The rapidly developing field of artificial intelligence (AI) has made significant advancements in areas such as image processing, language, decision-making, and diagnostics, providing new methods for solving complex problems. The increasing intelligence of electrical equipment, combined with the coupling of strong and weak electrical fields, has led to the emergence of multi-scale, multi-physical field coupling and nonlinear problems in electromagnetic fields. High-precision numerical modeling and optimization are increasingly challenging.

Therefore, this paper combines recent research outcomes from the author’s team to introduce deep learning methods for solving typical interdisciplinary problems, such as data-driven modeling, physics-driven PDE solving, and knowledge-embedding modeling. In particular, the paper discusses the current state of intelligent modeling for complex electromagnetic field problems driven by both data and knowledge. It also offers perspectives on the scientific challenges and important future directions in the research and engineering implementation of electromagnetic field intelligent modeling.

In the area of data-driven modeling, the paper explores its application in the performance analysis and optimization of electrical equipment. The discussion is divided into three parts: performance parameter calculation, electromagnetic thermal field prediction, and knowledge discovery modeling. By combining numerical simulation and experimental data, deep learning algorithms can mine potential knowledge from the data, enabling rapid computation of one-dimensional performance and two- and three-dimensional fields. This approach allows for real-time simulation of local performance, global performance, and micro characteristics.

Regarding physics-driven partial differential equation (PDE) solving, the paper discusses two main research directions: knowledge-embedding regularization methods and designing machine learning model structures based on physical meaning. Constructing loss functions or network structures that align with physical laws makesit possible to solve PDEs without relying on sample data. This method is beneficial when physical conditions are incomplete and sample data is scarce. Using AI to solve physical equations helps overcome traditional bottlenecks, improving computational efficiency and expanding application scope.

In the area of knowledge-embedding modeling, the paper discusses how to implicitly integrate domain knowledge, mainly through multi-fidelity models and neural network operator methods, to improve the precision and efficiency of computational models. By embedding the knowledge inherent in high-precision samples into the model, high-precision forward and inverse problem models can be built. As data accumulates, the model's accuracy and generalization ability will improve. This method fully utilizes the advantages of deep learning and integrates basic physical theories. As data grows, knowledge-embedding methods are expected to be crucial in solving more complex electromagnetic field problems and enhancing overall simulation outcomes.

In conclusion, the fusion of AI and knowledge has become a significant trend in the development of numerical simulation. Integrating data-driven, physics-driven, and knowledge-embedding methods has accelerated the advancement of electromagnetic field modeling and optimization. These methods have improved simulation accuracy and expanded the application range of numerical simulations for complex electromagnetic field problems. However, the exploration of AI in numerical simulation is still in its early stages, facing challenges such as insufficient model generalization, computational efficiency improvement, and physical constraint integration. Future research should focus on addressing these issues to promote the broader application and development of AI in the field of electromagnetic field numerical simulation.

The magnetic lift control rod drive mechanism (CRDM) is a critical electromagnetic actuator for regulating nuclear reaction rates. Its dynamic process is complex to predict due to the cross-coupling among current response, magnetic circuit saturation, and motion state. The latest equivalent magnetic network (EMN) model exhibits inaccuracies and relies on flux distribution during modeling, lacking generality. In multi-field coupling analysis, researchers often employ multi-software collaborative or semi-simulation methods, which incur significant time and hardware costs. This paper proposes a dynamic equivalent magnetic network (DEMN) model and a multi-physics field coupling calculation method considering transient current changes and saturation.

Firstly, the structure of the magnetic lift CRDM is introduced, and its lift solenoid valve is selected to analyze the electromagnetism-mechanics coupling during dynamic processes. Then, the mechanism is partitioned using orthogonal grid lines, and mesh units of multiple media are consolidated into a single medium to unify the reluctance calculation formula. During dynamic changes, only the grid size or position in the motion region is altered, thereby eliminating redundant modeling and reducing computational errors caused by mesh discrepancies. A connection relationship and calculation method for branch reluctance are established to address the misalignment between fixed and moving mesh units, facilitating continuous armature movement. A multi-physics field coupling calculation method is proposed by combining circuit models and kinematic formulas, which consider transient current changes and saturation. Finally, Compared with 3D finite element analysis (FEA) and experiments, the DEMN model and the proposed multi-field coupling calculation method are verified.

3D FEA results show that the magnetic density distribution, inductance, and electromagnetic force are highly consistent with the DEMN results, where the maximum error of inductance is 5.7%, and the maximum error of electromagnetic force is 3.4%. The experiments show that linear and saturated inductance variations are similar. The calculation accuracy of the release and suction currents under various loads exceeds 91%. Additionally, the dynamic results closely align with experimental results, with motion time calculation errors at 28 A and 40 A currents of 0.99% and 2.99%, respectively.

