In recent years, the rapid development of renewable energy has posed a significant challenge to the breaking capacity of DC circuit breakers in power systems. Gas-blowing arc extinguishing technology based on gassing materials can greatly enhance the breaking capacity of DC circuit breakers. However, the macroscopic and microscopic pyrolysis mechanisms of gassing materials are unclear.

Firstly, the micro-pyrolysis mechanism of typical gassing material polyamide 66 (PA66) at different pyrolysis temperatures and rates was analyzed based on the reactive force field (ReaxFF). The decomposition process of PA66 and the types and quantities of small molecule gases produced were discussed. It was found that the initial bond breaking of PA66 occurred in the C—C bond adjacent to the amide group. H₂ and H₂O were the main pyrolysis gases of PA66, and their production process was analyzed. The reaction rate of carbon-free small molecule gas at high temperatures accelerates, and the amount increases. The product amount with carbon atoms below four increases rapidly and decreases slightly after reaching a peak. The main reasons are the Diels-Alder reaction, C3/C4 reaction, and cyclization reaction in the unsaturated hydrocarbons in the product, which leads to the decrease of hydrocarbon molecules. The temperature increase aggravates the disintegration of the PA66 molecular chain and the formation of small molecular gas. The heating rate of the system affects the distribution of heat in the reaction system, thus affecting the formation of the product. The slower the heating rate of the system, the more conducive to the uniform distribution of heat in the reaction system. Additionally, the amount of carbon deposition during pyrolysis at 2 600 K was analyzed. Light tar was dominant, followed by heavy tar, with the least amount of coke.

Subsequently, pyrolysis experiments at four different heating rates were carried out. Based on the Flynn-Wall-Ozawa isoconversional model, the average activation energy of PA66 was 194.85 kJ/mol, which was very close to the activation energy of 195.015 kJ/mol obtained by molecular dynamics simulation. Additionally, the pyrolysis gas distribution of PA66 was analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments, which verified the accuracy and reliability of the pyrolysis kinetics calculation method. PA66 is suitable for the first-order reaction kinetic model, and the simulation data have high accuracy and reliability for the thermal decomposition reaction path and gas type of PA66 at the microscale.

Finally, simulation calculations and arcing experiments of three gas-producing materials, PA6, PA46, and PA66, were carried out. The gas generation rate and quantity changes during pyrolysis were observed, and the transient pressure changes during the arc-breaking experiment were analyzed. The order of transient pressure generated during the arcing process is PA6>PA46>PA66, consistent with the trend of the number of product gas molecules obtained by simulation calculation. The ReaxFF simulation results are confirmed and supplemented with the arc-breaking experiment, further verifying the reliability and accuracy of the research.

This paper offers a theoretical framework for understanding the macroscopic pyrolysis behavior and the microscopic pyrolysis mechanism of gassing materials. It contributes to a deep comprehension of material behavior under high-temperature and arc conditions, laying a methodological foundation for evaluating the performance of gassing materials in DC circuit breakers.

Due to its shared structure, the dual Buck/Boost-CLLC three-port converter has a simple structure and few power devices. The integrated interleaved parallel Buck/Boost unit significantly reduces input current ripple, while the integration of CLLC units endows the converter with excellent buck-boost conversion capability and soft-switching capability. However, the large number and volume of magnetic components in the shared structure are the main factors limiting the size of the power converter. Increasing the switching frequency or using magnetic integration can increase the power density of the power converter. However, in some studies, some schemes integrate two energy storage inductors and the resonant inductor in the converter to enhance coupled inductor current sharing and converter power density. Nonetheless, these schemes can only integrate full inverse coupling at a fixed duty cycle and cannot control the inverse coupling coefficient. Integration schemes with controllable coupling coefficients have been proposed, but two magnetic components remain after integration.

This paper proposes a fully integrated magnetic structure based on a dual Buck/Boost-CLLC three-port converter. By unevenly distributing the windings and establishing low reluctance paths, all magnetic components are integrated into a single magnetic element under variable duty cycle and coupling coefficient conditions. The proposed fully integrated magnetic component achieves inverse coupled inductor current sharing and ripple reduction, thereby enhancing system stability. Additionally, by integrating all magnetic components into a single magnetic element, the increased magnetic flux cancellation within the core further reduces core losses. Fig.A1 shows the proposed fully integrated magnetic structure, which consists of a cover magnetic core and a base magnetic core.

