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Fault ride-through is a prerequisite for ensuring continuous operation of a variable-speed pumped storage unit with a full-size converter (FSC-VSPU) and providing support for the renewable energy and power grid. This paper proposes low-voltage ride through (LVRT) and high-voltage ride through (HVRT) strategies for FSC-VSPU to address this issue. Firstly, the structure of FSC-VSPU and its control strategy under power generation and pumping conditions are described. Subsequently, the fault characteristics of the FSC-VSPU under different operating conditions are analyzed. More stringent fault ride-through technical requirements than those for wind turbines are proposed. On this basis, the fault ride-through strategies of combining fast power drop, rotor energy storage control, power anti-regulation control, dynamic reactive current control, low power protection, and DC crowbar circuit are proposed. Simulation case studies conducted in PSCAD/EMTDC verify the correctness of the theoretical analysis and the effectiveness of the LVRT and HVRT strategies in this paper. [ABSTRACT FROM AUTHOR]

The increasing penetration of photovoltaic (PV) and hydroelectric power generation and their coupling uncertainties have brought great challenges to multi-energy's coordinated dispatch. Traditional methods such as stochastic optimization (SO) and robust optimization (RO) are not feasible due to the unavailability of accurate probability density function (PDF) and over-conservative decisions. This limits the operational efficiency of the clean energies in cascaded hydropower and PV-enriched areas. Based on data-driven distributionally robust optimization (DRO) theory, this paper tailors a joint optimization dispatching method for a cascaded hydro-PV-pumped storage combined system. Firstly, a two-step model for a Distributed Renewable Optimization (DRO) dispatch is developed to create the daily dispatch plan, taking into account the system's complementary economic dispatch cost. Furthermore, the inclusion of a complementary norm constraint is implemented to restrict the confidence set of the probability distribution. This aims to identify the optimal adjustment scheme for the day-ahead dispatch schedule, considering the adjustment cost associated with real-time operations under the most unfavorable distribution conditions. Utilizing the MPSP framework, the Column and Constraint Generation (CCG) algorithm is employed to resolve the two-stage dispatch model. The optimal dispatch schedule is then produced by integrating the daily dispatch plan with the adjustive dispatch scheme. Finally, the numerical dispatch results obtained from an actual demonstration area substantiate the effectiveness and efficiency of the proposed methodology. [ABSTRACT FROM AUTHOR]

The variable speed pumped storage unit with a full-size converter (FSC-VSPSU) can provide fast and flexible regulation capacity for the power grid, assisting the rapid development of the new energy-dominated power systems, and its application is gradually becoming widespread. The excitation system of FSC-VSPSU is crucial for maintaining the motor-port voltage and further supports the stable operation of the entire unit. However, there is currently no research on excitation system modeling, and their essential operating characteristics have not been discussed in detail, which needs further study. With this aim, this paper firstly establishes a detailed transfer function model for FSC-VSPSU, which is then used to study the influence rules of FSC-VSPSU parameters on the operating characteristics. In addition, based on the summarized operating characteristics, the excitation system can be optimized, and its complexity is greatly reduced while ensuring the original performance of the unit. Finally, the results of the simulation can verify the correctness of the established model and the explored operating characteristics. [ABSTRACT FROM AUTHOR]

The ultra‐low frequency oscillation and poor speed regulation performance caused by the fast power control decrease the stability and efficiency of the variable speed pumped storage unit with a full size converter (FSC‐VSPSU). This paper presents a fast frequency control strategy to solve this problem. The small‐signal model of the FSC‐VSPSU in fast frequency mode is established, and the key parameters for the system stability are studied by the eigenvalue method. Aiming at the coupling oscillation mode caused by the governor and generator side converter (GSC), the corresponding control parameters optimisation method is proposed. In order to solve the power anti‐regulation problem, the strategy of combining rotor kinetic energy release, power slope adjustment, and delay acceleration control is proposed. PSCAD and RTDS simulation results show that the proposed strategy can effectively avoid the ultra‐low frequency oscillation caused by the fast power control and significantly improves the frequency and power control performance. [ABSTRACT FROM AUTHOR]

