Showing papers on "Power system simulation published in 1999"

Teaching distribution system reliability evaluation using Monte Carlo simulation

Abstract: Analytical techniques for distribution system reliability assessment can be effectively used to evaluate the mean values of a wide range of system reliability indices. This approach is usually used when teaching the basic concepts of distribution system reliability evaluation. The mean or expected value, however, does not provide any information on the inherent variability of an index. Appreciation of this inherent variability is an important parameter in comprehending the actual reliability experienced by a customer and should be recognized when teaching distribution system reliability evaluation. This paper presents a time sequential Monte Carlo simulation technique which can be used in complex distribution system evaluation, and describes a computer program developed to implement this technique. General distribution system elements, operating models and radial configurations are considered in the program. The results obtained using both analytical and simulation methods are compared. The mean values and the probability distributions for both load point and system indices are illustrated using a practical test system.

Test systems for harmonics modeling and simulation

Abstract: This paper presents three harmonic simulation test systems. The purpose is to demonstrate guidelines for the preparation and analysis of harmonic problems through case studies and simulation examples. The systems can also be used as benchmark systems for the development of new harmonic simulation methods and for the evaluation of existing harmonic analysis software.

Simultaneous stabilization of multimachine power systems via genetic algorithms

Abstract: This paper demonstrates the use of genetic algorithms for the simultaneous stabilization of multimachine power systems over a wide range of operating conditions via single-setting power system stabilizers. The power system operating at various conditions is treated as a finite set of plants. The problem of selecting the parameters of power system stabilizers which simultaneously stabilize this set of plants is converted to a simple optimization problem which is solved by a genetic algorithm with an eigenvalue-based objective function. Two objective functions are presented, allowing the selection of the stabilizer parameters to shift some of the closed-loop eigenvalues to the left-hand side of a vertical line in the complex s-plane, or to a wedge-shape sector in the complex s-plane. The effectiveness of the suggested technique in damping local and inter-area modes of oscillations in multimachine power systems is verified through eigenvalue analysis and simulation results.

A Norton approach to distribution network modeling for harmonic studies

Abstract: This paper presents a Norton approach for modeling distribution networks where the system configuration is not fully known. Traditionally harmonic studies use complex distribution networks modeled by harmonic current sources for specific frequencies. Although this approach has been proved to be adequate for some studies, this may not happen for other applications. When changing the operating condition of the supply-side system, the harmonic currents injected by the distribution network might change. This information is in this paper used to estimate a Norton model of the load-side distribution network. The estimated models can be used to analyze, for example, the effect of harmonic filters under different supply system configurations or operating conditions. The method of estimating the Norton models is illustrated on a test system, simulated on the well-known simulation program EMTDC. The performance of the estimated models is, for different configurations of the supply system, compared to the performance of the traditionally used "constant current" approach.

Application of a novel fuzzy neural network to real-time transient stability swings prediction based on synchronized phasor measurements

Abstract: The ability to rapidly acquire synchronized phasor measurements from around a power system opens up new possibilities for power system protection and control. In this paper, the authors develop a novel class of fuzzy hyperrectangular composite neural networks which utilize synchronized phasor measurements to provide fast transient stability swings prediction for use with high-speed control. Primary features of the method include constructing a fuzzy neural network for all fault locations, using a short window of realistic-precision post-fault phasor measurements for the prediction, and testing robustness to variations in the operating point. From simulation tests on a sample power system, it reveals that the proposed tool can yield a highly successful prediction rate in real-time.

Optimal active power flow incorporating power flow control needs in flexible AC transmission systems

Abstract: This paper presents a new method to incorporate the power flow control needs of flexible AC transmission system (FACTS) in studying the optimal active power flow problem. The linearized (DC) network model is used in this paper. Three main types of FACTS devices, namely thyristor controlled series compensators (TCSC), thyristor controlled phase shifters (TCPS) and unified power flow controllers (UPFC), are considered. The proposed method decomposes the solution of such modified OPF problem into two problems' iteration. The first problem is a power flow control subproblem while the second problem is a normal OPF problem. It is shown that the modified active power OFF can be solved by a new iterative strategy where a conventional LP-based technique may be used. Digital simulation studies on the IEEE 30 bus test system are presented to show the effectiveness of the proposed method.

A drum boiler model for long term power system dynamic simulation

Abstract: In the event of a power system contingency, the boiler has an important impact on the power output in the long term time frame of minutes to hours. This paper describes a drum boiler model developed from first principles and validated using data from tests carried out on an actual plant. The model can be used for dynamic simulation studies in long time frames, greater than 30 seconds, in particular where assessment of deviations of internal parameters, such as steam pressure, drum level and steam temperature, outside safety limits is essential.

