| 1. |
- Tran, Dien M., et al.
(author)
-
High prevalence of colonisation with carbapenem-resistant Enterobacteriaceae among patients admitted to Vietnamese hospitals : Risk factors and burden of disease
- 2019
-
In: Journal of Infection. - : Saunders Elsevier. - 0163-4453 .- 1532-2742. ; 79:2, s. 115-122
-
Journal article (peer-reviewed)abstract
- BackgroundCarbapenem-resistant Enterobacteriaceae (CRE) is an increasing problem worldwide, but particularly problematic in low- and middle-income countries (LMIC) due to limitations of resources for surveillance of CRE and infection prevention and control (IPC).MethodsA point prevalence survey (PPS) with screening for colonisation with CRE was conducted on 2233 patients admitted to neonatal, paediatric and adult care at 12 Vietnamese hospitals located in northern, central and southern Vietnam during 2017 and 2018. CRE colonisation was determined by culturing of faecal specimens on selective agar for CRE. Risk factors for CRE colonisation were evaluated. A CRE admission and discharge screening sub-study was conducted among one of the most vulnerable patient groups; infants treated at an 80-bed Neonatal ICU from March throughout June 2017 to assess CRE acquisition, hospital-acquired infection (HAI) and treatment outcome.ResultsA total of 1165 (52%) patients were colonised with CRE, most commonly Klebsiella pneumoniae (n=805), Escherichia coli (n=682) and Enterobacter spp. (n=61). Duration of hospital stay, HAI and treatment with a carbapenem were independent risk factors for CRE colonisation. The PPS showed that the prevalence of CRE colonisation increased on average 4.2 % per day and mean CRE colonisation rates increased from 13% on the day of admission to 89% at day 15 of hospital stay. At the NICU CRE colonisation increased from 32% at admission to 87% at discharge, mortality was significantly associated (OR 5•5, P < 0•01) with CRE colonisation and HAI on admission.ConclusionThese data indicate that there is an epidemic spread of CRE in Vietnamese hospitals with rapid transmission to hospitalised patients.
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| 2. |
- Kattge, Jens, et al.
(author)
-
TRY plant trait database - enhanced coverage and open access
- 2020
-
In: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 26:1, s. 119-188
-
Journal article (peer-reviewed)abstract
- Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.
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| 3. |
- Settele, Josef, et al.
(author)
-
Rice ecosystem services in South-east Asia
- 2018
-
In: Paddy and Water Environment. - : Springer. - 1611-2490 .- 1611-2504. ; 16:2, s. 211-224
-
Journal article (other academic/artistic)
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| 4. |
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| 5. |
- Do, Thanh Toan, et al.
(author)
-
Simultaneous feature aggregating and hashing for compact binary code learning
- 2019
-
In: IEEE Transactions on Image Processing. - 1941-0042 .- 1057-7149. ; 28:10, s. 4954-4969
-
Journal article (peer-reviewed)abstract
- Representing images by compact hash codes is an attractive approach for large-scale content-based image retrieval. In most state-of-the-art hashing-based image retrieval systems, for each image, local descriptors are first aggregated as a global representation vector. This global vector is then subjected to a hashing function to generate a binary hash code. In previous works, the aggregating and the hashing processes are designed independently. Hence, these frameworks may generate suboptimal hash codes. In this paper, we first propose a novel unsupervised hashing framework in which feature aggregating and hashing are designed simultaneously and optimized jointly. Specifically, our joint optimization generates aggregated representations that can be better reconstructed by some binary codes. This leads to more discriminative binary hash codes and improved retrieval accuracy. In addition, the proposed method is flexible. It can be extended for supervised hashing. When the data label is available, the framework can be adapted to learn binary codes which minimize the reconstruction loss with respect to label vectors. Furthermore, we also propose a fast version of the state-of-the-art hashing method Binary Autoencoder to be used in our proposed frameworks. Extensive experiments on benchmark datasets under various settings show that the proposed methods outperform the state-of-the-art unsupervised and supervised hashing methods.
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| 6. |
- Hoang, Tuan, et al.
(author)
-
Simultaneous compression and quantization: A joint approach for efficient unsupervised hashing
- 2020
-
In: Computer Vision and Image Understanding. - : Elsevier BV. - 1077-3142 .- 1090-235X. ; 191
-
Journal article (peer-reviewed)abstract
- For unsupervised data-dependent hashing, the two most important requirements are to preserve similarity in the low-dimensional feature space and to minimize the binary quantization loss. A well-established hashing approach is Iterative Quantization (ITQ), which addresses these two requirements in separate steps. In this paper, we revisit the ITQ approach and propose novel formulations and algorithms to the problem. Specifically, we propose a novel approach, named Simultaneous Compression and Quantization (SCQ), to jointly learn to compress (reduce dimensionality) and binarize input data in a single formulation under strict orthogonal constraint. With this approach, we introduce a loss function and its relaxed version, termed Orthonormal Encoder (OnE) and Orthogonal Encoder (OgE) respectively, which involve challenging binary and orthogonal constraints. We propose to attack the optimization using novel algorithms based on recent advance in cyclic coordinate descent approach. Comprehensive experiments on unsupervised image retrieval demonstrate that our proposed methods consistently outperform other state-of-the-art hashing methods. Notably, our proposed methods outperform recent deep neural networks and GAN based hashing in accuracy, while being very computationally-efficient.
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| 7. |
- Mai, Tam T., et al.
(author)
-
An overview of grid-edge control with the digital transformation
- 2021
-
In: Electrical Engineering. - : Springer Science and Business Media LLC. - 1432-0487 .- 0948-7921. ; 103:4, s. 1989-2007
-
Journal article (peer-reviewed)abstract
- Distribution networks are evolving to become more responsive with increasing integration of distributed energy resources (DERs) and digital transformation at the grid edges. This evolution imposes many challenges to the operation of the network, which then calls for new control and operation paradigms. Among others, a so-called grid-edge control is emerging to harmonise the coexistence of the grid control system and DER’s autonomous control. This paper provides a comprehensive overview of the grid-edge control with various control architectures, layers, and strategies. The challenges and opportunities for such an approach at the grid edge with the integration of DERs and digital transformation are summarised. The potential solutions to support the network operation by using the inherent controllability of DER and the availability of the digital transformation at the grid edges are discussed.
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| 8. |
- Ngo, Hai Hoang Tuan, et al.
(author)
-
Effect of light-touch intervention and associated factors to microbial contamination at small-scale pig slaughterhouses and traditional pork shops in Vietnam
- 2023
-
In: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 406
-
Journal article (peer-reviewed)abstract
- Traditional pork value chains dominate the production and distribution of pork in Vietnam; however, the high level of microbiological contamination in pork may increase the risk of food-borne disease for consumers. There is limited evidence about how to feasibly and scalably reduce microbial contamination in pork sold in traditional markets. This study aimed to assess the effectiveness of light-touch interventions for changing worker behaviour in small-scale slaughterhouses and vendors at traditional pork shops, as well as to identify risk factors for pork contamination. The intervention packages consisted of providing hygiene tools and delivering a food safety training which had been designed in a participatory way and covered 10 small-scale slaughterhouses and 29 pork shops. Pig carcasses, retailed pork, contact surfaces, and hands were sampled to measure the total bacterial count (TBC) and Salmonella contamination before, three and six weeks after the intervention, and trainee practices were observed at the same time. Linear and generalized linear mixed effects models were constructed to identify risk factors for TBC and Salmonella contamination at the slaughterhouses and pork shops. The interventions at slaughterhouses and pork shops both showed a slight reduction of TBC contamination in pig carcasses and Salmonella prevalence in retailed pork, while the TBC in retailed pork decreased only marginally. For slaughterhouses, the regression model indicated that smoking or eating during slaughtering (indicating poor hygienic practices) was associated with TBC increasing, while cleaning floors and wearing boots reduced TBC contamination. For pork shops, using rough materials (cardboard or wood) to display pork was the only factor increasing TBC contamination in pork, whereas cleaning knives was associated with lower TBC. Besides, the presence of supporters and wearing aprons reduced the probability of Salmonella contamination in pork. The findings highlight the effectiveness of light-touch interventions in reducing microbial contamination in pig carcasses at small-scale slaughterhouses and pork at traditional shops over the study period.