The conclusion is as follows. (1) By using orthogonal grid lines, the unified calculation of reluctance is achieved, accelerating the modeling speed. (2) By changing the grid size or position of local areas, the dynamic changes of the EMN model are achieved, avoiding the problem of repeated modeling in the multi-field coupling calculation process and reducing the calculation errors caused by differences in mesh partitioning. (3) Compared with FEA, the proposed DEMN model requires less computational resources and shorter computation time while ensuring accuracy. Compared with the experimental results, the effectiveness and accuracy of the DEMN model and multi-field coupling calculation method are verified. It can be extended to EMN modeling, performance analysis, and rapid optimization design of the entire CRDM.

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

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

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

This paper analyzes the electromagnetic energy flow and coupling characteristics in wireless power transmission (WPT) systems. Addressing the complexities in accurately depicting the electromagnetic energy transformation within WPT systems, the research overcomes challenges associated with the intricate mathematical methods and the absence of models capable of characterizing spatial energy flow distribution.

A model for electromagnetic energy flow in WPT under sinusoidal excitation is established based on Poynting’s theorem. A reduced-order mathematical model is developed by analyzing common electromagnetic energy flow characteristics of basic electrical components. This model qualitatively explores the energy coupling in the transmission space. The coexistence of inductive and capacitive coupling in WPT systems is discussed, emphasizing the significance of enhancing near-field electromagnetic coupling for overall system performance. The working mode of WPT in the electromagnetic near-field region is presented from the perspective of the energy flow mechanism. An experimental platform is constructed to verify the inductive and the capacitive coupling methods.

The electromagnetic energy flow characteristics of conductors, transformers, and capacitors are analyzed, facilitating power transmission through the electromagnetic fields in their vicinity rather than by themselves. The electromagnetic energy flow characteristics of WPT systems are discussed as a combination of multiple RLC circuits. It is found that electromagnetic power is partly stored in the electromagnetic fields of individual circuits (self-energy) and partly in the fields between circuits (mutual energy). The analysis is simplified by considering a system with two RLC series circuits, revealing that WPT relies on mutual coupling between the primary and secondary sides for contactless power transfer.

The paper also discusses typical magnetic resonant WPT systems using the image method to analyze the field strength distribution in the coupling space. The symmetry between inductive and capacitive coupling characteristics is revealed, offering guidance for practical engineering design. Experiments are conducted to verify the coexistence of inductive and capacitive couplings and to analyze their frequency characteristics. Results indicate that as the operating frequency increases, the ratio of capacitive coupling to inductive coupling increases, which is significant for understanding WPT technology.

In conclusion, the paper analyzes the electromagnetic energy flow and coupling characteristics in WPT systems, offering valuable insights for the theoretical research and practical application of WPT technology. It highlights the importance of understanding the coexistence of inductive and capacitive couplings and their frequency characteristics to enhance the performance of WPT systems.

As a non-contact power supply method, wireless power transfer (WPT) technology is widely used in medical, automotive, and cellular devices because of its reliability, safety, and high degree of freedom. However, the parameter drift phenomenon of the coupler inevitably occurs in practical applications, which leads to the fluctuation of self-inductance and makes the WPT system suffer from frequency detuning. Thus, its transmission characteristics and stability are affected. Traditional bilateral frequency tuning methods are non-uniform because of the type of topology, and some require communication equipment and complex optimization of control parameters. This paper proposes a unified decoupling control strategy of frequency tuning for high-order compensated WPT systems.

Four T-type higher-order compensation networks of LCC/LCC, LCC/S, CLC/CLC, and CLC/S are analyzed as examples. Based on the impedance model, the bilateral resonance characteristics of the primary-side LCC-compensated WPT system and the primary-side CLC-compensated WPT system are deduced. If the primary side is in a resonant state, the RMS value of the input current will reach the minimum. If the secondary side is in a resonant state, the RMS value of the current will reach the maximum. Finally, the generalized criterion is obtained for bilateral tuning decoupling control of higher-order compensated WPT systems.

This paper proposes a control strategy to realize the bilateral tuning decoupling control without communication or parameter identification. Instead of the inherent compensation capacitance, the switched capacitor converter (SCC) structure is used, and the equivalent capacitance of the SCC is varied by changing the conduction angle of the control signal. Based on the generalized tuning criterion, the conduction angle of the SCC control signal is changed with the help of the double-step perturbation observation method, and the primary and secondary currents are searched until the minimum value of the primary input current and the maximum value of the secondary coil current. Therefore, the WPT system reaches the resonant state while the conduction angle is optimal. The primary and secondary resonance parameters are realized independently and adaptively, and the bilateral tuning and decoupling control is achieved.

Finally, an experimental prototype of a 180 W LCC/LCC WPT system is built. The experimental results are consistent with the theoretical analysis, verifying the effectiveness of the proposed generalized tuning decoupling control strategy. The results show that the method can effectively suppress the frequency detuning problem caused by the parameter drift of the coupler and the self-inductance fluctuation, improving the transmission efficiency and stability of the WPT system. In addition, the proposed method is applicable to the high-order WPT system with a π-type compensation network.

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

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

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

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

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

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

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

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

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

In non-destructive testing (NDT), there is a growing demand for simulation tools that can predict magnetic characteristics, enhance understanding, and avoid harsh and uncertain experimental expectations. Due to the high sensitivity and non-destructive nature, the measurement and simulation of magnetic barkhausen noise (MBN) have become important in NDT.

