Energies

20 pages, 2000 KB

Open AccessArticle

Lightweight Cooperative Attention for Empowering YOLOv7-Tiny in Lithium Battery Surface Defect Recognition

by Jianhua Wang, Mengyu Liu, Caihong Yu, Shilin Ye and Jian Chen

Energies 2026, 19(4), 1044; https://doi.org/10.3390/en19041044 - 16 Feb 2026

In response to the challenges of complex lithium battery surface defect morphology, difficulties in detecting small targets, and the trade-off between accuracy and speed in existing detection methods, this paper proposes an improved object detection network based on YOLOv7-tiny. The method focuses on [...] Read more.

In response to the challenges of complex lithium battery surface defect morphology, difficulties in detecting small targets, and the trade-off between accuracy and speed in existing detection methods, this paper proposes an improved object detection network based on YOLOv7-tiny. The method focuses on enhancing the model’s adaptability to complex defects at the feature extraction level, primarily achieved through two key designs: First, we introduce a simple parameter-free attention module (SimAM) to enhance the network’s ability to characterize small-scale defect features with minimal computational overhead. Second, a lightweight large-kernel attention module is incorporated into the neck network, which builds long-range spatial dependencies to improve the model’s generalization and understanding of irregularly shaped defects. To validate the effectiveness of the model, comprehensive experiments were conducted on a self-built lithium battery surface defect dataset. The results show that the proposed method achieves an mAP@0.5 of 93.14%, representing an improvement of 3.08 percentage points over the baseline YOLOv7-tiny (You Only Look Once v7, lightweight variant) model. At the same time, the detection speed reaches 94 Frames Per Second (FPS), which is 17 FPS faster than the original YOLOv7. The experiments demonstrate that the network outperforms existing comparative methods in both detection accuracy and inference speed, providing an effective technical solution for high-precision, real-time online defect detection in lithium battery production processes. Full article

20 pages, 1781 KB

Open AccessArticle

Effect of Pyrolysis Temperature on Chemical Structure and Thermal Stability of Digestate-Based Biochar

by Justyna Kujawska, Wojciech Cel, Barbara Charmas and Dorota Szala

Energies 2026, 19(4), 1043; https://doi.org/10.3390/en19041043 - 16 Feb 2026

Abstract

Biochar obtained from digestate is a promising material in the context of digestate management. However, it is important to note that the properties of the resulting material are largely dependent on the parameters of the pyrolysis process, with temperature being a particularly significant [...] Read more.

Biochar obtained from digestate is a promising material in the context of digestate management. However, it is important to note that the properties of the resulting material are largely dependent on the parameters of the pyrolysis process, with temperature being a particularly significant factor. The objective of this study was to evaluate the impacts of the digestate pyrolysis temperature on the chemical structure, thermal stability, and thermal decomposition characteristics of biochar produced at temperatures of 400, 500, 600, and 800 °C in an inert nitrogen atmosphere. Material characterization was performed using a range of analytical techniques, including elemental analysis, FTIR spectroscopy, thermogravimetric analysis (TGA/DTG), and coupled TGA–FTIR analysis, in order to identify volatile products released during the heating process. The results demonstrated that elevating the pyrolysis temperature results in progressive carbonization and aromatization of the carbon structure. Concurrently, functional groups containing oxygen and hydrogen were eliminated, as evidenced by declines in the H/C and O/C atomic ratios. FTIR analysis confirmed the disappearance of aliphatic and hydroxyl bands, as well as the dominance of aromatic structures and mineral components in biochar subjected to high-temperature treatment. The TGA results demonstrated an enhancement in thermal stability with increasing pyrolysis temperature. Concurrently, the TGA–FTIR analysis revealed a substantial decline in the emission of volatile decomposition products from biochar obtained at temperatures ≥600 °C. Overall, the pyrolysis temperature of digestate determines the utilization potential of the resulting biochar; in particular, low-temperature biochar can be used as a soil amendment and methane fermentation stimulant, while high-temperature biochar can be used for contaminant immobilization in soil and long-term carbon sequestration. Full article

(This article belongs to the Special Issue Advances in Waste-to-Energy Technologies)

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31 pages, 2938 KB

Open AccessArticle

Reactive Power Optimal Configuration in Distribution Networks with UPQC Dynamic Voltage Regulation

by Bin Lin, Zhensong Zeng, Yan Huang, Xiangyu Wang, Cheng Lin and Yan Zhang

Energies 2026, 19(4), 1042; https://doi.org/10.3390/en19041042 - 16 Feb 2026

Abstract

To address voltage violation issues in active distribution networks, this paper proposes a reactive power optimal configuration method that considers the dynamic voltage regulation strategy of a unified power quality conditioner (UPQC). First, an adaptive network partitioning model based on reactive power–voltage modularity [...] Read more.