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| 9. |
- Ngo, Hai Hoang Tuan, et al.
(author)
-
Impact of perception and assessment of consumers on willingness to pay for upgraded fresh pork : An experimental study in Vietnam
- 2023
-
In: Frontiers in Sustainable Food Systems. - : Frontiers Media S.A.. - 2571-581X. ; 7
-
Journal article (peer-reviewed)abstract
- Traditional pork shops play an essential role in delivering pork, the most popular food in Vietnam, to consumers. Studies have shown the need for investment in training and equipment to improve the safety of pork sold at traditional shops. However, it remains unclear how consumers perceived improvement to the hygiene in pork shops and if they are ready to pay premium prices for safer products. This study used an experimental approach to determine consumers’ perception and assessment of improved pork shops and their willingness to pay (WTP) for pork products. A total of 152 respondents in two provinces in Vietnam joined in a Becker–DeGroot–Marschak (BDM) mechanism experiment to collect data on WTP for pork from typical and upgraded pork shops. A questionnaire was used to record consumers’ perceptions and assessments of the pork shops and products. Overall, consumers were willing to pay 20% more for upgraded fresh pork than for what is currently available on the market. Consumers trusted in the effectiveness of the upgraded intervention and the quality of pork at the pork shop, which increased their WTP for the upgraded pork. Concerns about contaminated pork had a negative impact on the WTP for typical pork, while the high frequency of pork consumption and the existence of elderly family members led to higher WTP for both products. The findings indicate the potential economic benefit of upgrading pork shops, which would be an important driver to motivate sellers to improve food safety.
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| 10. |
- Ngo, Hai Hoang Tuan, et al.
(author)
-
Microbial contamination and associated risk factors in retailed pork from key value chains in Northern Vietnam
- 2021
-
In: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 346
-
Journal article (peer-reviewed)abstract
- Pork and pork products are important staple food in the diet of Vietnamese consumers. The safety of pork, including biological contamination, is a concern to several public authorities and value chain actors. This crosssectional study aimed to identify Salmonella and total bacterial count (TBC) contamination of cut pork sold in different outlets, and determine the potential factors leading to contamination. A total of 671 pork samples were collected from different retail channels in three provinces in Northern Vietnam. Hygiene conditions and practices at pork vending premises were also observed and recorded. Data analysis used descriptive statistics and regression analysis. Overall, Salmonella prevalence in retailed pork was 58.1%. Salmonella contamination in pork from traditional retail, modern retail and food services were 60.5%, 50.9% and 80.5%, respectively. Eighty percent and 68% of fresh pork in canteen and street food was contaminated with Salmonella. Only a small proportion of a subset of the pork samples (6.2%) tested met the Vietnamese standard requirement for TBC contamination. Average concentration of TBC in fresh pork in traditional retail, modern retail and food services were 6.51 (SD: 0.64), 6.38 (0.65), and 6.96 (0.85) LogCFU/g, respectively. Transport time, use of the same tools for pork and other types of meat, storage temperature, and environment hygiene are important factors that might affect microbial contamination. The findings underline the high level of microbial contamination, which requires practical interventions to improve food safety hygiene practices and behavior of pork retailers.
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| 11. |
- Ngo, Hoang Tuan Hai, et al.
(author)
-
Assessment of a light-touch intervention to reduce microbial contamination at small-scale pig slaughterhouses and traditional pork shops in Vietnam
- 2023
-
In: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 406
-
Journal article (peer-reviewed)abstract
- Traditional pork value chains dominate the production and distribution of pork in Vietnam; however, there high microbiological contamination of pork may lead to health risks. There is limited evidence about how to sustainably and scalably reduce microbial contamination in pork sold in traditional markets. This study aimed to assess the effectiveness of light-touch interventions for changing worker behaviour in small-scale slaughterhouses and retailers at traditional pork shops, as well as to identify risk factors for pork contamination. The intervention packages consisted of providing hygiene tools and delivering a food safety training which had been designed in a participatory way and covered 10 small-scale slaughterhouses and 29 pork shops. Pig carcasses, retailed pork, contact surfaces, and hands were sampled to measure the total bacterial count (TBC) and Salmonella contamination and trainee practices were observed before, three and six weeks after the intervention. Linear and generalized linear mixed effects models were constructed to identify risk factors for TBC and Salmonella contamination at the slaughterhouses and pork shops. Intervention results showed a slight reduction of TBC contamination in pig carcasses from 4.46 to 4.23 log10 CFU/cm2 (p = 0.09) and Salmonella prevalence in retailed pork (reduction from 52% to 24% detection, p = 0.08), while the TBC in retailed pork decreased only marginally (5.47 vs. 5.36 log10 CFU/g, p = 0.23). For slaughterhouses, the regression model indicated that smoking or eating during slaughtering was a risk factor, associated with TBC increasing by 0.60 log10 CFU/g (95% confidence interval (CI): 0.12 to 0.96, p =0.02), while cleaning floors and wearing boots reduced TBC contamination with 0.53 log10 CFU/g (CI: –0.83 to 0.01, p = 0.03) and 1.04 log10 CFU/g (CI: –1.50 to –0.26, p = 0.03), respectively. For pork shops, using rough materials (cardboard or wood) to display pork was the only factor increasing TBC contamination in pork with 0.57 log10 CFU/g (CI: 0.22 to 0.91, p < 0.001), whereas wearing aprons was associated with lower TBC, with 0.45 log10 CFU/g (CI: –0.79 to –0.12, p = 0.02), and Salmonella contamination in pork (odds ratio (OR) = 0.13, CI: 0.02 to 0.72, p = 0.03). The findings highlight the effectiveness of light-touch interventions in reducing microbial contamination in pig carcasses and pork over the study period.
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| 12. |
- Nguyen, T. N. Anh, et al.
(author)
-
Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs
- 2014
-
In: Physical Review Applied. - 2331-7019. ; 2:4
-
Journal article (peer-reviewed)abstract
- We report on the magnetization depth profile of a hybrid exchange-spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element-specific x-ray magnetic circular dichroism of the Fe and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.
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| 13. |
- Srivastava, Ankur, 1989, et al.
