Power Flow Distribution Research Articles

Harmonic suppression control strategy of distribution networks based on the distributed power flow controller

New energy and multiple loads, such as distributed wind–solar storage and charging, are connected to the distribution network through power electronic converters, which increases the harmonic content in the distribution network and causes operational safety risks. In this paper, the mathematical model of harmonic current and harmonic power content in a distribution network is constructed by an equivalent circuit and vector diagram. The distributed power flow controller is proposed for harmonic control of the distribution network. The mathematical expressions of the harmonic current and harmonic power based on a distributed power flow controller are constructed, and the control strategy of the distributed power flow controller for harmonic control is proposed. The simulation results show that the proposed method can effectively suppress the fifth and seventh harmonics of the distribution network.

Improving the reliability of the energy balance management process in hybrid power complexes with green hydrogen and energy storage

In this paper, certain issues envisaged in the framework of development of design methodology for intelligent autonomous distributed hybrid power complexes (ADHPC) with green hydrogen and energy storage, functioning in grid mode and in the mode of interaction with the global (national) grid (GN) have been solved. Depending on their energy deficit or surplus, relative to the global grid, ADHPCs can operate as a load or as an energy source, respectively, as follows: based on the analysis of the energy balance management process in the ADHPC, a reasonable choice of the structure of the system of accumulation and distribution of power flows (SADCF) was made from the point of view of increasing the reliability of its functioning and ensuring the physical feasibility of the energy balance management process in this structure, i.e. keeping the actual power consumption of the consumers close to the required rated power at each given time t. This is achieved by including a condenser connected to the SADCF system on its assembly and distribution bus and a storage system BS with double-level ((BS1, BS2), double-circuit ((BS1(1), BS1(2)), (BS2(1), BS2(2))) structure, whereby: BS1of the level 1 - to manage the capacity balance in the SADCF under normal ADHPC regime and the variation of green hydrogen and consumption capacities within their confidence intervals assessed at the design stage; BS2 of the level 2 - to coordinate ADHPC and GN modes of operation and to control, together with BS1 of the level 1, GN, diesel generator (DG), the power balance in the SADCF when the ADHPC fails and when RES and consumption power are outside their confidence intervals; alternating charge/discharge operation of the parallel circuits will extend the life of the BS system; – a comprehensive definition of optimal ADHPC system situational energy balance management task is formulated.

Optimal Cooperative Eco-Driving of Multitrain With TLET Comprehensive System

Aiming to minimize the total electricity usage in realistic operation of urban rail transit (URT) trains, this paper establishes the coupled model for the train-line-electric network-timetable (TLET) comprehensive system, and proposes a multi-train cooperative eco-driving method to achieve the system energy optimal. The dynamic power flow within the DC railway system with multiple trains is analyzed by modeling the traction power supply system (TPSS), and an improved power flow calculation (PFC) method is proposed to calculate the dynamic power flow distribution. To achieve the total substation energy minimization, a space-time-speed (STS) three-dimensional network is presented to transform continuous train motion process into discrete states on space-speed plane, and a multiple individuals dynamic programming (MIDP) algorithm is throughly developed to cooperatively optimize the multi-train trajectories along the time horizon, with which the optimal speed profiles and timetables of each train can be obtained simultaneously. Moreover, a computationally efficient heuristic algorithm together with a train-to-train (T2T) communication policy are developed as a comparative study. Numerical experiment with field data from Guangzhou Metro Line 8 is implemented, to illustrate the energy-saving performance of the proposed methods.