This paper measured the MBN signals of soft magnetic materials under different stress conditions at a magnetic frequency of 10 Hz. The experimental results revealed the significant impact of tensile and compressive stresses on the MBN signals. Specifically, as tensile stress increases, the spacing between magnetic domain walls decreases, reducing energy loss in the movement of domain walls. The migration rate of the domain walls is accordingly increased, which in turn causes the MBN signals to rise. At the same time, due to the presence of additional domains in oriented silicon steel, the MBN signals exhibit a double-peak structure. As tensile stress increases, these additional domains are suppressed. Hence, peak-to-peak values one and two increase, and the increase in peak value two is significant. When a magnetic field and compressive stress are applied along the rolling direction, the compressive stress increases the energy of the magnetic domain walls, reducing their migration rate and weakening the MBN signals. Ithelpsto better understand the changes in the magnetic properties of soft magnetic materials under different stress conditions.

Existing MBN models can not accurately simulate the MBN signals of different soft magnetic materials under stress. This paper proposes a mathematical model based on the improved S-J-A hysteresis model. This model simulates MBN signals by considering the irreversible motion of magnetic domain walls in soft magnetic materials, thereby increasing the accuracy of the simulation. Specifically, the improved S-J-A hysteresis modelsimulates the irreversible hysteresis loops of soft magnetic materials, considering the relationship between magnetic anisotropy, model parameters, and stress. Then, these irreversible hysteresis loops are linked with the MBN envelope line to establish a mathematical model for the MBN envelope curve. Next, the MBN signals are simulated by modulating white noise in the 1~50 kHz range with this envelope curve. Finally, three different soft magnetic materials are selected: oriented electrical steel sheet (30QG120), non-oriented silicon steel (35WW230), and amorphous alloy (1K101). The proposed MBN model simulates MBN signals under different mechanical stress conditions.

The proposed MBN model accurately simulates the MBN signals of the oriented electrical steel sheet (30QG120), non-oriented silicon steel (35WW230), and amorphous alloy (1K101) under stress. A comparison of MBN signals between oriented silicon steel, non-oriented silicon steel, and amorphous alloy is conducted, revealing that the double-peak structure exhibited by oriented silicon steel under tensile stress is related to its anisotropy. Microscopic analysis gains a deep understanding of the stress effects on the magnetism of soft magnetic materials and the generation mechanism of MBN. The proposed MBN model provides a reliable tool in material characterization and non-destructive testing (NDT) applications, laying the foundation for further engineering applications.

As the power source of the robotic manipulators, the motors inside the joint servo systems generally start with a load directly and cannot execute position calibration due to the operating conditions. Therefore, the commonly used position acquisition scheme is the Hall position sensor during motor start-up. However, this scheme cannot start the motor with the maximum starting torque, as the Hall position sensor only provides the present sector of the motor rather than the precise angle. The traditional processing method utilizes a square-wave voltage to start up or take the middle value of the Hall sector as the angle input to the motor drive algorithm, thereby obtaining a large torque across the entire angle range of the Hall sector. These methods are simple but lose some torque in the event of a significant deviation in the position estimation.

This paper proposes a quick-startup method for surface-mounted permanent magnet synchronous motors (SPMSMs) based on a Hall position sensor. Firstly, the start-up process of different curves of random initial angles is analyzed. The deviation between the actual rotor position and the imprecise estimated position decreases the starting torque, as the Hall sector spans an angle range of 60°. Under these conditions, combined with the field-oriented control (FOC) algorithm and the maximum torque per ampere (MTPA) strategy, the quick start-up method is proposed, and the critical start-up curve parameters are numerically calculated. Although the initial and precise angles during the start-up process are not available, the proposed curve can be close to the average locus to a great extent.

The simulation and an experiment are conducted using an actual servo motor under different initial angles. The results show that when the initial rotor position is close to the minimum angle of the Hall sector, the proposed method exhibits a pronounced acceleration effect. Due to the short stroke, although the position tracking of the proposed method is slightly behind the traditional method, the time difference is negligible when the initial position approaches the maximum angle. Combined with the average start-up time of the entire initial angle in the Hall sector, the proposed method can effectively reduce the average start-up time.

A quick start-up method for SPMSM based on a Hall position sensor is proposed. In the conventional control method, the maximum starting torque and the minimum statistical value of the start-up time cannot be achieved over the entire range of initial angles. Therefore, the novel position curve is designed to improve the start-up time for small initial angles in each Hall sector while considering the start-up process at other angles. Statistical analysis has demonstrated a significant reduction in the start-up time expectation of the entire initial rotor positions. The method optimizes the torque reduction problem during the start-up process, which is caused by imprecise positioning in the first Hall sector. Moreover, the ease of transplantation allows the method to be applied to various motor drive algorithms.

