Search Results (175)

This study investigates the enhancement of long-distance microwave wireless power transfer (WPT) performance by utilizing naturally formed evaporation ducts near the sea surface. The parabolic equation method is applied to analyze how emission height, frequency, evaporation duct height and receiving aperture influence multiple convergence points and power distribution. Results show that increasing emission height transforms the power pattern from a single- to a multi-layer structure, improving spatial coverage and providing additional transmission options while slightly reducing near-surface power concentration. Higher frequencies strengthen beam confinement, with the power ratio $P_e$ at 12 GHz, about 2.7 times higher than that at 8 GHz. Furthermore, a higher EDH enhances power trapping, leading to a more complex vertical field structure and increased field strength. A larger receiving aperture also improves performance, with a 3 m aperture at 12 GHz achieving 2.5 times the power ratio of a 1 m aperture. Optimizing these parameters facilitates consistent and efficient power delivery over long distances. The findings provide theoretical support for developing sustainable wireless power transmission systems, particularly for offshore platforms, maritime vessels, and remote-area power networks. Full article

Modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission systems possess distinctive advantages such as massive transmission capacity and flexible control, making them increasingly popular for offshore wind power integration. However, offshore wind power via a MMC-HVDC transmission (OWPMMC-HVDC) system is highly susceptible to wideband oscillations caused by dynamic control interactions. Although traditional strategies can effectively mitigate oscillations within a specific frequency band, they frequently induce new oscillations in non-target bands—a phenomenon defined herein as the negative effect. To clarify the negative effect mechanism, this study first analyzes the impedance characteristics of the OWPMMC-HVDC system under traditional active and passive mitigation strategies. To reveal the damping drift characteristics across the full-frequency band, a multi-strategy coordinated oscillation mitigation approach based on the damping complementary principle is proposed. Finally, the effectiveness and superiority of the proposed coordinated oscillation mitigation strategy are verified through PSCAD/EMTDC electromagnetic transient simulations based on the 1100 MW/± 400 kV OWPMMC-HVDC system. The analysis results demonstrate that compared with the single-strategy approach, the proposed multi-strategy coordinated control successfully solves the negative effect issue. This comprehensively enhances wideband oscillation damping and the stable operation of the system, thus providing a robust oscillation mitigation strategy for practical engineering applications. Full article

To analyze the impact of the expansion of grid connections for renewable energy sources, such as offshore wind power, and the application of energy storage technologies, such as hydrogen energy storage, on the energy system, this paper develops a dynamic penetration-rate-driven analytical framework (DPRAF). It analyzes the impact of relevant factors on the dynamic renewable energy penetration rate, changes in energy structure, electricity prices, and environmental governance costs. An improved two-stage optimization process comprising planning and verification is used to obtain system schemes and hourly penetration rates across various scenarios. The study found that the scale of wind power grid connection has a significant impact, while the application of hydrogen energy storage technology has a cumulative effect. This article also clarifies the transmission mechanism of the impact of renewable energy grid connection on market electricity prices in an imperfectly competitive market environment. Every 8 GW increase in grid-connected offshore wind capacity results in a rise of approximately HKD 0.004 per kWh in the electricity price under peak-time mode. The 16–24 GW range is viewed as a pragmatic compromise zone where the benefits of emission reduction remain commensurate with the associated environmental costs; however, once installed capacity exceeds 24 GW, electricity prices and the burden of mitigation measures experience a sharp, non-linear surge. The increase in grid connection scale will widen the environmental governance cost gap between liquefied hydrogen storage solutions and other solutions. The findings of this study further highlight the necessity of balancing benefits and overall costs in the development and application of renewable energy, providing a reference for future related work. Full article

