Showing papers on "Power system simulation published in 2007"

Impacts of Wind Power on Thermal Generation Unit Commitment and Dispatch

Abstract: This paper proposes a new simulation method that can fully assess the impacts of large-scale wind power on system operations from cost, reliability, and environmental perspectives. The method uses a time series of observed and predicted 15-min average wind speeds at foreseen onshore- and offshore-wind farm locations. A Unit Commitment and Economic Dispatch (UC-ED) tool is adapted to allow for frequent revisions of conventional generation unit schedules, using information on current wind energy output and forecasts for the next 36 h. This is deemed the most faithful way of simulating actual operations and short-term planning activities for a system with large wind power penetration. The problem formulation includes ramp-rate constraints for generation schedules and for reserve activation, and minimum up-time and down-time of conventional units. Results are shown for a realistic future scenario of the Dutch power system. It is shown that problems such as insufficient regulating and reserve power-which are typically associated with the variability and limited predictability of wind power-can only be assessed in conjunction with the specifics of the conventional generation system that wind power is integrated into. For the thermal system with a large share of combined heat and power (CHP) investigated here, wind power forecasting does not provide significant benefits for optimal unit commitment and dispatch. Minimum load problems do occur, which result in wasted wind in amounts increasing with the wind power installed

Point Estimate Schemes to Solve the Probabilistic Power Flow

Abstract: This paper analyzes the behavior of Hong's point estimate methods to account for uncertainties on the probabilistic power flow problem. This uncertainty may arise from different sources as load demand or generation unit outages. Point estimate methods constitute a remarkable tool to handle stochastic power system problems because good results can be achieved by using the same routines as those corresponding to deterministic problems, while keeping low the computational burden. In previous works related to power systems, only the two-point estimate method has been considered. In this paper, four different Hong's point estimate schemes are presented and tested on the probabilistic power flow problem. Binomial and normal distributions are used to model input random variables. Results for two different case studies, based on the IEEE 14-bus and IEEE 118-bus test systems, respectively, are presented and compared against those obtained from the Monte Carlo simulation. Particularly, this paper shows that the use of the scheme provides the best performance when a high number of random variables, both continuous and discrete, are considered.

Impact on the Power System of a Large Penetration of Photovoltaic Generation

Abstract: This paper describes the impact on the power system of a large-scale penetration of photovoltaic (PV) generation. The dynamic response of a PV generation system to rapid change in irradiance is analyzed. Different types of voltage control techniques used to mitigate the negative effects of rapid changes in irradiance are investigated using simulation. The dynamic response of PV generation when subjected to faults is also analyzed.

A Simulation Model for the Evaluation of the Electrical Power Potential Harnessed by a Marine Current Turbine

Abstract: This paper deals with the development of a Matlab-Simulink model of a marine current turbine system through the modeling of the resource and the rotor. The simulation model has two purposes: performances and dynamic loads evaluation in different operating conditions and control system development for turbine operation based on pitch and speed control. In this case, it is necessary to find a compromise between the simulation model accuracy and the control-loop computational speed. The blade element momentum (BEM) approach is then used for the turbine modeling. As the developed simulation model is intended to be used as a sizing and site evaluation tool for current turbine installations, it has been applied to evaluate the extractable power from the Raz de Sein (Brittany, France). Indeed, tidal current data from the Raz de Sein are used to run the simulation model over various flow regimes and yield the power capture with time.

Improve the Stability and the Accuracy of Power Hardware-in-the-Loop Simulation by Selecting Appropriate Interface Algorithms

Abstract: The closed-loop stability and the simulation accuracy are two paramount issues in power hardware-in-the-loop simulation in regard to the operational safety and the experiment reliability. In this paper, the stability issue of the power HIL simulation is first introduced with a simple example. A stability analysis and accuracy estimation method based on the system's loop transfer function is later given. Five different interface algorithms are described and their respective characteristics with respect to the system stability are compared. Through Matlab simulations and field experiments of two representative power HIL examples, it is revealed that certain interface algorithms exhibit higher stability and accuracy than the others under the given conditions. A recommendation for selecting appropriate interface algorithms is finally proposed at the end of the paper.

