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The demand for low-speed (LS) and high-torque electrical machines is increasing in different applications. Previous research showed that dual-stator magnetically geared machines, such as Vernier pseudo-direct-drive machines (VPDDs), can have a high torque density and a high power factor. However, the size of their end-winding can affect heavily their torque density. Based on a distributed winding VPDD, we propose a concentrated-winding split-teeth VPDD (ST-VPDD), which can reduce the size of end-winding and output higher torque density. In this research, a model of the end-winding volume is given. Through preliminary design and finite element model (FEM) analysis, the torque density optimization has been performed to maximize the torque density. Taking the end-winding into account, there is a 93.8% improvement for the torque density, compared to the VPDD, to reach 78.1 Nm/L. After adding a sleeve for mechanical stability, the ST-VPDD still gives a 68.7% improvement compared to the VPDD. [ABSTRACT FROM AUTHOR]

Magnetic gears, an alternative to conventional mechanical gearboxes, have been extensively studied in the last decade. By combining a magnetic gear and a conventional permanent‐magnet machine into one frame, different magnetic‐gear‐integrated permanent‐magnet machines with a high‐torque density are obtained, among which the pseudo‐direct‐drive permanent‐magnet machine features both a high‐torque capability and a good power factor with an acceptable structural complexity. However, the stator PM array in the conventional pseudo‐direct‐drive permanent‐magnet machine obstructs the magnetic path and reduces the excitation torque due to the coils. Another problem is the large permanent‐magnet amount which increases the overall cost. The authors propose a novel topology which has an improved torque capability under the same excitation current with a reduced permanent‐magnet amount. The working principles of the proposed machine are analysed theoretically using the linear‐material assumption to decouple the permanent‐magnet‐machine part and the magnetic‐gear part. Its performance is then validated by the finite‐element method. A comparison study with the conventional topology is conducted to show its merits. [ABSTRACT FROM AUTHOR]

The coaxial magnetic gear is considered as a promising alternative to mechanical gearboxes. This paper proposes a novel single-permanent-magnet-array coaxial magnetic gear with only one layer of permanent magnets, which is stationary. The flux-modulating teeth are made of high-temperature-superconducting (HTS) material. Working principles of the proposed single-permanent-magnet-array coaxial magnetic gear are introduced analytically. A geometric optimization based on the ideal diamagnetic assumption of the superconducting bulks using the finite-element method is conducted to improve its torque capability. The performance is then evaluated by using the nonlinear E-J power law and compared with a single-permanent-magnet-array coaxial magnetic gear using ferromagnetic teeth. The result shows that the proposed topology can successfully magnify the input torque by a given gear ratio. The designed HTS-toothed single-permanent-magnet-array coaxial magnetic gear has a maximal output torque 1.73 times higher than its ferromagnetic-toothed counterpart. [ABSTRACT FROM PUBLISHER]

In low-speed high-torque applications, gearboxes are widely used to amplify the output torque of electrical machines, which inevitably introduce side effects caused by mechanical contact. Consequently, a gear-free system has become increasingly interesting. Although a Vernier permanent-magnet machine has good torque capability, the low power factor is its weakness. This paper proposes a novel topology called the Vernier pseudo-direct-drive (VPDD) machine. A two-stepped design methodology is adopted by combining the subdomain analytical method and finite-element method (FEM). According to the results, the exact subdomain analytical model allows a quick pre-optimization of the structure, and the FEM can be used for further adjustment, dealing with the saturation effect and demagnetization. The optimized VPDD is capable of reaching a very high torque density of 91.8 Nm/L, and the torque ripple is negligible. Its power factor is 0.94. [ABSTRACT FROM AUTHOR]

This article presents the process of building a hybrid analytical model (HAM) for surface-mounted permanent-magnet machines. The HAM couples a reluctance network (RN) model in the stator region with a magnetic scalar potential analytical model in the air gap and magnets regions. This hybrid model can deal with the slotting effect with straight teeth, and takes magnetic saturation into account in the stator iron material using the RN model. It is calculated under open-circuit and loaded conditions. The magnetic flux density, flux linkage, back electromotive force (EMF), and torque of the machines are also calculated. This hybrid model is compared with the subdomain method. It is also compared with the finite element method (FEM) both in terms of the size of the matrix that needs to be calculated and in terms of the torque error. We analyzed this method for two surface-mounted permanent-magnet machines, one with a symmetry factor of four and another with a symmetry factor of three. In both cases, HAM reduced the size of the matrix that needed to be solved compared to FEM. In the machine with a symmetry factor of three, when the matrix size of both FEM and HAM was around 1700 × 1700, the torque error of FEM was 2.62% compared to the high-mesh-density FEM simulation, while the torque error of HAM was only 0.17% compared to the same simulation. HAM also had significant advantages over the subdomain method, as it reduced the torque error from 16.8% to 0.08% in the case of high magnetic saturation. The HAM can, hence, play a significant role in the design and optimization of surface-mounted permanent-magnet machines, especially in cases where magnetic saturation is present. [ABSTRACT FROM AUTHOR]

A completely open magnet geometry satisfies the requirement of a MRI system for the surgical procedure. This paper presents a new flexible design method to facilitate the construction of a completely open MRI magnet by combining the magnetic dipole pair model and optimization algorithm. A numerical implementation shows that the method provides a main magnetic field with sufficient homogeneity and strength at the imaging region, which is defined outside of the magnet structure, and minimizes the cost of the MRI equipment. [ABSTRACT FROM AUTHOR]