The maximum torque per ampere (MTPA) control strategy can fully use the reluctance torque to output the maximum torque per unit stator current and improve the operating efficiency of interior permanent magnet synchronous motors (IPMSMs). Still, the traditional formula method or the high-frequency signal injection method requires the installation of at least two phase-current sensors to obtain the current information of the motor. Once the current sensor fails, the closed-loop control of the system will fail and cause unpredictable damage. The paper proposes an MTPA control strategy for IPMSM without current sensors. The strategy can accurately realize the MTPA control of the permanent magnet synchronous motor by calculating the optimal voltage control instruction only from the rotational speed information and the mathematical model of the system.

Firstly, the relationship between the control voltage command and the rotational speed is calculated using the formula method according to the mathematical model of the IPMSM and the conditions of the MTPA control. Secondly, inverter nonlinearity can cause the inverter output voltage to deviate from the commanded voltage, resulting in the motor deviating from the MTPA operating point. Therefore, the mean value compensation method is proposed to compensate the command voltage for the nonlinearity. Thirdly, the effect of current estimation error on the calculated voltage compensation value is analyzed. The analysis shows that even if the current estimation error exists, the average error of the voltage compensation value based on the estimated current is still 0. Finally, the effect of parameter deviation on the control strategy is analyzed, and the influence of parameter deviation on the optimal voltage command amplitude and the response current is given.

The experimental results for steady-state conditions show that the A-phase current fundamental wave amplitude of the motor with the proposed strategy is smaller than that with the traditional strategy. The effectiveness of the proposed method is verified. The experimental results at the same load torque under different speeds show that the current vector amplitude error of the MTPA control with the proposed method is small. Its maximum error does not exceeding 0.5%, while the traditional method is 14%~30%. The experimental results at the same speed with different load torques show that the current vector magnitude error of MTPA control with the proposed method is small, with the maximum error not exceeding 1%. In contrast, the traditional method’s maximum error is in the range of 2%~37%. The experimental results of dynamic operation and loaded starting conditions show that the proposed control strategy is robust to parameter deviations and has good dynamic performance.

The following conclusions can be drawn. (1) The proposed method can realize MTPA control of IPMSM without current sensors, which is of great significance to the fault-tolerant control capability of current sensor failures in the IPMSM drive system. (2) The proposed method has good dynamic performance and is robust in the variation of motor parameters. (3) The proposed MTPA control strategy considers the effect of VSI nonlinearity, and the control voltages are compensated, effectively improving the running accuracy in MTPA.

The linear induction machine (LIM) drive system can get direct thrust and linear motions without transmission, which enjoys strong climbing capability, high acceleration or deceleration ratio, and small mechanical losses. The LIM drive systems have been developed and commercialized in over 20 linear metro lines worldwide. However, due to the large air gap, end effects, and high-power, low-switching frequency drive, the LIM drive system in urban rail transit needs better efficiency. Although the existing efficiency optimization control strategies have improved machine efficiency, the parameter robustness and system efficiency still need to be addressed. This paper proposes a robust efficiency optimization strategy for three-level inverter-fed LIM systems under low switching frequency.

Firstly, the primary flux-based LIM loss model considering end effects is built, where the loss is expressed as a convex function of primary flux. Its parameter sensitivity and limitation are analyzed. Furthermore, combined with the gradient descent method, a hybrid optimal primary flux search method is proposed to eliminate the influence of parameter changes on optimal flux selection. Then, the cost function containing multiple objectives, such as primary flux control, switching frequency constraint, and neutral point voltage balance, is derived. A model-free predictive flux control based on the nonlinear-extended state observer is proposed to manipulate optimal flux flexibly under low switching frequency.

Finally, experimental comparisons with the existing methods on a 3 kW LIM confirm that efficiency and parameter robustness can be improved for the drive system under low switching frequency. The system efficiency with the proposed method can be improved by 1.22% and 0.64% compared with the mature control strategy and the existing efficiency optimization strategy under the working conditions of 8 m/s and 200 N.

The following conclusions can be drawn. (1) The proposed method takes the minimum DC-link current as the search objective, which considers the harmonic loss and inverter loss, thus improving the system’s efficiency. (2) Considering multiple objectives, such as the switching frequency constraint and neutral point voltage balance, a model-free predictive flux control with adaptive switching frequency regulation is developed. (3) By combining the hybrid optimal primary flux search method with model-free predictive flux control, the proposed method effectively avoids the influence of parameter changes and modeling errors on optimal flux selection and manipulation. In this way, the parameter robustness of the efficiency optimization control strategy is significantly enhanced.

Due to the advantages of high power level, small torque ripple, and strong reliability, dual three-phase permanent magnet synchronous motors (DTP-PMSM) have been widely used in electric vehicles, ship propulsion, and aerospace power systems. The high fault-tolerant capability for open-phase faults is an important application feature of DTP-PMSM. Developing fault-tolerant control strategies is crucial for improving fault-tolerant performance. While both the minimum loss (ML) and maximum torque (MT) control strategies offer their advantages, stator copper loss and torque output capacity cannot be simultaneously considered. The full range minimum loss (FRML) control strategy comprehensively considers both ML and MT optimization objectives. The stator copper loss is effectively reduced without sacrificing the output torque range. Currently, the FRML control strategies usually add the restriction of sinusoidal current mode. However, the restriction of the sinusoidal current mode narrows the solution space of the current reference and prevents further improvement of the fault-tolerant performance. Therefore, a FRML control strategy based on harmonic current injection is proposed.

