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This article introduces the concept of load aggregation, which involves a comprehensive analysis of loads to acquire their external characteristics for the purpose of modeling and analyzing power systems. The online identification method is a computer-involved approach for data collection, processing, and system identification, commonly used for adaptive control and prediction. This paper proposes a method for dynamically aggregating large-scale adjustable loads to support high proportions of new energy integration, aiming to study the aggregation characteristics of regional large-scale adjustable loads using online identification techniques and feature extraction methods. The experiment selected 300 central air conditioners as the research subject and analyzed their regulation characteristics, economic efficiency, and comfort. The experimental results show that as the adjustment time of the air conditioner increases from 5 minutes to 35 minutes, the stable adjustment quantity during the adjustment period decreases from 28.46 to 3.57, indicating that air conditioning loads can be controlled over a long period and have better adjustment effects in the short term. Overall, the experimental results of this paper demonstrate that analyzing the aggregation characteristics of regional large-scale adjustable loads using online identification techniques and feature extraction algorithms is effective.

Abstract The flexible distribution network presents a promising architecture to accommodate highly integrated distributed generators and increasing loads in an efficient and cost-effective way. The distribution network is characterised by flexible interconnections and expansions based on soft open points, which enables it to dispatch power flow over the entire system with enhanced controllability and compatibility. Herein, we propose a multi-resource dynamic coordinated planning method of flexible distribution network that allows allocation strategies to be determined over a long-term planning period. Additionally, we establish a probabilistic framework to address source-load uncertainties, which mitigates the security risks of voltage violations and line overloads. A practical distribution network is adopted for flexible upgrading based on soft open points, and its cost benefits are evaluated and compared with that of traditional planning approaches. By adjusting the acceptable violation probability in chance constraints, a trade-off between investment efficiency and operational security can be realised.

For dynamic stability analysis and instability mechanism understanding of multi-converter medium voltage DC power systems with droop-based double-loop control, an advanced system-level model reduction method is proposed. With this method, mathematical relationships of control parameters (e.g., current and voltage control parameters) between the system and its equivalent reduced-order model are established. First, open-loop and closed-loop equivalent reduced-order models of current control loop considering dynamic interaction among converters are established. An instability mechanism (e.g., unreasonable current control parameters) of the system can be revealed intuitively. Theoretical guidance for adjustment of current control parameters can also be given. Then, considering dynamic interaction of current control among converters, open-loop and closed-loop equivalent reduced-order models of voltage control loop are established. Oscillation frequency and damping factor of DC bus voltage in a wide oscillation frequency range (e.g., 10–50 Hz) can be evaluated accurately. More importantly, accuracy of advanced system-level model reduction method is not compromised, even for MVDC power systems with inconsistent control parameters and different number of converters. Finally, experiments in RT-BOX hardware-in-the-loop experimental platform are conducted to validate the advanced system-level model reduction method.

To achieve the goal of carbon neutrality, renewable energy integration through a voltage source converter based multi-terminal direct current (VSC-MTDC) system has been identified as a promising solution. To tackle the significant DC voltage over-limit problem in a VSC-MTDC system during disturbances, this paper proposes a mode-switching strategy of droop control considering maximum DC voltage regulation capability. The close relationship between node injection powers and node DC voltages in the MTDC system is elaborated, and the most effective regulation approach of local injection power for limiting DC voltage deviation is presented. The operating point trajectories of different droop control explains that the DC voltage deviation can be minimized by fully utilizing the capacity of converters. Therefore, the mode-switching strategy with the maximum DC voltage regulation capability is realized by the switching between the voltage droop control and the constant maximum power control. In addition, a mode recovery process and a smooth switching method are developed to make converters regain the capability of maintaining DC voltage and reduce power fluctuation during mode switching, respectively. Furthermore, three cases are investigated to verify the effectiveness of the proposed mode-switching strategy. Compared with simulation results of the conventional droop control and the DC voltage deviation-dependent droop control, better performance of transient and steady-state DC voltage deviation is achieved through the proposed strategy.

To provide guidance for photovoltaic (PV) system integration in net-zero distribution systems (DSs), this paper proposes an analytical method for delineating the feasible region for PV integration capacities (PVICs), where the impact of battery energy storage system (BESS) flexibility is considered. First, we introduce distributionally robust chance constraints on network security and energy/carbon net-zero requirements, which form the upper and lower bounds of the feasible region. Then, the formulation and solution of the feasible region is proposed. The resulting analytical expression is a set of linear inequalities, illustrating that the feasible region is a polyhedron in a high-dimensional space. A procedure is designed to verify and adjust the feasible region, ensuring that it satisfies network loss constraints under alternating current (AC) power flow. Case studies on the 4-bus system, the IEEE 33-bus system, and the IEEE 123-bus system verify the effectiveness of the proposed method. It is demonstrated that the proposed method fully captures the spatio-temporal coupling relationship among PVs, loads, and BESSs, while also quantifying the impact of this relationship on the boundaries of the feasible region.

The wind–thermal bundled power system achieves energy complementarity and optimized scheduling, which is an important way to build a new type of energy system. For the safe and stable operation of the wind–thermal bundled power system, accurate data-driven analysis is necessary to maintain real-time balance between electricity supply and demand. By summarizing the development and characteristics of wind–thermal bundled power system in China and different countries, current research in this field can be clearly defined in two aspects: short-term wind power prediction for wind farms and performance evaluation of automatic generation control (AGC) for thermal power generation units. For short-term wind power prediction, it is recommended to focus on historical data preprocessing and artificial intelligence methods. The technical characteristics of different data-driven wind power prediction methods have been compared in detail. For performance evaluation of AGC units, a comprehensive analysis was conducted on current evaluation methods, including the “permitted-band” and “regulation mileage” methods, as well as the issue of evaluation failure in traditional evaluation methods in practical engineering. Finally, the relative optimal dynamic performance of AGC units was discussed and the future trend of data-driven research in wind–thermal bundled power system was summarized.

