Showing papers on "Power system simulation published in 1991"

Distribution system power flow analysis-a rigid approach

Abstract: This approach is oriented toward applications in three phase distribution system operational analysis rather than planning analysis. The solution method is the optimally ordered triangular factorization Y/sub BUS/ method (implicit Z/sub BUS/ Gauss method) which not only takes advantage of the sparsity of system equations but also has very good convergence characteristics on distribution problems. Detailed component models are needed for all system components in the simulation. Utilizing the phase frame representation for all network elements, a program called Generalized Distribution Analysis Systems, with a number of features and capabilities not found in existing packages, has been developed for large-scale distribution system simulations. The system being analyzed can be balanced or unbalanced and can be a radial, network, or mixed-type distribution system. Furthermore, because the individual phase representation is employed for both system and component models, the system can comprise single, double, and three-phase systems simultaneously. >

Fuzzy dynamic programming: an application to unit commitment

Abstract: A new approach using fuzzy dynamic programming is proposed for the unit commitment of a power system. A characteristic feature of the approach is that the errors in the forecast hourly loads can be taken into account by using fuzzy set notations, making the approach superior to the conventional dynamic programming method which assumes that the hourly loads are exactly known and there exist no errors in the forecast loads. To reach an optimal commitment strategy under the fuzzy environment, a fuzzy dynamic programming model in which the hourly loads, the cost, and system security are all expressed in fuzzy set notations is developed. The effectiveness of the approach is demonstrated by the unit commitment of the Taiwan power system, which contains six nuclear units, 48 thermal units, and 44 hydro units. >

Dispatch of direct load control using dynamic programming

Abstract: An approach based on dynamic programming is presented for the dispatch of direct load control (DLC). The objective is to coordinate DLC strategies with system unit commitment such that the system production cost is minimized. To achieve this goal, the DLC dispatch is first integrated into the unit commitment problem. An optimization technique based on dynamic programming is then developed to reach the optimal DLC dispatch strategy and system generation schedule. To demonstrate the effectiveness of the approach, results from a sample study performed on the Taiwan power system are described. >

Feeder reconfiguration for loss reduction: an application of distribution automation

Abstract: The authors present a comparison of various methods applied to feeder reconfiguration for loss minimization. A new linear programming method using transportation techniques and a new heuristic search method are proposed for comparison with a previously developed heuristic technique which was based on an optimal load flow analysis. The methods are compared on simulations of both a small feeder distribution system, and a larger system based on a model of a public utility commission 44 kV distribution system. This study indicates that linear programming, in the form of transportation algorithms, is not suitable for real-time application to feeder reconfiguration, whereas heuristic approaches, although not optimal, can provide substantial savings if properly formulated and are suitable for real-time implementation. >

Maintenance scheduling by using simulated annealing method (for power plants)

Abstract: The thermal power plant generator maintenance scheduling problem is addressed. The problem is formulated as a mixed-integer programming problem, and it is solved by using an optimization method known as simulated annealing. Since the simulated annealing method assumes an analogy between a physical multiparticle system and a combinatorial optimization problem, a global minimum can be found with high probability through a careful annealing process. Numerical results on a real-scale test system are given, and the effectiveness of the proposed method is demonstrated. >

A new approach for solving extended unit commitment problem

Abstract: An original approach is presented for solving the extended unit commitment problem using the Lagrangian relaxation method. The unit ramp rates have been incorporated into a dual optimization algorithm, making it possible to use the feasible direction method for primal problem solution. The mathematical model developed also includes transmission capacity limits, regulation reserve requirements of a prespecified group of units, transmission losses, and fuel constraints. Standard unit commitment constraints such as power balance equations, fast spinning reserve constraints, and all local constraints are also taken into account. A computational package has been developed and tested over a 48 h time horizon on a large power system with 100 thermal units. The promising performance of this package makes it suitable for EMS application. >

Distribution system short circuit analysis-A rigid approach

Abstract: A rigid approach to short circuit analysis for large-scale distribution systems is introduced. The approach uses an individual (a-b-c) phase-based system representation, a nontrivial transformer model, and includes the contribution due to load. The method can, therefore, be applied to balanced or unbalanced, radial, network, or mixed-type distribution systems. This approach is oriented toward applications in distribution system operation analysis rather than the more typical planning-oriented analysis. The solution method is an iterative compensation method, which uses a single optimally ordered factorization of the bus admittance matrix (Y/sub Bus/), commonly used in power flow analysis, to simulate the fault condition. The use of this method in a short circuit analysis program enables a factorized Y/sub Bus/ solution, resulting in many advantages. Using a common factorization, both power flow and short circuit analyses are possible in a single execution. Since the factorization is unchanged, multiple faults of various types can be simulated in one run of the program. >