Fig.A1 Structure of the topology and fully integrated magnetic component structure

Firstly, based on the partially integrated structures and the proposed fully integrated structure, magnetic circuit models were established for both partially integrated and fully integrated magnetic components. The magnetic flux distribution and cancellation with different integration methods were compared. It is shown that the proposed fully integrated structure exhibits more magnetic flux cancellation and has lower losses. Next, the

performance-influencing parameters were analyzed, and a loss model was developed. Low losses for the fully integrated magnetic component were achieved through finite element parameterization scanning. Finally, a 500W prototype platform was built, and comparative experiments of non-integrated, partially integrated, and fully integrated magnets were conducted. Steady-state and dynamic experiments verified the feasibility of the integrated magnetic design. Efficiency and temperature comparison experiments validated the effectiveness of the integrated magnetic design.

The results show that the proposed fully integrated magnetic component maintains the same volume and footprint and exhibits more magnetic flux cancellation and uniform temperature distribution. The fully integrated magnetic component achieves an efficiency of 94.6% under full load, demonstrating higher power density and efficiency compared to non-integrated and partially integrated structures.

The large-scale development of wind power is a major demand for the development and utilization of new energy sources, and the high-performance service of the wind turbine fleet is an important guarantee for realizing the goal of the national carbon peaking and carbon neutrality goals. With the continuous increase of stand-alone capacity and installed capacity, wind conditions, sea conditions, and other complex environments make the synergistic optimization between service performance of large-scale wind turbine fleet- safe operation capacity-power generation benefits complex, and the unit safety and accurate warning and service quality control face serious challenges.

Firstly, the advantages and disadvantages of condition monitoring and fault diagnosis of key components of WTGs and reliability assessment are sorted out and compared. The current status of their service quality regulation is investigated. Secondly, the impacts of WTG’s healthiness, corrosive environment, and thunderstorms on the service quality of WTGs are elaborated, and the impacts of WTG FM strategy on the service quality are summarized. Then, the factors that affect the service quality of the wind turbine fleet are analyzed. The characteristics of voltage control strategy, operation and maintenance, and tail current control are analyzed.

High-quality power generation, operation and maintenance strategies, and tailing effects are analyzed at the level of the wind turbine fleet based on the service quality control methods of key components, wind turbines, and the wind turbine fleet. An outlook of the possible future direction is made to enhance the service performance of the wind turbine fleet and promote the healthy and sustainable development of the wind power industry.

The magnetic properties and loss characteristics of oriented silicon steel sheets exhibit significant deviation under stress. The traditional loss separation model generally overlooks the impact of mechanical stress on the loss characteristics, resulting in calculation errors. In recent years, most studies on the loss characteristics of oriented silicon steel sheets under mechanical stress have focused on qualitative analysis, with only a few studies making quantitative improvements to the loss separation model. This paper develops an improved loss separation model based on the traditional loss separation model by introducing stress terms into the hysteresis loss and excess loss.

Firstly, measurements from a single sheet tester with unidirectional stressing are utilized to analyze the stress dependency of the loss characteristics of the oriented silicon steel sheets. The experimental results demonstrate a significant enhancement in loss under compressive stress while exhibiting a slight decreasing trend under tensile stress. The magnetization mechanism in ferromagnetism explains the variation of the loss characteristics under mechanical stress. Secondly, the hysteresis loss and excess loss under stress are calculated based on the Bertotti traditional loss separation model. Since the stress component is not introduced into the hysteresis loss in the traditional loss separation model, the effect of stress on the hysteresis loss is only reflected by the hysteresis loss coefficient, leading to a significant error in the calculation of the hysteresis loss under stress. Although the excess loss parameter ${{V}_{0}}$, currently expressed by a constant coefficient, embodies the effect of stress, it fails to capture the effect of the applied mechanical stress on the losses of each magnetic induction intensity. Consequently, computational inaccuracies arise when employing the Bertotti traditional loss separation model.