To address voltage violation issues in active distribution networks, this paper proposes a reactive power optimal configuration method that considers the dynamic voltage regulation strategy of a unified power quality conditioner (UPQC). First, an adaptive network partitioning model based on reactive power–voltage modularity is developed. This model identifies high-sensitivity regions and determines preferred siting locations for UPQCs. Next, a voltage stability index is derived using a two-bus equivalent decoupled model. The classical holomorphic embedding method is then applied to track the variation in the voltage stability index, with respect to the embedding factor. Based on these results, weak buses are identified as key buses for evaluating the effectiveness of voltage control measures. Subsequently, a bi-level optimisation model that integrates planning and operation is formulated by incorporating the dynamic voltage regulation strategy of the UPQC. The model aims to minimise the equivalent annual total cost of the deployment scheme while reducing bus voltage deviations, thereby enabling proactive mitigation of voltage violations in active distribution networks. Finally, case studies conducted on an extended IEEE-33 bus power system and real-world distribution networks demonstrate that the proposed UPQC optimal configuration method effectively alleviates voltage violation problems. Full article

(This article belongs to the Topic Intelligent, Flexible, and Effective Operation of Smart Grids with Novel Energy Technologies and Equipment)

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42 pages, 25617 KB

Open AccessArticle

National-Scale Fast-Charging Infrastructure Planning Integrating Geospatial Analysis, MCDM, and Power System Constraints

by Carmen Selva-López, Rebeca Solís-Ortega, Gustavo Adolfo Gómez-Ramírez, Oscar Núñez-Mata and Fausto Calderón-Obaldía

Energies 2026, 19(4), 1041; https://doi.org/10.3390/en19041041 - 16 Feb 2026

Abstract

Electromobility is increasingly recognized as a cornerstone of sustainable transport, yet its adoption remains uneven across regions. This study develops an integrated framework that combines geospatial analysis, multi-criteria decision-making (MCDM), and power system evaluation to identify and prioritize fast-charging sites at the national [...] Read more.

Electromobility is increasingly recognized as a cornerstone of sustainable transport, yet its adoption remains uneven across regions. This study develops an integrated framework that combines geospatial analysis, multi-criteria decision-making (MCDM), and power system evaluation to identify and prioritize fast-charging sites at the national scale. Applied to Costa Rica’s national road network (NRN), encompassing both urban centers and peripheral regions, the framework integrates spatial suitability, socioeconomic priorities, and grid readiness across projected electric vehicle (EV) penetration scenarios. Critically, power system simulations reveal voltage instability at distribution nodes (as low as 89.88% p.u.) under 3% EV penetration despite 99% renewable generation, demonstrating that grid capacity, not planning methodology, constitutes the primary barrier to electric mobility adoption. This finding, derived from the first national-scale analysis that integrates equity-driven spatial prioritization with comprehensive grid validation using real fleet projections, challenges conventional assumptions in transport-focused infrastructure planning. The framework provides a transferable tool for countries seeking to align EV infrastructure planning with sustainability and decarbonization objectives, while highlighting that grid reinforcement must precede, not follow, the deployment of fast-charging infrastructure. Full article

(This article belongs to the Section A: Sustainable Energy)

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25 pages, 6667 KB

Open AccessArticle

Influence of Magnetization Nonlinearity and Non-Sinusoidal MMF Spatial Distribution on Harmonic Content of Current and Electromagnetic Torque in Three-Phase Induction Machine

by Andriy Kutsyk, Mykola Semeniuk, Mariusz Korkosz, Marek Nowak and Wojciech Rząsa

Energies 2026, 19(4), 1040; https://doi.org/10.3390/en19041040 - 16 Feb 2026

Abstract

In recent years, improving the energy efficiency of induction machines (IM) has become a key research focus, with particular attention to loss reduction. Losses in IM are significantly influenced by two design-related factors: the nonlinear magnetization characteristic and the non-sinusoidal distribution of the [...] Read more.

In recent years, improving the energy efficiency of induction machines (IM) has become a key research focus, with particular attention to loss reduction. Losses in IM are significantly influenced by two design-related factors: the nonlinear magnetization characteristic and the non-sinusoidal distribution of the magnetomotive force (MMF) in stator slots. These effects lead to harmonic distortions in stator and rotor currents as well as pulsations of the electromagnetic torque. This paper presents a comprehensive harmonic analysis of the interaction between the nonlinear magnetization curve and the non-sinusoidal MMF distribution in induction machines. A mathematical model in phase coordinates was developed, incorporating both effects through the introduction of harmonic components into the magnetizing inductance. The proposed model enables the evaluation of the impact of these phenomena on stator and rotor currents, as well as on the electromagnetic torque. The validity of the model is verified by experimental results, which show close agreement with simulations. The analysis demonstrates that the nonlinearity of the magnetization curve results in the appearance of the third harmonic in stator currents and the second harmonic in torque, while the non-sinusoidal MMF distribution produces the fifth and seventh harmonics in stator currents and the sixth harmonic in torque. Additionally, the study reveals that in no-load conditions, the third harmonics are dominant, whereas with increasing load, their magnitudes decrease, and the amplitudes of the fifth and seventh harmonics increase due to the interaction between stator and rotor currents. The proposed modeling approach provides an effective tool for accurate performance evaluation and design optimization of induction motor drives. Full article