The Pearl River Delta (PRD) region in South China is abundant of geothermal water resources whereas geochemical evolution of the geothermal water is still poorly understood. In this study, geothermal water is sampled to investigate the provenance of CO2 and sulphate, residence time, recharge elevation, circulation depth, and water-interaction processes by analyzing chemistry of major ions and isotope geochemistry. The range of δ13C and content of bicarbonate reveal multiple sources of soil CO2, carbonate rocks, and small amounts of mantle CO2. The δ34S ratio and sulphate concentration are attributed to evaporites dissolution, input of atmospheric sulphur, seawater intrusion, and oxidation of pyrite. The residence time of up to 21.01 ka for geothermal water likely suggests the earliest precipitation recharge during the Late Pleistocene. Mountains or/and hills at an altitude of 300–760 m in north PRD region are currently the major recharge areas for the geothermal water which can circulate at the depths of up to 3000–4800 m along regional structures. The isotopic and hydrochemical analysis confirms that extensive water interaction with silicate rock, carbonate rock and evaporite, evaporation-crystallization process, and cation exchange are the key mechanisms that control the geochemical evolution of geothermal water in the PRD geothermal system.

Abstract During the Cretaceous, there were two factors that had important influences on the East Asian climate, the East Asian coastal mountains and Earth's orbital cycling. An important question is how the coastal mountains modulated the variability of East Asian climate over orbital timescales. Here, we perform simulations with the coastal mountains of 0, 2, and 4 km high and three orbital configurations to answer the question. Our results show that a mountain range at the East Asian coast can amplify the impacts of orbital forcing on East Asian climate. Specifically, precipitation over the Songliao Basin in Northeastern China has significant changes as the coastal mountain range is about 4 km high. Combining our simulation results with orbitally‐controlled sedimentary deposits from the Songliao Basin, we conclude that the altitude of the coastal mountain range was very likely higher than 2 km in the Late Cretaceous.

Energy storage is an effective way to address the instability of renewable energy generation modes, such as wind and solar, which are projected to play an important role in the sustainable and low-carbon society. Economics and carbon emissions are important indicators that should be thoroughly considered for evaluating the feasibility of energy storage technologies (ESTs). In this study, we study two promising routes for large-scale renewable energy storage, electrochemical energy storage (EES) and hydrogen energy storage (HES), via technical analysis of the ESTs. The levelized cost of storage (LCOS), carbon emissions and uncertainty assessments for EESs and HESs over the life cycle are conducted with full consideration of the critical links for these routes. In order to reduce the evaluation error, we use the Monte Carlo method to derive a large number of data for estimating the economy and carbon emission level of ESTs based on the collected data. The results show that lithium ion (Li-ion) batteries show the lowest LCOS and carbon emissions, at 0.314 US$ kWh-1 and 72.76 gCO2e kWh-1, compared with other batteries for EES. Different HES routes, meaning different combinations of hydrogen production, delivery and refueling methods, show substantial differences in economics, and the lowest LCOS and carbon emissions, at 0.227 US$ kWh-1 and 61.63 gCO2e kWh-1, are achieved using HES routes that involve hydrogen production by alkaline electrolyzer (AE), delivery by hydrogen pipeline and corresponding refueling. The findings of this study suggest that HES and EES have comparable levels of economics and carbon emissions that should be both considered for large-scale renewable energy storage to achieve future decarbonization goals.

The climate paleogeography, especially the climate classifications, helps to interpret the global and regional climate changes and intuitively compare the climate conditions in different regions. However, the application of climate classification in deep time (i.e., climate paleogeography) is prohibited due to the usually qualitatively constrained paleoclimate and the inconsistent descriptions and semantic heterogeneity of the climate types. In this study, a climate paleogeography knowledge graph is established under the framework of the Deep-Time Digital Earth program (DDE). The hierarchical knowledge graph consists of five paleoclimate classifications based on various strategies. The classifications are described and their strengths and weaknesses are fully evaluated in four aspects: “simplicity, applicability, quantifiability, and comparability”. We also reconstruct the global climate distributions in the Late Cretaceous according to these classifications. The results are compared and the relationships among these climate types in different classifications are evaluated. Our study unifies scientific concepts from different paleoclimate classifications, which provides an important theoretical basis for the application of paleoclimate classifications in deep time.

The volatile and intermittent nature of distributed generators (DGs) in active distribution networks (ADNs) increases the uncertainty of operating states. The introduction of distribution phasor measurement units (D-PMUs) enhances the monitoring level. The trade-offs of computational performance and robustness of state estimation in monitoring the network states are of great significance for ADNs with D-PMUs and DGs. This paper proposes a second-order cone programming (SOCP) based robust state estimation (RSE) method considering multi-source measurements. Firstly, a linearized state estimation model related to the SOCP state variables is formulated. The phase angle measurements of D-PMUs are converted to equivalent power measurements. Then, a revised SOCP-based RSE method with the weighted least absolute value estimator is proposed to enhance the convergence and bad data identification. Multi-time slots of D-PMU measurements are utilized to improve the estimation accuracy of RSE. Finally, the effectiveness of the proposed method is illustrated in the modified IEEE 33-node and IEEE 123-node systems.

To improve the equivalent inertia of DC microgrids (DCMGs), a unified control is proposed for the first time for a bi-directional DC-DC converter based super-capacitor (SC) system, whereby power smoothing and SC terminal voltage regulation can be achieved in a DCMG simultaneously. The proposed control displays good plug-and-play features using only local measurements. For quantitative analysis and effective design of the critical parameter of unified control, two indices, equivalent power supporting time and inertia contributed by the unified controlled SC system, are introduced firstly. Then, with a simple but effective reduced-order model of a DCMG, analytical solutions are obtained for the two indices. In addition, a systematic design method is presented for the proposed unified control. Finally, to verify the proposed unified control, a switching model is developed for a typical DCMG in PSCAD/EMTDC, and theoretical analyses are conducted for different operating conditions.

Featuring low communication requirements and high reliability, the voltage droop control method is widely adopted in the voltage source converter based multi-terminal direct current (VSC-MTDC) system for autonomous DC voltage regulation and power-sharing. However, the traditional voltage droop control method with fixed droop gain is criticized for over-limit DC voltage deviation in case of large power disturbances, which can threaten stable operation of the entire VSC-MTDC system. To tackle this problem, this paper proposes an adaptive reference power based voltage droop control method, which changes the reference power to compensate the power deviation for droop-controlled voltage source converters (VSCs). Besides retaining the merits of the traditional voltage droop control method, both DC voltage deviation reduction and power distribution improvement can be achieved by utilizing local information and a specific control factor in the proposed method. Basic principles and key features of the proposed method are described. Detailed analyses on the effects of the control factor on DC voltage deviation and imbalanced power-sharing are discussed, and the selection principle of the control factor is proposed. Finally, the effectiveness of the proposed method is validated by the simulations on a five-terminal VSC based high-voltage direct current (VSC-HVDC) system.

