Subjects: Dynamic and Electric Engineering >> Electrical Engineering submitted time 2023-11-29
Abstract： With the development of renewable energy, the voltage support strength of renewable energy multi-infeed systems is gradually decreasing, and there is an urgent need for strength evaluation methods. If considering that converters are all at the rated operating conditions, accurate quantification of strength can be achieved by utilizing existing power grid strength indices and threshold; However, the actual operating conditions are diverse and complex, which disrupts the existing criteria for defining indices and leads to the failure of existing methods. Therefore, this paper focuses on the quantification of voltage support strength under actual operating conditions. Firstly, the mapping relationship between the dynamic characteristics of grid-following converters, operating conditions, and parameters is discovered. Secondly, based on the perturbation theory of characteristics subspaces, an equivalent single-infeed system that can approximate the stability of the actual system is solved. On this basis, the operational generalized short circuit ratio(OgSCR) are defined. A rigorous method for quantifying voltage support strength can be formed based on the OgSCR and the device critical operational short-circuit ratio (OSCR0). In addition, this paper reveals the effect of actual operating conditions on strength. Finally, a numerical example is used to verify the feasibility of the proposed method
Peer Review Status:
Awaiting Review
Subjects: Dynamic and Electric Engineering >> Electrical Engineering submitted time 2022-05-29
Abstract：
Many methods and criteria of stability assessment have been proposed due to the complex dynamics of renewable power system. The physical implications of these methods/criteria and their scopes of adaptation are different. It is difficult to theoretically answer that, for certain stability issue, which stability criterion is suitable and whether the corresponding physical interpretation is reasonable. This paper was divided into two parts. The methods for assessing the adaptation of stability criteria were put forward, and the question whether the corresponding physical interpretations were reasonable were answered in part I. While the adaptation of each stability criterion was analyzed by applying the method and the physical interpretation of each stability problem was derived in part II. In part I, the derivation process of the existing stability criteria and their underlying physical significance were reviewed at first. Secondly, the selection principles of stability criteria were proposed from 3 aspects, namely stability equivalence, nominal performance and robust stability. And the quantitative index named loop gain sensitivity was proposed. Finally, the adaptation of several impedance criteria of grid-connected converters were analyzed.?It was shown that the nominal performance and robustness of these impedance criteria were not equivalent in frequency domain modal analysis. The adaptation of other typical stability criteria and the corresponding physical interpretation were analyzed in part II.
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Peer Review Status:Awaiting Review
Subjects: Dynamic and Electric Engineering >> Electrical Engineering submitted time 2022-05-29
Abstract：
From the perspective of stability equivalence, nominal performance and robustness, the qualitative principles and quantitative evaluation index of stability criterion adaptation are proposed in Part Ⅰ. In addition, the adaptation of the existing stability criteria and the physical interpretation of instability corresponding to the suitable stability criterion are analyzed for the typical equipment in power system, such as synchronous machines, doubly-fed induction generators (DFIG) and converters in Part II. Thereby the stability classification of the renewable power system is discussed based on dominant output variable. Firstly, aiming at low-frequency and sub-synchronous oscillation/resonance (SSO/SSR) of synchronous machine, the rationality of the existing stability analysis methods and physical interpretation is verified by using the proposed evaluation index. Secondly, the proposed evaluation index is used to analyze the oscillation of converters and DFIG, and the suitable stability criterion, derivation mechanism and dominant output variable are further discussed. Finally, a novel idea of equipment stability classification based on physical mechanism and dominant output variables are proposed, which classifies equipment stability from the vector perspective into three categories: phase-dominated synchronous stability, amplitude-dominated voltage stability, and electrical resonance formed by their special combination. Issues such as the concept of wide-band oscillation, the distinction between equipment stability and system stability, and the extensibility of their classification are further explored.