Zero and partial gravities (ZPG) increase cardiovascular risk, while the corresponding theoretical foundation remains uncertain. In the article, the ZPG were generated through a rotating frame with two degrees of freedom in combination with the random walk algorithm. A precise 3D geometric configuration of the cardiovascular system was developed, and the Navier-Stokes laminar flow and solid mechanics were used as governing equations for blood flow and the surrounding tissue in the cardiovascular system. The ZPG were designed into governing equations through the volume force term. The computational fluid dynamics' (CFD) simulations in combination with proper boundary conditions were carried out to investigate the influences of ZPG on the distribution of blood flow velocity, pressure, and shear stress in the cardiovascular system. The findings show that as simulated gravity gradually decreases from 0.7 g to 0.5 g to 0.3 g to 0 g, as opposed to normal gravity of 1 g, the maximum values of blood flow velocity, pressure, and shear stress on the walls of the aorta and its ramification significantly increase, which would lead to cardiovascular diseases. The research will lay a theoretical foundation for the comprehension of the ZPG effect on cardiovascular risk and the development of effective prevention and control measures under the circumstance of ZPG. [ABSTRACT FROM AUTHOR]

Based on the realization of efficient utilization of cotton stalk lignin, the degradation of cotton stalk lignin by a CDs/CuO synergistic emulsion system was investigated. Copper oxide (CuO) nanoparticles with monoclinic crystal structure were prepared and carbon dots (CDs) synthesized by microwave method was combined with CuO. Under visible light, water and n-butanol were used to construct a waterâ€"oil (W/O) emulsion reaction system to achieved depolymerisation of lignin into small molecule compounds. The involvement of hydrogen peroxide (H2O2) makes the degradation of lignin in this system even more effective. The final high value-added monophenolic compound of 57.70 mg gâˆ'1 was obtained, among which the most abundant were six monophenolic compounds such as vanillin, eugenol and vinyl guaiacol and so on. The results of GC-MS and FTIR characterization indicated that H-type monomers were the main products of lignin degradation in this system. The process conditions for lignin hydrogenolysis in this system were optimized and the best ratio of CDs/CuO was obtained by product analysis. There were characterized by SEM, TEM, XRD, XPS, FTIR, and USâ€"vis. The results show that CDs/CuO aggregates into flower clusters, in which CDs are uniformly distributed on the surface of rhomboidal CuO monoliths. The analysis shows that the doping of CDs improves the absorption efficiency of CuO in the visible region, while reducing the complexation of CuO photogenerated electrons and holes, which achieves the purpose of improved photocatalytic activity of CuO. [ABSTRACT FROM AUTHOR]

To enable power supply in rural areas and to exploit clean energy, fully renewable power systems consisting of cascaded run‐of‐the‐river hydropower and volatile energies such as photovoltaic (pv) and wind are built around the world. In islanded operation, the primary and secondary frequency controls, that are hydro governors and automatic generation control (AGC), are responsible for the frequency stability. However, due to limited water storage capacity of run‐of‐the‐river hydropower and river dynamics constraints, without coordination between the cascaded plants, the traditional AGC cannot fully exploit the adjustability of hydropower. When imbalances between the volatile energy and load occur, load shedding can be inevitable. To address this issue, this paper proposes a coordinated tertiary control approach by jointly considering power system dynamics and the river dynamics that couples the cascaded hydropower plants. To unify the multi‐timescale dynamics of the power system and river dynamics to establish a controller that coordinates the cascaded plants, the relation between AGC parameters and turbine discharge is approximated by a polynomial surrogate model. The cascaded plants are coordinated by optimising AGC participation factors in a receding‐horizon manner. Simulation of a real‐life system shows the proposed method significantly reduces load loss under pv volatility. [ABSTRACT FROM AUTHOR]

Designing a new absorber to overcome the Shockley–Queisser limit for single-junction solar cells is of great importance for solar cell advancements. Here, a theoretical model of tandem intermediate band absorber is proposed based on the interface of Sn-doped AgAlTe2 and LiInTe2. Sn-doped AgAlTe2 and LiInTe2 are imminent to produce ideal heterojunctions as they possess similar lattice constants and the type-II band offset, providing an approach to overcome the Shockley–Queisser limit. [ABSTRACT FROM AUTHOR]

To exploit the massive solar energy available in the region, photovoltaic plants have been built in the mountain areas in Southwest China, coexisting with many small cascaded run-of-the-river hydropower plants, interconnected by short-distance transmission lines. Network constraints inside these systems are often negligible. However, due to the volatile nature of solar power and the weak connection to the external power grid, without proper coordination, solar power curtailment and water spillage are inevitable. To address this issue, this paper proposes an ultra-short-term stochastic generation control method for cascaded hydropower to mitigate solar power volatility. Two technical challenges are specifically addressed: to tackle the time-varying stochastic volatility of solar power, the Itô process model is introduced; to characterize the spatial-temporal hydraulic coupling of the cascaded hydropower plants and river operation constraints, a state-space dynamic river model derived from shallow water equations is included. Followingly, a stochastic control (SC) approach for hydropower generation based on stochastic programming is proposed, where hydropower generation commands are parameterized as affine functions of measured solar power, enabling quick response to solar power volatility. Simulation of a real-life cascaded hydro-solar system and a modified system verifies the proposed control method. [ABSTRACT FROM AUTHOR]