15 pages, 2137 KB

Open AccessArticle

Influence of Skin Factor on Oil Recovery and Economic Performance in Synthetic Layered Carbonate Models Based on Pre-Salt Well Profiles

by Edson de Andrade Araújo, Mateus Palharini Schwalbert, Rafael Japiassú Leitão, Lorena Cardoso Batista Aum and Pedro Tupã Pandava Aum

Energies 2026, 19(4), 1039; https://doi.org/10.3390/en19041039 - 16 Feb 2026

Abstract

Formation damage near the wellbore reduces permeability and limits well productivity, with its effect commonly quantified by the skin factor. This parameter can strongly influence both the technical performance and the economic feasibility of oil recovery projects. In Brazilian pre-salt carbonate reservoirs, acidizing [...] Read more.

Formation damage near the wellbore reduces permeability and limits well productivity, with its effect commonly quantified by the skin factor. This parameter can strongly influence both the technical performance and the economic feasibility of oil recovery projects. In Brazilian pre-salt carbonate reservoirs, acidizing is widely applied, often conducted immediately after well completion. However, the long-term production and economic implications of these treatments remain insufficiently quantified. In this study, synthetic carbonate reservoir models were constructed using porosity and permeability profiles derived from well data representative of pre-salt conditions. Ten models with flow capacities ranging from 3000 to 130,000 mD·m were simulated over 30 years of water injection, considering skin factors from −3 to +20. The results show that wells with flow capacities below 10,000 mD·m exhibited the strongest response to stimulation, achieving up to 35% higher cumulative oil recovery and more than a 100% increase in net present value (NPV) compared with unstimulated cases. For flow capacity values between 10,000 and 40,000 mD·m, production and economic improvements were marginal, with NPV differences typically within 10%. At higher flow capacity (>60,000 mD·m), the stimulation response became negligible, with NPV variations below 0.1%. These findings demonstrate that stimulation effectiveness is primarily governed by reservoir flow capacity. The integrated reservoir–economic evaluation framework developed in this study provides quantitative guidance for optimizing acidizing strategies in carbonate systems representative of deepwater pre-salt environments. Full article

(This article belongs to the Section H1: Petroleum Engineering)

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17 pages, 2070 KB

Open AccessArticle

Direct-Drive Gerotor Pump—A New Approach to Design of Hydraulic Pumps

by Piotr Antoniak

Energies 2026, 19(4), 1038; https://doi.org/10.3390/en19041038 - 16 Feb 2026

Abstract

This paper presents a new approach to the design of hydraulic pumps, exemplified by a prototype gerotor pump with an integrated direct drive, based on an original concept constituting the basis of the Polish patent PL 236677. One of the objectives of the [...] Read more.

This paper presents a new approach to the design of hydraulic pumps, exemplified by a prototype gerotor pump with an integrated direct drive, based on an original concept constituting the basis of the Polish patent PL 236677. One of the objectives of the study is to demonstrate that, despite the long-standing and widespread use of this class of devices, further development potential still exists. To this end, the study focuses on the experimental proof-of-concept validation of the proposed solution, specifically aiming to verify the correctness of the gerotor unit and the BLDC-type magnetic drive circuit design, and to assess the impact of direct integration on the pump’s hydraulic characteristics, thermal behaviour, and control performance. Emphasis is placed on demonstrating the feasibility of the presented solution and its potential for future practical applications. Accordingly, an experimental prototype direct-drive gerotor pump was designed and manufactured, together with a dedicated miniature test stand required for experimental investigations. The research programme comprised preliminary start-up tests, no-load operation, and pump operation under various operating conditions, including different rotational speeds and working pressures. The experimental investigations were successfully carried out, and the obtained results clearly confirmed the correctness of the proposed concept and the proper operation of the prototype. As discussed in the paper, the presented prototype currently exhibits specific limitations, primarily low efficiency and a limited rotational speed range. However, these represent typical early-stage issues that further development can relatively easily eliminate. Full article

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27 pages, 1048 KB

Open AccessReview

Exploring Dynamics of Korea’s Short-Term Energy Transition: A Multi-Level Perspective Approach

by Myunghee Kim

Energies 2026, 19(4), 1037; https://doi.org/10.3390/en19041037 - 16 Feb 2026

Abstract

The energy transition takes a long time and requires a complex process involving stakeholder consensus. This study aims to explore the political, economic, and sociocultural dynamics that emerged during the short-term energy transition between the Moon and Yoon administrations in Korea, assessing the [...] Read more.

