With the global increase in demand for sustainable energy, energy storage technology has become a key factor in achieving the green energy transition. Supercapacitors, as an important electrochemical energy storage device, have shown broad application prospects in fields such as consumer electronics, grid frequency regulation, rail transportation, electric buses, military, and aerospace, due to their excellent fast charge-discharge capability, high power density, and long cycle life. This paper mainly reviews the three basic types of supercapacitors: electric double-layer capacitors, pseudocapacitors, and hybrid supercapacitors, analyzing their energy storage mechanisms and electrode materials, with a focus on the development and classification of lithium-ion capacitors. Additionally, this paper introduces new types of supercapacitor devices and their applications, and compares the safety characteristics of lithium-ion capacitors with lithium-ion batteries, highlighting the significant advantages of lithium-ion capacitors in terms of safety.

Molten salt heat storage utilizes liquid salt to absorb heat as the temperature increases and release heat as the temperature decreases. The molten salt used for heat storage is generally a eutectic mixed salt formed by mixing two or more inorganic salts in a certain proportion, which has the advantages of wide liquid temperature range, large temperature difference, high heat storage density, and long service life. Molten salt thermal storage generally uses a dual tank liquid sensible heat storage scheme, which has the advantages of constant inlet and outlet parameters of the heat storage and release heat exchanger/electric heater, small temperature difference between hot fluid outlet and hot salt tank, and simple control. It has a wide range of application scenarios in the fields of solar thermal power generation, peak shaving system of coal-fired unit aided by molten salt heat storage, molten salt direct/heat pump thermal storage and power generation, molten salt thermal storage for heating and steam supply, compressed air energy storage and compressed heat storage, etc. It is a medium to long term energy storage technology with low-cost, large capacity and long-life. The key technologies and difficulties of molten salt thermal storage are the research and development of mixed molten salt and its composite thermal storage materials with low melting point, high decomposition temperature, low corrosion, low-cost and thermally stable, the research and development of large inlet and outlet temperature difference molten salt heat exchangers and high-voltage molten salt electric heaters, and the integrated regulation and optimization of a new energy system coupled with molten salt thermal storage. At present, more than 30 integrated large capacity thermal storage solar thermal power plants have been put into commercial operation worldwide (with a total installed capacity of over 3 million kilowatts). The longest molten salt thermal storage solar thermal power plant has been successfully operating for 18 years. In recent years, in China, Huaneng Weijiamao, Guoxin Jingjiang, Huaneng Haimen, Shandong Dezhou and other thermal power plants have successively built several molten salt thermal storage peak shaving demonstration projects. At the same time, several molten salt thermal storage heating and steam supply demonstration projects have also been built in Hebei, Beijing, Zhejiang and other places. The Liaohe Oilfield has built an electric molten salt energy storage injection test station. At present, Beijing University of Technology has successfully developed a series of low melting point, high decomposition temperature, wide liquid temperature range mixed molten salt optimization formulas with melting points between 100~160 ℃ and decomposition temperatures between 560~740 ℃, and has been widely used in molten salt heat transfer and storage engineering for a long time. Zhejiang Green Storage, Huayuan Frontline and other companies have successively developed high-voltage molten salt electric heaters.

Concentrating solar power (CSP) is endowed with the capabilities of large-scale deployment, cost-effectiveness, and high-safety long-duration thermal energy storage, and generates electricity through steam turbine generator. It can replicate the grid support and regulation functions of coal-fired power plants, demonstrating significant potential as a green, low-carbon base load power source. As an effective approach to achieve the safe and reliable replacement of traditional energy with renewable energy, CSP serves as a robust underpinning for enhancing the security and flexibility of power supply.To provide a comprehensive overview of CSP technologies and the current status of the industry, and to further advance the development of the CSP sector in China, this paper summarizes the progress of China’s CSP industry in 2025. The key aspects covered include: an overview of CSP technologies, market development status, operational performance of CSP demonstration projects, industrial chain layout, R&D advancements in CSP technologies, economic viability of CSP technologies, and carbon emission reduction benefits of CSP. Finally, targeted recommendations for the future development of the CSP industry are proposed.

Driven by the national dual carbon goals and the establishment of a new power system dominated by renewable energy, large-scale pumped storage power stations (defined as those with a total installed capacity ≥ 1 200 MW) have become critical components for integrating renewable energy into the new power system. This has led to unprecedented rapid development, accompanied by a significant transformation in the role of pumped storage technology. Technological parameters are also advancing towards higher specifications, such as larger capacity, higher head, and broader load range. This paper first provides a brief introduction to the fundamental principles of pumped storage power stations, with a focused analysis of the development status and challenges of large-scale pumped storage power stations (total installed capacity ≥ 1 200 MW) both domestically and internationally. Subsequently, it examines high-parameter pumped storage units (defined as those with a unit capacity ≥ 300 MW, head > 700 m, or load variation range > 40%), discussing research progress in key unit-level technologies (such as ultra-high head hydraulic design, large-capacity structural strength, and wide-range control strategies). The paper also identifies current research shortcomings and key technical problems that need to be addressed. Finally, considering China’s current context, it proposes key research and development directions encompassing the system integration of large-scale power stations and core technologies for high-parameter units, along with recommendations for accelerating the development of key technologies for large-scale pumped storage power stations. This aims to provide theoretical guidance for the advancement of pumped storage technology in China and support the implementation of the national dual carbon goals.

Gravity energy storage technology based on solid weights is expected to become one of the important energy storage technologies in the water-scarce areas in the future due to its advantages of independent of water resources, flexible location and abundant resources, high efficiency, and no self-discharge, and can well meet the demand of energy storage technology for new energy power system. However, due to the discreteness and non-fluidity of solid objects, power fluctuations will occur during the load/unload and acceleration/deceleration process of solid objects, and will simultaneously have a certain impact on mechanical transmission and power grid systems. In addition, the heavy-load lifting machinery is still difficult to meet the needs of energy storage systems in terms of power, efficiency and stability currently. This paper first introduces the principle and classification of solid gravity energy storage technology, and puts forward the key scientific and technical problems that need to be solved. And then, aimed at three typical gravity energy storage technologies, such as underground shaft, ground building and mountain slope, the research status and challenges of the key technologies such as heavy load lifting, automatic connection and horizontal transfer, grid connection and power smoothing are analyzed, and then the engineering application status of three technologies are given. Finally, the future development trend of three gravity energy storage technologies is forecast.