Firstly, considering the control complexity and optimization effect, third harmonics are injected into the fault-tolerant phase current to expand the solution space. By optimizing the current references, the fault-tolerant performance of ML and MT control strategies is further improved. Secondly, considering the stator copper loss and torque output capacity holistically, an allocation coefficient is introduced to combine the ML and MT strategies nonlinearly. The fault-tolerant trajectory can be smoothly switched online by adjusting the allocation coefficient under various load conditions. The proposed FRML control strategy simplifies the implementation complexity and produces a unified expression of current reference, which effectively reduces stator copper loss over the torque range. Finally, the proposed control strategy is verified on a surface-mounted DTP-PMSM platform. The quasi-proportional resonance controllers ensure accuracy in tracking the AC current reference. Both ML and MT control strategies achieve smaller stator copper loss and larger torque output capacity after the third harmonic injection than the sinusoidal current mode. When the FRML control strategy based on harmonic current injection is applied, the allocation coefficient is modified in real-time with the change of load condition. Under the rated load of 65.5%, 67.7%, and 69.7%, the stator copper loss is lowered by 6.2%, 4.91%, and 3.1%, respectively, compared to the MT control strategy. The fault-tolerant control strategy is verified.

The following conclusions can be drawn. (1) The strategies with the injection of third harmonic exhibit the superior performance of copper losses and torque output capability than that with sinusoidal current mode thanks to the more thorough current optimization. Therefore, the fault-tolerant control strategy based on third harmonic injection is more favorable for the stator copper loss optimization in the full torque range. (2) The proposed FRML control strategy based on harmonic current injection can further expand the range of torque optimization and enhance adaptability to various load conditions. (3) The proposed fault-tolerant control strategy is scalable. Future work will be focused on extending the applicability of the proposed control strategy to other polyphase motors, such as nine-phase motors.

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

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

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

Traditional control parameter design methods of grid-connected converters (GCCs) are usually carried out under rated operation conditions. The stability margin is generally characterized by the magnitude margin (GM) and phase margin (PM). The bandwidth of the phase-locked loop (PLL) needs to be sacrificed for enough system stability margin, which ensures that the system can operate safely under non-rated working conditions. Therefore, traditional parameter design methods make it difficult to achieve a compromise between the stability and rapidity of GCC. Furthermore, the relationship between the stability margin and the output limit of the system is difficult to obtain, which relies on simulations or experiments. To address this issue, this paper proposes a control parameter design method based on the system stable operation domain, which com- prehensively considers the variable working conditions and different stability requirements.

Firstly, the complex vector open-loop transfer function G_s(s) is derived, which can analyze the stability of the system in a wide operating range or under different parameters. Secondly, varying the values of the PLL and current loop control parameters, the feasible domain of control parameters can be obtained by numerical analysis. PLL and current loop are coupled to each other due to the grid impedance. Therefore, the phase-locked loop parameter has a stable parameter boundary. Thirdly, based on the upper limit of the obtained PLL parameter, the three-dimensional diagram between the PLL parameter and the output current of the dq-axis is plotted, which shows the stable operation boundaries of GCC under different PLL parameters. Finally, taking the operation margin as the stability margin, the PLL parameter can be flexibly designed to realize the balance between the stability margin and the dynamic performance. Theoretical analysis results show that the control parameter design method based on the stable domain can ensure the safe and reliable operation of the system. Compared with traditional parameter design methods, determining the value of control parameter based on operation margin can improve the dynamic performance of PLL. At the same time, the corresponding relationship between different stability margin and the output current limit of the system can be obtained. Finally, the simulation and experiment results verify the correctness of the theoretical analysis and the effectiveness of the proposed design method.

The following conclusions can be drawn from the theoretical analyses: (1) The derived open-loop complex transfer function can be used to plot the control parameter feasible domain and the stable operation domain of GCC. The PLL control parameter satisfying the operation margin can be obtained quickly without repeated trial and error in the parameter design. (2) The analysis results show that the grid strength is positively correlated with the parameter feasible domain and the PLL cutoff frequency is negatively correlated with the stable operation domain. The cutoff frequency value of PLL is limited by the current loop parameter. The smaller the operating current in the parameter design, the wider the range of PLL cutoff frequency, and the better the dynamic performance of the PLL. (3) The control parameter design method based on the stable operation domain can directly quantify the influence of stability margin on the limit of the output current, which can be used for obtaining the stable boundaries under different stability margin. At the same time, the control parameters of PLL can be flexibly designed according to the actual needs of rapidity.

LLC converters are widely used in the power stage of battery energy storage converters due to their excellent soft switching performance and low output impedance. Under low voltage and high current conditions, matrix transformers are often used on the secondary side of LLC to reduce current stress. In practical circuits, the volume of matrix transformers accounts for about 25% of the total main power, which seriously restricts the improvement of device power density. This paper proposes an integrated optimization design of LLC four-element-matrix planar transformer considering loss and parasitic parameters. Decoupling the influence of various structural parameters of transformers on parasitic parameters this method achieves efficient operation of transformers and controllable parasitic parameters. Voltage drop and oscillation are effectively suppressed.