Integrated Hybrid-Simulation of Electric Power and Communications Systems

Abstract: The modern power grid is strongly integrated with its communication network. While a power system primarily consists of elements that are modeled by continuous equations, a communication system has discrete event dynamics. We model the integrated operation of these two systems with a hybrid modeling and simulation technique. Systematically combining continuous and discrete event system models is necessary for correctly simulating critical system behaviors. This paper discusses an approach based on the discrete event system specification (DEVS) that characterizes the interaction of the two systems formally to preserve simulation correctness. We demonstrate the implementation of our integrated hybrid simulation technique with detailed generator and network models in a wide-area cooperative automatic load-control scenario.

Optimized Restoration of Unbalanced Distribution Systems

Abstract: A novel formulation for service restoration algorithm for unbalanced three phase distribution systems is described. This problem is a constrained multiobjective optimization formulated as a mixed integer non-linear programming problem. A comparison of the solutions with and without switch pairs has been made. The formulation was first validated using already developed three-phase unbalanced power flow software. The three-phase unbalanced power flow equations were embedded in the formulation, and hence separate calculations were not needed. Simulation results are presented for modified IEEE 13-node and IEEE 37-node test cases

Study on Impact of Wind Power Integration on Power System

Abstract: The impact of large-scale wind power integration on power system is studied. By means of the dynamic modeling of wind turbines based on doubly-fed induction generator (DFIG) and power system simulation containing large amounts of wind farms, the impact of wind power integration on grid voltage level and on transferred power of transmission line, the contribution of DFIG based wind turbines to short-circuit current and short-circuit capacity of the grid, the impact of wind power integration on power system transient stability are investigated. The simulation results show that the large-scale wind power integration may cause overload of transmission lines, increase of short-circuit capacity and change of power system transient stability. Corresponding countermeasures to handle above- mentioned issues emerged after the wind farm integration are recommended.

High-Order Modeling of Hydraulic Power Plant in Islanded Power Network

Abstract: Numerical simulations of the transient operation of an islanded power network subject to load rejections are performed. The islanded power network case study consists of a 1-GW hydroelectric power plant featuring four generating units, a long penstock, and a surge tank connected to four 1.3-GW thermal power plants and passive consumers. The modeling of every network component is described and special care is paid to the modeling of the hydroelectric power plant. In particular, the high-order modeling used for these investigations enables the detailed simulation of water hammer, mass oscillations, and nonlinear hydraulic characteristics of the turbines interacting with the electrical components of the network. Moreover, the stability analysis of the systems is performed for different load conditions and the damping performances of a power system stabilizer IEEE PSS2B are investigated.

Hydrothermal Scheduling Using Benders Decomposition: Accelerating Techniques

Abstract: A new decomposition method is presented that includes the network through ac modeling within the hydrothermal scheduling optimization process including the losses. In short-term hydrothermal scheduling, the transmission network is typically modeled with dc power flow techniques. Such modeling, however, can lead to impractical solutions when it is verified with ac power flow. Another proposal considers in thermal systems the ac network modeling but not the optimization of losses. The approach presented here addresses issues such as congestion management and control of service quality that often arise in large and weakly meshed networks - the typical pattern of power systems in Latin America. Generalized Benders decomposition and traditional, well-known optimization techniques are used to solve this problem. The master problem stage defines the generation levels by regarding the inter-temporal constraints, whereas the subproblem stage determines both the active and the reactive economical dispatches for each time interval of the load curve. It meets the electrical constraints through a modified ac optimal power flow (OPF). Another important contribution is the inclusion of accelerating techniques aimed at reducing the number of iterations and CPU time. The methodology was proven in a real system and test systems. Results are discussed in this paper.

Uniform Voltage Distribution Control for Series Connected DC–DC Converters

Abstract: This paper investigates applications of current-mode, shared-bus commercial-off-the-shelf (COTS) dc-dc converters to power system architectures configured as parallel-input, series-output (PISO) and series-input, parallel-output (SIPO). By employing a PISO (or SIPO) architecture, current-mode COTS converters can transform their system input voltage to higher (or lower) system output voltage, provide ease and flexibility of power expansion, and preserve system efficiencies equal to those of standalone converters. Nonuniform output (or input) voltages still exist within a PISO (or SIPO) power system using identical converters when the system lacks proper distribution control of the series connected output (or input) voltages-and thus, system reliability suffers from thermal overstress to the converters that contribute a greater portion of the output power. Through unified approaches of voltage distribution control for the PISO and SIPO architectures, a series-connected converter power system attains robust stability and reliability. Two effective approaches to uniform voltage distribution control-the central-limit and maximum-limit voltage distribution-will be discussed. Both computer simulation and experimental prototypes validate both of the uniform voltage distribution power converter architectures.

