A dynamic game model for assessing risk of coordinated physical-cyber attacks in an AC/DC hybrid transmission system

The widely used intelligent measuring equipment not only makes the operation of AC/DC hybrid transmission system more safe and reliable, but also inevitably brings new problems and challenges such as the threats and hidden dangers of cyber attacks. Given this, how to effectively and comprehensively assess the inherent vulnerabilities of AC/DC hybrid transmission systems under the coordinated physical-cyber attacks is of critical significance. In this paper, a three-stage physical-cyber attack and defense risk assessment framework based on dynamic game theory is proposed. In the framework, the dynamic game process between attacker and defender is carried out for the power grid risk, which is expressed as the product of the attacker’s success probability in attacking the substation and the load loss caused by the attack. Regarding the probability of a successful attack, it depends on the number of funds invested by both attacker and defender sides considering the marginal effect, while the corresponding load loss caused depends on the cyber attack vector and the optimal load shedding scheme. For the solution of the proposed three-stage dynamic game framework, it is converted into a bi-level mathematical programming problem, in which the upper-level problem is solved by using the backward induction method to get the subgame perfect Nash equilibrium, and the lower-level problem is solved by using an improved particle swarm optimization algorithm to get the optimal amount of load shedding. Finally, the case study is performed on a modified IEEE 14-node AC/DC hybrid transmission test system, and the inherent weaknesses of the power grid are identified based on the risk assessment results, verifying the effectiveness of the proposed framework and method

Chinese investigation and research in Southern Ocean physical oceanography and meteorology during the Chinese Polar Programs 2011–2015

Within the context of developing a research presence in the Antarctic region, the first phase of the Chinese Polar Programs covered the period 2011–2015, which almost coincided with the 12th Five-Year Plan (2011–2015). For the promotion of full understanding of the progress of Chinese expeditions and research in Antarctica, the observations and achievements of cruises during 2011–2015 are summarized in this paper. Four Antarctic cruises (28th–31st) were performed in the Prydz Bay and Antarctic Peninsula regions during the first phase of the Polar Programs. These cruises performed systemic collections of physical oceanographic and meteorological data to support further research on the ice–ocean–atmosphere interactions in Antarctica. Overall, 248 CTD/LADCP stations, 66 microstructure profiles, 507 XBT/XCTDs, 181 air sounding balloons, 58000 total gaseous mercury (TGM) concentrations, 452 aerosol samples, 294 atmospheric samples, 11 moorings, and 28 surface drifters were acquired or deployed during the four cruises. Using these extensive observations and other data, Chinese scientists have achieved new recognition in the fields of Southern Ocean physical oceanography and meteorology, as well as in other interdisciplinary subjects. These studies, which have been associated with scientific techniques, instrumentation, ocean circulation, water mass formation, energy transformation, and carbon uptake, have elucidated the dynamic mechanisms and potential effects of climate change in Antarctica. Finally, some observations based on experience gained during previous Chinese Antarctic Research and Expedition campaigns are summarized with advice for the improvement of future investigations in the Antarctic region

Persistent warm-eddy transport to Antarctic ice shelves driven by enhanced summer westerlies

The offshore ocean heat supplied to the Antarctic continental shelves by warm eddies has the potential to greatly impact the melting rates of ice shelves and subsequent global sea level rise. While featured in modeling and some observational studies, the processes around how these warm eddies form and overcome the dynamic sub-surface barrier of the Antarctic Slope Front over the upper continental slope has not yet been clarified. Here we report on the detailed observations of persistent eddies carrying warm modified Cir- cumpolar Deep Water (CDW) onto the continental shelf of Prydz Bay, East Antarctica, using subsurface mooring and hydrographic section data from 2013-2015. We show the warm-eddy transport is most active when the summer westerlies strengthen, which promotes the upwelling of CDW and initiates eddy formation and intrusions. Our study highlights the important role of warm eddies in the melting of Antarctica’s ice shelves, both now and into the future. Keywords: Antarctic Deep Water, ocean heat, warm eddie

A tri‐level optimization strategy incorporating wind power against coordinated cyber‐physical attacks

