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Michal Regula - One of the best experts on this subject based on the ideXlab platform.
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the influence of power quality indices on active power losses in a Local Distribution grid
Energies, 2019Co-Authors: Alena Otcenasova, Andrej Bolf, Juraj Altus, Michal RegulaAbstract:This paper deals with the topic of power quality in a Local Distribution grid. It is aimed to analyze the individual influences, which aggravate the power quality of the Distribution grid. Based on the analysis, the most adverse effects were determined, and they were the voltage drops and supply voltage interruptions, supply voltage unbalance, load power factor, and also higher harmonics. These influences cause the technical losses in a Distribution grid, which subsequently have a financial impact not only on the Distribution, but also on the transmission of electricity. Only the load voltage unbalance, the load power factor, and the higher harmonics, which mainly cause the technical losses, were analyzed in this paper. The measurement of the influences of the adverse effects was performed on the model of a 22-kV Distribution grid. The measurement was performed on the basis of three types of power line conductors and their different lengths, three types of active power consumption, and the different values of these adverse effects. According to this measurement, a simulation in program Matlab-Simulink was created. This simulation represented part of a 22-kV Distribution grid, which was influenced by the abovementioned adverse effects. The results of the measurements were compared with the results of the simulation. Based on the evaluation of the technical losses from the measurement and the simulation, the financial losses during a certain period were calculated for the Distribution system operators.
Jan Vondrak - One of the best experts on this subject based on the ideXlab platform.
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Local Distribution and the symmetry gap approximability of multiway partitioning problems
Symposium on Discrete Algorithms, 2013Co-Authors: Alina Ene, Jan VondrakAbstract:We study the approximability of multiway partitioning problems, examples of which include Multiway Cut, Node-weighted Multiway Cut, and Hypergraph Multiway Cut. We investigate these problems from the point of view of two possible generalizations: as Min-CSPs, and as Submodular Multiway Partition problems. These two generalizations lead to two natural relaxations that we call respectively the Local Distribution LP, and the Lovasz relaxation. The Local Distribution LP is generally stronger than the Lovasz relaxation, but applicable only to Min-CSP with predicates of constant size. The relaxations coincide in some cases such as Multiway Cut where they are both equivalent to the CKR relaxation. We show that the Lovasz relaxation gives a (2--2/k)-approximation for Submodular Multiway Partition with k terminals, improving a recent 2-approximation [2]. We prove that this factor is optimal in two senses: (1) A (2--2/k -- e)-approximation for Submodular Multiway Partition with k terminals would require exponentially many value queries (in the oracle model), or imply NP = RP (for certain explicit submodular functions). (2) For Hypergraph Multiway Cut and Node-weighted Multiway Cut with k terminals, both special cases of Submodular Multiway Partition, we prove that a (2--2/k -- e)-approximation is NP-hard, assuming the Unique Games Conjecture. Both our hardness results are more general: (1) We show that the notion of symmetry gap, previously used for submodular maximization problems [19, 6], also implies hardness results for submodular minimization problems. (2) Assuming the Unique Games Conjecture, we show that the Local Distribution LP gives an optimal approximation for every Min-CSP that includes the Not-Equal predicate. Finally, we connect the two hardness techniques by proving that the integrality gap of the Local Distribution LP coincides with the symmetry gap of the multilinear relaxation (for a related instance). This shows that the appearance of the same hardness threshold for a Min-CSP and the related submodular minimization problem is not a coincidence.
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SODA - Local Distribution and the symmetry gap: approximability of multiway partitioning problems
2013Co-Authors: Alina Ene, Jan VondrakAbstract:We study the approximability of multiway partitioning problems, examples of which include Multiway Cut, Node-weighted Multiway Cut, and Hypergraph Multiway Cut. We investigate these problems from the point of view of two possible generalizations: as Min-CSPs, and as Submodular Multiway Partition problems. These two generalizations lead to two natural relaxations that we call respectively the Local Distribution LP, and the Lovasz relaxation. The Local Distribution LP is generally stronger than the Lovasz relaxation, but applicable only to Min-CSP with predicates of constant size. The relaxations coincide in some cases such as Multiway Cut where they are both equivalent to the CKR relaxation. We show that the Lovasz relaxation gives a (2--2/k)-approximation for Submodular Multiway Partition with k terminals, improving a recent 2-approximation [2]. We prove that this factor is optimal in two senses: (1) A (2--2/k -- e)-approximation for Submodular Multiway Partition with k terminals would require exponentially many value queries (in the oracle model), or imply NP = RP (for certain explicit submodular functions). (2) For Hypergraph Multiway Cut and Node-weighted Multiway Cut with k terminals, both special cases of Submodular Multiway Partition, we prove that a (2--2/k -- e)-approximation is NP-hard, assuming the Unique Games Conjecture. Both our hardness results are more general: (1) We show that the notion of symmetry gap, previously used for submodular maximization problems [19, 6], also implies hardness results for submodular minimization problems. (2) Assuming the Unique Games Conjecture, we show that the Local Distribution LP gives an optimal approximation for every Min-CSP that includes the Not-Equal predicate. Finally, we connect the two hardness techniques by proving that the integrality gap of the Local Distribution LP coincides with the symmetry gap of the multilinear relaxation (for a related instance). This shows that the appearance of the same hardness threshold for a Min-CSP and the related submodular minimization problem is not a coincidence.