The stochasticity of photovoltaic (PV) generation output makes it necessary to smooth the output using other flexible power sources to realize the scale development of PV power. Small cascade hydropower stations (SCHSs) are also widely distributed in space, like PV generation. Therefore, it is proposed to utilize the regulation capability of SCHSs to complement PV generation. Targeting the maximization of the utilization rate of outgoing lines (utilization rate for short) of the system, the minimization of the curtailment rate, and the maximization of the minimum output within a time frame, a model for exploring the capability of SCHSs for regulating PV generation was established and solved by a hierarchical optimization method. By taking two small hydropower stations (the Mupo and Yangjiawan stations) on the Fabian River with a total installed capacity of 105 MW and the surrounding PV power source in China's Sichuan Province as examples, it was found that SCHSs can regulate a certain level of PV generation through the combined operation of cascade reservoirs and reduce the fluctuations and stochasticity of the PV generation output. The results have far-reaching significance on the large-scale development of PV generation. [ABSTRACT FROM AUTHOR]

Background: Prevention and control of cardiometabolic conditions and cardiovascular disease (CVD) in China may contribute to sustainable CVD reduction globally, given the fact that one-fifth of the worldwide population is in China. Knowing the distribution of behavioral risk factors (e.g., smoking and physical inactivity), especially at a national level in China, would be extremely relevant to the field of public health and CVD prevention. The objectives of this study were to investigate the nationwide prevalence of obesity, smoking, heavy drinking, and physical inactivity in Chinese adults, and further explore whether cardiometabolic conditions would modify the distribution of behavioral risk factors.Methods: This population-based study is based on the China Health and Retirement Longitudinal Study (2011-2012), including 17,302 adults (≥45 years, mean age 59.67 years, female 51.66%) from 25 provinces in China. Data on demographics, lifestyle factors, health status and history of diseases were collected via structured interviews and laboratory tests. Smoking, heavy drinking, obesity, and physical inactivity were defined following standard guidelines. We performed descriptive analysis and logistic regressions in this study.Results: The overall prevalence of heavy drinking, obesity, current smoking, and physical inactivity among middle-aged and older adults was 7.23% (95% confidence interval 6.53-7.29%), 11.53% (10.43-12.62%), 27.46% (26.30-28.62%), and 44.06% (41.19-46.92%), respectively. The prevalence varied between rural and urban areas as well as among geographic areas, with higher prevalence in the Northern and Northeastern regions. Heavy drinking and obesity were significantly associated with incident hypertension, diabetes, and high cholesterol; while current smoking was significantly associated with incident hypertension. Compared with healthy individuals, participants who self-reported a diagnosis of hypertension, high cholesterol, or diabetes were less likely to smoke currently and drink alcohol heavily, but more likely to be physically inactive and obese.Conclusions: Among Chinese middle-aged and older adults, the prevalence of behavioral risk factors varies by geographic region. Further effort is required to improve physical activity and fitness for Chinese adults, especially those with cardiometabolic conditions. [ABSTRACT FROM AUTHOR]

Converting surplus renewable electricity into hydrogen by electrolyzers has been recognized as a promising scheme to reduce renewable energy spillage and to meet the increasing hydrogen demand. However, the scheme is challenged by the inherent spatiotemporal imbalance between renewable energy and hydrogen demand. Seasonal storages and interregional hydrogen supply chains (HSCs) are commonly employed in the literature to eliminate this imbalance, but long-distance hydrogen transportation can be costly. In this paper, we incorporated the electric network (EN) into the HSC for its ability to promptly and economically deliver energy at long distances. The uniform hierarchical time discretization method is utilized to achieve the unified operation of the HSC and the EN. On this basis, an integrated HSC-EN model is elaborated upon to investigate the optimal investment and operation of electrolyzers and storage. Finally, an industrial case in Sichuan province, China is analyzed to illustrate the benefits of incorporating the EN to reduce the investment cost and improve electrolyzers’ utilization. [ABSTRACT FROM AUTHOR]