(author)
-
Development of a DSO Support Tool for Congestion Forecast
- 2021
-
In: IET Generation, Transmission and Distribution. - : Institution of Engineering and Technology (IET). - 1751-8687 .- 1751-8695. ; 15:23, s. 3345-3359
-
Journal article (peer-reviewed)abstract
- This paper presents a novel DSO support tool with visualisation capability for forecasting network congestion in distribution systems with a high level of renewables. To incorporate the uncertainties in the distribution systems, the probabilistic power flow framework has been utilised. An advanced photovoltaic production forecast based on sky images and a load forecast using an artificial neural network is used as the input to the tool. In addition, advanced load models and operating modes of photovoltaic inverters have been incorporated into the tool. The tool has been applied in case studies to perform congestion forecasts for two real distribution systems to validate its usability and scalability. The results from case studies demonstrated that the tool performs satisfactorily for both small and large networks and is able to visualise the cumulative probabilities of nodes voltage deviation and network components (branches and transformers) congestion for a variety of forecast horizons as desired by the DSO. The results have also shown that explicit inclusion of load-voltage dependency models would improve the accuracy of the congestion forecast. For demonstrating the applicability of the tool, it has been integrated into an existing distribution management system via the IoT platform of a DMS vendor, Atos Worldgrid.
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| 14. |
- Trung, Hieu Tran, et al.
(author)
-
Anti-inflammatory and Antiphytopathogenic Fungal Activity of 2,3-seco-Tirucallane Triterpenoids Meliadubins A and B from Melia dubia Cav. Barks with ChemGPS-NP and In Silico Prediction
- 2023
-
In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 8:40, s. 37116-37127
-
Journal article (peer-reviewed)abstract
- Two new rearranged 2,3-seco-tirucallane triterpenoids, meliadubins A (1) and B (2), along with four known compounds, 3-6, were isolated from the barks of Melia dubia Cav. Compound 2 exhibited a significant inflammatory inhibition effect toward superoxide anion generation in human neutrophils (EC50 at 5.54 +/- 0.36 mu M). It bound to active sites of a human inducible nitric oxide synthase (3E7G) through interactions with the residues of GLU377 and PRO350, which may benefit in reducing the neutrophilic inflammation effect. The ChemGPS-NP interpretation combined with bioactivity assay and in silico prediction results suggested 2 to be an agent for targeting iNOS with different mechanisms as compared to a selected set of current approved drugs. Moreover, compounds 1 and 2 showed remarkable inhibition against the rice pathogenic fungus Magnaporthe oryzae in a dose-dependent manner with IC50 values of 137.20 +/- 9.55 and 182.50 +/- 18.27 mu M, respectively. Both 1 and 2 displayed interactions with the residue of TYR223, a key active site of trihydroxynaphthalene reductase (1YBV). The interpretation of 1 and 2 in the ChemGPS-NP physical-chemical property space indicated that both compounds are quite different compared to all members of a selected set of reference compounds. In light of demonstrated biological activity and in silico prediction experiments, both compounds possibly exhibited activity against phytopathogenic fungi via a novel mode of action.
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| 15. |
- Wang, Feng, 1975, et al.
(author)
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An extended OPF incorporating multi-terminal VSC-HVDC and its application on transmission loss evaluation
- 2013
-
In: 2013 IEEE Grenoble Conference PowerTech, POWERTECH 2013. - 9781467356695
-
Conference paper (peer-reviewed)abstract
- This paper proposes an extension of the traditional ac Optimal Power Flow (OPF) model to incorporate the Voltage Source Converter based Multi-terminal High Voltage Direct Current system (VSC-MTDC). In the extended OPF model, the detailed VSC-MTDC system model is included, and the key technical limits of VSC (e.g., the maximum VSC valve current and the maximum dc voltage) are used as the operating constraints of the VSC-MTDC system. The extended OPF model is applied to a case study using the Nordic 32-bus system to evaluate the contribution of the embedded VSC-MTDC system on the overall system loss reduction. The study results show that the overall system loss of an ac transmission grid is not necessarily reduced by embedding a VSC-MTDC system into it. The reduction of the system loss by embedded VSC-MTDC system depends on their configuration and location, and the VSC station loss ratio as well.
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| 16. |
- Agathokleous, Christos, 1993, et al.
(author)
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Stochastic Operation Scheduling Model for a Swedish Prosumer with PV and BESS in Nordic Day-Ahead Electricity Market
- 2019
-
In: 2019 IEEE Milan PowerTech, PowerTech 2019.
-
Conference paper (peer-reviewed)abstract
- In this paper, an optimal stochastic operation scheduling model is proposed for a prosumer owning photovoltaic (PV) facility coupled with a Battery Energy Storage System (BESS). The objective of the model is to maximize the prosumer’s expected profits. A two-stage stochastic mixed-integer nonlinear optimization (SMINLP) approach is used to cope with the parameters’ uncertainties. Artificial Neural Networks (ANN) are used to forecast the markets’ prices and the standard scenario reduction algorithms are applied to handle the computational tractability of the problem. The model is applied to a case study using data from the Nordic electricity markets and historical PV production data from the Chalmers University of Technology campus, considering a scaled up 5MWp power capacity. The results show that the proposed approach could increase the revenue for the prosumer by up to 11.6% as compared to the case without any strategy. Furthermore, the sensitivity analysis of BESS’s size on the expected profit shows that increasing BESS size could lead to an increase in the net profits.
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| 17. |
- Ahlberg, Martina, et al.
(author)
-
Freezing and thawing magnetic droplet solitons
- 2022
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
-
Journal article (peer-reviewed)abstract
- Magnetic droplets are a type of non-topological magnetic soliton, which are stabilised and sustained by spin-transfer torques for instance. Without this, they would collapse. Here Ahlberg et al show that by decreasing the applied magnetic field, droplets can be frozen, forming a static nanobubble Magnetic droplets are non-topological magnetodynamical solitons displaying a wide range of complex dynamic phenomena with potential for microwave signal generation. Bubbles, on the other hand, are internally static cylindrical magnetic domains, stabilized by external fields and magnetostatic interactions. In its original theory, the droplet was described as an imminently collapsing bubble stabilized by spin transfer torque and, in its zero-frequency limit, as equivalent to a bubble. Without nanoscale lateral confinement, pinning, or an external applied field, such a nanobubble is unstable, and should collapse. Here, we show that we can freeze dynamic droplets into static nanobubbles by decreasing the magnetic field. While the bubble has virtually the same resistance as the droplet, all signs of low-frequency microwave noise disappear. The transition is fully reversible and the bubble can be thawed back into a droplet if the magnetic field is increased under current. Whereas the droplet collapses without a sustaining current, the bubble is highly stable and remains intact for days without external drive. Electrical measurements are complemented by direct observation using scanning transmission x-ray microscopy, which corroborates the analysis and confirms that the bubble is stabilized by pinning.
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| 18. |
- Al-Salihi, Hayder, et al.
(author)
-
A Successive Optimization Approach to Pilot Design for Multi-Cell Massive MIMO Systems
- 2018
-
In: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 22:5, s. 1086-1089
-
Journal article (peer-reviewed)abstract
- In this letter, we introduce a novel pilot designapproach that minimizes the total mean square errors of theminimum mean square error estimators of all base stations (BSs)subject to the transmit power constraints of individual users inthe network, while tackling the pilot contamination in multicellmassive MIMO systems. First, we decompose the originalnon-convex problem into distributed optimization sub-problemsat individual BSs, where each BS can optimize its own pilotsignals given the knowledge of pilot signals from the remainingBSs. We then introduce a successive optimization approach totransform each optimization sub-problem into a linear matrixinequality form, which is convex and can be solved by availableoptimization packages. Simulation results confirm the fast convergenceof the proposed approach and prevails a benchmarkscheme in terms of providing higher accuracy.
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| 19. |
- Alavijeh, Nima Mirzaei, et al.
(author)
-
A toolbox for comparing congestion management solutions for distribution networks
- 2023
-
In: 2023 IEEE Belgrade PowerTech.