The energy transition takes a long time and requires a complex process involving stakeholder consensus. This study aims to explore the political, economic, and sociocultural dynamics that emerged during the short-term energy transition between the Moon and Yoon administrations in Korea, assessing the current energy transition, which stands at a crossroads, and provides conclusions and implications to inform future decisions on the findings. To this purpose, a multi-level perspective analytical framework was applied to investigate the two administrations’ conflicting energy transition mechanisms on the level of actors, technologies, and rules/institutions. According to the results, the Moon administration pursued a reconfiguration pathway of limited changes by attempting to phase out nuclear power plants and expand renewable energy, while the Yoon administration promoted a transformation pathway of partial change by abandoning the policy of phasing out nuclear power plants and further expanding existing nuclear energy. Differences in pathways were found to stem from differentiation based on political ideology and political purposes among key actors, rather than socio-technological innovation. This paper argues that Korea’s short-term energy transition was hastily pursued amidst a lack of public discourse, insufficient technological development, and institutional deficiencies, ultimately blocking the pathway to a desirable energy transition and having Korea locked in its existing energy system. This paper also suggests that no single pathway exists to carbon neutrality, and that future administrations can find desirable pathways by overcoming challenges and dilemmas through continuous improvement and adjustment. Full article

(This article belongs to the Special Issue Sustainable Energy Systems: Progress, Challenges and Prospects)

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25 pages, 1716 KB

Open AccessArticle

Physics-Regularized and Safety-Enhanced Bi-GAT Reinforcement Learning Framework for Voltage Control

by Hui Qin, Binbin Zhong, Kai Wang, Youbing Zhang and Licheng Wang

Energies 2026, 19(4), 1036; https://doi.org/10.3390/en19041036 - 16 Feb 2026

Abstract

With more renewables being integrated into distribution grids, the problem of voltage fluctuation has become prominent. Effective Volt/VAR regulation is a commonly used method to ensure the safe operation of distribution networks. Model-based approaches tend to work well only if detailed network parameters [...] Read more.

With more renewables being integrated into distribution grids, the problem of voltage fluctuation has become prominent. Effective Volt/VAR regulation is a commonly used method to ensure the safe operation of distribution networks. Model-based approaches tend to work well only if detailed network parameters are available, while data-driven approaches can suffer from overfitting and may not generalize well. We created the PHY-GAT-SAC framework to address these issues. Physics-regularized reinforcement learning uses bidirectional graph attention, which combines a physics-informed model with a safety projection method that relies on sensitivity matrices. This makes it so that the voltage regulation is practical, interpretable, and secure. The framework works with two combined branches. One branch takes care of the nonlinear mapping from power injections to voltage states using a forward graph encoder and a reverse consistency constraint. At the same time, another branch extracts features directly from the voltages to improve the perception of system violation risk. The framework has a sensitivity-based safety layer as well. This layer projects every control action into a feasible area formed by linearized voltage restrictions, thus securing operation safety. Experiments on an IEEE 33-node system show that the framework works well. A safety layer guarantees a safe operating range without exact impedance values. And PHY-GAT-SAC greatly lowers voltage violations compared to multi-agent deep reinforcement learning. By successfully combining physics with learning, this study gives a unified framework for merging graph neural networks and reinforcement learning within intricate grid management. Full article

(This article belongs to the Special Issue Advanced in Modeling, Analysis and Control of Microgrids)

19 pages, 3691 KB

Open AccessArticle

Energy Flexibility Evaluation for Building Passive Thermal Storage Mass

by Haiyang Yuan, Yongbao Chen, Alessandra Di Gangi and Zhe Chen

Energies 2026, 19(4), 1035; https://doi.org/10.3390/en19041035 - 16 Feb 2026

Abstract

This study proposes a systematic methodology to evaluate the energy flexibility and operational performance of air-conditioning systems (ACSs) in residential buildings, leveraging the passive thermal storage capacity of building thermal mass through indoor temperature setpoint adjustment. A comparative analysis was conducted between inverter-controlled [...] Read more.

This study proposes a systematic methodology to evaluate the energy flexibility and operational performance of air-conditioning systems (ACSs) in residential buildings, leveraging the passive thermal storage capacity of building thermal mass through indoor temperature setpoint adjustment. A comparative analysis was conducted between inverter-controlled and intermittent on-off air conditioners under a baseline indoor temperature of 24 °C. Two additional temperature setpoint scenarios (26 °C and 28 °C) were tested to quantify variations in the building’s electricity consumption demand. To characterize the dynamic thermal response across different floor levels, ground-floor, middle-floor, and top-floor apartments were investigated in a three-story residential building, enabling a controlled, floor-level comparison under identical control logic and climatic conditions. Dymola simulation software was employed to model and calculate ACS energy consumption and energy flexibility under the three temperature setpoint conditions (24 °C, 26 °C, and 28 °C). Results indicate that a strategy of scheduled ACS shutdown and automatic restart, enabled by the thermal inertia capacity of building thermal mass, effectively enhances ACS energy flexibility. Specifically, adjusting the zone temperature setpoint reduced the total ACS load by approximately 40% in two hours of a demand response event. This temperature setpoint adjustment strategy demonstrates significant potential to mitigate grid peak-load demand without compromising indoor thermal comfort and requiring additional building retrofitting investments. The findings provide a technical basis for optimizing residential ACS operation and promoting demand-side management in power systems. Full article