Nested Fast and Simultaneous Solution for Time-Domain Simulation of Integrative Power-Electric and Electronic Systems

Abstract: As power electronics are increasingly used in power-electric networks, there is an interest in the creation of time-domain simulation techniques that can model the diversity of the integrative power-electric and electronic system while achieving high accuracy and computational speed. In the proposed method, generation of electric network equivalents (GENE), this is supported through the nested structure of the overall simulation process. One or multiple parent simulations, in which the unknown voltages are calculated using nodal analysis, launch multiple child simulations concerned with diakoptic subdivisions of the system under study. The interfaces for information exchange between parent and child levels are designed to provide encapsulation. This makes the subdivisions appearing from outside in the form of network branches compatible with the nodal analysis approach. It also facilitates the use of diverse solution methods for different child simulations, as it is shown for the simultaneous solution of equations formulated with nodal analysis and state space methods. Computational efficiency is obtained through the coordinated application of sparse-matrix methods, piecewise linear approximation of nonlinear characteristics, and precalculation of operations pertaining to recurring power-electronic switch statuses. The resulting overall solution process is simultaneous, distributed, and suitable for real-time simulation. The devised methodology is validated through simulation of the CIGRE HVdc benchmark model, comprising ac networks, twelve-pulse power-electronic converter stations, harmonic filters, and dc transmission

A Novel Approach Based on Nonactive Power for the Identification of Disturbing Loads in Power Systems

Abstract: In this paper, a new approach is proposed for the detection of harmonic sources in polluted power systems. It is a single- point strategy, based on a comparison among different "nonactive" power quantities proposed in literature that, in the same working conditions, assume different values at the same metering section. Some simulations tests were carried out on a standard IEEE test system proposed by other authors as a benchmark system for the analysis of multipoint measurement techniques for harmonic pollution monitoring. The obtained results show that the proposed single-point approach is in agreement with other strategies already proposed in the literature and can provide useful indications for the detection of the dominant harmonic source upstream or downstream the metering section also in some critical cases.

Investigating the Impact of Pulsed Power Charging Demands on Shipboard Power Quality

Abstract: The impact of pulsed power loads on shipboard power systems need to be properly determined to prevent pulsed loads from causing unacceptable power quality deviations, interference with other loads and degradation of overall system performance. This paper uses a high fidelity modeling and simulation approach to investigate the impact of real and reactive power, pulse ramp rate, pulse duration and frequency of occurrence of the pulsed power load. For this purpose, a notional shipboard power system, modeled in a real-time digital simulator, is used. Most pulsed loads on shipboard systems are not fed directly from the prime power system but via an energy storage system. This energy storage system in turn is interfaced with the shipboard prime power system typically through an electronic front-end charging circuit. In order to evaluate the impact of pulsed loads, existing power quality standards (related to voltage transients, harmonic distortions, and frequency variations) are applied.

A Combined Model for Analyzing the Interdependency of Electrical and Gas Systems

Abstract: With increasing investment in natural gas powered generation technologies, limitations in gas delivery capabilities are becoming increasingly relevant to operational planning for power systems. This paper presents a combined model for the electrical and natural gas operation based on mixed integer linear programming. This combined model can be used for analyzing the interdependencies of electrical and natural gas systems, as well as identifying critical vulnerabilities which cannot be observed by studying the electrical and natural gas systems separately. A three-bus system with four gas nodes is presented to demonstrate the proposed model.

Systems and methods for a real-time synchronized electrical power system simulator for "what-if" analysis and prediction over electrical power networks

Abstract: A system for real-time modeling of electrical system performance is disclosed. The system includes a data acquisition component, a power analytics server and a client terminal. The power analytics server is comprised of a virtual system modeling engine, an analytics engine and a power system simulation engine. The virtual system modeling engine is configured to generate predicted data output utilizing a first virtual system model. The analytics engine is configured to synchronize the first virtual system model when a difference between the real-time data output and the predicted data output exceeds a threshold. The power system simulation engine is configured to store and process patterns and facilitate modification of parameters on the first virtual system model to create a second virtual system model; and forecast an aspect of the electrical system operating under parameters of the second virtual system model. The client terminal displays the forecasted aspects.

