Search

Distribution networks feature distinct topologies than transmission networks, such as radial or weakly meshed structures with tens of thousands of nodes. They have more points of power injection owing to the integration of distributed generators and high R/X ratios. Furthermore, there has recently been a surge of interest in DC distribution networks. In the planning and operation of modern distribution systems, load flow needs to be executed in series considering short intervals of time in the order of minutes or even less. Hence, these networks require a load flow solver that can converge fast with low computational burden. In this paper, we propose a unique iterative power flow solver based on graph theory for DC distribution networks. The proposed formulation is flexible and can handle both radial and mesh configurations with just one connectivity matrix. To validate the proposed method, we used the IEEE 33 bus test feeder and compared the results with an existing methodology. Results suggest that the proposed method is robust and possesses fast convergence.

There is an increasing interest in low voltage direct current (LVDC) distribution grids due to advancements in power electronics enabling efficient and economical electrical networks in the DC paradigm. Power flow equations in LVDC grids are non-linear and non-convex due to the presence of constant power nodes. Depending on the implementation, power flow equations may lead to more than one solution and unrealistic solutions; therefore, the uniqueness of the solution should not be taken for granted. This paper proposes a new power flow solver based on a graph theory for LVDC grids having radial or meshed configurations. The solver provides a unique solution. Two test feeders composed of 33 nodes and 69 nodes are considered to validate the effectiveness of the proposed method. The proposed method is compared with a fixed-point methodology called direct load flow (DLF) having a mathematical formulation equivalent to a backward forward sweep (BFS) class of solvers in the case of radial distribution networks but that can handle meshed networks more easily thanks to the use of connectivity matrices. In addition, the convergence and uniqueness of the solution is demonstrated using a Banach fixed-point theorem. The performance of the proposed method is tested for different loading conditions. The results show that the proposed method is robust and has fast convergence characteristics even with high loading conditions. All simulations are carried out in MATLAB 2020b software.

This paper outlines a procedure for loss allocation in both radial and meshed distribution networks with distributed generation that could be regulated in various ways. The method is analytically developed based on the theory of electrical circuits combined with game theory based on Aumann–Shapley, which guarantees both the electrical principles and the fair axioms of game theory. The proposed method obtains unitary participation coefficients for each network user based on the currents demanded/injected by each user and the network topology. The proposed allocation method based on Aumann–Shapley has been compared with other traditional allocation methods, is adaptable to distribution networks, and shows great potential and ease of implementation. Moreover, it can be applied to any kind of distribution network (radial or meshed) with distributed energy resources. [ABSTRACT FROM AUTHOR]

Power systems are increasingly operated in a corrective rather than preventive security mode, which means that appropriate control actions must be taken immediately after a contingency has occurred. This paper proposes an online algorithm for automatically alleviating contingencies such as voltage limit violations and line overloads. Unlike previously proposed approaches, the network itself serves as a natural solver of the power flow equations. This makes it possible to start the implementation immediately and avoids problems caused by modeling errors. Every time the controller receives measurements from the grid, it evaluates the presence of contingencies and computes the optimal corrective actions that can be implemented before the next sampling period, subject to ramping constraints of the generators. These corrective actions are implemented through the standard automatic generation control. Finding the optimal incremental corrective actions is fast because this problem is linearized. The effectiveness of this algorithm at correcting both line overloads and voltage violations is demonstrated using the IEEE-118 Bus test system. [ABSTRACT FROM AUTHOR]

Transient-based earth fault protection is widely used in all types of resonant grounded networks, and though the operating principles of the commonly available relays are usually derived from radial networks, manufacturers claim applicability in meshed networks as well. This paper utilizes a laboratory setup to study the directional indication of four transient earth fault relays in non-radial resonant grounded networks. Two of the relays considered are widely used analog single-purpose transient earth fault relays, whereas the other two relays represent two transient-based earth fault functions found in modern protective devices. The paper verifies the location of crossover points according to the presented theory, i.e. fault locations for which relays transition between seeing faults as forward and reverse faults, and demonstrates the viability of the proposed theoretical analysis of crossover points. However, presented analytical formulae only describe the two analog relays accurately, whereas the two modern relays have a more complex operating principle which requires further analysis to quantify properly. Finally, it is shown that relay misoperation which is not easily fixed by communication between relays can occur, and it is suggested that network operators conduct detailed relay coordination when applying transient earth fault relays instead of relying on standardized settings. • Transient earth fault protection directionality in non-radial networks. • Comparison of relays based on first-half-wave-principle and on zero-sequence energy. • Verification of theoretical analysis using physical relays in laboratory. • Transient earth fault protection devices in the network should be coordinated. [ABSTRACT FROM AUTHOR]

A quadratic voltage (QV) model with modifications is proposed to formulate the meshed networks' optimal power flow (OPF) problem. In the QV model, convex relaxations are imposed without approximated terms. The modifications aim to drive the convex relaxations to be exact so that the obtained solution will be feasible to OPF. In the modifications, the set of nonlinear equality constraints with quadratic and bi-linear terms of voltages' variables are convexified with the convex–concave procedure (CCP). An iterative algorithm is imposed, of which the convergence and its applicability are proved with the mathematical analysis. The superiority of the QV model with modifications is tested over several systems, which indicates the practicality of the proposed model and algorithm. • A novel quadratic voltage model with modifications for meshed network is proposed. • With the convex-concave procedure, the exactness of convex relaxations is guaranteed. • For the iterative algorithm, the analytical and mathematical proof are provided. • The applicability of the QV model is tested over systems, indicating the superiority. [ABSTRACT FROM AUTHOR]

