Characteristics Of Power Grid Research Articles

A Review of the Research on the Wide-Band Oscillation Analysis and Suppression of Renewable Energy Grid-Connected Systems

With the continuous expansion of the scale of power generated by grid-connected renewable energy, the form and operation characteristics of power grids have undergone significant changes, and the power electronic characteristics of power systems are prominent, resulting in the frequent occurrence of wide-band oscillation problems when renewable energy power generation equipment is connected to a power grid. Oscillation has the characteristics of nonlinearity and has an oscillation frequency ranging from a few hertz to several thousand hertz or more, which seriously threatens the stable operation of power grids. This paper summarizes the wide-band oscillation events that occur worldwide under the background of renewable energy access to power grids, classifies the wide-band oscillation events according to the distribution of oscillation frequency bands, and sorts out the characteristics of various oscillations. From the perspectives of the source side and network side, the existing oscillation suppression measures are classified and prospected.

Improvement of the Power System's Transient Stability Using the Unified Power Flow Controller with Fuzzy Logic Technique

By combining the functions of many FACTS (flexible alternative current transmission systems) devices into a single unit, the UPFC (unified power flow controller) is the most efficient FACTS device available. Two voltage converters work together to form the Unified Power Flow Controller, a flexible tool for enhancing voltage regulation, power flow management, and power system stability. Both converters rely heavily on their control methods. This article discusses the power flow mechanism in a transmission line, which is necessary for understanding the functioning of UPFC in a transmission line and using a standard PI controller with voltage references in the control circuit of both converters. This study aims to enhance the power system's dependability and stability by developing a smart support-based UPFC device. Fuzzy logic is a useful tool for controlling UPFC equipment in a variety of failure scenarios. The fuzzy logic controller contrasts power grid characteristics such as a rotor speed deviation to a reference value to create operational pulses for the voltage source converter in the UPFC system. The suggested model will be tested using MATLAB simulation. The success of the proposed model is shown by thoroughly comparing simulation results to those of previously established models. This research paper's original contribution is the creation of a smart support-based UPFC device with fuzzy logic control. By comparing power system parameters such as rotor speed deviation to a reference value and generating operational pulses for the voltage source converter in the UPFC system, this technique increases the electricity grid's dependability and stability. The effectiveness of the suggested model is proved by a comparison of simulation results obtained in a MATLAB environment with those obtained from previously developed models.

Research on Parallel Control Strategy of Grid-forming of Power Conversion System

A high proportion of power electronic equipment, distributed energy, and other new energy access to the grid system, low inertia and low damping to the power grid system, these kinds of power grid characteristics in power electric wire aging remote mountains or island areas, therefore, need energy storage system under the microgrid can provide inertial support for load or grid, improve the system damping characteristics. On this basis, the grid-forming control is proposed, so that the power conversion system can work under the off-grid, and can provide inertia and damping to maintain the system stability. In addition, large-scale energy storage systems often require multiple machines operating in parallel. In this paper, the topology of NPC for a power conversion system is studied and analyzed in off-grid mode.

Modelling and analysis of LCC‐HVDC converter station for harmonic coupling of AC/DC power grid during geomagnetic storm

AbstractIn this paper, the problem of harmonic coupling between the converter transformer and the converter under the action of geomagnetically induced current (GIC) is proposed to be investigated. Firstly, a model of a 12‐pulse line commutated converter high voltage direct current (LCC‐HVDC) converter station based on harmonic state space (HSS) theory is established. Secondly, the harmonic components of the interaction between the AC‐side harmonic current and the DC‐side harmonic voltage are qualitatively analyzed by using the harmonic modulation theory. Through the simulation model and harmonic state space (HSS) calculation model, the harmonic coupling characteristics of power grid are analyzed. Finally, the harmonic current and voltage amplitude of AC / DC power grid under different GIC are calculated, and the characteristics and rules of AC / DC harmonic propagation are revealed. Among them, the amplitude of the 2nd harmonic current on the AC side and the 3rd harmonic current on the DC side increases linearly with the GIC. In addition, the 3rd and 9th harmonics on the AC side are also greatly affected by the magnetic bias of the converter.