Addressing building related energy burden, air pollution, and carbon emissions of a low-income community in Southern California

This study examines the impact of low-income assistance and electrification programs on a disadvantaged community in Southern California. An urban building energy model is paired with an AC power flow and electric distribution system degradation model to evaluate how the cost of energy, carbon emissions, and pollutant emissions change after applying building weatherization, energy efficiency, and electrification measures to the community. Results show that traditional weatherization and energy efficiency measures (upgrading lighting and appliances, improving insulation to current building code standards) are the most cost-effective, reducing the cost of energy and carbon emissions by 10–20 % for the current community. Heat pump water heaters offer a 40 % average reduction in carbon emissions and almost 50 % decrease in criteria pollutant emissions, but at a cost increase of 17–22 %. Appliance electrification also reduces carbon emissions 5–10 % but increases cost by 7 % to 25 %. For reducing carbon, government programs that support building electrification are most cost-effective when they combine switching from natural gas to electricity with high efficiency system. Electrifying hot water and appliances effectively reduces emissions but must be paired with improved low-income assistance programs to prevent increased energy burden for low-income families. The urban building energy model and electrical distribution simulations used in this study can be replicated in other low-income communities.

A Modern Distribution Power Flow Controller With A PID-Fuzzy Approach : Improves The Power Quality

Technological improvements have led to an increase of nonlinear loads, which in turn has a significant impact on the quality of power transmission. It is imperative that the level of energy purity conveyed by a transmission line be elevated. The key factors influencing power transmission are line impedance, sending end voltage, and receiving end voltage. Harmonic currents are made by nonlinear loads, which can cause system resonance, capacitor overloading, less efficiency, and a change in the amount of the voltage. The Distributed Power Flow Controller (DPFC) is a recently developed Flexible AC Transmission System (FACTS) device that utilizes the distributed FACTS (D-FACTS) idea. Unlike the Unified Power Flow Controller (UPFC), which employs a single large-sized three-phase series converter, the DPFC incorporates several small-sized single-phase converters.

Analysis of the influence of large‐scale offshore wind power on the steady‐state voltage of the vicinity region of grid connection point

AbstractThe power characteristics of offshore wind power will change the regional power flow distribution and affect the regional voltage. Here, the direct‐drive wind turbine generator controlled by unity power factor is selected as the research object, and the influence of change of wind power on voltage at the grid connection point is analyzed from the simple integration model. Based on the two critical states of the external equivalent power of the grid connection point, an analytical expression of the output of wind power in the corresponding state is obtained, and the relationship among the critical state outputs, the output of wind power and the parameters at the grid connection point is drawn, hence the related influence laws is analyzed. The influence of change of wind power on voltage and regional reactive power and the reactance distribution of transmission lines near the grid connection point is considered to analyze the influence of offshore wind power on the vicinity region of grid connection point. The rationality of the conclusion is verified by study the cases of the integration of offshore wind power into Guangdong power grid, and some suggestions are put forward for the planning of offshore wind power integration.

Identification of Critical Links Based on Electrical Betweenness and Neighborhood Similarity in Cyber-Physical Power Systems.

Identifying critical links is of great importance for ensuring the safety of the cyber-physical power system. Traditional electrical betweenness only considers power flow distribution on the link itself, while ignoring the local influence of neighborhood links and the coupled reaction of information flow on energy flow. An identification method based on electrical betweenness centrality and neighborhood similarity is proposed to consider the internal power flow dynamic influence existing in multi-neighborhood nodes and the topological structure interdependence between power nodes and communication nodes. Firstly, for the power network, the electrical topological overlap is proposed to quantify the vulnerability of the links. This approach comprehensively considers the local contribution of neighborhood nodes, power transmission characteristics, generator capacity, and load. Secondly, in communication networks, effective distance closeness centrality is defined to evaluate the importance of communication links, simultaneously taking into account factors such as the information equipment function and spatial relationships. Next, under the influence of coupled factors, a comprehensive model is constructed based on the dependency relationships between information flow and energy flow to more accurately assess the critical links in the power network. Finally, the simulation results show the effectiveness of the proposed method under dynamic and static attacks.

