Showing papers on "Electric power system published in 1997"

Dynamic simulation of electric machinery : using MATLAB/SIMULINK

Abstract: 1. Introduction. 2. Introduction to MATLAB/SIMULINK. 3. Basics on Magnetics and Line Modeling. 4. Transformers. 5. Basics of Electric Machines and Transformations. 6. Three-Phase Induction Machines. 7. Synchronous Machines. 8. DC Machines. 9. Control of Induction Machines. 10. Synchronous Machines in Power Systems and Drives. Appendix A: Numerical Methods. Appendix B: Website. Bibliography. Index.

Contributions of individual generators to loads and flows

Abstract: Because of the introduction of competition in the electricity supply industry, it has become much more important to be able to determine which generators are supplying a particular load, how much use each generator is making of a transmission line and what is each generator's contribution to the system losses. This paper describes a technique for answering these questions which is not limited to incremental changes and which is applicable to both active and reactive power. Starting from a power flow solution, the technique first identifies the busses which are reached by power produced by each generator. Then it determines the sets of buses supplied by the same generators. Using proportionality assumption, it is then possible to calculate the contribution of each generator to the loads and flows. The applicability of the proposed technique is demonstrated using a 30-bus example.

Static Synchronous Series Compensator: A Solid-State Approach to the Series Compensation of Transmission Lines

Abstract: This paper describes an active approach to series line compensation, in which a synchronous voltage source, implemented by a gate turn-off thyristor (GTO) based voltage-sourced inverter, is used to provide controllable series compensation. This compensator, called static synchronous series compensator (SSSC), can provide controllable compensating voltage over an identical capacitive and inductive range, independently of the magnitude of the line current. It is immune to classical network resonances. In addition to series reactive compensation, with an external DC power supply it can also compensate the voltage drop across the resistive component of the line impedance. The compensation of the real part of the impedance can maintain high X/R ratio even if the line has a very high degree of series compensation. Concurrent and coordinated modulation of reactive and real compensation can greatly increase power oscillation damping. The paper discusses the basic operating and performance characteristics of the SSSC, and compares them to those characterizing the more conventional compensators based on thyristor-switched or controlled series capacitors. It also presents some of the results of TNA simulations carried out with an SSSC hardware model.

Flexible AC transmission systems (FACTS)

Abstract: The paper reviews literature which addresses the application of Flexible AC Transmission System (FACTS) concepts to the improvement of Power System utilisation and performance. It summarises literature on using high speed thyristor based control of HVAC power system elements to enhance the power carrying capacity of existing transmission circuits without compromising reliability. It describes a study system representative of existing power systems that has been developed to evaluate the economic and technical issues of loading transmission lines to their thermal limits. Considered are two scenarios, a multi-line corridor and a long radial interconnection, where the issues addressed are transient and dynamic stability, power flow control, reactive support and voltage stability. A benchmark system is developed to validate performance of die more simple devices. It is concluded that FACTS devices have the potential to significantly increase system stability margins thereby increasing loading capabil...

Use of local measurements to estimate voltage-stability margin

Abstract: Estimating the proximity of power systems to voltage collapse in real-time still faces difficulties. Beside the data management and computational issues, any central-control method is subject to the reliability of long-distance data communications. In the paper, the authors describe a new data-processing method to estimate the proximity to voltage collapse. The method (code-named SMARTDevice, for Stability Monitoring And Reference Tuning Device) employs only local measurements-bus voltage and load current-and calculates the strength of the transmission system relative to the bus. The collapse occurs when the local load approaches this value. The method is simple enough so that it can be implemented in a numerical relay. The performance of SMARTDevice is compared against the conventional undervoltage relays. It is shown that the latter can misoperate while the new device does not. SMARTDevice is in fact a new breed of voltage relay whose setpoint is automatically tuned to the power system condition.