Overview on Transactive Energy—Advantages and Challenges for Weak Power Grids

This document lists some challenges that researchers face when implementing transactive energy in weak power grids. These challenges often include high voltage fluctuations, limited generation, high line loadability, and unbalanced grids. The operation of transactive energy, as well as optimization techniques, are also considered, highlighting the performance and functionalities depending on power grid characteristics and market topology. Some of the most used optimization techniques for market clearing, considering the characteristics and topology, are presented as part of the research work.In addition, this paper compares different market topologies and highlights their advantages and challenges. Furthermore, this paper contains a brief description of the interoperability frameworks applied to a smart grid.As a result, it was determined that interoperability is necessary for the proper functioning of the grid. Moreover, all methods were found to be effective for their purpose from the user’s point of view as each technique has different characteristics relevant to the user and the grid. It was concluded that it is convenient to combine the optimization techniques to consider different constraints in the market clearing.

Reliable Framework for the Optimal Allocation of Harmonic Emission Limits

Power quality issues have been investigated for decades, but the changes in power grid characteristics and the trend to power-electronic-coupled installations raises additional requirements and puts harmonics into the spotlight. The increasing share of distorting installations and the change of harmonic dissipation paths emphasize the need for reliable harmonic allocation methods. The methods reported in VDE-AR-N 4130 and IEC/TR 61000-3-6 do not reliably allocate harmonic emission limits and can result in harmonic voltages exceeding the planning levels. A novel approach based on non-linear constraint optimization is presented, which promises reliable allocation and the compliance to planning levels while relying on the same input data. This paper conducts a comparison of the three methods regarding their allocation performance, reliability and suitability for embedding in a power quality grid planning process. The study case is developed based on an IEC example grid. The results indicate that the novel method avoids the shortcomings of the VDE and IEC method namely under- and over-allocation as well as their significant uncertainty and may form the basis of a reliable harmonic grid planning process.

Time Sequence Machine Learning-Based Data Intrusion Detection for Smart Voltage Source Converter-Enabled Power Grid

Smart inverters of distributed energy resources can enable cloud computing, condition monitoring, result visualization, remote control, and peer-to-peer energy trading in advanced power systems. However, the advent of data injection attacks in the communication architecture can alter measurement characteristics of power grids and have devastating consequences. In this article, we propose a time sequence machine learning-based anomaly detection methodology for detecting cyber intrusion into control signal setpoints and dc voltage signal measurement bias of the voltage source converter (VSC) in wind generators. We first investigated the effects of four types of denial of service, tampering signal, and stealthy-type data intrusion attacks on smart VSCs and overall wind farms. We then proposed a novel time sequence machine learning-based intrusion detection framework that can be implemented to detect different cyberattacks in the VSCs. The performance of the proposed framework has been compared with that of autoencoder and clustering-based intrusion detection framework. The proposed framework was validated by using the IEEE 39 bus power system in the presence of four wind farms in different locations. Using several metrics for intrusion detection performance, we validated the effectiveness of the proposed framework.

Inertia and Grid Impedance Emulation of Power Grid for Stability Test of Grid-Forming Converter

The virtual synchronous generator (VSG) control is a promising solution for the grid-forming converters to enhance the inertia of the converter-based power grid. The virtual inertia and output impedance of the VSG are the important behaviors to be focused. However, the virtual inertia of grid-forming converters may cause active power oscillation due to the interaction with the power inertia of grid through the low-frequency band grid impedance. Besides, the resonance can be also triggered by the interaction between middle-frequency impedance of power grid and output impedance of converter. In order to test the stability of grid-forming converter, accurate emulation of grid behaviors from more aspects, including inertia and impedance under wider frequency ranges, is becoming critical. This article proposes a grid emulation method to mimic the inertia and impedance characteristics of power grid, targeting for the stability test of grid-forming converter under multifrequency bands. A high-switching-frequency converter and a low-switching-frequency converter are adopted in the proposed emulator structure to achieve both high capability in respect to control bandwidth and power level. Moreover, the virtual impedance control is integrated with the VSG control to emulate the line impedance and inertia within relatively wider frequency ranges. The realization of virtual impedance is achieved without derivation terms nor low pass filter. Finally, the performance of the proposed emulator is verified by various simulations and experimental measurements.

