Search Results (122)

Bidirectional Interleaved Converters (BICs) are widely used in Battery Energy Storage Systems (BESSs) due to their modular structure, high efficiency, and reduced current ripple. However, under partial-load operation, conventional control strategies with fixed or purely current-based phase shedding repeatedly activate the same converter branches, resulting in increased switching losses, thermal imbalance, and uneven aging of power semiconductors. This paper proposes a temperature-adaptive control strategy for BICs aimed at improving light-load efficiency while actively balancing thermal stress between converter branches. The approach combines a current-adaptive phase-shedding algorithm with a temperature-based branch rotation mechanism, where real-time transistor junction temperature is used as the primary decision variable for branch activation and deactivation. An electro-thermal real-time simulation model of a two-branch BIC is developed using the Controller Hardware-in-the-Loop (CHIL) methodology in the Typhoon HIL environment. The proposed control strategy is validated through real-time CHIL experiments in both boost and buck operating modes under representative battery load profiles. The results demonstrate a reduction in average and peak transistor junction temperatures, improved thermal distribution between converter branches, and more uniform branch utilization, while preserving stable current regulation and power flow. The presented method represents a practical extension of conventional phase-shedding techniques and provides an implementation solution for improving efficiency and reliability of BICs in BESS applications. Full article

The rapid increase in electric vehicle (EV) adoption necessitates advanced charging infrastructures that are compact, efficient, and capable of bidirectional power flow for both vehicle-to-grid (V2G) and grid-to-vehicle (G2V) operation. Unlike traditional silicon and SiC-based chargers, this work introduces a Ga₂O₃-based bidirectional smart charging system integrated with a hybrid energy storage system to deliver superior performance. A coordinated control strategy is developed to regulate power sharing between a supercapacitor and a lithium-ion battery pack, thereby extending battery life, reducing current stress, and providing effective transient support. This hybrid system employs PI-based control and advanced modulation techniques to minimize current ripple, maintain the unity power factor, and ensure stable DC-link voltage regulation. MATLAB/Simulink simulation results demonstrate robust DC-link stability, smooth bidirectional power transfer, and very low total harmonic distortion. Comparative loss analysis shows that Ga₂O₃ MOSFETs offer significantly lower conduction and switching losses, enabling efficiencies up to 98% across the rated operating range. These results confirm that the proposed charger is highly suitable for next-generation EV infrastructures requiring high power density, reliable grid interfacing, and enhanced operational longevity. A hardware prototype was also developed and tested, with experimental results validating reliable grid-side performance and efficient energy sharing under typical operating conditions. Full article

Proton exchange membrane fuel cells (PEMFCs) are attractive energy sources for clean and efficient power generation; however, their nonlinear characteristics and sensitivity to operating condition variations make maximum power point tracking (MPPT) a challenging control problem. Conventional MPPT techniques often exhibit slow convergence, steady-state oscillations, and degraded performance under dynamic fuel flow variations. This paper proposes a machine learning–driven MPPT control strategy for a PEMFC system integrated with a DC–DC boost converter. The MPPT problem is formulated as a supervised classification task, where machine learning classifiers generate duty-cycle commands to regulate the converter and ensure operation at the maximum power point. A detailed PEMFC–converter model is developed in MATLAB/Simulink-2025b, and a dataset of 3000 labeled samples is generated under varying fuel flow conditions. Several classification algorithms, including decision trees, support vector machines (SVM), k-nearest neighbors (kNN), and ensemble learning methods, are systematically evaluated within an identical simulation framework. Simulation results show that the proposed machine learning-based MPPT controller significantly improves dynamic and steady-state performance. Ensemble Boosted Trees achieve the best overall response with a settling time of approximately 32 ms, peak power overshoot below 4.5%, and steady-state power ripple limited to 1.5%. Quadratic SVM and weighted kNN classifiers also demonstrate stable tracking behavior with power ripple below 2.1%, while overly complex models such as Cubic SVM suffer from large oscillations and reduced accuracy. These results confirm that classification-based machine learning offers an effective, fast, and robust MPPT solution for PEMFC systems under dynamic operating conditions. Full article