Real-Time Digital Time-Varying Harmonic Modeling and Simulation Techniques IEEE Task Force on Harmonics Modeling and Simulation

Abstract: With the growing importance of power quality problems to electric utilities and customers, there is an increased focus on the search for new tools and techniques for accurate analysis and resolution of such problems. This paper reviews currently available techniques for the modeling and simulation of time-varying harmonics in real-time. Following a brief summary of the currently used off-line harmonics modeling and simulation methods, the principles and system element representations using wave digital filter (WDF) and discrete wavelet transform (DWT) methods are discussed. Hardware and software architectures of real-time network simulator (RTNS), HYPERSIM, and PC-cluster based real-time simulator are presented. Towards the end, two case studies are given to demonstrate the real-time analysis of time-varying harmonics generated by a three-phase arc furnace using the PC-cluster based real-time simulator, and a real-time hardware-in-the-loop (HIL) equipment testing using the real-time digital simulator (RTDS)

Online Inference of the Dynamic Security Level of Power Systems Using Fuzzy Techniques

Abstract: Dynamic security assessment (DSA) is the evaluation of the ability of the power system to withstand sudden disturbances and to survive the transition to an acceptable steady state condition. During system operation, the online determination of the dynamic security level is fundamental in order to take appropriate countermeasures, with the goal of bringing the system, if necessary, to a more secure operation condition. The most important drawbacks are the lack of "easy to use" and "comprehensive" DSA tools for system operators and the speed of computation that make online DSA to be still not fully operational, particularly when complex models are required for analyzing large interconnected systems. To overcome this, a new approach for power system online DSA is presented in this paper. The proposal is based on a three-stage fuzzy inference system, which composes a fuzzy index making use of seven performance indexes herein defined. The calculation of the performance indexes is based on results obtained through full simulations of the system behavior in front of each one of the credible contingencies in a given operation state. The full simulation, the calculation of the performance indexes and the composing of the fuzzy index are made using distributed processing. The performance of the methodology herein proposed is evaluated using 115-node electric grid, and the results obtained are shown and discussed

Design of an Optimal Hybrid Energy System Model for Remote Rural Area Power Generation

Abstract: This paper deals with the design of a hybrid energy system consisting of wind, photovoltaic, biomass and small/micro hydro to supply continuous power to the load. A diesel generator is added to ensure continuous power supply and to take care of intermittent nature of wind and photovoltaic. The paper reports the results of optimization of hybrid energy system model of a remote area of Jaunpur block of Uttaranchal state of India. The model has been developed with the objective of minimizing cost function based on demand and potential constraints and optimized using computer programme developed in C++. The economic analysis has resulted in the calculation of capital cost, cost of energy for different types of resources and optimized cost of hybrid energy system. To consider the fluctuation in the discharge and power generation from SHP, the EPDF has been varied from 1.0 to 0.0. The EPDF is Electric Power Delivery Factor (also called optimizing power factor) has maximum value equal tol.

Load frequency control in interconnected power system using modified dynamic neural networks

Abstract: This paper present power system load frequency control by modified dynamic neural networks controller. The controller has dynamic neurons in hidden layer and conventional neurons in other layers. For considering the sensitivity of power system model, the neural network emulator used to identify the model simultaneously with control process. To have validation of proposed structure of neural network controller the results of simulation demonstrated that the proposed controller offers better performance than conventional neural network controller.

Fuzzy Stabilization of Power Systems in a Co-Generation Scheme Subject to Random Abrupt Variations of Operating Conditions

Abstract: In this brief, a new stabilizing controller for the power system of an industrial plant operating in a co-generation scheme is proposed. The main source of perturbations considered in the operating conditions are random abrupt fluctuations in the local load, corresponding to the industrial processes being turned on and/or off. These fluctuations are described as Markovian jumps in the parameters of the power system. The proposed controller follows a standard structure which combines an automatic voltage regulator with a supplementary stabilizing term. This term is obtained with a fuzzy-model-based control technique formulated in the context of linear matrix inequalities under damping and control input constraints. Simulations performed on both a single-machine infinite-bus model and on a multimachine model show the effectiveness of the proposed fuzzy control strategy in reducing the oscillations as well as in maintaining a desired operating condition

Electric power control center visualization using Geographic Data Views

Abstract: The paper introduces a new technique for power system visualization known as geographic data views, or GDVs. The impetus behind the development of GDVs is to use dynamically created visualization in order to show a wider range of power system information than is possible using the existing geographically based wide-area visualizations that are becoming common in electric power control centers. With the GDV approach power system visualizations can be dynamically created by operators or engineers using power system information along with geographic information imbedded in the power system model. The paper demonstrates the approach for several sample data sets.