Firstly, establish an accurate transformer loss model based on the proposed distributed magnetic core loss calculation method. Select the key parameters of the magnetic core that meet the efficiency and volume requirements: the radius of the magnetic core's central pillar r and the total width of the winding c. Afterward, select the winding layer structure. Establish a leakage inductance model based on transformer leakage magnetic field energy, determine the feasibility of leakage inductance integration through PCB thickness constraints, and design leakage inductance values.

The experiment shows that the secondary-side V_ds voltage oscillation is significantly reduced after integration optimization, reducing the parasitic capacitance value. By matching the resonant inductance to ensure that LLC operates in critical continuous mode at 300 kHz, the magnitude of the transformer's primary leakage inductance before and after integration can be calculated. The resonant inductance before integration is 1.8 μH, indicating the original edge leakage is 0.7 μH. After integrated optimization, the resonant inductance is 2.3 μH, indicating the original edge leakage is 0.2 μH. When operating in reverse, with the same input voltage of 3.2 V, the LLC output voltage rises from 34 V to 35 V. This means that the secondary edge leakage has decreased after integration. After resonance point matching, the secondary leakage inductance can be reduced from 33 nH to 12 nH. The secondary side V_ds oscillation caused by parasitic capacitance is close and small, which verifies the control effect of parasitic parameters.

This method can achieve the following effects. (1) The proposed distributed magnetic core loss calculation method for planar transformers based on P-B curves eliminates the influence of uneven magnetic density distribution on the accuracy of the magnetic core loss model, achieving accurate modeling of integrated transformer losses. (2) This method provides a judgment method for the feasibility of leakage inductance integration. (3) The prototype parasitic parameters can be controlled by accurately modeling the leakage inductance and parasitic inductance. This method provides theoretical support for designing and optimizing energy storage converters in LLC low-voltage and high-current scenarios.

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

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

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

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

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

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

In distributed power supply and distributed energy storage technologies, a bidirectional AC-DC converter is an important energy conversion device connecting AC-DC hybrid microgrids, and its performance index directly affects the overall performance and effect of hybrid microgrids. Compared with the two-stage topology, the single-stage dual active bridge (DAB) AC-DC converter removes the intermediate DC bus capacitance with a large capacitance value, reduces the conversion link, and has apparent power density and cost advantages. The traditional DAB AC-DC converter mainly adopts the modulation strategy of phase shift, which has the problems of high current stress and narrow soft-switching range. In addition, only adopting the phase shift control leads to the nonlinear relationship between the system input current and the shift ratio, increasing the control complexity. Therefore, this paper proposes a linearization-based minimum current stress control strategy for the converter to address the problems of modulation nonlinearity and high current stress in a single-stage dual active bridge AC-DC converter. This control strategy reduces the converter’s control complexity and current stress, ensuring a wide zero voltage switch (ZVS) range of the switching tubes.

Firstly, the switching characteristics of the extended phase-shift (EPS) modulation strategy are analyzed. For the nonlinearity between the input current and the shift ratio, the input current i_ac and the shift ratio D₁ are linearly related by introducing the phase shift index k and the maximum switching frequency f_smax. The expressions of the shift ratio D₁ and the switching frequency f_s are obtained combined with power factor correction. The switching characteristics of the EPS modulation strategy are analyzed. The trajectory of the phase-shift index k under the minimum current stress is obtained by the differential polarity method. Then, the expression of the shift ratio D₂ is obtained. Finally, the soft-switching ranges are analyzed for switch tubes S₂, S₅, and S₈. Except for the DC-side switch tube S₅, which is difficult to realize soft-switching in the small range under extreme light-load conditions, the other two switch tubes can realize ZVS in the wide range in other cases.

This paper verifies the proposed control strategy by combining simulation and experiment. Firstly, regarding simulations, the proposed control strategy can achieve the linearization between the input current and the shift ratio, effectively reducing the converter current stress. An experimental prototype is constructed with an AC 50 V input, DC 12 V output, and 100 W output power. The current stress is compared before and after optimization under different input voltages and the soft-switching realization under different load conditions. The control strategy effectively reduces the current stress of the converter while ensuring that the switching tubes have a wide ZVS turn-on range.

Recently, the bus voltage of data center power architectures has been gradually increased from the traditional 12 V to 48 V to reduce the current in the distribution lines, thus reducing distribution losses. In 48 V bus-powered architectures, the uninterruptible power supply (UPS) system is connected in parallel with the 48 V bus, which causes the bus voltage to fluctuate over a wide range (40 V to 60 V). To better manage the bus voltage and energy flow, a bidirectional DC-DC converter must be inserted between the UPS and power-using systems. The four-switch Buck-Boost converter is attractive because of its high efficiency and wide voltage regulation capability. In order to reduce the energy consumption in data centers, it becomes crucial to improve the efficiency of FSBB.

