This paper designs a double-side linear vernier permanent-magnet motor, which incorporates the merits of high thrust force capability, high power factor, and high efficiency. Since the parameters of the motor are very sensitive and the high thrust force capability comes along with the high force ripple, a framework of multiobjective optimization is proposed to improve the overall motor performances. The sensitivity analysis is used to select significant variables and the multiobjective differential evolution with ranking-based mutation operator is conducted with the response surface models to generate the Pareto solution set. The electromagnetic performances of the optimal motor are compared with the initial motor by simulating step by step based on finite-element analysis. Finally, a prototype motor is manufactured and the experimental results validate the improved motor performances.

Multiobjective Optimization of a Double-Side Linear Vernier PM Motor Using Response Surface Method and Differential Evolution

Flux-switching permanent magnet (FSPM) machines have been gaining interest over the last few decades. This is due to the several advantages that this type of machines provides. These advantages include high torque density due to the flux-focusing effects, favorable thermal management due to the location of PMs on the stator, passive and hence robust rotor structure which is suitable for high-speed applications, etc. The two-part companion articles are going to provide a comprehensive analysis of FSPM machines in terms of opportunities and challenges. In the first part of these two-part series, it covers the principle theory, computation methods, various topologies of FSPM machines, and the comparison with other PM machines. Meanwhile, the basic performance characteristics and design requirements, viz. torque density, over-load torque capability, flux-weakening capability, fault-tolerance capability, as well as the latest development, are also provided.

Flux-Switching Permanent Magnet Machines: A Review of Opportunities and Challenges—Part I: Fundamentals and Topologies

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.

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

Magnetic Levitation systems are nonlinear, frictionless and noiseless which use electromagnetic fields to hover ferromagnetic objects in air. For this purpose, we have proposed Supertwisting and Integral Backstepping sliding mode controllers. The designed controllers ensure the air gap to be maintained at the desired value while tracking the magnetic flux and momentum to their respective references. The stability analysis of the proposed controllers has been presented using Lyapunov theory which proves the global asymptotic stability of the system. The performance of the proposed controllers is analyzed using ODE 45 solver in MATLAB/Simulink environment. The proposed controllers reduce the chattering and improves the dynamic response of the system. Robustness of the proposed controllers has been checked by adding noise and disturbance in system's state space model. Furthermore, comparison of proposed controllers with each other, with conventional PI and recently published nonlinear controllers for MagLev system in terms of dynamic response has also been presented. The results show that the dynamic behavior of supertwisting sliding mode controller is best among analyzed controllers.

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Control of MagLev System Using Supertwisting and Integral Backstepping Sliding Mode Algorithm

In this article, a terminal sliding mode control (SMC) strategy based on the nonlinear disturbance observer (NDO) and prescribed performance method is proposed to deal with the speed tracking problem for permanent-magnet linear synchronous traction systems in urban rail transit. First, to improve the dynamic and static performances, a prescribed performance control characterizing the tracking performance employed for error transformation. This limits the tracking error of the original system to a prescribed bound if the transformed system is stable. Then, a terminal SMC is designed with backstepping, which guarantees the states converge to equilibrium point in finite time, realizing fast transient response of the system. Considering the existence of the uncertain disturbance, an NDO is utilized to estimate perturbations, and then, the estimation is used for the feedforward compensation, further improving system stability. Finally, the effectiveness and advantages of the proposed scheme are illustrated by computer simulations and experiments in dSPACE.

Disturbance-Observer-Based Terminal Sliding Mode Control for Linear Traction System With Prescribed Performance

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.

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

To incorporate the merits of simple and robust movers of induction linear motors and higher power factor and high efficiency of permanent magnet linear motors, a new long primary double-sided linear flux-switching permanent magnet (DSLFSPM) motor is proposed, investigated, and quantitatively compared with linear induction motors (LIM) for the electromagnetic launch system. First, the topology, operation principle, and electromagnetic performance of the DSLFSPM motor have been investigated. Then, in order to analyze the LIMs comprehensively, three LIMs have been designed based on the same overall dimensions and other key parameters. Finally, the electromagnetic performance of DSLFSPM motor and LIMs have been compared and summarized. The results show that the DSLFSPM motor has some merits such as higher efficiency, higher power factor, more robust mover, larger thrust force, and smaller force ripple than LIM motors. In order to validate the simulation results, a small-scale prototype of DSLFSPM motor has been built and measured.

Quantitative Comparison of Linear Flux-Switching Permanent Magnet Motor With Linear Induction Motor for Electromagnetic Launch System

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

A new series of linear flux-switching permanent magnet (LFSPM) motors has elicited considerable attention. This series incorporates the merits of the high efficiency of permanent magnet linear motors and the low cost of linear switched reluctance motors for a long-distance drive system. However, the vector control of the LFSPM motor requires an expensive and unreliable linear encoder, which must be as long as the entire railway (or at least the whole linear motor). Such a large encoder will lead to extra costs and will even weaken the benefit of the motor performance. Thus, developing its sensorless control for engineering applications is necessary. Sliding-mode sensorless control has the advantage of strong robustness to parameter variations and external disturbances, as well as high dynamic performance, which is important for long-distance drive systems. The proposed algorithms can extend the minimum operating speed, thereby enabling the motor to work at a lower speed. Both simulation and experimental results are provided for verification.

Lu Minghang

Papers

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

Quantitative Comparison of Linear Flux-Switching Permanent Magnet Motor With Linear Induction Motor for Electromagnetic Launch System

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

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

Sliding-mode observer based sensorless vector control of LFSPM motor for long-distance drive system