Large Power System Networks Research Articles

An Analysis of The Effect of Heterogeneously Distributed Inertia Constant in Generation Mix Power System by Using the Graph Theory and Dijkstra’s Algorithm

A modern power system with a generation mix of conventional and renewable energy sources (RES) creates stability issues. This requires a detailed analysis of the system with an exact share of active power through the generating sources according to nature, location, and control. The interconnected network with a large number of rotating machines at the generation side works coherently with each other. As the share of RES increases, it leads to reduce rotational inertia in the power system. The most important factor affected by inertia is the rate of change of frequency (RoCoF). The higher RoCoF leads the system more vulnerable to small disturbances in the power system. In a large power system network with numerous generating sources and transmission lines, it is difficult to determine the availability of inertia in the system. This paper incorporates the concept of graph theory in the IEEE 30 bus system to analyze the impact of heterogenous inertia distribution on frequency stability. The graph theory network gives the idea about the distance between the nodes and it is helpful to find the share of power from the generating sources. In this paper, we calculate the shortest path between the nodes or substations by using Dijkstra's algorithm. The betweenness centrality of the node detects the vulnerable nodes in the system from the frequency response point of view.

Multimachine Stability Enhancement using Fuzzy- Logic based PSS tuning with Shunt FACTS Device

In Large power system network the dynamic behaviour of system is nonlinear in nature. Due to disturbance the system stability cannot be maintained, which leads to outage of power equipment. In order to restore the system parameter after perturbance, coordination control damping is essential. Coordination control damping can be achieved by using fuzzy based PSS and STATCOM in multimachine system for sever disturbance. Due to perturbance the system loss its synchronism and the system parameter deviate from the nominal value. With the effective damping control technique proposed in this article is to minimize the integral square error of speed deviation. Two area 4-Machine 11-bus test system considered and the simulation of proposed system is developed in Matlab/Simulink R2018a.

Detailed Transients Simulation of a Doubly Fed Induction Generator Wind Turbine System with the EMTP-Type OVNI Simulator

Doubly fed induction generator wind turbines are increasingly used in new wind turbine installations all over the world. Growing concerns about the impact of a large number of these generators on transient and voltage stability of power system networks has led engineers to revisit modelling and simulation practices used for system stability analyses. In this paper, the latest advancements in design of the general purpose power system simulator OVNI developed at the University of British Columbia are presented, and its application to the simulation of a doubly fed induction generator (DFIG) wind turbine system is shown. Because OVNI is based on the EMTP methodology for accurate detailed modelling, and the Multilevel MATE (Multi-Area Thévenin Equivalent) concept, which, combined with hardware solutions, allows for fast simulation of large power system networks, it represents an ideal tool for testing and developing benchmark models of different wind turbine installations. Using the EMTP approach for modelling of a DFIG wind turbine system and its feeding power network we were able to study the responses of the wind turbine generator to different network events. The ultimate goal of our investigations is the development of a benchmarking process for testing different models of wind turbine generators and determining the range of validity of various degrees of approximations normally used for stability simulation purposes. Due to the rapid development of wind generation technology, it is essential to determine the minimum requirements for dynamic modeling of wind turbine generators for assessing impacts of their installations on the dynamic security and stability of power systems.

Review of Methods to Accelerate Electromagnetic Transient Simulation of Power Systems

Converter-based generators are increasingly replacing classical synchronous generation, resulting in significant challenges to the operation and planning of modern power systems. Power electronics (PE)-based equipment, along with non-linear PE-driven loads, introduce time-varying characteristics and fast switching behavior that increases the complexity of the power system model. Faster control actions are needed to overcome the fast switching dynamics to ensure the reliability and stability of future power systems. Thus, this requires advanced and detailed simulation methods and tools with highly accurate equivalent models to embody the relatively slower electromechanical to faster electromagnetic transient (EMT) phenomena. Conventional transient stability analysis using positive-sequence simulators has become inadequate for representing converter-dominated power systems, while EMT simulators suffer from the high computational burden. This review paper presents accelerated EMT simulation methods and tools that are categorized and discussed in three topics: system equivalents, simulation methods, and accelerating tools. Dynamic system equivalent techniques are discussed to model small to large interconnected external systems of the grid network. Moreover, a systematic review is made for existing EMT simulation methods, along with advanced co-simulation methods, for addressing simulation speed and accuracy issues in large power system networks. Emerging hardware-based simulation tools are reviewed that reduce the computational burden and increase the simulation efficiency of the power system model. Challenges and trends in EMT simulation are also presented and concluded by providing perspectives on this research topic.