The load demand and distributed generation (DG) integration capacity in distribution networks (DNs) increase constantly, and it means that the violation of security constraints may occur in the future. This can be further worsened by short-term power fluctuations. In this paper, a scheduling method based on a multi-objective chance-constrained information-gap decision (IGD) model is proposed to obtain the active management schemes for distribution system operators (DSOs) to address these problems. The maximum robust adaptability of multiple uncertainties, including the deviations of growth prediction and their relevant power fluctuations, can be obtained based on the limited budget of active management. The systematic solution of the proposed model is developed. The max term constraint in the IGD model is converted into a group of normal constraints corresponding to extreme points of the max term. Considering the stochastic characteristics and correlations of power fluctuations, the original model is equivalently reformulated by using the properties of multivariate Gaussian distribution. The effectiveness of the proposed model is verified by a modified IEEE 33-bus distribution network. The simulation result delineates a robust accommodation space to represent the adaptability of multiple uncertainties, which corresponds to an optional active management strategy set for future selection.

Abstract The real‐time simulation of active distribution networks (ADNs) can provide an accurate insight into transient behaviours, but faces challenges in simulation efficiency and flexibility brought by larger system scales and wider time‐scale ranges. This paper presents an asynchronous multi‐rate (AMR) method and design for the real‐time simulation of large‐scale ADNs. In the proposed method, the entire ADN was decoupled into different subsystems according to accuracy requirements, and optimized time‐steps were allocated to each subsystem to realize a fully distributed simulation. This not only alleviated the time‐step coordination problem existing in multi‐rate real‐time simulations, but also enhanced the flexible expansion capabilities of the real‐time simulator. To realize the AMR real‐time simulation, a multi‐rate interfacing method, synchronization mechanism, and data communication strategy are proposed in this paper, and their hardware design is also presented in detail. A modified IEEE 123‐node system with photovoltaics and wind turbine generators was simulated on a 3 field‐programmable gate arrays (FPGAs)‐based AMR real‐time simulator. The real‐time results were captured by the oscilloscope and verified with PSCAD/EMTDC, which demonstrated the superiority in simulation flexibility and accuracy compared with the synchronous multi‐rate (SMR) method.

Abstract The desiccation (extreme drying) of rivers has important implications for the broader Earth System. However, the desiccation history and its linkage to climate are rarely known for numerous major river systems, primarily due to difficulties in recognizing desiccation events from available stratigraphic records. Here, using a combination of geochemical techniques (major and rare‐earth element geochemistry, detrital zircon geochronology, and optically stimulated luminescence dating), we demonstrate that the Yellow River, which maintains the highest sediment load on Earth, became desiccated during the Last Glacial Maximum at approximately 20 thousand years ago. This finding implies that transportation of sediments and dissolved constituents to the oceans via the Yellow River may have decreased substantially or ceased during glacials, which would have ramifications for ocean chemistry and biology. Furthermore, our work highlights the importance of desiccated riverbed sediments as potential dust sources during glacial periods, a finding that is different from what is observed today.

Abstract With the rapid development of flexible interconnection technology in active distribution networks (ADNs), many power electronic devices have been employed to improve system operational performance. As a novel fully-controlled power electronic device, energy storage integrated soft open point (ESOP) is gradually replacing traditional switches. This can significantly enhance the controllability of ADNs. To facilitate the utilization of ESOP, device locations and capacities should be configured optimally. Thus, this paper proposes a multi-stage expansion planning method of ESOP with the consideration of tie-line reconstruction. First, based on multi-terminal modular design characteristics, the ESOP planning model is established. A multi-stage planning framework of ESOP is then presented, in which the evolutionary relationship among different planning schemes is analyzed. Based on this framework, a multi-stage planning method of ESOP with consideration of tie-line reconstruction is subsequently proposed. Finally, case studies are conducted on a modified practical distribution network, and the cost–benefit analysis of device and multiple impact factors are given to prove the effectiveness of the proposed method.

Abstract The new technologies, such as soft open points (SOPs) and demand response (DR), offer original approaches to stabilize the system operation and accommodate the high penetration of distributed generators (DGs). However, the applied effects of these technologies are closely affected by the uncertainties of the consumer's willingness and the outputs of DGs. To solve the problems caused by the uncertainty of the resources in active distribution system, this paper proposes a distributionally robust co‐optimization model for the demand side resources and SOPs, which realizes the combination of investment economy and operation robustness. Next, using equivalent substitution and polyhedron linearization technique, this paper proposes the mathematical method which transforms the original non‐linear programming model into a mixed‐integer linear programming model, and obtains the solution to the distributionally robust model with column and constraint generation (CCG) algorithm. Finally, the effectiveness of the proposed model is verified with the sample from a power distribution system in northern China. The result demonstrates that the co‐optimization model can realize complementary advantages of the demand side resources and SOPs, which can not only guarantee the economy of scheme, but also improve the accommodation of DGs.

The major facies changes documented in shallow-marine sediments of the northern Indian passive margin of Neo-Tethys throughout the Jurassic, from widespread platform carbonates in the Early Jurassic to organic-rich black shales in the Late Jurassic, imply a substantial turnover in oceanic conditions. All along the Tethys (Tibetan) Himalaya, from the Zanskar Range to southern Tibet, a peculiar interval characterized by ooidal ironstones of Dingjie Formation (Ferruginous Oolite Formation, FOF) marks the base of the organic-rich Spiti Shale. This laterally-extensive ooidal ironstone interval is a fundamental testimony of the mechanisms that led to major paleoceanographic changes that occurred in the eastern Neo-Tethys during the Middle Jurassic. In this article, we illustrate in detail the petrology, mineralogy, and geochemistry of ooidal ironstones and the major element contents of the entire Lanongla section. The FOF is characterized by significantly high contents of Fe2O3 (56.80% ± 9.07%, n = 7) and P2O5 (1.72% ± 1.19%, n = 7). In contrast, the Fe2O3 and P2O5 contents average 3.58% and 0.15% in the overlain carbonates of Lanongla Fm., and 5.55% and 0.16% in the overlying Spiti Shale. The ooidal ironstones are mainly composed of iron ooids with a few quartz grains and bioclasts cemented by sparry calcite. The iron ooids consist of concentric dark layers of francolite (carbonate fluorapatite), hence enriched in Ca, P, and F, and bright layers of chamosite, enriched in Fe, Si, Al, and Mg. Precipitation of francolite ensued from oversaturation of phosphorous ascribed to intensified upwelling, high biogenous productivity, and degradation of organic matter, whereas the formation of chamosite reflects enhanced continental weathering and erosion leading to increased Fe input to the ocean during transgressive stages characterized by low sedimentation rate and scarce oxygenation at the seafloor. Modern upwelling zones in outer shelf or slope areas perform similar geochemical characteristics to those as observed in this study. Under the Mesozoic greenhouse background, fluctuating redox conditions induced the alternate growth of francolite under anoxic conditions and of chamosite under suboxic conditions. Ooids were thus formed on the seafloor during continued resuspension and vertical oscillations of the chemocline rather than from interstitial waters after burial. The mineralogy of iron ooids indicates mainly reducing conditions in the water column, suggesting that extensive upwelling along the continental margin of eastern Neo-Tethys contributed significantly to the transition from carbonate deposits to organic-rich black shales during the Jurassic, as testified by the transition from well-oxygenated in Lanongla Fm. To a reduceing condition in Spiti Shale indicated by the Mn/Al ratios compared to PAAS.

