Large-scale Electric Power Systems Research Articles

Analysis of Subsynchronous Oscillation in a Multi Turbo-Generator Sets Power System Based on Electromechanical Wave Model

Electromechanical wave model is a new method in the research of generator-grid dynamic response of large scale electric power systems. Based on wave equations of elastic bearing transmit mechanical power and transmission line transmit magnetic power respectively, this paper built integrate electromechanical wave model of turbine-generator-grid with the example of No. 3 unit in Yimin Power Plant. With the help of electromechanical wave model, subsynchronous oscillation (SSO) example was given which indicated that the higher disturbance voltage, the bigger SSO amplitude; the larger damp, the smaller SSO amplitude, which will make the fluctuation become stable earlier. This conclusion has significant engineering value on reducing SSO amplitude of Yimin power plant.

A New Network Reduction Methodology for Power System Planning Studies

System planning on a large-scale electric power system is computationally challenging. Network reduction into a small system can significantly reduce the computational expense. The Ward equivalent technique is widely used for the reduction; however, it may not yield the same flow pattern as the original network. In this paper, a new methodology for network reduction is proposed and the results are compared with those from other methodologies.

Annual preventive maintenance scheduling for thermal units in an electric power system

The system approach to the problem of preventive maintenance scheduling for thermal units in a large scale electric power system is considered in this paper. The maintenance scheduling program determines a set of thermal units maintenance switch off for a time period of one year. This paper considers the application of dynamic programming and successive approximations method in determination of annual thermal unit maintenance schedules. The objective function is multiple component and consists of system operation costs and system reliability indices (loss-of-load-probability and expected unserved energy). The evaluation of these costs is performed through a simulation method which uses a cumulant load model. The software package, developed in FORTRAN and integrated with an ORACLE data base, produces many useful outputs.

AN INTELLIGENT LOAD SHEDDING SCHEME USING NEURAL NETWORKS AND NEURO-FUZZY

Load shedding is some of the essential requirement for maintaining security of modern power systems, particularly in competitive energy markets. This paper proposes an intelligent scheme for fast and accurate load shedding using neural networks for predicting the possible loss of load at the early stage and neuro-fuzzy for determining the amount of load shed in order to avoid a cascading outage. A large scale electrical power system has been considered to validate the performance of the proposed technique in determining the amount of load shed. The proposed techniques can provide tools for improving the reliability and continuity of power supply. This was confirmed by the results obtained in this research of which sample results are given in this paper.

Exploiting structure in large-scale electrical circuit and power system problems

The rapid increase in complexity of systems such as electrical circuits and power systems calls for the development of efficient numerical methods. In many cases, direct application of standardized methods for numerical problems is computationally not feasible or inefficient. However, the performance of such methods can be improved considerably by taking into account the structure of the underlying problem. In this paper, we describe when and how this – mathematical and/or physical – structure can be exploited to arrive at efficient algorithms that also suffer less from other numerical issues such as round-off errors. Eigenvalue and stability problems are considered in particular, but applications to other problems are shown as well.

Adaptive intelligent power systems: Active distribution networks

Electricity networks are extensive and well established. They form a key part of the infrastructure that supports industrialised society. These networks are moving from a period of stability to a time of potentially major transition, driven by a need for old equipment to be replaced, by government policy commitments to cleaner and renewable sources of electricity generation, and by change in the power industry. This paper looks at moves towards active distribution networks. The novel transmission and distribution systems of the future will challenge today's system designs. They will cope with variable voltages and frequencies, and will offer more flexible, sustainable options. Intelligent power networks will need innovation in several key areas of information technology. Active control of flexible, large-scale electrical power systems is required. Protection and control systems will have to react to faults and unusual transient behaviour and ensure recovery after such events. Real-time network simulation and performance analysis will be needed to provide decision support for system operators, and the inputs to energy and distribution management systems. Advanced sensors and measurement will be used to achieve higher degrees of network automation and better system control, while pervasive communications will allow networks to be reconfigured by intelligent systems.

Periodic Steady-State Analysis of Large-Scale Electric Systems Using PoincarÉ Map and Parallel Processing

An advanced time-domain representation suitable for accelerated periodic, steady-state solutions of large-scale electric power systems is introduced in this paper. The power system, which is three-phase in nature, is modeled by a set of ordinary differential equations. In addition to the all-important transmission lines' geometric imbalances, frequency-dependency and long-line effects, the transformers' saturation characteristics are also incorporated. In order to provide realistic initial conditions, the data needed for the modeling of the electric system is obtained from power-flow studies. The time domain solution of the overall set of differential equations is computed very reliably using a powerful blend of Newton methods and parallel processing techniques. Whereas the computation of the periodic steady-state solution is obtained with an acceleration procedure based on Newton methods and the Poincare/spl acute/ map, the application of parallel processing techniques using multithread programming speeds up further the time taken by the acceleration process to get to the periodic, steady-state solution. To show the effectiveness and versatility of the newly developed environment, transient and steady-state analysis are carried-out for a three-phase version of the IEEE 118-node system, where nonlinearities are incorporated in the form of the transformers' saturation characteristics and a static var compensator.