In the 1980s, Sweden pioneered the construction of megawatt-scale seasonal thermal storage systems under the framework of the International Energy Agency, making this technology popular worldwide. Empirical evidence demonstrates that seasonal thermal storage can eliminate the source-load mismatch in large-scale solar heating systems, enhance the solar fraction and heat supply stability, and reduce heat prices to levels comparable to those of coal-fired systems. For China, this technology holds strategic significance in alleviating energy supply-demand contradictions and improving the utilization efficiency of renewable energy. Since 2017, seasonal thermal storage in China has entered a period of rapid growth: a series of high-level applied basic research and technology demonstration projects have been successively implemented, driving a relatively rapid decline in thermal storage costs. This paper systematically reviews the development trajectory over more than 40 years: first, it analyzes the “heat collection-storage-release” energy chain; then, it summarizes three thermal storage methods—sensible heat, latent heat, and thermochemical—and details key materials, particularly anti-seepage materials, thermal storage media, heat exchangers, system integration, and intelligent control technologies; finally, it introduces and analyzes some representative projects. Looking to the future, long-life low-cost solar seasonal thermal storage will achieve applications on the scale of tens of millions of square meters in clean heating for northern urban areas, heat supply for industrial parks, and agricultural drying, providing a paradigm for China’s “dual carbon” goals.

With the gradual promotion of the construction of the new power system, offshore wind power, tidal energy, and other offshore renewable energies have made considerable progress. At the same time, the demand for flexible underwater energy storage resources has become increasingly urgent. Therefore, this paper reviews the research progress and development prospects of underwater compressed air energy storage. Firstly, the basic principles and technical features of underwater compressed air energy storage systems are introduced. Secondly, the representative demonstration projects and current development status of underwater compressed air energy storage systems at home and abroad are summarized. Thirdly, the key technologies of underwater compressed air energy storage are outlined, including underwater gas storage, heat storage, anchoring, and other assistant operation technologies. Finally, based on the current technical bottlenecks, the future research direction and application research focus of underwater compressed air energy storage are clarified. This paper aims to provide reference for the research in the field of underwater energy storage and to improve the coordinated development of offshore renewable energy and energy storage technology.

Superconducting materials possess excellent properties such as zero resistance, diamagnetism, and the electron tunneling effect. By using them as the materials for the rotor or stator coils of motors, high-temperature superconducting motors (HTS motors) can be fabricated. Relying on their technical advantages of high efficiency, low loss, and high-power density, HTS motors have demonstrated important engineering application values in the fields of megawatt-level power equipment, such as large-scale wind turbine generator systems, marine vessel electric propulsion, and electric aviation propulsion systems. This paper first provides an overview of the application scenarios of HTS motors, including HTS motors, HTS generators, HTS linear motors, HTS motors with special structures, and HTS synchronous condensers, and introduces the research progress of HTS motors both at home and abroad. Secondly, it elaborates and summarizes the key technologies of HTS motors, including high-temperature superconducting materials, cryogenic cooling technology, and quench protection. Finally, it explores the feasible optimization approaches of HTS motors in aspects such as the motor structure, superconducting materials, cooling technology, and quench protection mechanism.

Carbon dioxide energy storage technology stands out as an efficient, stable, flexible and cost-effective solution in the realm of novel energy storage technologies. It provides powerful safeguard for the new energy system construction of China, and has promising prospects for future development. The paper first introduced the overall research progress of CO2 energy storage. And then, the basic principles and advantages, engineering applications as well as improvement ideas of gas-liquid phase change CO2 energy storage system were illustrated. Finally, the future prospects of CO2 energy storage technologies were outlined, providing valuable insights and references for subsequent research in this field.

Pumped storage is a large-scale long-term energy storage system with the best comprehensive performance, which will provide important support for the new power system dominated by new energy. However, the resources of pumped storage sites in our country are seriously insufficient, and are far from meeting the actual demand. At the same time, the seasonal output of new energy fluctuates greatly, which does not match the seasonal changes of power load, and puts forward a higher demand for the development of large-scale cross-seasonal energy storage. In view of this, research on new pumped storage systems has been carried out at home and abroad in recent years, dedicated to solving the above problems by expanding the resources and models of pumped storage. This paper defines and classifies new pumped energy storage systems, including underground pumped storage, underwater pumped storage, semi-underground pumped storage, cross-seasonal and cross-regional pumped storage, and energy storage systems based on compressed air/pumped water.

Flywheel energy storage technology as an efficient and long-lasting physical energy storage method effectively addresses the grid volatility issues caused by renewable energy sources such as wind and solar power. It is an essential part of the modern energy transition. However, the widespread application of flywheel energy storage faces technical challenges, including high costs and rotor fatigue life issues. This paper reviews the development and application of flywheel energy storage technology, with a focus on the design optimization and fatigue life analysis of flywheel rotors. To enhance energy storage density and reduce costs, significant research has been conducted on rotor shape and structural optimization, including designs for various types of disk-shaped and cylindrical structures. Frequent charging and discharging during high-speed operation cause stress variations, which in turn affect the rotor’s fatigue life. Therefore, predicting rotor fatigue life has become a key area of research. Traditional stress-strain-based fatigue life prediction methods have certain limitations under complex loading and multi-axial fatigue conditions. However, recent advancements in new prediction methods based on energy approaches, critical plane methods, and neural networks have shown stronger adaptability and accuracy. In particular, combining traditional methods with artificial intelligence technologies has greatly improved the accuracy of fatigue life predictions. In summary, significant progress has been made in materials, structural optimization, and fatigue life prediction for flywheel energy storage technology. However, challenges such as cost control and long-life design still need to be addressed in order to promote its widespread adoption in large-scale energy storage and grid frequency regulation applications.

This paper conducts a comparative study on virtual impedance and virtual admittance control strategies for grid-forming static var generators (SVGs). An SVG impedance model is established using the harmonic state-space (HSS) method to analyze small-signal stability, with frequency scanning validation implemented through a simulation platform. By deriving the inner-loop transfer functions, similar equivalence conditions between the two control strategies are identified. The impedance differences of grid-forming SVGs under both control methods are systematically investigated from a small-signal stability perspective, along with their adaptability to varying grid strength conditions. Based on the stability analysis results, parameter design principles for virtual impedance and admittance are proposed. Furthermore, leveraging the fundamental differences between the two strategies, the virtual impedance control method is optimized to enhance its stability in strong grid scenarios. Finally, a hardware-in-the-loop (HIL) experiment is conducted on the RT-LAB platform to validate the effectiveness of the theoretical analysis and optimization method proposed in this study.

