Showing papers on "Electric power system published in 2004"

Definition and classification of power system stability IEEE/CIGRE joint task force on stability terms and definitions

Abstract: The problem of defining and classifying power system stability has been addressed by several previous CIGRE and IEEE Task Force reports. These earlier efforts, however, do not completely reflect current industry needs, experiences and understanding. In particular, the definitions are not precise and the classifications do not encompass all practical instability scenarios. This report developed by a Task Force, set up jointly by the CIGRE Study Committee 38 and the IEEE Power System Dynamic Performance Committee, addresses the issue of stability definition and classification in power systems from a fundamental viewpoint and closely examines the practical ramifications. The report aims to define power system stability more precisely, provide a systematic basis for its classification, and discuss linkages to related issues such as power system reliability and security.

Power Electronics as Efficient Interface in Dispersed Power Generation Systems

Abstract: The global electrical energy consumption is rising and there is a steady increase of the demand on the power capacity, efficient production, distribution and utilization of energy. The traditional power systems are changing globally, a large number of dispersed generation (DG) units, including both renewable and nonrenewable energy sources such as wind turbines, photovoltaic (PV) generators, fuel cells, small hydro, wave generators, and gas/steam powered combined heat and power stations, are being integrated into power systems at the distribution level. Power electronics, the technology of efficiently processing electric power, play an essential part in the integration of the dispersed generation units for good efficiency and high performance of the power systems. This paper reviews the applications of power electronics in the integration of DG units, in particular, wind power, fuel cells and PV generators.

Microgrid: a conceptual solution

Abstract: Application of individual distributed generators can cause as many problems as it may solve. A better way to realize the emerging potential of distributed generation is to take a system approach which views generation and associated loads as a subsystem or a "microgrid". During disturbances, the generation and corresponding loads can separate from the distribution system to isolate the microgrid's load from the disturbance (providing UPS services) without harming the transmission grid's integrity. This ability to island generation and loads together has a potential to provide a higher local reliability than that provided by the power system as a whole. In this model it is also critical to be able to use the waste heat by placing the sources near the heat load. This implies that a unit can be placed at any point on the electrical system as required by the location of the heat load.

Analytical approaches for optimal placement of distributed generation sources in power systems

Abstract: Power system deregulation and the shortage of transmission capacities have led to increased interest in distributed generation (DG) sources. Proper location of DGs in power systems is important for obtaining their maximum potential benefits. This paper presents analytical methods to determine the optimal location to place a DG in radial as well as networked systems to minimize the power loss of the system. Simulation results are given to verify the proposed analytical approaches.