Analysis of the effects of a passing cloud on a grid-interactive photovoltaic system with battery storage using neural networks

Abstract: In this paper, a combined radial-basis-functions (RBF) and backpropagation network is used to predict the effects of passing clouds on a utility-interactive photovoltaic (PV) system with battery storage. Using the irradiance as input signal, the network models the effects of random cloud movement on the electrical variables of the maximum power point tracker (MPPT) and the variables of the utility-linked inverter over a short period of time. During short time intervals, the irradiance is considered as the only varying input parameter affecting the electrical variables of the system. The advantages of artificial neural network (ANN) simulation over standard linear models is that it does not require the knowledge of internal system parameters, involves less computational effort, and offers a compact solution for multiple-variable problems. The model can easily integrated into a typical utility system and resulting system behavior can be determined. The viability of the battery-supported PV power system as a dispatchable unit is also investigated. The simulated results are compared with the experimental results captured during cloudy days. This model can be a useful tool in solar energy engineering design and in PV-integrated utility operation.

A power system simulation tool based on Simulink

Abstract: This paper describes the Power System Blockset (PSB) from The MathWorks, Natick, MA, which is a new software package for the simulation of electric circuits, power systems, power electronic devices, and electric drives. The PSB is developed in the graphical Simulink environment of the general-purpose Matlab software. This blockset inherits a number of advantages from its development environment, namely, an open architecture, a powerful graphical user interface, and versatile analysis and graphics tools. The user can integrate control systems implemented with Simulink blocks directly into a diagram built with the PSB. Solution of differential equations is accomplished using the state-space approach with variable-step variable-order integration algorithms. A simulation example is presented, and the results are compared with those obtained with PSPICE.

A genetic algorithm for solving the unit commitment problem of a hydro-thermal power system

Abstract: The paper presents a two layer approach to solve the unit commitment problem of a hydro-thermal power system. The first layer uses a genetic algorithm (GA) to decide the on/off status of the units. The second layer uses a nonlinear programming formulation solved by a Lagrangian relaxation to perform the economic dispatch while meeting all plant and system constraints. In order to deal effectively with the constraints of the problem and prune the search space of the GA in advance, the difficult minimum up/down-time constraints of thermal generation units and the turbine/pump operating constraint of storage power stations are embedded in the binary strings that are coded to represent the on/off-states of the generating units. The other constraints are handled by integrating penalty costs into the fitness function. In order to save execution time, the economic dispatch is only performed if the given unit commitment schedule is able to meet the load balance, energy, and begin/end level constraints. The proposed solution approach was tested on a real scaled hydro-thermal power system over a period of a day in half-hour time-steps for different GA-parameters. The simulation results reveal that the features of easy implementation, convergence within an acceptable execution time, and a highly optimal solution in solving the unit commitment problem can be achieved.

Security Constrained Unit Commitment for open markets

Abstract: For many electric power systems the limitations of the transmission network strongly affect the system operation. In traditional regulated power systems, the operator follows operating rules and procedures to schedule generation so that the power system operates reliably. As the power industry moves towards open markets, it is necessary to develop power system schedules that produce high-quality nondiscriminatory schedules that are consistent with secure operation. This paper describes the Security Constrained Unit Commitment (SCUC) program that has been developed to meet this need. The SCUC program optimizes the scheduled generation and price-sensitive load while satisfying generation, reserve requirements, transmission constraints, and generator operating constraints such as minimum up and down times. The transmission constraints modeled are of two types: branch-flow constraints insuring that line and interface thermal limits are satisfied (for steady-state operating conditions) for the forecasted network configuration and for the configuration with a specified set of network and generator outages (i.e. contingencies). These constraints, which are enforced in a preventive mode, an automatically generated by the program; and import and export constraints limiting the generation from specified generators and loads. These constraints which can be used to model voltage and dynamic security constraints, are developed using offline analysis and are inputs to the program. This paper describes the methods used to develop secure schedules and describes our experience using this program.

Sequential synthesis of structured singular value based decentralized controllers in power systems

Abstract: This paper presents a systematic procedure for the design of decentralized controllers for multimachine power systems. The robust performance in terms of the structured singular value (SSV or /spl mu/) is used as the measure of control performance. A wide range of operating conditions were used for testing. Simulation results have shown that the resulting /spl mu/- controllers would effectively enhance the damping torques, providing better robust stability and/or performance characteristics both in the frequency and time-domain compared to conventionally designed power system stabilizers (PSSs).

Approaches for analog VLSI simulation of the transient stability of large power networks

Abstract: This paper suggests several approaches for determining the transient stability of a power network by using an analog VLSI chip for simulating the system behavior. The main advantages of using this method are the much shorter computation time and lower complexity compared to the currently used methods, which are based on numerical calculations or discrete analog emulators.