The high proportion of renewable energy integration in distribution systems under the dual-carbon strategy has introduced power quality issues such as voltage violations, harmonic distortions, and three-phase imbalances. Grid-forming converters, with their active regulation capabilities, provide a feasible technical solution to address these power quality challenges. This paper focuses on the research progress in power quality enhancement technologies for grid-forming converters in high-penetration renewable energy systems and their regulation capability evaluation. First, grid-forming control strategies for power quality improvement are analyzed from two perspectives: individual converter control and cluster operation. Subsequently, evaluation methods for assessing the regulation capability of grid-forming converters are discussed, including inertia support and other key performance metrics in renewable energy-integrated grids. Furthermore, solutions for mitigating different power quality issues using grid-forming converters are systematically reviewed. Finally, future research directions for grid-forming converters in high-penetration distribution networks are outlined, providing theoretical support for power quality enhancement in high-proportion renewable energy systems.

Temperature significantly influences the performance of power batteries, with an optimal operating range of 20~50 ℃. To effectively control the battery temperature rise and prevent thermal runaway, passive battery thermal management systems based on thermal energy storage technology have proven to be an effective solution. However, the low thermal conductivity of traditional inorganic or organic thermal storage materials often limits their application, making it crucial to enhance their thermal conductivity. This paper reviews the research progress on using carbon nanotubes, carbon fibers, graphene, and expanded graphite to improve the thermal conductivity of thermal energy storage materials. Among those, expanded graphite exhibits excellent adsorption properties for organic thermal storage materials and, after hydrophilic modification, significantly enhances the adsorption capability for hydrated inorganic salt thermal storage materials. This enables the preparation of expanded graphite composite thermal storage material powders. Through compression processing, continuous carbon-based thermal conduction pathways are formed within these composite materials, increasing their thermal conductivity by more than an order of magnitude compared to the original organic or inorganic thermal storage materials, which is far superior to other carbon-based materials such as carbon nanotubes, carbon fibers, and graphene. By introducing natural rubber into organic/expanded graphite-based composite thermal storage materials, a flexible insulating network can be formed, resulting in a dual-network encapsulated structure of flexible composite phase change thermal storage materials. These materials can effectively control the temperature rise of batteries and improve the temperature consistency between cells. Hydrated inorganic salt/expanded graphite composite thermal storage materials possess both phase change and chemical thermal storage capabilities, with a thermal storage density an order of magnitude higher than that of phase change thermal storage, providing a novel solution for mitigating battery thermal runaway. Looking ahead, further development of novel flexible thermal storage materials with both phase change and chemical thermal storage functionalities is required to meet the thermal management demands of batteries across a wide temperature range.

The traditional fixed-parameter virtual synchronous generator (VSG) control strategy is difficult to maintain when it comes to ensuring long-term stable operation in the face of grid frequency disturbance and active output reference value disturbance. This strategy facilitates the multi-parameter adaptive optimal control of VSG by constructing a mathematical model of VSG and its adaptive control model. The exponential function is adopted to optimize the inertia and damping coefficients of VSG, and the tanh function is introduced to optimize the control of active sag coefficients. On the basis of these functions, and considering the process of angular frequency oscillation, the multi-parameter adaptive optimal control of VSG is realized. In conclusion, the simulation analysis and hardware in the Loop (HIL) experiment demonstrate the efficacy of the strategy proposed in this paper in enhancing the support of the grid frequency and ensuring the stable operation of the system.

To facilitate the low-carbon transition of offshore oil and gas fields, utilizing marine renewable energy becomes an important development direction for the power supply of offshore oil and gas platforms. Wind power attracts widely attention owing to its advantages of rich resources and high power generation efficiency. However, the fluctuation and intermittency may cause frequency fluctuation during grid connection. The problem becomes more serious with the gradual exit of gas turbines, leading to the reduction of inertia and frequency response resource. Aiming at the problem of frequency stability and wind power utilization in the integration of high percentage wind power into offshore oil and gas grid, a collaborative configuration method of grid-forming and grid-following energy storage systems is proposed. The frequency response characteristics of system with grid-forming energy storage are analyzed. The models of grid-forming energy storage, grid-following energy storage, gas turbine generator, and wind turbine are constructed. An energy storage configuration optimization model aimed at minimizing the average daily cost is constructed, considering operational constraints and frequency constraints induced by wind power output fluctuations as disturbance power. By applying the convex hull relaxation method, constraint linearization is achieved, enabling efficient solution of the energy storage configuration. Degradation of BESS for the configuration scheme is checked. Case studies demonstrate that the proposed method can collaboratively configurate grid-forming and grid-following energy storage. The method substantially enhances frequency stability and wind power consumption, and reduces system costs.

Household all vanadium flow battery energy storage systems for photovoltaic-storage applications are difficult to assess the energy loss economics due to the low average system efficiency under operations such as intermittent power supply, hot standby, and multiple applications, and the unbalanced distribution of energy consumption. This paper proposes a dynamic assessment method for energy loss of household all vanadium batteries, which includes loss calculation methods for flow resistance, battery polarization, ion crossing, branch current and auxiliary thermal management. The paper takes 10 kW vanadium flow battery equipment as the test research object to analyze the distribution of each energy loss parameter of the battery over time for multiple charging and discharging experiments in the constant-voltage, constant-power charging and discharging modes under photovoltaic access and to establish a loss assessment. The probability distribution function of the energy loss rate and SOC/SOD is established to evaluate the energy loss interval during the long charge/discharge cycle of the household system. The results show that the energy loss of the household system varies linearly with SOC between 266% and 402%, and the flow resistance loss accounts for 6%~7% of the interval in the long cycle operation, with the largest value near SOC=25%; the battery polarization loss accounts for 8%~9% of the interval, with the largest value near SOC=85%; the ionic cross-loss accounts for 1%~2% of the interval, with the largest value at the end of the charging and discharging period when SOC=75%; and the branch circuit loss accounts for 1%~2% of the interval. The loss value is largest near SOC=75% at the end of charging and discharging period; the branch circuit loss accounts for 4%~5% of the interval, and the loss value is largest near SOC=85%; and the loss of auxiliary thermal management equipment accounts for 5%~6% of the interval in the high temperature environment in summer, and the loss value is largest near SOC=25%. This study provides experimental guidance for the operation optimization of the optical storage and charging multi-scenario vanadium flow battery energy storage system, and the experimental data provide effective support for the improvement of system parameter design.