Generalized discrete equivalent model for PV system with various types of faults and PV penetration levels

As the rapid and continually proliferation of photovoltaic (PV) systems are connected to the power system, the load structure are changeable to lack an accurate dynamic discrete equivalent model to describe its characteristics of power grid. In this study, the generalized discrete-time equivalent model (GDEM) of PV system using a fourth-order dynamic equivalent model for representing the physical characteristics of PV power stations are proposed in power system dynamic studies. The paper then investigates the inherent relations among GDEM parameters in the discrete-time models of PV system to facilitate the GDEM parameters estimation in PV system. Finally, the least square method (LSM) was to identify the GDEM of PV system parameters, and various types of ground faults and PV penetration rate levels is adopted to verify the dynamic characteristics of the proposed GDEM of PV system in power system simulations.

Real-World Subsynchronous Oscillation Events in Power Grids With High Penetrations of Inverter-Based Resources

This paper presents a survey of real-world subsynchronous oscillation events associated with inverter-based resources (IBR) over the past decade. The focus is on those oscillations in the subsynchronous frequency range known to be influenced by power grid characteristics, e.g., series compensation or low system strength. A brief overview of the historical events is presented followed by detailed descriptions of a series of events. This paper also examines causation mechanisms and proposes future research directions to meet grid needs worldwide.

An integrated modeling framework for cascading failure study and robustness assessment of cyber-coupled power grids

The extensive deployment of information and communication technologies significantly changes the characteristics of power grids. In this paper, we propose an integrated modeling framework for studying cascading failure and assessing the robustness of cyber-coupled power grids. By taking the perspective of cyber–physical systems, this framework depicts the electrical characteristics of the physical network, the realistic monitoring, control, and protection functions provided by the coupled cyber network, and integration with decentralized functions. It also includes a flow chart that generates a sequence of failure events in cyber-coupled power grids for simulating cascading failure. Based on the framework, a series of specific models can be constructed by incorporating concrete considerations. We demonstrate the robustness assessment of cyber-coupled power grids by one specific case study based on the modeling framework with appropriate assumptions made. Simulation results on four power test cases show that the cyber network can help effectively mitigate cascading failure and thus enhance the robustness of the grid. Moreover, the faults from the cyber layer can intensify the failure cascade and lead to a catastrophic power outage.

Measurement of Power Grid Resilience Based on a Dynamic Inoperability Input–Output Model

The increase in global natural disasters, emergencies, and terrorist attacks brings great challenges to the flexible operation of power grids. The research on the flexibility of power grids becomes more and more important. At the same time, the rapid development of renewable energy and smart grids also provides new opportunities for research of flexible power grids. Based on the dynamic inoperability input–output model (DIIM), this study creatively uses the node transmission power to represent the relationship between nodes in the power grid and then studies the resilience measurement of the power grid. First, the significance of studying power grid resilience is discussed, and the absorption and recovery capacity of power grid resilience is described. Second, the power grid resilience measurement model based on the DIIM is established, and a theoretical analysis is carried out. Using the characteristics of inoperability, the power grid resilience is measured from the time aspect, and the characteristics of the model are analyzed at the same time. On the basis of theoretical analysis, this study also provides a control strategy to improve the grid resilience, which has good convenience and applicability. Finally, the theoretical analysis method is applied to a power grid example, and the correctness and effectiveness are verified. The measurement model can intuitively display the resilience characteristics of power grids and provide theoretical support for management and emergency response.

Understanding Communities From a New Functional Perspective in Power Grids

The contributions of this article include a new concept, a new question, and a new method. This article proposes the concept of functional community, which is different from conventional topological community. Functional community is defined with two meanings: (1) tighter internal coupling for better efficiency within the same community; (2) more internal transmission from source to sink nodes within the same community. Then a new question about how to detect functional communities in power grids is analyzed, and most existing algorithms are not applicable. Therefore, a new method is put forward. Corresponding to meaning 1, electrical coupling strength (ECS) is defined to replace conventional adjacency matrix; corresponding to meaning 2, power supply strength is defined and integrated with ECS to form the newly defined electrical functional strength. Based on these two changes, we apply the proposed power supply modularity as a benchmark to evaluate any partitioning of power grids. Moreover, the Newman fast algorithm is modified with power supply modularity maximization to detect functional communities in power grids. The capability of the proposed partitioning method is demonstrated via the IEEE-118, IEEE-300 bus systems, and an Italian power grid. We argue that the conventional topological modularity may exaggerate the community characteristics of power grids and is inferior to the power supply modularity in detecting some functional features in communities. The work can also give inspiration to other engineering networks for functional communities.