A transmission-constrained unit commitment method in power system scheduling

Abstract: This paper presents a transmission-constrained unit commitment method using a Lagrangian relaxation approach. Based on a DC power flow model, the transmission constraints are formulated as linear constraints. The transmission constraints, as well as the demand and spinning reserve constraints, are relaxed by attaching Lagrange multipliers. A three-phase algorithmic scheme is devised including dual optimization, a feasibility phase and unit decommitment. A large-scale test problem with more than 2200 buses and 2500 transmission lines is tested along with other test problems.

Thermal power generation scheduling by simulated competition

Abstract: This paper presents a new method for solving the unit commitment problem by simulation of a competitive market where power is traded through a power exchange (PX). Procedures for bidding and market clearing are described. The market clearing process handles the spinning reserve requirements and power balance simultaneously. The method is used on a standard unit commitment problem with minimum up/down times, start-up costs and spinning reserve requirement taken into account. Comparisons with solutions provided by Lagrangian relaxation, genetic algorithms and Chao-an Li's unit decommitment procedure demonstrate the potential benefits of this new method. The motivation for this work was to design a competitive electricity market suitable for thermal generation scheduling. However, performance in simulations of the proposed market has been so good that it is presented here as a solving technique for the unit commitment problem.

Direct load control using fuzzy dynamic programming

Abstract: The paper develops a fuzzy dynamic programming (FDP) approach to solving the direct load control (DLC) problem of large air conditioner loads (ACLs). In the formulation, the cycling capacities of the ACLs and the system load demands are all regarded as fuzzy variables. The scheduling of the DLC and the unit commitment (UC) is integrated into an FDP structure to reduce the system peak loads as well as the system operation costs. The solution approach has been tested on the data for the Taiwan Power (Taipower) 38-unit system with 15 ACL groups. In the tests, the Monte-Carlo simulation technique is employed to assess the robustness of the solution obtained from the proposed FDP approach for various load uncertainties. The results are presented and compared to those without consideration of the load uncertainties.

Existence of solutions for the network/load equations in power systems

Abstract: Virtually all power-system analysis algorithms require the solution of a network/load model. During a numerical simulation of medium and long term dynamic events, this model is solved at every timestep. In all cases it is important that there exists a solution to the model. In this paper we study the quasistatic network/load models for use in steady-state and dynamic power-system analyses and present a set of sufficient conditions which ensures that the network/load model is solvable for voltages and currents.

Optimal operation of industrial CHP-based power systems in liberalized energy markets

Abstract: This paper presents the implementation of a new method in calculating the optimal unit commitment and economic dispatch of industrial enterprises with its own energy supply system, mostly with CHP-plants To yield the most synergetic effects, both the marketplace and the demand of disposable industrial processes are taken into account Because of the complexity of the formulated mathematical model and, thus, of the optimization problem, a new dynamic search strategy (DSS) based on mixed integer linear programming (MILP) is presented With DSS, a considerable acceleration of calculation time could be achieved

Transient analysis of integrated diesel-wind-photovoltaic generation systems

Abstract: The paper deals with the implementation in a continuous simulation language of the dynamic model of an integrated generation system (IGS) named "Combined Multiple Renewable Energy Sources System Simulator" (CMRESSS). The software package is a useful tool to evaluate the IGS electric transient behavior during the planning stage. Dynamic transients in normal and faulted conditions are simulated exploiting the main features of the package which are flexibility and graphic user interface (GUI) for easy handling of input data and events scheduling. Simulation results are discussed and validated to demonstrate the validity of the proposed approach. The results confirm the consistence of the simulation package and the benefits achievable in preliminary design by comparative analysis of different power plants.

Hybrid high frequency AC power distribution architecture for telecommunication systems

Abstract: A novel high frequency hybrid power distribution system for telecommunication applications is presented. The proposed hybrid system combines the advantages of both the sinusoidal voltage and current types of high frequency distribution systems and it has advantages such as connectorless power transfer, fuseless protection, sinusoidal voltage and current distribution and, high overall system efficiency. The different operating modes of the proposed power distribution system are described in detail and performance characteristics are presented. Finally experimental results are given to validate the concepts developed and to demonstrate the system performance.

Time-frequency analysis of power system disturbance signals for power quality

Abstract: In this paper, we utilize fundamental concepts of time-frequency analysis to analyze transient disturbance signals in power systems. Within the restriction of the uncertainty principle, time-frequency analysis provides localized information of the disturbance signal as a function of time and frequency. Using simulation and actual power disturbance data, we show that the so-called reduced interference distribution (RID) appears to be most suitable for investigating the time-frequency characteristics of power disturbances. In this paper, the potential assessment of power quality via application of time-frequency analysis is also briefly discussed.