Although wind and solar power is the major reliable renewable energy sources used in power grids, the fluctuation and unpredictability of these renewable energy sources require the use of ancillary services, thereby increasing the integration cost. This study proposes a wind, solar, and pumped-storage cooperative (WSPC) model that can be applied to large-scale systems connected to dispersed renewable energy sources. This model provides an optimized coordinated bidding strategy in the day-ahead market, along with a method to facilitate revenue distribution among participating members. This model takes advantage of the natural complementary characteristics of wind and solar power while using pumped storage to adjust the total output power. In the coordinated bidding strategy, a proportion of the energies is provided as firm power, which can lower the ancillary service requirement. Moreover, a multi-period firm power-providing mode is adopted to reflect the wind-solar output characteristics of each period accurately. The duration of each period is selected as a variable to accommodate seasonal characteristics. This ensures that the provision of firm power can maintain a high proportion under varied connected ratios of wind-solar, thereby obtaining higher revenue. By using the revenue distribution method, the short-term influencing factors of the cooperative model are considered to provide the economic characteristics of wind farms and photovoltaic stations. In this way, revenue distribution can be fairly realized among the participating members. Finally, the effectiveness and economy of the proposed model are validated based on actual data obtained from the power grid in California, USA.

Abstract Identification of the diverse channel patterns of meander‐bend migration is essential when reconstructing the historical evolution of sedimentary processes in meandering rivers. However, reconstruction of the spatio‐temporal evolution of ancient meandering fluvial deposits for hydrocarbon exploration is difficult due to the limited research on the patterns and styles of meander‐bend migration. To reconstruct the geomorphologic and sedimentary evolution of subsurface meandering palaeochannels, this study proposes an approach based on combining meander‐bend planforms and cross‐sectional architectural elements of clastic sedimentary successions of ancient meandering rivers. The research was applied to meandering fluvial deposits of the lower Cretaceous Quantou Formation in the north‐eastern Songliao Basin, China. High‐resolution satellite images of modern meandering rivers were used to classify and evaluate the meander‐bend planform transformations of expansion, rotation and contraction (also known as bend tightening, i.e. narrowing of the neck of the meander‐bend showing a tendency towards neck tightening or cut‐off). Major meander‐bend transformations were related to cross‐sectional bedding architecture (i.e. bed dipping or bounding surface), which was identified through well‐log and core characteristics, to construct the migration patterns of subsurface meander‐belt deposits. Integration of well‐log and core analysis from a dense array of wells allowed the stratigraphic architecture of ancient meandering rivers and stacking patterns of fluvial sandbodies to be characterised. Furthermore, major reservoir architectural elements and bounding surfaces of meandering channels were identified. Ultimately, the 3D meandering fluvial architecture was represented on 2D vertical sections so that, planform transformations and the evolutionary processes of point bars and meander bends could be elucidated. Reconstruction of meander‐bend migration is of practical value for deciphering ancient fluvial systems and the development of subsurface fluvial reservoir models.

Multi-type unconventional gas-bearing reservoirs with different lithologies and gas accumulation potential occur in the deep part of the Songliao basin. However, the reservoirs are non-homogeneous, the gas components differ substantially, and not all types of gas-bearing reservoirs have been identified or evaluated. The International Continental Scientific Drilling Program (ICDP) is used as an example to conduct qualitative and quantitative evaluations of deep multi-type unconventional gas-bearing reservoirs using conventional and specialized logging data. The core test data are used to determine the physical properties. The porosity and permeability are compared and analyzed using different methods and models. The results show that the reservoirs have low to ultra-low porosity and ultra-low permeability. Based on the comparison of the rock mechanical parameters and mineral composition, brittleness evaluation parameters are proposed for different types of deep reservoirs in the study region. The mineral brittleness index is highly consistent with the brittleness index based on rock mechanics. An identification method for deep multi-type gas-bearing reservoir and a classification approach for different gas properties are established based on the logging response and parameter interpretation. The methane gas reservoirs have low density (DEN) and low compensated neutron logging (CNL) values and high acoustic (AC) time difference and high resistivity (RT) values. The CO2 gas reservoirs have lower RT values and higher CNL values than the hydrocarbon gas reservoirs. The comprehensive analysis of deep gas source rock conditions and of the source-reservoir relationship provides insights for the evaluation of deep multi-type unconventional gas reservoirs. The discovery of high hydrogen content is of significant importance for developing new areas for deep natural gas exploration.

Abstract Frequency stability is important for microgrid with renewable energy. However, the deterioration of frequency and the increased energy storage equipment are caused by source‐load uncertainty. Therefore, a frequency coordinated control strategy based on sliding mode method for a microgrid with hybrid energy storage system (HESS) is proposed. First of all, the detailed frequency regulation is designed, which divides deviation of frequency and area control error into different components as power reference value of different power supply. Secondly, the power threshold of HESS, which is consisted of ultra‐capacitor and battery, is set by designed fuzzy controller to reduce reserve power of HESS and avoid unreasonable power output. Thirdly, a load frequency control model with HESS is built and a sliding mode control is designed by using the detailed frequency regulation. Finally, the effectiveness of the proposed frequency coordinated control strategy is verified through comparison of different cases.