AUTOMATED MONITORING OF TIME SYNCHRONISATION DEVICES AND DIGITAL PROCESSING OF VECTOR MEASUREMENTS OF DYNAMIC CHARACTERISTICS OF SMART GRID POWER SYSTEMS

Currently, customers of energy companies use devices to generate electricity (solar panels, windmills, etc.) and return energy to the grid to save costs or generate income. Therefore, it is urgent to solve the problem of creating an automated system for diagnosing the quality of electricity for consumers who use renewable sources of electricity. The purpose of this study was to improve the efficiency of management in intelligent SMART Grid power systems. To fulfil the said purpose, it was proposed to use an automated system for monitoring synchro signals of PMU microprocessor equipment and software tools for digital processing and statistical analysis of the results of synchronised vector measurements of dynamic characteristics of power grids. Software tools for digital processing and statistical analysis of the obtained vector measurement data were developed. Linear regression, Random Forest Regression, and Ridge regression methods were employed to analyse and predict electricity quality indicators. The results of a comparative analysis of the obtained results of the predictive model were presented. To conduct experimental studies, a laboratory sample of a quality control device for generating synchro signals was developed and manufactured, which directly affects the reliability of digital data from distributed synchronised vector measurements in transient modes (in real time). The multichannel nature of the device increases the performance and reliability of the automated monitoring system. The paper presents the results of experimental studies of the device as a part of the developed laboratory stand, which is connected to the current local IP network of the National University of Life and Environmental Sciences of Ukraine. The practical significance of the conducted experimental studies lies in the establishment of the technical possibility of simultaneous monitoring of time synchronisation signals generated by two GPS receivers. In this case, it is obvious to increase the performance of the developed and manufactured device for monitoring the quality of clock signal generation, compared to a single-channel one. This material can be useful for engineers who design electrical systems connected to renewable energy sources.

Architecture, Key Technologies and Applications of Load Dispatching in China Power Grid

With the development of renewable energy and the changes in the characteristics of power grid, it is becoming increasingly difficult to balance power supply and demand in space and time. In addition, the requirement for improved dispatching capability of power grid is increasing. Therefore, the potential of flexible load dispatching should be realized, which can promote the large-scale consumption of renewable energy and the construction of new power grid. Based on the analysis of existing load dispatching studies and the differences in the characteristics of domestic and foreign load dispatchings, a technical architecture and several key technologies are proposed for load resources to participate in power grid dispatching under the new situation, i.e., the autonomous collaborative control system of load dispatching. This system implements the multi-layer coordinated control of main, distribution and micro grids (load aggregators). Adjustable load resources are aggregated through an aggregator operation platform and connected with a dispatcher load regulator platform to realize real-time data interaction with dispatching agencies as well as the monitoring, control, and marketing of aggregators. It supports the load resources to participate in network-wide dispatching optimization via continuous power adjustment. Several key technologies such as the control mode, load modeling, dispatching strategy, and safety protection are also elaborated. Through the closed-loop control of orderly charging piles and energy storage clusters in the North China Power Grid, the feasibility of the proposed architecture and key technologies is verified. This route has successively supported multiple adjustable load aggregators to participate in the ancillary services market of North China Power Grid for peak-shaving. Finally, the technical challenges of load resources participating in power grid dispatching under the dual carbon goals are discussed and prospected.

The multi-depot electric vehicle scheduling problem with power grid characteristics