With the rapid development of wind power generation, submarine cables have become a critical transmission channel for delivering offshore wind energy to onshore power stations. Because of the difficulty of submarine-cable maintenance, particular attention should be paid to their overvoltage characteristics during operation. Taking a ±200 kV DC submarine-cable project as the research background, this paper establishes a PSCAD/EMTDC model of a two-terminal MMC-HVDC submarine-cable system and compares the conductor-to-ground overvoltages caused by faults at different electrical locations. Among the investigated AC-side cases, single-line-to-ground faults on the valve sides of the connecting transformer and bridge-arm reactor produce relatively high cable overvoltages, with the bridge-arm-reactor valve-side fault reaching a maximum of 2.48 p.u. (496.48 kV). Among all investigated cases, the grounding fault on the valve side of the DC reactor produces the highest overvoltage, reaching 2.93 p.u. (586.18 kV) at approximately 30 km along the cable. After the initial transient associated with the DC-side grounding faults, the healthy-pole conductor-to-ground voltage remains at approximately 2.0 p.u. The results identify the relatively severe fault locations and cable sections requiring particular monitoring attention and provide a case-specific reference for DC submarine-cable monitoring and subsequent project-specific insulation-coordination studies. Full article

To establish quantitative criteria for selecting the operating frequency of diode rectifier unit (DRU)-based medium-frequency AC collection and DC transmission systems, this paper proposes a life-cycle frequency-selection method for far-offshore wind power. A power-flow model incorporating wind-turbine Q–f droop control and frequency-dependent submarine-cable parameters is developed to evaluate voltage distribution, reactive-power accumulation, power factor, and steady-state losses. An electromagnetic transient model is then used to quantify energy losses caused by single-phase and three-phase AC-side short-circuit faults. These electrical results are integrated with cable and converter investment costs in a multi-stage life-cycle economic model that accounts for equipment aging and loss growth. For the studied Rudong 500 MW case under the adopted baseline parameters, medium-frequency operation increases submarine-cable reactive-power accumulation and fault losses, while the total life-cycle cost first decreases and then increases with frequency. The minimum cost occurs at 180 Hz. The proposed framework links steady-state performance, transient fault losses, and long-term economics, providing a project-oriented basis for selecting the operating frequency of DRU-based offshore wind transmission systems. Full article

Offshore wind farms are rapidly expanding into deeper and more remote ocean regions. Their structural safety and operational reliability in harsh marine environments have garnered widespread global attention. Sensing technologies capture structural and environmental conditions and are indispensable to structural monitoring. Accordingly, this review examines the applications of environmental monitoring, supervisory control and data acquisition, condition monitoring, and structural health monitoring systems covering both the horizontal-axis and vertical-axis types of fixed and floating offshore wind turbines. It also summarizes key technologies for data transmission and optimal sensor placement. However, uncertainty in sensing data can significantly affect monitoring results, yet existing studies lack an adequate summary and in-depth discussion. We therefore focus on sources of sensing uncertainty, including the marine environment, the host platform, variations in environmental and operational conditions, and sparse sensing. By analyzing their effects on monitoring data, we explore key methods for overcoming data uncertainties and improving sensing accuracy. This paper also evaluates the application potential of cutting-edge artificial intelligence and digital twin technologies. Furthermore, the study points out that fusing multi-source signal data to establish a highly reliable intelligent decision-making and early warning framework is likely to become an important development direction for offshore wind power monitoring. This review aims to provide valuable support for the safe development of offshore wind farms towards deep-sea regions over the coming decades. Full article

To meet the demand for large-capacity and long-distance transmission of deep-sea offshore wind power and coordinated export of multiple energy sources in coastal clean-energy bases, this paper investigates the topology configuration and operating characteristics of a multi-energy DC collection system for offshore wind power integration. Based on the characteristics of offshore wind power, nuclear power, onshore photovoltaic generation and pumped storage, a source-type–converter-topology–control-function matching relationship is established. A ±800 kV true-bipolar DC large-bus system is then constructed, in which the four sources are configured as a lightweight offshore wind export branch, a stable power-export branch, a fast controllable renewable-energy branch and a system regulation resource, respectively. A polarity-interface conversion link is introduced to match the local offshore wind export structure with the main true-bipolar DC system, and the power-balance relationship among sending-end injection, receiving-end absorption and DC-bus voltage is formulated. PSCAD/EMTDC simulations are performed under steady-state operation, wind-speed step disturbance, a sending-end AC three-phase metallic grounding fault and a submarine-cable pole-to-ground fault. The results confirm that the proposed differentiated topology can support multi-energy collection, true-bipolar voltage coordination and continuous stable operation under typical disturbances. Full article

