Characteristics Of Distribution Network Research Articles

Hybrid data-driven method for distribution network topology and line parameters joint estimation under small data sets

Time-varying characteristics of distribution network makes the measurement data of intelligent instrument in the same state not sufficient, which cannot satisfy the required amount of data in existing topology and parameter estimation methods. This paper proposes a hybrid data-driven method for distribution network topology and line parameters joint estimation under small data sets. Based on the sparse characteristics of distribution network, a partial correlation analysis-based neighbor node selecting mechanism is designed, and the initial topology under small data sets is robustly identified with OR criterion. Combined with approximate linear power flow equation, initial values of line parameters and phase angle are estimated based on the linear regression. Furthermore, initial topology, line parameters, phase angle are optimized iteratively based on Newtonian method, with the decoupled linear power flow model introduced to simplify Jacobian matrix to accelerate iterative speed. Test results show that the proposed method only depends on small data sets to estimate the topology and parameters accurately and stably, adapting to different network scales and types. Compared with existing methods, it has faster calculation speed without loss of accuracy, and is robust to the noise and sampling resolution.

Prediction method of line loss rate in low‐voltage distribution network based on multi‐dimensional information matrix and dimensional attention mechanism‐long‐and short‐term time‐series network

Line loss accounts for most of the energy loss in low-voltage distribution network. Accurate prediction of line loss rate (LLR) is of great significance to eliminate abnormal transmission line faults in time and ensure power supply safety. The existing prediction methods for LLR seldom consider the seasonal trend data that affect it, and there is a hysteresis effect in predicting non-stationary line loss sequences. To solve the above problems, this paper proposes a prediction method based on multi-dimensional information matrix and dimensional attention mechanism-long-and short-term time-series network (DAM-LSTNet). Firstly, the maximum information coefficient (MIC) method is used to screen the distribution network characteristics and seasonal trend parameters. Secondly, the variational mode decomposition (VMD) method optimized by the genetic algorithm is used to decompose the historical line loss data and form a multi-dimensional information matrix with the screened characteristic parameters of the network. Finally, the multi-dimensional information matrix is put into the LSTNet network with dimensional attention mechanism to predict the LLR. The example analysis shows that compared with the existing methods, it has the advantages of sufficient consideration of prediction parameters, adaptive changes of prediction weights, weak hysteresis effect and high prediction accuracy.

Analysis of Security Operational Characteristics of Distribution Network considering Electric Vehicle Load Access Forecast

In recent years, electric vehicles have been widely promoted by virtue of environmental protection and pollution-free advantages. In the future, they are expected to become a mainstream means of transportation. However, as new services and business models become more and more closely related to the distribution network, the traditional AC distribution district has limited ability to respond to the large-scale access of electric vehicles. Therefore, it is becoming increasingly important to improve the ability to respond to electric vehicle access, reduce the negative impact of large-scale electric vehicle access on the grid, and predict and calculate the uncertainty caused by electric vehicle load access. Therefore, this paper proposes the concept of flexible distribution district, constructs the security operational boundary model for flexible distribution district, and uses “security margin percentage” as the measurement mechanism to provide dispatchers with an intuitive system operating status. In addition, this paper also proposes an effective uncertainty quantification method for the problem that it is difficult to measure the changes of bus voltage and line current at network nodes when large-scale electric vehicles are connected to the network. Numerical results demonstrate both the extensibility and the practicality of the proposed security operational boundary. In addition, the proposed uncertainty quantification method can reflect the impact of load changes on the characteristics of the power grid, which is helpful to study the improvement significance of adjusting electric vehicle load changes to distribution network optimization.

Robust comprehensive PV hosting capacity assessment model for active distribution networks with spatiotemporal correlation