Overheating caused by electrical contact failure of tulip contacts is a common fault in switchgear. Traditional temperature detection techniques are difficult to directly observe and measure the hot spot temperature of the tulip contact in switchgear by going deep into the equipment. It is of great significance to use mechanical contact pressure to predict the hot spot temperature of the tulip contact. This article calculates the contact resistance through the contact pressure of the tulip contact, constructs a pressure-electromagnetic-heat-flow multi-physics coupling simulation model, and analyzes the effects of fault current, ambient temperature, and contact pressure on the temperature rise of the tulip contact. Finally, a reasonable orthogonal experiment is designed to generate a sample database of tulip contacts in switchgear. Multiple physical field coupling simulation data is used as training samples to establish a support vector regression model for predicting the hot spot temperature of tulip contacts. The research results can provide theoretical basis and technical support for the accurate prediction of the hot spot temperature of the tulip contacts of circuit breakers in KYN type switchgear and the intelligent operation and maintenance of equipment.

When the robot joint motor runs under high overload conditions, the short-term high temperature rise at the end winding will endanger the insulation of the motor winding, which will bring hidden dangers to the operation performance and reliability of the permanent magnet motor. In this paper, a transient equivalent thermal network modeling method based on lumped parameter thermal network method (LPTN) is proposed to solve the transient short-term high temperature rise of a permanent magnet motor with epoxy potting structure at the winding end under high overload conditions. The method considers the change of epoxy specific heat capacity with time and the equivalent heat capacity of each node, and deduces the iterative calculation formula of transient temperature by finite difference method. Based on the proposed model and calculation method, the instantaneous temperature rise characteristics under natural convection and epoxy encapsulation of end-winding were calculated respectively for the short-time operation of the prototype under 4 times overload, and the simulation results were compared with the Computational Fluid Dynamics(CFD) method. In addition, the effects of the thermal conductivity and overload time ratio on the temperature characteristics of epoxy were analyzed by using the established model. Finally, through the overload temperature rise experiment of the prototype, the rationality of the transient thermal network modeling method and the accuracy of the transient temperature calculation method are proved.

The Grid-forming converter(GFM) face a contradiction between transient stability and power quality under asymmetric faults. The currently dominant fault ride-through (FRT) method based on command switching fails to effectively address the issues of suppressing power double-frequency components and reducing current asymmetry. To resolve these problems, this paper proposes a multi-objective optimal control method. First, by analyzing the modification mechanism of power loop control parameters, it is clarified that the reasonable design of commands and control variables under faults is critical to achieving smooth FRT. Second, the active power reference, voltage reference, and damping parameters of GFM under symmetric faults are integrally adjusted to enhance their transient stability. Next, the impact of asymmetric faults on the transient characteristics of GFM is analyzed. Building on the symmetric FRT method, smooth FRT under asymmetric faults is realized by additionally applying the integral feedback of angular frequency deviation upon detecting negative-sequence components. Meanwhile, a multi-objective strategy for suppressing power double-frequency components and balancing current asymmetry is designed using fuzzy control to select the current reference in the negative-sequence loop. Finally, simulation results verify that the proposed method enhances FRT performance and improves the flexibility in power quality.

The inherent fluctuations and low inertia characteristics of current renewable energy generation systems lead to degraded frequency stability in power systems. Conventional DC capacitance inertia-synchronization control methods, which lack damping components, tend to cause system oscillations under disturbances. To address this issue, this paper proposes a feedforward damping strategy suitable for grid-forming converters in flexible DC receiving-end systems. By introducing DC-side voltage deviation and damping coefficients to construct feedforward damping, this strategy can compensate for the missing damping components in control systems. Through comparative analysis of small-signal models with/without damping components can regarding inertia, synchronization coefficients, and damping characteristics, we demonstrate that this strategy can effectively provide system with damping. The mathematical model of feedforward damping aligns with the physical principles of synchronous machines, overcoming the interpretability limitations of existing research methods while facilitating parameter matching and ensuring full-frequency applicability, thereby enhancing model universality. Simulation models and experimental platforms for flexible DC grid-connected systems were established, with results confirming that the proposed feedforward damping control strategy effectively suppresses system oscillations under various disturbance conditions.

As the core equipment of the power system, the temperature rise of the transformer is an important representation of its health status. The internal temperature monitoring of the transformer is of great significance to the safe and stable operation of the power grid. Aiming at the problem that it is difficult to arrange distributed sensors inside the transformer for direct temperature monitoring, this paper proposes an inverse method for measuring the internal temperature based on multi-point inverse transformation mapping of transformer surface temperature. This method constructs the matrix inverse problem model of the internal and external temperature mapping of the transformer, solves the inverse matrix through the electromagnetic heat flow coupling finite element simulation data of the transformer, and then realizes the internal temperature inversion by combining the temperature data of the outer measuring points. In this paper, the validity of the multi-point inverse transformation model is verified by multi-physical field simulation and the D-800/35 scaled transformer model. The results show that the average error of the internal temperature inversion error of the transformer is less than 1 K under the condition of less temperature input of the measuring point on the surface of the transformer, and has higher accuracy and lower computational complexity. This method can inverse the internal temperature of the transformer quickly and without sensor intrusion, and can provide theoretical support and technical support for the temperature monitoring and fault diagnosis of the transformer.