Optimising power system frequency stability using virtual inertia from inverter‐based renewable energy generation

The objective of this study is to optimise the use of virtual inertia given a virtual inertia budget and a network topology. Following a brief investigation into inertia distribution, it was observed that distributed inertia is more effective than centralised inertia for a large and sparse power system network. A subsection of the South African transmission network, the Western Transmission network, is expected to host large-scale inverter-based generation. The total power system inertia is in decline due to the large-scale integration of inverter-based renewable energy generation. In the literature, mitigation methods such as virtual inertia and ‘noise-cancelling’ network topology design has been proposed to improve frequency stability. In this study, the Western Transmission network is modelled as a network of coupled oscillators. A state-space model for the power system network is developed with virtual inertia as a feedback control loop. The H 2 -norm is used to design optimal feedback control through virtual inertia allocation/distribution, to increase power system frequency stability. The results show that the optimal distribution significantly improves system frequency stability by decreasing the rate of change of frequency and delaying the time to reach similar frequency nadir values.

Reduced Order Modeling of Large Power Grid Model with POD-DEIM

This paper addresses the issue of computational complexity of a large power system network, specifically the swing dynamics problem. Swing equation is nonlinear model which required mathematical model to be solved for simulating the swing dynamics. It has been seen that numerical computation becomes intractable for such models. This issue can be solved with model order reduction. Dynamics of interest is represented by a minimum size aims to reduce the computational time and memory requirement. Proper Orthogonal Decomposition technique is most often used to reduce computational efforts. However, it does not reduce the size of the nonlinear function. The discrete empirical interpolation method was proposed for POD to overcome the large size of nonlinear function by providing its discrete computations. The POD-DEIM approach is experimented on power grid network model to show significant reduction in computational cost with high degree of accuracy.

Hybrid approach for congestion management using optimal placement of distributed generator

ABSTRACTCongestion management (CM) in a large power system network is a difficult task which can be solved by placing one or more distributed generators (DGs) on congested lines. The first concern is to determine the exact location of congested line for the placement of optimal size of DG so that cost can be minimised. In this work, hybridisation of firefly technique and differential evolution optimisation search has been proposed, which manages congestion effectively by rescheduling of generators satisfying the system constraints both technically and economically in the deregulated market scenario. To validate the proposed hybrid approach, results have been compared with firefly optimisation technique results. It is observed that the hybrid approach is an efficient tool in handling CM resulting in a secure operation to reduce flows in the heavily loaded lines with low system loss and increasing power capability with improved stability of network by controlling power flows in the network.

A methodology for computing robust dynamic equivalents of large power systems

This paper presents a simple and computationally efficient methodology for computing robust dynamic equivalents. While simple to implement, the methodology involves many factors, and these are discussed, explained and justified throughout the paper. It classifies clusters of generators to be equivalenced by their electrical distances, and identifies second order reduced models for them. It maps them into classical synchronous machine models and aggregates them. Reduction of the network is based on the Ward PV method. The quality of the dynamic equivalent, in terms of flexibility and reduced dependence on disturbances, is automatically verified by performance indices. The methodology can easily be embedded in time domain simulation packages. Two large real power system networks are used for testing the performance of the approach.

A Community-based Partitioning Approach for Phasor Measurement Unit Placement in Large Systems

A phasor measurement unit placement scheme is developed in this article that ensures complete observability of large systems while reducing the computational burden of optimization. Redundancy in measurement of the critical buses of the network that are identified based on system studies and/or topologies is also provided by the proposed methodology. The community-based islanding approach initially partitions the system into smaller islands. Placement of phasor measurement units in these islands is then computed using integer linear programming. A bound is also developed to find the maximum error from a global optimal solution. The proposed technique is applied to standard IEEE systems as well as on more realistic power system networks. The results indicate that the proposed technique optimizes the benefits of having phasor measurement units at strategic locations of a large power system network without the associated computational burdens.