Analysing renewable energy flow distribution and its influence on grid electricity prices

The paper presents an approach to the assessment of technical and economic efficiency for an electric energy (EE) transport in a distribution grid. It is focused on the extent of renewable energy sources (RES) integration efficiency according to energy prices in a grid. A two-step procedure for calculation is used in terms of the approach. The first one includes the obtaining of energy flows distribution in a grid. The next step provides the calculation of costs flows and nodal prices for electric energy. Both stages are performed using a developed branch flow model. Unlike power flow distribution describing the instant point of time, energy flow distribution developed for any operation duration deals with the integral values of the flows. This is of great importance for the deeply varying output profiles of the intermittent renewables. The model provides the direct utilization of electric energy meters data available in a grid. The approach presented is essential for locating the particular consumers of the renewable energy in terms of a grid’s deep state and circuit diversity as well as for analyzing the influence of a renewable energy for electricity prices, and estimating the necessary renewables’ levelised cost of energy (LCOE).

Optimal power flow research of AC–DC hybrid grid with multiple energy routers

AC/DC hybrid grids are the future development trends of grids, and energy routers (ERs) can play key roles in controlling power flow, realizing the regulation of electric energy and improving power quality in the grids. At present, there have been many studies on the structure and control strategy of ERs, but only a few studies are on the power flow distribution and optimization of AC/DC hybrid grids with ERs. To enhance the efficacy of ERs in system-wide regulation and operational optimization, a multi-objective optimal power flow model is formulated for AC–DC hybrid systems with multiple ERs. In order to make ERs play a better role in overall regulation and operation optimization, the multi-objective optimal power flow model of AC–DC hybrid system with multi-ERS is established based on Newton–Raphson method (NR) and alternating iteration method with power consumption and voltage deviation as optimization objectives. The multi-objective evolutionary algorithm based on decomposition (MOEA/D) is used to optimize the model, and a smoother Pareto solution set is obtained compared with multi-objective particle swarm optimization (MOPSO). Then, fuzzy membership method is used to make compromise decision on the Pareto solution set to obtain the optimal compromise solution. Simulation and analysis on an enhanced IEEE 69 bus system verifies the validity of the model. In addition, the results obtained from the compromise solution are compared with the optimization results of MOPF obtained by MOPSO and that of single-objective power flow (SOPF) obtained by Particle Swarm Algorithm (PSO) in the same system. It is proved that the optimization model established can achieve the optimization objectives of reducing voltage deviation and power loss simultaneously to improve the overall performance of the system and optimize the operation state of the system.

A Study on Power Flow Analysis in Power Systems with the Participation of Double-Fed Induction Generators based Wind Turbine System

This paper focuses on double-fed induction generator (DFIG) based wind turbine system (WTS) and evaluate its effect to the distribution of power flow in power system. The structure of DFIG based WTS will be make detailed, including a rotor, stator and back-to-back converters. Power flows in itself are analyzed in both over and under synchronous operating modes. Control structure of DFIG is shown corresponding to rotor-side controller and grid-side controller to harness wind power and synchronize to the power grid. Operating scenarios that can happen in a proposed grid with the participation of DFIG based WTS are also shown to analyze the distribution of power flows in whole system whenever there are variations of power consumption and power generation. Simulation process will be carried out by MATLAB software to demonstrate proposed operating scenarios. Simulation results will show the power flows in whole system, the power adaptability corresponding to variation of load steps, the decrease of power from DFIG based WTS and the variation of currents at buses. Moreover, power exchange between power source and considered grid and current going through main units also can be determined and provided to dispatch center to ensure system stability.

Fast Tuning-Free Distributed Algorithm for Solving the Network-Constrained Economic Dispatch

With the increasing penetration of distributed energy resources (DERs) and their participation in the electricity market, it becomes more desirable to apply distributed algorithms for resource allocation in order to address the resulting computational and communicational challenges. Most of the existing distributed algorithms for solving the network-constrained economic dispatch (NCED) problem require the tuning of certain auxiliary parameters. As a result, the robustness of these algorithms against the varieties in DERs is greatly undermined. In this paper, a new distributed algorithm, optimality condition consensus (OCC), is proposed to solve the NCED problem by using distributed power flow (DPF) and ratio consensus as fundamental tools. It inherits the advantages of existing distributed algorithms for the NCED problem but removes the need for parameter tuning to improve performance in practice. The effectiveness of the proposed distributed algorithm in terms of efficiency, scalability, and robustness is demonstrated through detailed case studies.