Harmonic currents significantly increase the harmonic losses and temperature rise in transformer windings. Quantifying the impact of harmonic currents on transformer temperature distribution and thermal aging life is crucial for accurately modeling transformer lifespan. This paper investigates the temperature distribution and thermal aging life of transformer windings under the influence of harmonic currents. The study is structured as follows: First, a simulation model for an 110 kV oil-immersed AC transformer, incorporating electromagnetic, thermal, and fluid flow fields, is constructed to analyze the temperature distribution characteristics of the windings under different load currents and harmonic currents. Second, a quantitative calculation model for winding hotspot temperature, considering the influence of harmonic currents, is developed and experimentally validated. Finally, an improved thermal aging life model for oil-paper insulation, accounting for harmonic currents, is proposed to quantify the impact of harmonic currents on thermal aging life. The results indicate that the winding hotspot temperature increases exponentially with the load factor and decreases exponentially with the inlet flow rate. The maximum error percentage between the simulated and measured temperatures under power frequency currents is 1.06%, while the maximum relative error between the simulated and calculated hotspot temperatures under harmonic currents is 0.855%. The thermal aging life of the windings decreases exponentially with the increase in harmonic current frequency and content. When the 250 Hz harmonic current content increases from 5% to 30%, the reduction percentage in the thermal aging life of the oil-paper insulation reaches 97.02%. The findings provide a scientific basis for addressing temperature rise detection and aging life assessment of transformers under the influence of harmonic currents.

Currently, the parallel use of silicon carbide (SiC) MOSFETs is the mainstream solution for high current carrying cases. However, under long time service conditions, the accumulation of time-varying non-uniform electro-thermal stresses will lead to different aging trajectories of the parallel devices, and this aging variability will trigger a positive feedback mechanism with different degrees of parameter drift-deterioration of parallel equalization of currents-local overstress- and accelerated parameter drift, which poses a threat to the reliability of the system. To this end, this paper proposes a parallel current sharing regulation method for SiC MOSFETs under different aging degree based on driving voltage compensation, aiming to achieve parallel dynamic current sharing under threshold voltage mismatch. First, a double-pulse test (DPT) platform and a Boost experimental platform for parallel connection of two tubes were built to deeply investigate the coupling effect between the different aging degree and the parallel current sharing; Then, the mathematical relationship between threshold voltage dispersion and turn-on voltage regulation is theoretically derived, and an current sharing regulation strategy based on driving voltage compensation is proposed and experimentally verified under different aging degrees. The results of this paper help to improve the reliability of SiC MOSFETs in parallel applications.

SiC MOSFET devices face chip aging issues caused by gate oxide degradation, with their electrical characteristics evolving during the aging process, which critically impacts key parameters such as power loss and junction temperature. To evaluate the operational performance of SiC MOSFETs and associated power electronics systems during aging, it is essential to clarify the device aging mechanisms and develop simulation models that characterize device behavior across various aging states. This paper investigates the threshold voltage degradation mechanisms of SiC MOSFETs under AC gate stress and establishes a corresponding characterization model. A device simulation model is proposed to capture the impact of threshold voltage variations on electrical characteristics. The effects of gate voltage amplitude, frequency, and temperature on threshold voltage drift are systematically analyzed through AC gate bias accelerated aging tests, enabling the development of a degradation model for threshold voltage. Key physical processes governing channel current are modeled, with threshold voltage serving as the aging indicator, to derive a channel current model reflecting the influence of aging on static characteristics. This model is integrated with nonlinear capacitance models to construct a comprehensive device simulation framework. Finally, the accuracy of the proposed model in characterizing static properties across aging states is validated through simulation-measurement comparisons. The model’s capability to simulate switching behavior before and after aging is further verified via double-pulse tests.

For the quantitative analysis of system strength of receiving end system, the formula of short circuit ratio about the network structure parameters is obtained by deducing the Thevenin equivalent circuit of receiving end system. The power stability of Thevenin equivalent circuit is analyzed. It is shown that the value of short-circuit ratio is related to the equivalent impedance angle, the phase angle difference between grid-connected voltage and Thevenin equivalent potential, and the critical short-circuit ratio under some limit conditions is further discussed. The phase angle difference index is proposed to evaluate system strength of receiving end system, and the standard of dividing system strength of receiving end system by the phase angle difference index is given. The relationship between the phase angle difference index and the potential phase in the generator is analyzed. A simulation example is given to verify the validity of the phase angle difference index in evaluating system strength of receiving end system.

To address the instability and insufficient detection accuracy of density peak clustering (DPC) caused by manual setting of the cutoff distance, this study proposes an anomaly detection method combining improved grey wolf optimization and DPC. An improved chaotic mapping is employed to uniformly initialize the grey wolf population, and a nonlinear decaying convergence factor is designed to dynamically balance global exploration and local exploitation. The Davis-Bouldin index is used as the fitness function to automatically optimize key DPC parameters, achieving parameter adaptivity. Case studies on electricity consumption datasets from multiple regions and comparative experiments against mainstream anomaly detection algorithms show a notable improvement in AUC relative to the baseline, validating the method’s significant advantages in detection accuracy and stability.

In order to improve the quality of power supply and the ability of stable operation of power system, the method of additional damping is usually used to suppress the harmonic resonance generated by the system. Compared with passive damping, the active damping strategy not only has well harmonic suppression effect, but also has the advantages of low loss and easy realization, so it has been widely used in recent years. However, the traditional active damping strategy mainly adopts the fixed control parameter design, which may cause the harmonic resonance problem when the working condition changes greatly. To solve this problem, based on the compound control strategy composed of harmonic compensation and resonance suppression in hybrid compensation system, an adaptive additional active damping composite control strategy is proposed in this paper. Firstly, we establish the parallel resonance equivalent model of the hybrid compensation system, and analyze the shortcomings of the traditional compound control strategy. On this basis, the harmonic voltage at PCC point is extracted by the second-order generalized integrator-frequency lock loop (SOGI-FLL), and the harmonic resonance suppression in the power supply system is designed and realized by adapting the parameters of the resonant suppression controller with the method of harmonic content limitation. Finally, the feasibility and effectiveness of the proposed method are verified by simulation experiments.

To enhance the accuracy and reliability of photovoltaic power prediction, this paper proposes a short-term photovoltaic irradiance prediction model based on the improved grey wolf optimizer (GWO), variational mode decomposition (VMD), particle swarm optimization (PSO), and long short term memory (LSTM). First, LGWO optimizes the key decomposition parameters K and α1 of VMD to construct a parameter optimization model. Then, LSTM predicts each mode parameter decomposed by the optimized VMD. Simultaneously, the improved PSO, using root mean square error as the objective function, optimizes the neural network parameters, including the number of LSTM hidden layers, LSTM iterations, and LSTM learning rate. This ultimately improves the prediction accuracy and reliability of the model. Finally, the output modeling and prediction analysis of a photovoltaic power plant in Gansu Province are conducted. The results show that, compared with the traditional LSTM prediction model, the proposed algorithm significantly improves the prediction accuracy.