Mihály Szalay - One of the best experts on this subject based on the ideXlab platform.
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Local Distribution of the parts of unequal partitions in arithmetic progressions II
Publicationes Mathematicae Debrecen, 2012Co-Authors: Cécile Dartyge, Mihály SzalayAbstract:International audienceThis is the continuation of the paper "Local Distribution of the parts of unequal partitions in arithmetic progressions I",Pub. Math. Debrecen (79) 3-4, (2011) 379-39
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Local Distribution of the parts of unequal partitions in arithmetic progressions II
Publicationes Mathematicae Debrecen, 2012Co-Authors: Cécile Dartyge, Mihály SzalayAbstract:This is the continuation of the paper "Local Distribution of the parts of unequal partitions in arithmetic progressions I", Pub. Math. Debrecen (79) 3-4, (2011) 379-393
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Local Distribution of the parts of unequal partitions in arithmetic progressions I
Publicationes Mathematicae Debrecen, 2011Co-Authors: Cécile Dartyge, Mihály SzalayAbstract:In [4], András Sárközy and the authors proved that for almost all unequal partitions of an integer n, the parts are evenly distributed in residue classes modulo d for d = o(n^(1/2)). In this paper, we study very precisely the Local Distribution in arithmetic progressions of the parts of unequal partitions. We obtain some asymptotic formulae for the number of unequal partitions of n with exactly N r parts congruent to r mod d, 1 6 r 6 d. Our results show that (N 1 ,. .. , N d) behaves like a random Gaussian vector. This illustrates the fact that the Distribution of the parts of unequal partitions in residue classes is much more uniform that in the case of unrestricted partitions.
Alena Otcenasova - One of the best experts on this subject based on the ideXlab platform.
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the influence of power quality indices on active power losses in a Local Distribution grid
Energies, 2019Co-Authors: Alena Otcenasova, Andrej Bolf, Juraj Altus, Michal RegulaAbstract:This paper deals with the topic of power quality in a Local Distribution grid. It is aimed to analyze the individual influences, which aggravate the power quality of the Distribution grid. Based on the analysis, the most adverse effects were determined, and they were the voltage drops and supply voltage interruptions, supply voltage unbalance, load power factor, and also higher harmonics. These influences cause the technical losses in a Distribution grid, which subsequently have a financial impact not only on the Distribution, but also on the transmission of electricity. Only the load voltage unbalance, the load power factor, and the higher harmonics, which mainly cause the technical losses, were analyzed in this paper. The measurement of the influences of the adverse effects was performed on the model of a 22-kV Distribution grid. The measurement was performed on the basis of three types of power line conductors and their different lengths, three types of active power consumption, and the different values of these adverse effects. According to this measurement, a simulation in program Matlab-Simulink was created. This simulation represented part of a 22-kV Distribution grid, which was influenced by the abovementioned adverse effects. The results of the measurements were compared with the results of the simulation. Based on the evaluation of the technical losses from the measurement and the simulation, the financial losses during a certain period were calculated for the Distribution system operators.
Zhifang Wang - One of the best experts on this subject based on the ideXlab platform.
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Optimized solar photovoltaic generation in a real Local Distribution network
2017 IEEE Power & Energy Society Innovative Smart Grid Technologies Conference (ISGT), 2017Co-Authors: Hamidreza Sadeghian, Mir Hadi Athari, Zhifang WangAbstract:Remarkable penetration of renewable energy in electric networks, despite its valuable opportunities, such as power loss reduction and loadability improvements, has raised concerns for system operators. Such huge penetration can lead to a violation of the grid requirements, such as voltage and current limits and reverse power flow. Optimal placement and sizing of Distributed Generation (DG) are one of the best ways to strengthen the efficiency of the power systems. This paper builds a simulation model for the Local Distribution network based on obtained load profiles, GIS information, solar insolation, feeder and voltage settings, and define the optimization problem of solar PVDG installation to determine the optimal siting and sizing for different penetration levels with different objective functions. The objective functions include voltage profile improvement and energy loss minimization and the considered constraints include the physical Distribution network constraints (AC power flow), the PV capacity constraint, and the voltage and reverse power flow constraints.
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ISGT - Optimized solar photovoltaic generation in a real Local Distribution network
2017 IEEE Power & Energy Society Innovative Smart Grid Technologies Conference (ISGT), 2017Co-Authors: Hamidreza Sadeghian, Mir Hadi Athari, Zhifang WangAbstract:Remarkable penetration of renewable energy in electric networks, despite its valuable opportunities, such as power loss reduction and loadability improvements, has raised concerns for system operators. Such huge penetration can lead to a violation of the grid requirements, such as voltage and current limits and reverse power flow. Optimal placement and sizing of Distributed Generation (DG) are one of the best ways to strengthen the efficiency of the power systems. This paper builds a simulation model for the Local Distribution network based on obtained load profiles, GIS information, solar insolation, feeder and voltage settings, and define the optimization problem of solar PVDG installation to determine the optimal siting and sizing for different penetration levels with different objective functions. The objective functions include voltage profile improvement and energy loss minimization and the considered constraints include the physical Distribution network constraints (AC power flow), the PV capacity constraint, and the voltage and reverse power flow constraints.