Early prediction of surge arrester failures by dielectric characterization

Metal oxide varistors based on ceramic technology are extensively used nowadays as limiting voltage devices, covering an amazing range of systems from microelectronics equipment up to very large power system networks. These varistors are formed through the sintering of a mixture of ZnO or SnO2 metal oxides with several other metal oxide dopants containing the elements of O<sub<2, Bi, Sb, and Cr [1], [2]. The electrical behavior is governed by the microstructure in which the conductive zinc oxide grains are surrounded by a resistive intergranular boundary of other oxides, forming “microcomponents” and acting like diodes with relatively low voltage turn-on [3]. This results in a highly nonlinear voltage-dependent conduction mechanism, or the I-V characteristic.

Innovative Modeling and Simulation of Electric Power Systems

Abstract: In the last decades many papers and textbooks devoted to the computer modeling and analysis of large power system network have been written. For the most part the models and analysis techniques have been developed for large interconnected transmission systems (TS) and synchronous generators. Little, relatively, attention was devoted to the distribution systems (DS) and its major components. As a result, the distribution engineer has not had the same number of tools as the systems engineer to analyze the distribution system under steady-state (power flow) and fault (short circuit) conditions. Without these tools the distribution engineer has been left in the dark (no pun intended) as to the operating characteristics of distribution feeders. Line segments in distribution systems are inherently unsymmetrical. That is, the spacing distances between phases are not equal and the lines are not transposed; as is typically done on high voltage transmission lines. The non-symmetry results in unequal self and mutual impedances. Couple this with line currents that are typically unbalanced and a potential for severe voltage unbalances can occur along with additional line power losses. For a four wire grounded Wye line, the unbalanced operation leads to currents flowing in the neutral and dirt. Original literature uses the term “dirt current”. In other literature, the reader will also find the terms “ground” or “earth dirt”. This presentation will develop a method for the computation of the “neutral” and “dirt currents” and the power losses that are a result of these currents.

A Real-Time Attack Localization Algorithm for Large Power System Networks Using Graph-Theoretic Techniques

We develop a graph-theoretic algorithm for localizing the physical manifestation of attacks or disturbances in large power system networks using real-time synchrophasor measurements. We assume the attack enters through the electro-mechanical swing dynamics of the synchronous generators in the grid as an unknown additive disturbance. Considering the grid to be divided into coherent areas, we pose the problem as to localize which area the attack may have entered using relevant information extracted from the phasor measurement data. Our approach to solve this problem consists of three main steps. We first run a phasor-based model reduction algorithm by which a dynamic equivalent of the clustered network can be identified in real-time. Second, in parallel, we run a system identification in each area to identify a transfer matrix model for the full-order power system. Thereafter, we exploit the underlying graph-theoretic properties of the identified reduced-order topology, create a set of localization keys, and compare these keys with a selected set of transfer function residues. We validate our results using a detailed case study of the two-area Kundur model and the IEEE 39-bus power system.

Distributed Optimization Algorithms for Wide-Area Oscillation Monitoring in Power Systems Using Interregional PMU-PDC Architectures

In this paper, we present a set of distributed algorithms for estimating the electro-mechanical oscillation modes of large power system networks using synchrophasors. With the number of phasor measurement units (PMUs) in the North American grid scaling up to the thousands, system operators are gradually inclining toward distributed cyber-physical architectures for executing wide-area monitoring and control operations. Traditional centralized approaches, in fact, are anticipated to become untenable soon due to various factors such as data volume, security, communication overhead, and failure to adhere to real-time deadlines. To address this challenge, we propose three different communication and computational architectures by which estimators located at the control centers of various utility companies can run local optimization algorithms using local PMU data, and thereafter communicate with other estimators to reach a global solution. Both synchronous and asynchronous communications are considered. Each architecture integrates a centralized Prony-based algorithm with several variants of alternating direction method of multipliers (ADMM). We discuss the relative advantages and bottlenecks of each architecture using simulations of IEEE 68-bus and IEEE 145-bus power system, as well as an Exo-GENI-based software defined network.