Risk Assessment Of Power Systems: Models, Methods, and Applications

Abstract: Preface. 1 Introduction. 1.1 Risk in Power Systems. 1.2 Basic Concepts of Power System Risk Assessment. 1.3 Outline of the Book. 2 Outage Models of System Components. 2.1 Introduction. 2.2 Models of Independent Outages. 2.3 Models of Dependent Outages. 2.4 Conclusions. 3 Parameter Estimation in Outage Models. 3.1 Introduction. 3.2 Point Estimation of Mean and Variance of Failure Data. 3.3 Interval Estimation of Mean and Variance of Failure Data. 3.4 Estimating Failure Frequency of Individual Components. 3.5 Estimating Probability from a Binomial Distribution. 3.6 Experimental Distribution of Failure Data and Its Test. 3.7 Estimating Parameters in Aging Failure Models. 3.8 Conclusions. 4 Elements of Risk Evaluation Methods. 4.1 Introduction. 4.2 Methods for Simple Systems. 4.3 Methods for Complex Systems. 4.4. Conclusions. 5 Risk Evaluation Techniques for Power Systems. 5.1 Introduction. 5.2 Techniques Used in Generation--Demand Systems. 5.3 Techniques Used in Radial Distribution Systems. 5.4 Techniques Used in Substation Configurations. 5.5 Techniques Used in Composite Generation and Transmission Systems. 5.6 Conclusions. 6 Application of Risk Evaluation to Transmission Development Planning. 6.1 Introduction. 6.2 Concept of Probabilistic Planning. 6.3 Risk Evaluation Approach. 6.4 Example 1: Selecting the Lowest--Cost Planning Alternative. 6.5 Example 2: Applying Different Planning Criteria. 6.6 Conclusions. 7 Application of Risk Evaluation to Transmission Operation Planning. 7.1 Introduction. 7.2 Concept of Risk Evaluation in Operation Planning. 7.3 Risk Evaluation Method. 7.4 Example 1: Determining the Lowest--Risk Operation Mode. 7.5 Example 2: A Simple Case by Hand Calculations. 7.6 Conclusions. 8 Application of Risk Evaluation to Generation Source Planning. 8.1 Introduction. 8.2 Procedure for Reliability Planning. 8.3 Simulation of Generation and Risk Costs. 8.4 Example 1: Selecting Location and Size of Cogenerators. 8.5 Example 2: Making a Decision to Retire a Local Generation Plant. 8.6 Conclusions. 9 Selection of Substation Configurations. 9.1 Introduction. 9.2 Load Curtailment Model. 9.3 Risk Evaluation Approach. 9.4 Example 1: Selecting Substation Configuration. 9.5 Example 2: Selecting Transmission Line Arrangement Associated with Substations. 9.6 Conclusions. 10 Reliability--Centered Maintenance. 10.1 Introduction. 10.2 Basic Tasks in RCM. 10.3 Example 1: Transmission Maintenance Scheduling. 10.4 Example 2: Workforce Planning in Maintenance. 10.5 Example 3: A Simple Case Performed by Hand Calculations. 10.6 Conclusions. 11 Probabilistic Spare--Equipment Analysis. 11.1 Introduction. 11.2 Spare--Equipment Analysis Based on Reliability Criteria. 11.3 Spare--Equipment Analysis Using the Probabilistic Cost Method. 11.4 Example 1: Determining Number and Timing of Spare Transformers. 11.5 Example 2: Determining Redundancy Level of 500 kV Reactors. 11.6 Conclusions. 12 Reliability--Based Transmission--Service Pricing. 12.1 Introduction. 12.2 Basic Concept. 12.3 Calculation Methods. 12.4 Rate Design. 12.5 Application Example. 12.6 Conclusions. 13 Probabilistic Transient Stability Assessment. 13.1 Introduction. 13.2 Probabilistic Modeling and Simulation Methods. 13.3 Procedure. 13.4 Examples. 13.5 Conclusions. Appendix A Basic Probability Concepts. A.1 Probability Calculation Rules. A.2 Random Variable and its Distribution. A.3 Important Distributions in Risk Evaluation. A.4 Numerical Characteristics. Appendix B Elements of Monte Carlo Simulation. B.1 General Concept. B.2 Random Number Generators. B.3 Inverse Transform Method of Generating Random Variates. B.4 Important Random Variates in Risk Evaluation. Appendix C Power--Flow Models. C.1 AC Power--Flow Models. C.2 DC Power--Flow Models. Appendix D Optimization Algorithms. D.1 Simplex Methods for Linear Programming. D.2 Interior Point Method for Nonlinear Programming. Appendix E Three Probability Distribution Tables. References. Index. About the Author.

A modified adaptive hill climbing MPPT method for photovoltaic power systems

Abstract: Maximum power point tracking (MPPT) must usually be integrated with photovoltaic (PV) power systems so that the photovoltaic arrays are able to deliver maximum available power. In this paper, a modified adaptive hill climbing (MAHC) MPPT method is introduced. It can be treated as an extension of the traditional hill climbing algorithm. The simulation and experimental results show that the proposed MPPT control can avoid tracking deviation and result in improved performance in both dynamic response and steady-state.