Variate but similar microclimate in different buses of a distribution system usually leads to correlated photovoltaic (PV) outputs. Such correlation may reduce the PV output uncertainty and enhance the hosting capacity of active distribution networks (ADNs). To fully elucidate the hosting capacity of geographically dispersed PV, this paper proposes a novel robust comprehensive PV capacity assessment model that considers both the spatiotemporal correlation of PV output and active distribution network management (ADNM) techniques. In the proposed model, the historical PV output data of the vicinity region are employed to generate the empirical spatial and temporal correlation matrix and ellipsoidal uncertainty sets for arbitrary PV site pairs. The uncertainty of PV outputs is addressed by a two-stage robust optimization. Concerning distribution network characteristics, the proposed capacity assessment model employs a convex conic quadratic format of AC power flow equations that are transformed into second-order cone programming. A historical PV output dataset from Suzhou China and a 59-bus rural distribution system in an adjacent city was used to demonstrate the effectiveness of the proposed PV hosting capacity assessment methodology. The hosting capacity results indicate that both spatial and temporal correlations can enhance the PV hosting capacity. Considering both the spatial and temporal leads to a significant increase in PV hosting capacity. To obtain an accurate PV hosting capacity, both spatial and temporal features should be simultaneously considered.

An energy storage location method with comprehensive sensitivity of timing voltage

The voltage problem caused by a large number of distributed generation in distribution network is becoming more and more obvious. Energy storage system has flexible four quadrant power regulation ability, which is an effective means of voltage management in distribution network. In the energy storage location selection of active distribution network, a weight coefficient selection method considering the load growth direction is proposed to solve the problem that the TOPSIS (the Technique for Order Preference by Similarity to Ideal Solution) is difficult to select the weight coefficient. Combined with the voltage / active and reactive power sensitivity matrix, the comprehensive sensitivity index is established. Then, the sensitivity index between two nodes in the traditional single time period is improved, and the voltage offset weight factor is added to establish the comprehensive sensitivity index of timing voltage. The indicator can be applied even if the size of the distribution network changes. The example results show that this method fully considers various characteristics of active distribution network and is more reasonable and effective than the traditional sensitivity method.

Dual graph characteristics of water distribution networks—how optimal are design solutions?

Urban water infrastructures are an essential part of urban areas. For their construction and maintenance, major investments are required to ensure an efficient and reliable function. Vital parts of the urban water infrastructures are water distribution networks (WDNs), which transport water from the production (sources) to the spatially distributed consumers (sinks). To minimize the costs and at the same time maximize the resilience of such a system, multi-objective optimization procedures (e.g., meta-heuristic searches) are performed. Assessing the hydraulic behavior of WDNs in such an optimization procedure is no trivial task and is computationally demanding. Further, deciding how close to optimal design solutions the current solutions are, is difficult to assess and often results in an unnecessary extent of experiment. To tackle these challenges, an answer to the questions is sought: when is an optimization stage achieved from which no further improvements can be expected, and how can that be assessed? It was found that graph characteristics based on complex network theory (number of dual graph elements) converge towards a certain threshold with increasing number of generations. Furthermore, a novel method based on network topology and the demand distribution in WDNs, specifically based on changes in ‘demand edge betweenness centrality’, for identifying that threshold is developed and successfully tested. With the proposed novel approach, it is feasible, prior to the optimization, to determine characteristics that optimal design solutions should fulfill, and thereafter, test them during the optimization process. Therewith, numerous simulation runs of meta-heuristic search engines can be avoided.

Robust three-phase state estimation for PV-Integrated unbalanced distribution systems

As the increasing penetration of renewable energy brings uncertainty and fluctuation into the operating conditions of distribution systems, distribution system state estimation (DSSE) needs to track not only the state of the network, but also the state of the renewable energy sources robustly and under unbalanced conditions. Aiming at delivering comprehensive situational awareness of distribution systems hosting solar photovoltaic (PV) power plants, this paper proposed a joint state estimation model for unbalanced distribution systems integrated with single-phase and three-phase PV power plants, as well as an extended weighted least absolute value (EWLAV) estimation algorithm for handling simultaneous measurement errors and control input errors. The proposed state estimation model considers various loss components of single-phase and three-phase power electronic converters, and is applicable to general unbalanced conditions including unbalanced phasing and parameters of distribution lines, PV power plants, and loads. The proposed EWLAV algorithm leverages sparse l1 optimization principles and can identify and suppress the gross errors in both measurements and converter control inputs. Simulation results show that the developed model can reliably reflect the characteristics of three-phase unbalanced distribution networks and PV plants, and the EWLAV algorithm produces unbiased results under simultaneous measurement errors and control input errors, which conventional estimators such as the weighted least squares (WLS) and weighted least absolute values (WLAV) cannot achieve.

