scholarly journals Analyses and Comparisons of Generic and User Writing Models of HVDC System Considering Transient DC Current and Voltages

Energies ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7897
Author(s):  
Dohoon Kwon ◽  
Youngjin Kim

Analyses and comparisons of generic models and a novel modeling method of line-commutated converter (LCC)-based high voltage direct current (HVDC) systems are presented for the power system simulator for engineering (PSS/E) simulation tool. The main purposes are to describe the dynamics of the DC voltage and current of HVDC system and to improve estimation of the maximum values using the generic and proposed HVDC models when AC line-to-ground faults are occurred. For the generic HVDC models, the characteristics and limitations as well as parameter investigations are conducted. Three modules are also are developed for the proposed HVDC model, which are composed of (a) AC/DC conversion; (b) controller selection; and (c) DC line model. Case studies were conducted considering the real-operated HVDC system in Korea under the PSS/E and power systems computer aided design (PSCAD) simulation environments. The simulation results were compared with measured data from the real-operated HVDC system and the results from the PSCAD HVDC models considering single- and three-phase line-to-ground faults. The case study results show that a specific generic HVDC model in PSS/E can simulate the dynamics of the DC voltage and current after the AC line-to-ground faults. The case studies also showed that the proposed modeling method is effectively improves the estimation of the maximum DC voltage and current values for the AC line-to-ground faults.

2021 ◽  
Vol 2021 (169) ◽  
pp. 65-77
Author(s):  
Jennifer Brown Urban ◽  
Miriam R. Linver ◽  
Lisa M. Chauveron ◽  
Thomas Archibald ◽  
Monica Hargraves ◽  
...  

2021 ◽  
pp. 027836492098785
Author(s):  
Julian Ibarz ◽  
Jie Tan ◽  
Chelsea Finn ◽  
Mrinal Kalakrishnan ◽  
Peter Pastor ◽  
...  

Deep reinforcement learning (RL) has emerged as a promising approach for autonomously acquiring complex behaviors from low-level sensor observations. Although a large portion of deep RL research has focused on applications in video games and simulated control, which does not connect with the constraints of learning in real environments, deep RL has also demonstrated promise in enabling physical robots to learn complex skills in the real world. At the same time, real-world robotics provides an appealing domain for evaluating such algorithms, as it connects directly to how humans learn: as an embodied agent in the real world. Learning to perceive and move in the real world presents numerous challenges, some of which are easier to address than others, and some of which are often not considered in RL research that focuses only on simulated domains. In this review article, we present a number of case studies involving robotic deep RL. Building off of these case studies, we discuss commonly perceived challenges in deep RL and how they have been addressed in these works. We also provide an overview of other outstanding challenges, many of which are unique to the real-world robotics setting and are not often the focus of mainstream RL research. Our goal is to provide a resource both for roboticists and machine learning researchers who are interested in furthering the progress of deep RL in the real world.


2021 ◽  
Vol 13 (14) ◽  
pp. 7889
Author(s):  
Carlos Efrain Contreras Inga ◽  
Gabriel Walton ◽  
Elizabeth Holley

The ability to predict the mechanical behavior of brittle rocks using bonded block models (BBM) depends on the accuracy of the geometrical representation of the grain-structure and the applied micro-properties. This paper evaluates the capabilities of BBMs for predictive purposes using an approach that employs published micro-properties in combination with a Voronoi BBM that properly approximates the real rock grain-structure. The Wausau granite, with Unconfined Compressive Strength (UCS) of 226 MPa and average grain diameter of 2 mm, is used to evaluate the effectiveness of the predictive approach. Four published sets of micro-properties calibrated for granites with similar mineralogy to the Wausau granite are used for the assessment. The effect of grain-structure representation in Voronoi BBMs is analyzed, considering grain shape, grain size and mineral arrangement. A unique contribution of this work is the explicit consideration of the effect of stochastic grain-structure generation on the obtained results. The study results show that the macro-properties of a rock can be closely replicated using the proposed approach. When using this approach, the micro-properties have a greater impact on the realism of the predictions than the specific grain-structure representation. The grain shape and grain size representations have a minor effect on the predictions for cases that do not deviate substantially from the real average grain geometry. However, the stochastic effect introduced by the use of randomly-generated Voronoi grain-structures can be significant, and this effect should be considered in future studies.