Development of a new adaptive LQG system generator for high‐speed damping control techniques of power system oscillation

AbstractWith the advent of interconnection of large‐scale electric power systems, many new dynamics power system problems have emerged, which include low‐frequency intersystem oscillations and many others. To date, most major generators in trunk electric power systems in Japan are equipped with supplementary excitation control, commonly referred to as the conventional single and two input PSS. However, low‐frequency oscillations still occur. It is difficult for these conventional PSS to improve the additional damping of power system oscillation, because of the hardware and design of fixed PSS control constants from a one‐machine infinite‐bus model. It has therefore become necessary to develop a new adaptive LQG system generator. This paper explains the development of the new adaptive LQG system and the simulation of low‐frequency and local mode oscillation for this new adaptive LQG system. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 30–40, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10109

Efficient simulation of the dynamic behaviour of large-scale electric power systems

A new algebro-differential equation system for the computation of dynamics and transients in electric power systems is formulated with the extended node voltage method exclusively on the basis of Kirchhoff's current law. Using the Singular Perturbation method, the systematic derivation of reduced-order power system models, which are adapted to the respective setting of tagles, is shown. The complete power system can be decomposed into a non-linear slow and a mid and a fast subsystem, which are homogeneous and usually linear and can thus also be solved analytically. Simulation examples show a good agreement with the results of the complete state equation system as well as large computing time gains.

Electric power systems operation by decision and control. The case revisited

We have witnessed sweeping changes in the organization of the electric power industry. This has had a profound effect on the industry's system operations and planning rules and has created a need to revisit its modeling, decision-making, and control principles. Historically, the decision and control of large-scale electric power systems has developed as the system interconnection has grown. The article begins by assessing principles of operation by decision and control for today's fully regulated industry. Following this summary, several major ongoing changes are interpreted from a systems point of view. It turns out that major challenges-economic, policy, and technical-are inherently systems problems. To illustrate this claim, new decision-making problems essential to having a successful generation business in a competitive industry are defined. This section is very detailed and describes the challenge created by introducing profit-based and risk management issues in the context of under the highly uncertain, often volatile, market price of electricity. Following that, the modified objectives of and decision making by future power delivery companies are described. The discussion shows how these regulatory issues directly impact the hierarchies and complexity of the related dynamic systems problem. Moreover, the so-called load serving entities or energy service providers will be critical to the technologies potentially useful to specific customers.

Optimal scheduling of large-scale hydrothermal power systems using the Lagrangian relaxation technique

This paper describes a method for scheduling large-scale hydrothermal power systems based on the Lagrangian relaxation technique. Lagrangian multipliers are introduced to decompose the original problem into small independent subproblems one for each generating unit, which are solved through a three level calculation structure. Using this approach, a large-scale hydrothermal electric power system could be treated as a precise general problem that takes into account the following among other factors: (a) random load demand; (b) non-linear cost function of thermal production; (c) variations of water head in hydroelectric plants; (d) non-linear function of hydroelectric output; (e) a system of cascaded hydroelectric plants including regulation reservoirs with limited spillage capacity. An economic interpretation of the results is given and an illustrative application of the technique is presented.

The large scale electric power system as a distributed continuum

By modeling an electric power system of generators and transmissions lines as a continuum, a nonlinear partial differential equation is written which exhibits the travelling wave behavior that has been observed in experiments with synchronized phasor measurements. The fact that disturbances spread through the interconnected power system with a certain velocity of propagation is reasonable but not quantitatively well understood. The model relates the velocity of propagation to parameters in the distributed model. Numerical simulations of the continuum model are presented.

A structure-based modeling and control of Electric power systems

This paper addresses the modeling and closed-loop control of large-scale electric power systems operating under normal conditions. A new structure-based modeling approach is introduced—an approach which reveals fundamental properties of power system dynamics, and offers physical insight into the interactions between its constituent subsystems. These properties and insights lead to the formulation of simple, higher level models which represent slow interactions among subsystems driven by slow load variations. The models which evolve from this structure-based approach enable hierarchical control design, without any a priori assumptions regarding the strength of the interactions among the subsystems. New control designs are thus proposed at both the subsystem and the interconnected system levels, a key element in their formulation being that both react to variables reflecting interactions between subsystems. Reactive power/voltage ( Q V ) control problems are used to illustrate the proposed modeling and control approach.

A past global optimization approach to VAr planning for the large scale electric power systems

In this paper, an innovative fast global optimization technique, hybrid partial gradient descent/simulated annealing (HPGDSA), for optimal VAr planning is presented. The HPGDSA is introduced to search the global optimal solution considering both quality and speed at the same time. The basic idea of the HPGDSA is that partial gradient descent and simulated annealing alternate with each other such that it reduces the CPU time of the conventional simulated annealing (SA) method while retaining the main characteristics of SA, i.e., the ability to get the global optimal solution. The HPGDSA was applied to a practical power system, Taiwan Power System (Tai-Power System), with satisfactory results.