Based on the correlation between parameters ${{V}_{0}}$ in excess loss, hysteresis loss, and stress, the traditional separation formula for losses is improved by introducing stress components into the excess loss parameters ${{V}_{0}}$ and hysteresis loss. An improved loss separation model is established and verified by varying the frequency of excitation and the type of oriented silicon steel sheet. The results indicate that the improved loss separation model can accurately separate and calculate the losses of oriented silicon steel sheets under different stresses while maintaining a remarkable precision level.

Experimental measurement and calculation analysis are performed, and the conclusions are as follows. (1) The excess loss parameter ${{V}_{0}}$ is correlated with stress, and incorporating the stress component into the excess loss parameter can effectively mitigate the calculation error caused by stress in the traditional loss separation model. (2) An improved loss separation model is proposed based on the traditional mode by incorporating the excess loss and hysteresis loss into stress-related functions. (3) The improved loss separation model is confirmed through testing with different frequency excitations and oriented silicon steel sheets, demonstrating its ability to accurately separate losses under different stresses.

The high peak-to-average ratio of low-frequency pulse power loads seriously affects the safe and stable operation of airborne power supply systems. The conventional approach requires stacking numerous energy storage capacitors due to the DC bus voltage ripple limitation, which substantially increases the system’s volume. Although current active pulse power suppression method can reduce the required capacitance by increasing voltage fluctuations, the considerable power ratings and additional power processing stages of active suppression circuits impact system efficiency significantly.

This paper presents a low-frequency pulse power active suppression method based on voltage compensation. The active suppression circuit is inserted between the DC bus and the energy storage capacitor C_d. By compensating for the voltage difference between C_d and DC bus with the output voltage v_s of the active suppression circuit, the voltage range of C_d is not constrained by the DC bus, allowing for a reduction in C_d. Since the active suppression circuit only compensates for capacitor voltage fluctuations, its power rating and losses are much smaller than the average power of pulse loads, which greatly reduces the volume, weight, and losses. The active suppression circuit takes power from the DC bus. Considering that its input and output terminals are non-common ground and have a wide output voltage range, the LLC-DC transformer (DCX) cascaded Buck converter is chosen for the active suppression circuit. The LLC-DCX functions operate in an open loop as a high- frequency DC transformer, and a dual-loop control strategy is implemented for the Buck converter. The outer voltage loop adjusts the voltage fluctuation range of C_d, while the inner current loop suppresses the input current ripple.

The design guidelines for key parameters are also presented, with size and efficiency as the main considerations. The size of the power supply is influenced by C_d, while the power rating of the active suppression circuit affects system efficiency. Therefore, a detailed study of both aspects is conducted. The results reveal that once the load is determined, C_d decreases as the voltage fluctuation Δv_d increases, and the decreasing rate gradually slows. Additionally, the power rating of the active suppression circuit increases linearly with the average voltage V_dav and Δv_d. The lower limit of V_dav is also affected by Δv_d to ensure that the output voltage of the Buck converter remains positive. Therefore, a balance must be achieved between V_dav and Δv_d to optimize capacitance and power rating.

An experimental prototype is constructed. The experimental results are consistent with the theoretical analysis, and the active suppression circuit effectively regulates the voltage fluctuation range of C_d and suppresses the input current. Efficiency tests reveal that the active suppression scheme maintains an efficiency above 98.1% throughout the entire range, with a peak efficiency reaching 99.1%. This scheme is compared with existing active suppression schemes, showing clear advantages. In addition, results from various literature are normalized and compared.

The electromagnetic rail launch process exists in high current, ultra-high speed, high temperature-rise, strong friction, and extreme impact conditions. The high heat generated causes the surface of the aluminum armature to melt, resulting in a transition at the pivot-rail interface from solid-solid electrical contact to a solid-liquid-solid melt process. Eventually, molten aluminum solidifies on the rail surface, forming a complex deposition layer. This deposition layer has implications for the performance of the pivot rail system during subsequent launches. The operational environment characterized by ultra-high-speed friction during repeated launches results in a low melting point in the armature. A portion of molten material forms a liquid transferred onto the rail, enhancing the interface and diminishing the electromagnetic rail's longevity. Consequently, it is imperative to investigate the impact of the aluminum deposition layer on the sliding electrical contact at the pivot-rail interface.

