finite Element Method (FEM). As evaluation, its performance is compared against a traditional DSHTS-LFSM.

Reduction of Thrust Force Ripple of High Temperature Superconducting Linear Flux-Switching Motors using Asymmetry Mover Structure

Compared with traditional linear motors, such as Linear Permanent Magnet Motors (LPMs) and Linear Induction Motors (LIMs), Linear Flux-Switching Permanent Magnet (LFSPM) motors have the merits of high efficiency, power density, with simple and robotic secondary structure. Despite these advantages, the flux-weakening ability of LFSPM motor is limited and thus the speed range of it is not ideal. As a promising choice, it is feasible to replace the PMs of LFSPM motors with coils made with High Temperature Superconducting (HTS) tapes. By using HTS material, High Temperature Superconducting Linear Flux-Switching Motors (HTS-LFSMs) have good flux-weakening ability while inheriting the edges of LFSM motors. Since the existence of HTS coils, the cooling system has a minimum size and has to take up certain room of the motor. When it comes to applications where the volume of motor is strictly restrained, there may not be enough room for a basic pattern of typical pole pitch combinations for HTS-LFSM, such as 12-7 or 12-9, leading to large thrust ripple. To solve this problem, a method of reducing thrust force using asymmetry mover structure is proposed based on a 9-5 pole pitch ratio. The mechanism and working principle are analyzed and the validation is verified with the help of Finite Element Method (FEM).

Investigation of High Temperature Superconducting Linear Flux-Switching Motors With Different Secondary Structures

Compared with Linear Induction Motor (LIM), which is widely adopted for urban railway transit system, Linear Flux-Switching Permanent Magnet (LFSPM) motor has the merits of high efficiency, power factor and simple secondary structure. Therefore, LFSPM motor is claimed to be promising for urban railway transit system. However, research shows that speed range of LFSPM motor is limited due to Permanent Magnets (PMs). But for Linear Wound Field Flux-Switching (LWFFS) motor, electromagnetic performance is influenced by the large airgap. To incorporate the merits of LWFFS motor and LFSPM motor, High Temperature Superconducting Linear Flux-Switching Motor (HTS-LFSM) is proposed. However, it remains unknown which secondary structure of HTS-LFSM is suitable for urban railway transit. Hence, two HTS-LFSMs of slotted and segmented secondaries are designed, optimized, compared and analyzed in this paper. Finite Element Method (FEM) is adopted to calculate their performance.

Comparative Study of Permanent Magnet Assisted Linear Switched Reluctance Motor and Linear Flux Switching Permanent Magnet Motor for Railway Transportation

Linear switched reluctance motor (LSRM) has been investigated and supposed as a good candidate in railway system. Recently, permanent magnet assisted switched reluctance motor (PMA-SRM) has attracted extensive attention because of the high torque, robust structure and low cost. However, all these researches focus on the application of small air gaps. How does PMA-SRM perform in large air gap? No research has been conducted until now. As we know, there are many similarities between linear flux switching permanent magnet (LFSPM) motor and permanent magnet assisted linear switched reluctance motor (PMA-LSRM) such as similar primary iron, winding structure, robust secondary and a small amount of permanent magnets. In this case, what are the similarities and differences between these two kinds of motors in terms of electromagnetic characteristics? This paper will compare these two kinds of motors based on the volume of rail transit from the following aspects: thrust force, thrust ripple, efficiency. First, the topology, operation principle of the two LSRMs are introduced and designed. Then, the electromagnetic performance of LSRM is optimized through two dimensional finite element analysis (FEA) based on ANSYS software. The optimization objectives of PMA-LSRM are to maximize the thrust and to minimize the ripple at the given dimensions and the rated condition. The comparison of electromagnetic characteristics between LFSPM motor and PMA-LSRM is completed. Finally, it is concluded that the permanent magnets are not conducive to improving the power of LSRM. And the PMA-LSRM is not outstanding compared with LFSPM motor under the condition of large air gap for rail transit.

Comparative Study of Novel Doubly-Fed Linear Switched Flux Permanent Magnet Machines With Different Primary Structures

To enhance the thrust force density and move a part of copper loss from the primary to the secondary of linear switched flux permanent magnet machines (LSFPMMs), this paper proposes a novel kind of doubly-fed LSFPMMs (DFLSFPMMs) by adding another set of armature winding on the secondary of LSFPMMs. The design and working principles of the new winding are analyzed first. It is found that the optimal coil pitch depends on the primary structure. Then, the parameters of DFLSFPMMs with U-core, C-core, E-core, and multi-tooth primary structures are globally optimized, and their electromagnetic performances are investigated by 2D finite element method. The result shows that the average thrust force of U-core DFLSFPMM is 30% higher than that of conventional LSFPMM counterpart, and it is also 23%-29% higher than those of DFLSFPMMs with other three primary structures. Besides, the U-core machine with tubular structure is analyzed for the potential application of electromagnetic shock absorbers, which shows the U-core DFLSFPMM has 10% higher peak-to-peak damping force than linear spoken-type PM machine. Finally, a prototype of U-core DFLSFPMM is manufactured and tested to validate the analysis.

Comparison Between Linear Induction Motor and Linear Flux-Switching Permanent-Magnet Motor for Railway Transportation

Linear induction motors (LIMs) have been extensively adopted in urban railway transportation given their nonadhesion thrust and simple stator structure. However, these LIMs undergo unfavorable power factor and efficiency considering their copper and eddy losses. Recently, linear flux-switching permanent-magnet motors (LFSPMs) have attracted the attention of researchers due to their high power density, simple structure, easy heat dissipation, high efficiency, and high power factor. However, so far, no quantitative comparison exists between LFSPMs and LIMs of the size 1:1 to prove the feasibility of LFSPMs to be used in railway transit systems. Therefore, a comparative analysis between the two motors is conducted in this paper. First, this paper investigates the LIMs for railway transit using the finite element method (FEM). Second, the LFSPMs for railway transit is designed and optimized. Third, the electromagnetic performance of the two motors is compared and analyzed through the FEM. Finally, a small-sized prototype of the LFSPMs is constructed to validate the FEM results. It is concluded that LFSPMs offer a favorable thrust force, have high efficiency, and high power factor but have large normal force and force ripple. Therefore, applying LFSPM requires a reliable supporting device and a shock absorber.

