Abstract: Under the context of energy structure transition and rapid advancement in power electronics, DC-DC converters, as key interface circuits for efficient power conversion and stable power supply, have become core components in modern power systems. Among various DC-DC converter topologies, the CLLC resonant converter features high power density and excellent galvanic isolation. Its topology typically integrates a high-frequency transformer for energy transfer, which not only provides electrical isolation between input and output but also reduces the size of magnetic components by increasing the switching frequency, thereby enhancing system power density. However, parameter design of the CLLC resonant converter remains challenging, requiring a trade-off between gain flatness and soft-switching range in bidirectional operation, coordination of the complex coupling among multiple resonant elements and parasitic parameters, and satisfaction of frequency regulation and efficiency optimization under wide input/output voltage ranges-constraints that are numerous and mutually restrictive. During the control process, the system suffers from long settling time and slow dynamic response. To address these issues, this paper first introduces the topology of the CLLC resonant converter. In view of the difficulties in parameter design, the fundamental harmonic analysis (FHA) method is adopted to design the parameters of the CLLC resonant converter. Combined with the control strategy, a prototype design method for the CLLC converter is completed. Read More

Abstract: In high-altitude areas, resources are abundant and energy consumption is decentralized, and the energy system has not achieved interconnection. Hydrogen energy, as a clean energy source, can fully utilize the resources in high-altitude areas and achieve large-scale utilization of energy and chemicals, cross-time and regional transportation, and integration of various energy sources. Based on this, this paper constructs a multi-energy complementary system including electricity, heat, oxygen, and hydrogen, focusing on multi-path collaborative improvement of hydrogen and oxygen production, full utilization of photothermal resources, and enhancing system economic efficiency. It proposes an innovative operation framework for a photothermal-biomass combined hydrogen production plant. By integrating CO2 electrolysis oxygen circulation technology and photovoltaic green hydrogen auxiliary mechanism, a photothermal-biomass collaborative hydrogen production system is constructed. Firstly, a system mathematical model is built and chemical simulation analysis is conducted to verify the feasibility of the hydrogen production route. Secondly, the energy/energy efficiency of the hydrogen production system is analyzed from the perspectives of hydrogen/oxygen production rate and energy/energy efficiency. Finally, economic analysis is conducted to calculate the levelized hydrogen production cost to verify economic feasibility. Read More

Abstract: Multivariate, multi-step power load forecasting represents a classic complex time series modeling challenge, with its core difficulty lying in simultaneously capturing long-term dependencies and local non-stationary fluctuations. In this paper, the calculations of MSE and MAE are performed using standardized data scales. Consequently, the experimental results presented in subsequent chapters represent dimensionless errors on a standardized scale, rather than absolute errors measured in physical units such as megawatts. Thus, subtle numerical differences among models under this evaluation protocol remain clearly comparable. Read More

Abstract: In industrial intelligent operation and maintenance, the bearing fault signals, after dimensionality reduction through manifold learning, tend to exhibit discontinuous "fragmented" characteristics, making it difficult to depict the continuous evolution pattern of the fault. Moreover, the absence of intermediate state samples can easily lead to diagnostic errors. Therefore, this paper proposes a fault evolution trajectory reconstruction and manifold interpolation method based on parallel transport mechanism (TR-MIPT). This method utilizes local principal component analysis to construct the manifold topology, and generates pseudo-time degradation sequences based on geodesic metric; through tangent space estimation, orthogonal Procrustes alignment and discrete Riemannian connection, it realizes the distortion-free transmission of evolution gradients across coordinate systems; and combines local normal curvature and second-order geometric retract mapping to generate virtual samples and continuous evolution trajectories. Experimental results on the datasets from Case Western Reserve University and Northeast Petroleum University show that TR-MIPT can effectively reconstruct the degradation path, reduce the reconstruction error of intermediate states, and improve the diagnostic accuracy for small sample sizes and unseen intermediate-state faults. Read More

Abstract: The Russia–Ukraine conflict and subsequent European Union sanctions have reshaped Europe’s energy landscape, transforming energy from a predominantly economic commodity into a central instrument of interstate competition and strategic bargaining. Situated at the intersection of Russia’s traditional sphere of influence and the eastward expansion of the European Union and NATO, Central and Eastern Europe has long constituted a key arena in which Moscow has sought to project influence through energy relations. Existing studies often treat Russian energy assistance in broad and ambiguous terms, thereby overlooking such key dimensions as non-market concessions, political conditionality, and state-led coordination. Drawing on a state-interest perspective and combining historical analysis with contemporary evidence, this article systematically examines the mechanisms through which Russia has structured and utilized energy relations in Central and Eastern Europe. It traces the continuities and transformations from Soviet-era energy arrangements to contemporary Russian practices, arguing that energy has consistently served as a key instrument for maintaining security buffers, extending regional influence, and securing economic returns. However, the mode of engagement has shifted from planned and institutionalized subsidy-based arrangements toward more conditional and flexible practices increasingly coordinated through state-owned enterprises. Based on Russia’s differentiated strategic interests in Central and Eastern Europe, the article develops a threefold typology of partner states: “exceptional partners,” “traditional partners,” and “frontier partners.” Through case studies of Hungary, Serbia, and Moldova, it demonstrates how Russia adopts differentiated energy strategies according to the strategic position of each partner state. These include a pattern of “binding and exchange” toward exceptional partners, “redistribution and binding” toward traditional partners, and … Read More