The DC electrical application potential of epoxy resin/Aluminum Nitride (AlN) nanocomposites applied for the packaging material in the double-sided cooling structure of 15 kV SiC-IGBT are evaluated in this paper based on experiment and simulation. The effect of the silicone gel and epoxy/AlN nanocomposites combined with the geometrical techniques on the electric stress reduction are compared under DC voltage with different temperatures. The influence of AlN nanoparticles on the electrical properties of epoxy resin is presented and a new physical resistive model is proposed to depict the electric field distribution in the packaging structure under DC voltage. The results show that the effect of the electrical properties of packaging materials on the electric field of the packaging structure is influenced by offset of metallization layers. When the offset of metallization layers is zero, the maximum electric stress in the silicone gel is larger than that in the epoxy/AlN nanocomposites at temperature above 60 °C. Maximum DC electric stress in epoxy/AlN nanocomposites as packaging materials is not sensitive to the temperature change. The 1 wt% epoxy/AlN nanocomposite has the best effect to suppress the space charge accumulation. For epoxy/AlN nanocomposites, both the electric stress reduction effect and electrical properties should be considered.

To tackle poor DC-voltage dynamics and power excursions in VSC-MTDC-connected offshore wind farms under high renewable penetration, an abnormal-condition-aware master–slave hierarchical control is proposed. A primary/auxiliary converter coordination scheme that blends voltage-margin and droop methods is first derived from station-level dynamics. Next, a dynamic layer-assignment algorithm weighs the size of DC-power swings against each station’s regulating capacity, continuously rebalancing active power after disturbances. Finally, an on-line participation policy and parameter tuner adapt the number of active converters and their settings to the prevailing state, suppressing power fluctuations and sharpening voltage response. The strategy is validated on a five-terminal offshore-wind VSC-MTDC model in PSCAD/EMTDC under severe contingencies.

This study investigates the feasibility of using epoxy resin/aluminum nitride (EP/AlN) nanocomposites as encapsulation materials for 3.3 kV four-switch IGBT power modules. EP/AlN nanocomposites with nano-AlN loadings of 1, 3, and 5 wt% were prepared. The DC electrical conductivities and charge trap distributions of the nanocomposites were characterized by isothermal polarization current (IPC) and isothermal depolarization current (IDC) measurements. Based on the bipolar charge transport model, space charge accumulation within the EP materials was simulated under varying trap densities and energy levels. Coupled electro-thermal finite element simulations were performed at elevated temperatures to compare the maximum electric field and power loss density in the packaging modules encapsulated with EP/AlN nanocomposites versus conventional silicone gel. Additionally, AC partial discharge (PD) tests were conducted on the modules encapsulated with pure epoxy and its nanocomposites at 100 degrees C to evaluate encapsulation reliability. The results show that filler dispersion is uniform up to 3 wt% but becomes densely packed at 5 wt%. This higher loading also increases the mixture viscosity to 2.6 times that of pure epoxy, adversely affecting processability. The 1 wt% EP/AlN nanocomposite exhibits the lowest space charge accumulation, trap density, and activation energy among all formulations, although elevated temperature still induces considerable space charge buildup. Simulations indicate that the module encapsulated with the 3 wt% EP/AlN nanocomposite achieves the lowest power loss density while maintaining stable electric field distribution across different temperatures. PD tests further demonstrate that the modules encapsulated with 3 wt% nanocomposite yield the lowest PD intensity and density, along with the highest PD inception voltage. The superior PD suppression of the 3 wt% nanocomposite is attributed to its optimal filler dispersion, balanced viscosity for defect-free encapsulation, and favorable charge transport behavior, as elucidated by the proposed microscopic charge transport model and macroscopic encapsulation morphology analysis.

With the increasing proportion of wind power in power systems, fast frequency response from wind turbines can effectively enhance frequency stability in high-penetration wind power systems. However, in current wind farms participating in grid frequency support, the switching among multiple control modes across different time stages can lead to a noticeable issue of secondary frequency drop. This paper proposes a coordinated control strategy of wind farms and energy storage systems (ESS) for fast frequency support, considering secondary frequency drop. The complete wind turbine frequency response process is divided into three stages and designed accordingly. In the first stage, additional power control is employed to achieve rapid frequency response from wind turbines. The second stage addresses the secondary frequency drop when wind turbines withdraw from frequency support by coordinating the output of energy storage systems for transient frequency support. Besides, during the smooth transition stage, a preset control is designed for ESS to achieve a smooth transition from the rotor speed recovery stage back to maximum power point tracking control. The case study is simulated and validated using an AC power system with a wind farm and ESS. Simulation results demonstrate the effectiveness of the proposed control framework, and comparative studies confirm its superiority.