Abstract Harmonic resonance in a system with multiple inverters connecting to a single AC bus has been well studied in previous literature. However, in reality, a large number of distributed inverters are often classified into several groups using a few matching transformers. Due to the impact of matching transformers’ leakage impedance, the entire system presents a multi‐AC‐bus grid‐tied system with more complicated resonance interactions. In this work, a completed analytical method is developed. It reveals that there are different resonance types in such a system, and the determining factors of these resonance types are analysed. Moreover, the simplified calculation formulas for each resonance frequency are derived. For parallel resonance problems, under normal circumstances, the harmonic source tends to cause resonance with its neighbouring converters, but it has little effect on remote converters with long electrical distances. However, under special circumstances, the harmonic source has almost no effect on neighbouring converters, but causes resonance with the remote converters. In this situation, the resonance path passes through the transformer and multiple AC buses. Verification results are provided to validate the correctness of theoretical analysis.

The Songliao Basin in Northeast Asia is the largest and longest-lived rift basin and preserves a near-continuous continental succession of the most of the Cretaceous period, providing great material to investigate the adaption of the terrestrial systems to the Cretaceous greenhouse climate and tectonic events. However, the paucity of precise and accurate radioisotopic ages from the Early Cretaceous strata of the Songliao Basin has greatly held back the temporal and causal correlation of the continental records to the global Early Cretaceous records. Three tuff layers intercalated in the Yingcheng Formation have been intercepted by the SK-2 borehole, which offer excellent materials for radioisotopic dating and calibration of the chronostratigraphy of the Lower Cretaceous sequence of Songliao Basin. Moreover, the Yingcheng Formation recorded the largest and the last of the two major volcanic events in Songliao Basin, which also represents a turning point in the basin evolution history of Songliao from syn-rift stage to post-rift stage. Here we report high-precision U–Pb zircon geochronology by the CA-ID-TIMS technique on three tuff samples from the Yingcheng Formation of the SK-2 borehole in the Songliao Basin to construct a greatly improved, absolute age framework for the Yingcheng Formation and provide crucial age constraints for the Songliao Lower Cretaceous Strata. The new CA-ID-TIMS geochronology constrained the Yingcheng Formation at 102.571 + 0.320/−2.346 Ma to ca. 113 Ma, correlating to the Albian Stage. Combined with the previous published Songliao geochronology, the Quantou Formation is constrained to between 96.442 + 0.475/−0.086 Ma and 91.923 + 0.475/−0.086 Ma; the Denglouku Formation is constrained to between 102.571 + 0.320/−2.346 Ma and 96.442 + 0.475/−0.086 Ma; the age of the Shahezi Formation is estimated at ca. 113 Ma to ca. 118 Ma, which could extend to ca. 125 Ma in some locations in Songliao Basin. The major unconformity between the Yingcheng Formation and the Denglouku Formation, which represents the transition of the basin from syn-rift to post-rift is thus confined to between 102.571 + 0.320/−2.346 Ma and 96.442 + 0.475/−0.086 Ma. This is roughly contemporaneous with the change in the direction of the paleo-Pacific plate motion from west-southwest to north or northwest in mid-Cretaceous, suggesting their possible connections.

Abundant hydrocarbon resources were discovered in the Xiazijie fan-delta in the Triassic Baikouquan Formation in Mahu sag, Junggar Basin. However, the maximum depositional age of Baikouquan Formation and provenance of this fan-delta are still unclear, which would be unfavourable for further hydrocarbon exploration. In this study, we used detrital zircon U-Pb dating and composition statistics of conglomerate clast and sandstone grain from Baikouquan Formation to constrain the maximum depositional age and provenance of the Xiazijie fan-delta. The results showed that (1) the conglomerate clast compositions of Xiazijie fan-delta mainly consisted of tuff and intermediate-felsic magmatic rocks, and sandstone samples could be classified as litharenite type with the lithic fragments were almost entirely volcanic lithic fragments; (2) the average Qt:F:L values of sandstone samples (M152-S1 and M152-S2) were 26:7:67 and 21:8:71, respectively, and they plotted in the magmatic arc domain in the Qt-F-L ternary diagram, indicating the tectonic setting of source area of Xiazijie fan-delta was magmatic arc; (3) M152-S1 yielded U-Pb ages ranging from 417 Ma to 253 Ma, with a dominant age peak at 313 Ma and two secondary age peaks at 411 Ma and 268 Ma, respectively, while M152-S2 yielded U-Pb ages ranging from 467 Ma to 256 Ma, with a dominant age peak at 307 Ma and two secondary date peaks at 405 Ma and 262 Ma; (4) the mean age of youngest two zircon grains of M152-S1 was 254.8 ± 4.7 Ma, while that of M152-S2 was 257.6 ± 3.8 Ma, suggesting the Baikouquan Formation might be deposited after the Changhsingian to Olenekian; (5) the magmatic rock ages of central West Junggar were distributed mostly between 450–260 Ma, with a dominant age peak at 307 Ma. The ages distribution between magmatic rock of central WJ and detrital zircons of M152-S1 and M152-S2 were similar, indicating the central WJ domain should be the major source area of the Xiazijie fan-delta; (6) the magmatic rock of Hakedun–Hongguleleng area in the Central WJ was characterized by a peak age at 305 Ma, which was consistent with the peak ages of M152-S1 and M152-S2, indicating the Hakedun-Hongguleleng area was likely to be their major source area; and (7) one minor peak age at 411 Ma and another at 405 Ma were obtained from M152-S1 and M152-S2, respectively, and a zircon grain with Middle Ordovician age at 467 Ma was obtained from M152-S2, indicating Late Silurian–Early Devonian Chagankule pluton in the Saier Mountain and Ordovician Honggleleng ophiolite mélange in the Sharburt mountain were the minor source areas. This research has significant implications for stratigraphic correlation in Junggar Basin and hydrocarbon exploration in the Xiazijie fan-delta conglomerate reservoir.

Abstract Fischer plots are widely used in paleoenvironmental research as graphic representations of sea- and lake-level changes through mapping linearly corrected variation of accumulative cycle thickness over cycle number or stratum depth. Some kinds of paleoenvironmental proxy data (especially subsurface data, such as natural gamma-ray logging data), which preserve continuous cyclic signals and have been largely collected, are potential materials for constructing Fischer Plots. However, it is laborious to count the cycles preserved in these proxy data manually and map Fischer plots with these cycles. In this paper, we introduce an original open-source Python code “PyFISCHERPLOT” for constructing Fischer Plots in batches utilizing paleoenvironmental proxy data series. The principle of constructing Fischer plots based on proxy data, the data processing and usage of the PyFISCHERPLOT code and the application cases of the code are presented. The code is compared with existing methods for constructing Fischer plots.