Standard model predictive control is an optimization-based control strategy that can handle multiple control objectives and system nonlinear constraints. However, it typically suffers from the limitation of the uncertainties in practical systems, such as external unknown disturbances and parametric uncertainties. Motivated by aforementioned limitation, in this article, a novel robust model predictive control framework, endowed with the merits of fuzzy logic system and finite control-set model predictive control solution, is proposed. The main objective of this article is to enhance the system robustness while guaranteeing adaptability to different conditions. More specifically, a fuzzy approximation point of view, which has a good potential to approximate the unknown nonlinear functions, is deployed and incorporated into the proposed design, which allows one to explicitly take the system nonlinear dynamics and uncertainties into account. The novelty of the proposed methodology relies on the fact that any prior knowledge and explicit information of system model parameters are not required, thereby resulting in considerable enhancement of robustness. Furthermore, the input-to-state stability of the approximation error system is proven through Lyapunov analysis, and it demonstrates that the estimated errors are uniformly ultimately bounded. Finally, the interest of the proposal is experimentally confirmed for modular multilevel converter. [ABSTRACT FROM AUTHOR]

In recent developments, Cu–Cr–Nb alloys have emerged as promising materials offering a desirable balance between mechanical properties and electrical conductivity, rendering them suitable for intricate high heat flux applications. However, the laser additive manufacturing of Cu–Cr–Nb alloys has encountered notable challenges, primarily stemming from limitations associated with Cu–Cr–Nb alloy powders. Recognizing the pivotal role of powder feedstock in additive manufacturing, this study exerts the utilization of ball milling techniques to tackle pertinent challenges. Specifically, a kind of powder obtained by mechanical ball milling of elemental powders of Cu, Cr and Nb is employed to fabricate Cu–Cr–Nb raw materials, which exhibits a distinctive sesame ball structure and effectively mitigates the inherent high reflectivity of Cu powder. The resulting milled powder represents a notable departure from the conventional reliance on argon gas atomization for Cu–Cr–Nb alloy powder production. Then the study encompasses the fabrication of five distinct Cu–Cr–Nb bulk alloys, ranging from Cu–1Cr–0.5Nb to Cu–12Cr–6Nb, using laser directed energy deposition. The as-printed Cu–Cr–Nb alloys exhibit commendable density, surpassing 99% based on visual analysis, and demonstrate mechanical properties akin to casts achieved through traditional melting and powder metallurgy methods. Notably, Cr2Nb particles were observed within all bulk alloys, with their size increasing proportionally with the Cr + Nb content. Tensile strength demonstrated a positive correlation with Cr + Nb content, while elongation and conductivity exhibited an inverse relationship. These findings hold considerable promise for advancing the utilization of Cu–Cr–Nb alloys in various applications requiring tailored performance characteristics. [ABSTRACT FROM AUTHOR]

With the wide application of motors in deep sea exploration, deep-sea motors require a higher power density and a longer lifetime. Motor lifetime mainly depends on the thermo-mechanical stress (TMS) load on its stator insulation. Unlike normal motors, deep-sea motors are usually filled with oil to compensate for the high pressure generated by seawater, which leads to high additional viscous drag loss. This, combined with the high pressure, will greatly change the TMS distribution and further influence motor insulation lifetime. Thus, the insulation degradation analysis of deep-sea oil-filled (DSOF) motors due to TMS has become important. This paper presents a TMS analytical model of DSOF motor insulation, considering the joint effects of high pressure and motor temperature. The CFD method is adopted to perform motor thermal analysis, considering temperature effects on viscous drag loss. The FEA method is adopted for thermo-mechanical analysis and to verify the analytical model accuracy. Rainflow counting and the Miner fatigue method are adopted to evaluate motor lifetime. Results show that compared with motors working in normal environments, TMS on DSOF motor insulation can be reduced by up to 59.5% due to high pressure and the insulation lifetime can be increased by up to 16.02%. Therefore, this research can provide references for high power density DSOF motor design. [ABSTRACT FROM AUTHOR]

The low-carbon martensitic stainless steel CA6NM is widely used in the impellers of hydroelectric and nuclear power units due to its advantages of high hardness, corrosion fatigue strength, and good fracture toughness. In order to analyze the number of repair welding times on the properties of heat-affected zone (HAZ, the most unstable area of welded joint property) in CA6NM, the microstructure and mechanical properties of HAZ with once-repaired welds (1R) and twice-repaired welds (2R) were tested. Through data analysis, the following conclusions are drawn for welded joints: (1) the grain size of HAZ with a different number of repair welding processes is smaller than that of the base material; (2) the density of texture concentration is reduced and the directionality is not obvious; (3) the density of twins and dislocations are increased; (4) the hardness and impact energy of HAZ of the 1R and 2R specimens are higher than that of the base material. [ABSTRACT FROM AUTHOR]

This article proposes a novel doubly fed flux reversal machine (DF-FRM) with two sets of armature windings wound on both stator and rotor teeth. The proposed DF-FRM can provide much higher torque density than conventional FRM due to better utilization of rotor space. Moreover, the DF-FRM exhibits higher fault tolerance and it can still offer almost the desired output torque of FRM during fault operation, albeit one set of armature windings is malfunctioning. The machine topology as well as operation principles of a 12-stator-slot/14-rotor-slot DF-FRM is introduced and explained. Furthermore, the electromagnetic performances of FRM and DF-FRM with optimized structure aiming at maximum torque density are analyzed and compared using finite element (FE) method. The results show that DF-FRM can yield 60% higher torque density than the conventional FRM. Finally, a prototype is manufactured and tested to validate the FE results. [ABSTRACT FROM AUTHOR]