Short term scheduling in a wind/diesel autonomous energy system

Abstract: An algorithm is developed for determining the optimal operation scheduling over a period of T hours for an autonomous energy system consisting of diesel units and wind generators. The proposed algorithm requires the load and wind velocity statistics during the scheduling period. Thus, the solution procedure involves the sequential execution of two separate algorithms solving the following two problems: the short term forecasting of load and wind speed, and the short term unit commitment. The simulation period is divided into m intervals of duration t minutes each. For each interval the mean value and standard deviation of the load and wind velocity are estimated using ARMA models. The unit commitment problem is solved by a heuristic algorithm based on a predetermined loading priority list of diesel units. The algorithm decomposes the problem into subproblems that are sequentially solved. Reliability constraints and technical constraints involving the operation of the units are taken into consideration. For the simulation of the generating system, probabilistic techniques are utilized. >

A knowledge-based method for making restoration plan of bulk power system

Abstract: A method that uses general-purpose restoration knowledge not dependent on preoutage system states in order to generate postrestoration target systems (where postoutage systems are taken as initial states) is proposed for use during power systems outages. Traditionally, postoutage system states are made to emulate as closely as possible preoutage system states, with system operations preformed only within blackout systems. Therefore, depending on the amount of preoutage load, some outage, loads may be experienced in the restored system. A method is proposed by which system operations in both blackout systems and sound systems are combined according to the amount of load in the preoutage systems, so that postrestoration system states with minimal outage loads from postoutage systems will be generated. A prototype system incorporating actual power systems and utilizing this method was built and tested under simulated conditions. The effectiveness of the proposed system is discussed on the basis of the test results. >

Computer Simulation Applications: An Introduction

Abstract: Thinking about Simulation The Pieces that Make the Whole A Model for All Seasons Simulation in Theory-Building and Policy Analysis Designing a Computer Simulation How to Build Your Own Steps in the Simulation-building Process Technical Aspects of Simulation Programming, Validating, and Analyzing a Computer Simulation Model Simulation Number 1 An Exercise in Theory Building Simulation Number 2 An Exercise in Policy Analysis Simulation Number 3 An Exercise Incorporating Stochastic Variation The Art and Science of Simulation

Parallel implementation of a power system dynamic simulation methodology using the conjugate gradient method

Abstract: The authors present results of tests with a parallel implementation of a power system dynamic simulation methodology for transient stability analysis in a parallel computer. The test system is a planned configuration of the interconnected Brazilian South-Southeastern power system with 616 buses, 995 lines, and 88 generators. The parallel machine used in the computer simulation is a distributed memory multiprocessor arranged in a hypercube topology architecture. The nodes are based on the Inmos T800 processors with 4 Mbytes of local memory. The simulation methodology is based on the interlaced alternating implicit integration scheme in which the network equations are re-ordered such that the network admittance matrix appears in the block bordered diagonal form and is then solved by a combined application of the LU factorization and the conjugate gradient method. The results obtained show considerable reduction in the simulation time. >

Analysis and design of multi-stage distributed power systems

Abstract: Multistage distributed power systems are analyzed, focusing on the dynamic interactions between two cascaded converter stages. An unterminated modeling and design approach is proposed to design a converter driving other converters downstream. Results of the analysis were verified by both frequency- and time-domain simulations. >

An integrated personal computer graphics environment for power system education, analysis and design

Abstract: An integrated graphics environment for power system analysis and design (PSADE) is presented. The environment runs on a personal computer with standard memory and graphics hardware requirements (VGA or EGA). PSADE is based on a general purpose graphics development software which provides numerous tools to facilitate the creation and modification of particular power system analysis applications. The integrated environment contains extensive color graphics representations of power systems, interface with external power system simulation programs, dynamic display of the results on the graphical representation of the network, and straightforward communication among the external and the internal databases. The use of this environment is illustrated by several particular applications. PSADE is specially useful to universities and industry for teaching and training purposes, as well as being a valid research tool for preliminary study of planning or operational schemes. >

Tuning of power system stabilizers using optimization techniques

Abstract: The application of a numerical optimization scheme to the tuning of power system stabilizers is studied. The scheme is based on minimax optimization techniques with multiple objectives given by relevant system perturbations, aggregated by means of a weighted sum. The large number of constraints is handled by separating the optimization and simulation in two levels which interchange limited information. Three different optimization techniques were tested with applications to the Venezuelan power system for the years 1989 and 2005. The overall method is shown to be accurate and reliable. >