Abstract During the Late Cretaceous, Earth's climate oscillated between warm and cool states, and global oceans changed between anoxic and oxic conditions, resulting in black/gray shales and oceanic red beds (ORBs) deposition, respectively. To understand such climate/ocean dynamics, this study investigated bulk Hg and Hg isotopes, as well as Fe3+/Fe2+ in Upper Cretaceous sediments deposited in southern Tibet and the North Atlantic. In both areas, black/gray shales show much higher Hg concentrations than ORBs, indicating enhanced Hg flux to global oceans during time of black/gray shale deposition. Black/gray shales show lower Fe3+/Fe2+ and positive Δ199Hg, suggesting a significant input of Hg into the anoxic/dysoxic ocean via atmospheric deposition. The isotope values are consistent with a volcanic source for this excess Hg. ORBs show high Fe3+/Fe2+ and negative shifts of Δ199Hg, suggesting that the dominant source of Hg into the oxic oceans was via terrestrial runoff. This study suggests that volcanism was an important driver of the climate/ocean dynamics during the Late Cretaceous.

With the extensive integration of high-penetration renewable energy resources, more fast-response frequency regulation (FR) providers are required to eliminate the impact of uncertainties from loads and distributed generators (DGs) on system security and stability. As a high-quality FR resource, community integrated energy station (CIES) can effectively respond to frequency deviation caused by renewable energy generation, helping to solve the frequency problem of power system. This paper proposes an optimal planning model of CIES considering FR service. First, the model of FR service is established to unify the time scale of FR service and economic operation. Then, an optimal planning model of CIES considering FR service is proposed, with which the revenue of participating in the FR service is obtained under market mechanism. The flexible electricity pricing model is introduced to flatten the peak tie-line power of CIES. Case studies are conducted to analyze the annual cost and the revenue of CIES participating in FR service, which suggest that providing ancillary services can bring potential revenue.

The large-scale integration of renewable energy sources (RESs) brings huge challenges to the power system. A cost-effective reserve deployment and uncertainty pricing mechanism are critical to deal with the uncertainty and variability of RES. To this end, this paper proposes a novel locational marginal pricing mechanism in day-ahead market for managing uncertainties from RES. Firstly, an improved multi-ellipsoidal uncertainty set (IMEUS) considering the temporal correlation and conditional correlation of wind power forecasting is formulated to better capture the uncertainty of wind power. The dimension of each ellipsoidal subset is optimized based on a comprehensive evaluation index to reduce the invalid region without large loss of modeling accuracy, so as to reduce the conservatism. Then, an IMEUS-based robust unit commitment (RUC) model and a robust economic dispatch (RED) model are established for the day-ahead market clearing. Both the reserve cost and ramping constraints are considered in the overall dispatch process. Furthermore, based on the Langrangian function of the RED model, a new locational marginal pricing mechanism is developed. The uncertainty locational marginal price (ULMP) is introduced to charge the RES for its uncertainties and reward the generators who provide reserve to mitigate uncertainties. The new pricing mechanism can provide effective price signals to incentivize the uncertainty management in the day-ahead market. Finally, the effectiveness of the proposed mechanism is verified via numerous simulations on the PJM 5-bus system and IEEE 118-bus system.

Abstract Limited to the Atlantic and its surrounding basins, the expression of the Coniacian–Santonian oceanic anoxic event (OAE3) was discovered in the non-marine Cretaceous Songliao Basin, Eastern Asia not long ago. In this study, based on spectral gamma ray logs data recorded in three basins, the self-similarity of the OAE3 was studied through the analysis of the scaling properties of thorium–potassium and thorium–uranium distributions both in marine and terrestrial environments using the multifractal detrending fluctuation analysis. The results indicate that, in both marine and terrestrial systems, the OAE3 intervals are characterized by their multifractal nature due to long-range correlation. However, the multifractal features of the studied OAE3 intervals are different in the three basins, although some common trends were observed. By comparing the degree of multifractality of the OAE3 deposits with the clay minerals and the redox conditions, it appears that the changes of the multifractal features are controlled by local changes such as clay mineralogy and redox conditions in both milieus under different sedimentation patterns. At all sites, the left side shortened spectrum of the thorium–potassium distribution suggests the presence of local fluctuations with minor amplitudes during the OAE3. Furthermore, the shortened singularity spectrum of the thorium–uranium distribution reflects the existence of small-scale fluctuations with large amplitudes at marine sites while in the non-marine Songliao Basin, the thorium–uranium distribution suggests the presence of local fluctuations with small amplitudes during the OAE3. Therefore, a more local behavior of the event is considered although the regional character is not neglected.

Uplift of the Gangdese Mountains is important to the evolution of Asian monsoons and the formation of Tibetan Plateau, but its paleoaltitude before the India-Asia collision (Late Cretaceous) is less constrained so far. In this study, we investigate whether the geological records, which are indicators of soil dryness, discovered in East Asia can provide such a constraint. Through climate modeling using the Community Earth System Model version 1.2.2, it is found that the extent of dry land in East Asia is sensitive to the altitude of the Gangdese Mountains. It expands eastwards and southwards with the rise of the mountain range. Comparison of the model results with all the available geological records in this region suggests that the Gangdese Mountains had attained a height of ∼2 km in the Late Cretaceous.

The Qamdo Basin in eastern Tibet has significant petroleum potential and previous studies indicate that the basin contains thick potential source rocks of the Late Permian and the Late Triassic ages. In this paper, the petroleum potential of samples from measured the Upper Permian and Upper Triassic outcrop sections were evaluated on the basis of sedimentological, organic petrographic and geochemical analyses. Initial evaluations of total organic carbon contents indicated that shale samples from the Upper Permian Tuoba Formation and the Upper Triassic Adula and Duogala Formations have major source rock potential, while carbonate rocks from the Upper Triassic Bolila Formation are comparatively lean in organic matter More detailed analyses of OM-rich shale samples from the Tuoba, Adula and Duogala Formations included Rock-eval, elemental analyses, gas chromatography and organic petrography. Maceral compositions and plots of atomic O/C versus H/C indicate that the organic matter present in the samples is primarily Type II with a mixed source. Analyses of acyclic isoprenoid biomarkers indicate the organic matter was deposited under reducing and sub-to anoxic conditions. Based on the high vitrinite reflectance (Ro>1.3%) and Rock-eval data, the samples are classified as highly to over-mature, suggesting that the Tuoba, Adula and Duogaila Formation shales may generate thermogenic gas. Source rock intervals in the three formations are interpreted to have been deposited in marginal-marine environment during transgressions and under a warm and moist climatic condition.