China’s offshore wind power is rapidly developing towards the direction of “deep-water and far-shore, large-scale, and clustered”. Existing offshore wind power transmission schemes based on the MMC are technologically mature but highly expensive. Although transmission schemes based on the DRU possess economic advantages, they lack AC voltage support and reverse power flow capability. To combine the control performance of the MMC and the economic advantages of the DRU, this paper proposes a heterogeneous DC transmission system for offshore wind power based on the parallel operation of MMC-HVDC and DRU-HVDC, which can realize the clustered transmission of deep-water and far-shore wind power. First, the configuration scheme of the system is introduced, and the basic control strategy is proposed. Secondly, the small-signal model of the system is established, and the small-signal stability analysis is conducted. Then, the control strategies for the system under near-zero power conditions and AC/DC faults are proposed, respectively. Finally, the effectiveness of the proposed topology and control strategies is verified through PSCAD electromagnetic transient simulations. Full article

This paper systematically analyses the fault characteristics and investigates fault ride-through (FRT) control strategies for a low-frequency (LF) transmission system in offshore wind power based on Modular Multilevel Matrix Converter (M3C). The study addresses transient issues of power imbalance, submodule capacitor overvoltage, and bridge-arm overcurrent arising from three-phase ground faults on both the industrial-frequency (IF) and LF sides. The underlying mechanisms of power surplus and submodule capacitor overvoltage, induced by decoupling control and current-limiting protection during IF-side faults, are examined in detail, along with the transient characteristics of bridge-arm currents under voltage sags on the LF side. Two innovative control strategies are proposed to enhance system resilience: (1) For IF-side faults, a controllable energy dissipation device on the LF side achieves precise dissipation of surplus power via real-time monitoring of the average submodule capacitor voltage. (2) For LF-side faults, the FRT strategy based on dynamic adjustment of the LF modulation voltage rapidly reduces the reference to 0.1 p.u. and restores it linearly at a predefined rate, thereby enabling fault information transmission and wind turbine derating. The effectiveness and feasibility of the proposed scheme are verified through simulations on a 1000 MW system model. Full article

Low-frequency alternating current (LFAC) transmission has attracted increasing attention for medium- and long-distance offshore wind power transmission, as this application scenario is typically characterized by long transmission distance and large installed capacity. Converting offshore low-frequency alternating current into onshore power-frequency alternating current requires a dedicated frequency conversion device. Compared with power–electronic converter-based schemes represented by the modular multilevel matrix converter (M3C), grid connection via a motor–generator pair (M-G) enables the renewable energy port to retain intrinsic synchronous-machine characteristics, including inertial support, voltage support, and fault isolation. This paper elaborates the operating principles and mathematical models of the two types of frequency conversion solution for LFAC transmission systems, and systematically analyzes the frequency support, voltage support, and fault-isolation capabilities of the M-G scheme. Simulation results demonstrate that under a sudden increase in onshore active power load, the M-G system can provide strong frequency support by releasing rotor kinetic energy, and a larger inertia time constant mitigates the frequency drop more effectively. Under a sudden increase in onshore reactive power load, the M-G scheme offers a greater reactive power margin benefiting from its strong short-term overcurrent capability. Moreover, increasing the excitation gain on the motor side and installing shunt reactors at both ends of the submarine cable can effectively improve the voltage profile along the cable. Full article