Short-Term Operation Planning of Integrated Hydrothermal and Natural Gas Systems

Abstract: This paper integrates the natural gas and hydrothermal systems in terms of power and gas optimal short- term operations planning and unit commitment. In this paper, the natural gas network model including storages and pipelines are integrated with hydrothermal systems to optimize short-term operation of both systems simultaneously. The proposed model considers the constraints at the hydrothermal system, natural gas extraction, natural gas storage operation and pipeline. The proposed model results in a large-scale mixed-integer nonlinear programming problem where the objective function is to minimize the integrated gas-electricity system operation costs. To solve the integrated electricity-gas optimal short-term planning problem an approach based on Dual Decomposition, Lagrangian Relaxation and Dynamic Programming is employed. A didactic integrated hydrothermal and gas system case study is presented. The proposed model shows the importance of the integration of the two systems in terms of operation, planning, security and reliability.

Measurement-based Load Modeling using Genetic Algorithms

Abstract: Load modeling is very important to power system operation and control. Measurement-based load modeling has been widely practiced in recent years. Mathematically, measurement-based load modeling problem are closely related to the parameter identification area. Consequently, an efficient optimization method is needed to derive the load model parameters based on the feedback of estimation errors between the measurements and model outputs. This paper reports our work on applying genetic algorithms on measurement-based load modeling research. Due to its robustness to the initial guesses on the load model parameters, genetic algorithms are very suitable for load model parameter identification. Two cases including both the real measurement in a power station and the digital simulation are studied in the paper. For comparison purpose, the classical nonlinear least square estimation method is also applied to find the load model parameters. The simulated outputs from the load model confirm the efficiency of genetic algorithms in measurement-based load modeling analysis. Future work will focus on fastening the converging speed of the genetic algorithms, and/or utilizing more efficient evolutionary computation methods.

Design and Modelling of Thermostatically Controlled Loads as Frequency Controlled Reserve

Abstract: Using demand as frequency controlled reserve (DFR) is beneficial to power systems in many aspects. To study the impacts of this technology on power system operation, control logics and simulation models of relevant loads should be carefully developed. Two advanced control logics for using demand as reserve have been presented in this paper. Electricity loads that are applicable for the technique in practical power systems are analysed. Moreover, a simulation model of thermostatically controlled loads, which can provide frequency activated reserve by controlling their set points according to system frequency, is developed. The developed simulation model is able to represent a variety of aggregated thermostatically controlled loads, such as heaters or refrigerators. Uncertainties including customer behaviours and ambient temperature variation are also modelled. Preliminary simulation results are presented and analysed, which demonstrates the great potentials of the DFR technology.

The cross-entropy method for power system combinatorial optimization problems

Abstract: We present an application of a cross-entropy based combinatorial optimization method for solving some unit commitment problems. We report simulation results and analyze, under several perspectives (accuracy, computing times, ability to solve efficiently large-scale problems), the performances of the approach.

Load Transient Mitigation For Stand-alone Fuel Cell Power Generation Systems

Abstract: Summary form only given. A load transient mitigation technique is proposed in this paper for stand-alone fuel cell-battery power systems. The technique can be used not only to improve the output power quality of the overall system, but also to mitigate or eliminate the electrical feedback stresses upon fuel cells caused by load transients. As a result, the durability of fuel cell can also be improved. System analysis and controller design procedure for the proposed technique are given in the paper. Simulation studies have been carried out for proton exchange membrane fuel cell (PEMFC) and solid oxide fuel cell (SOFC) based power systems. Simulation results show the effectiveness of the proposed technique in preventing load transients to affect fuel cell performance.

Simulink Model for Hybrid Power System Test-bed

Abstract: The Hybrid Power System Test-bed currently being constructed at NAVSEA Philadelphia is designed to serve as a developmental platform for the evaluation of hybrid power and propulsion options related to unmanned surface vehicles (USVs) Prior to component integration, a Matlab/Simulink model of the test-bed was created to simulate the system interactions and assist in the detailed electrical design A reduced order system model was required before a detailed analysis of the individual components was performed This paper describes the evolution of the test-bed model and the work to date in developing detailed component models for the system