2013 ◽  
Vol 3 (2) ◽  
Author(s):  
Guo-Jie Li ◽  
Si-Ye Ruan ◽  
Tek Lie

AbstractA multi-terminal voltage-source-converter (VSC) based high voltage direct current (HVDC) system is concerned for its flexibility and reliability. In this study, a control strategy for multiple VSCs is proposed to auto-share the real power variation without changing control mode, which is based on “dc voltage droop” power regulation functions. With the proposed power regulation design, the multiple VSCs automatically share the real power change and the VSC-HVDC system is stable even under loss of any one converter while there is no overloading for any individual converter. Simulation results show that it is effective to balance real power for power disturbance and thus improves operation reliability for the multi-terminal VSC-HVDC system by the proposed control strategy.


2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Carole Lunny ◽  
Dawid Pieper ◽  
Pierre Thabet ◽  
Salmaan Kanji

Abstract Background Overviews often identify and synthesise a large number of systematic reviews on the same topic, which is likely to lead to overlap (i.e. duplication) in primary studies across the reviews. Using a primary study result multiple times in the same analysis overstates its sample size and number of events, falsely leading to greater precision in the analysis. This paper aims to: (a) describe types of overlapping data that arise from the same primary studies reported across multiple reviews, (b) describe methods to identify and explain overlap of primary study data, and (c) present six case studies illustrating different approaches to manage overlap. Methods We first updated the search in PubMed for methods from the MOoR framework relating to overlap of primary studies. One author screened the studies titles and abstracts, and any full-text articles retrieved, extracted methods data relating to overlap of primary studies and mapped it to the overlap methods from the MOoR framework. We also describe six case studies as examples of overviews that use specific overlap methods across the steps in the conduct of an overview. For each case study, we discuss potential methodological implications in terms of limitations, efficiency, usability, and resource use. Results Nine methods studies were found and mapped to the methods identified by the MOoR framework to address overlap. Overlap methods were mapped across four steps in the conduct of an overview – the eligibility criteria step, the data extraction step, the assessment of risk of bias step, and the synthesis step. Our overview case studies used multiple methods to reduce overlap at different steps in the conduct of an overview. Conclusions Our study underlines that there is currently no standard methodological approach to deal with overlap in primary studies across reviews. The level of complexity when dealing with overlap can vary depending on the yield, trends and patterns of the included literature and the scope of the overview question. Choosing a method might be dependent on the number of included reviews and their primary studies. Gaps in evaluation of methods to address overlap were found and further investigation in this area is needed.


2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Chien-Ho Ko

Purpose Additive manufacturing of concrete (AMoC) is an emerging technology for constructing buildings. However, due to the nature of the concrete property and constructing buildings in layers, constraints and limitations are encountered while applying AMoC in architecture. This paper aims to analyze the constraints and limitations that may be encountered while using AMoC in architecture. Design/methodology/approach A descriptive research approach is used to conduct this study. First, basic notions of AMoC are introduced. Then, challenges of AMoC, including hardware, material property, control and design, are addressed. Finally, strategies that may be used to overcome the challenges are discussed. Findings Factors influencing the success of AMoC include hardware, material, control methods, manufacturing process and design. Considering these issues in the early design phase is crucial to achieving a successful computer-aided design (CAD)/computer-aided manufacturing (CAM) integration to bring CAD and CAM benefits into the architecture industry. Originality/value In three-dimensional (3D) printing, objects are constructed layer by layer. Printing results are thus affected by the additive method (such as toolpath) and material properties (such as tensile strength and slump). Although previous studies attempt to improve AMoC, most of them focus on the manufacturing process. However, a successful application of AMoC in architecture needs to consider the possible constraints and limitations of concrete 3D printing. So far, research on the potential challenges of applying AMoC in architecture from a building lifecycle perspective is still limited. The study results of this study could be used to improve design and construction while applying AMoC in architecture.


Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 2978 ◽  
Author(s):  
Sherong Zhang ◽  
Dejun Hou ◽  
Chao Wang ◽  
Xuexing Cao ◽  
Fenghua Zhang ◽  
...  