-
Conference paper (peer-reviewed)abstract
- To address the emerging challenges in electricity distribution networks, various solutions have been proposed such as alternative tariff design, local flexibility markets (LFMs), bilateral contracts, and local energy markets (LEMs). However, choosing a suitable solution is not straightforward due to multi-dimensional complexity of the challenges which may vary under different circumstances. This paper proposes a toolbox for qualitative and quantitative comparison of the different solutions. The toolbox includes a multi-dimensional analytical framework and a flexible modeling and demonstration platform for conducting quantitative comparison studies. Four solutions i.e. LFM, LEM, cost-reflective tariffs, and bilateral contracts are compared qualitatively using the framework and a real demonstration example of an LFM design is presented utilizing the modeling platform. The toolbox can facilitate research on the local grid challenges and contribute to finding a suitable solution from a multi-dimensional perspective.
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| 20. |
- Alghamdi, Baheej, et al.
(author)
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A Comparative Study on SVC and STATCOM in Dynamic Voltage Stability Improvement of a System with Different Load Characteristics
- 2017
-
In: 2017 SAUDI ARABIA SMART GRID CONFERENCE (SASG). - 9781538618769
-
Conference paper (peer-reviewed)abstract
- This paper presents a comparison between the dynamic performance of Static Var Compensators (SVC) and Static Synchronous Compensators (STATCOM) in improving the voltage stability of the system and reducing the post disturbance voltage recovery time. The dynamic simulation has been done on the Nordic-32 test system which mimics the characteristics of the Swedish transmission system. The simulation has been carried out using a time-domain simulation software called PSS/E. The simulation has been done while taking into account different load characteristics including induction motor loads which are prevalent in the Swedish power grid. A methodology for sizing and placement of the SVC and STATCOM has been proposed to mitigate the voltage instability of the system. It has been found that STATCOMs have shown superior performance over SVCs in improving the post-disturbance voltage recovery time and the voltage stability of the system. It has been found that the post disturbance voltage recovery time was reduced down by 60% for the case with STATCOM while for the case with SVC, the voltage recovery time was reduced down by 26% for the same capacitive rating as that of the STATCOM(1).
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| 21. |
- Alghamdi, Baheej, et al.
(author)
-
A comparative study on SVC and STATOCM in dynamic voltage stability improvement of a system with different load characteristics
- 2018
-
In: 2017 Saudi Arabia Smart Grid Conference, SASG 2017. ; , s. 1-5
-
Conference paper (peer-reviewed)abstract
- This paper presents a comparison between the dynamic performance of Static Var Compensators (SVC) and Static Synchronous Compensators (STATCOM) in improving the voltage stability of the system and reducing the post disturbance voltage recovery time. The dynamic simulation has been done on the Nordic-32 test system which mimics the characteristics of the Swedish transmission system. The simulation has been carried out using a time-domain simulation software called PSS/E. The simulation has been done while taking into account different load characteristics including induction motor loads which are prevalent in the Swedish power grid. A methodology for sizing and placement of the SVC and STATCOM has been proposed to mitigate the voltage instability of the system. It has been found that STATCOMs have shown superior performance over SVCs in improving the post-disturbance voltage recovery time and the voltage stability of the system. It has been found that the post-disturbance voltage recovery time was reduced down by 60% for the case with STATCOM while for the case with SVC, the voltage recovery time was reduced down by 26% for the same capacitive rating as that of the STATCOM1.
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| 22. |
- Alghamdi, Baheej, 1985, et al.
(author)
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Investigation of Impacts of Solar PV on Transmission System Voltage Stability Considering Load Characteristics and Protection
- 2017
-
In: 7th International Workshop on the Integration of Solar Power into Power Systems, 24-25 October 2017, Berlin, Germany.
-
Conference paper (peer-reviewed)abstract
- This paper presents an investigation on possible effects of large scale integration of solar photovoltaics (PVs) on the voltage stability of the transmission grid. The time-domain simulation approach has been used in a case study using the Nordic-32 test system which approximately represents the Swedish transmission system. The simulation study has been carried out in PSS/E for different penetration levels of solar PVs and solar irradiance conditions considering different load characteristics and detailed model of distance relays. The main question to be addressed by the study is how the location and size of the PV plants, load characteristics and the transmission system distance protection can adversely affect the post-disturbance voltage recovery time and thereby the overall voltage stability. It has been found that the post-disturbance voltage recovery time increased by 100% with 30% PV penetration. Another interesting finding is that in the case of high PV penetration, the PV plants can either support or adversely affect the voltage stability of the system, depending on changes in the irradiance and the load level during the day. That is that during periods when the PV plants produce their rated active power, the system was more prone to voltage instability after being subjected to a disturbance compared to the periods where the PV plants produce only reactive power which supports the voltage stability.
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| 23. |
- Alvarez Quispe, Erik Fransisco, et al.
(author)
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Values and Impacts of Incorporating Local Flexibility Services in Transmission Expansion Planning
- 2022
-
In: Electric Power Systems Research. - : Elsevier BV. - 0378-7796. ; 212
-
Journal article (peer-reviewed)abstract
- This paper presents a cost-based TSO-DSO coordination model to quantify the value of local flexibility services and analyze its impact on the transmission grid expansion and the system operation. Flexibility is provided to the DC power flow transmission grid model by microgrids within the integrated AC power flow distribution grid model. The model's objective is to minimize the overall cost of transmission investments and procured flexibility and is achieved using a bilevel optimization approach where the power exchanges on all connected grid interfaces are controlled. Case studies using a combined test system of the IEEE RTS-96 transmission network interfacing multiple 33-bus distribution grids were performed to validate the model and assess the values and impacts of local flexibility on the transmission system expansion. The results showed that the proposed model modified the investment plan and dispatch of flexibility resources reducing the investment and operation cost of the transmission system.
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| 24. |
- Antoniadou-Plytaria, Kyriaki, 1989, et al.
(author)
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Chalmers Campus as a Testbed for Intelligent Grids and Local Energy Systems
- 2019
-
In: IEEE International Conference on Smart Energy Systems and Technologies (SEST). - 9781728111568
-
Conference paper (peer-reviewed)abstract
- This paper presents an overview of a testbed for intelligent distribution grids, local energy systems, and energy flexible buildings, which is being developed at the campus of Chalmers University of Technology in Gothenburg, Sweden. It describes the test sites, the functionalities, and the planned demonstration activities within the scope of on-going research projects. The proposed demonstrations include a local energy market platform, energy management solutions for microgrids and smart buildings, as well as voltage control in distribution grids. The paper aims to show how the physical energy supply systems of the university are being adapted to integrate the communication and control set-ups that provide the technical requirements for smart grid interoperability. As an example, the on-site implementation of remote battery control is presented, where initial results show the feasibility and potential benefits of the external control. Finally, challenges and lessons learned during the development of the testbed are highlighted.
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| 25. |
- Antoniadou-Plytaria, Kyriaki, 1989, et al.