Sensorless Control of Linear Flux-Switching Permanent Magnet Motor Based on Extended Kalman Filter

Linear flux-switching permanent magnet (LFSPM) motors have drawn extensive concern for rail transit drive systems because permanent magnets and armature windings are all located on the short primary, whereas the long secondary is made up of iron only. Thus, the LFSPM motor with low cost and high efficiency is an excellent choice for urban rail transportation system. However, the installation of linear encoders that are expensive and unreliable along with the long stator will bring about increased costs and reduced reliability. To overcome the shortcomings and fully exert the advantages of LFSPM motors, extended Kalman filter (EKF) is adopted to achieve sensorless control of LFSPMs for its better stability, robustness, and low requirements for working environment in this article. An improving tracking performance can be obtained using EKF considering the end effects of LFSPMs and the presence of noise. Both simulation and experimental results indicate that the motor can run reliably from standstill without position sensors, which is advantageous compared with other sensorless control methods based on electromotive force.

Segmented power supply control of double‐sided linear flux‐switching permanent magnet motor

Current research shows that the double-sided linear flux-switching permanent magnet (DLFSPM) motor is suitable for electromagnetic launch systems, in which the armature windings and permanent magnets are set on the long primary stator, whereas the mover is only composed of yokeless iron. Thus, the DLFSPM motor incorporates the merits of high power density and efficiency of the linear permanent magnet synchronous motor and simple and robust structure of linear induction motor. To improve the power factor and decrease the inverter capacity, the segmented power supply control methods of the DLFSPM motor are investigated in this study. First, the structure, electromagnetic parameters, and the segmented power supply method of the DLFSPM motor are explored. Then, the mathematical models and the control strategies of the DLFSPM motor are deduced and proposed. Finally, the simulations and experiments of the DLFSPM motor are conducted to validate the study of segmented power supply method.

A New Double-Sided Linear Flux-Switching Permanent Magnet Motor With Yokeless Mover for Electromagnetic Launch System

A new double-sided linear flux-switching permanent magnet (DSLFSPM) motor with a yokeless mover is proposed in this paper. First, the topology and structure of the proposed motor are presented, and the pole pitch ratio and segment number are shown to strongly affect performance. Second, the electromagnetic performance of DSLFSPM motors with a secondary yoke and without a secondary yoke are compared and described. Third, according to analytical models, air-gap flux-density levels and corresponding harmonics are investigated, and force production mechanisms of the proposed motor are presented. The analytical results match to the FEA results. Finally, experiments on a prototype are carried out to validate the simulation results. Back EMF, cogging force, and inductance values of the prototypes are measured and experimental results for the drive systems are presented.

Model Predictive Thrust Force Control of a Linear Flux-Switching Permanent Magnet Machine With Voltage Vectors Selection and Synthesis

To reduce the thrust force ripple of a complementary and modular linear flux-switching permanent magnet machine, a model predictive thrust force control (MPTFC) is developed and implemented in this paper based on the active voltage vectors selection (AVVS) and two-voltage-vector synthesis (TVVS). First, the active voltage vectors are screened and assigned to the specific sector, instead of traversing all the possible vectors, and consequently, significantly decrease prediction workload. Second, for the elimination of the weighting factor in the conventional MPTFC, the control object is transformed from the thrust force and stator flux to the stator flux only by using the load angle. Third, to achieve the steady-state performance improvement, the TVVS approach is applied in each control period, where the optimal TVVS and its dwell time are simultaneously obtained by only one cost function. Both simulated and experimental results verify that the steady-state performance improvement can be realized by the developed MPTFC through comparing with normal hysteresis current control and conventional MPTFC strategies.

Electromagnetic Characteristic of a Novel Linear Flux Switching Machine With Three-Dimensional Magnetic Circuit

The novel linear flux switching permanent magnet machine with a three-dimensional magnetic circuit is proposed in this paper, which is suitable for aerospace, missile launch, and other fields, benefiting from high thrust force and low cost. First, the basic structure and working principle of the machine are introduced. Second, the equivalent magnetic circuit model considering the variable reluctance is established and the equations are put forward for magnetic analysis. Third, the simplified finite element model is performed to calculate the field distribution, the air-gap flux density, the flux linkage of winding, and the back electromotive force. Finally, a prototype is constructed and experiments show a good agreement with analysis.

A Novel Method to Reduce of Cogging Force in a Linear Flux-Switching Permanent Magnet Brushless AC Machine

The primary linear flux-switching permanent magnet (LFSPM) motor has the merits of high speed, high response, and direct drive. However, the presence of the cogging force in LFSPM motors compromises position and speed control accuracy, which can be particularly troublesome at low speeds. A novel approach of suppressing the slot effect cogging force for LFSPM is proposed according to repetitive control of time-varying periodic signals. The time-varying periodic thrust disturbance in t-domain is transformed to the signals defined in the x-domain, and a repetitive controller is designed. Furthermore, a series of specific harmonic currents are added into q-axis reference current, resulting in additional force components to counteract the end effect cogging force. Finally, experimental evaluations of the control strategy are performed on an AD5435-controlled LFSPM drive platform. The simulations and experiments verify that the proposed method can suppress the thrust ripple effectively.