Application of simultaneous active and reactive power modulation of SMES unit under unequal /spl alpha/-mode for power system stabilization

Abstract: A simple and novel control strategy for damping electromechanical oscillations through control of power converter firing angles /spl alpha//sub 1/ and /spl alpha//sub 2/ of a superconducting magnetic energy storage (SMES) unit is proposed. Both active and reactive power modulations are used under unequal /spl alpha/-mode of operation. The choice of unequal mode is discussed in detail. The gains of the proposed SMES controller are determined once offline depending on the power system and the rating of the SMES unit. Simulation results show that the SMES unit can effectively suppress power system oscillations by utilizing its active and reactive power modulation capabilities. The control algorithm is simple and its realization will require very little hardware.

Power systems dynamics simulation using object-oriented programming

Abstract: Object-oriented programming is an alternative to overcome the problems associated with the development, maintenance and update of large software by electrical utilities. However many applications in the electrical industry depend critically on the computational efficiency of the implementation. This paper applies the object-oriented approach to the problem of power system dynamics simulation. A decomposition of the electric power system into classes, suitable to include all elements required in this problem, is presented. A structure for linear systems solution aiming at computational efficiency for large-scale systems applications, is proposed. Tests using four equivalents of the South-Southeastern Brazilian interconnected power system are carried out. The performance of the object-oriented program, developed in C++, is assessed in several computers. Real-time simulation was achieved for medium-sized power systems in lower cost high performance computers. The implementation is compared with an industry program written in Fortran and similar performances are achieved.

Design and implementation of the parallelable active power filter

Abstract: This paper presents a multi-module parallelable three-phase active power filter to solve the problems of capacity enlargement and load unbalance compensation encountered by the shunt APF with A three-arm topology. Systematic design procedures of the complete system are described and some simulated and experimental results are provided for demonstrating the effectiveness of the proposed approach.

A multiobjective operations planning model with unit commitment and transmission constraints

Abstract: This paper presents a modeling framework for operations planning for generation and transmission for a period of a year or few months that incorporates (in an approximate way) the dynamic constraints on generator output and the static transmission constraints. The model is capable of performing the following tasks: generation scheduling, interutility transmission scheduling, maintenance scheduling, fuel allocation to thermal/nuclear plants, reactive power planning, DSM and nonutility generation purchase planning. The model checks the operating feasibility of the long term planning decisions by unit commitment and OPF modules in an interactive way. There is a feedback mechanism to modify the long term generation and transmission schedule to reflect the operational feasibility of the long term planning exercise. The model makes use of compromise programming to perform multiobjective analysis. A case study for a 120-bus test system (four area IEEE 30-bus systems) is carried out to illustrate the application of the proposed modeling framework.

Real time digital power system simulator design considerations and relay performance evaluation

Abstract: Environmental pressures, right of way problems for new transmission lines, large scale system interconnection and increasing power demand especially in developing countries call for new transmission technologies. Use of FACTS and HVDC is gaining momentum. Relaying problems in such systems require a sophisticated approach and numerical technology using high grade processors offers a promising solution. To establish the performance of such relays which are designed more as powerful schemes rather than as a conglomeration of individual relays, detailed testing is required using an elaborate real-time simulator model. These tests are not only necessary during design and development but also are required by the utilities as a part of their acceptance. Highlighting the requirements of a hybrid real-time simulator including the complete spectrum of power system dynamics, this report describes an analog cum digital model used for real-time assessment of system performance. SVCs, HVDC, ASC and CSC can be modelled fully digitally by computer simulation and transient real-time data injection as well as by an analog method using physical simulation with original converter controllers for performance evaluation of numerical relays under real system conditions. As an example of the use of this simulator, tests on a numerical EHV-line relay are described and the relay performance is analyzed.

Power system dynamic load modeling using adaptive-network-based fuzzy inference system

Abstract: The representation of the dynamic characteristics of power system loads is widely used for obtaining power system operations, controls and stability limits and becomes a critical factor in power system dynamic performance. In this paper, the performance of power system dynamic load modeling using adaptive-network-base fuzzy inference system (ANFIS) is compared with traditional architectures. The ANFIS models can represent nonlinear systems performance accurately, and they are promising for dynamic load models. Computer simulations show excellent results using this approach for power system dynamics.

Semidefinite programming relaxations for {0,1}-power dispatch problems

Abstract: Semidefinite programming (SDP) relaxations for two {0,1}-power-dispatch problems are presented in this paper. The first problem deals with the solution of a static quadratic economic dispatch problem, where generators status (on or off) and power levels to supply a load are to be determined. Within Lagrangian relaxation approaches to solve generation unit commitment (UC) problems, the solution to single-unit subproblems has always been carried out using dynamic programming (DP) algorithms. The second problem deals with a SDP-relaxation of such UC-subproblems. Preliminary results show that SDP-relaxations represent a promising approach to solve these and other {0,1}-power dispatch problems.