In this article, two doubly fed (DF) flux-reversal permanent magnet (FRPM) machines with different PM arrangements are proposed, both of which have an additional set of armature winding in their rotor slots to further enhance the torque performance. Together with their one-set armature winding counterparts, comprehensive analyses and comparison among these four machines are conducted. The operation principles and winding configurations of these four machines are firstly introduced. Then, based on finite-element (FE) method, the electromagnetic performances of four machines after optimization with the purpose of maximum torque are compared in terms of no-load, on-load, and over-load capabilities. The results show that the DF-FRPM machine with consequent-pole structure offers the highest average torque and lowest torque ripple, which make it a promising candidate for low-speed and high-torque applications. A prototype machine has been manufactured and the FE results have been verified. [ABSTRACT FROM AUTHOR]

In terms of analytical models used in the initial motor design, the subdomain (SD), complex permeance (CP), and relative permeance (RP) models are among the main ones. This article presents an analysis and comparison of these three models for a wide family of permanent-magnet (PM) machines. The finite-element models are used as a reference for comparison. The fundamental harmonic of the flux-linkage generated by the PMs is selected to evaluate the precision of the analytical model in the initial design step. The number of slots, PM pole-pairs, and ratio of tooth are selected as the key parameters to generate 749 designs for the test. The error distributions and the relationships between the error and the key parameters in the different analytical models are illustrated in this article. The SD and CP models give the best and worst results, respectively. This article also explains how to select the analytical model for the high-torque-density motors. [ABSTRACT FROM AUTHOR]

Gene expression programming (GEP) is one of the most prominent algorithms in function mining. In order to obtain a more accurate function model in configuration parameters-execution efficiency (CP-EE) of map-reduce job in the high-speed railway catenary monitoring system, this paper proposes a novel algorithm, called GEP based on multi-strategy (MS-GEP). Compared to traditional GEP, the proposed algorithm can escape premature convergence and jump out of local optimum. First, an adaptive mutation rate is designed according to the evolutionary generations, population diversity, and individual fitness values. A manual intervention strategy is then proposed to determine whether the algorithm enters the dilemma of local optimum based on the generations of population evolutionary stagnation. Finally, the average quality of the population is changed by randomly replacing individuals, and the ancestral population is traced to change the evolutionary direction. The experimental results on the benchmarks of function mining show that the proposed MS-GEP has better solution quality and higher population diversity than other GEP algorithms. Furthermore, the proposed MS-GEP has higher accuracy on the function model of CP-EE of high-speed railway catenary monitoring system than other commonly used algorithms in the field of function mining. [ABSTRACT FROM AUTHOR]

In this article, a novel doubly-fed flux-switching permanent magnet (DF-FSPM) machine is proposed, whose armature windings are wound on both stator poles and rotor teeth. Different from the conventional FSPM machine in which the armature windings are only located in the stator, the rotor slot area is fully utilized in the DF-FSPM machine to improve the electrical loadings and, thus, the torque density. Moreover, it has the potential of fault-tolerant operation, since it comprises two sets of armature windings, which can work individually. The topology and the operating principle of the machine are introduced with reference to a 12-stator-pole/10-rotor-tooth DF-FSPM machine. The electromagnetic performances of the optimized DF-FSPM machine and its FSPM counterpart machine are compared, including the induced voltage, inductances, torque capability, flux weakening capability, efficiency, and power factor. It shows that the DF-FSPM machine can exhibit about 46.5% higher torque density than the FSPM machine, while its torque production per magnet volume is also improved by about 39.6%. In addition, the efficiency and power factor of the DF-FSPM machine are higher than those of the FSPM machine. Finally, experimental validation is conducted on a prototype machine. [ABSTRACT FROM AUTHOR]

In railway traction applications, the six-step operation of traction inverters is frequently applied at high speed due to the limitation of switching frequency of the converter which is installed in very limited space on the train. Meanwhile, without hardware filters installed, fluctuation components of dc-link voltage will emerge due to the input power ripple introduced by the single-phase rectifier, and can cause significant current and torque ripple in the motor. In this article, a direct torque control scheme for permanent magnet synchronous motor in a six-step operation is proposed to suppress the dc-link voltage fluctuation-induced current and torque ripple without extra hardware. It adjusts the duration of voltage space vectors according to the predicted dc-link voltage waveform six times per fundamental cycle, and minimizes the error between output torque and reference torque at the end of each time. Experimental results on an interior permanent magnet synchronous motor demonstrate that the proposed control can more effectively suppress current and torque ripple than state-of-the-art controls and achieve torque control with high dynamics and accuracy. [ABSTRACT FROM AUTHOR]

This letter focuses on a finite-level-state model predictive control strategy for sensorless three-phase four-arm modular multilevel converter (MMC). The aim of this letter is to enhance the reliability of the whole system under the arm and sensor fault conditions. First, a three-phase four-arm MMC topology, which has a good potential to further improve the fault tolerance ability of the MMC, is presented. Next, a novel control strategy for sensorless three-phase four-arm MMC is proposed by combining an adaptive linear-neuron-based submodule voltage estimation scheme with a currentless sorting-based capacitor-voltage-balancing approach. Thus, the complexity of the control system and the associated costs can be reduced. Finally, comprehensive experiments are conducted to demonstrate the effectiveness and feasibility of the proposed methodology for three-phase four-arm MMC. [ABSTRACT FROM AUTHOR]

In this paper, a novel hybrid permanent magnet variable flux memory machine using two-part rotor is proposed whose rotor comprises an AlNiCo part and a NdFeB part adjacent to each other on the same shaft. With the proposed topology, flexible flux controllability can be achieved since the magnetization state of AlNiCo can be adjusted by a temporary current pulse. The detailed operating principles are described, and the split ratio and some key design parameters are optimized. Then, the electromagnetic performance of the proposed machine with emphases on back electromotive force, flux density, flux-weakening performance, and torque characteristics is investigated. Finally, 3-D finite-element validation is implemented and a machine prototype has been manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

