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A conventional coil configuration of electromagnetic levitation melting (ELM) systems consists of a main coil connected with an anti-loop coil to provide the stability of the levitating workpiece. The reversed current in the anti-loop coil produces a reversed magnetic field that depreciates the total magnetic flux at the workpiece. In many cases, a smaller reversed current is sufficient to provide stabilization for a levitating workpiece. This paper proposes a mutually coupled stabilization coil in place of the anti-loop coil to improve the performance of ELM systems. The proposed stabilization coil system consists of two coils, an isolated upper coil, and a main levitation coil. The two coils are galvanically isolated while magnetically linked. The upper coil current is adjustable through the distance between the coils. This allows the upper coil to operate at a lower current than the main coil current but sufficient for the workpiece stabilization. Simulation results have confirmed that the magnetic flux density at the workpiece is higher in the isolation configuration than in the conventional anti-loop configuration. Experimental results have shown that the proposed system can improve the ELM system performance by reducing the heating time and power consumption of the melting process.

The electromagnetic levitation (EML) system serves as a key subsystem in maglev trains for the purpose of levitation. It is highly dynamic, open-loop unstable, and safety-critical. The expense of establishing an accurate model out of the Maglev train, in addition to the varying operating conditions, results in an imperfectly known model in engineering practice. Thus high-performance levitation control, w.r.t. an imperfectly known model, is of considerable practical interest. Motivated by such an observation, this article investigates real-time levitation performance optimization of the EML system, with an imperfectly known model. The EML system is first modeled and an equivalent demonstration benchmark is developed. Then, the structure for levitation performance optimization is presented on top of the coprime factorization technique. Furthermore, the real-time levitation performance optimization algorithm is developed, utilizing only the input and output data. In the end, the proposed methods are validated on the benchmark. [ABSTRACT FROM AUTHOR]

The running environment of a magnetic levitation (maglev) vehicle is complex, with problems such as track irregularity, external disturbance, varying system parameters, and time delays, which bring great challenges to the design of a high-performance levitation controller. In this article, an adaptive neural network controller with input delay compensation and a control parameter optimization scheme is proposed for the electromagnetic levitation system of a maglev vehicle, which can solve the key engineering problems of external disturbance, input time delay, and time-varying mass. Aiming at the problem of input time delay, a sliding-mode surface with time-delay compensation is constructed, and a double-layer neural network and adaptive law are utilized to approximate the uncertain dynamics; thus, a finite time adaptive tracking control law is proposed. Based on the Lyapunov method, the stability of the proposed controller in finite time is analyzed. The proposed method does not only update the input and output weights of the neural network online, but also introduces reinforcement learning (Actor–Critic network) to optimize the key controller parameter in real time and enhance system robustness. Simulation and experimental results show that the proposed controller can effectively suppress the air gap vibration with time delay and uncertain dynamics, and significantly improve the performance of levitation control. [ABSTRACT FROM AUTHOR]

In this article, we propose an unconventional method, i.e., generalized finite difference method (GFDM), to analyze the electromagnetic performance of surface-mounted permanent magnet (SPM) machine with eccentric rotor shape. The remarkable characteristic of this method is that it is meshless. In this method, the solution region is discretized in the form of nodes, and the nodes can move with the moving structure. This is very helpful in modeling the SPM machine because there is no remeshing process during the rotation. However, mesh generation is required in the traditional finite-element analysis (FEA). First, the basic principle of the proposed GFDM is introduced. Second, the whole field domain is divided into five types of regions, viz., PMs, air gap, slot openings, slots, and stator core. Third, the differential equations satisfied by each region are discretized into algebraic equations by the GFDM. The interfaces need to be dealt with separately because of the discontinuity of the derivative of the vector potential. Then, the systems of equations are solved to analyze the electromagnetic performance of an SPM machine. Finally, this method is implemented on a 12-slot, 10-pole SPM machine. Meanwhile, the effectiveness of this method is verified by an FEA and experiment. [ABSTRACT FROM AUTHOR]

Traditional multipoint hybrid maglev systems cannot realize the zero-power horizontal levitation state under eccentric load, which means the steady-state current is zero, and the air gap of each magnet is equal. This article proposes a new maglev system with two rotary magnets to solve this problem. The two magnets can move on an annular guideway to counteract the moment caused by the eccentric load. At first, we established the linear parameter varying model of this maglev system. Then, the control strategy is designed, which consists of a zero-power horizontal levitation controller and rotation controller. The levitation control is realized by introducing feedback of integral current and deviation of air gap in the proportional-derivative control system. The rotation controller employs a centroid observer and centroid Jacobian. It outputs the rotating angle at the demand of the zero-power and horizontal levitation. Experimental results demonstrate that the proposed maglev system has a better zero power and horizontal levitation performance than without rotary magnets. The direction of the air gap variation is opposite to that of the loading direction. The variation size of air gap length depends on the load weight, whereas rotation angle is related to the load weight and loading position. [ABSTRACT FROM AUTHOR]

