Local Power Flow Research Articles

Grid Quality Services from Smart Boilers: Experimental Verification on Realistic Scenarios for Micro-Grids with Demand-Side Management Oriented to Self-Consumption

The deeper penetration of renewables in the energy mix is an intense requirement in order to reduce global carbon dioxide emissions. In addition, new technologies are being developed, such as electric mobility and Distributed Generation (DG) in urban areas. However, the unpredictable fluctuations in energy generation from roof-installed PVs and the switching operation of their inverters greatly aggravate the already-present grid quality problems. In this paper, the Smart Boiler (SB) concept for grid quality improvement is presented. Furthermore, its experimental verification is implemented on a flexible testbed that accurately emulates several realistic scenarios for the low voltage distribution grid, under complex operating conditions. The proposed low-cost electronic kit, which contains a converter of fairly simple topology and requires connection to the internet, is used to upgrade conventional domestic boilers to smart devices. The SB automatically regulate the local reactive power flow, helping to stabilize the voltage level and suppress the grid current harmonic content, with both services provided in a matter of seconds. The higher the active power consumed and the denser the SB cluster, the wider the beneficial impact on the affected network area. While this service is provided, excess energy generated by PVs is temporarily stored as heat in the boiler tanks, given the users’ hot water consumption habits. The whole application, as a powerful demand-side management tool, proves beneficial for both the network operator and the end-user, especially when self-consumption is desirable in order to achieve a Nearly Zero Energy Building.

Generalized acoustic impedance metasurface

Impedance theory has become a favorite method for metasurface design as it allows perfect control of wave properties. However, its functionality is strongly limited by the condition of strict continuity of normal power flow. In this paper, it is shown that acoustic impedance theory can be generalized under the integral equivalence principle without imposing the continuity of power flow. Equivalent non-local power flow transmission is instead realized through local design of metasurface unit cells that are characterized by a passive, asymmetric impedance matrix. Based on this strategy, a beam splitter loosely respecting local power flow is designed and demonstrated experimentally. It is concluded that arbitrary wave fields can be connected through arbitrarily shaped boundaries, i.e. transformed into one another. Generalized impedance metasurface theory is expected to extend the possible design of metasurfaces and the manipulation of acoustic waves.

Local power flow control

Show the prospects for the development of local electric networks with distributed generation. Recent changes in the electric power industry are forcing the revision of the requirements for both infrastructure and power facilities. Show that the connection of distributed generators and consumers of electrical energy to the network is fraught with certain difficulties. Solving the problem of high-quality and uninterrupted power supply to consumers requires a new approach associated with the use of modern Smart Grid technologies, equally related to energy and information technology. It is noted that for the implementation of such a large-scale task, the "road map" "Energynet" of the National Technology Initiative was developed, among the main directions of which are the digitalization of the infrastructure of distribution networks and the deep decentralization of electricity production. Consider, in accordance with the identified areas, the segments of the smart energy market, which include: reliable and flexible distribution grids, smart distributed energy and consumer services. Propose a solution to the problem using the example of a local low voltage microgrid with distributed generation. METHODS. The solution to the problem is proposed on the basis of creating a simulation model, with the help of which it is possible to perform a number of tests and obtain the optimal network mode within a given error area. implement various options for the structure of the microgrid, the number and type of generators, the load level. The structural diagram of the local network is proposed. RESULTS. The article describes the process of managing power flows between producers (local distributed sources) and consumers of electricity. This process is carried out through a single control center, which receives information about the state of the micro-grid objects - the level of electricity generation by generators and the level of the current load of consumers. Based on the results of information processing in the control center, a decision is made on the redistribution of power between objects. A scheme describing the dynamic process of power transfer for efficient resource management in the power distribution network is proposed. CONCLUSION. The considered power management algorithm is a simple implementation of classical load balancing, and at the same time allows for optimal energy distribution within a given error. Optimal, in this case, will be the state of the system, in which all distributed renewable energy sources are used in full to meet the needs of the local micro-network, while reducing to a minimum the consumption from the network. At the same time, it is also necessary to introduce corrections for the unevenness and instability of electricity generation by renewable energy sources.