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Peer Review Status:Awaiting Review
Subjects: Computer Science >> Computer Software submitted time 2022-01-01
Abstract： Serious noise affects the rendering of global illumination using Monte Carlo (MC) path tracing when insufficient samples are used. The two common solutions to this problem are filtering noisy inputs to generate smooth but biased results and sampling the MC integrand with a carefully crafted probability distribution function (PDF) to produce unbiased results. Both solutions benefit from an efficient incident radiance field sampling and reconstruction algorithm. This paper summarizes the latest advancement in using deep reinforcement learning in the adaptive sampling and reconstruction of the incident radiance field. "
Peer Review Status:Awaiting Review
Subjects: Psychology >> Management Psychology submitted time 2021-10-13
Abstract： Occupational stigma reflects a society’s disapproval of, and discrimination against, an individual or group based on their occupation. Workers in stigmatized occupations, such as sewer workers, garbage collectors, street cleaners, and slaughterhouse workers, can internalize this occupational stigma, which can lower their self-esteem and motivate them to conceal their occupations or even leave their jobs to seek a higher status position. Many studies have explored the effects of occupational stigma on employees’ job attitudes and performance and some demonstrate that workers who feel stigmatized by their work devalue it and themselves, and this motivates them to not fully engage in their work, and considering other work options. However, extant studies focus primarily on the effect of occupational stigma mediated by occupational identity, and overlook the fact that occupational stigma also can influence employees’ perception of their family’s identity. Based on identity boundary theory, this study examines whether occupational stigma spills over to workers’ family identity and whether this results in negative job outcomes. That is, employees perceive their families as being stigmatized because of their “dirty” occupations, which is referred to as implicated family stigma. Moreover, this study explores whether this mediating effect of implicated family stigma is moderated by the employee’s level of family involvement. In such a way, occupational stigma is perceived as a threat to the family identity of workers who do “dirty work”. In other words, ‘dirty workers’ perceive their occupational stigma as implicating their families as well. Moreover, this study finds that individuals who are highly involved in their family’s life are more likely to leave their jobs because of implicated family stigma. We surveyed 390 employees across various jobs in China to test these predictions; 384 participants completed the entire three-wave survey, and the resulting data were analyzed. Results show that family involvement moderates both the relationship between occupational stigma and implicated family stigma, and the relationship between implicated family stigma and employees’ intent to leave a job, such that these two relationships are stronger when individuals’ family involvement is high rather than low. Furthermore, this mediating effect is more salient for individuals with a high-level of family involvement compared to those with a low-level. Our findings extend the research on occupational stigma by introducing a mechanism that influences employees’ intent to leave their job due to their family’s implicated stigma rather than on their negative personal occupational identity. Additionally, this study contributes to the literature by demonstrating that occupational stigma may crucially influence employees’ families in addition to negatively affecting the workers. Moreover, this is a pioneering explorative study that tests the identity boundary theory and offers practical suggestions on managerial strategies to address occupational stigma, including methods to maintain workers facing occupational stigma. "
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2020-09-28 Cooperative journals: 《计算机应用研究》
Abstract： Aiming at the problem of long time-consuming and high equipment energy consumption for task scheduling in mobile cloud computing environment, a task scheduling strategy based on improved bird group algorithm is proposed, a task scheduling strategy based on Improved Bird Swarm Algorithm (IBSA) is proposed. Firstly, a mobile cloud task scheduling model based on energy consumption and time is constructed. Secondly, adaptive sensing coefficients and social coefficients are proposed to prevent the algorithm from falling into a local optimum. Learning factors are optimized to optimize flight behavior and ensure that Superior ability. Finally, . the task scheduling objective function is used as the fitness function of the bird group to participate in the iterative updating of the algorithm. The simulation results show that the algorithm has good effects in mobile cloud computing task scheduling compared with ant colony algorithm, particle swarm algorithm, whale algorithm and bird swarm algorithm, which can effectively save time and reduce energy consumption.