With the development of hydraulic turbine generators towards higher rated voltages and larger single-unit capacities, higher requirements are placed on their insulation systems and corona protection performance. The electric field at the generator end is concentrated and unevenly distributed, making it a weak link prone to corona discharge. The currently adopted three-stage corona protection structure can meet the insulation performance requirements of generators under conventional operating conditions. However, with the increase in altitude, the influence of environmental parameters becomes gradually significant, necessitating a higher level of insulation corona protection capability to ensure the safe and stable operation of the generator set.In this paper, the Nelder-Mead algorithm is used to perform finite element electromagnetic simulations on the stator bars of a hydropower station's hydraulic turbine generator, optimizing the original three-stage corona protection structure and improving the generator's insulation corona protection capability. The results show that using the Nelder-Mead algorithm to optimize the corona protection materials and structure of the bars is fast in calculation speed and low in computational cost. Compared with the initial state, the optimized scheme reduces the maximum electric field strength on the bar surface by 20% under the rated operating voltage, and the optimized scheme performs well under other operating voltages. The optimal design method proposed in this paper can provide a reference for the insulation optimization design of high-voltage and large-capacity hydraulic turbine generators.

This paper addresses the practical problems of slow speed and low efficiency in traditional voltage regulation in transformer areas, and proposes a multi-time-scale voltage feedback correction control and its optimization strategy aimed at the comprehensive management of voltage over-limit, fluctuation and imbalance. Firstly, a priority evaluation mechanism for adjustable resources in transformer areas based on voltage sensitivity was established. The voltage sensitivity of reactor groups, energy storage, and flexible interconnection devices was derived and analyzed. Considering multi-dimensional weight characteristics, a comprehensive evaluation of the regulation priority of adjustable resources was conducted. Based on this, for the key nodes of the transformer area, combined with the proposed multi-scenario equipment adjustment scheme, the multi-time-scale voltage feedback correction control strategy was analyzed from three modules: data input, voltage prediction and instruction output. Further considering the influence of measurement errors and unknown disturbances, based on the design of the optimal prediction window, corresponding optimization strategies are proposed.

Moisture ingress is one of the key factors that leads to the degradation of silicone oil performance and induces partial discharge, posing a serious threat to the operational safety of power equipment. This study investigates the discharge behavior of silicone oil under different moisture content conditions by controlling exposure durations (0, 1, 2, 3, and 5 days) to regulate its water content. A systematic analysis is conducted on how varying moisture levels influence the partial discharge characteristics of typical insulation defects within cable terminals. Two types of discharge models (needle-plate and surface discharge structures) are constructed to simulate typical defects. Partial discharge signals are collected and analyzed to quantify discharge magnitude, frequency, and phase-resolved characteristics. The results show that silicone oil becomes saturated with moisture after approximately five days of exposure, with increased moisture content significantly intensifying partial discharge activity. Under the needle-plate defect model, the discharge magnitude at the same voltage level increased by 478%, 586%, and 546% compared to new oil; under the surface defect model, the increases were 226%, 379%, and 518%, respectively. Furthermore, under identical conditions, the maximum discharge quantity induced by the surface defect was at least 23 times greater than that of the needle-plate defect.

With the gradual increase of photovoltaic(PV) penetration in low-voltage distribution network(LVDN), solving the voltage overrun problem at the grid-connection point by PV inverter power control has received wide attention. Therefore, this paper proposes a voltage control strategy for grid-connected points based on power adaptive adjustment, considering the operating constraints of PV inverter and the relationship between output powers. Firstly, the PV inverter operation process is divided into two modes and six different zones, and the limit values of inverter output power in different operation intervals are clarified. Then, the power outputs of the inverter in the two modes are analysed in detail, and the voltage overruns are classified into the priority of governance in different operation zones. Finally, considering the influence of power output on grid-connected point voltage when voltage crosses the limit, the power reduction effect coefficient is defined respectively when voltage crosses the upper and lower limits, and the governance effect after active reduction is analysed, making full use of the adjustable capacity of the inverter, and reducing the PV grid-connected active reduction as much as possible.The simulation results show that the proposed control strategy can effectively suppress the voltage overrun at the PV grid-connected point.

In China, the transmission voltage level is getting higher and higher, and the density of transmission lines is getting bigger and bigger. Under the background of energy green low-carbon transformation, the absolute amount of power loss of overhead ground wire cannot be underestimated. The analysis of current distribution and power loss of ground wire is the basis of the study of loss reduction. However, existing calculation methods ignore the influence of distribution parameters and spatial structure of ground wire, resulting in a low calculation accuracy, and the simulation is the main research method for related researches. To solve this problem, this paper proposes a calculation method of current distribution and power loss of the overhead ground wire with different grounding modes. The dual-ground line network model is disassembled into multiple units, and the grounding, merging, and blocking operations of Thevenin’s theorem and the indeterminate conductivity matrix are used to integrate and equate multiple spacing, simplify the left and right side models of the ith spacing, and ultimately obtain the current along the ground line, and then calculate the loss of the ground line. Through the validation, it is concluded that the accuracy of the proposed method is not less than 93.69% in calculating the current distribution of ground wire with the ground mode that double ground wires are grounded tower by tower, 95.29% in calculating the current distribution of the ground wire with the ground mode that ordinary ground line is segmental insulation and single point grounding and optical fiber composite overhead ground wire（OPGW）is grounded tower by tower, and 92.54% in calculating the power loss. This method provides a theoretical foundation for the research of power loss reduction strategy of ground wire.