The increasing demand for high-power electric vehicle charging systems with Vehicle-to-Grid (V2G) capability highlights the need for modular, scalable power converters. This paper proposes a hierarchical control strategy for a high-power, multi-port electric vehicle charging station. The system, based on a Series-Parallel Modular Multilevel Converter (SP-MMC) with isolated modules, is managed by a coordinated control strategy that integrates proportional-integral-resonant regulators, nearest-level control with voltage sorting, and single-phase-shifted modulation. The proposed system enables simultaneous, independent regulation of multiple bidirectional, isolated direct current ports while maintaining grid-side power quality and internal variables of the SP-MMC. The proposed control is validated using real-time Model-In-the-Loop (MIL) simulations that include sequential port activation, bidirectional power flow, and charging operation. MIL results demonstrate stable operation with controlled DC-link voltage ripple, accurate per-port current tracking, and near-unity grid power factor under multi-port operation. Full article

Functional steel surfaces engineered through tailored micro-nano structures are increasingly vital for various applications such as high-performance aerospace components, energy conversion systems and defense equipment. Femtosecond laser filament processing is a recently proposed remote fabrication technique, showing the capability of fabricating micro-nano structures on irregular and large-area surfaces without the need of tight focusing. Nevertheless, the mechanisms underlying the formation of filament-induced structures remain not fully understood. Here we systematically investigate the formation mechanisms of filament-induced micro-nano structures on stainless steel surfaces by processing stainless steel in three manners: point, line, and area. We clarify the decisive role of the unique core–reservoir energy distribution of the filament in the formation of filament-induced micro-nano structures, and reveal that ablation, molten metal flow, and metal vapor condensation jointly drive the structure evolution through a dynamic interplay of competition and coupling, giving rise to the sequential morphological transitions of surface structures, from laser-induced periodic surface structures to ripple-like, crater-like, honeycomb-like, and ultimately taro-leaf-like structures. Our work not only clarifies the mechanisms of femtosecond laser filament processed morphological structures on steels but also provides insights onto intelligent manufacturing and design of advanced functional steel materials. Full article

Traditional diode-based rectifiers (TDRs) in railway traction substations (TSSs) are inefficient at handling bidirectional power flow and cannot recover regenerative braking energy (RBE). Replacing these conventional systems with reversible traction substations (RTSSs) requires detailed modeling, extensive simulations, and validation using real data. This paper presents a DT-oriented real-time modeling and Hardware-in-the-Loop (HIL) platform for the analysis and performance assessment of RTSSs in DC railway systems. The integration of interleaved PWM rectifiers enables bidirectional power flow, allowing efficient RBE recovery and its return to the main grid. Modeling railway networks with moving trains is complex due to nonlinear dynamics arising from continuously varying positions, speeds, and accelerations. The proposed approach introduces an innovative multi-train simulation method combined with low-level transient and power-quality analysis. The validated DT model, supported by HIL emulation using OPAL-RT, accurately reproduces real-world system behavior, enabling optimal component sizing and evaluation of key performance indicators such as voltage ripple, total harmonic distortion, passive-component stress, and current imbalance. The results demonstrate improved energy efficiency, enhanced system design, and reduced operational costs. Meanwhile, experimental validation on a small-scale RTSS prototype, based on data from the Italian 3 kV DC railway system, confirms the accuracy and applicability of the proposed DT-oriented framework. Full article

The present study concerns the re-scour of a submarine pipeline after its scour-sagging-burial by modeling a tilting pipeline with varying embedment along the pipeline axis. The effect of the tilting angle on characteristics of three-dimensional scour was investigated, in terms of the scour topographies, the scour depth, as well as the scour propagation along the pipeline. Two previously undetected scour topographies, i.e., sand ripples that extend along the pipeline axis in the downstream direction of the pipeline and scour pits below the pipeline perpendicular to the pipeline axis, were found to significantly affect the development of the scour propagation and the scour depth. The whole scour propagation along the pipeline can be divided into the rapid scouring phase and the slow scouring phase. The transition point between the two phases takes place at the initial embedment-to-diameter ratio of 0.3. With the increase of the incident angle from 0° to 45°, the scour propagation rate increases during the rapid scouring phase but decreases during the slow scouring phase. A predictive model of the scour propagation rate was established based on the erosion characteristics of sediment and the shear stress magnification factor under the pipeline. The newly predictive model of scour propagation rate is found to provide satisfactory results for a tilting submarine pipeline under different flow incident angles. Full article