A New Fast Decoupled-Like Algorithm for Radial Distribution Power Flow Problem by Using Rectangular Coordinates

A New Fast Decoupled-Like Algorithm for Radial Distribution Power Flow Problem by Using Rectangular Coordinates

Ecological Robustness-Oriented Grid Network Design for Resilience Against Multiple Hazards

Power systems are critical infrastructure for reliable and secure electric energy delivery. Incidents are increasing, as unexpected multiple hazards ranging from natural disasters to cyberattacks threaten the security and functionality of society. Inspired by resilient ecosystems, this paper presents a resilient network design approach with an ecological robustness (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ECO</sub> )-oriented optimization to improve power systems' ability to maintain a secure operating state throughout unknown hazards. The approach uses R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ECO</sub> , a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">surprisal</i> -based metric that captures key features of an ecosystem's resilient structure, as an objective to strategically design the electrical network. The approach enables solvability and practicality by introducing a stochastic-based candidate branch creation algorithm and a Taylor series expansion for relaxation of the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ECO</sub> formulation. Finally, studies are conducted on the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ECO</sub> -oriented approach using the IEEE 24 Bus RTS and the ACTIVSg200 systems. Results demonstrate improvement of the system's reliability under multiple hazards, network properties of robust structure and equally distributed power flows, and survivability against cascading failures. From the analysis, we observe that a more redundant network structure with equally distributed power flows benefits its resilience.

An accounting method of REDD reduction of renewable energy based on power flow distribution matrix

An accounting method of REDD reduction of renewable energy based on power flow distribution matrix

Identification of Critical Nodes in Power Grid Based on Improved PageRank Algorithm and Power Flow Transfer Entropy

Identifying critical nodes in the power grid is a crucial aspect of power system security and stability analysis. However, the current methods for identification fall short in fully accounting for the power transfer characteristics between nodes and the consequences of node removal on the security and stability of power grid operation. To enhance the effective and accurate identification of critical nodes in the power grid, a method is proposed. This method is based on improved PageRank algorithm and node-weighted power flow transfer entropy, referred to as IPRA-PFTE. Firstly, based on the power flow and equivalent impedance between nodes, and the introduction of virtual nodes, an improved PageRank algorithm is obtained. Then the node-weighted power flow transfer entropy is derived by considering the uniformity of the transfer power flow distribution in the system following the removal of a node. Finally, the importance of nodes is obtained by combining the improved PageRank algorithm with the node-weighted power flow transfer entropy. The method’s effectiveness and accuracy are validated through simulation using the IEEE 39-bus example and subsequent comparison with existing methods.

Optimal Economic Scheduling Method for Power Systems Based on Whole-System-Cost Electricity Price

At present, the traditional scheduling mode of power grids generally dispatches according to the power generation cost within the safe range. Transmission costs are evenly distributed to customers according to their load ratios. There are no methods for the rational distribution of transmission costs according to the utilization degree of generation and load to transmission network resources. This traditional scheduling mode will render transmission cost distribution unfair, and it is difficult to guide reasonable load distribution in time and space. Therefore, an optimal economic scheduling method for power systems based on the whole-system-cost electricity price is proposed in this paper. For the power generation and the transmission sides, the whole-system-cost electricity price model was constructed according to the power flow tracking method. For the load side, a demand-side response model of users’ responses to electricity price changes was established. Finally, the IEEE 57 node standard model was used to simulate optimal economic scheduling. The results show that the proposed method can guide the rational distribution of power flow. The power flow is shifted moderately from far away to near the power generation center, allowing for the load demand to be guided to meet nearby customers’ demands and preventing the line from blocking, the latter of which is conducive to ensuring the safety of the power grid.