This paper analyzes the voltage gain of the FSBB converter. Then, a graphical approach compares the control strategies of the FSBB converter. The unimodal control strategy has large ripples. The bimodal control strategy system is unstable. Tri-modal solves the problems of duty cycle limitation and system stability, but the duty cycle varies greatly when the transition mode is switched. Four-mode control can add a control mode in the transition section to realize smooth conversion between different modes, and the ripple of inductor current is small. It is a control strategy with excellent performance.

Then, the minimum ripple condition of the inductor current is analyzed based on four-mode control. The inductor current ripple of the FSBB converter is minimized when the phase shift time between the Buck and Boost bridge arms is controlled to zero. The average value of the inductor current is related to the output voltage, input voltage, maximum duty cycle, and output current, and it is almost the same for all four-mode control strategies. Therefore, the control method to minimize the inductor current can be obtained by simultaneously controlling the phase shift time to zero.

Next, an accurate loss model of the FSBB converter is developed. When the voltage gain is constant, the loss of the converter increases as the load current increases. When the load is fixed, the lower the switching frequency, the lower the loss. Under the same load conditions, if the voltage gain is greater than 1, the loss decreases with the gradual increase of the gain at the same switching frequency until the loss is minimized when the voltage gain equals 1. On the contrary, if the voltage gain is less than 1, the loss gradually decreases as the gain gradually increases. Thus, this paper proposes a frequency reduction control strategy to reduce the converter loss in the transition mode and improve the conversion efficiency by reducing the switching.

Finally, an experimental platform is established to test the inverter control strategy for the FSBB converter in steady states. The minimum ripple control strategy is then validated. The results show that the transition mode’s inductor current ripple with the proposed control strategy is much smaller than the conventional four-mode control strategy. Among them, the inductor current ripple of the proposed minimum ripple control strategy is 35.2% of the conventional control strategy under the operating conditions of 51 V input voltage and 48 V output voltage. After reducing the switching frequency, the inductor current ripple of the minimum ripple control strategy is still smaller than that of the conventional control strategy. The efficiency of the proposed low ripple inverter control strategy is improved over the whole load variation range compared with the traditional fixed frequency control. Among them, the peak efficiency of the proposed inverter control strategy reaches 98.52% and full-load efficiency 98.4%, which is improved by 2.46% and 2.35% compared to the conventional scheme, respectively.

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

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

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

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

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

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

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

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

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

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

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

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

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

As China advances its dual carbon strategy, integrating new energy sources into power grids has grown significantly, making power system operations more complex and dynamic. For deep learning-based models used in transient stability assessment to be reliable, the training data and the data encountered in real-world applications must be independent and identically distributed. However, because power systems are time-varying and uncertain, models trained offline may not perform well in new operational scenarios. This paper proposes a transient stability assessment-discriminative domain adaptive (TSA-DDA) framework to address variations in operating scenarios.

Firstly, an inter-domain dual distribution adaptation method was proposed. While aligning the marginal probability distributions of the source and target domains, this method also used Bayes' theorem to align the conditional probability distributions, achieving optimal domain adaptation. Secondly, both mean and variance differences between the source and target domains were comprehensively considered in the domain adaptation process. A new transfer regularization term was constructed to measure the inter-domain distribution differences, improving the model's domain adaptation capability. Finally, a discriminant Softmax function with adjustable parameters was developed to make intra-class sample features more compact while keeping inter-class sample features away by adjusting the parameters. This improvement can enhance the applicability of the assessment model to power grids.

In the case studies, the TSA-DDA framework's ability to address variations in operational scenarios was first validated on the New England 10-machine 39-bus system. Subsequently, four alternative TSA-DDA frameworks, each with specific modules removed, were established to evaluate the effectiveness of individual components. The prediction accuracy of the target and source domain test sets was compared using a fine-tuning algorithm and the TSA-DDA. The TSA-DDA’s capacity for continual learning is confirmed. The TSA-DDA was then benchmarked against mainstream transferred learning approaches to verify its effectiveness in scenarios with limited new data. Finally, to assess the generalization capability of the proposed scheme, experiments were conducted on a larger and more complex provincial power grid in Southwest China. The experimental simulations utilized the PSD Power Tools and Dynamic Simulation Program to offer high-fidelity power system simulation data for model training and testing.

The conclusions of this paper are given as follows. (1) The inter-domain dual distribution adaptation method comprehensively measures differences in marginal and conditional probability distributions between domains from both mean and variance perspectives. It constantly forces the feature extractor to narrow these differences, ensuring effective feature alignment across domains and enhancing the model’s adaptability. (2) The discriminant Softmax function improves the model’s learning of discriminative features by compacting intra-class features and separating inter-class features, which enhances the performance of the domain adaptation framework in transient stability assessment tasks. (3) Using voltage trajectory clusters with clustering and convergence properties as model inputs, the proposed framework ensures effective transferability across systems with varying structures and scales.