Unavoidable track irregularities continuously excite a traveling high-speed electromagnetic suspension (EMS) train. This issue deteriorates the levitation performances such as stability and comfortability. A robust levitation controller is critical for the EMS unit to suppress irregularities. In this work, a novel composite control scheme is proposed for high-speed maglev trains. It combines a fixed-time disturbance observer (FTDO) and a global finite-time controller (FTC). The FTDO is designed to estimate irregularities precisely within desired bandwidth, while the FTC is to address the fast dynamics of the levitation system of a high-speed maglev train. In addition, the command filter is integrated to increase the practicability of the composite control scheme. Theoretical analysis establishes the stability of the whole system. With ideal irregularity models and the field data measured from a commercial line, numerical simulations under various operation scenarios, including high speed, time-varying speed, gust and slope, verify that the proposed control scheme improves the air gap response while maintaining the stationarity of primary levitation and the ride comfortability for passengers. The simulations on a full bogie with load also demonstrate effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Superconducting (SC) electrodynamic suspension (EDS) has a wide application prospect due to the advantages of no active control, self-stability and large gap, especially in the ultra-high speed maglev, rocket launching, Electromagnetic Aircraft Launching System and other high speed fields. SC coils and null-flux Ground Coils which are the primary and secondary windings respectively are applied in a typical EDS system, in that the null-flux ground coils provide levitation and guidance force. The calculation of electromagnetic forces that has been extensively studied by scholars all over the world is the basis of the design and optimization of the system. However, due to the limitation of complex structure, the calculation formula is often so complicated that the results have to be obtained by means of finite element method and numerical simulation. This paper aims to derive an analytical calculation of electromagnetic forces for SC EDS system based on some reasonable assumptions. The experimental data of MLX01 on the Japanese Yamanashi testline was used to verify the calculation model of this paper. In order to get a further validation, a small EDS rotary table was built based on null-flux ground coils and permanent magnets. The results of the experiment confirms the effectiveness of the proposed analytical calculation model. [ABSTRACT FROM AUTHOR]

Inspired by the superconducting electrodynamic suspension (EDS) system in Japan, a new permanent magnet (PM) EDS system combining PM and 8-shaped null-flux coils has emerged in recent years. In general, the structure of a single PM was used as the onboard magnet. This single magnet structure is difficult to further optimize the core magnetic field resource of the EDS system. Facing this issue, we proposed a PM EDS system combining a Halbach PM array (HPMA) with good magnetic collecting capability and the 8-shaped null-flux coils. Furthermore, we established a numerical model for this new HPMA EDS system. The core of the calculation method is to discretize each PM in the HPMA into a coil group. By calculating the mutual inductance between the equivalent coil groups and the null-flux coils, the interaction electromagnetic force is obtained. In order to verify the correctness of our numerical model, the calculation results of the finite-element method (FEM) simulation model are compared with those of the numerical model. The results of two models are basically consistent. It shows that the numerical calculation model has high accuracy. On this basis, the effects of various parameters on three main electromagnetic forces are studied to better explore the application characteristics of the HPMA EDS system. To sum up, this established numerical model can effectively avoid the calculation error caused by the edge effect of the discontinuous magnet array. It provides an accurate calculation method for the optimization of the EDS system combining the PM array and the null-flux coils. [ABSTRACT FROM AUTHOR]

