The economic benefits of interconnecting the power grids of Europe (EU)and China (CN)were assessed considering 100% reliance on renewable energy (RE).Four different scenarios,energy storage without interconnection,installing additional renewable energy sources without interconnection,energy storage with interconnection,and installing additional RE sources with interconnection,were considered for the economic benefit analysis.A comparative study of these four scenarios was conducted to identify the best option for achieving hourly power balance.Further,sensitivity analysis was carried out to demonstrate the robustness of the results.Electricity interconnection between CN and EU decreases the annual additional costs by more than 30% when compared to the absence of interconnection,which demonstrates the necessity and benefits of CN-EU electricity interconnection.

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We propose a restoration strategy using microgrids for restoring power supply to critical loads after an extreme event and thereby enhancing the resilience of the distribution power grid.The limited capacities of distributed generators(DGs)within the microgrids and those of intermittent energy sources such as wind and photovoltaic power are considered.An enhanced strategy model of the distribution network is established for maximizing the power supply to critical loads.Firstly,the importance of the load is quantified by using the analytic hierarchy process (AHP)and the model of the microgrid output is further improved.In the demand response mechanism,an interruptible load is used to suppress the fluctuation in the distributed power output.Secondly,piecewise linearization method is applied to address the power flow constraints.Then,the resilience enhancement model of the distribution network is transformed into a mixed integer quadratic programming problem.The CPLEX solver is adopted to solve the above problem on the MATLAB platform.Finally,the proposed method is verified by applying it to practical scenarios.

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To address the issue of climate change caused by the use of polluting,non-renewable energy sources,the use of renewable energy has gained momentum worldwide.Consequently,the increased integration of renewable energy sources into power grids has necessitated the inclusion of flexible capacities in the power systems to solve problems of intermittent and fluctuating characteristics associated with renewable generation outputs.In this work,we study the regulating cost of a power system with high renewable penetration using an improved time-series system production simulation analysis method.The operational cost of the system is considered as the objective function.Three different methods to increase regulating capacities,including using interconnection lines,building additional flexible power capacities,and retrofitting existing thermal power plants,are adopted and simulated to compare the costs of accommodating renewable energy in the system in these cases.Our results indicate that increasing the flexibility of thermal power plants and developing crossregional connection lines are cost-effective methods of increasing renewable energy consumption.

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With the development of superconducting technology,the electrical performance of insulating materials is drawing increasing concern.This paper is devoted to investigating resin materials and aims to test the resin requirements of impregnating procedures and design curing molds.First,the samples are prepared,and then the power-frequency breakdown,lighting surges,relative dielectric constant,and loss angle tangent of the impregnation resin are measured at room temperature and liquid nitrogen temperature.We also present the testing reference for cryogenic and high-voltage insulating materials of superconducting power devices.

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Wave energy is an important renewable energy source.Previous studies of wave energy conversion (WEC)have focused on the maximum power take-off (PTO)techniques of a single machine.However,there is a lack of research on the energy and power quality of wave farm systems.Owing to the pulsating nature of ocean waves and popular PTO devices,the generated electrical power suffers from severe fluctuations.Existing solutions require extra energy storage and overrated power converters for wave power integration.In this study,we developed a master-slave wave farm system with rotor inertia energy storage;this system delivers self-smoothed power output to the grid and reduces the number of converters.Two control methods based on the moving average filter (MAF)and energy filter (EF)are proposed to smooth the output power of wave farms.RTDS simulations show that the proposed systems and control methods facilitate simple and smooth grid integration of wave energy.

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This paper presents a method of tuning governor control parameters of an isolated hydropower generator considering the primary frequency performance and small-signal stability.First,generators that can be operated in isolated state are identified.Second,different schemes are proposed for generator mode switching from on-grid to off-grid state through comparison and mechanism analysis.Third,the time domain model and frequency domain model of the isolated generator governor are constructed to respectively estimate the primary frequency performance and small signal stability.Parameter sets that satisfy the primary frequency performance and small signal stability are acquired as optimal values of governor control parameters.Finally,the measurement-based parameters of the governor are identified and validated using simulations to demonstrate the feasibility and effectiveness of the method.