Probabilistic load flow computation using the method of combined cumulants and Gram-Charlier expansion

Abstract: Open access transmission has created a deregulated power market and brought new challenges to system planning. This paper proposes a new method to compute a probabilistic load flow in extensive power systems for the purpose of using it as a quick screening tool to determine the major investment on improving transmission system inadequacy. This innovative method combines the concept of Cumulants and Gram-Charlier expansion theory to obtain probabilistic distribution functions of transmission line flows. It has significantly reduced the computational time while maintaining a high degree of accuracy. This enables probabilistic analysis of power flow problems to be treated objectively and allows quantitative assessment of system reliability.

Comparison of the response of doubly fed and fixed-speed induction generator wind turbines to changes in network frequency

Abstract: Synchronous and fixed-speed induction generators release the kinetic energy of their rotating mass when the power system frequency is reduced. In the case of doubly fed induction generator (DFIG)-based wind turbines, their control system operates to apply a restraining torque to the rotor according to a predetermined curve with respect to the rotor speed. This control system is not based on the power system frequency and there is negligible contribution to the inertia of the power system. A DFIG control system was modified to introduce inertia response to the DFIG wind turbine. Simulations were used to show that with the proposed control system, the DFIG wind turbine can supply considerably greater kinetic energy than a fixed-speed wind turbine.

Analysis of electric grid security under terrorist threat

Abstract: We describe new analytical techniques to help mitigate the disruptions to electric power grids caused by terrorist attacks. New bilevel mathematical models and algorithms identify critical system components (e.g., transmission lines, generators, transformers) by creating maximally disruptive attack plans for terrorists assumed to have limited offensive resources. We report results for standard reliability test networks to show that the techniques identify critical components with modest computational effort.

A model of PV generation suitable for stability analysis

Abstract: This paper describes a model of photovoltaic (PV) generation suitable for studying its interactions with the power system. Experimental results suggest that the maximum power point tracking part of the control system of the PV generator dominates the dynamic behavior of the system. These experimental results are used to develop and validate the proposed model. It is shown that the model accurately reflects the behavior of the generator following both small and fast changes in irradiance and AC grid voltage. The proposed model is designed to be integrated in a dynamic simulation program.

Power System Optimization

Abstract: Electric power systems have experienced continuous growth in all the three major sectors of the power system namely, generation, transmission and distribution. Electricity cannot be stored economically, but there has to be continuous balance between demand and supply. The increase in load sizes and operational complexity such as generation allocation, non-utility generation planning, and pricing brought about by the widespread interconnection of transmission systems and inter-utility power transaction contracts, has introduced major difficulties into the operation of power system. Allocation of customers' load demands among the available thermal power generating units in an economic, secure and reliable way has been a subject of interest since 1920 or even earlier. However practically, the generating units have non-convex input-output characteristics due to prohibited operating zones, valve-point loadings and multi-fuel effects considered as heavy equality and inequality constraints, which cannot be directly solved by mathematical programming methods. Dynamic programming can treat such types of problems, but it suffers from the curse of dimensionality. Over the past decade, many prominent methods have been developed to solve these problems, such as the hierarchical numerical methods, tabu search, neural network approaches, genetic algorithm, evolutionary programming, swarm optimisation, differential evolution and hybrid search methods. Review of evolutionary method has been presented.

Evaluation of time delay effects to wide-area power system stabilizer design

Abstract: Centralized control using system-wide data has been suggested to enhance the dynamic performance of large interconnected power systems. Because of the distance involved in wide-area interconnections, communication delay cannot be ignored. Long time delay may be detrimental to system stability and may degrade system performance. The time delay tolerance of a centralized controller and the associated performance tradeoff is analyzed using a small gain criterion. Special attention is paid to the choice of weighting functions in a robust control design. As expected, it is found that time delay tolerance decreases when the system bandwidth increases, while the nominal system time-domain performance is concomitantly improved. Several approaches which can maintain a good system performance while increasing the time delay tolerance are suggested and compared. A modern controller design technique, like gain scheduling via linear matrix inequalities, is evaluated for the design of the supervisory power system stabilizer accounting for various time delays.