The increasing global demand for marine energy resources, coupled with the deployment of offshore oil and gas pipelines and submarine power cables, highlights the requirement for reliable subsea infrastructure. To protect these assets from environmental hazards and anthropogenic disturbances, seabed burial via trenching is widely adopted, with submarine trenchers serving as the main installation equipment. Trenching involves excavating a trench on the seabed to place pipelines, cables, or other subsea infrastructure. These operations involve complex soil–tool interactions that fundamentally govern cutting resistance, trench-wall stability, and overall equipment performance. Specifically, distinct engineering challenges arise across different trencher configurations: plough trenchers often encounter complex seabed structures, jet-type trenchers are prone to trench sidewall collapse, and mechanical trenchers face cutting difficulties in hard clay. A thorough understanding of these interactions is therefore critical for resolving operational challenges and optimizing trencher efficiency in engineering practice. To deeply understand these type-specific issues, this review summarizes the geomechanical problems associated with various trenching technologies, synthesizes recent research advances from analytical frameworks, physical experiments, and numerical simulations, and identifies existing knowledge gaps. By consolidating these findings, the paper provides a reference for addressing trencher-related engineering challenges, supporting equipment optimization, and facilitating the deployment of offshore energy transmission networks. Full article

Self-drilling hollow bar micropiles (HBMPs), which integrate drilling, grouting, and reinforcement into a single process, have broad application prospects in mountainous transmission lines and offshore wind power projects. However, existing research has focused mainly on friction piles in soil layers, and there is a lack of systematic understanding of the load-transfer mechanism and bearing capacity calculation method for rock-socketed HBMPs. Based on field static load tests of rock-socketed HBMPs, this study systematically investigates the vertical bearing behavior and capacity calculation method of single rock-socketed HBMPs through a combination of test data analysis, finite element numerical simulation, and theoretical analysis. The field test results show that the load-settlement curves of rock-socketed HBMPs are of a slowly varying type, exhibiting mixed friction-end-bearing characteristics. After data screening, the average Q-s curve of Pile No. 1 and Pile No. 5 was taken as the benchmark, and the representative ultimate bearing capacity of a single pile determined by the 40 mm settlement criterion is 5860 kN. The test data of Pile No. 3 and Pile No. 4 were retained as independent validation data. A three-dimensional finite element model considering the cohesive contact behavior at the pile–rock/soil interface was established using ABAQUS. After calibration with the test results, the error between the simulated and measured bearing capacity is −3.4%, demonstrating good model reliability. Parametric analysis indicates that the bearing capacity increases linearly with the grouting volume increase rate $V_{\mathrm{inc}}$, with the expansion effect being the main enhancement mechanism; the improvement amplitude under hard rock conditions is significantly smaller than that in cohesive soils. The effect of uniaxial compressive strength $q_u$ of hard rock on bearing capacity is negligible because the capacity is controlled by the pile–rock interface shear strength. The bearing capacity increases approximately linearly with the rock-socketed depth $L_r$, and a minimum rock-socketed depth of 1.0 m is recommended. Analysis of the load-transfer mechanism shows that rock-socketed HBMPs rely mainly on shaft resistance (accounting for 90.6%), and the axial force decays significantly along the pile length. Elastic compression of the pile accounts for 78% of the pile head settlement, and the limited displacement at the pile tip leads to insufficient mobilization of end bearing. A modified bearing capacity formula considering the grouting expansion effect is established with shaft resistance as the core. A hierarchical validation strategy is adopted to test its predictive ability: for the finite element cases not participating in parameter calibration, the prediction error is within ±2%; for the field test piles, the prediction error is +7.9%; and for Pile No. 3 and Pile No. 4, the errors are +1.7% and −2.1%, respectively. These values are significantly better than those of existing methods (errors ranging from −72.1% to +54.5%). The research results can provide a theoretical basis for the design of single HBMP bearing capacity under rock-socketed conditions. Full article