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Global renewable energy has maintained a steady growth in recent years,mainly fostered by national policies and increasing demand.Analyzing the experience of renewable energy development in developed countries can be important to provide reference and guidance for its adoption in other countries.First,we compare and summarize definitions of distributed generation from 18 leading countries and organizations in renewable energy.On this basis,we provide three basic characteristics for successful distributed generation using renewable resources.Then,we empirically analyze the distributed and centralized development of renewable energy in Germany with focus on wind and photovoltaic power.We determined that 95% of the photovoltaic generation and 85% of the wind power generation is distributed in Germany,suggesting that the most suitable generation mode for renewable energy is the distributed approach.

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The intense application of Voltage Source Converter based HVDC interconnections and grids will result in a hybrid AC-HVDC-system.The operation of such a system becomes complex regarding system security and system operation.This paper describes major challenges and proposes potential solutions,including a combined security assessment,preventive optimization and curative actions.A coordination of both systems enables an efficient application of existing transport capacity.

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The demands for massive renewable energy integration,passive network power supply,and global energy interconnection have all gradually increased,posing new challenges for high voltage direct current (HVDC)power transmission systems,including more complex topology and increased diversity of bipolar HVDC transmission.This study proposes that these two factors have led to new requirements for HVDC control strategies.Moreover,due to the diverse applications of HVDC transmission technology,each station in the system has different requirements.Furthermore,the topology of the AC-DC converter is being continuously developed,revealing a trend towards hybrid converter stations.

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The diode rectifier unit (DRU)-based high-voltage DC (DRU-HVDC)system is a promising solution for offshore wind energy transmission thanks to its compact design,high efficiency,and strong reliability.Herein we investigate the feasibility of the DRU-HVDC system considering onshore and offshore AC grid faults,DC cable faults,and internal DRU faults.To ensure safe operation during the faults,the wind turbine (WT)converters are designed to operate in either current-limiting or voltage-limiting mode to limit potential excessive overcurrent or overvoltage.Strategies for providing fault currents using WT converters during offshore AC faults to enable offshore overcurrent and differential fault protection are investigated.The DRU-HVDC system is robust against various faults,and it can automatically restore power transmission after fault isolation.Simulation results confirm the system performance under various fault conditions.

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Conventional power systems are being developed into grid cyber physical systems (GCPS)with widespread application of communication,computer,and control technologies.In this article,we propose a quantitative analysis method for a GCPS.Based on this,we discuss the relationship between cyberspace and physical space,especially the computational similarity within the GCPS both in undirected and directed bipartite networks.We then propose a model for evaluating the fusion of the three most important factors:information,communication,and security.We then present the concept of the fusion evaluation cubic for the GCPS quantitative analysis model.Through these models,we can determine whether a more realistic state of the GCPS can be found by enhancing the fusion between cyberspace and physical space.Finally,we conclude that the degree of fusion between the two spaces is very important,not only considering the performance of the whole business process,but also considering security.

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In recent years,a large number of high voltage direct current (HVDC)transmission projects have been connected to AC systems.This has started to have an impact on AC/DC hybrid power grids,particularly receiving terminal power grids.An HVDC system is a large-scale power electronic integrated nonlinear system,and it includes a primary system and a control and protection system.Hence,the precision and degree of detail of HVDC systems directly affect the actual effect of simulation.In recent years,in the case of the normal operation and failure of AC power grids,the abnormal fluctuation and even locking of HVDC systems caused by the inappropriate strategies of the control and protection system component have strongly affected power grids.This has significantly affected the safety and stability of receiving power grids and normal operation.In this study,the actual engineering HVDC control logic provided by a manufacturer is analyzed and simulated based on the user defined component library of the ADPSS electromagnetic transient calculation program,and an HVDC control model based on an actual system is established.The accuracy of the DC control custom model based on ADPSS is verified through the simulation of an actual power grid.

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