(This article belongs to the Special Issue Integrated Energy Storage System for Decarbonization)

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19 pages, 2559 KB

Open AccessArticle

A CPO-Optimized BiTCN–BiGRU–Attention Network for Short-Term Wind Power Forecasting

by Liusong Huang, Adam Amril bin Jaharadak, Nor Izzati Ahmad and Jie Wang

Energies 2026, 19(4), 1034; https://doi.org/10.3390/en19041034 - 15 Feb 2026

Abstract

Short-term wind power prediction is pivotal for maintaining the stability of power grids characterized by high renewable energy penetration. However, wind power time series exhibit complex characteristics, including local turbulence-induced fluctuations and long-term temporal dependencies, which challenge traditional forecasting models. Furthermore, the performance [...] Read more.

Short-term wind power prediction is pivotal for maintaining the stability of power grids characterized by high renewable energy penetration. However, wind power time series exhibit complex characteristics, including local turbulence-induced fluctuations and long-term temporal dependencies, which challenge traditional forecasting models. Furthermore, the performance of hybrid deep learning models is often compromised by the difficulty of tuning hyperparameters over non-convex optimization surfaces. To address these challenges, this study proposes a novel framework: CPO—BiTCN—BiGRU—Attention. Adopting a physically motivated “Filter–Memorize–Focus” strategy, the model first employs a Bidirectional Temporal Convolutional Network (BiTCN) with dilated causal convolutions to extract multi-scale local features and denoise raw data. Subsequently, a Bidirectional Gated Recurrent Unit (BiGRU) captures global temporal evolution, while an attention mechanism dynamically weights critical time steps corresponding to ramp events. To mitigate hyperparameter uncertainty, the Crowned Porcupine Optimization (CPO) algorithm is introduced to adaptively tune the network structure, balancing global exploration and local exploitation more effectively than traditional swarm algorithms. Experimental results obtained from real-world wind farm data in Xinjiang, China, demonstrate that the proposed model consistently outperforms State-of-the-Art benchmark models. Compared with the best competing methods, the proposed framework reduces MAE and MAPE by approximately 30–45%, while maintaining competitive RMSE performance, indicating improved average forecasting accuracy and robustness under varying operating conditions. The results confirm that the proposed architecture effectively decouples local noise from global trends, providing a robust and practical solution for short-term wind power forecasting in grid dispatching applications. Full article

(This article belongs to the Section A3: Wind, Wave and Tidal Energy)

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22 pages, 1088 KB

Open AccessArticle

Coordinated Optimal Scheduling of Transmission Grid and Multi-Parks Considering Source-Load Uncertainties with Multi-Spatial–Temporal Scales

by Zhenghong Tu, Fangzong Wang and Jin Wang

Energies 2026, 19(4), 1033; https://doi.org/10.3390/en19041033 - 15 Feb 2026

Abstract

With the ongoing transformation of energy systems and the expanding scale of multi-park integrated energy systems, this paper proposes a novel multi-spatiotemporal scale scheduling framework that integrates robust optimization with distributed coordination to address the challenges of complex spatiotemporal coupling and significant uncertainties [...] Read more.

With the ongoing transformation of energy systems and the expanding scale of multi-park integrated energy systems, this paper proposes a novel multi-spatiotemporal scale scheduling framework that integrates robust optimization with distributed coordination to address the challenges of complex spatiotemporal coupling and significant uncertainties in the coordinated operation of transmission grids and multi-park integrated energy systems under high renewable energy penetration. The proposed framework establishes a hierarchical optimization model encompassing day-ahead, intra-day rolling, and real-time scheduling stages, incorporating multi-energy coupling constraints and accounting for load uncertainty. Robust optimization is employed to effectively manage source-load fluctuations arising from renewable intermittency. For solution implementation, the analytical target cascading (ATC) method is adopted to enable distributed collaborative optimization between the transmission system and individual park-level systems. Simulation results demonstrate that the proposed approach significantly enhances both the economic efficiency and operational reliability of the integrated energy system. Full article

(This article belongs to the Section F1: Electrical Power System)

22 pages, 4912 KB

Open AccessArticle

Parameter Design Method of Variable Frequency Modulation for Grid-Tied Inverter Considering Loss Optimization and Thermal and Harmonic Constraints

by Wei Cheng, Panbao Wang, Wei Wang and Dianguo Xu

Energies 2026, 19(4), 1032; https://doi.org/10.3390/en19041032 - 15 Feb 2026

Abstract

Electromagnetic interference (EMI) rectification of grid-tied inverters is crucial for their practical application, and the variable frequency modulation (VFM) technique is a low-cost and simple way for EMI reduction. However, changes in loss and harmonic behaviors make it hard for parameter determination of [...] Read more.