With the escalating proportion of renewable energy sources such as offshore wind and solar PV in global energy portfolios, their inherent intermittency and variability pose significant challenges to the stability and power balance of flexible DC transmission systems. By deploying energy storage systems such as pumped hydro storage and electrochemical energy storage, the objectives of power quality management and system stability can be achieved. To address these issues, this paper proposes a cascaded high-voltage direct-connected energy storage and dissipation integrated device, featuring a modular multilevel topology that enables collaborative fault ride-through control and its engineering solutions, systems and control strategies in the application field are explored. The DC energy storage device proposed in this work exhibits favorable battery operating conditions, requires fewer batteries, and has a low cost. The proposed system effectively reduces battery capacity requirements by approximately 50

Distribution network topology identification is crucial for power system analysis and serves as a prerequisite for applications such as power flow calculation, network reconfiguration, and optimized dispatch. This paper reviews existing distribution network topology identification techniques, categorizing them into two main types: the first comprises mechanism-based optimization approaches, including matrix methods, linear programming, and clustering analysis; the second encompasses data-driven techniques, focusing on deep learning-based topology identification. Finally, it provides a comparative analysis of existing algorithms and outlines future research directions.

The continuous growth of distributed generation and loads is driving the evolution of distribution networks towards greater flexibility and intelligence. As a key enabler of this transformation, flexible interconnection devices can effectively enhance the controllability, reliability, and renewable energy hosting capacity of distribution networks. This paper firstly outlines the basic structures and operational principles of typical flexible interconnection devices. Subsequently, it systematically summarizes the current research status and challenges in key technologies within the planning and design dimension. Finally, the paper delves into the future application bottlenecks and development trends in this field, aiming to provide valuable references for in-depth research and the scaled deployment of flexible interconnected distribution networks.

The distribution network demands low loss in new transformer gear like flexible loops. Given oil-immersed transformers’ inefficiencies, this paper uses advanced genetic algorithms for optimization, slashing design time. The optimized scheme outperforms the original, verified by fluid-thermal coupling tests. It meets standards, offers practical value, and addresses industry challenges, enhancing design efficiency and temperature balance.

To address the challenges in multimodal intelligent diagnosis of transformer faults, such as limited sample size, imbalanced data distribution, insufficient feature fusion capability, and consequently low diagnostic accuracy, this paper proposes a fault diagnosis method based on Wasserstein Conditional Generative Adversarial Network with Gradient Penalty (WCGAN-GP) and deep multimodal feature fusion. A WCGAN-GP model is constructed by integrating Wasserstein distance with conditional generative adversarial learning to achieve high-quality augmentation of small-sample data. An improved Residual Network (ResNet) and an enhanced Densely Connected Network (DenseNet) are employed to perform deep feature extraction from multimodal data. A Multi-Layer Cross-Attention (MLCA) mechanism is introduced within the network to fuse deep multimodal features, enabling early fault diagnosis of transformers. Finally, the proposed intelligent diagnosis method is validated using both simulation data and dynamic model test data, demonstrating its effectiveness in improving diagnostic accuracy.

LLC resonant converters have gained widespread attention, particularly in the fields of renewable energy, electric vehicle charging, server power supplies, and so on. This paper proposed a novel LLC resonant converter, in which the resonant inductor is integrated into the transformer to form an integrated magnetic transformer. In this paper, a new type of integrated magnetic transformer structure is first proposed. Based on this structure, the corresponding magnetic circuit model is established, and the design of relevant parameters of the transformer is completed. Subsequently, the magnetic field distribution and magnetic flux line distribution diagram of the integrated magnetic transformer are obtained through Ansys simulation. Finally, experiments are conducted to verify the effectiveness of the integrated magnetic transformer in LLC topology applications.