This paper presents a flexible compensation strategy for voltage source converter (VSC) connected to an unbalanced and harmonic distorted grid, which can achieve flexible tradeoff between the two common control targets, i.e., compensating the voltage at the point of common coupling (PCC), and compensating the output current of the VSC. To achieve the control target, a hybrid virtual impedance method is proposed, which uses both the feedforward of the PCC voltage and the feedback of the output current to develop the harmonic (including the negative sequence) voltage references. Compared with the conventional virtual impedance methods using only feedforward or only feedback, the proposed hybrid method can control the harmonic output impedance of the VSC in a wider range, without the potential overmodulation or instability problems caused by the conventional methods when the desired virtual impedance varies in a wide range. The effectiveness and superiority of the proposed strategy is theoretically analyzed and experimentally verified. [ABSTRACT FROM AUTHOR]

Background: The overall incidence of hyperphenylalaninemia (HPA) in China is 1:11,763, with tetrahydrobiopterin (BH4) deficiency accounting for 8.55% of patients with HPA in the mainland. Much progress has been made in the diagnosis and treatment of BH4 deficiency with the introduction of neonatal screening in China. However, the screening rate is still low and screening is not universally available. Methods: A total of 44 BH4-deficient patients were enrolled in this study, of which 39 were diagnosed with BH4 deficiency, while the remaining five showed typical characteristics of BH4 deficiency at a later period. The entire coding regions and adjacent intronic regions of GCH1, PTS, PCBD1 and QDPR genes were analyzed using target sequencing. Results: Nineteen (n=19) different mutations in the PTS gene including four novel mutations and one mutation in QDPR were identified. p.P87S, p.D96N, IVS1-291A>G, p.N52S, p.K91R, p.V56M, p.T106M and p.F40GfsX53 in PTS were the prevalent mutations with ≥3% relative frequency. The mutation p.R221X in the QDPR gene was found with relatively lower frequencies (2.27%). The remaining 12 mutations in PTS were found at relative frequencies of 1.14%. Conclusions: The results could be of value for genetic counseling and prenatal diagnosis in the patients’ families and for the molecular diagnosis of BH4 deficiencies. Furthermore, four novel mutations expand and improve the PTS mutation database. [ABSTRACT FROM AUTHOR]

This paper proposes an improved direct power control (DPC) strategy for the rotor-side converter (RSC) and grid-side converter (GSC) of the doubly fed induction generator under unbalanced and distorted voltage conditions. The proposed scheme is implemented in a synchronous reference frame with the fixed angular speed, so that the phase-locked loop can be removed and relevant potential instability issues can be avoided. Besides, the sequential separations and complex calculations of the power compensating items can be eliminated with the direct-resonant method based on a dual-frequency frequency adaptive vector PI. Thus, the negative and harmonic components can be directly eliminated, achieving balanced and sinusoidal current injected into the power grid. Meanwhile, the control strategy can achieve self-adaptive to the grid frequency variation in the practical situation with the proposed frequency estimation scheme. Finally, the experimental results validate the availability of the proposed DPC strategy. [ABSTRACT FROM AUTHOR]

In the risk assessment of cascading outages, the rationality of simulation and efficiency of computation are both of great significance. To overcome the drawback of sampling-based methods that huge computation resources are required and the shortcoming of initial contingency selection practices that the dependencies in sequences of outages are omitted, this paper proposes a novel risk assessment approach by searching on Markovian Tree. The Markovian tree model is reformulated from the quasi-dynamic multitimescale simulation model proposed recently to ensure reasonable modeling and simulation of cascading outages. Then, a tree search scheme is established to avoid duplicated simulations on same cascade paths, significantly saving the computation time. To accelerate the convergence of a risk assessment, a risk estimation index is proposed to guide the search for states with major contributions to the risk, and the risk assessment is realized based on the risk estimation index with a forward tree search and backward update algorithm. The effectiveness of the proposed method is illustrated on a four-node power system, and its convergence profile as well as efficiency is demonstrated on the RTS-96 test system. [ABSTRACT FROM AUTHOR]