This study conducted small-diameter electromagnetic launching tests with varying launching times to examine the carrier friction wear behavior of the friction sub-material of the pivot rail. The results revealed that a significant amount of molten aluminum was transferred to the rail surface after multiple launches, increasing the roughness of the pivot-rail interface due to the residual deposit layer. As a result, the pivot-rail friction sub-contact deteriorated, characterized by organizational features such as gouges and cracks on the rail surface. The wear intensity escalated with an increase in the number of launches. However, after a certain number of launches, the aluminum alloy oxide layer on the rail surface reached a critical thickness, reducing the wear on the rail body. Nonetheless, mechanical and electrical wear simultaneously intensified the environmental conditions at the pivot-rail contact surface.

Finally, a liquid film fusion deposition model at the pivot-rail interface was developed, and the deposited layer’s impacts on the operational dynamics of the liquid film and the electrical contact condition of the pivot-rail interface were studied. The study involved the calculation of the thickness of the deposited layer and the deposition efficiency for varying launch times. During high-speed launches, the aluminum liquid layer experienced significant viscous forces, and pronounced velocity variations of the liquefied layer at the armature tail exit increased viscous dissipation forces. With multiple launches, heightened interfacial friction can counteract the viscous forces within the aluminum liquid layer, destabilizing the interfacial liquid film. Thickening the aluminum deposition layer on the rail surface can exert extrusion effects on the liquid film, introducing destabilizing factors to the flow of the liquefied layer. Consequently, the aluminum liquid layer, which serves as a lubricant between the armature and the rail, may be extruded from the interface. Therefore, the armature’s normal operation is compromised, and the rail's longevity is diminished.

With the remarkable growth of renewables, distributed power generation systems (DPGSs) are starting to take over the dominant role of synchronous machines. As an essential interface between renewables and power grids, the grid-connected inverter plays an important role in the safe and stable operation of DPGSs. Among two types of grid-connected inverters, i.e., grid-following (GFL) and grid-forming (GFM) ones, attention has gradually turned to the GFM inverter in recent decades, owing to its synchronous-machine-like characteristics and capability of operating in weak grid or even forming a stand-alone grid. However, similar to the GFL inverter, the GFM inverter may exhibit non-passive characteristics in the mid/high-frequency bands, leading to mid/high-frequency resonance risk.

The existing research mainly focuses on sub-synchronous oscillation, but the mid/high-frequency resonance issue still needs to be explored. In order to mitigate the mid/high-frequency resonance and harvest the desired performance, this paper provides the optimal design procedure for controller parameters from the perspective of internal stability and the impedance reshaping method via the grid current feedforward from the perspective of external stability.

Firstly, a mathematical model of the voltage-current double-loop controlled GFM inverter is established. The control block diagram of the inverter’s control system is depicted, and its equivalent transformation is performed. Accordingly, the impedance model of the GFM inverter is obtained as a controlled source in series with the output impedance.

After that, the stability of the GFM inverter is divided into internal stability and external stability, which characterize the stability of the equivalent voltage source and the interaction stability between the equivalent impedance and the grid, respectively. From these two stability dimensions, the stability mechanism and resonance risk of the GFM inverter are analyzed based on the Nyquist stability criterion and the passivity theory, and the main factors affecting the system stability are revealed.

According to the internal stability constraints, stability margin requirements, and steady-state error, an optimal design procedure for the control parameters is provided, which avoids repeated trials and ensures internal stability and low steady-state error. Additionally, based on the external stability constraints, the impedance shaping scheme with the grid current feedforward is proposed, and the corresponding feedforward function is derived. The proposed scheme is simple to implement and can effectively enhance the inverter's robustness against grid impedance variations.

Finally, experiments are carried out on a 10 kW GFM inverter prototype. The results confirm that under different grid conditions, the inverter can with the designed parameters and the proposed scheme continuously operate stably, and the power quality is high, which verifies the theoretical analyses and the proposed scheme.