Cascading Failure Propagation and Mitigation Strategies in Power Systems

In this article, we investigate the local and nonlocal failure propagation patterns in power systems and propose effective mitigation strategies. It is widely acknowledged that the sequence of failure events of component overloading is determined by power flow redistribution. To understand the power flow redistribution process, we analyze the prefault power flow condition using network flow theory and by clustering the system into several regions with balanced local power flow. We observe that faults triggering local power imbalance would lead to remote power transfer and faults causing no local power imbalance would lead to local power redistribution. The improved understanding of the failure process permits us to develop effective mitigating strategies consisting of adaptive power balance restoration and selective edge protection for cascading failure propagation. In addition, we propose a set of indexes to measure the local and nonlocal propagation risks of cascading failures. Numerical simulations on the IEEE 118- and 300-bus systems demonstrate that the proposed mitigation strategies can significantly reduce the blackout sizes and are tolerant to incorrect transmission line tripping.

A simple wave/power flow analysis method for vibration control of large cable-frame structures

A cable-frame structure typically has low damping and a low fundamental frequency and is modally rich. It is likely to generate sustained vibration when disturbed. Unwanted vibration of such a structure must be caught and controlled to ensure its structural safety and design performance. To overcome the disadvantages of high frequency distortion and modal truncation arising from modal control methods, wave control methods have been suggested. However, they generally involve establishing and solving numerous wave equations, an expensive procedure that may make the vibration control for large and/or complex structures inefficient or even impractical. This study presents a simple analytical approach for the vibration control of large cable-frame structures. The approach is divided into two stages. First, the exact frequency-domain solution is obtained by a dynamic stiffness method in which the infinite degrees of freedom of each flexible component are reduced into only several degrees of freedom at its two endpoints. Second, formulas for calculating the local wave and power flow are deduced based on the global exact solution so that the local wave control information can be extracted from the global response solution. Using this approach, the dynamic response and wave and power flow analysis are carried out for two typical cable-frame structures, leading us to suggest several control measures for suppressing vibration. The approach, if proven to be effective, can be readily applied to vibration control of large cable-frame structures.

Modeling and Analysis for Global and Local Power Flow Operation Rules of UPFC Embedded System Under Typical Operation Conditions

The unified power flow controller (UPFC) is recognized as one of the most promising flexible ac transmission system (FACTS) devices for modern power systems, due to its versatile functionalities. Based on typical operation conditions, this paper investigates the global and local power flow operation rules of the UPFC embedded transmission system theoretically. First, the detailed global power flow model (GPFM) and the local power flow model (LPFM) are established concerning several selected critical points (SCPs) in the system. The theoretical power flow operation rules for the ranges, the movements and the trajectories of GPFM and LPFM are analyzed, respectively. Then, the case study is performed based on the proposed simplified model, and the results are analyzed from GPFM and LPFM perspectives respectively. The operation rules and the power flow ranges is studied. Further case studies based on the proposed original mathematical model are also carried out, and the results are listed from different viewpoints of two-dimensional planes and three-dimensional spaces. All types of results are also analyzed from GPFM and LPFM perspectives, which verify that the UPFC is adaptive to various operation conditions for power flow regulation.

Operation Strategy of Shared ESS Based on Power Sensitivity Analysis to Minimize PV Curtailment and Maximize Profit

Nowadays, due to the renewable energy policy, the penetration of photovoltaic (PV) has increased, but the curtailment of PV output power has also increased. However, for PV power producers, who earn profit from selling power to the utility, this kind of curtailment will lead to a decline in their profit. Thus it is necessary to determine how to perform proper curtailment for them. This study proposes a shared energy storage system (ESS) operation strategy based on the power flow at the points of common coupling (PCC) and the power sensitivity of the line loss effect between buses where each PV power producer is located. The proposed algorithm maximizes the overall regional profit through arbitrage trading of shared ESS and performs a curtailment that reduces the effect of line loss at the PCC points. The performance verification of the proposed algorithm is conducted through a simulation on MATLAB, the benefits of shared ESS and the economic feasibility of reducing the curtailment are also analyzed. Moreover, the results of shared ESS benefits and curtailment allocations based on power sensitivity are analyzed for each PV power producer. The results show an improved local profit and PCC power flow.

Effective Dynamic Scheduling of Reconfigurable Microgrids

This paper develops an effective model for microgrid optimal scheduling with dynamic network reconfiguration. Network reconfiguration can effectively alter local power flow and thus provide an opportunity to reduce microgrid distribution network losses during grid-connected operation (supporting microgrid economic objectives) and to reduce potential load curtailments during the islanded operation (supporting microgrid reliability objectives). The proposed optimal scheduling model is decomposed into a grid-connected operation master problem and an islanded operation subproblem. A novel and highly accurate dynamic linear power flow model, with the ability of line switching, is developed and included in both problems. The optimal schedule determined in the master problem is assessed to meet the microgrid islanding feasibility in the subproblem. If infeasible, the decision variables are amended using the islanding cuts, which will accordingly revise the network reconfiguration, as well as the schedule of dispatchable units, energy storage, and adjustable loads. The simulation results on a test microgrid demonstrate the effectiveness and satisfying performance of the proposed model.