Electromagnetic interference (EMI) rectification of grid-tied inverters is crucial for their practical application, and the variable frequency modulation (VFM) technique is a low-cost and simple way for EMI reduction. However, changes in loss and harmonic behaviors make it hard for parameter determination of VFM. In this paper, the parameters required for switching frequency (SF) function are determined for loss optimization of MOSFETs and inductors, while total harmonic distortion (THD) and temperature rise in MOSFETs and inductor core are constrained to guarantee the feasibility of the calculated parameters. Current transient is derived through multidimensional Fourier decomposition (MFD) and characteristics of Bessel function for loss estimation of MOSFET and inductor. Modified Steinmetz equation (MSE) is applied for core loss estimation and AC resistance is considered for copper loss estimation. With the constraints of THD and temperature, the loss optimization problem is solved by the augmented Lagrangian (AL) method. With the assistance of the proposed method, total loss optimization can be realized in feasible regions while the temperature rise in essential components can be restricted to the preset values. Full article

(This article belongs to the Special Issue Condition Monitoring, Reliability Analysis, and Fault Detection of Power Electronics)

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18 pages, 5442 KB

Open AccessArticle

Computationally Efficient Online Adaptation Method for PM Machine LPTN Model

by Jiaye Shi and Zhiyu Sheng

Energies 2026, 19(4), 1031; https://doi.org/10.3390/en19041031 - 15 Feb 2026

Abstract

Accurate long-term temperature prediction is critical for the reliable operation of mass-produced electrical machines. However, due to the randomness inherent in the manufacturing process, machines with identical design parameters often exhibit distinct thermal properties. The aging of the insulation system can also lead [...] Read more.

Accurate long-term temperature prediction is critical for the reliable operation of mass-produced electrical machines. However, due to the randomness inherent in the manufacturing process, machines with identical design parameters often exhibit distinct thermal properties. The aging of the insulation system can also lead to variation in thermal performance. Conventional lumped-parameter thermal network (LPTN) models with fixed parameters fail to account for these factors, thus leading to biased prediction results for long-term temperature forecasting of mass-produced machines. To enhance the robustness of LPTN models, this paper proposes a methodology for adaptive online parameter updating. Based on the mathematical formulation of LPTN, a fast Jacobian matrix calculation method for model prediction errors is developed, which avoids the time-consuming numerical computation process. To further alleviate the computational burden, key parameters with significant impacts on prediction errors are screened prior to each optimization iteration. These improvements collectively reduce computational resource requirements and enable real-time online implementation. Finally, experimental verification is conducted on a 10 kW permanent magnet machine. Comparative analyses against the numerical method and extended Kalman filter (EKF) demonstrate that the proposed method can be efficiently realized and is more effective in estimating the model parameters online. Full article

(This article belongs to the Section F: Electrical Engineering)

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20 pages, 3241 KB

Open AccessArticle

A GIS-Based Approach to Identifying Suitable Areas for Positive Energy Districts Development

by Iván Ramos-Diez, Sofía Mulero-Palencia and José L. Hernández

Energies 2026, 19(4), 1030; https://doi.org/10.3390/en19041030 - 15 Feb 2026

Abstract

Positive Energy Districts (PEDs) have been proposed as a holistic approach to urban decarbonization. PEDs are defined as delimited areas that produce, annually, more energy than they consume. The methodology proposed for PED assessment integrates multicriteria decision-making geospatial analysis and weighted overlay techniques [...] Read more.

Positive Energy Districts (PEDs) have been proposed as a holistic approach to urban decarbonization. PEDs are defined as delimited areas that produce, annually, more energy than they consume. The methodology proposed for PED assessment integrates multicriteria decision-making geospatial analysis and weighted overlay techniques to assess PED suitability across different dimensions. Data harmonization is included as part of the modeling process, ensuring methodological consistency across diverse contexts. The approach employs a layer overlay and aggregation through a weighting average process, calibrated through stakeholder input, to reflect local priorities and urban-specific conditions in order to identify the potential areas for PED implementation. Geospatial datasets provided as inputs are processed to produce maps that reflect the PED suitability index for the city districts according to the selected dimensions. As a result, the open-source developed MCDA algorithm provides maps that facilitate the identification of relevant zones for PED feasibility. The algorithm was applied in Bratislava city, understanding its identification potential, adaptability and scalability to other cities. The obtained results highlight the most interesting districts in which to build a PED in Bratislava, promoting the algorithm as a replicable decision-making tool for advancing PED identification and deployment. Full article

(This article belongs to the Special Issue Selected Papers from the SDEWES 2025 Conference on Sustainable Development of Energy, Water, and Environment Systems)

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22 pages, 4239 KB

Open AccessReview

Silver–Tin Sulfide/Selenide Semiconductor for Super-Narrow-Bandgap Photovoltaics and Thermoelectric Applications: A Review

by Padmini Pandey, Han-Gyun Lim and Dong-Won Kang

Energies 2026, 19(4), 1029; https://doi.org/10.3390/en19041029 - 15 Feb 2026

Abstract

Ag-Sn-S/Se semiconductors, particularly Ag₈SnS₆ and Ag₈SnSe₆, have emerged as promising thermoelectric (TE) materials due to their intrinsically low lattice thermal conductivity and favorable electronic transport properties. Owing to their direct and super-narrow bandgaps, these semiconductors also [...] Read more.