Conventional settlement monitoring techniques are inadequate for seawall construction environments due to severe physical impacts, the absence of terrestrial communication networks, and highly dynamic disturbances. This research proposes a multi-source fusion settlement monitoring system designed specifically for the construction phase to overcome these constraints. An integrated inclinometer–magnetoresistive sensing unit is the central component of this system. The unit achieves physical isolation from the severe impact loads of rock backfilling, guarantees protection in high-salinity and high-humidity environments, and accommodates the large deformations typical of soft foundations by utilizing a structural design that includes a rigid channel steel sheath, anti-corrosion sealing, and flexible joints. In terms of computation, a cascaded attitude fusion framework is developed that combines a Multiplicative Extended Kalman Filter (MEKF) with Quaternion Estimator (QUEST) initialization. High-precision displacement inversion via quaternion rotation is made possible by the introduction of an adaptive mechanism based on the Mahalanobis distance that precisely detects and suppresses transient acceleration disturbances induced by construction machinery and waves. Additionally, data transmission issues in remote offshore areas are resolved by combining solar power and BeiDou short-message communication technologies. This adaptive technique minimizes attitude estimate errors in dynamic situations by approximately 84.56%, as demonstrated by experimental and field validation. The system was deployed as a 165 m array comprising 49 sensing units and monitored continuously for 458 days, achieving a normalized RMSE of 9.44–11.02% compared to reference settlement tubes and capturing a maximum settlement of 1.7 m in the core high-fill section. These results confirm the system’s high monitoring accuracy and resilience in harsh construction conditions. Full article

With the rapid development of offshore wind power, the fractional frequency offshore wind power system based on the modular multilevel matrix converter (M3C) faces severe frequency stability challenges due to the reduced inertia under high wind power penetration. This paper focuses on its frequency control and proposes a set of coordinated strategies. Modified frequency regulation schemes for wind turbines (WTs) under different operating states avoid secondary frequency drop (SFD) and accelerate rotor speed recovery. A coordinated power allocation strategy combining energy storage (ES) and automatic generation control (AGC) suppresses wind-induced power fluctuations, with a reducing pitch angle variation method to extend WTs’ life. Meanwhile, an adaptive virtual inertia control strategy for M3C enhances sustained inertia support. A coordinated frequency control scheme between wind farm, M3C, and ES is further constructed to achieve faster and better frequency stabilization under wind and load variations. Simulation results under a 10.5 MW load disturbance show that, compared with the uncontrolled scheme, the proposed scheme raises the frequency nadir from 49.01 Hz to 49.67 Hz, limits the maximum rate of change of frequency (ROCOF) to 0.583 Hz/s with a 49.8% reduction, fully eliminates SFD, and provides theoretical support for the stable grid integration of fractional frequency offshore wind power. Full article

The electrification of floating production, storage, and offloading (FPSO) units has emerged as a strategic solution to meet the growing demand for increased oil production while reducing carbon emissions associated with onboard gas turbine generation. Power-from-shore (PFS) systems represent a promising approach to achieving this goal, with transmission technologies based on high-voltage direct current (HVDC) and high-voltage alternating current (HVAC) solutions. Although HVDC is more suitable for long-distance and high-power applications, HVAC systems offer advantages in terms of robustness, simplicity, and operational maturity. Nevertheless, the reactive power compensation requirements arising from the high capacitance of submarine cables remain a major technical challenge. This study investigates and compares several reactive power compensation topologies applied to three distinct PFS systems. The proposed methodology enables a comprehensive evaluation of both onshore and subsea reactor placement strategies under technically and technologically feasible conditions. The results demonstrate that long-distance transmission of 75 MW over 250 km was achieved exclusively through subsea compensation configurations, which maintained efficiencies above 90% and voltage and current profiles within operational limits. Conversely, onshore-only compensation proved to be the most efficient solution for shorter transmission distances. The results demonstrate that the full electrification of an FPSO is technically feasible, with voltage and current profiles remaining within acceptable operational limits. The findings also indicate that mid-cable reactor placement (at 50%) is not the most effective configuration, with superior results observed for placements at 20–80% and 40–70% of the cable length. Overall, the outcomes confirm that subsea reactor placement enables higher power transfer over longer distances, significantly extending the technical boundaries traditionally separating HVDC and HVAC solutions. These results emphasize the need for continued technological development to make subsea shunt reactor installation a viable and reliable option for future FPSO electrification projects. Full article