The connected and autonomous vehicle (CAV) is promised to ease congestion in the future with the rapid development of related technologies in recent years. To explore the characteristics of mixed-traffic flow and the dynamic transmission mechanism, this paper firstly detailed the car-following model of different vehicle types, establishing the fundamental diagram of the mixed-traffic flow through considering the different penetration rates and fleet size of CAV. Secondly, this paper constructed the lane-changing judgment mechanism based on the random utility theory. Finally, the paper proposed a lane-level dynamic cell transmission process, combined with a lane-changing strategy and cell transmission model. The effectiveness and feasibility of the model are verified using simulation analysis. This model makes a systematic, theoretical analysis from the perspective of the internal operation mechanism of traffic flow, and the lane-level traffic strategy provides a theoretical basis for balancing urban lane distribution and intelligent traffic management and control. [ABSTRACT FROM AUTHOR]

DC-link voltage fluctuation, originated from the single-phase power supply, has a significant impact on the railway traction drive system. Instead of employing a large LC filter to suppress the fluctuation, software solutions are of more interests, since they do not add additional components to the system. A state-of-the-art feedforward strategy predicts the dc-link voltage pattern based on its repetitive nature and directly modifies the duty cycle fed to the inverter to eliminate the impact of the fluctuation. Yet this strategy requires a symmetrical and consistent pulse pattern. In this paper, a compensation approach for synchronous space vector modulation with multiple pulse patterns is proposed. It utilizes the prediction of the dc-link voltage pattern and, based on the volt–second balancing principle, modifies the switching instants corresponding to different pulse patterns. Simulation and experimental results show that the proposed method can significantly eliminate the impact of the fluctuation. [ABSTRACT FROM PUBLISHER]

This paper presents the first approach to a current control problem for the direct matrix converter (DMC), which makes use of the deep reinforcement learning algorithm. The main objective of this paper is to solve the real-time capability issues of traditional control schemes (e.g., finite-set model predictive control) while maintaining feasible control performance. Firstly, a deep Q-network (DQN) algorithm is utilized to train an agent, which learns the optimal control policy through interaction with the DMC system without any plant-specific knowledge. Next, the trained agent is used to make computationally efficient online control decisions since the optimization process has been carried out in the training phase in advance. The novelty of this paper lies in presenting the first proof of concept by means of controlling the load phase currents of the DMC via the DQN algorithm to deal with the excessive computational burden. Finally, simulation and experimental results are given to demonstrate the effectiveness and feasibility of the proposed methodology for DMCs. [ABSTRACT FROM AUTHOR]

An event-triggered control technique has been developed recently. This technique explicitly reduced the signal transmission by introducing a flexible design of threshold inequalities. It was later extended to event-triggered model-predictive control for power converter systems. In this letter, by incorporating this control technique into an extended state-observer-based finite-control-set model-predictive control framework, we have developed a new model-predictive control architecture for power converter systems with parametric uncertainties. Meanwhile, a novel cost function with respect to the angle minimization term is embedded into this proposal. The novelty of our development lies not only in integrating the event-triggered mechanism with the suggested finite-control-set model-predictive control architecture for facilitating the alleviation of performance deterioration caused by parameter variations and model uncertainties, but also in a multiobjective optimization design that allows the switching frequency in a low value. Finally, extensive simulative and experimental investigations for a modular multilevel converter confirm the interest and the viability of the proposed design methodology. [ABSTRACT FROM AUTHOR]

A novel precipitation strengthening Cu–Fe–Zr alloy was designed and prepared based on the results of calculation of the phase diagram. After solid solutionizing, rolling and aging at 450 °C for 1 h, the alloy had a tensile strength of 515 MPa and an electrical conductivity of 72% IACS. There were two kinds of precipitates in the alloy after aging at 450 °C for 1 h. Fe precipitates with an average diameter of 4.3 nm were present in the deformed grains. Fe2Zr precipitates with an average diameter of 29.1 nm were present in the recrystallized grains. Both the Fe and Fe2Zr precipitates had coherent interfaces with the Cu matrix. The precipitation kinetics and effects on the properties of the alloy were discussed. It is found that the cold rolling enhanced the driving energy of precipitation. The precipitation of Fe and Fe2Zr had a dominant effect on the increase in electrical and mechanical properties of the alloy. [ABSTRACT FROM AUTHOR]

As one of the most widely used contact materials, CuCr alloys put forward higher requirements for their comprehensive properties, especially the resistance to arc erosion under the demand of miniaturization. In this work, a hetero-structured CuCr/Cu contact with metallurgical bonding was successfully fabricated by high-speed laser cladding. The fabrication process was investigated, and the optimized process window was determined. The CuCr layer is free of cracks and contains about 48 wt.% Cr. The average size of Cr particles is 0.82 μm, and the Cu grains grow epitaxially across the CuCr/Cu interface. The shear strength of the interface is as high as 223.3 MPa. The hardness of the aged CuCr layer is much higher than the commercial CuCr alloy, while both materials have similar electrical conductivities. The aged CuCr/Cu contact has the lower arc erosion rate and the wear rate than the commercial CuCr contact. The excellent performances of the CuCr/Cu contact are attributed to the hetero-structure design and the metallurgical bonding. [ABSTRACT FROM AUTHOR]