The central Tibet AC interconnection project (CTAIP), which connects the Tibet power grid and the Sichuan power grid through a long distance transmission line of more than 1400 km, has a significant problem of voltage regulation. In order to improve the voltage regulation performance, six sets of ±60 Mvar static VAR compensators (SVC) were installed in the CTAIP. However, the SVCs may lead to electromagnetic oscillation below 50 Hz while improving voltage regulation capability. In this paper, the electromagnetic oscillation modes and the sensitivity of control parameters of SVC are analyzed. Then, the characteristics and influencing factors of the oscillation are discussed. It was found that there is an inherent electromagnetic oscillation mode below 50 Hz in the ultra-long distance transmission system. The employ of SVCs weaken the damping of this mode. Large proportional gain and integral gain (PI) parameters of SVCs can improve the voltage regulation performance, but weaken the electromagnetic oscillation mode damping. Therefore, a suppression method based on SVC PI parameters optimization is proposed to damp the oscillation. The essential of this method is to use the rising time of voltage response and setting time of SVCs as performance indicators of voltage regulation, and take the damping level of the electromagnetic oscillation mode as the performance index of SVC electromagnetic oscillation suppression ability. Combining the two indicators to form a comprehensive optimization index function, an intelligent optimization algorithm is applied. The process of SVC parameter optimization and the steps of multi-SVC parameter optimization in large power grids is proposed. Finally, PSCAD and real-time digital simulation (RTDS) simulation results verified the correctness of the proposed method. The optimization strategy was applied to CTAIP. The artificial grounding short circuit experimental results proved the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

• An intermediate band is presented in the main band gap of SnS 2 after Sb doping. • Sb can be doped at Sn site in SnS 2. • Sb-doped SnS 2 as a low cost and non-toxic absorber for IBSC has been proposed. Tin disulfide has attracted much attention on solar cell study due to its excellent optoelectronic properties in addition to just containing low-cost and non-toxic elements. Based on the HSE06-hybrid function calculations combined with Grimme's dispersion-correction method, a half-filled and delocalized intermediate band(IB) is presented in the main band gap of SnS 2 after partially Sb substituting on Sn site, which is made of the antibonding states of Sb-s and S-p states. Three-photon absorption can be realized in the doped sample and its corresponding absorption coefficient is enhanced at the visible light region thanks to the isolated and half-filled IB above the original valence band. Furthermore, Sb Sn always has the lowest formation energy than other Sb-related defects (i.e. Sb S and Sb i) based on the defect formation energy calculations. Therefore, Sb-doped SnS 2 is suggested as a promising candidate for the absorber of intermediate band solar cell. [ABSTRACT FROM AUTHOR]

Background and Objectives: Chinese women in rural areas who are currently >=55 years old have experienced extreme undernutrition during their childbearing age. Their specific experiences provided us with a natural quasiexperimental field for assessing the effects of consuming eggs to obtain nutrients during the childbearing period on preventing nonfatal coronary events (NCE) during the postmenopausal period in the framework of life course epidemiology.Methods and Study Design: A population-based matched case-control design for NCE was conducted in Yiyuan County, Shandong Province, China. In this study, 462 women with NCE (cases; onset age >=55 years) were included from the Active Surveillance System for Chronic Diseases, and 462 age-matched women without NCE and stroke (controls) from the same village were included. Conditional logistic model analysis was used to determine the association between egg intake and NCE during the postmenopausal period in 3 specific life-periods, namely age 18 to 49 years (childbearing period), age 50 years to NCE onset (perimenopausal and postmenopausal period), and age 18 years to NCE onset (total period).Results: We found that >=12 eggs vs. 0 egg intake per month under extreme undernutrition status during childbearing period exhibited a strong preventive effect against NCE during the postmenopausal period (OR=0.588, 95% CI=0.358-0.964). The window of protective effect was in the age 28 to 49 years, suggesting a critical period model of life course epidemiology.Conclusions: Egg intake under extreme undernutrition status during the childbearing period plays a critical role in preventing NCE during the postmenopausal period. [ABSTRACT FROM AUTHOR]

Chalcopyrite compounds like Cu(In,Ga)(S,Se) 2 have been widely studied as the absorber for single-junction solar cell. Other wide band gap Chalcopyrite compounds like CuGaS 2 have been utilized as the host of the absorber for intermediate band solar cell (IBSC). Here, a Chalcopyrite compound LiGaTe 2 with a suitable band gap as the host of the absorber for IBSC has been investigated by HSE06 first-principles calculations. Our results revealed that a partially-filled and isolated intermediate band (IB) is generated in the forbidden band gap of LiGaTe 2 after group ⅣA elements (i.e., Si, Ge and Sn) substituting at Ga site and three-photon absorption can be achieved in the doped systems. Combining the suitable IB position induced by Sn-doping and its low formation energy, Sn-doped LiGaTe 2 as a promising candidate has been proposed to be the absorber for IBSC. [ABSTRACT FROM AUTHOR]