(author)
-
Effect of Short-term and High-resolution Load Forecasting Errors on Microgrid Operation Costs
- 2022
-
In: IEEE PES Innovative Smart Grid Technologies Conference Europe. - 9781665480321 ; 2022-October
-
Conference paper (peer-reviewed)abstract
- The aim of this paper is to evaluate the effect of the load forecasting errors to the operation costs of a grid-connected microgrid. To this end, a microgrid energy scheduling optimization model was tested with deterministic and stochastic formulations under two solution approaches i.e., day-ahead and rolling horizon optimization. In total, twelve simulation test cases were designed receiving as input the forecasts provided by one of the three implemented machine learning models: linear regression, artificial neural network with backpropagation, and long short-term memory. Simulation results of the weekly operation of a real residential building (HSB Living Lab) showed no significant differences among the costs of the test cases for a daily mean absolute percentage forecast error of about 12%. These results suggest that operators of similar microgrid systems could use simplifying approaches, such as day-ahead deterministic optimization, and forecasts of similar, non-negligible accuracy without substantially affecting the microgrid's total cost as compared to the ideal case of perfect forecast. Improving the accuracy would mainly reduce the microgrid's peak power cost as shown by its 20.2% increase in comparison to the ideal case.
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| 26. |
- Antoniadou-Plytaria, Kyriaki, 1989, et al.
(author)
-
Energy Scheduling Strategies for Grid-connected Microgrids: A Case Study on Chalmers Campus
- 2019
-
In: Proceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe, ISGT-Europe 2019.
-
Conference paper (peer-reviewed)abstract
- This paper focuses on the optimal energy management of grid-connected microgrids with battery energy storage systems. The microgrid energy management and the optimal power flow of the distribution network are formulated as mixed-integer linear optimization problems to evaluate microgrid energy scheduling strategies including cost minimization, maximum use of own resources, and minimum energy exchange with the upstream network. The real distribution network of Chalmers University of Technology campus is used as a case study. The study results show that economic optimization yields an annual microgrid cost reduction of 4%. Alternatively, if the microgrid minimizes the energy exchange, virtual islanding operation (zero energy exchange) for 3211 hours can be achieved within a year. The results also present the effects on the operation and cost of the distribution system and highlight a trade-off between microgrid cost minimization and battery lifetime.
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| 27. |
- Antoniadou-Plytaria, Kyriaki, 1989, et al.
(author)
-
Market-based Energy Management Model of a Building Microgrid Considering Battery Degradation
- 2021
-
In: IEEE Transactions on Smart Grid. - 1949-3053 .- 1949-3061. ; 12:2, s. 1794-1804
-
Journal article (peer-reviewed)abstract
- This paper presents a model for energy management system of a building microgrid coupled with a battery energy storage. The model can be used to dispatch the battery as a flexible energy resource using a market-based setting. The battery is modeled considering battery degradation and real-life operation characteristics derived from measurements at a residential building. The performance of the model was evaluated first with simulations and integrated afterwards to an energy management system, which was demonstrated at a real residential building (HSB Living Lab) equipped with photovoltaic and battery storage systems. The simulation results showed that the building owner, and subsequently the residents, could benefit from the proposed model in reduced annual cost up to 3.1% under the considered pricing scheme. The demonstration results showed that dispatch under the measurement-based model could decrease the undelivered energy over the daily requested amount from the battery from 13.3% to 3.7%. Thus, the proposed model, which couples the measurement-based dispatch with battery degradation, can lead to a more accurate estimation of the building operation cost and an improved overall performance of battery as a flexible resource in building microgrids.
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| 28. |
- Antoniadou-Plytaria, Kyriaki, 1989, et al.
(author)
-
Scenario-based Stochastic Optimization for Energy and Flexibility Dispatch of a Microgrid
- 2022
-
In: IEEE Transactions on Smart Grid. - 1949-3053 .- 1949-3061. ; 13:5, s. 3328-3341
-
Journal article (peer-reviewed)abstract
- Energy storage is one of the most important components of microgrids with non-dispatchable generators and can offer both energy and flexibility services when the microgrid operates in grid-connected mode. This paper proposes a scenario-based stochastic optimization model that can be used to determine the energy and flexibility dispatch of a residential microgrid with solar and stationary battery systems. The objective of the model is to minimize the expected energy and peak power cost as well as the battery aging cost, while maximizing the expected revenue from flexibility. The formulated stochastic optimization problem is solved in rolling horizon with the uncertainty model being dynamically updated to consider the most recent forecast profiles for solar power and electricity demand. The benefits of the proposed approach were demonstrated by simulating the daily operation of a real building. The results showed that the estimated flexibility was successfully dispatched yielding an economic value of at least 7% of the operation cost of the building microgrid. The model can be used by flexibility providers to assess their flexibility and design a bidding strategy as well as by system operators to design incentives for flexibility providers.
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| 29. |
- Antonis, Papaemmanouil, et al.
(author)
-
A cost-benefit analysis of transmission network reinforcement driven by generation capacity expansion
- 2010
-
In: IEEE Power & Energy Society (PES) General Meeting 2010, Minneapolis, USA, July 25 - 29, 2010. - 9781424483570
-
Conference paper (peer-reviewed)abstract
- This paper assesses the effects of the future European power generation system with strict CO2 emission reduction targets on the planning of cross-border interconnection lines. Results from a techno-economic energy systems model have been used as input to this work, regarding the development of the European power generation system until the year 2050, meeting the EU 2020 CO2 target and a 85% emissions reduction until the year 2050. A simplified UCTE power system model was developed in order to analyze how the cross-border interconnections in continental Europe are affected by the generation plans using an iterative method. The paper also attempts to identify the congestion points and proposes solutions based on nodal price modeling. A cost-benefit analysis (CBA) is used to evaluate the appropriate transmission planning strategy, with the costs being the long-term investment costs and the benefits being both the avoided environmental costs and the total congestion costs. The effects of new investments on the nodal prices are also studied. The results show that the profitability of the investments is influenced by the available production mix and the forecasted CO2 prices. The avoided congestion costs participate rather insignificantly in the CBA, which means that congestions are not relieved, showing that many interconnections are insufficient for nodal pricing market structure.
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| 30. |
- Antonis, Papaemmanouil, et al.
(author)
-
Improved Cost-Benefit Analysis for Market-Based Transmission Planning, A European Perspective
- 2013
-
In: Energy Policy. - : Elsevier BV. - 0301-4215. ; 63, s. 215-223
-
Journal article (peer-reviewed)abstract
- This paper addresses the problem of transmission planning in interconnected power systems under the uncertainty of future generation parks and fast varying marginal production costs. The decision maker has to consider many different aspects during the denition of dierent transmission planning strategies, that sometimes might even be contradicting. Major contributions are the incorporation of energy policy measurements in the evaluation process of candidate transmission plans and the inclusion of short and long-term uncertainties. The proposed methodology, so called C-TRAP, is based on a semi-dynamic heuristic approach, that solves the social welfare maximization problem for several discrete steps considering different preferences for energy policy and transmission network reinforcements. The flexibility provided through the heuristic analysis is very important for decision makers in the new uncertain environment in power systems.
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| 31. |
- Antonis, Papaemmanouil, et al.
(author)
-
Improved cost-benefit analysis for reliable long-term transmission planning
- 2011
-
In: 2011 IEEE PES Trondheim PowerTech: The Power of Technology for a Sustainable Society, POWERTECH 2011; Trondheim; 19 June 2011 through 23 June 2011. - 9781424484195
-
Conference paper (peer-reviewed)abstract
- The aim of this paper is to incorporate reliabilityaspects in the transmission planning process presentedin previous work. The decision maker has to consider manydifferent aspects during the definition of transmission planning strategy, that sometimes might be contradicting. In the whole planning framework the decision is made by combining economic, environmental, and security of supply criteria in a single pseudodynamic algorithm. However, here only the part of security of supply is analyzed. After a sensitivity analysis for identification of critical/important transmission lines, a contingency analysis is performed and the probability of expected unserved energy is calculated together with the costs of expected unserved energy as an indicator. It is also shown that the amount of expected unserved energy is decreasing when additional transmission capacity is added to the connected lines of an unbalanced node. However, this may not be enough to reach zero unserved energy due to limitations of other transmission lines. After all,transmission network reinforcements can be evaluated based on benefits in avoided environmental costs, avoided congestion costs and avoided unserved energy costs in order to provide sufficient information to the decision maker.