In this letter, a neural predictor-based dynamic surface predictive control framework, endowed with the merits of adaptive dynamic surface control and finite control-set model predictive control, is proposed where the estimation of neural predictor is incorporated to identify the system dynamics and lumped unknown uncertainties. The key features of the proposal are that, first, the issue of “explosion of complexity” inherent in the classical back-stepping control is avoided, second, the model uncertainties and disturbances are explicitly dealt with, and, third, the tedious determination procedure of weighting factors is removed. These features lead to a much simpler adaptive predictive control solution, which is convenient to implement in applications. Furthermore, a Lyapunov function is constructed, and the stability analysis is given. It demonstrates that all signals in the closed-loop system are uniformly ultimately bounded. Finally, this proposal is experimentally assessed, where the performance evaluation of steady-state and transient-state confirms the availability of the proposed solution for modular multilevel converter. [ABSTRACT FROM AUTHOR]

The subcutaneous implant, which can realize on-demand drug release, is used for the treatments of some chronic diseases such as chronic pain, diabetes, and osteoporosis. This paper proposes a new type of wireless actuator for potential use in active implantable drug delivery systems. The proposed structure suits both wireless power well, which requires far-field flux traveling and receiving, and actuator design, which should take advantage of strong local magnetic fields. The mover in the actuator generates mechanical movement when power is transferred wirelessly to the actuator, and the mover restores to its original position when the wireless power stops. The maximum oscillation amplitude of the mover can be achieved when the ON and OFF frequency of the wireless power transfer is equal to the mechanical resonant frequency of the mover. Experimental results on a prototype actuator with 20 mm in diameter and 10.3 mm in thickness are given for validating the proposed new idea. [ABSTRACT FROM AUTHOR]

The degradation of mechanical components is non-stationary and their degradation level can only be detected through offline discrete inspection in most cases. Aiming at the effect of the non-stationary feature and the delay of state detection caused by discrete inspection on long-run operation cost, this paper focuses on proposing an optimal inspection-based maintenance policy for three-state mechanical components subject to competing failure modes. A double-Wiener-process degradation model is established to describe the two operation states, which includes two Wiener process models under the same law but with different parameters. In addition, a preventive maintenance policy including a degradation threshold, an age threshold and a degradation control limit are adopted. A five-scenario probability-based model is proposed to describe the state evolution during one inspection interval and then the analytical model of the impact of delay on detecting state-transition and degradation-level on preventive maintenance policy is proposed. An optimization model of an inspection- based maintenance is established. Finally, sensitivity analysis in terms of the decision variables for state-transition time distribution and parameters in wear-out state is carried out based on numerical examples and the efficiency and superiority of the proposed policy is demonstrated by comparing with the current two-state maintenance policy. [ABSTRACT FROM AUTHOR]

This letter proposes a data-driven iterative learning predictive control architecture for power converters. The main objectives of this letter are to enhance the robustness and remain the high performance of finite control-set model predictive control (FCS-MPC) under unmodeled dynamics and parameter mismatch conditions. More specifically, an iterative dynamic linearization technique is utilized to equivalently reformulate the nonlinear power converter system at each operating point. Based on this, a model-free adaptive control scheme is presented to iteratively determine the optimal control actions. Due to the incorporation of iterative learning control and data-driven concept into the FCS-MPC framework, the effect of parameter perturbations can be alleviated in the proposed method, while creating a positive effect on the tracking error. Finally, a convergence analysis is provided and experimental investigations on a three-level neutral-point-clamped (NPC) converter confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

As an important equipment for high-speed railway (HSR) to obtain electric power from outside, the state of the pantograph will directly affect the operation safety of HSR. In order to solve the problems that the current pantograph detection method is easily affected by the environment, cannot effectively deal with the interference of external scenes, has a low accuracy rate and can hardly meet the actual operation requirements of HSR, this study proposes a pantograph detection algorithm. The algorithm mainly includes three parts: the first is to use you only look once (YOLO) V4 to detect and locate the pantograph region in real-time; the second is the blur and dirt detection algorithm for the external interference directly affecting the high-speed camera (HSC), which leads to the pantograph not being detected; the last is the complex background detection algorithm for the external complex scene "overlapping" with the pantograph when imaging, which leads to the pantograph not being recognized effectively. The dirt and blur detection algorithm combined with blob detection and improved Brenner method can accurately evaluate the dirt or blur of HSC, and the complex background detection algorithm based on grayscale and vertical projection can greatly reduce the external scene interference during HSR operation. The algorithm proposed in this study was analyzed and studied on a large number of video samples of HSR operation, and the precision on three different test samples reached 99.92%, 99.90% and 99.98%, respectively. Experimental results show that the algorithm proposed in this study has strong environmental adaptability and can effectively overcome the effects of complex background and external interference on pantograph detection, and has high practical application value. [ABSTRACT FROM AUTHOR]

The consequent-pole (CP) Vernier permanent-magnet (VPM) machine has been developed over the last decade. In VPM machine, the CP structure can produce considerable torque with a half volumn of the PMs compared with the regular structure, so the cost is reduced and the mechanical strength is increased. In this paper, an improvement of chamfering structure on a CPVPM machine is proposed to alleviate the flux leakage and increase the torque density. The chamfered structure is easily machined and will not influence the robustness of the rotor. The comparison results show that under the same volume and copper loss constraint, the proposed structure has smaller cogging torque, smaller torque ripple, larger torque density and larger power factor. [ABSTRACT FROM AUTHOR]