Performance simulation of distributed energy management systems

Abstract: The performance simulation of an open architecture energy management system (EMS) can provide detailed quantitative performance information long before a system is built. A method for simulating the performance of LAN-based EMSs is presented. The simulation shows how the performance of the system with respect to throughput and response time can be predicted. The results of the simulation of a generic LAN-based EMS for a typical operating scenario in a control center are presented. The simulation models the system hardware, including processor workstations, dispatcher consoles, memories, disks, LANs, file servers, etc. The LAN protocol and LAN data traffic are simulated. Typical EMS software functions are simulated. Dispatcher actions are simulated by random time event generators, which also simulate random power system events. Sensitivity analysis is performed by varying a number of system parameters to determine their effect on the simulated system. Outputs of the simulation show: utilization of the processors, consoles, LANs, and servers; LAN statistics; response times of display callups and supervisory control; and elapsed times of key EMS functions. >

A personal computer based system for the laboratory evaluation of high performance power system protection relays

Abstract: The power system simulation system described provides a relay under evaluation with current and voltage input similar to that encountered under service and fault conditions. Using digital transient simulation programs to model power system behaviour, the facility provides an effective bandwidth of from DC to 4 kHz for both the current and voltage relay input. The relay's output is automatically monitored during the test, enabling a detailed report of its response to be produced. The application of the system is illustrated by the evaluation of a new EHV teed feeder relaying system. >

Power system restoration incorporating interactive graphics and optimization

Abstract: A new power system restoration planning methodology which incorporates interactive graphics and an optimization algorithm is presented. The interactive graphics provides a tool to define restoration scenarios, view the restoration process, and display the optimization and simulation results. By introducing the concept of optimal restoration scenario, the process of selecting the control variables can be formulated as a mathematical problem which can be solved by nonlinear programming. This approach removes most of the guesswork found in conventional restoration planning and provides a systematic and optimal solution in the sense of minimizing the variations from normal, and the number of control variable adjustments from stage to stage. The optimization reduces the duration of the restoration procedure and guarantees the security of all variables during the restoration process by respecting all steady-state operating constraints. >

A power system CAD package for the workstation and personal computer environment

Abstract: A CAD package has been developed for power system analysis. It integrates the simulation programs under a single database and has the capability to switch between system editing, simulation, and result analysis without leaving the environment. It can perform load flow, fault, and harmonic analysis simulations. Power systems can be graphically constructed, modified, and stored, and any of the above simulations can be run at any time using an easy-to-use CAD drawing and data editing module. The package is suitable for educational and industrial use. >

An expert system based diagnosis and advisor tool for teaching power system operation emergency control strategies

Abstract: Interactive software to be used for power engineering education is considered. It is shown how the student-computer interaction can be improved by adding an expert system to already existent software used as a teaching aid as part of an undergraduate power system operation course. An online diagnosis and advisor tool recently incorporated in a microcomputer based power network control center simulator is described together with application examples related to emergency control strategies in power network operation. The students initial reaction is discussed. >

Interactive relay controlled power system modeling

Abstract: Four fundamental algorithms that make it possible to simulate numerous types of protective relay systems are identified. The characteristics of these fundamental modules necessary for building an embedded relay model within an EMTP (electromagnetic transient program) are discussed. A directional time overcurrent relay model is used to provide a detailed demonstration of relay model development and to illustrate the utilization of the fundamental modules. The results of using this relay model in a modeled power system reveal the power of this concept to enhance power systems education, applications engineering, and relay design procedures. >

A database for diverse power system simulation applications

Abstract: The authors describe a database capable of supporting a diverse set of power system simulation applications ranging from harmonics and transient analysis to conventional load flow and short-circuit calculations. The wide range of applications requires that the data be modeled in a more basic, or lower-level, form than is required for many traditional power system analysis programs. The need for the database, the design objectives, and the evolution of the design are described. A strictly relational database was attempted at first. Difficulties in modeling complex data structures resulted in changing the database to a more object-oriented form. Several of the key data structures are presented as well as typical programming techniques for accessing the database. >

Application of artificial neural networks to unit commitment

Abstract: Artificial neural networks are currently being applied to a variety of complex combinatorial optimization and nonlinear programming problems. In this paper, a combination of Hopfield Tank type, and Chua-Lin type artificial neural networks is applied to solve simultaneously the unit commitment and the associated economic unit dispatch problems. The approach is based on imbedding the various constraints in a generalized energy function, and then defining the network dynamics in such a way that the generalized energy function is a Lyapunov function of the artificial neural network. The novel feature of the proposed approach is that the nonlinear programming and the combinatorial optimization problems are solved simultaneously by one network. An illustrative example is also presented. >