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| 32. |
- Arafat, Yasir, 1985, et al.
(author)
-
Customer-Utility Interface for 2030 - Identification of functionalities and applications
- 2015
-
Reports (other academic/artistic)abstract
- Smart metering is considered to become a central part in distribution grid management in the future and will be able to provide a lot of new functions if they have the right specifications. Many DSOs are in the process of preparing for the next generation of Smart Meters (SMs) – which is referred to as the future customer-utility interface (CUI) and thereby needs to know the required specifications. This report is proposed to assist in this process by providing suggestions of research to establish minimum technical CUI specifications with regards to the different possible functionalities of CUI. To investigate the requirement of new functionalities, the report addresses how both the distribution system operator (DSOs) and customers could benefit from the new functionalities and what challenges the functionalities can meet. The project focused specifications for increasing the efficiency of grid management. Moreover, the report discuss functionalities required to enable customers’ participation in Demand Response (DR). The report is based on a literature review on functionalities requirement for the future CUI which satisfy the general requirement by the European Commission (EC) and Swedish Energy Market Inspectorate (EI) and at the same time will enhance the operation and planning practices of the DSOs, and promote more active customers. Based on how the grid may look like in 2030 in terms of electric power generations, loads and equipment of the grid and the expected changes in electricity demand but also other demands from the rest of the society is research issues selected and discussed. In the end the challenges are ranked and the risk of congesting due to higher covariant between loads and due to customer’s participation in different types of markets may be the most challenging is considered the most challenges in the nearby future for the distribution grid. There is therefore an urgent need to developing methods for more load forecasting and market modelling to understand where in the grid problem will appear before they actually happen. There are different methods on how to meet the congestions but more load modelling is needed to explore the potential of changes between different operation strategies. Finally there is also a need to develop a method to be able to compare the different method to find the most cost efficient way to solve each problem.
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| 33. |
- Axelson, D.G., et al.
(author)
-
Dynamic axis scale with high accuracy for high speed measurement of vehicle mass
- 2010
-
In: IMEKO 2010. ; , s. 61-64
-
Conference paper (peer-reviewed)abstract
- As the demand for measuring objects in motion is increasing the need for a system to measure vehicles has been developed to measure mass of vehicle in dynamic motion. Using the concept of measuring the inertial mass of a moving vehicle instead of gravitational mass has proven successful for a purely dynamic problem. Since the measurement of a dynamic motion requires high speed sampling a scanning speed of the signal information is set at 1μs/sample. This is to ensure the movement of the structure is captured to full extent. Using dynamics, the inertial mass correlation between the Dynamic Axis Scale and the vehicle can be calculated from the dynamic state of the vehicle in motion. The achieved result is instantaneous and currently reliable from 0 km/h up to 80 km/h with an high accuracy with ± 5% of error tolerance of the measured mass provided the vehicle mass is restricted to EU regulation for public roads of 20 ton. Measuring the momentum of the vehicle and calculating the speed to the relation of mass, it can verify the dynamic calculation and thus confirm the inertial mass of the vehicle.
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| 34. |
- Babaei, Saman, et al.
(author)
-
Effects of PHEVs in power distribution systems: reviews and analyses
- 2010
-
In: CIRED Workshop on Sustainable Distribution Asset Management and Financing, 7-8 June 2010, Lyon, France.
-
Conference paper (peer-reviewed)abstract
- This paper deals with the analysis of the impacts of plug-in hybrid electric vehicles (PHEVs) on the power system, with focus on the low voltage power distribution system. First a review of the technical challenges in the power system due to the mass introduction of PHEVs in the transportation sector is given. Then the paper shows on an analysis of the overloading effects of PHEVs on the distribution system with normal charging and quick charging of PHEVs for an IEEE 13-node distribution test system using power flow analysis. The results of the study show that introduction of PHEVs in the transportation sector will lead to overloading of distribution system and cause voltage problems at the end-users. The paper also analyzes the effects of PHEVs in the transmission system, using the Nordic 32-bus test system. The study results showed that the overloading problem is not prominent. However, one interesting and important result is that PHEVs may lead to overvoltages in some buses in the transmission system which requires the voltage control measures. PHEVs would also lead to increased number of network violations in the contingency analysis.
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| 35. |
- Babaei, Saman, et al.
(author)
-
Effects of Plug-in Electric Vehicles on Distribution Systems: The Real Case of Gothenburg
- 2010
-
In: IEEE PES Conference on Innovative Smart Grid Technologies Europe, Gothenburg, Sweden, October 10-13, 2010. - 9781424485109
-
Conference paper (peer-reviewed)abstract
- The electric power system is changing and, especially, the electrical distribution system will meet new features. One of the large changes is a transformation of the transportation sector with the use of electricity, with introduction of electrical vehicles and Plug-in Electric Vehicles (PEVs). This will pose new challenges and opportunities for the electric distribution companies. This paper analyzes the effects of PEVs charging on the local 400 V and 10 kV electric distribution systems in the city of Gothenburg, Sweden, using steady-state power flow analysis. Two different areas representing residential area and commercial area have been simulated for the worst-case scenario, which is simultaneous charging of all the vehicles during the peak load period. The number of PEVs used has been estimated based on the load level at each customer location. The study results have shown that overloading of lines would occur when simultaneous charging of the vehicles during the peak load period. There would, however, be no problem with the voltage drop at the customer’s location during PEVs charging. An iterative method is proposed to estimate the maximum number of possible vehicles charging in the distribution system without resulting in any line overloaded. This method is also applied when one of the feeders is on outage to ensure the N-1 reliability criterion.
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| 36. |
- Bachiller, Raul, et al.
(author)
-
Optimal Market Settlements Incorporating Voltage Stability
- 2008
-
In: 2008 IEEE International Conference on Sustainable Energy Technologies, ICSET 2008; Singapore; Singapore; 24 November 2008 through 27 November 2008. - 9781424418886 ; , s. 1145-1150
-
Conference paper (peer-reviewed)abstract
- This study aims at investigating the changes in power market transaction levels when taking into account the voltage stability consideration in the market settlement scheme. The study is based on a security constrained optimal power flow (SC-OPF) framework for a combined bilateral-and-pool electricity market. An IEEE 30-bus test system is used in the study. It is found that the voltage security constraints could help independent market operators to include a sufficient margin for allowable power transactions to ensure the system security while maximizing the social welfare. In that case, the power systems will be operating with a larger security margin. It is, however, important to note that the social welfare is compromised with the increased security margin.
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| 37. |
- Balram, Pavan, 1986, et al.