Abstract With the fast development of cyber‐physical power systems, coordinated cyber‐physical attacks have become one of the main threats to the security of modern power grid. Considering that it is difficult for attackers to obtain full information of the entire power grid, the coordinated cyber‐physical attack problem for partitioned power grid is studied in this paper, and a tri‐level defender‐attacker‐dispatcher optimization model with consideration of wind power uncertainty in a specific coordinated cyber‐physical attack mode is proposed. The Karush‐Kuhn‐Tucker (KKT) condition and an improved implicit enumeration algorithm are applied to obtain the solution of the complicated optimization problem effectively. In addition, two risk assessment indices pertinent to the physical lines and load measurements are proposed according to the obtained total amount of optimized load shedding and coordinated attack‐defense strategy under valid attack‐defense scenarios. Taking a partitioned IEEE 39‐bus test system as example, the risks of physical transmission lines and load measurements in different areas under attacks are elaborately studied, and the impact of wind power uncertainty on attack‐defense strategies is discussed as well. Numerical simulation results illustrate the effectiveness of the proposed optimization model and risk assessment indices, and some significant conclusions are drawn

Detailed modelling and simulations of an all-DC PMSG-based offshore wind farm

A detailed modelling method and corresponding simulations for an all-DC offshore wind farm equipped with a permanent magnet synchronous generator (PMSG) are elaborately discussed and conducted. This all-DC wind farm is designed in series-connected topology with an offshore DC substation and a voltage-sourced converter−high-voltage direct current (VSC-HVDC) transmission system. Some major components including wind turbine, synchronous generator, VSC, and isolated full bridge converter are all modelled based on the complete electrical models and engineering parameter settings. Containing the start process of the system, the simulations under various wind speed conditions and the specific faults analysis under different situations are carried out in the MATLAB/Simulink^TM environment. Simulation results reveal the comprehensive operating characteristics of this all-DC offshore wind farm and its system response to faults

Multi-Indicator Fused Resilience Assessment of Power Grids Considering Wind-Photovoltaic Output Uncertainty during Typhoon Disasters

Extreme weather events such as typhoons pose a serious threat to the safe operation of power grids. In the field of power system resilience assessment during typhoon disasters, a parametric typhoon wind field model combined with actual historical meteorological data has not been well adopted, and the conventional renewable energy uncertainty modeling methods are not suitable for typhoon disaster periods. In this paper, a multi-indicator fused resilience assessment strategy considering wind-photovoltaic uncertainty and component failure during typhoon disasters is proposed. Firstly, based on the actual historical meteorological data of typhoons, an uncertainty model of typhoon wind speed is established by a rolling non-parametric Dirichlet process Gaussian mixture model. Then, a spatial–temporal contingency set is constructed by considering the best-fit wind field model and stress–strength interference model for failure probability of transmission lines. On this basis, a holistic resilience assessment framework is established from the perspectives of priority, robustness, rapidity, and sustainability, and the entropy weight method combined with the technology for order preference by similarity to an ideal solution is leveraged to obtain the comprehensive resilience indicator. Finally, numerical studies are performed on the IEEE-30 bus test system to identify vulnerable lines and improve system resilience during typhoon disasters

Fluid-solid coupling simulation of a new hydraulic self-adaptive PDC cutter for improving well-drilling efficiency in complex formations

A new type of hydraulic self-adaptive polycrystalline-diamond-compact (PDC) cutter (SAPC) is designed for controlling cutting depth of the PDC bit flexibly and reducing the harm of stick-slip vibration to drilling operation. The fluid-solid coupling movement of SAPC under different well-drilling conditions are simulated and analyzed. The results show that the up-going time of SAPC can be increased by reducing the diameter of the thin connecting pipe, increasing the diameter of the SAPC liquid-cavity, increasing the height of the cavity, increasing the liquid viscosity and increasing the initial spring force/decreasing the elasticity coefficient. Among them, reducing the diameter of thin connecting pipeline and increasing cavity diameter are the most sensitive. The up-going time can also be increased by the way of changing liquid viscosity without changing the structure of SAPC. Increasing the initial spring force and decreasing the elasticity coefficient can also increase the up-going time of the SAPC, however, the response window to the linkage force is reduced. The double-pipeline embedded SAPC can effectively reduce the volume and installation difficulty. The reasonable thin pipeline diameter is 0.2-0.5 mm, and the thick pipeline diameter is more than 2 mm, and the cavity diameter is more than 18 mm. Based on the results of the numerical simulation study, the up-going time of the SAPC is designed over 1.25 s, which meets the performance requirements of the hydraulic SAPC using in complex reservoir drilling, such as carbonate-sandstone reservoir. (C) 2021 The Authors. Published by Elsevier Ltd