Pseudo-Pitchfork Bifurcation of Feasible Regions in Power Systems

Local bifurcations occur in power systems, causing changes in power system dynamic behaviors. These local bifurcations include the saddle-node bifurcation, Hopf bifurcation, and structure-induced bifurcation. This paper presents a new type of bifurcation that can occur in the optimal power flow (OPF) problem. This new type of bifurcation, termed pseudo-pitchfork bifurcation, involves bifurcations of the feasible components of the OPF problem and the disappearance of local optimal power flow solutions. The main features of this special type of bifurcation are demonstrated on several power systems with different loading condition parameters and different constraint parameters. Then the computation consideration and physical meaning of the pseudo-pitchfork bifurcation are roughly discussed. It is also demonstrated that a pseudo-pitchfork bifurcation occurring between feasible components can help us interpret the loss or birth of optimal power flow solutions and can lead to powerful numerical methods for computing high-quality optimal power flow solutions.

Stochastic Resilient Post-Hurricane Power System Recovery Based on Mobile Emergency Resources and Reconfigurable Networked Microgrids

This paper develops an effective two-stage stochastic post-hurricane recovery framework to improve networked microgrid resilience using mobile emergency resources (MERs) and a proposed reconfiguration strategy. In the first stage, network reconfiguration actively alters the local power flow path and provides opportunities for restoring critical loads, thus reducing the energy not supplied to electric consumers. The optimal schedule determined in the first stage problem is also used to determine the islanded loads that need MERs for restoration. In the second stage, truck-mounted MERs will deliver power to islanded loads, observing the shortest path and post-hurricane transportation infrastructure constraints. Dijkstra’s algorithm is used to produce the shortest path and avoid possible out-of-service roads. In order to model the uncertainties of the problem, a stochastic framework based on unscented transform is employed. The proposed problem is formulated as a two-stage stochastic single-objective optimization problem maximizing system resilience. Simulation results on a test networked microgrid demonstrate the effectiveness and satisfying performance of the proposed model.

Grid-tie three-phase inverter with active power injection and reactive power compensation

This paper proposes a methodology for the active and reactive power flow control, applied to a grid-tie three-phase power inverter, considering local and/or regionalized power flow control necessity in the forthcoming distributed generation scenario. The controllers are designed by means of robust pole placement technique, which is determined using the Linear Matrix Inequalities with D-stability criteria. The linearized models used in the control design are obtained by means of feedback linearization, aiming to reduce system nonlinearities, improve the controller's performance and mitigate potential disturbances. Through multi-loop control, the power loop uses active and reactive power transfer adapted expressions to obtain the magnitude of the voltage and power transfer angle to control the power flow between the distributed generation and the utility grid. The methodology main idea is to obtain the best controllers with the lowest gains as possible placing the poles in the left-half s-plane region, resulting in fast responses with reduced oscillations. In order to demonstrate the feasibility of the proposal a 3 kVA three-phase prototype was implemented and a comparison with conventional controller is performed to demonstrate the proposed methodology performance. In addition, anti-islanding detection and protection against over/under voltage and frequency deviations are demonstrated through experimental results.

Control strategies and configurations of hybrid distributed generation systems

Abtract Nowadays the use of distributed generating systems, which use a renewable energy source, has experienced a fast development. Moreover their intrinsic intermittent nature can be overcome using hybrid systems which combine more energy sources. This paper discusses the main topologies which can be adopted for a general hybrid generation system and it focuses on a particular hybrid system which combines two different energy sources, evidencing high level and local level power flow control strategies in both stand-alone and grid connected operation. A full experience in the realization of a hybrid plant which uses an internal combustion engine with cogeneration functionalities and solar source, installed in Delebio, Italy is then presented. System design aspects, with particular attention to the possible topologies and power flow control strategies, are analyzed. After the analysis of the design aspects, experimental results of the real plant are reported.

Modal power flow analysis of a damaged plate

Variation of the modal reactive power distribution of a damaged plate is analyzed. Large variation of local reactive power flow in or around the damage region of a plate under resonant vibration is related to the change of strain and kinetic energies in the damage region. Feasibility of damage identification based on the detection of this local variation of modal reactive power flow in a structure is studied. Compared with the damage identification techniques based on the determination of the active power flow in a damaged plate, the proposed method only requires data of a vibration mode shape of the structure and it is easier to apply in practice. Two common types of damage have been tested for identification, the first with a region of reduced stiffness in the plate while the second with a small hole in the plate. Numerical tests show that the proposed method is effective for both types of damage and the modal power flow is more sensitive to the change of plate stiffness than the strain mode shape in the test case.