The Modular Multilevel Converter (MMC) has gained significant popularity over the past decade due to its versatility. The MMC features have been leveraged in numerous fields, including high-voltage DC transmission, electric vehicle power trains, motor drives, and wind energy conversion. In controlling the MMC, the circulating current (i.e., the current flowing through both the upper and lower converter arms without delivering power to the load) has consistently been the most critical variable. In early applications, it was perceived as a source of losses, but more recently, it has become evident that injecting a specific current could reduce voltage and energy ripples. This paper presents a theoretical framework, based on time-scale analysis, useful for modeling and controlling MMCs. The new approach is adopted for generating the circulating current reference, which is expressed as a linear combination of orthogonal functions. The goals are to decouple the control of the voltages of the upper and lower converter arms and manage additional harmonic components of the circulating current for voltage ripple reduction on module capacitors. The simulations and experimental results demonstrate the effectiveness of the proposed control strategy. Full article

Traditional symmetric voltage multiplier-based structures offer low current stress and high scalability. However, the equalization current flowing into each energy storage cell must overcome four diode voltage drops per switching cycle, significantly degrading energy transfer efficiency. A compact integrated equalizer based on multi-stacked buck-boost converters for large-scale energy storage systems is proposed. By replacing diodes with inductors, the design achieves high-efficiency cell balancing even at low cell voltages. The integrated design leverages the boost circuit’s inherent current ripple for driving the balancing system, eliminating extra switches and minimizing size and cost. Additionally, it provides independent balancing channels for each cell, eliminating equalization current superposition. This reduces cell current stress while enabling large-scale system balancing. Experimental validation on an eight-cell setup demonstrated successful balancing with 87.5% system efficiency. Full article

For power electronic transformer (PET) based Modular Multilevel DC-Link Based T-type Converters (MMDTC) with Double Active Bridges (DABs) (namely DABs-based MMDTC-PET), the sub-module capacitor voltages exhibit relatively large ripples. To reduce the voltage ripple of sub-module capacitors, this paper proposes a novel MMDTC-PET structure that utilizes the Three-Port Active Bridges (TABs) to replace the DABs as the isolation stage (TABs-based MMDTC-PET). When the two full bridges of the TAB on the primary side adopt identical phase-shift modulation, the two sub-module capacitors within the upper and lower arms form a parallel connection. This configuration endows the sub-module capacitors with switched-capacitor characteristics, suppressing voltage ripple in the sub-module capacitors and enabling power ripple flow to the secondary side. Meanwhile, by leveraging the characteristic that the AC power components of the upper and lower arm sub-modules have equal amplitudes but opposite phases, these AC power components are mutually canceled on the secondary side of the TAB. Simulation and experimental results verify the effectiveness of the proposed scheme. Full article

Hastelloy X exhibits outstanding thermal fatigue resistance, making it a promising material for repairing 50CrVA landing gear via directed energy deposition (DED). However, the substantial differences in composition and thermophysical properties between 50CrVA and Hastelloy X pose challenges by affecting interfacial microstructure and surface quality. This study investigates the effect of DED process parameters (laser power p, powder feed rate f, scanning speed v, and overlap rate) on the dilution ratio (η), microscopic morphology, surface flatness (ζ), and porosity of Hastelloy X claddings on a 50CrVA substrate. An optimization methodology integrating thermal–flow coupled simulation models and orthogonal experiments is developed to fabricate high-quality claddings. Furthermore, the corrosion–wear performance of the claddings is evaluated. The results indicate that the η of a single track increases with higher p or lower f, while it first increases and then decreases with the increase in v. Ablation marks tend to occur at excessive p or insufficient f, while low v causes surface ripples. The ζ of a single layer initially improves and subsequently deteriorates with increasing overlap rate. Porosity is significantly influenced by p and f. The optimal p, f, v, and overlap rate are 1600 W, 2.4 g/min, 240 mm/min, and 55%, respectively. The wear resistance of the cladding is nearly identical to that of the substrate, while corrosion resistance is significantly improved. This work provides a theoretical foundation for high-performance repair of 50CrVA landing gear in aircraft. Full article