A new approach is proposed for obtaining a non‐linear area‐based equivalent model of power systems to express the inter‐area oscillations using synchronised phasor measurements. The generators that remain coherent for inter‐area disturbances over a wide range of operating conditions define the areas, and the reduced model is obtained by representing each area by an equivalent machine. The parameters of the reduced system are identified by processing the obtained measurements, and a non‐linear Kalman estimator is then designed for the estimation of equivalent area angles and frequencies. The simulation of the approach on a two‐area system shows substantial reduction of non‐inter‐area modes in the estimated angles. The proposed methods are also applied to a ten‐machine system to illustrate the feasibility of the approach on larger and meshed networks. [ABSTRACT FROM AUTHOR]

This paper presents a biologically inspired approach for distributed slot synchronization in wireless networks. This is facilitated by modifying and extending a synchronization model based on the theory of pulse-coupled oscillators. The proposed Meshed Emergent Firefly Synchronization (MEMFIS) multiplexes synchronization words with data packets and adapts local clocks upon the reception of synchronization words from neighboring nodes. In this way, a dedicated synchronization phase is mitigated, as a network-wide slot structure emerges seamlessly over time as nodes exchange data packets. Simulation results demonstrate that synchronization is accomplished regardless of the arbitrary initial situation. There is no need for the selection of master nodes, as all nodes cooperate in a completely self-organized manner to achieve slot synchrony. Moreover, the algorithm is shown to scale with the number of nodes, works in meshed networks, and is robust against interference and collisions in dense networks. [ABSTRACT FROM AUTHOR]

This paper deals with Distribution Network reconfiguration for loss minimization. A special attention is paid to the partially meshed operation. To solve this combinatorial problem, a set of optimization methods is mandatory to overcome this problem (losses reduction and topological constraints fulfillment). After a survey of some optimization algorithms, the proposed method is described step by step. Results are presented on a real network for the partially meshed networks optimization and operation including favored customers with high reliability index. [ABSTRACT FROM AUTHOR]

This paper describes the architectural study of an innovative ultra-fast packet-switched transparent processor dealing efficiently with unicast and multicast applications. The proposed architecture aims at outperforming current packet processor architectures in terms of total throughput and efficiency. In order to cope with the limitations of today's on board processors, three new concepts are introduced: transparent burst switching, channel multiplexing, and bandwidth asymmetry. Some of these concepts are already well known in the field of optical terrestrial networks but need further improvements and adaptations to cope with the requirements of satellite processors and systems. Transparent burst switching is used to enhance the transparency of the processor: the packet payload is processed transparently and only the header is demodulated onboard. The channel multiplexing and bandwidth asymmetry techniques are used to consolidate bufferless switch architectures, which appear to be very attractive for increasing the overall throughput of switches. Finally, the paper introduces an innovative efficient and scalable hybrid optical/digital implementation of this processor. The focus here is on a satellite-switched code/time-division multiple-access type of system but the results and concepts provided in this paper can apply to other satellite-switched systems. [ABSTRACT FROM AUTHOR]

• A quadratic voltage model for optimal power flow of meshed power system is proposed. • The cone relaxation is driven to be exact with the designed penalty method. • Analytical representation and mathematical proof are provided for penalty factors. • The superiority of the proposed approach is tested over several systems. A quadratic voltage model is proposed to formulate the optimal power flow problem of the meshed networks with maximum phase angle differences between buses less than π / 2. The quadratic voltage model uses the real and imaginary parts of node voltage directly so as to avoid the problem of inexact angle relaxation, which is the Achilles' Heel in previous researches. The nonlinear equalities between quadratic terms of voltages' variables are relaxed into convex second-order cone constraints. A penalty term is added into the objective function to guarantee the exactness of the relaxation, which is proved with the strict inequality on the upper and lower bounds of power generation nodes. For the proper value of the penalty factors, analytical representation and mathematical proof are provided. The applicability of the proposed model is tested over several systems, which shows better efficiency and less computational time. [ABSTRACT FROM AUTHOR]

There is an increasing interest in low voltage direct current (LVDC) distribution grids due to advancements in power electronics enabling efficient and economical electrical networks in the DC paradigm. Power flow equations in LVDC grids are non-linear and non-convex due to the presence of constant power nodes. Depending on the implementation, power flow equations may lead to more than one solution and unrealistic solutions; therefore, the uniqueness of the solution should not be taken for granted. This paper proposes a new power flow solver based on a graph theory for LVDC grids having radial or meshed configurations. The solver provides a unique solution. Two test feeders composed of 33 nodes and 69 nodes are considered to validate the effectiveness of the proposed method. The proposed method is compared with a fixed-point methodology called direct load flow (DLF) having a mathematical formulation equivalent to a backward forward sweep (BFS) class of solvers in the case of radial distribution networks but that can handle meshed networks more easily thanks to the use of connectivity matrices. In addition, the convergence and uniqueness of the solution is demonstrated using a Banach fixed-point theorem. The performance of the proposed method is tested for different loading conditions. The results show that the proposed method is robust and has fast convergence characteristics even with high loading conditions. All simulations are carried out in MATLAB 2020b software. [ABSTRACT FROM AUTHOR]