Generating capacity adequacy associated with wind energy

Abstract: The wind is a highly variable energy source and behaves far differently than conventional energy sources. This paper presents a methodology for capacity adequacy evaluation of power systems including wind energy. The results and discussions on two representative systems containing both conventional generation units and wind energy conversion systems (WECS) are presented. A Monte Carlo simulation approach is used to conduct the analysis. The hourly wind speeds are simulated using an autoregressive moving average time-series model. A wide range of studies were conducted on two different sized reliability test systems. The studies show that the contribution of a WECS to the reliability performance of a generation system can be quantified and is highly dependent on the wind site conditions. A WECS can make a significant reliability contribution given a reasonably high wind speed. Wind energy independence also has a significant positive impact on the reliability contribution of multiple WECS.

Wide-area measurement-based stabilizing control of power system considering signal transmission delay

Abstract: Recent technological advances in the area of wide-area measurement systems (WAMS) has enabled the use of a combination of measured signals from remote locations for centralized control purpose. The transmitted signals can be used for multiple swing mode damping using a single controller. However, there is an unavoidable delay involved before these signals are received at the controller site. To ensure satisfactory performance, this delay needs to be taken into account in the control design stage. This paper focuses on damping control design taking into account a delayed arrival of feedback signals. A predictor-based H/sub /spl infin// control design strategy is discussed for such time-delayed systems. The concept is utilized to design a WAMS-based damping controller for a prototype power system using a static var compensator. The controller performance is evaluated for a range of operating conditions.

Power system security assessment

Abstract: Security refers to the degree of risk in a power system's ability to survive imminent disturbances (contingencies) without interruption to customer service It relates to robustness of the system to imminent disturbances and, hence, depends on the system operating condition as well as the contingent probability of disturbances DSA refers to the analysis required to determine whether or not a power system can meet specified reliability and security criteria in both transient and steady-state time frames for all credible contingencies Ensuring security in the new environment requires the use of advanced power system analysis tools capable of comprehensive security assessment with due consideration to practical operating criteria These tools must be able to model the system appropriately, compute security limits in a fast and accurate manner, and provide meaningful displays to system operators Online dynamics security assessment can provide the first line of defense against widespread system disturbances by quickly scanning the system for potential problems and providing operators with actionable results With the development of emerging technologies, such as wide-area PMs and ISs, online DSA is expected to become a dominant weapon against system blackouts

Optimal choice and allocation of FACTS devices in deregulated electricity market using genetic algorithms

Abstract: This paper deals with the optimal choice and allocation of FACTS devices in multimachine power systems using genetic algorithm. The objective is to achieve the power system economic generation allocation and dispatch in deregulated electricity market. Using the proposed method, the locations of the FACTS devices, their types and ratings are optimized simultaneously. Different kinds of FACTS devices are simulated in this study: UPFC, TCSC, TCPST, and SVC. Furthermore, their investment costs are also considered. Simulation results validate the capability of this new approach in minimizing the overall system cost function, which includes the investment costs of the FACTS devices and the bid offers of the market participants. The proposed algorithm is an effective and practical method for the choice and allocation of suitable FACTS devices in deregulated electricity market environment.

Evidence for self-organized criticality in a time series of electric power system blackouts

Abstract: We analyze a 15-year time series of North American electric power transmission system blackouts for evidence of self-organized criticality (SOC). The probability distribution functions of various measures of blackout size have a power tail and rescaled range analysis of the time series shows moderate long-time correlations. Moreover, the same analysis applied to a time series from a sandpile model known to be self-organized critical gives results of the same form. Thus, the blackout data seem consistent with SOC. A qualitative explanation of the complex dynamics observed in electric power system blackouts is suggested.

Energy price forecasting in the Ontario competitive power system market

Abstract: This paper introduces a method for forecasting energy prices using artificial intelligence methods, such as neural networks and fuzzy logic, and a combination of the two. The new approach is compared with some of the exiting methods. Various factors affecting the market clearing price are investigated. Results for the Ontario electricity market are presented.