Motoring Protection Model Implementations and Simulations for Generator Protection

2 Abstract: One of the most delicate, costlier and important component of the power system is synchronous generator and a principal requisite for the power system stability and reliability. Since synchronous generators are rotating machines and always operate in parallel with a large power system network, so they might be prone to a number of internal faults or abnormal operating conditions such as loss of field, over excitation, overvoltage, current unbalance, loss of prime mover etc. Thus, the synchronous generators need to be protected very cautiously from such types of abnormal conditions. This paper has presented the modelling, simulation and analysis of a complete motoring protection system constructed on the software MATLAB/SIMULINK ® for the motoring condition of a large

Applying a robust control technique to damp low frequency oscillations in the WECC

This paper demonstrates the application of a robust technique for damping low frequency oscillations in the WECC. The control is designed by extending the logic of SMA and integrating it with the LMI technique to develop a single-gain feedback controller that is capable of damping oscillations in large systems. It is an integrated form of control because it combines different controllers together so as to prevent any negative interaction between the individual controls. The proposed technique is initially applied to an equivalent model of the WECC system developed in MATLAB and then transferred to a larger and more detailed version created in PSLF. The controllers initially used for the design are the two HVDC lines and an SVC. Three ESDs are added to the model for the improvement of the control. The results indicate that the technique proposed in this paper provides adequate damping to the relevant modes of oscillations and that it can be easily applied to large and complex power system networks.

Parallel solution of large power system networks using the Multi-Area Thévenin Equivalents (MATE) algorithm

An implementation of the Multi-Area Thévenin Equivalents (MATE) partitioning framework for the parallel solution of large power system matrices is described in this paper. The solution of the Western Electricity Coordinating Council (WECC) system, of approximately 15,000 buses, obtained using both traditional sparse techniques and MATE were compared. As the main result of this project, the MATE algorithm achieved speedups of up to 7 times with respect to a well-known sparse linear system solver. Theoretical background in addition to the implementation approach, results, as well as limitations of the MATE algorithm are discussed.

A Common Information Model (CIM) Toolkit Framework Implemented in Java

The common information model (CIM) is an object-oriented representation of a power system and is used primarily as a data exchange format for power system operational control systems. CIM has the potential to be used as much more than an intermediary exchange language. This paper explores the possible use of CIM as the core of a power systems analytical toolkit for storing, processing, extracting, and exchanging data directly from CIM objects. To this end, this paper discusses solutions to some of the challenges in storing and processing large power system network models as native Java objects without sacrificing reliability and robustness. This paper highlights the advantages provided by such a system when dealing with extensions to the CIM standard and overcoming the problems posed with simultaneously maintaining backward compatibility without sacrificing a higher level of detail. This paper also addresses the issue of data processing performance in contrast to other approaches.

A DIAKOPTICAL TECHNIQUE FOR SHORT CIRCUIT STUDIES OF LARGE SIZE POWER SYSTEM NETWORKS

ABSTRACT The paper presents a diakoptical technique for deriving the impedance matrices required for short circuit studies of large size power system networks by tearing the system into smaller subsystems by cutting appropriate tie lines. The bus admittance matrix is formed for the sequence networks of each subsystem and then modified later by means of diakoptics. The simulation of mutual couplings is taken into account in the zero sequence networks. Only columns of the impedance matrices corresponding to the faulted buses are computed in the proposed technique which is based on factorized bus admittance matrices and full exploitation of sparsity. The proposed technique can either be used in a single–processor computer for sequential solution of torn subsystems or in a multicomputer configuration for a faster solution by parallel processing of torn subsystems. Both symmetrical and unsymmetrical faults are studied by using the proposed technique which produces exact results as the untorn system. No iterati...

Efficient treatment of parameter errors in power system state estimation

This paper presents efficient data structure management algorithms to reduce the amount of CPU time required during the recomputational process of updating the Jacobian matrix and mismatching vector for power system state estimation. This updating is required after the identification of bad data, such as a parameter error of a line in a power network, in order to remove their influence on the state estimation process. The performance of the proposed algorithms is evaluated using several large power system networks. A considerable reduction in the CPU time is obtained with the proposed algorithms.

Two-level state estimation for large power system. Part 1: Algorithms and Part 2: Computational experience

The author comments on static state estimation for large power system networks and the six two-level algorithms which were discussed in the original paper. He also looks at the results of extensive simulations carried out on a realistic power system network. One of the authors of the original paper replies to the comments. >