Situation awareness method of the distribution network based on EMD-SVD and Elman neural network

In order to ensure reliability and security of power supply, the situation awareness of some elements in the distribution network is studied in this paper. Considering the influence of the interference signal, Empirical Mode Decomposition (EMD) is introduced to reduce it. Subsequently, according to operation characteristics of the actual distribution network, several evaluation indexes are proposed to describe the operation situation of the overall distribution network and internal elements, especially evaluation of fragile nodes. Based on these indexes and characteristics of actual distribution network, the comprehensive evaluation method of fragile nodes (CEMFN) is constructed, which mainly aims at the fragile nodes in the distribution network and synthesizes the single index coefficient to realize the identification of fragile nodes. Through the simulation calculation, it can be seen that the result of CEMFN is more accurate than that of the traditional evaluation model, which provides an important theoretical support for the operation and maintenance of distribution network and reliable power supply.

Research and Assumption on the Grid Structure of DC Distribution Network

Based on the typical structural characteristics of DC distribution network, this paper analyzes the application scenarios of different types of DC distribution systems based on the development planning and industrial layout of some cities. The differentiated demands, load types and user-side power consumption environment in different scenarios are studied. Determine the appropriate voltage level for various scenarios, the connected source terminal, energy storage terminal, and grounding method. On the premise of considering the user-side scenarios of typical DC applications, based on different power grid structures and operation modes, the optimal network topology relationship is studied, and a multi-scenario typical DC network topology architecture suitable for urban construction is constructed.

Volt-VAR control for distribution networks with high penetration of DGs: An overview

Continuously improving the ability to accept distributed renewable energies is the trend of future grid development, and a large number of papers have been published in recent years to study the problem of Volt-VAR control (VVC) for distribution networks with high penetration of distributed generations. This paper summarizes the relevant modeling and solution methods for VVC problems, mainly including VVC based on multiple time scales, hierarchical partitioning, multi-stage and network reconstruction, in conjunction with the operational characteristics of distribution networks containing distributed renewable energies; meanwhile, it analyzes the advantages and disadvantages of traditional optimization methods, heuristic intelligent algorithms and random variable processing methods used to solve VVC problems, and then introduces the application of model-free deep reinforcement learning as a latest decision method in VVC of distribution networks. Most of the models and methods compiled in this article are from the research results of the last three years and have some reference value.

Analysis of Fault Characteristics of Distribution Network with PST Loop Closing Device under Small Current Grounding System

With the rapid development of cities and the increasing complexity of distribution network systems, the cableization of transmission lines and the diversification of power users have brought new challenges to the supply reliability of distribution networks. Short-time outages caused by power outages and maintenance are one of the factors that affect the reliability of the power supply in the distribution network. The non-stop load transfer through a phase-shifting transformer (PST) operation can effectively improve the reliability of power supply to complex distribution systems. Considering the operation mode and structure form and fault type of the urban distribution network in China, comparing and analyzing the applicable scenarios of different neutral grounding methods, and based on the structure and zero sequence path characteristics of PST, an improved PST-based phase shifting and grounding transformer loop closing device with low power consumption is proposed. The fault characteristics of the PST-based loop closing device under the small current grounding system are also analyzed by the sequence component method, and, finally, the effectiveness of the phase-shifting and grounding transformer device is verified by simulation under PSCAD/EMTDC for fault routing and protection configuration of the urban distribution network in China.

Wind-Photovoltaic-Energy Storage System Collaborative Planning Strategy Considering the Morphological Evolution of the Transmission and Distribution Network

The collaborative planning of a wind-photovoltaic (PV)-energy storage system (ESS) is an effective means to reduce the carbon emission of system operation and improve the efficiency of resource collaborative utilization. In this paper, a wind-PV-ESS collaborative planning strategy considering the morphological evolution of the transmission and distribution network is proposed. Firstly, aiming at the optimal economy of transmission and distribution network and considering the constraints of safe and stable operation of the system, the planning model of the transmission network based on DC power flow and the planning model of the distribution network based on AC power flow are constructed. Further, considering the coupling interaction between the transmission and distribution networks, a collaborative planning model of transmission and distribution networks based on second-order cone relaxation (SOCR) is constructed. Secondly, in order to reduce the computational complexity of the model and ensure the global optimality of the model solution, a fast model solution method based on heterogeneous decomposition architecture is proposed. Thirdly, the multiple driving factors of the morphological evolution of transmission and distribution network are analyzed, the morphological evolution path and typical characteristics of transmission and distribution network are determined, and a wind-PV-ESS collaborative planning strategy considering the morphological evolution of a transmission and distribution network is proposed. Finally, the results show that, compared with the sprouting period, the overall economy of the development period and maturity period is improved by 3342 k$ and 5751 k$ respectively, and the effectiveness and necessity of the collaborative planning strategy proposed in this paper is verified.