The high-frequency electromagnetic noise caused by a frequency converter power supply has become the main composition of the vibration and noise of frequency-converter-driven PMSMs. Determining how to reduce this kind of noise is very important to improve motor performance. This paper analyzes the frequency characteristics of the high-frequency noise generated by an inverter, using the magnetic circuit analysis and Maxwell tensor methods. The switching frequency and the natural frequencies of the main modes are optimized according to the modal characteristics of the motor in order to reduce the vibration and noise of the motor. The results show that the high-frequency electromagnetic vibration and noise generated by the inverter is mainly caused by the high-frequency switching harmonic current. The frequencies of the vibration and noise are related to the switching frequency and the modulation wave frequency. At the same time, the simulation calculation of the natural frequencies of the main modes and the noise spectrum obtained from the experiment provide direction for the optimization of the vibration noise near the switching frequency. The switching frequency optimization and the natural frequency optimization based on the main modes of the motor can effectively reduce vibration and noise. This work has certain reference significance for the design of low-noise PMSMs. [ABSTRACT FROM AUTHOR]

This article proposes a novel data-driven neural predictors-based robust finite control-set model predictive control (FCS-MPC) methodology for power converters, which aims to enhance the robustness of the control system and the flexibility of multiple control objectives. To be specific, the data-driven predictors-based neural network solution, which has a good potential to estimate the unknown nonlinear system dynamics by deploying real-time and historical data, is incorporated into the proposed design with a cost function derived intuitively from Lyapunov’s control theory. The key feature of this work is that the undesired effects of the uncertainties and the complex multiobjective optimization procedure can be explicitly dealt with, without involving accurate modeling information and weighting factor combinations, while guaranteeing adaptability to unknown nonlinear system dynamics, model variations, and environment changes. Finally, the stability analysis is given, and the effectiveness of the proposed FCS-MPC methodology is verified analytically and confirmed by comprehensive results that prove the theoretical investigations for active front-end modular multilevel converter. [ABSTRACT FROM AUTHOR]

Cathode ablation shortens the cathode lifetime and hinders the development of arc heaters. Surface-modified Zr/Cu cathodes realize combinations of ablation-resistant surface and conductive matrix, while the cracking problem limits their applications. In this work, Nb cladding and Zr cladding were prepared on Cu matrix successively. The Nb cladding was effective in serving as a blocking layer against diluting of Cu and suppressing forming Cu Zr intermetallics. The surface Zr content reached as high as 85.6 at.% and no Cu Zr intermetallic was detected inside the cladding. Besides, the intermediate Nb cladding contributed to tight interlayer metallurgical bonding. The arc discharge behaviors of bi-layered Zr/Nb/Cu cathodes were investigated compared to Cu cathodes. The bi-layered Zr/Nb/Cu cathode exhibited an improved arc discharge homogeneity with shallow and smooth ablated areas. The cathode ablation rate (1.30 μg C−1) was 37.5 % lower than that of Cu cathodes. The Zr/Nb/Cu layered structure improved the cathodic arc ablation-resistance without cracking, which guaranteed its application in large-area manufacturing process. [Display omitted] • Nb and Zr layers were successively prepared on Cu substrate through laser cladding. • No detrimental Cu Zr intermetallic was formed among the claddings. • High Zr content (85.58 at.%) was realized, beneficial for discharge homogeneity. • Bi-layered Zr/Nb/Cu arc discharges homogeneously with a lower ablation rate than Cu. [ABSTRACT FROM AUTHOR]

Surface roughness and mechanical strength are significant properties of copper foils for printed circuit boards. Stable performance is highly required for the copper foils across the whole roll (length of ~ 7000 m) in industrial manufacture. In this work, the main attention is focused on the performance stability of the obtained 18-μm copper foils by different additives. The available concentration range of saccharin sodium was expanded and the performance stability of copper foils was improved by the co-addition of hydroxyethyl cellulose or bis-(3-sulfopropyl)-disulfide. The copper foils prepared under the condition of bi-component additives remained low roughness and high tensile strength, due to the uniform surface microtopography related to the continuous high relative intensity of (220) crystal face varying with additive concentration. It is found that the change of the electrochemical reaction caused by the variation of the saccharin sodium concentration was weakened by the different adsorption behaviors of those introduced additives. The bi-component additives expanded the concentration of each additive and the stability of the copper foil products was improved as a result. It is advantageous to industrial applications for higher production efficiency, higher product quality, and lower production cost, brought by bi-component additives. [ABSTRACT FROM AUTHOR]

With the wide application of inverter-fed motors (IFMs), it is necessary to monitor the groundwall (GW) insulation status to guarantee the reliable operation of motor drive system. This article first proposes a mathematical model of leakage current in IFM to analyze its time domain characteristics, and then an online GW insulation monitoring method is proposed based on the transient characteristics of leakage current. By using the initial oscillation amplitude, oscillation period, and attenuation time of leakage current, the phase, position, and severity of GW insulation degradation can be identified. The proposed method is validated using an IFM, and the experimental results agree well with theoretical analysis. [ABSTRACT FROM AUTHOR]

Vernier permanent-magnet machines have been attracted more and more attention because of their high torque density. In this paper, the sensorless control strategy of the novel axially magnetized Vernier permanent-magnet (AMVPM) machine is presented. First, the inductance non-linearity is investigated under different load conditions. Second, the mathematical model is established in cooperation with the finite element method. After that, the back electromotive force based sensorless control strategy is developed according to the state equation of the motor. In the sensorless drive, the model reference adaptive system (MRAS) technique incorporated with the inductance non-linearity is used for the speed estimation. The modified control strategy not only increases the stability but also improves the dynamic response of the system. Finally, the simulation results show that the modified MRAS is of high estimation precision, and the AMVPM machine can be well controlled, and the experimental results validated the theoretical design process. [ABSTRACT FROM AUTHOR]