Transmission loss evaluation based on probabilistic power flow

Abstract: A simulation method for composite power systems is proposed for the purpose of evaluating the probability distribution function of transmission losses. The method accounts for the uncertainty of the electric load, availability of generating units, nonlinearities in the power flow equations, and major operating practices. The method is based on the following procedure. First, given the probabilistic electric load model, the probability distribution function of the power injection at generation buses is computed by taking into consideration the availability of generating units and economic dispatch practices. Next, transmission losses are expressed as a piecewise linear function of power injections at generation buses. Subsequently, the probability distribution function of transmission losses is computed. Validation of the method was performed via a Monte Carlo simulation. The method was applied to the 24-bus IEEE reliability test system, and the results are validated by comparing it to Monte Carlo simulation results. >

Accelerating power versus electrical power as input signals to power system stabilizers

Abstract: Power system stabilizers (PSSs) using electrical and accelerating power as supplementary signals are compared. The effect on terminal voltage and volt-ampere reactive, offset and damping of a simulated single-machine-infinite-bus system is investigated. The results show that the damping offered by a PSS using accelerating power and electrical power feedback is very similar even in the presence of large mechanical power disturbances. The benefits of accelerating power over electrical power as the supplementary signal to the PSS are not evident in the simulation studies considered. Considering the relative ease of measuring the electrical power signal compared to accelerating power signal, it is concluded that a PSS using electrical power as a supplementary signal is sufficient for damping rotor oscillations. Frequency response data are shown to support this point of view. >

An online implementation of transient stability in a dispatcher training simulator

Abstract: An integrated online transient stability program in the power system dispatcher training simulator (DTS) environment is presented. The DTS stability simulation completes the training system by allowing engineers and training specialists preparing the various scenarios with an opportunity to validate the events sequence for each scenario and to review and evaluate the operator's performance during a training session. The simulation can be directly initialized from the DTS state. The computer program uses the same models which are used in the DTS augmented by the extra modeling needed for the transient capabilities of the generators and DC systems. The interactive user interface is compatible with the DTS/energy management system environment. The output events of the simulation can be directly inserted into the events database of the DTS. Easy data entry capabilities for model building exist. Data security and organization via a database management system is provided. The results of testing are very favorable under various system conditions. >

Short term scheduling in cogeneration systems

Abstract: Combined generation of power and heat offers great economic advantage and serves the requirements of environmental conservation. However, the operation of such integrated cogeneration systems is a complex problem because the demand for power and for heat must be satisfied simultaneously with regard to many different constraints. The development of an advanced procedure for short-term operational planning in cogeneration systems based on the method of mixed-integer linear programming completed by some supporting measures for problem reduction is reported. Test results for sample systems derived from actual cogeneration systems indicate the procedure's ability to calculate optimal economic schedules under realistic conditions. >

Vector input-output linearization for a class of descriptor systems (multi-machine AC/DC power system)

Abstract: An exact input-output linearization procedure is outlined for a class of nonlinear descriptor systems, motivated by applications to large-scale systems. A vector control law was derived for a multi-machine AC/DC power system, and the feasibility of the approach was verified through simulation. >

Physical simulation power system laboratory

Abstract: The authors introduce the newly completed power system simulation laboratory in the Energy Systems Research Center at the University of Texas at Arlington. This new and unique laboratory is a scaled-down three-phase physical model which correlates well with the important components of a real power system. Its configuration is sufficient to simulate significant system behaviour, such as transient and dynamic stability phenomena and all forms of steady-state operational phenomena. This physical model provides a unique opportunity for operator training as well as for validating digital simulation accuracy of each component.

Frequency domain transient stability simulation of power systems: implementation by supercomputer

Abstract: Summary form only given, as follows. This paper reports the results of performing transient stability simulations of a power system using frequency domain methods and makes comparisons with a standard time domain simulation of the same events, both simulations being run on both a VAX and CRAY machine. Because of their inherent structure. one is usually forced to implement time domain simulations by serial techniques that are not capable of effectively exploiting parallel and vector processing capabilities. Frequency Domain techniques, on one hand are more likely to give rise to vector and matrix operations which are amenable to parallel and vector processing, while on the other hand they are generally less efficient in dealing with nonlinearities. This study is aimed at estimating the relative benefits of one simulation method over the other.