(author)
-
Centralized charging control of plug-in electric vehicles and effects on day-ahead electricity market price
- 2015
-
In: Plug In Electric Vehicles in Smart Grids. - Singapore : Springer. - 9789812873163 - 9789812873170 ; 88, s. 267-299
-
Book chapter (peer-reviewed)abstract
- Global policy targets to reduce greenhouse gas emissions have led to increased interest in plug-in electric vehicles (PEV) and their integration into the electricity network. Existing electricity markets, however, are not well suited to encourage direct participation of flexible demand from small consumers such as PEV owners. The introduction of an aggregator agent with the functions of gathering, aggregating, controlling and representing the energy needs of PEV owners in the electricity market could prove useful in this regard. In this chapter, a mathematical model of PEV aggregator for participation in the day-ahead electricity market is described. The modeling is done by treating each of the individual vehicle batteries as a single large battery. The centralized charging and discharging of this battery is then scheduled based on the traveling needs of the PEV owners determined by an aggregated driving profile and the cumulative electrical energy needs of vehicles over the optimization horizon. Two methods for scheduling PEV demand named as joint scheduling method (JSM) and aggregator scheduling method (ASM) are presented. The two methods are subsequently used to observe the effects of introducing flexible scheduling of PEVs on the day-ahead market price in an IEEE test system and a Nordic test system. Results from the IEEE test system case studies will indicate that the scheduling of PEV energy through direct centralized control at high PEV penetration levels of 50 % or greater could lead to potential lowering of day-ahead market prices as compared to an indirect control method such as the use of fixed period charging. Results from the Nordic test system case study shows that controlled scheduling of PEV demand could lead to only a small increase in day-ahead market price of electricity.
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| 38. |
- Balram, Pavan, 1986, et al.
(author)
-
Comparative study of MPC based coordinated voltage control in LV distribution systems with photovoltaics and battery storage
- 2018
-
In: International Journal of Electrical Power and Energy Systems. - : Elsevier BV. - 0142-0615. ; 95, s. 227-238
-
Journal article (peer-reviewed)abstract
- This paper compares traditional local voltage control strategy with coordinated, optimization-based ones in LV distribution systems with photovoltaics and battery energy storage systems. Optimization-based strategies are formulated within a model predictive control (MPC) framework. Three strategies based on MPC are proposed and implemented, namely, centralized, decentralized and distributed MPC. The formulated strategies for voltage control are compared in a case study using a modified CIGRE European 3-area low-voltage network. Results indicate that decentralized MPC gives a better voltage profile in the network when compared to local voltage control strategy, since the latter inherently fails to maintain voltages of buses in the network not connected to photovoltaics or battery storage system within limits. Centralized MPC strategy is able to provide the optimal voltage profile across the network but utilizes 13% higher reactive power from the control devices to achieve this when compared to decentralized MPC. The latter performs well as long as the reactive power reserves within an area is sufficient but faces drawbacks similar to that of local voltage control strategy when the reactive reserves are completely exhausted. Distributed MPC utilizes 1:3% higher amount of reactive power reserves compared to centralized MPC in order to provide a network voltage profile similar to that of the latter while also yielding architectural advantages of decentralized MPC.
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| 39. |
- Balram, Pavan, 1986, et al.
(author)
-
Demonstration of Voltage Control in a Real Distribution System using Model Predictive Control
- 2017
-
In: IET Generation, Transmission and Distribution. - : Institution of Engineering and Technology (IET). - 1751-8687 .- 1751-8695. ; 11:16, s. 3922-3929
-
Journal article (peer-reviewed)abstract
- This paper presents the results from field tests that were carried out with the aim of verifying the performance of a model predictive control-based voltage controller. A voltage source converter capable of producing or consuming 4 MVAr was used as the reactive power source, which was able to influence the voltage magnitude at a remote bus within a real distribution system in Gothenburg, Sweden. The voltage controller is designed to maintain the remote bus voltage within a pre-defined range while respecting the reactive power output capability of the voltage source converter and an objective of minimum changes to the reference value of its local reactive power controller. Results from the field tests demonstrate that the voltage controller was able to successfully regulate the voltage even with significant errors in the state-space prediction model. An important lesson learned from the field test is that a smoothened voltage measurement feedback is critical to a satisfactory functioning of the controller. Furthermore, it is recommended to design the voltage controller to observe an initial delay, before it is activated for bus voltage control- this would deter it from unnecessarily reacting at the very instant it is brought online.
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| 40. |
- Balram, Pavan, 1986, et al.
(author)
-
Effects of Plug-in Electric Vehicle Charge Scheduling on the Day-ahead Electricity Market Price
- 2012
-
In: IEEE PES Innovative Smart Grid Technologies 2012. - 2165-4816. - 9781467325950 ; , s. 8-
-
Conference paper (peer-reviewed)abstract
- With the advent of plug-in electric vehicles (EV), it becomes increasingly important to study the impact of charge scheduling of a large number of EVs on the day-ahead electricity market price. In this paper, two scheduling models are proposed- joint scheduling model and aggregator scheduling model. They are used to study the effects of scheduling of EV charging on the day-ahead market price of electricity at various penetration levels of the EVs. Results from studies on an IEEE 30-bus test system show that, at lower penetration of EVs, a simple scheduling method using fixed-period charging during low demand periods can be used, without a large increase in market price. But at higher penetration levels, the opposite holds true, requiring advanced scheduling methods such as proposed in this paper. Between the two, joint scheduling model results in a lower increase in electricity price and is further tested on a simplified Nordic day-ahead market model. An overall conclusion is that the Nordic day-ahead market can accommodate large penetration of EVs without a significant increase in market price.
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| 41. |
- Balram, Pavan, 1986, et al.
(author)
-
Modeling of Regulating Power Market Based on AC Optimal Power Flow Considering Losses and Electric Vehicles
- 2013
-
In: IEEE Conference on Innovative Smart Grid Technologies - Asia (ISGT Asia). - 9781479913466 ; , s. 6-
-
Conference paper (peer-reviewed)abstract
- This paper proposes a model for the regulating power market incorporating electric vehicles (EV) participation that considers the locational aspects of the market participants in the regulating power activation process. The contributions of the regulating power to the system total power loss and network congestion are accounted for. In the proposed market model, the submitted marginal regulation prices are appropriately re-valued to reflect their location in the power system. The price revaluation is based on an ac optimal power flow (OPF) framework where the actual power flows and power loss can be evaluated. The participation of EVs in providing regulating power in the market is additionally modeled. A case study is carried out based on the proposed market model using the Nordic 32-bus test system. Results from the proposed market model indicate that regulating power from EVs could benefit the system by reducing the total cost of balancing. Furthermore, the inclusion of locational aspects may aid in the selection of regulating power from EVs that most likely would be electrically close to the existing load buses.
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| 42. |
- Balram, Pavan, 1986, et al.
(author)
-
Power system islanding operation support by wind power plants
- 2011
-
In: 4th EPE Joint Wind Energy and T and D Chapters Seminar 2011; Trondheim; Norway; 9 May 2011 through 11 May 2011. - 9781612841670
-
Conference paper (peer-reviewed)abstract
- Power system islanding operation support by wind power plants during an underfrequency, undervoltage event is studied. Influence of inertia control and active power control is analyzed in the presence and absence of voltage control by WPP. Effects of variation in wind speed on the frequency and voltage support is observed.
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| 43. |
- Balram, Pavan, 1986, et al.
(author)
-
Predictive voltage control of batteries and tap changers in distribution system with photovoltaics
- 2016
-
In: Power Systems Computation Conference (PSCC). - 9788894105124
-
Conference paper (peer-reviewed)abstract
- This paper proposes a model predictive control approach for coordinated secondary voltage control of on-load tap changing transformers and battery energy storage systems in a distribution system to maintain the bus voltage levels in the presence of photovoltaic generation. Optimal control actions are obtained based on a quadratic objective function with linear constraints. The control actions are implemented in a case study using a modified CIGRÉ European low voltage distribution network with corresponding models of the constituent devices and their local controllers. The results indicate that battery energy storage system could aid the system voltages and reduce the number of transformer tap operations if the control is performed in a coordinated manner enabled by the model predictive control framework.