The dynamic transformer rating (DTR) and thermal life loss of oil-immersed transformers under on-site variable load operation conditions are closely related to the transient temperature rise of the equipment. However, as an implicit solution method, the traditional finite element analysis and finite volume method need to be iteratively solved in each sub-step of transient thermal analysis, which has many computational resources and is time consuming. It is challenging to meet the requirements of fast calculation. The rapid and accurate solution of the temperature field (especially the hot spot temperature rise) of the oil-immersed transformer in field operation is the premise to realize the digital operation and maintenance of the transformer and the DTR evaluation. Therefore, this paper proposes a lattice Boltzmann (LBM) physical in the loop simulation model for coupled electrical networks. The real time evaluation of DTR under electrical network constraints is realized through the rapid solution of the transformer temperature field.

Firstly, the D2Q9 model is used to solve the fluid flow and thermal lattice Boltzmann equations (LBEs) to capture the transient oil flow and temperature rise process inside the transformer. In the Simulink environment, the equivalent current source model is used to construct the electrical network constraints of multi-level load scenarios, and the established transformer LBM model is used as a component for numerical encapsulation to complete the construction of the physical-in-the-loop simulation model. Secondly, to verify the effectiveness of the proposed method, the finite volume method (FVM) is used to simulate the same oil-immersed transformer model. The grid independence test determines the optimal number of grids. The number of grids is 1 250×420 for LBM modeling and simulation, and the number of units is 43 654 for FVM meshing. Compared with the constructed LBM-Simulink model with the FVM model, LBM still has the advantages of speed and memory occupation when the number of lattices is higher than the number of FVM units. If commercial software is used, this advantage will be further expanded. Thirdly, the steady state solution results of the hot spot temperature rise of the established LBM model are compared with the FVM solution, and the error is 2.60%. According to the load curve given in the transformer guidelines, it is used as input to solve the transient temperature rise of the established LBM and FVM simulation models. Finally, the results show that the LBM and FVM calculations are better than the transformer guide calculation. The maximum error between the hot spot temperature calculated by LBM and FVM is 6.44%. Moreover, the hot spot temperature rise trend of LBM is consistent with the transformer load guidelines, which verifies the effectiveness of the proposed method.

Based on the constructed LBM model, the load capacity of oil-immersed transformers under constant 25℃ and typical ambient temperature changes in summer and winter are evaluated at 6~18 hours during the day. The results show that under the premise that the relative insulation life loss of oil-immersed transformers is less than 1. The maximum load capacity coefficients are 1.20, 1.10, and 1.60 under the constant ambient temperature of 25℃, typical temperature changes in summer, and typical temperature changes in winter. The simulation model based on the proposed LBM provides an effective method for real-time monitoring of temperature rise, load capacity evaluation, and dynamic capacity increase of oil-immersed transformers.

The low-voltage power supply and distribution system is directly connected to the user at the end of the power system. Its wide distribution, diverse applications, and complex structure make overhauling difficult and lack safety maintenance. Due to its negative resistance characteristics, the series arc can decrease line current, exhibiting high concealment of fault characteristics. It is a loophole in traditional relay protection methods. The series arc fault can produce high temperatures in a short time, which can cause a fire very quickly. The temperature characteristics of AC fault arcs have not been thoroughly studied, the development process and influencing factors of fault arc temperature are not apparent, and the mechanism of arc ignition and disaster needs to be clarified. This paper builds a real experimental platform for arc ignition, constructs a numerical simulation model of AC arc fault based on magnetohydrodynamics, verifies the temperature characteristics of arc fault through simulation and experiment, clarifies the ignition mechanism of arc fault, and puts forward suggestions for the improvement of relevant standards.

Firstly, based on the IEC 62606 standard, combined with a temperature acquisition device, an experimental platform for arc fault ignition risk is built to simulate arc faults. The current, voltage, temperature, and thermal imaging images are collected. Secondly, the physical characteristics of AC fault arc and related test standards are analyzed, and a complete set of fault arc simulation schemes is designed. Thirdly, the control equation, calculation domain, and boundary conditions of the arc fault magnetohydrodynamic simulation model are defined, the material parameters are designed, and the division of the simulation grid is refined. Finally, by analyzing the simulation model's calculation results, the fault arc's temperature characteristics are obtained, and experiments verify the simulation results.

The simulation results show that the temperature of the AC fault arc increases periodically, and the maximum temperature of the arc appears near the instantaneous peak value of the current. At this time, the influence range of arc temperature also increases significantly. The arc temperature is a cumulative process but develops rapidly in half an AC cycle. The arc current level and arc gap distance are the main factors influencing the maximum temperature of the arc, and the current level plays a decisive role in directly affecting the severity of the arc fire risk. The maximum temperature of the arc increases linearly with the current level below the 32 A current level, and the maximum temperature growth rate slows down after the 32 A current level.

The existing arc fault product standards can effectively limit the maximum temperature of arc fault and the influence range of arc temperature. However, even in the time specified in the standard, the arc center temperature can still reach more than one thousand degrees. Therefore, the standard can be improved by limiting the influence range of arc temperature to reduce the fire risk. Low current arc ignition ability cannot be ignored. The current level range covered by the relevant standards should be expanded, and the maximum removal time of 1 A and 2 A current level arc faults is recommended to be 3 s and 1.5 s, respectively. The standard action characteristic requirements should be refined to prevent arc fault hazards and reduce electrical fires comprehensively.