A steady state voltage monitoring and control algorithm using localized least square minimization of load voltage deviations

This paper describes recent work on the theoretical and algorithmic enhancements of the MIT method for power system steady-state voltage monitoring and control. Under the conditions that no dynamic voltage problems are present, the method is intended primarily: to monitor steady-state voltage and reactive power conditions; to identify potential problem situations; and to make decisions regarding their severity. The developed method utilizes various reactive power resources on the power system to remedy voltage violations. The corrective actions suggested are either in the order assigned by the operator or according to efficiency criteria, determined by this algorithm. The corrective actions ensure minimum possible voltage deviations from a given desired voltage profile. Corrective actions are considered to be optimal in this sense. The method has the unique feature of identifying minimum number of most effective corrective actions so that voltages are maintained within the given limits. The method does not solve the exact load flow equations, and therefore it avoids inversion of a full system size matrix. Reactive power scheduling is computed so that the resulting load voltages, are within pre-specified target values. The computational time does not increase significantly with increase of power system size, since no inversion of a system size matrix is needed. Numerical tests on a small and large scale electric power system (IEEE 39 and New England 1726) are presented and analyzed.

Multimachine power system stabiliser design based on new LQR approach

The paper presents a novel systematic procedure for the design of excitation based stabilisers for large-scale interconnected electric power systems. The design method is based on newly obtained results in optimal linear quadratic regulator (LQR) design, and is superior to previously reported LQR approaches. A model of a five-machine interconnected power system which includes detailed representation of synchronous machines, excitation systems, turbines and speed governing mechanisms is considered. Stabilisers of structures are proposed. It is shown, through simulation studies, that the stabilisers improve the power system performance markedly, without excess demand for control action.

A new approach for optimal VAr sources planning in large scale electric power systems

A new approach is presented for contingency-constrained optimal volt ampere reactive (VAr) source planning in large-scale power systems. Features distinguishing the proposed approach from many of the existing methods include that it allows a more realistic problem formulation, and that it can find the (global) optimal solution. The new problem formulation takes into consideration practical aspects of VAr sources and the load constraints and operational constraints at different load levels. This methodology based on simulated annealing determines the location to install VAr sources; the types and sizes of VAr sources to be installed; and the settings of VAr sources at different loading conditions. To speed up the solution algorithm, the authors make a slight modification of the fast decoupled load flow and incorporate it into the solution algorithm. This method is suitable for large-scale power systems and has been tested on several power systems with promising results. Simulation results on the IEEE 30-bus system and the Tai-power 358-bus system are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On Load Frequency Control

AbstractThis paper addresses the design of decentralized controllers for interconnected large-scale electric power systems. The system is modelled as a collection of independent subsystems or control areas interconnected through high voltage tie-lines. For each control area an independent model is derived using the information contained in the interface variables. Conditions are given for the existence of these local models. Decentralized controllers are designed to solve the “Load Frequency Control” problem. The proposed decentralized control method is not limited to power systems. It is applicable to any interconnected large-scale dynamical system.

Multivariable frequency-domain techniques for the systematic design of stabilizers for large-scale power systems

A novel application of multivariable frequency-domain control theory to the design of excitation based stabilizers for large-scale electric power systems is presented. The stabilizers are designed to coordinate the global performance of the multimachine system, and in some cases may turn out to be of a decentralized structure. The design procedure is based on the direct Nyquist array, supplemented by the characteristic function. The control design procedure is applied to a sample twelve-machine electric power system which includes detailed models of synchronous machines, excitation systems, turbines, and speed governing mechanisms. Simulation results show that the design method leads to the removal of the underdamped oscillations, to a reduction in the interaction between the generating units, and to a significant improvement in the dynamic performance of the system. This is the first successful application of the direct Nyquist array method to the systematic design of excitation-based power system stabilizers for large-scale power systems. >

A Study on the Digital Distance Relaying Scheme Using Kalman Filter

To maintain the high reliability and stability in the large scale electric power system for a stabilized power supplying, it requires an accurate high speed digital distance relaying techniques. For this purpose, when it comes to faults with the power system, the digital distance relaying techniques must be investigated to extract the fundamental frequency component and to predict fault location. Fault voltage and current contain noise which causes many of these problems. This affects the accuracy of fault location estimation as well as the reliability of digital distance relay.In this thesis, it is presented the methodology of FFT (fast Fourier transform), which accompanied aliasing, picket-fence effect, and leakage in the process of extracting fundamental frequency component and an algorithm of extracting fundamental frequency component, using the Kaiman filter theory to improve upon these disadvantages. It is derived noise modelling from fault voltage and current to use the Kaiman filtering technique, and also got rid of noise components from the measurement values. Also a two-state and three-state Kaiman filter are considered for the symmetrical components estimation of voltages and currents respectively. It is presented an efficient digital distance relaying techniques for the purpose of extracting fundamental frequency component. Also, to confirm the validity of Kaiman filtering techniques, it is shown the experimental results obtained by using the digital simulation of power system. And, it is discussed the extracted results of fundamental frequency components by means of the Fourier transform and Kaiman filtering techniques.