Coordinated cyber-physical attack on power grids based on malicious power dispatch

This paper proposes a new mode of cyber-physical attack based on injecting false commands, which poses an increasing risk to modern power systems as a typical example of Cyber-Physical Systems (CPS). Such attacks can trigger physical attacks by driving the system into vulnerable states. To address the critical issues arising from this new mode, we define an inverse-community (IC) in power flow distribution and evaluate it using inverse-modularity. To identify the most vulnerable state of the IC that represents the inherent vulnerability of the system, we employ a full malicious power dispatch problem. We also analyze an example of the proposed mode, where a partial malicious power dispatch that maximizes inverse-modularity is combined with physical attacks aimed at disconnecting vulnerable IC boundary lines, making cascading failures highly likely. To demonstrate the potential impact of this coordinated cyber-physical attack, we use the IEEE-118 and IEEE-300 bus systems for simulation. The results show the effectiveness of this attack strategy and provide a new perspective to analyze cyber-physical security issues in modern power systems.

Abnormal line loss identification of distributed PV low-voltage distribution area based on data driven

The identification of line loss anomalies in low-voltage distribution networks has been a very challenging problem for a long time. The large-scale access of distributed photovoltaics to the distribution network changes the power flow distribution and further increases the difficulty of identifying abnormal line losses in low-voltage distribution areas. In this paper, an identification method for abnormal line loss in distributed photovoltaic access low-voltage distribution area is proposed. Firstly, we analyze the correlation between the line loss rate and other indicators in the area of distributed photovoltaic access. Secondly, according to the gray correlation degree results, the appropriate indicators are selected, and the k-means clustering algorithm is used to cluster these indicators, through the clustering results, we can detect outliers to determine whether there is a line loss anomaly in the area. Finally, by analyzing the time dispersion degree of the cluster where the outlier point is located, the anomaly coefficient of the area is obtained, and the line loss anomaly is judged according to the anomaly coefficient. To verify the effectiveness of this method, we conduct an empirical analysis of typical containing distributed photovoltaics. Experimental results show that this method can effectively identify the line loss abnormalities in the distribution area containing distributed photovoltaics.

Mitigating the impacts of geomagnetic disturbances on the small signal stability

Geomagnetically induced currents (GICs) caused by geomagnetic disturbances (GMDs) flow through the transformers, which lead to the increase of reactive power loss (QGIC). As reactive loads added to the system, QGIC causes the change of power flow distribution, which connects GMDs with small signal stability. Installing blocking devices (BDs) in the neutral points can reduce the negative effects on the grids. Obtaining the best effect is challenging, because the amplitude and direction of induced geoelectric fields (IGFs) are uncertain and non-stationary. Taking the credibility of damping ratio less than 0.05 as an index, the impact of GMDs on small signal stability is quantitatively evaluated. It is found that when intense GMDs occur, the risk of small signal instability increases significantly. Based on the voltage/damping ratio sensitivity joint feature space, the sensitivity scenario is obtained through scenario clustering. Moreover, upon optimal placement of BDs based on joint sensitivity (JS) scenarios, it is observed that the risk index can be significantly reduced compared to that in constant induced geoelectric fields (CIGF) and varying induced geoelectric fields (VIGF) scenarios.

Linearized power flow calculation of bipolar DC distribution network with multiple flexible equipment

The bipolar direct current distribution network (BDCDN) has the advantages of high reliability, large transmission, and high efficiency. However, voltage unbalance is a crucial power quality problem of BDCDN. On one hand, flexible equipment, such as DC electric spring, DC power flow controller, and DC transformer, can effectively suppress unbalanced voltage. On the other hand, the diversity of topology and control methods of multiple types of flexible equipment complicates power flow calculation. In this study, a linear power flow algorithm is proposed. First, the structural characteristics of a BDCDN with multiple types of flexible equipment are analyzed. Second, a linear ZIP load model based on Taylor expansion is derived. The steady-state model of multiple types of flexible equipment is established by analyzing the topological structure and control mode. Third, a network modeling and power flow calculation method of BDCDN with multiple types of flexible equipment are proposed. Finally, the modified IEEE14-node case and IEEE33-node case are used to verify the validity and correctness of the proposed algorithm. The effectiveness of flexible equipment on the power quality issue is demonstrated through comparison studies of power flow distributions.