Appropriate Volt–Var Curve Settings for PV Inverters Based on Distribution Network Characteristics Using Match Rate of Operating Point

This paper describes the process of setting up an appropriate volt–var curve for the reactive power control of a photovoltaic (PV) inverter interconnected to a distribution line that is voltage controlled by a load ratio control transformer (LRT). Computer simulations with 360 patterns of volt–var curves applied to five actual distribution line models are presented. The number of patterns was narrowed down to 23 by using voltage, distribution-line loss, number of LRT tap operations, and a new evaluation index, the match ratio. When a power-factor constraint is imposed on the PV inverter, it may not output the reactive power according to the volt–var curve depending on the active power output. The match rate is an index to show the percentage of the operating points of the PV inverter that conform with the volt–var curve. By evaluating the match rate, it can be demonstrated if the PV inverter efficiently contributes to the voltage control, which greatly contributes to narrowing of the volt–var curve. It is demonstrated that the volt–var curve obtained using the proposed method is superior in terms of voltage controllability, distribution line losses, and the number of LRT tap controls.

Economic Evaluation Method of Incremental Distribution Network Project Based on Value Theory

In order to improve the weight calculation accuracy and overall evaluation accuracy of incremental distribution network project economic evaluation, a new incremental distribution network project economic evaluation method based on value theory is proposed in this paper. Firstly, based on the value theory, the economic characteristics of incremental distribution network are analyzed. Secondly, the economic benefits of the incremental distribution network project are calculated from the perspectives of DG owned operators and DG owned users. Finally, based on the calculation results of economic benefits, this paper constructs the evaluation index system, calculates the evaluation weight from both subjective and objective aspects, and finally completes the economic evaluation of incremental distribution network project. The experimental results show that compared with the traditional evaluation methods, this method can accurately calculate the evaluation weight, so as to obtain more accurate evaluation results.

State Estimation for Medium- and Low-Voltage Distribution Systems Considering Measurement Characteristics and Grounded Slack Bus

The medium voltage (MV) and low voltage (LV) distribution systems are usually built in a mixed three-phase three-wire and three-phase four-wire pattern, in which the conventional measurements are obtained through the two-wattmeter method (TWM) and three-wattmeter method (HWM). The existing three-phase state estimation (SE) models only involve the measurement characteristics of the HWM. Instead, a set of new and improved measurement equations are formulated in this paper for such buses measured by TWM, and the measurements include line-to-line complex power and virtual zero-sequence current. Along with the increasing underground cable, the neutral point of MV feeder head is normally grounded through a small resistance, and its voltage magnitude is not equal to zero. Accordingly, an accurate model for the slack bus together with its measurement equations is proposed herein, based on the conventional measurements and neutral point virtual measurement. Moreover, this work presents a three-phase SE model for MV and LV distribution systems that incorporates the constraints of zero-sequence current and zero injection, in combination with the exponentially weighted least squares method. The test results of the IEEE 34 bus system and IEEE 123 bus system verify that the proposed formulation takes full advantage of the measurements and structural characteristics of practical distribution networks, and simultaneously boosts the estimation accuracy.

Scheduling Strategy Optimization and Security Protection Technology in Smart Distribution Network

In the power system, distribution network is a very important link, and its operation quality and power supply reliability have a great impact on the whole social and economic development. Firstly, this paper analyzes the structure, function and characteristics of intelligent distribution network. Then it introduces the research status of optimization strategy based on genetic algorithm and its security protection technology, as well as the relevant basic theoretical knowledge. Then, aiming at the existing problems, the security protection system is designed for the power grid. Finally, through the performance test of the system, it is verified that the method is efficient and practical, and can effectively improve the security and stability of the power system, promote the further acceleration of China’s sustainable construction process, improve the benefit level of power supply enterprises, and achieve the goal of social and economic development.