Modeling of transfer Characteristics for the broadband power line communication channel

Abstract: This paper presents a novel approach to model the transfer function of electrical power lines for broadband power line communication. In this approach, the power line is approximated as a transmission line and the two intrinsic parameters, the characteristic impedance and the propagation constants, are derived based on the lumped-element circuit model. Using these intrinsic parameters, the transfer characteristics for a N-branch power distribution network are derived based on the scattering matrix method. Detail derivation of this line model is given in this paper. The model has been verified with practical measurements conducted on actual power networks. It is demonstrated that the model accurately determine the line characteristics under different network configuration and when different household appliances are connected.

HVDC and FACTS Controllers: Applications of Static Converters in Power Systems

Abstract: Preface. Acronyms. 1: Introduction to HVDC Transmission. 1.1. Introduction. 1.2. Comparison of AC-DC Transmission. 1.3. Types of HVDC Systems. 1.4. References. 2: Types of Converters. 2.1. Introduction. 2.2. Current Source Converters (CSC). 2.3. Voltage Source Converters (VSC). 2.4. Closing Remarks. 2.5. References. 3: Synchronization Techniques for Power Converters. 3.1. Introduction. 3.2. Review of GFUs. 3.3. GFUs - Design And Analysis. 3.4. Tests On GFUs. 3.5. EMTP Simulation Of A Test System. 3.6. Conclusions. 3.7. Acknowledgement. 3.8. References. 4: HVDC Controls. 4.1. Historical Background. 4.2. Functions of HVDC Controls. 4.3. Control Basics for a Two-terminal DC Link. 4.4. Current Margin Control Method. 4.5. Current Control at the Rectifier. 4.6. Inverter Extinction Angle Control. 4.7. Hierarchy of Controls. 4.8. Action By Controls After a Disturbance. 4.9. References. 5: Forced Commutated HVDC Converters. 5.1. Introduction. 5.2. Commutation Techniques for HVDC Converters. 5.3. Examples of FC Converters for HVDC Transmission. 5.4. References. 6: Capacitor Commutated Converters for HVDC Systems. 6.1. Capacitor Commutated Converters (CCC). 6.2. Controlled Series Capacitor Converter (CSCC). 6.3. Comparison of CCC and CSCC. 6.4. Garabi Interconnection between Argentina-Brazil. 6.5. Closing Remarks. 6.6. Acknowledgement. 6.7. References. 7: Static Compensators: STATCOM Based on Chain-Link Converters. 7.1. Introduction. 7.2. The Chainlink Converter. 7.3. Advantages of the Chain Circuit STATCOM. 7.4. Design for Production. 7.5. Acknowledgement. 7.6. References. 8: HVDC Systems Using Voltage Source Converters. 8.1. Introduction. 8.2. Basic Elements of HVDC using VSCs. 8.3. Voltage Source Converter. 8.4. Applications. 8.5. Tjaereborg Windpower Project in Denmark. 8.6. Power Supply to Remote Locations (i.e. Islands). 8.7. Asynchronous Inter-Connections. 8.8. Concluding Remarks. 8.9. Acknowledgement. 8.10. References. 9: Active Filters. 9.1. Introduction. 9.2. DC Filters. 9.3. AC Filters. 9.4. Concluding Remarks. 9.5. Acknowledgement. 9.6. References. 10: Typical Disturbances in HVDC Systems. 10.1. Introduction. 10.2. CIGRE Benchmark Model for HVDC Control Studies. 10.3. Details of Control Systems Used. 10.4. Results. 10.5. Closing Remarks. 10.6. Acknowledgement. 10.7. References. 11: Advanced Controllers. 11.1. Introduction. 11.2. Application of an Advanced VDCL Unit. 11.3. Conclusions. 11.4. Acknowledgement. 11.5. References. 12: Measurement/Monitoring Aspects. 12.1. Introduction.

Application of linear matrix inequalities for load frequency control with communication delays

Abstract: Load frequency control has been used for decades in power systems. Traditionally, this has been a centralized control by area with communication over a dedicated and closed network. New regulatory guidelines allow for competitive markets to supply this load frequency control. In order to allow an effective market operation, an open communication infrastructure is needed to support an increasing complex system of controls. While such a system has great advantage in terms of cost and reliability, the possibility of communication signal delays and other problems must be carefully analyzed. This paper presents a load frequency control method based on linear matrix inequalities. The primary aim is to find a robust controller that can ensure good performance despite indeterminate delays and other problems in the communication network.