Electric buses can bring significant environmental and social benefits in the future public transportation systems. However, the large-scale adoption of electric buses faces major technical challenges caused by not only the limited running range and long charging time, but also the complex power grid characteristics, such as time-of-use (TOU) electricity tariffs and peak load risk. On one hand, the operation cost is determined by the TOU pricing and vehicle schedule. On the other hand, the unbalanced charging demand resulting from the vehicle schedule will cause peak load risk and pose a potential threat to the power grid safety. With the increasing penetration of electric buses, there is a real need to carefully design and manage electric bus scheduling to not only reduce the system costs but also ensure power grid safety. In this paper, we introduce a bi-objective multi-depot electric vehicle scheduling problem, a new generalization to the vehicle scheduling problem where the effects of TOU pricing and peak load risk are explicitly considered. The dual objectives are to minimize the total operation cost and to minimize the peak load resulting from concurrent recharging activities, as constrained by the running range of the electric buses and the capacity of charging depots/stations. A time-expanded network model is devised to represent this problem, while the bi-objective optimization model is reformulated by the lexicographic method. We propose a tailored branch-and-price method to solve the problem. Heuristics and a trip chain pool strategy are embedded into the branch-and-price method to expedite the computation time. Our method is validated through a benchmark network and a real-world bus network in Guangzhou, China. The results demonstrate that our method is effective in cost savings and peak load leveling, and far outperforms the off-the-shelf solver with respect to solution quality and computation efficiency. The real-world application results show that compared to state-of-the-practice, the peak load can be significantly reduced, on top of cost and fleet size savings.

Research on multi-label classification method of transformer based on DBSCAN (Density-Based Spatial Clustering of Applications with Noise) clustering algorithm

With the improvement of the intelligent level of power grid and the enhancement of the integrated characteristics of power grid, the degree of discretization of massive data of power equipment gradually increases, which brings great challenges to the safe and stable operation of power grid. How to process and analyze data effectively has become an important research content. Transformer is an important electrical equipment, therefore it is of great significance to monitor the operation status of transformer, to construct transformer operation characteristic label system based on multi-source heterogeneous data, and to realize multi-label classification function. In this paper, a transformer multi-label classification method of transformer based on DBSCAN(Density-Based Spatial Clustering of Applications with Noise) clustering algorithm is proposed, which can accurately identify outliers as Noise without input of the number of clustering to be divided, realize the key feature mining of transformer state, and to realize to provide flexible information association and historical data for dispatch and control operators.

Design and Implementation of Real-time Power Grid WebGIS Visualization Framework Based on New Generation Dispatching and Control System

With the strengthening of the integrated characteristics of power grid and the construction of the New Generation Dispatching and Control System with “physical distribution, logical integration”, the demand for global monitoring and analysis of power grid has gradually increased. On the basis of understanding of design of the new generation real-time dispatching and control data platform system, with the principles of componentization and servitization, the real-time power grid WebGIS visualization framework is designed and implemented. And this paper further introduces the design of the front-end secondary development interface and examples, as well as the cartographic generalization of the power grid WebGIS visual map. This framework has successfully supported the construction and online operation of several real-time power grid WebGIS visualization applications.

An Eigenvalues Method for Stability Analysis of Power Grid with Energy Storage Devices Based on Discrete Time Domain Model

The eigenvalue analysis based on state space model is an important method to study stability of power grid. With the large-scale access of energy storage devices and power electronics converters in power grid, the conventional state space modelling method suffers from complicated process of determining state variables and large calculation amount of eigenvalues, and nonlinear stability characteristics of power grid cannot be accurately reflected. To obtain the eigenvalues of power grid with energy storage devices more efficiently, this paper proposes a method for constructing state space model of power grid based on discrete time domain model (DTDM) and presents the corresponding stability criterion. Compared with the conventional state space modelling method, the nonlinear characteristics of components under proposed method can be linearized, and the constructed state space model can capture a wider range of system information including energy storage devices. Besides, the complete state space model of power grid can be obtained only according to the connection between component's DTDM and grid. Moreover, because eigenvalue solution under proposed method relies on the sparse grid node voltage matrix, the calculation of eigenvalues is simple and efficient, and it visually presents variation trend of eigenvalue and investigates the stability of system. Simulation results in Simulink/Matlab verify the correctness and effectiveness of proposed method.

How modular structure determines operational resilience of power grids

The synchronization stability has been analyzed as one of the important dynamical characteristics of power grids. In this study, we bring the operational perspective to the synchronization stability analysis by counting not only full but also partial synchronization between nodes. To do so, we introduce two distinct measures that estimate the operational resilience of power-grid nodes: functional secureness centrality and functional robustness centrality. We demonstrate the practical applicability of the measures in a model network motif and an IEEE test power grid. As a case study of German power grid, we reveal that the modular structure of a power grid and particular unidirectional current flow determine the distribution of the operational resilience of power-grid nodes. Reproducing our finding on clustered benchmark networks, we validate the modular effect on power grid stability and confirm that our measures can be the insightful tools to understand the power grids’ synchronization dynamics.