Review on Reactive Power and Voltage Optimization of Active Distribution Network with Renewable Distributed Generation and Time-Varying Loads

With a high proportion of renewable distributed generation and time-varying load connected to the distribution network, great challenges have appeared in the reactive power optimization control of the active distribution networks. This paper first introduces the characteristics of active distribution networks, the mechanism and research status of wind power, photovoltaic, and other renewable distributed generators, and time-varying loads participating in reactive power and voltage optimization. Then, the paper summarizes the methods of reactive power optimization and voltage regulation of active distribution network, including multi-timescale voltage optimization, coordinated optimization of network reconfiguration and reactive power optimization, coordinated optimization of active and reactive power optimization based on model predictive control, hierarchical and zoning control of reactive power, and voltage and power electronic switch voltage regulation. The pros and cons of the reactive power optimization algorithms mentioned above are summarized. Finally, combined with the development trend of the energy Internet, the future directions of reactive power and voltage control technology in the active distribution network are discussed.

Iteration-Based Linearized Distribution-Level Locational Marginal Price for Three-Phase Unbalanced Distribution Systems

Distributed energy resources (DERs) are rocking the utilities’ business landscape. It calls for competitive market environments that incentivize DERs to form maximum operating efficiency. Among proposed pricing schemes, distribution-level locational marginal price (DLMP) is effective in signaling the marginal generation cost differences driven by energy losses and network constraints. It can be derived from a distribution-level optimal power flow (OPF) framework, as it essentially presents the sensitivity of optimized generation cost towards incremental loads. However, due to the high resistance-to-inductance ratio and unbalanced characteristics of distribution networks, computational affordable DLMPs are highly challenged. This article provides a linear-approximated DLMP that can be solved efficiently and generalized to account for reactive power flow, three-phase unbalanced loads and meshed network structure. The successive linear programming technique is introduced to enhance the model accuracy. Case studies on an IEEE 123-Bus system validate its accuracy against a nonlinear benchmark and capability in offering proper incentives.

Supplementary control based on current source coupling for improving dynamic characteristics of active distribution network

Supplementary control (SC) technology is widely leveraged by power supply companies in active distribution networks (ADNs) to improve their stability and dynamic characteristics. Yet, the existed SCs are generally implemented from inside the converter controllers of distributed generators (DGs) or active loads, so there is a need to redesign the internal physical structure of the existing controller, resulting in the increasing work amount of assembling and workability. This paper studies the specific R & D process of a novel external coupling type SC (ECSC), which is based upon current source injection (CSI-ECSC) for improving the dynamic characteristics of ADN. The SC current signals are coupled to the current sampling loop from outside the converter controller. And the employment of the existing current sample makes it unnecessary to redesign the internal physical structure of the existing controller. As a result, the SC assembling is simplified and its workability is improved. In this paper, a detailed exemplary ADN with direct-drive permanent magnet synchronous generator (PMSG) is firstly set up in math for full eigenvalue analysis. Then, the CSI-ECSC is designed with its control loop, interface circuit, and parameter setting. Furthermore, by using PSCAD/EMTDC, groups of case studies are conducted in ADNs where photovoltaics (PVs) and energy storage (ES) are included. Finally, the real-time hardware-in-the-loop (HIL) testing validates the functionality of the realized CSI-ECSC in RTDS.

Modeling and Control Strategy for Multiterminal Flexible DC Distribution Network with Echelon Utilization Power Battery

With the integration of distributed renewable energy to the distribution network and the development of multiterminal flexible DC transmission technology, multiterminal flexible DC distribution network has broad application prospects. At the same time, with the rapid development of new energy vehicles, the echelon utilization of power battery has become a research hotspot. By analyzing the characteristics of flexible DC distribution network and echelon utilization battery, the structure and control strategy of modular multilevel converter (MMC), DC solid-state transformer, photovoltaic power generation, wind power generation, and echelon utilization battery energy storage system are established, respectively, in this paper. To achieve a DC network connection of various types of power supply and load, this paper proposes a starting method of multiterminal flexible DC distribution network and a cooperative control strategy of the wind-solar-storage system. A six-terminal ring-shape DC distribution network model is built in real-time digital simulation (RTDS) platform. The simulation results show that the modeling methods and control strategies of each component in the real-time simulation model meet the operation requirements of the multiterminal flexible DC distribution network, which provides a reference for the construction and research of the flexible DC distribution network.