Developing high-voltage silicon carbide (SiC) devices has enabled breakthroughs in voltage levels, power density, and efficiency in power electronic systems. Research institutions and manufacturers have recently created high-voltage SiC devices with ratings over 10 kV and 15 kV. These devices can increase the voltage level of large-capacity converters to 10 kV or higher and achieve megawatt power levels using only two- or three-level topologies. However, as voltage levels rise, the isolated power supplies for the SiC device drive circuits face greater challenges in voltage-withstand capability. These isolated power supplies draw power from the low-voltage side to supply the high-potential drive circuits. While they only need a few watts, they must withstand isolation voltages from several kilovolts to tens of kilovolts because they connect to the main circuit of the converter.

The high-frequency current transformer (HCT) is a promising isolated power supply structure known for its strong resistance to dv/dt. This advantage comes from the high integration of ultrahigh-frequency electromagnetic coupling and the low coupling capacitance of single-turn coils on the primary side. However, current research on HCT-isolated power supply mainly targets optimizing transmission efficiency, power, and coupling capacitance. There has been little systematic study of its unique insulation characteristics. As a result, the optimization design methods are unclear, and assessing insulation voltage capacity is challenging.

This paper investigates the insulation characteristics of the HCT-isolated power supply for high-voltage SiC devices. It examines six key structural factors: the inner diameter, height, and thickness of the magnetic core, as well as the winding method and wire diameter for both primary and secondary windings. This paper proposes an electric field optimization design method under compact size constraints. Additionally, a high voltage experimental platform was established to clarify the relationship between key structural parameters and the initiation voltage and discharge magnitude of partial discharges. The voltage withstand characteristics of the HCT isolated power supply were also verified. Simulation and experimental results indicate that using concentrated winding for the secondary winding results in a more uniform electric field within the structure. The inner diameter and height of the magnetic core, as well as the turns and diameter of the secondary winding, have significant effects on the electric field and partial discharge. However, the thickness of the magnetic core has a relatively weak influence on insulation capability. This study provides a theoretical basis for the design and optimization of the HCT-isolated power supply and experimentally verifies the specific effects of key structural parameters on insulation performance.

Epoxy resin (EP) possesses advantages such as low cost, high mechanical strength, robust chemical resistance, and excellent electrical insulation properties, making it extensively utilized in various epoxy cast electrical equipment like dry transformers and reactors. Nonetheless, the three-dimensional cross-linked network of resins exhibits non-melting characteristics, posing challenges in the degradation and recycling of retired epoxy electrical equipment. Nowadays, researchers have achieved epoxy resin recycling by incorporating dynamic covalent bonds into the epoxy resin crosslinking network to develop degradable Vitrimer epoxy resin materials. However, when applied to complex environments like high temperature, humidity, and intense electric fields, the internal crosslinking network of epoxy Vitrimers material may deteriorate, impacting its operational longevity. Therefore, besides ensuring favorable electrical, mechanical, and thermal properties, the enduring reliable performance of Vitrimer resin cannot be disregarded. This paper prepared dual-dynamic bonds Vitrimer resin with varying disulfide bond contents. The micromorphology, electrical characteristics, mechanical properties, dynamic thermodynamic properties, and degradation properties of Vitrimer resin at diverse aging stages were regularly investigated and the life evaluation model is constructed at last.