Traditional transformer expansion techniques commonly involve increasing the physical capacity of transformers to cope with the continuous and steady growth of electrical loads. However, this expansion method struggles to address short-term load spikes, requiring additional investment costs and often leading to idle transformer capacity. To solve these issues, this paper proposes a transformer capacity expansion scheme based on energy storage devices, leveraging the advantages of additional power support from energy storage systems and the maturity of traditional transformer control and protection technologies to provide diversified ancillary services for future smart distribution networks. Firstly, this paper proposes an annual average cost model for the collaborative configuration of transformers and energy storage systems. Subsequently, a collaborative optimal configuration model for transformers and energy storage systems is established, with the objectives of minimizing load curtailment indices and comprehensive economic cost indicators. To evaluate the effectiveness of capacity expansion, three comprehensive benefit evaluation indicators are introduced: namely, average effective utilization rate of transformers, peak shaving and valley filling capability, and comprehensive economic cost. Finally, simulation results demonstrate that this optimal configuration scheme can alleviate transformer overload levels in the overall power grid, balance short-term transformer overload costs with energy storage unit construction investment costs, and provide a reference for developing more scientific and reasonable application practices for the collaborative configuration of transformers and energy storage systems in future scenarios.

The gearbox of a wind turbine is the core component for energy transmission in wind turbine units. Vibration signals, serving as a critical data source for fault diagnosis of the gearbox, can accurately reflect the internal dynamic characteristics of wind turbines. However, during actual operation, internal vibration signals of gearboxes are susceptible to multi-source compound noise interference, causing traditional signal denoising techniques to face bottlenecks in effectively separating noise. There is an urgent need to develop adaptive denoising methods for wind turbine gearboxes operating in complex service environments. This paper proposes a hybrid denoising method integrating complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN), genetic algorithm (GA), and wavelet threshold denoising (WTD). By constructing three-dimensional time-frequency-energy evaluation metrics under unknown ground truth conditions and establishing a parameter space mapping model, the method achieves multivariate collaborative optimization of wavelet basis functions, decomposition levels, threshold rules, and correlation coefficient thresholds. The system overcomes the limitations of single metrics through complementary validation of smoothness, spectral entropy, and residual energy ratio. Experimental results demonstrate that this method elevates the signal-to-noise ratio (SNR) to 12.16 dB in simulated signals, and achieves a root mean square error of 0.78×10-2, significantly outperforming traditional algorithms in SNR and transient feature preservation. Through the hierarchical noise elimination mechanism combining CEEMDAN modal decomposition and WTD, along with GA’s global parameter optimization capability, it breaks through the bottlenecks of traditional methods that rely on empirical settings and struggle with coupled parameter optimization. This provides a high-fidelity signal preprocessing solution for early fault diagnosis of wind turbine gearboxes, holding significant engineering implications for enhancing the reliability of wind turbine condition monitoring systems.

Since a large number of renewable units are integrated to the power system, the system inertia level is reduced, and the frequency stability of the power grid is faced with serious challenges. Therefore, a day ahead scheduling model of combined generation systems of thermal power plants and battery energy storage system (BESS) considering frequency security constraints of N-1 failure for thermal power plants is proposed. Firstly, for combined generation systems of thermal power plants and BESS, a frequency safety constraint is established for the N-1 fault of thermal units. Then, on this basis, the day-ahead scheduling model of combined generation systems of thermal power plants and BESS is established, which can rapidly increase the power by using the characteristics of the instantaneous discharge of BESS under N-1 failure of thermal power plants, and thus ensure that the system frequency can be operated in the secure range, while making the life damage percentage of the energy storage battery relatively low. Finally, this paper simulates and analyzes this proposed day ahead scheduling model in a practical case study, and verifies the effectiveness of the proposed model.

特约主编肖立业研究员致开篇词：

以光伏和风电为主的可再生能源替代化石能源，是实现国家能源独立和“碳中和”目标的必由之路。2021年10月24日，《中共中央  国务院关于完整准确全面贯彻新发展理念做好碳达峰碳中和工作的意见》提出：到2060年，我国绿色低碳循环发展的经济体系和清洁低碳安全高效的能源体系全面建立，非化石能源消费比重达到80%以上。综合多方面的分析和预测，到2060年，我国电力总装机将达到100~110亿kW；其中，火电（含煤电、气电、生物质/垃圾焚烧发电）12~15亿kW、水电约6亿kW、核电约2亿kW、太阳能热发电1~2亿kW、风电15~20亿kW、光伏装机60~65亿kW，总发电量将达到22~23万亿kW·h，电力占能源生产的比重将超过80%，而最大电力负荷（储能系统用电除外）将达到约30亿kW。

   风电和光伏出力具有随机性、波动性和季节性的特点，光伏发电的出力还具有昼夜周期性。根据中国电力科学研究院郭剑波院士提供的数据，各省、各区和国家电网公司经营范围内，风电光伏某天最小日平均出力水平分别为3.6%、8.0%和10.7%；3天内最小日平均出力水平分别为5.9%、9.1%、11.6%。这就是说，即使考虑较大范围内的风光时空互补性，其最小置信容量也只有装机容量的10%左右，即2060年我国全国范围内风电光伏总的最小日平均出力仅为7.5~8.0亿kW。与此同时，风电和光伏的出力还具有强烈的短时不稳定性。例如，在出现快速云层遮挡时，某些光伏电站的出力可以在1 min内下降90%；风力观测数据表明，单个站点的风功率1  min内的波动值最大可达20%、10 min内的波动最大值达到了100%。此外，由于风电和光伏装机都是通过电力电子装置并网，因而不具备同步惯量。由此可见，以新能源为主体的新型电力系统中，新能源资源的不确定性、低惯量或无惯量支撑将对电网的电力平衡与灵活调节（调频或调峰）和安全运行带来巨大挑战。

   采用直流电网模式，虽然可以避免频率稳定性问题，但以新能源为主的直流电网的电压稳定性问题将成为新的挑战，且在无储能支撑情况下，直流电网内的潮流分布波动频繁，加之电力电子装置的频繁控制和快速响应，可能导致系统出现新的电磁振荡现象。此外，将交流系统全部改造为直流系统的代价也很大。因此，未来电力系统仍将以交流同步电网为主，直流电网虽有可能因地制宜地存在于电网之中，但仍将需要交流电网作为基础与支撑。

   为应对上述问题，迫切需要发展多种形式的储能系统。为解决不同时间尺度的功率和能量调节需求，一般需要发展长周期能量转移型（周内、月内、跨季节储能）、短周期能量转移型（日内削峰填谷）、短时间尺度功率型（短时调频）三种类型的储能系统。特别是，当光伏发电成为主要电源后，日内调峰将成为储能系统最重要的任务之一。