An analytical calculation method for the reliability sensitivity indexes of distribution systems is proposed to explicitly quantify the impact of various influence factors on system reliability. Firstly, the analytical calculation formulas for the reliability indexes of distribution systems are derived based on the fault incidence matrix (FIM). Secondly, the factors that affect system reliability are divided into two categories: quantifiable parameter factors and non-quantifiable network structure factors. The sensitivity indexes for the quantifiable parameter factors are derived using the direct partial derivation of the reliability calculation formulas. The sensitivity indexes for the non-quantifiable network structure factors are derived using the transformation of FIMs. Finally, the accuracy and efficiency of the proposed sensitivity calculation method are verified by applying them to an IEEE 6-bus RBTS system. This paper sums up the factors that influence system reliability in detail and gives the explicit analytical calculation method for the sensitivity of each factor. Repetitive calculation of the reliability index can be avoided during the sensitivity analysis. The bottleneck that affects the reliability level of distribution systems can be identified efficiently, and valuable information and guidance can be provided to enhance the reliability of distribution systems.

In recent years, primary energy consumption in China’s urban areas has increased rapidly, facing the problems of extensive use of energy, high energy consumption and insufficient intensified use of energy resources. Improving multienergy supply, increasing the proportion of clean energy and integrated energy efficiency are the main goals of urban development. The integrated energy system with multi-functional synergy and open trading will become one of the new directions for the development of new urban energy systems. This paper summarizes the main problems faced by the current towns and the characteristics of the new urban energy system, analyzes the development of new urban energy system from three aspects including energy interconnection hub infrastructure construction, energy management platform construction and energy value sharing, and forecasts the future development direction of new urban energy systems. Keywords: New towns, Integrated energy systems, Intensification, Energy interconnection hub infrastructure, Energy management platform, Energy value sharing

The surface uplift of the Tibetan Plateau (TP) and its geomorphology evolution has triggered aridification of Asia's interior and drainage development at the eastern margin of the plateau. However, how the pre-Cenozoic early growth histories of the TP impact the drainage system and climate is poorly constrained. The Late Mesozoic Lacustrine evaporite-bearing basins on the eastern margin of the TP record significant information on the uplift of the source terranes, source-to-sink system development and climate change. In this study, we presented detrital zircon U–Pb ages from the Upper Cretaceous Yunlong Formation in the Lanping Basin, as well as Hf isotopic, petrographic, direct statistical, and multidimensional scaling analyses, and use them to characterize the provenance and reconstruct the drainage system. All of the samples have five major age peaks at 200–290 Ma, 400–490 Ma, 750–1000 Ma, 1750–1950 Ma, and 2400–2600 Ma with mostly negative ɛHf(t) values (81%). We infer the sediments are primarily derived from recycled sediments of the Songpan-Garze terrane, and partly from the Sichuan Basin and the Southern Qiangtang terrane, as well as the exposed magmatic rocks of the Yidun Arc and Songpan-Garze terrane. The provenance features of the contemporaneous sediments from the Sichuan, Xichang, Chuxiong, and Simao basins indicate a complex hierarchical drainage pattern on the eastern margin of the TP during the Late Cretaceous. The hierarchical drainage system exhibits a complete gradational cycle of lake-basin types from overfilled freshwater Sichuan Basin through balanced fill saline Xichang Basin and underfilled hypersaline Chuxiong, Lanping, Simao, and Khorat Plateau basins from proximal to distal. The early growth of the TP primarily controlled the drainage and lake-basin evolution by not only causing the uplift and exhumation of the source areas and providing large amounts of clastic material to the proximal sub-drainage areas but also intensifying the aridity and deposition of evaporites.

Abstract The timing of formation of the low‐gradient, internally drained landscape of the Tibetan Plateau is fundamental to understanding the evolution of the plateau as a whole. Well‐dated sedimentary records of internal drainage of rivers into lakes are used to reveal the timing of this evolution. Here we redate the youngest continental sedimentary successions of central Tibet in the Lunpola Basin and propose a new age range of ca. 35 to 9 Ma, significantly younger than previously thought. We demonstrate long‐standing internal drainage in central Tibet since the late Eocene and stable sedimentary environments, source regions, and low topographic relief since at least the early Miocene. We suggest that sediment aggradation of internal drainage and reduction of hillslope gradients by erosion dominate the formation of low‐relief landscapes and that the late Cenozoic drainage basins in central Tibet developed in response to flow in the lower crust and/or mantle lithosphere.

Large-scale distributed energy resources, such as electric vehicles (EVs) asymmetric access to low-voltage distribution systems, may cause security problems, including line congestion, voltage violation, and three-phase unbalance. In this paper, a congestion management method of low-voltage active distribution networks is proposed. The soft open point, a flexible power electronic device, is considered as a direct control means to solve the congestion problem first. A semidefinite programming model based on a symmetrical component method is constructed to optimize the operation strategy that can be efficiently solved to meet the demands of rapid centralized control. To guide the charging behaviors of flexible load represented by EVs, a market mechanism suitable for the low-voltage unbalanced network is further considered. Though linear approximation and sensitivity analysis, a pricing model of flexible load is established accounting for the effect of network loss, voltage variation, voltage three-phase unbalance, and line overload to distribution locational marginal price. Case studies are carried out on the modified IEEE 33-node and IEEE 123-node system to verify the effectiveness and efficiency of the proposed method.