Magnetically levitated artificial hearts impose stringent requirements on the blood-pump motor: zero friction, minimal heat generation and full biocompatibility. Traditional mechanical-bearing motors and permanent-magnet bearingless motors fail to satisfy all of these demands simultaneously. A bearingless switched reluctance motor (BSRM), whose rotor contains no permanent magnets, offers a simple structure, high thermal tolerance, and inherent fault-tolerance, making it an ideal drive for implantable circulatory support. This paper proposes an 18/15/6-pole dual-stator BSRM (DSBSRM) that spatially separates the torque and levitation flux paths, enabling independent, high-precision control of both functions. To suppress torque ripple induced by pulsatile blood flow, a variable-overlap TSF-PWM-DITC strategy is developed that optimizes commutation angles online. In addition, a grey-wolf-optimized fast non-singular terminal sliding-mode controller (NRLTSMC) is introduced to shorten rotor displacement–error convergence time and to enhance suspension robustness against hydraulic disturbances. Co-simulation results under typical artificial heart operating conditions show noticeable reductions in torque ripple and speed fluctuation, as well as smaller rotor radial positioning error, validating the proposed motor and control scheme as a high-performance, biocompatible, and reliable drive solution for next-generation magnetically levitated artificial hearts. Full article

With China’s emergence as a major global economy, its involvement in tackling climate change and fostering sustainable growth has garnered considerable focus. What impact does global direct investment have on carbon emissions within Belt and Road economies? This study innovatively utilizes a quantile regression model to analyze the varied impacts of international direct investment across distinct carbon emission quantiles, further delving into the conditional probability distribution of the dependent variable to provide a strong theoretical basis for precise policy-making by relevant departments and integrating time and space delays in examining the effects of carbon reduction strategies within the Belt and Road Initiative. Furthermore, this study aims to concentrate its research efforts on the host nations. Findings from this study indicate that global direct investments could escalate carbon emissions in economies with lower carbon emissions; yet, with the rise in the host nation’s carbon emissions, the ripple effect of international direct investments in green technology becomes increasingly evident. Empirical evidence indicates that global direct investment in Belt and Road economies demonstrates a significant mitigating effect on carbon emissions, thereby amplifying the decarbonization benefits associated with such cross-border capital flows. Full article

This study presents, for the first time, a detailed linear stability analysis (LSA) of bedform evolution under low-flow conditions using a one-dimensional vertically averaged and moment (1D-VAM) approach. The analysis focuses exclusively on bedload transport. The classical Saint-Venant shallow water equations are extended to incorporate non-hydrostatic pressure terms and a modified moment-based Chézy resistance formulation is adopted that links bed shear stress to both the depth-averaged velocity and its first moment (near-bed velocity). Applying a small-amplitude perturbation analysis to an initially flat bed, while neglecting suspended load and bed slope effects, reveals two distinct modes of morphological instability under low-Froude-number conditions. The first mode, associated with ripple formation, features short wavelengths independent of flow depth, following the relation F² = 1/(kh), and varies systematically with both the Froude and Shields numbers. The second mode corresponds to dune formation, emerging within a dimensionless wavenumber range of 0.17 to 0.9 as roughness increases and the dimensionless Chézy coefficient $C^{\ast }$ decreases from 20 to 10. The resulting predictions of the dominant wavenumbers agree well with recent experimental observations. Critically, the model naturally produces a phase lag between sediment transport and bedform geometry without empirical lag terms. The 1D-VAM framework with Exner equation offers a physically consistent and computationally efficient tool for predicting bedform instabilities in erodible channels. This study advances the capability of conventional depth-averaged models to simulate complex bedform evolution processes. Full article

Pelton turbines are susceptible to hydro-abrasive erosion from sediment-laden flows, resulting in a progressive loss of efficiency. Typical defect classes can be derived from the analysis of such damage observed in hydropower plants. A systematic strategy was developed to investigate the effect of locally damaged Pelton runners on the efficiency in laboratory tests using a model turbine. For this purpose, nine identical runners were fabricated and machined with an increasing size, depth, or number of different artificial defect types, such as splitter, rounded or sharp-edged, defects at the cutout, defects in the bucket base, and added ripples on the bucket sides. The processing steps, the efficiency measurement, and the extracted slopes of the efficiency drops are discussed in detail. The main findings are that the efficiency losses due to the various defects increase in a good approximation linearly with the machining depth and that the individual defect types can be superimposed. Defects at the splitter, bucket base, and bucket side dominate the losses at partial load of the turbine, while those at the cutout dominate at full load. Based on the results of this measurement campaign, power plant operators can estimate the magnitude of efficiency losses in their plant. Full article