Geology uncertainties and real-time construction modification induce an increase of construction risk for large-scale slope in hydraulic engineering. However, the real-time evaluation of slope safety during construction is still an unsettled issue for mapping large-scale slope hazards. In this study, the real-time safety evaluation method is proposed coupling a construction progress with numerical analysis of slope safety. New revealed geological information, excavation progress adjustment, and the support structures modification are updating into the slope safety information model-by-model restructuring. A dynamic connection mapping method between the slope restructuring model and the computable numerical model is illustrated. The numerical model can be generated rapidly and automatically in database. A real-time slope safety evaluation system is developed and its establishing method, prominent features, and application results are briefly introduced in this paper. In our system, the interpretation of potential slope risk is conducted coupling dynamic numerical forecast and monitoring data feedback. The real case study results in a comprehensive real-time safety evaluation application for large slope that illustrates the change of environmental factor and construction state over time.


2014 ◽  
Vol 17 (4) ◽  
pp. 319-335 ◽  
Author(s):  
Alessio Cavicchi ◽  
Cristina Santini ◽  
Lucia Bailetti

Purpose – This purpose of this paper is to introduce a research model inspired by the basic principles of experiential research and apply it to the food and beverage industry. Thinkers and doers often do not speak the same language: many scholars have pursued the goal of reducing the gap between academicians and practitioners by introducing new research models or adapting existing ones. Two case studies with wine and olive oil producers illustrate how the model works and highlight its applicability. Background literature is provided to support the model. Design/methodology/approach – In defining the model, we have followed several steps. First, we searched the literature to identify research needs and insights that might be useful in formulating the model. Second, we constructed a model following some procedural steps suggested in the literature. Third, we tested a model to verify its applicability and functionality. The paper is structured as follows: the first section explores the issue of academic–practitioner collaboration to identify the obstacles to effective collaboration and to define possible benefits from reducing the gap. The second section presents background literature on methodologies for enhancing cross-profession collaboration. Finally, the model is described and two case studies are described to flesh out how the model works. Findings – According to our experience and research results, this model is, paraphrasing Phillips (1987), “warrantable” because it proposes continuous reflection to improve the alignment between thinkers and doers: this method of conducting research is objective and bridges the gap between researchers and practitioners. Because this model centres on experience, participant behaviours and beliefs can be elicited about a host of nondurable goods. Having entrepreneurs put themselves in the consumers’ position, and providing them the results of their experiment can be considered the real value added of this approach. The model proposed in this paper opens a wider perspective in qualitative research, and the two case studies demonstrate that it is particularly flexible for adaptation to various businesses. Research limitations/implications – More case studies could be useful to demonstrate the validity of this model. Particularly, a longitudinal case study aiming at collecting data about the participants’ feedback in the long run could help in understanding the deep value of the proposed model. Practical implications – While this paper illustrates two applications of the model with entrepreneurs and managers of the wine and olive oil industry, this model offers potential for analysis not only in the food and beverage sector but all fast-moving consumer goods sectors, as it can be adapted to techniques other than sensory analysis once researchers have confirmed that they fit with the aim of the research and the peculiarities of the problem observed. Social implications – Tools and methodologies must be chosen according to the type of business the problem refers to, and, while this presents a considerable challenge in organizing ad hoc research teams, it also offers an opportunity for an interdisciplinary approach and an exchange of knowledge and skills from different research fields. In this case, the choice of research methodology is much more driven by the real needs that emerge from the phenomenon observed, rather than by the researchers’ specific skills. Originality/value – This paper has helped us broaden our perspective on research and has encouraged us to reflect on critical issues such as validity of a research process and usefulness of research. Some questions about the role of research in relation to practitioners are still open, but we think that this work has the merit of further highlighting the importance of bridging the gap between researchers and practitioners during research, and the usefulness being flexible and open-minded when carrying out an investigation.


RELIGIA ◽  
2017 ◽  
Vol 20 (1) ◽  
pp. 85
Author(s):  
Muhamad Rifa'i Subhi

Islam teaches the difference in someone's level of religiosity. The level of human religiosity can change from one moment to another. Humans have evolved a religious life. Including human experience in adulthood elderly in life and face the problems of life. This study focused on the real description of the attitude of religiosity which is owned by the elderly. The study was taken from the students at the boarding school Elderly Islamic boarding school (Pesantren) of Roudlotul Muta'allimin Dracik Kramat Batang. The research method used descriptive qualitative approach to straight dialogue (interview) of the respondents, namely the students of Elderly Islamic Boarding School (Pesantren). The study results showed that each of the students have the different religious involvement in filling elderly period (retirement). The involvement includes Ritual Involvement, Ideological Involvement, Intellectual involvement, experimental involvement, and consequential involvement.


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