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| 44. |
- Balram, Pavan, 1986, et al.
(author)
-
Stochastic Model of Electricity Retailer Incorporating Aggregated Electric Vehicle Charging Uncertainty
- 2013
-
Reports (other academic/artistic)abstract
- This paper is a short version of a conference paper published at International Conference on European Energy Market (EEM), 28-31 May 2013, Stockholm, Sweden. It propose a model of an electricity retailer considering a future scenario where controlled charging of an aggregate of electric vehicles (EV) becomes a viable option. The retailer plans for purchase of electricity from the spot market while hedging its risks in the financial market, specifically the forward market. In a planning environment where the retailer has to make decisions for purchase of forward contracts ahead of spot market clearing, it faces uncertainties from spot market prices and customer demand. A stochastic programming approach with a financial risk measure is used to take into consideration the uncertainties described. A case study using the model is performed, the results of which indicate that EV customers and the retailer would benefit monetarily with increasing penetration of electric vehicles. The studies consecutively show that this is also the case when increasing fraction of customers opting for variable price contracts.
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| 45. |
- Balram, Pavan, 1986, et al.
(author)
-
Stochastic Programming Based Model of An Electricity Retailer Considering Uncertainty Associated with Electric Vehicles Charging
- 2013
-
In: International Conference on the European Energy Market, EEM. - 2165-4077 .- 2165-4093. - 9781479920082 ; , s. 8-
-
Conference paper (peer-reviewed)abstract
- In this paper, a mathematical model is proposed for optimization of the portfolio of an electricity retailer in the forward and spot markets considering flexibility offered by electric vehicles (EV). The model provides a guideline to the elec- tricity retailer for aggregated scheduling of EV battery charging, contracting of power in the forward market and setting of retail prices for customers under fixed and variable price electricity retail contracts. The objective of the model is to maximize the retailer’s expected profit. A stochastic programming approach is used to account for the uncertainties associated with spot price, customers’ demand and EV demand. The model is applied to a case study using data from the Nordic electricity markets, future scenarios for EVs in Sweden and an electricity retailer in Sweden. Results indicate that cost savings from flexibility of EV demand would increase with increasing EV penetration level and the number of customers with variable price contracts as opposed to fixed price contracts. It is also found that the retailer’s expected profits would increase with a greater share of variable price contracts.
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| 46. |
- Banda, Ernest, 1969, et al.
(author)
-
Modeling of Demand Response in Electricity Markets: Effects of Price Elasticity
- 2007
-
In: IASTED International Conference on Power and Energy Systems (PES 2007), January 3-5, 2007, Florida, USA.
-
Conference paper (peer-reviewed)abstract
- This paper deals with design of a mechanism of optimal participation of customer load in the energy market demand response programs. The proposed mechanism is based on an optimal power flow framework and can aid the Independent System Operator (ISO) in real-time selection of demand response offers. The structure of the market is also proposed for implementation. Various issues associated with procurement of demand-response offerings such as advance notification, locational aspect of load, power factor of the loads, are explicitly considered. It is shown that demand response can help the ISO maintain operating reserves during peak load periods and can mitigate the price volatility. The paper also investigates the effects of price elasticity of demand on the net benefit of the demand-response program. The potential benefits of the demand response program would be reduced when price elasticity of demand is taken into account, which is most likely to occur in actual developed open electricity markets, such as Nordpool of the Nordic countries. The intention of this paper to further understanding and recognition of the importance of the effects of elasticity of demand when attempting to create demand response models in general. The CIGRE 32-bus system, which represents the Swedish high voltage power system, appropriately modified to include various customer characteristics, is used for the study.
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| 47. |
- Bengtsson, Linus, et al.
(author)
-
Implementation of Web-Based Respondent-Driven Sampling among Men Who Have Sex with Men in Vietnam
- 2012
-
In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:11, s. e49417-
-
Journal article (peer-reviewed)abstract
- Objective: Lack of representative data about hidden groups, like men who have sex with men (MSM), hinders an evidence-based response to the HIV epidemics. Respondent-driven sampling (RDS) was developed to overcome sampling challenges in studies of populations like MSM for which sampling frames are absent. Internet-based RDS (webRDS) can potentially circumvent limitations of the original RDS method. We aimed to implement and evaluate webRDS among a hidden population. Methods and Design: criteria were men, aged 18 and above, who had ever had sex with another man and were living in Vietnam. Participants were invited by an MSM friend, logged in, and answered a survey. Participants could recruit up to four MSM friends. We evaluated the system by its success in generating sustained recruitment and the degree to which the sample compositions stabilized with increasing sample size. Results: Twenty starting participants generated 676 participants over 24 recruitment waves. Analyses did not show evidence of bias due to ineligible participation. Estimated mean age was 22 years and 82% came from the two large metropolitan areas. 32 out of 63 provinces were represented. The median number of sexual partners during the last six months was two. The sample composition stabilized well for 16 out of 17 variables. Conclusion: Results indicate that webRDS could be implemented at a low cost among Internet-using MSM in Vietnam. WebRDS may be a promising method for sampling of Internet-using MSM and other hidden groups.
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| 48. |
- Bertling, Lina, 1973, et al.
(author)
-
On the use of reliability test systems: A literature survey
- 2011
-
In: 2011 IEEE Power & Energy Society General Meeting, 24 – 28 July 2011, Detroit, Michigan, USA.. - 1944-9933. - 9781457710001
-
Conference paper (peer-reviewed)abstract
- Over the years the reliability test systems such as the IEEE Reliability Test System (RTS) and Roy Billinton Test System (RBTS) have been used extensively by researchers, as a bench mark system, for reliability assessment and other developments in the field of probabilistic applications in power systems. This paper presents an extensive literature survey of previous publications in which the RTS and RBTS or other test systems have been used. From the survey, several observations can be made, such as on the purpose of the use of the test systems, or where the studies were made. With the development of the electric power system, both in size and technology, this survey serves as a basis for assessing the appropriateness of the existing IEEE RTS system to address these developments. Such developments would mainly include wind energy, increased use of HVDC transmission and the state-of-the-art communication systems applied to power systems. The survey shows that it is necessary to extend the existing test systems to better address the demands of future electric power system.
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| 49. |
|
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| 50. |
- Bouloumpasis, Ioannis, 1987, et al.
(author)
-
Congestion Management using Local Flexibility Markets: Recent Development and Challenges
- 2019
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In: Proceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe, ISGT-Europe 2019. ; 2019
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Conference paper (peer-reviewed)abstract
- Increasing amount of renewable based distributed generation at distribution systems, leads to an increased need for active distribution network management dealing with local network congestion and voltage issues. Development of local flexibility markets aims to provide a market-based solution to these issues. This paper presents a comprehensive review of proposed approaches towards markets exploiting the flexibilities from the demand-side. Efforts have been made on presenting a systematic overview of market design, including e.g. framework, participation, bidding and clearing mechanisms, of local flexibility market proposals developed in recent years. The implementation and regulatory issues and challenges are also discussed. The paper also presents the conceptual framework of the local flexibility service market which is currently being developed within UNITED-GRID project. This proposal aims to provide a holistic approach on local service markets, so that Distribution System Operators (DSOs) are provided with a market-based instrument to manage their networks efficiently.
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