This article investigates the influences of end turn length on consequent-pole Vernier permanent-magnet (CPVPM) machines. Four structures are compared to discuss the tradeoff between the end turn length and the gear ratio, and nine structures are compared to discuss the tradeoff between the end turn length and the winding factor. It is found that, when the end turn length is taken into account, the CPVPM machines with concentrated winding have the potential to produce larger torque than those with the distributed winding. Motivated by the above observations, an integral slot concentrated winding CPVPM machine is proposed to be a promising candidate in VPM machine family, which has high torque capability, small end turn length, good fault tolerance, and desired power factor. The influences of key design parameters are investigated. The machine prototype is manufactured, and the electromagnetic performances are experimentally validated. [ABSTRACT FROM AUTHOR]

This article analyzed and compared the complex permeance model (CPM) and nonlinear analytical model (NAM) for surface-mounted permanent magnet (SPM) motor using a voltage source inverter (VSI). For linear CPM, the slotting effect is represented using the improved complex permeance function that describes the real slot shape rather than infinitely deep slot. NAM is extended from CPM and it replaces the magnetic potential drop of stator iron by the equivalent virtual current in the slot-opening and tooth-tip to account for the nonlinearity effect. The nonlinear inductance of SPM motor including the main phase inductance, slot leakage inductance, tooth-tip leakage inductance, and end winding leakage inductance is calculated using the frozen permeability method, which is the key to solve the electric circuit with VSI. The instantaneous back electromotive force (EMF) is calculated from the nonlinear back EMF coefficient and the back EMF neglecting iron nonlinearity. The electromagnetic torque obtained from motor model is used in the mechanical model and then the rotational speed and rotor position are obtained for the electric circuit model. Hence, the iterative solving process for the motor system is established to calculate the transient performance of SPM motor using VSI. Compared with CPM, NAM can greatly improve the calculation accuracy, which is also validated by both finite-element model and experiment. Besides, the proposed NAM is computationally efficient, which is useful for both motor design and motor control. [ABSTRACT FROM AUTHOR]

This paper presents an exact analytical subdomain model of slotted permanent-magnet (PM) machines, taking into account the diffusion effect. The model gives the magnetic fields, both the eddy currents and the power losses in the PM, the instantaneous and average torque. In the model, eddy currents are not assumed to be resistance limited, contrary to what is done in the conventional exact subdomain models of the slotted machines. The model is hence general and valid both at low and high frequencies. It shows that it is possible to calculate the power losses in the PMs, only knowing the fields in the air gap. The model takes into account the presence of tooth-tips. The comparison with conventional exact subdomain models shows that the model presented in this paper is more accurate. The model is validated using the finite-element methods. [ABSTRACT FROM AUTHOR]

Magnetic gears (MGs), a promising alternative to conventional mechanical gear boxes, have gained growing attention in the last decade. This paper proposes a novel topology of flux-focusing MG, which makes use of both axial and transverse magnetic fluxes. Important geometrical parameters are optimized using a sequential parametric sweeping analysis. Performances are validated by a 3-D finite-element method and compared with the existing MGs. The result indicates that by reducing the saturation in soft magnetic materials and the flux leakage, the new topology has a significantly high torque density within a wide length–diameter ratio. [ABSTRACT FROM AUTHOR]

Traditional predictive control schemes dominated the research field of numerous power electronic applications over the past few years, since they usually lead to control solutions with good dynamic and steady results. However, these solutions strongly depend on the available knowledge of the control system (e.g., accurate modeling information), which often results in the lack of robustness in the presence of parametric uncertainties. Furthermore, unnecessary energy loss heavily correlates with high switching frequency, which directly affects efficiency. Aiming to cumbersome aforementioned scarcities, this letter is concerned with a novel approach to the controller design for a modular multilevel converter, which makes use of event-triggered neural-predictor-based finite-control-set model-predictive control methodology under low-switching-frequency operation. The salient feature of the proposed controller is that the uncertainties and unnecessary energy loss in practical systems can be explicitly dealt with, while keeping the switching frequency in a low value. Finally, steady-state and transient-state performance tests together with the analysis of the simulation and experimental results confirm the interest of the proposal, and the results found are promising and motivate further research in this field. [ABSTRACT FROM AUTHOR]

This work aims to improve the combined flow and thermal network (CFTN) accuracy for radially air-cooled generators by investigating the possible error stemming from the flow part. The nonlinear resistance characteristics of the T-junction dividing flow are first time considered for such cooling arrangement, which is achieved by employing the Gardel equations and the blend equation as the governing equations. Compared with the CFD model results as the benchmark, the nonlinear CFTN predicts an accurate flow rate in the radially extended airducts, making only 9% root mean square (rms) error for all the airducts. On the contrary, the linear CFTN fails to obtain a reliable flow distribution, as the rms error is as large as 34%. As a result, the nonlinear CFTN improves the accuracy of the maximum winding temperature by 6.4% over the linear CFTN and gives a more reasonable temperature gradient in the axial direction. Furthermore, the relative difference between the linear and nonlinear CFTNs is found to be even larger in the following conditions: large cooling air flow rate, wide airgap, low slot fill factor, and large airduct number. The proposed nonlinear CFTN modeling approach is also validated against experimental measurements for a prototype. The modeled temperatures match well with the measurements at different axial positions. According to the aforementioned findings, the nonlinear CFTN modeling approach is considered to be a reliable thermal analysis tool for the radial air-cooling arrangement. [ABSTRACT FROM AUTHOR]

