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The transient electromagnetic method,with its unique advantages of non-excavation and little influence by terrain,has been widely used and recognized in the field of non-destructive testing of surface and underground structures,especially in the detection of corrosion defects in grounding networks.In order to further break through the limitations of the current transient electromagnetic detection system in terms of detection efficiency,accuracy and adaptability,this paper proposes a transient electromagnetic detection method based on pulse modulation.Combined with scanning imaging,the corrosion location of the grounding network can be effectively detected and lo-cated.A pulse modulation-based defect detection model is established through theoretical derivation.This model quantitatively analyzes the mapping relationship between the peak information of the pulse-modulated signal and ap-parent resistivity,accompanied by sensitivity analysis and modulation frequency selection analysis.Leveraging tran-sient response signals of the grounding grid computed using COMSOL Multiphysics in conjunction with scan ima-ging,the imaging results for several typical defect locations within a 3×3 grounding grid are thoroughly analyzed.This analysis demonstrates the effectiveness and feasibility of the proposed method.Experimental validation con-firms that this approach provides a novel and more efficient solution for the non-destructive detection of corrosion defects in grounding networks.

[Objectives]Pumped storage units have gray start potential.Integrating this capability with the multi-energy complementary advantages of an integrated energy system(IES)makes it suitable for system recovery under extreme events.To investigate the post-disaster recovery mechanism of IES,this paper proposes an optimization scheduling model for a cold-heat-electricity integrated energy system(CHEIES)under pumped storage gray start.[Methods]First,stochastic scenario optimization is employed to address the uncertainties in wind,solar,cold,and thermal power.Latin hypercube sampling is used to generate a large number of random wind-solar-cold-heat scenarios,and a probability distance-based rapid reduction method is applied to reduce the number of scenarios.Then,for CHEIES under gray start,pumped storage serves as the gray start power source to provide startup power for the combined heat and power unit.A single-objective optimization scheduling model is established with gray start benefit as the core consideration,incorporating cold-heat-electricity power balance constraints to ensure the stable operation of IES under various load conditions.Finally,simulations are conducted to solve the model,and optimization scheduling strategies and economic benefits under different operation schemes are analyzed.[Results]CHEIES with pumped storage ash start-up shows high flexibility and operation efficiency in response to extreme natural disasters.Compared with the scheme without pumped storage ash start-up,the system operation cost is reduced by 12.14%.[Conclusions]The proposed method fully explores the reliability,economic efficiency,and flexibility of CHEIES under emergency conditions,providing strategic support for the rapid recovery of IES after extreme events.

When photovoltaic grid-connected inverters adopt voltage-oriented control(VOC),their dynamic response is slow,struggling to meet the national standard requirements for low-voltage ride-through(LVRT)capability in photovoltaic power generation systems.To address these issues,this paper proposed a novel hybrid control strategy to enhance the LVRT capability and dynamic performance of photovoltaic systems while improving their robustness under dis-turbance conditions.During normal grid-connected operation,the strategy employed virtual syn-chronous generator(VSG)control to achieve better grid interaction.For LVRT,proportional res-onant control(PRC)was utilized,and the functionality of model predictive control(MPC)was integrated into a single predictive repetitive control,ensuring the required LVRT capability while improving control robustness.Additionally,the vector signal before control switching was re-tained as the initial signal after switching to achieve smooth control transitions.Simulation and experimental results demonstrate that the proposed hybrid control strategy significantly enhances the LVRT capability of photovoltaic systems under fault conditions,meeting relevant national standard requirements.Moreover,the system's robustness under grid disturbances is notably im-proved.Notably,this method also effectively reduces the total harmonic distortion(THD)of grid-connected current.Through grounding fault experiments on the photovoltaic grid-connected system,THD is successfully reduced to 2.52%,far below the industry standard limit,further im-proving the system's power quality.