Though Global Navigation Satellite System (GNSS) has been pretty mature and widely used in our daily life, the positioning of the indoor environment cannot be realized due to the shielding of concretes or glasses by GNSS. Many positioning methods have been proposed to solve that problem, and Bluetooth Low Energy (BLE) is one of the most widely used wireless technologies. This paper takes BLE Angle of Arrival (AOA) as the research object and proposes a method based on signal fitting and Propagator Direct Data Acquisition (PDDA) angle estimation algorithm. This method can be applied to both linear antenna array and rectangular antenna array and has good positioning performance. The method proposed in this paper does not need to calculate the phase differences between antennas, making it unnecessary to calculate the intersection of cones during spatial positioning. The angle estimation is divided into two steps. Firstly, the frequency deviation of Constant Tone Extension (CTE) is calculated based on the IQ samples captured during the reference period, and the received signal matrix of all antennas is fitted based on frequency deviation. Secondly, the antenna received signal model is established based on hardware antenna arrangement, and the arrival angle is estimated by the PDDA algorithm. In order to verify the effectiveness of the proposed method, the plane and spatial positioning experiments are carried out using the BLE devices of Nordic Company, which shows a good positioning accuracy. In spatial positioning, the average positioning accuracy of BLE in channel 37, channel 38, and channel 39 is 0.59m, 0.74m, and 0.77m, respectively, which can meet the basic indoor positioning requirements and cover a large area by one receiver. Compared with the classical MUSIC algorithm, the PDDA algorithm has the same positioning accuracy but lower computational complexity, so it has certain advantages. [ABSTRACT FROM AUTHOR]

Maglev train is a new vehicle of rail transit. The time-varying load caused by large capacity is an important test of suspension system. If the state variable matrix and parameter matrix caused by time-varying mass cannot be estimated effectively, it is very likely to lead to the decline of suspension performance and instability. Firstly, an NNs state observer based on neural network is proposed to effectively estimate the system state and parameter matrix. Secondly, based on the NNs observer model, an inverse control algorithm with stronger regulation ability is designed by integrating the output limited characteristics and Lyapunov function, which can ensure the stability of the system when disturbed. The simulation results show that the control algorithm proposed in this paper can have faster response speed and stability in the flotation process of 16mm-10mm, and has better anti-disturbance ability in the face of time-varying mass disturbance. Finally, based on the single point suspension experimental platform, the effectiveness and practicability of the proposed control algorithm are verified, and the correctness of the proposed NNs observer model is also verified. [ABSTRACT FROM AUTHOR]

The commercial operation of the maglev train puts critical demands on reliability and operation performance. Since maglev trains’ levitation system is open-loop unstable, its closed-loop stability under various operation conditions is a primary consideration. This paper thus addresses real-time stability performance monitoring and evaluation of maglev trains’ levitation system. First, a novel real-time performance indicator for stability performance monitoring is proposed. It utilizes only the online data of the levitation system, without knowing its accurate model. Then, performance evaluation is carried out by grading the monitored stability performance into different levels for further handling. Moreover, the proposed methods offer a way of controller evaluation for the levitation system before the train is put into commercial operation. It is noteworthy that, the proposed methods do not require the model of the levitation system to be known and run in real-time. The effectiveness and efficiency of the proposed methods are validated on a levitation system. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method (AM) based on the air-gap magnetomotive force (MMF) permeance model is proposed to predict the nonlinear instantaneous torque of switched reluctance machines (SRMs). The analytical expression of the air-gap MMF is first obtained from the winding function and current profile, while the air-gap magnetic permeance considering the double-sided slotting effects is also derived. Then, the nonsaturated field distribution along the air-gap circumference is presented based on which the instantaneous torque can be calculated from the Lorentz force law. Furthermore, the model is enhanced with a saturation distribution factor to include the nonlinear characteristics. The proposed method is free from preliminary data or empirical coefficient and benefits from the simplified model and solution. The AM will be validated by the two-dimensional finite-element method based on four SRMs with different structures. Moreover, an SRM prototype is manufactured for experimental verification. [ABSTRACT FROM AUTHOR]

In this article, a state-constraints adaptive backstepping control (ABC) strategy is proposed and presented to accomplish precise rotor displacement control for a kind of nonlinear active magnetic bearing (AMB) system considering the presence of parameters nonstationarities and uncertainties. Since the control properties of the AMB system is strong nonlinear, uncertain, and nonstationary owing to external disturbance and the variation of geometry and material dependent on operation condition, a nonlinear AMB system model with switched parameters is established to describe the AMB dynamics. Subsequently, a nonlinear ABC algorithm is designed for the rotor position control of radial magnetic bearing. For the purpose of making the rotor displacement confined to a prescribed range in consideration of physical limitations and security concerns, barrier Lyapunov function (BLF) is founded to construct the adaptive backstepping controller. Thus, the proposed BLF-based adaptive backstepping controller is able to restrict the position states without exceeding the prescriptive constraint spaces and then to improve the system performance. Additionally, the extended development for n-order controller and the stability proof is given in this article as well. Simulation and experiment results demonstrate the effectiveness and the potential application of the proposed control approach. [ABSTRACT FROM AUTHOR]