   长周期能量平衡，一般可以通过备用化石能源或可再生能源制备燃料来应对。可再生能源制备燃料主要包括生物质制燃料、电解水制氢、电解水制氢加CO₂制备清洁碳氢燃料、人工光合作用等方式，这种类型的储能属于化学储能领域，是解决大规模能量的跨周、跨月、跨季平移问题的主要方向。

   随着可再生能源占比不断增大，惯量支撑（毫秒至秒级）、一次调频（数秒至分钟级）或二次调频需求（分钟至十分钟级）、小时级功率和能量调节、日内调峰、数日内（2~3天）调峰的储能需求量十分巨大。仅从功率响应特性和能量平移需求角度来讲，电池储能在这些方面均可发挥作用。然而，电池储能也存在明显的不足。首先，对于惯量支撑或一次调频的应用场景来说，需要储能系统频繁充放电，从而严重影响其使用寿命。在日内调峰或数日内调峰应用方面，与抽水储能系统、储热发电、压缩空气储能等物理储能相比，电池储能的综合性能（提供旋转惯量、环保性、安全性、经济性等）仍有较大差距。目前，锂离子电池是使用最多的电化学储能，但存在较大安全隐患，锂资源也较为有限。综合多方面的分析认为，电池储能在紧急功率支撑、小时级储能（1~4h）或分布式储能方面具有较大的优势。

   物理储能包括抽水蓄能、压缩空气储能、重力储能、飞轮储能、超级电容器储能、超导储能、显热储热、相变储热等。物理储能的共同特点是使用寿命长、环境友好、报废后处理简单容易。在惯量支撑或一次调频应用场景，飞轮储能和超级电容器储能都是优选方案。

   抽水蓄能具备惯量支撑、黑启动、调频、调相、调峰等多方面的综合优势，是建设以新能源为主体的新型电力系统中最为理想的储能方式之一。然而常规抽水蓄能资源不足，发展地下抽水蓄能等新型抽水蓄能，可以大大拓展抽水蓄能的站点资源，且具有与常规抽水蓄能基本相当的经济性，因而将成为抽水蓄能的重要发展方向；同时，高水头抽水蓄能电站、大规模跨季节抽水蓄能电站也日益受到关注。

   在日内调峰方面，压缩空气储能也是较好的储能系统。当前，依靠盐穴等天然洞穴作为储气室的压缩空气储能具有良好的经济性，已经得到了较为广泛的应用。为拓展压缩空气储能的资源，基于人工硐室的压缩空气储能近年来也开展了应用示范。基于高水头的恒压压缩空气储能，可有效提高储气硐室的储能利用率和系统能量转化效率，近年来也日益受到关注。此外，作为压缩空气储能的相近技术方案，压缩二氧化碳储能、液态空气储能也取得了良好的发展。

   随着储能需求的快速增长，人们在不断探索各种新型储能的同时，重力储能这类传统机械储能系统近年来也重新受到广泛关注。依托垂直竖井、斜坡和人造建筑物形成落差的各种重力储能系统的研究和示范项目越来越多。

   热能在终端能源中的占比超过50%以上，当前主要依靠化石能源来供应。随着碳中和目标的实施，供热用热低碳化也是物理储能的重要发展方向。为此，加快热储能技术的研究发展也成为当前的重要任务。热储能形式多样，电加热储能（熔盐储热、固体储热）、相变储热、冰蓄冷、跨季节储热采暖等都得到了较快的发展。其中，电加热熔盐储热还可与火电机组（煤电、气电、燃气-蒸汽联合循环、太阳能光热发电等）有机结合起来，或直供汽轮机组发电，是实现日内调峰和数日内调峰的重要储能技术方向。

   诚然，解决可再生能源规模化并网与消纳利用，需要有机融合多种形式储能系统的功能特点，使混合储能系统耦合新能源发电系统具备等效为常规火电机组所具有的各种特性，从而新能源电力系统面临的各种问题提供解决方案，但物理储能将以其良好的安全性、环保性、经济性、长寿命、可用资源可拓展性、可为电网提供机械惯量等综合优势，必将在新能源和新型电力系统建设中发挥关键作用。

   以上就是开设物理储能专刊的原因。

                                          

                                                                                                          专刊特邀主编

             肖立业

            2025年8月22日

Long-stator linear motors typically operate with sectionalized power supply, requiring rapid power transfer between stator units during linear motion. However, frequent switching induces abrupt load variations that generate current surges, threatening the reliable operation of both the motor and the power supply system. This paper proposes a fast and smooth power switching strategy integrating time-optimal control with PI regulation. The approach establishes a mathematical model of the linear motor during switching transitions and derives time-optimal turn-off/on voltage vectors alongside their corresponding minimum switching durations through time-optimal control theory. By applying the time-optimal turn-off voltage for rapid decay of the outgoing segment’s current while combining the time-optimal turn-on voltage with a PI controller output reuse mechanism for precise current establishment in the incoming segment, the proposed strategy eliminates current overshoot while compressing the switching process to 2 electrical radians. Finally, a computer simulation model validates the proposed approach, with results conclusively demonstrating the effectiveness of the switching strategy.

In complex and narrow environment, the stable power supply for downhole intelligent valve is one of the core technologies of intelligent stratified oil and gas production. It is difficult to solve the efficient transmission problem of wireless power transfer technology under coaxial misalignment in this application, which seriously affects the efficient and stable power supply of downhole intelligent valves. Therefore, this paper presents a series of wireless power transfer systems with stable and high efficiency under coaxial migration, which can effectively ensure the stability of the optimal load point under coaxial misalignment. Firstly, the optimal loads of four hybrid topologies are designed and analyzed, and the variation of optimal loads characteristics are summarized. Secondly, a kind of coaxial annulus Double-D (DD) coil is designed to be used in the hybrid topology under the narrow gap environment, and based on this, the coaxial misalignment characteristics of the magnetic coupler are analyzed. Then, the parameters of the hybrid topology are configured, and the parameters are designed according to the optimal load variation trend in different scenarios. Finally, a set of experimental prototype based on input-parallel-output-series type hybrid topology is built. The experimental results show that the optimal load fluctuation range of the system is only 12.6% and the average efficiency reaches 90.47% when the coaxial misalignment is 30 mm (mutual induction change 61.63%), which verifies the correctness of the theoretical analysis and it has certain engineering application value.