The DC bus neutral point of the three-level neutral point clamped (3L-NPC) converter is always connected to the neutral wire of the power system due to the requirement of zero-sequence output current, based on which the additional common resonance loop via the neutral wire will be introduced. The analysis of this introduced common-mode resonance is presented in this article, and the neutral point voltage fluctuation model is established considering the coupling of multi-frequency. The proposed neutral point voltage fluctuation model reveals that the output current of the 3L-NPC causes the fluctuation excitation sources of different frequencies, and the resonance will occur when the DC capacitors and the line inductance form a resonance loop at exactly this frequency. An additional extra active filter circuit is proposed in the article to suppress the fluctuation excitation sources, and the common-mode resonance won't be motivated as a matter of course. The control strategy and the stability are analyzed based on the structure of the proposed active filter circuit. Finally, simulation results verify the accuracy of the derived neutral point voltage fluctuation model and the effectiveness of the proposed active filter circuit.

In recent years, with the large-scale integration of new energy sources such as photovoltaic and wind power and nonlinear loads into distribution transformer areas, the problem of voltage fluctuations in distribution transformers has become increasingly prominent, and the power quality issue in distribution transformer areas has become increasingly prominent. Therefore, in order to better predict and analyze the voltage trend changes of regional distribution transformers, this paper proposes a voltage prediction method based on data-driven and graph neural networks, and conducts experiments based on the operation data of 32 distribution transformers in a certain area of Shanghai. The results show that the ATGCN-TCN graph neural network model proposed in this paper has a very good fitting ability for the simultaneous prediction of multiple distribution transformer voltages.

With the large-scale integration of distributed generation and diversified loads, traditional distribution networks can no longer meet the current operational demands. To ensure the reliability of load power supply and maintain power quality, the introduction of series parallel transformers has become a critical approach for efficient integration of distributed generation and ensuring load supply reliability in distribution networks. This paper aims to analyze the operational characteristics of distribution networks incorporating series parallel transformers by developing both component-based and instantaneous value-based electromagnetic transient models, thereby validating the effectiveness of series parallel transformers and the accuracy of the instantaneous value model. Firstly, the topology and working principles of series parallel transformers are elucidated. Subsequently, a distribution network model with series parallel transformers is constructed, and corresponding control strategies are proposed. Finally, an instantaneous value model is developed based on practical application scenarios, and a component-based simulation environment is established using the PSCAD platform to verify the accuracy and effectiveness of the model. The results demonstrate that series parallel transformers significantly enhance the reliability of power supply and the quality of electric energy in distribution networks, and the instantaneous value model accurately reflects the actual operating conditions of the system.

In recent years, China has made significant breakthroughs in photovoltaic and hydroelectric power generation, effectively alleviating the problem of energy shortage. However, the high proportion of new energy access has led to an increase in power electronic devices, and has also exacerbated the problem of sub synchronous oscillations below the synchronous frequency caused by their interaction with the power grid. In order to reduce the impact of photovoltaic grid connection on the stability of the power system and avoid significant economic losses caused by sub synchronous oscillations, it is necessary to conduct research and analysis on photovoltaic grid connection systems. This article focuses on the problem of sub synchronous oscillation in photovoltaic grid connected systems. Firstly, a mathematical model of the photovoltaic power generation system is established, which includes photovoltaic arrays, inverters and their control systems, phase-locked loops, L-shaped filters, and transmission lines. Secondly, based on the mathematical model of the photovoltaic power generation system, modular modeling methods are used to derive and establish small signal models for each subsystem, and obtain the state space model of the photovoltaic power generation system. Finally, using the eigenvalue analysis method, the impact of different inverter and phase-locked loop control parameters, as well as the root locus of photovoltaic output changes, on system stability is studied and analyzed. The experimental results indicate that changes in control parameters and photovoltaic output will have varying degrees of impact on the sub synchronous oscillation generated by the photovoltaic power generation system.

The Thyristor Controlled Hybrid Transformer (TCHT) is a novel flexible interconnection device used to achieve interconnected power supply and power flow regulation in distribution networks. However, it introduces changes in the fault characteristics of distribution network lines, which may lead to unreliable operation of relay protection devices, thus affecting system stability. To ensure the safe and stable operation of the distribution network, this paper proposes a method for analyzing line faults in distribution networks containing TCHT and thoroughly examines the impact of faults on current protection. Initially, this study investigates the principles and control characteristics of TCHT, with particular emphasis on the impact of Low Voltage Ride Through control strategies during line faults in the distribution network. Subsequently, it analyzes the fault characteristic s of distribution network lines containing TCHT during interphase short circuit faults, exploring the specific impact of these faults on the various components of three-stage current protection. Finally, the analysis is validated through simulations on the PSCAD/EMTDC platform, highlighting significant changes in the fault characteristics of distribution network lines containing TCHT. This study provides a theoretical basis for the design of protection systems in distribution networks with TCHT.