Lightning protection near the fan is the key point of wind farm lightning protection,which af-fects the safe and effective delivery of wind power resources.At present,the three-phase multi gap ar-rester installed on a base tower behind the collector can cooperate with the zinc oxide arrester to reduce the system failure caused by the arrester failure.However,the chopped wave generated by the multi gap arrester when it acts is transmitted to the fan box transformer along the line,which may threaten the insu-lation of the transformer winding.Based on the above problems,the author builds a simulation model on ATP to analyze the impact of wave clipping of multi gap arrester on the insulation of fan transformer wind-ings,by considering the conventional installation mode and the limit installation mode of multi gap arrest-er,and calculates that the wave clipping over-voltage generated by multi gap arrester after being struck by lightning in two cases is the impact on the insulation of fan transformer.Through the simulation analy-sis,it is found that the higher the amplitude of the lightning current,the larger the amplitude of the over-voltage generated by the truncated wave,the steeper the wave head,and the greater the threat to the in-sulation of the fan box.The damage degree of round lightning is less than that of counter lightning;When a multi-gap arrester is installed in a collector tower,the 100 kA lightning current may destroy the insu-lation of the fan box transformer winding and require additional protective measures.It is recommended that the multi-gap arrester be installed from the next pole tower of the collector tower in the wind farm.

Sodium-ion batteries,as an emerging secondary battery technology,have rapidly gained prominence in the electrochemical energy storage device market in recent years,largely due to their distinctive cost advantages and the abundant availability of sodium resources.These factors make sodium-ion batteries highly promising for large-scale applications,particularly in the energy storage sector,where cost and resource considerations are crucial.Among the various cathode materials for sodium-ion batteries,layered transition metal oxides have emerged as one of the most promising options.These materials have demonstrated significant achievements in laboratory research and have begun to show potential for commercialization.However,layered sodium transition metal oxides still face several challenges in practical applications,with the most notable bottleneck being the complex phase transition processes and their limited energy density,which hinder their performance and longevity.In the field of lithium-ion battery research,the development of lithium-rich manganese-based cathode materials has provided valuable insights for advancements in battery technology.Specifically,the involvement of lattice oxygen in redox reactions for charge compensation can significantly enhance the capacity and discharge voltage of electrodes.This mechanism not only lays the foundation for increasing the energy density of lithium-ion batteries but also offers new opportunities for the development of high-energy-density sodium-ion batteries.Compared to lithium ions,sodium ions have a larger ionic radius,leading to more diverse and complex structures and elemental compositions in sodium-layered oxides.For instance,sodium-deficient P2/P3 phase materials also exhibit oxygen redox behavior,indicating that the mechanism triggering oxygen redox is no longer limited to lithium elements but can also be achieved using more economically viable elements such as magnesium,zinc,aluminum,and iron.This broadens the possibilities for sodium-ion batteries in terms of cost control and performance enhancement.Nevertheless,while the lattice oxygen redox mechanism offers significant advantages in terms of increased energy density,it also introduces a series of potential issues.These challenges include irreversible lattice oxygen loss,complex structural changes,and ultimately,capacity loss,voltage decay,and voltage hysteresis.These phenomena severely impact the energy storage and conversion efficiency of the batteries,thereby limiting the widespread application of these materials in practice.Therefore,in-depth research on the oxygen redox mechanism in sodium-layered oxide materials is essential not only for understanding its fundamental principles but also for addressing the challenges encountered in practical applications.This review aims to systematically summarize the overall research progress on the oxygen redox mechanism,tracing developments from lithium-rich manganese-based materials to sodium-layered oxides.The research experiences gained from Li-rich cathode materials are also introduced to provide a comprehensive overview of the anionic redox mechanism's research history.Investigations into sodium-based materials have contributed new perspectives,deepening the understanding of anionic redox fundamentals.Typical oxygen redox-based sodium cathodes are classified by their structure and elemental composition.We also focus on discussing the key issues and challenges faced by these cathode materials in practical applications.Through the analysis and comparison of existing studies,this paper seeks to provide a reference for the future development of sodium-ion battery cathode materials and proposes potential solutions for enhancing their energy density and cycle stability,ensuring their viability in real-world applications.