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2019-01-28 Cooperative journals: 《计算机应用研究》
Abstract： The hard threshold tracking algorithm is an important reconstruction algorithm in compressed sensing, which is essentially a least squares problem and has the disadvantages of high complexity, poor convergence and long running time. This paper introduced the Nesterov method to optimize the convex relaxation phenomenon of sparse solutions, and introduced the successive relaxation iterative method to optimize the traditional hard threshold linear equations. The theory proves that the optimization results have good convergence. Simulation experiments show that the optimized algorithm effectively reduces the complexity of the algorithm and the running time.
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2018-08-13 Cooperative journals: 《计算机应用研究》
Abstract： Aiming at the low efficiency and low utilization rate of traditional cloud computing task scheduling algorithms, this paper proposed an improved algorithm using the improved fruit fly optimization algorithm (IFOA) and genetic algorithm (GA) for task scheduling. Firstly, the task scheduling is converted into a DAG (Directed Acyclic Graph) , and the task scheduling sequence is simplified through the kruskal algorithm. Secondly, the population of Drosophila algorithm is initialized using orthogonal arrays and quantization techniques. The boundaries of the Drosophila algorithm algorithm are processed, the exploration step size is dynamically adjusted, and the individual selection is processed using the GA algorithm. Finally, the fusion algorithm IFOA-GA is used in cloud computing task scheduling in the simulation platform. Compared with IGA, IFOA and IPSO algorithm, it has certain advantages in the comparison of four indexes of QoS, which shows that the IFOA-GA algorithm can be effective in mproving cloud computing scheduling efficiency
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2018-06-19 Cooperative journals: 《计算机应用研究》
Abstract： Due to the low efficiency of cloud computing resource task scheduling and uneven resource allocation, this paper combined the improved fireworks algorithm and artificial bee colony algorithm into IFWA-ABC. Firstly, this paper described the cloud computing resource task scheduling. Secondly, it used the chaotic reverse learning and Cauchy distribution to optimize the FWA initialization. The radii of the core fireworks and the non-core fireworks are optimized respectively. The optimal individuals in the FWA are obtained by improving the ABC algorithm. Finally, the IFWA-ABC algorithm is used for cloud computing task scheduling. In the simulation experiment, IFWA-ABC has obvious advantages compared with FWA and ABC in terms of virtual machine, execution time, consumption cost and Energy consumption index, which can effectively improve cloud computing resource allocation efficiency.
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2018-05-24 Cooperative journals: 《计算机应用研究》
Abstract： In order to solve the problem of low efficiency of resource scheduling in cloud computing, it is proposed to schedule the improved chicken swarm optimization. First, the concept of reverse learning is used to initialize the chicken swarm and improve the global search capability. Secondly, the position of chick is introduced into the concept of weight value and learning factor in particle swarm optimization to improve the individual position of the flock; the individual position of the chicken swarm optimization is again optimized by the difference algorithm, and finally the whole is processed by boundary processing to prevent possible cross-border of individual locations in the optimization. In the simulation experiment, the optimized chicken swarm optimization and the basic chicken swarm optimization, the particle swarm optimization algorithm and the ant colony algorithm are compared in terms of completion time, cost, energy consumption and load balance, and good results have been achieved.
Subjects: Mathematics >> Geometry and Topology submitted time 2017-11-23
Abstract： In this paper, first we give a notion for linear Weingarten spacelike hypersurfaces $M^{n}$ with $R=aH+b_{1}$ in a locally symmetric Lorentz space $L_{1}^{n+1}$, where $R$ and $H$ are the normalized scalar curvature and the mean curvature of $M^{n}$, respectively. Furthermore, we study complete or compact linear Weingarten spacelike hypersurfaces in locally symmetric Lorentz spaces $L_{1}^{n+1}$ satisfying some curvature conditions. By modifying Cheng-Yau's operator $\square$ given in {\cite{ChengYau77}}, we introduce a modified operator $L$ and give new estimates of $L(nH)$ and $\square(nH)$ of such spacelike hypersurfaces. Finally, we give partial generalizations of some Conjectures in locally symmetric Lorentz spaces $L_{1}^{n+1}$.
Peer Review Status:Awaiting Review
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