The rise of the energy internet and prolific renewable energy growth highlights a key deficiency: conventional radial distribution systems lack the power regulation flexibility needed for large-scale integration. To overcome this limitation, this paper introduces a flexible interconnected distribution system architecture. We utilize the Gaussian Mixture Model (GMM) to represent the probabilistic nature of power sources and loads, which facilitates an analysis of the system's overvoltage risks. Subsequently, an optimal scheduling strategy is developed based on chance-constrained theory. Simulation results on a modified IEEE 33-node system confirm that the proposed strategy reduces network losses by 17.6 % and achieves a solution time of 14.2 s, significantly outperforming genetic algorithms. It effectively resolves voltage violations and enhances the overall capacity for integrating renewable energy.

Leakage magnetic field differential protection, which uses the symmetry of the leakage magnetic field as the diagnostic criterion, can detect short-circuit currents within the faulted turns, thereby achieving high sensitivity. However, determining the precise setting values for leakage magnetic field differential protection is challenging, complicating its practical application. Considering core saturation characteristics and the dimensional parameters of the core, yoke, and windings, this study establishes a multi-winding, multi-state analytical model of winding currents and leakage magnetic fields with electrical-magnetic coupling. By varying the winding voltage and load impedance, the model calculates the winding current and leakage magnetic field distribution, enabling the determination of the magnetic balance coefficient for the "three measurement points" in magnetic differential protection. Using a dry-type transformer at a hydropower station as a case study, the electromagnetic composite multi-state analytical model is applied to set the values for magnetic differential protection, and the magnetic balance coefficient is validated through ANSYS simulations.

Power supply reliability of distribution networks can be improved by loop-closing operations, but there is a risk of feeder overcurrent tripping. Existing loop-closing devices are characterized by complex structure, large size, high cost, and low compensation accuracy. Therefore, a loop-closing device based on a New Single-core Asymmetric Phase Shifting Transformer (NSAPST) is proposed in this paper. Firstly, the topology and input-output voltage characteristics of the NSAPST are introduced. Secondly, a typical loop-closing network model for distribution networks based on NSAPST is established. Finally, the loop-closing transfer of distribution networks based on NSAPST is verified through PSCAD/EMTDC numerical simulation and actual case analysis. The simulation results indicate that the loop-closing transfer method of distribution networks based on NSAPST is safer and more reliable compared to direct loop-closing.

The new Controllable Line-Commuted Converter (CLCC) with controllable turn-off capability employs a hybrid design of thyristors, combining the low cost and high reliability of conventional converters. During AC faults or disturbances, it uses a flexible DC auxiliary circuit to achieve forced commutation, thereby addressing the commutation failure issues of LCC converters and enhancing the stability and reliability of high-voltage direct current (HVDC) transmission systems. To study the characteristics of electric power quality and improvement measures in the AC/DC transmission system at the receiving end after integrating the new converter, a theoretical derivation based on modulation theory and commutation principles was conducted to explore the formation mechanisms of characteristic and non-characteristic harmonic components in the DC voltage and AC current. The harmonics of LCC-HVDC and CLCC-HVDC were analyzed in detail using FFT method on measured data from the converter stations.

With the wide application of large-scale photovoltaic power generation system, subsynchronous oscillation below the synchronous frequency has become an important problem affecting the stability of the power system and the safety of equipment. In order to reduce the risk of subsynchronous oscillation in photovoltaic grid-connected systems, this paper proposes a method to suppress subsynchronous oscillation in photovoltaic grid-connected systems by additional damping control of photovoltaic inverters. The additional damping control is introduced into the control link of the PV inverter with the DC voltage as the feedback input signal, so as to enhance the sub-synchronous mode damping of the PV grid-connected system. In addition, the suppression effect of different access positions of the damping controller is analyzed and compared, and the access position with the best suppression effect is proposed.