The increasing penetration of uncontrollable distributed generators (NDGs) exacerbates the risk of voltage violations in active distribution networks (ADNs). It is difficult for a centralized control strategy to meet the requirements of fast voltage and reactive power control because of the heavy computational and communication burdens. Local voltage control based on real-time measurements can respond quickly to the frequent fluctuations of distributed generators (DGs). In this paper, a local voltage control strategy of DGs with reactive power optimization based on a kriging metamodel is proposed. First, to build the metamodel for local voltage control, the steps for determining the input variables are presented in detail, and the effects of different variables on the accuracy of the metamodel are analyzed. Then, taking minimum network losses and voltage deviations as the objective function, we construct the metamodel for local voltage control based on kriging methods. Finally, operation strategies for DGs are developed by calculating the optimally weighted vector based on real-time measurements, and the operation strategies for DGs will be added into the original sample set to improve the accuracy of the metamodel. The proposed local voltage control strategy based on only the local measurements can quickly respond to the frequent DG fluctuations, reduce the communication burden for large networks and improve the adaptability of local voltage control in ADNs. Case studies under different scenarios on the IEEE 33-node system and the IEEE 123-node system are conducted to verify the effectiveness of the proposed method, and the results show that the proposed method can effectively solve the problems of voltage deviation and voltage fluctuation caused by the high penetration of DGs.

Various stand-alone hybrid power systems are widely used to fulfil the electric loads for remote, rural villages. Although there are many investigations based on various aspects of renewable hybrids energy microgrids, the discussions about the application of biomass combustion power plants are rare. Also, detailed investigations of the system steady and transient stability analysis, and the power curtailment control optimization of wind turbines in these stand-alone hybrid systems are seldom found. This paper focuses on wind/biomass/diesel/battery stand-alone microgrids and discusses the system operation, energy management and dispatch issues detailed. The renewable and controllable biomass power is localized to follow the load fluctuations over a long timescale to decrease the power production from diesel and the peak-load shifting demands of the battery banks. An optimization strategy of the wind power curtailment control is also proposed to effectively decrease the frequency and amplitude of the pitch actor and, to some extent, improve the power generation through the combination of the active turbine speed control and pitch regulation. Then a parallel double-mode optimal operation strategy with a “fault detector” is presented to realize economic optimization dispatch under the normal mode and emergency power control for large disturbance scenarios. Finally, case studies of a microgrid on a remote Canadian aboriginal community are conducted to demonstrate the performance of the proposed methods.

Hybrid ac/dc microgrids (MGs) integrated with traditional diesel generators, distributed energy storage systems (ESSs), and high penetration of renewable energy sources (RESs)-based distributed generators (DGs) have become an attractive power supply solution for isolated remote areas and islands, which can effectively reduce environmental protection pressure and improve power supply reliability. However, in such inherent low-inertia systems, randomness and fluctuation of the output power of RESs and uncertain load consumption can easily incur dynamic stability issues, such as transient power impact, unacceptable frequency deviations, and operation mode transitions for security. To solve the above problems and enhance the dynamic stability of the system, an enhanced dynamic stability control (EDSC) scheme with locally measured signals only is proposed in this paper. In this control scheme, the bi-directional interlinking dc-ac converter uses the ac frequency in ac MG as the reference value of dc voltage and adopts the current feedforward control to control the dc voltage in the dc MG to be consistent with the ac frequency. By electrically coupling dc voltage and ac frequency, power disturbances in ac or dc sides will cause almost identical variation degrees in both ac frequency and dc voltage. Under the proposed EDSC scheme, the distributed ESSs in both ac and dc sides are then automatically coordinated and controlled by the unified droop control to balance transient power disturbances and smooth output of diesel generator under normal condition, which can effectively improve stability and controllability of such low-inertia systems. Furthermore, in an emergency such as failure of diesel generator, the operation mode can be switched seamlessly with the proposed EDSC scheme. The detailed theoretical analysis including control system design, small signal model analysis of key parameter influence on system dynamics, and simulation verifications in the PSCAD/EMTDC environment is presented to verify the effectiveness and practicality of the proposed EDSC scheme.

From flexible interconnection among feeders to hybrid alternating current (AC) and direct current (DC) distribution structures of future smart distribution systems, medium-voltage DC distribution centers with flexibly interlinked multiple microgrids (MGs) will have wide applications on the demand side. A generic coordinated control framework based on a distributed cooperation scheme is proposed for such DC centers, as opposed to centralized control structures. A novel unified control only using local measurements is proposed for these interlinking converters. During normal power disturbances, automatic coordinated power control and mutual support among sub-systems can be realized, thereby improving DC voltage and AC frequency stability to enable multiple MGs to be treated as a real unified cluster. Moreover, with this method, interlinking converters can realize seamless transition in power dispatching mode, common DC bus voltage control mode, and MG support mode without communication and control system switching. A simplified dynamic model has been developed to verify the proposed control strategy. This work is expected to provide a new solution for flexible interconnection and operational control of large-scale MG clusters.

The application of synchronized phasor measurement technology at distribution networks provides new options for voltage-to-power sensitivity estimation and voltage regulation. An augmented sensitivity estimation-based voltage control strategy with a phasor measurement unit (PMU) measurement is proposed for active distribution networks (ADNs). The voltage control records are extracted from historical synchronized phasor measurements. The voltage-to-power sensitivities reflecting the relationship of voltage change and power fluctuation are estimated with the obtained voltage control records. In addition to the linear parameter, parameters to match the nonlinearity between voltage and power variation and to track the operation conditions are introduced in the fitting model to improve the accuracy of the voltage control strategy. Rule-based and sensitivity-based optimization voltage control methods are proposed using the sensitivities estimated in which the measurements of partial nodes at the distribution network are the only needed data. The voltage control is also realized with faster computation speed. Case studies and analysis on the IEEE 33-node test feeder verify the correctness and effectiveness of the proposed method.

With increasing integration of various distributed energy resources, electric distribution networks are changing to an energy exchange platform. Accurate voltage-to-power sensitivities play a vital role in system operation and control. Relative to the off-line method, measurement-based sensitivity estimation avoids the errors caused by incorrect device parameters and changes in network topology. An online estimation of the voltage-to-power sensitivity based on phasor measurement units is proposed. The sparsity of the Jacobian matrix is fully used by reformulating the original least-squares estimation problem as a sparse-recovery problem via compressive sensing. To accommodate the deficiency of the existing greedy algorithm caused by the correlation of the sensing matrix, a modified sparse-recovery algorithm is proposed based on the mutual coherence of the phase angle and voltage magnitude variation vectors. The proposed method can ensure the accuracy of estimation with fewer measurements and can improve the computational efficiency. Case studies on the IEEE 33-node test feeder verify the correctness and effectiveness of the proposed method.