Firstly, dual dynamic crosslinked Vitrimer resin basded on ester bonds and varied disulfide bonds were prepared with 3,3’-dithiodipropionic acid (DTDPA) and hexahydro-4-methylphthalic anhydride (MHHPA) as the curing agent, with Triethanolamine acting as the catalyst. Subsequently, the accelerated thermo-oxygen aging tests were carried out, during which the microscopic morphology, electrical properties, bending characteristics, dynamic thermodynamic attributes, and degradation properties of vitrimer resin were periodically evaluated. Experiment results revealed alterations in the resin's microstructure under hot oxygen aging, leading to random internal cross-linked network fractures that generate abundant free radicals, ultimately causing resin failure. The resin's bending strength diminishes, rigidity increases, toughness notably decreases, and the bending fracture transitions to a brittle fracture pattern. As aging progresses, a denser cross-linked network forms on the resin's surface, elevating T_g. The integration of disulfide bonds makes the resin system more susceptible to oxidation and molecular chain breakage, resulting in reduced breakdown voltage, heightened dielectric loss factor, and increased insulation deterioration. Throughout the aging process, the degradation rate of Vitrimer resin in glycol solution decreases due to surface ester bond reduction and oxide layer formation, while the destruction of the disulfide crosslinking network prevents resin degradation in dithiothreitol solution. Lastly, a life evaluation model for the dual dynamic crosslinked Vitrimer resin was formulated based on the results of bending strength and TGA tests.

The dual dynamic crosslinked Vitrimer resin has excellent comprehensive properties and can realize the recycling of decommissioned epoxy electrical equipment. In this paper, the effect of thermal oxygen aging on the properties of dual dynamic crosslinked degradable resin was studied, which laid the experimental and theoretical foundation for the long-term service of vitrification epoxy resin in electrical equipment.

Insulator is one of the most common and widely used electrical components in transmission lines, which plays a critical role in electrical insulation and mechanical support, ensuring that the current flows along the specified path and reducing electromagnetic interference with the surrounding environment. Since insulators are installed outdoors, they are exposed to wind, sunlight, rain, ice, frost and other bad weather for a long time, and their surface defects are inevitable. If the insulator appears self-explosion or drop string, which will cause leakage due to the loss of insulation, leading to electric shock accidents, thus resulting in huge economic losses. Relying on computer vision and deep learning technology, insulator defect detection from massive UAV aerial images has become an urgent problem for power operation and maintenance. However, the backgrounds of aerial images from overhead transmission line corridors are complex. Under different lighting conditions, shooting angles, shooting distances, etc., the scale of insulators in aerial images varies greatly, and the insulator strings are prone to occlusion, the defect area of the insulator is much smaller than the insulator itself. Therefore, there are numerous difficulties in detecting insulator defects in practical applications.

In recent years, compared with the traditional object detection methods, deep learning methods can quickly and accurately identify insulators and their defects from power inspection images. There is still a lack of comprehensive review of the latest progress in insulator defect detection in existing literature, without introducing object detection algorithms such as anchor free algorithm, YOLOv7, Transformer, and knowledge extraction techniques. In view of this, this article summarizes and analyzes a large number of visual methods for insulator defects detection, systematically reviews deep learning methods for insulator defect detection in drone aerial images, aiming to select appropriate detection methods for specific insulator defects and provide valuable reference for researchers engaged in transmission lines fault diagnosis.

This paper reviews the research progress of deep learning methods for insulator defect detection in UAV aerial images. Firstly, the current research status of transmission lines inspection based on deep learning is briefly reviewed. Then, the insulator defect detection methods based on deep learning are explained, mainly from the target detection models, lightweight network models, cascade detection models and other methods are summarized, which is conducive to the comparison between different deep learning methods and more helpful for power inspection personnel to select appropriate deep vision detection methods for fault diagnosis of specific electrical component. And the target detection models based on two-stage algorithms, one-stage algorithms and anchor-free algorithms are elucidated. The lightweight network models based on model pruning, knowledge distillation, low-rank decomposition, network quantization and the target detection model based on Transformer are summarized. Next, the self-built and public datasets for insulator defect detection are introduced. Due to the lack of training samples and unified dataset for insulator defect detection, scholars mostly conduct defect detection research through self-built datasets in different detection scenarios. Finally, the challenges faced by insulator defect detection methods based on deep learning are elucidated, including insufficient defect samples, low defect detection accuracy, difficulty in detecting small target defects, and feature extraction, etc. Based on existing deep learning techniques and recent research ideas, several important research directions in the future are pointed out, including expanding insulator defect samples, establishing unified performance evaluation indicators, small and zero sample learning, new defect detection frameworks, multi-level detection of small defects, deep fusion of multiple learning technologies, cloud-edge-end collaborative fusion, and improving network model stability and real-time performance.