Ag-Sn-S/Se semiconductors, particularly Ag₈SnS₆ and Ag₈SnSe₆, have emerged as promising thermoelectric (TE) materials due to their intrinsically low lattice thermal conductivity and favorable electronic transport properties. Owing to their direct and super-narrow bandgaps, these semiconductors also hold significant potential for photovoltaic (PV) applications, especially in near-infrared (NIR) energy harvesting and tandem architecture. This review provides a detailed analysis of the synthesis strategies, crystallographic evolution, phase transition mechanisms, and bandgap modulation in Ag-Sn-S/Se semiconductors. Particular focus is given to the structural adaptability of argyrodite-type compounds, where intrinsic cationic disorder and halogen-assisted anion substitution collectively enable the fine-tuning of electronic transport and lattice dynamics. TE performance is evaluated in terms of carrier mobility and thermal conductivity, highlighting a significant improvement in figure of merit. The review further explores the potential of Ag-Sn-S/Se semiconductors in energy conversion PVs, particularly as photoabsorber layers and counter electrode materials. Despite initial demonstrations, systematic studies on device integration remain limited, highlighting substantial opportunities for future research aimed at optimizing their optoelectronic interfaces and overall PV performance. This review ultimately discusses the potential of Ag-Sn-S/Se semiconductors, emphasizing their tunable properties as being key to next-generation PV and thermoelectric technologies. It highlights the current achievements and unresolved challenges, outlining strategic pathways for future research and device integration. Full article

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23 pages, 3871 KB

Open AccessArticle

Optimization of CCGT Start-Up Ramp Rate to Improve Voltage Quality in a 110/220 kV Power System Node

by Madina Maratovna Umysheva, Yerlan Aliaskarovich Sarsenbayev and Dias Raybekovich Umyshev

Energies 2026, 19(4), 1028; https://doi.org/10.3390/en19041028 - 15 Feb 2026

Abstract

With the active modernization of power facilities and the increasing deployment of maneuverable combined-cycle gas turbines (CCGTs), the selection of rational start-up strategies becomes increasingly important from the perspective of power quality. Excessive acceleration of power ramp-up may lead to undesirable voltage deviations, [...] Read more.

With the active modernization of power facilities and the increasing deployment of maneuverable combined-cycle gas turbines (CCGTs), the selection of rational start-up strategies becomes increasingly important from the perspective of power quality. Excessive acceleration of power ramp-up may lead to undesirable voltage deviations, particularly in transmission networks with limited grid stiffness. This study investigates the impact of CCGT start-up ramp rate on voltage dynamics and power quality indicators at a 110/220 kV grid node. A detailed model of the Almaty power hub was developed in MATLAB/Simulink, taking into account the network structure, generating units, transformers, and aggregated loads. Three start-up scenarios were analyzed: an existing combined heat and power plant, a 504 MW combined-cycle gas turbine unit, and a 560 MW combined-cycle gas turbine unit with fuel afterburning. Voltage dynamics were evaluated using RMS-based indicators and a stabilization criterion incorporating a 5 s sliding time window and an 80% admissibility threshold. The simulation results reveal a nonlinear relationship between the start-up ramp rate and voltage quality. Increasing the ramp rate reduces the voltage stabilization time; however, beyond approximately 0.05 MW/s, further acceleration does not lead to additional improvement in power quality. The results indicate the existence of an optimal range of start-up ramp rates that provides a compromise between start-up speed and voltage quality requirements. The proposed approach can be used in the development of start-up algorithms for modern combined-cycle power plants connected to 110/220 kV transmission networks. Full article

(This article belongs to the Special Issue Advanced Techniques for Power Transmission, Distribution and Transformation Equipment)

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28 pages, 2482 KB

Open AccessArticle

Virtual Synchronous Machine Testing and System Split Resilience: A Comparative Analysis with Grid-Following PV Inverters

by Ibrahim Okikiola Lawal, Horst Schulte and Salman Ammar

Energies 2026, 19(4), 1027; https://doi.org/10.3390/en19041027 - 15 Feb 2026

Abstract

The increasing penetration of converter-interfaced generation raises critical concerns for power system stability, especially during rapid transients and system split events that are not yet adequately addressed in current grid code compliance tests. This paper assesses the resilience of a Virtual Synchronous Machine [...] Read more.