Local Network Power Flow Analysis: An Accuracy Level Comparison for Two Sets of Equations

This paper addresses the problem of network power flow analysis by comparing two sets of power flow equations: power flow equations based on Tellegen's theorem and conventional power flow equations. The comparison is based on local performance. A good local performance of power flow equations is important for network planning as network planning requires many thousands of power flow analyses. This paper shows that the equations based on Tellegen's theorem outperform conventional equations when used in a reduced local model, i.e., for a few selected equations. For the same number of equations selected, Tellegen's equations give much more accurate results. Numerical examples are provided

Fields in Planar Anisotropic Transmission-Line Metamaterials

An electromagnetic analysis of wave propagation in planar anisotropic transmission-line metamaterials is presented. It is shown that a planar square-celled grid, series-loaded with orthogonal inductors and capacitors and positioned over a ground plane, is magnetically anisotropic and may be described in terms of a diagonal permeability tensor. Resonance cone field concentrations form when two of the three diagonal elements of the permeability tensor are opposite in sign and the dispersion surface becomes hyperbolic. A theoretical treatment of an electric line current source excitation shows that the formation of resonance cones is a consequence of the singularity associated with the characteristic surface of a hyperbolic equation. The resonance cone angle, which also describes the direction of local power flow in the region between the grid and the ground plane, can be predicted to a good degree of accuracy. To the authors' best knowledge, the present work also verifies experimentally for the first time that current flow reverses direction across the resonance cone. Experiments, simulations, and analytical calculations of the cone angle are in good agreement

Combining local and optimised power flow remedial measures in bulk reliability assessment

In traditional Newton-Raphson power flow algorithms, the terminal and remote bus voltages are obtained using a local control logic, i.e. reactive power and LTC taps are adjusted to meet pre-specified voltage settings. On the other hand, most of the optimal power flows (OPF) utilised in available reliability programs adopt an optimised logic for voltage control, i.e. the voltage level is optimised inside the pre-specified bounds, meaning that new settings can be calculated in order to avoid or minimise load shedding. However, in several practical situations this is not a feasible approach, due to operational constraints. Local voltage control logic is introduced into the non-linear interior point (IP) optimal power flow of a bulk power system reliability evaluation program in order to represent actual operational practices with increased accuracy. The impact of these two voltage control logics on the reliability indices is then analysed using the new IEEE Reliability Test System (RTS-96) and a 89-bus network derived from the North/Northeastern Brazilian System (NNBS).

ローカル潮流情報に基づくTCSC制御

ローカル潮流情報に基づくTCSC制御

The relation of edge confinement to global confinement in ASDEX Upgrade (Axially Symmetric Divertor Experiment)

Experimental evidence is presented from the ASDEX Upgrade (Axially Symmetric Divertor Experiment) tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1993 (International Atomic Energy Agency, Vienna, 1994), Vol. I, p. 127] of a robust relation between the edge radial pressure gradient and the global confinement of the plasma. This relation transcends the power flowing across flux surfaces near the edge and thus suggests that the usual model of cross-field heat transport, where local gradients increase with increasing local power flow, is not appropriate.

Rigorous solutions for nonlinear TE waves guided by a waveguide that has a buried secant hyperbolic profile in the film

Abstract Dispersion relations for nonlinear TE waves guided by a waveguide that has a buried secant hyperbolic profile in the film with a self-focusing nonlinear cover medium have been obtained rigorously. It is shown that for the same diffusion depth, the local maximum power flow for TE0, and TE1 modes increases as the buying depth is increased.

Coupling rod energy models using local energy density

To couple medium‐ and high‐frequency models of rod vibration in terms of energy density and intensity, relationships that enforce continuity of power flow and compatibility of energy density are required at the joint. The continuity relationship for local power flow at a joint between two rods is straightforward. However, for joints of rods with different properties, there is a jump discontinuity of local energy density at the joint. An exact relationship for the power flow can be found using the receptance method. A good frequency‐averaged approximation of the power flow can be found using the so‐called wave transmission method commonly used in statistical energy analysis. In this investigation, a relationship for the jump discontinuity of the local energy density, which uses the ratio of the local kinetic energy density to the total density, is examined. The technique is capable of deterministic or statistical prediction of energy in the coupled rods. [This investigation was supported by the NASA Langley Research Center.]