Active input-voltage and load-current sharing in input-series and output-parallel connected modular DC-DC converters using dynamic input-voltage reference scheme

Abstract: This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.

Performance evaluation of PLL algorithms for single-phase grid-connected systems

Abstract: Phase angle, frequency and amplitude of the utility voltage vector are basic information for an increasing number of grid-connected power conditioning equipments, such as PWM rectifiers, uninterruptible power systems (UPS), voltage sag compensators and the emerging distributed generation systems. For these applications, accurate tracking of the utility voltage vector is essential to ensure correct operation of the control system. This paper presents a comparative study of synchronous reference frame PLL algorithms for single-phase systems. Simulation and experimental results, including operation of the PLL structures under distorted utility conditions are presented, to allow a performance evaluation of the PLL algorithms.

Performance evaluation of PLL algorithms for single-phase grid-connected systems

Abstract: Phase angle, frequency and amplitude of the utility voltage vector are basic information for an increasing number of grid-connected power conditioning equipments, such as PWM rectifiers, uninterruptible power systems (UPS), voltage sag compensators and the emerging distributed generation systems. For these applications, accurate tracking of the utility voltage vector is essential to ensure correct operation of the control system. This paper presents a comparative study of synchronous reference frame PLL algorithms for single-phase systems. Simulation and experimental results, including operation of the PLL structures under distorted utility conditions are presented, to allow a performance evaluation of the PLL algorithms.

Dynamic and transient analysis of power distribution systems with fuel Cells-part I: fuel-cell dynamic model

Abstract: The first part of this two-part-paper develops a comprehensive nonlinear dynamic model of a solid-oxide fuel cell (SOFC) that can be used for dynamic and transient stability studies. The model based on electrochemical and thermal equations, accounts for temperature dynamics and output voltage losses. The output voltage response of a stand-alone fuel-cell plant to a step load change, a fuel flow step change, and fast load variations are simulated to illustrate the dynamic behavior of SOFC for fast and slow perturbations. A method for interfacing the proposed fuel-cell models to a power system stability package is developed.

Market-based transmission expansion planning

Abstract: Restructuring and deregulation has exposed transmission planner to new objectives and uncertainties. Therefore, new criteria and approaches are needed for transmission planning in deregulated environments. A new market-based approach for transmission planning in deregulated environments is presented in this paper. The main contribution of this research is: i) introducing a new probabilistic tool, named probabilistic locational marginal prices, for computing the probability density functions of nodal prices; ii) defining new market-based criteria for transmission expansion planning in deregulated environments; and iii) presenting a new approach for transmission expansion planning in deregulated environments using the above tool and criteria. The advantages of this approach are: i) it encourages and facilitates competition among all participants; ii) it provides nondiscriminatory access to cheap generation for all consumers; iii) it considers all random and nonrandom power system uncertainties and selects the final plan after risk assessment of all solutions; and iv) it is value based and considers investment cost, operation cost, congestion cost, load curtailment cost, and cost caused by system unreliability. The presented approach is applied to IEEE 30-bus test system.

A comparison of the AC and DC power flow models for LMP calculations

Abstract: The paper examines the tradeoffs between using a full ac model versus the less exact, but much faster, dc power flow model for LMP-based market calculations. The paper first provides a general discussion of the approximations associated with using a dc model, with an emphasis on the impact these approximations will have on security constrained OPF (SCOPF) results and LMP values. Then, since the impact of the approximations can be quite system specific, the paper provides case studies using both a small 37 bus system and a somewhat larger 12,965 bus model of the Midwest U.S. transmission grid. Results are provided comparing both the accuracy and the computational requirements of the two models. The general conclusion is that while there is some loss of accuracy using the dc approximation, the results actually match fairly closely with the full ac solution.