The increasing penetration of converter-interfaced generation raises critical concerns for power system stability, especially during rapid transients and system split events that are not yet adequately addressed in current grid code compliance tests. This paper assesses the resilience of a Virtual Synchronous Machine (VSM) in comparison with a grid-following photovoltaic (PV) inverter through a combined framework of standardized benchmark tests and realistic system split scenarios. In benchmark testing, the VSM provided synthetic inertia by delivering a transient-power burst from a 0.30 p.u. setpoint to 0.545 p.u. (on a 20 MVA base, representing 54.5% of rated capacity) under a

- 0.4

Hz/s frequency ramp, corresponding to an equivalent inertia constant of approximately 15 s. With the limited frequency-sensitive mode–underfrequency (LFSM-U) function enabled, it sustained additional active power up to 0.61 p.u. once the frequency fell below 49.8 Hz. The PV inverter, by contrast, demonstrated compliance with conventional grid requirements: it curtailed power through LFSM-O during overfrequency conditions and injected 0.25 p.u. of reactive current during a fault ride-through (FRT) event at 1.129 p.u. voltage. In system split tests, the VSM absorbed surplus PV generation, stabilizing frequency after a transient rise to 52.8 Hz and containing voltage excursions beyond 1.2 p.u. During imbalance stress, it absorbed 1.266 MW against its 1.0 MW rating for approximately 2–3 s, corresponding to a 26.6% overload that falls within typical IGBT transient thermal capability but would require supervisory intervention (e.g., PV curtailment or load management) if sustained. These results demonstrate that while the PV inverter contributes valuable voltage support, only the grid-forming VSM maintains frequency stability and ensures secure islanded operation. The novelty of this study lies in integrating standardized compliance tests with system split scenarios, providing a comprehensive framework for evaluating grid-forming controls under both regulatory and resilience-oriented perspectives and informing the evolution of future grid codes. Full article

(This article belongs to the Special Issue Algorithmic Approaches and Control Techniques for Energy Optimization in Power Converters and Grid Transmission)

16 pages, 17031 KB

Open AccessArticle

Simulation-Based Analysis of Polarization Effects on the Shielding Effectiveness of a Metal Enclosure with an Aperture Exposed to High-Power Subnanosecond Electromagnetic Pulse

by Jerzy Mizeraczyk and Magdalena Budnarowska

Energies 2026, 19(4), 1026; https://doi.org/10.3390/en19041026 - 15 Feb 2026

Abstract

Intentional high-power electromagnetic (EM) interference poses a serious threat to sensitive electronic systems and often manifests as ultra-wideband (UWB) sub- and nanosecond pulses. Metallic shielding enclosures with technological apertures are commonly used for protection; however, apertures enable electromagnetic coupling into the enclosure and [...] Read more.

Intentional high-power electromagnetic (EM) interference poses a serious threat to sensitive electronic systems and often manifests as ultra-wideband (UWB) sub- and nanosecond pulses. Metallic shielding enclosures with technological apertures are commonly used for protection; however, apertures enable electromagnetic coupling into the enclosure and limit shielding performance. While most existing studies focus on transient disturbances with durations exceeding the enclosure transit time, this work addresses an ultrashort high-power subnanosecond UWB plane-wave pulse whose duration is significantly shorter than the enclosure transit time, a regime that remains insufficiently explored. A time-domain numerical analysis is performed for a low-profile rectangular metallic enclosure with a front-wall aperture, focusing on internal EM field evolution, internal pulse formation, and polarization-dependent shielding effectiveness. Three-dimensional full-wave simulations were carried out using CST Microwave Studio over a 90 ns observation window. The results show that the incident pulse excites primary subnanosecond EM waves inside the enclosure, which subsequently generate secondary waves through multiple reflections from the enclosure walls. Their interaction produces complex, long-lasting, time-varying internal field patterns. Although attenuated, the resulting internal subnanosecond pulses repeatedly traverse the enclosure interior, forming a pulse train-like sequence that may pose a cumulative electromagnetic threat to internal electronics. A key contribution of this work is the quantification of time-dependent local shielding effectiveness for both electric and magnetic fields, derived directly from the internal pulse train-like series obtained in the time domain. The concept of local, time-dependent shielding effectiveness provides physical insight that cannot be obtained from a single globally averaged SE value. In the case of ultrashort electromagnetic pulse excitation, the internal field response of an enclosure is strongly non-stationary and highly non-uniform in space, with local field maxima occurring at specific times and locations despite good average shielding performance. Time-dependent local SE enables identification of worst-case temporal conditions, repeated high-amplitude internal exposures, and critical regions inside the enclosure where shielding is significantly weaker than suggested by global metrics. Therefore, while conventional SE remains useful as a summary measurand, local time-dependent SE is essential for assessing the actual electromagnetic risk to sensitive electronics under ultrashort pulse disturbances. In addition, a global shielding effectiveness metric mapped over selected enclosure cross-sections is introduced to enable rapid visual assessment of shielding performance. The analysis demonstrates a strong dependence of internal wave propagation, internal pulse formation, and both local and global shielding effectiveness on the polarization of the incident subnanosecond EM pulse. These findings provide new physical insight into aperture coupling and shielding behavior in the ultrashort-pulse regime and offer practical guidance for the assessment and design of compact shielding enclosures exposed to high-power UWB EM threats. Full article

(This article belongs to the Special Issue Advanced Power Electronics for Renewable Integration)

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