This article investigates the influence of start rotor position on three-phase short-circuit (3PSC) current in dual three-phase surface-mounted permanent magnet (DTPSPM) machines. For DTPSPM machines with symmetrical winding configurations, the 3PSC analytical model considering PM flux linkage harmonics is developed. It shows that the variations of 3PSC peak current with start rotor position mainly repeat every multiple of π/3 in an electrical period due to the fifth and seventh harmonics. The start rotor positions causing the largest 3PSC peak currents heavily depend on the harmonic magnitudes and phases. Then, the 3PSC analytical model for DTPSPM machines with asymmetric mutual inductances in one winding group is developed. It shows that the variations of 3PSC peak current with start rotor position mainly repeat every multiple of π. For winding configurations with smaller Mac, Mbc, and Mab, start rotor positions causing the largest d-axis peak current are about π/6+kπ, π/2+kπ, and 5π/6+kπ (k = 1, 2, 3…), respectively. To obtain the largest q-axis peak current, such start rotor positions are about 7π/24+kπ, 5π/8+kπ, and 23π/24+kπ (k = 1, 2, 3…). In addition, the influence of rotor speed and asymmetric level is discussed. Finally, finite-element simulation is performed and experiments are conducted to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual-armature (DA) flux reversal permanent magnet (PM) machine with halbach array magnets in the stator slot opening is proposed, which is abbreviated as DA-Halbach machine. Besides the stator armature windings, another set of windings is added in the rotor slots to further enhance torque performance via fully utilizing the rotor space. The influences of major geometric parameters on torque performance are investigated. Both DA-Halbach machine and conventional Halbach machine are optimized with the goal of maximum torque under the same copper loss using finite element (FE) method. The electromagnetic performance of two optimized machines are compared, the results show that the proposed DA-Halbach has larger torque and smaller torque ripple than conventional Halbach machine. When compared with surface-mounted PM machines, the proposed DA-Halbach machine still show better torque performance. [ABSTRACT FROM AUTHOR]

This letter investigates the possibility of deploying a novel finite control-set model predictive control solution for solving the ongoing research challenges in predictive control regulated modular multilevel converter, i.e., model parameter sensitiveness and excessive computational burden as well as weighting factors selection. Specifically, it is realized by cascading a predictor-based neural network design, which enables a smooth and fast identification of system dynamics, and a computationally efficient finite-set predictive control, which is responsible for simplifying the rolling optimization and reducing the computational complexity. The main contribution of the proposed methodology relies on the fact that no knowledge of any model parameters and weighting factors in whole control process are required, which leads to a significant enhancement in the robustness and reliability of the control system in the presence of parametric uncertainties, while remaining computationally feasible. Finally, the stability analysis is given, and the proposed methodology is experimentally assessed for modular multilevel converter, where steady-state and transient-state performance tests confirm the interest of the proposal. [ABSTRACT FROM AUTHOR]

Doubly salient permanent magnet (DSPM) machines suffer from a large torque ripple due to unbalanced three phases, nonsinusoidal-phase back electromotive force, large cogging torque, etc. To suppress the torque ripple, this article proposes a new type of stator/rotor-pole number combinations. The number of stator poles is 18, while the number of rotor poles differs from the conventional counterpart (i.e., 12) by one. The DSPM machines with different stator/rotor-pole number combinations are globally optimized under the fixed copper loss and machine envelope. It shows that compared with the 18/12 stator/rotor-pole DSPM machine, the torque ripples of 18/11 and 18/13 stator/rotor-pole DSPM machines are reduced significantly, while their torque densities remain almost the same. An 18/13 stator/rotor-pole DSPM machine is built and tested so as to experimentally verify such improvement. [ABSTRACT FROM AUTHOR]

Abstract: The upper and lower bounds of the linear variance decay (LVD) dimension density are analytically deduced using multivariate series with uncorrelated and perfectly correlated component series. Then, the normalized LVD dimension density () is introduced. In order to measure the complexity of a scalar series with , a pseudo-multivariate series was constructed from the scalar time series using time-delay embedding. Thus, is used to characterize the complexity of the pseudo-multivariate series. The results from the model systems and fMRI data of anxiety subjects reveal that this method can be used to analyze short and noisy time series. [Copyright &y& Elsevier]

High-strength and high-conductivity Cu alloys are widely required in railway and lead frames. As a conventional element, Si reduces the electrical conductivity of Cu alloys significantly. In this work, Co is introduced into Cu–Si alloys for improving the mechanical and electrical properties. The results show that the Co-containing alloy possesses much higher hardness and conductivity than the Co-free alloys. The added Co reacts with Si to produce high density of CoSi nanoprecipitates that have a semi-coherent interface with the Cu matrix in the aged Cu–Co–Si alloy. The presence of CoSi nanoprecipitates is sufficiently verified by X-ray, energy-dispersive spectrometer and electron diffraction pattern. The formation of CoSi nanoprecipitates can pin dislocation motion, prevent the recrystallization and reduce the Si solute concentration in the Cu matrix. The effects of precipitate hardening and precipitation purification from CoSi phase result in the better performance of the aged Co-containing alloy than the Co-free alloys. The success in Cu–Co–Si alloys opens a door to overcome the disadvantage of Si alloying in Cu-based alloys. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a novel valley V2 control scheme for interleaved boost converter is presented to improve the transient response performance of system and realize the current sensorless control, and its stability is analyzed by a nonlinear analysis technique. In this proposed methodology, the current sensor is saved by the proposed control signals sharing algorithm, and the nonlinear dynamics is investigated by employing a nonlinear analysis method based on the Monodromy matrix. Meanwhile, the information of the converter parameters' influence on the system stability can be obtained by calculating the Monodromy matrix of switching event. It is worth mentioning that the location of eigenvalues of this matrix can be utilized to analyze the relationship between converter parameters and stability margin. Furthermore, by adopting the knowledge gained from this analysis, an auto‐tuning resonant parametric perturbation is proposed to ensure an excellent performance of converter with an extended range of stable operation. Finally, the simulation and experimental results are presented to verify the effectiveness and theoretical analysis of the proposed method. [ABSTRACT FROM AUTHOR]