Use of UPFC for optimal power flow control

Abstract: This paper deals with optimal power flow control in electric power systems by the use of a unified power flow controller (UPFC). Models suitable for incorporation in power flow programs are developed and analysed. The application of UPFC for optimal power flow control is demonstrated through numerical examples. It is shown that a UPFC has the capability of regulating the power flow and minimising the power losses simultaneously. An algorithm is proposed for determining the optimum size of UPFC for power flow applications. The performance of UPFC is compared with that of a phase shifting transformer (PST).

Unit sizing and control of hybrid wind-solar power systems

Abstract: The aim of this paper is to provide the core of a CAD/CAA tool that can help designers determine the optimal design of a hybrid wind-solar power system for either autonomous or grid-linked applications. The proposed analysis employs linear programming techniques to minimize the average production cost of electricity while meeting the load requirements in a reliable manner, and takes environmental factors into consideration both in the design and operation phases. While in autonomous systems, the environmental credit gained as compared to diesel alternatives can be obtained through direct optimization, in grid-linked systems emission is another variable to be minimized such that the use of renewable energy can be justified. A controller that monitors the operation of the autonomous/grid-linked systems is designed. Such a controller determines the energy available from each of the system components and the environmental credit of the system. It then gives details related to cost, unmet and spilled energies, and battery charge and discharge losses.

Control topology options for single-phase UPS inverters

Abstract: Four control topologies for single-phase uninterruptible power system (UPS) inverters are presented and compared, with the common objective of providing a dynamically stiff, low total harmonic distortion (THD), sinusoidal output voltage. Full-state feedback, full-state command controllers are shown, utilizing both filter inductor current and filter capacitor current feedback to augment output voltage control. All controllers presented include output voltage decoupling in a manner analogous to "back EMF" decoupling in DC motor drives. Disturbance input decoupling of the load current and its derivative is presented. An observer-based controller is additionally considered and is shown to be a technically viable, economically attractive option. The accuracy transfer function of the observer estimate is used to evaluate its measurement performance. Comparative disturbance rejection is evaluated by overlaying the dynamic stiffness (inverse of output impedance) frequency response of each controller on a single plot. Experimental results for one controller are presented.

Coarse-grained distributed optimal power flow

Abstract: We present an approach to parallelizing optimal power flow (OPF) that is suitable for coarse-grained distributed implementation and is applicable to very large interconnected power systems. We demonstrate the approach on several medium size systems, including IEEE Test Systems and parts of the ERCOT system. Our simulations demonstrate the feasibility of distributed implementation of OPF. Rough estimates are made of parallel efficiencies and speed-ups.

Power system dynamics and stability

Abstract: Power System Components. The Power System in the Steady-State. Electromagnetic Phenomena. Electromechanical Dynamics - Small Disturbances. Electromechanical Dynamics - Large Disturbances. Voltage Stability. Frequency Variations. Stability Enhancement. Advanced Power System Modelling. Power System Model Reduction - Equivalents. Steady-State Stability of Multi-Machine System. Power System Dynamic Simulation. Appendix. References. Index.

Sensitivity of the loading margin to voltage collapse with respect to arbitrary parameters

Abstract: Power system loading margin is a fundamental measure of a system's proximity to voltage collapse. Linear and quadratic estimates to the variation of the loading margin with respect to any power system parameter or control are derived. Tests with a 118-bus system indicate that the estimates accurately predict the quantitative effect on the loading margin of altering the system loading, reactive power support, wheeling, load model parameters, line susceptance and generator dispatch. The accuracy of the estimates over a useful range and the ease of obtaining the linear estimate suggest that this method will be of practical value in avoiding power system voltage collapse.

Initial results in electromechanical mode identification from ambient data

Abstract: Power system loads are constantly changing. Over a time-span of a few minutes, these changes are primarily random. The random load variations act as a constant low-level excitation to the electromechanical dynamics of the power system which shows up as ambient noise in field measured voltage, current and power signals. Assuming the random variations are white and stationary over an analysis window, it is theoretically possible to estimate the electromechanical modal frequencies and damping from the spectral content of the ambient noise. In this paper, field collected ambient noise is analyzed by solving the Wiener-Hopf linear prediction equations to estimate the modal frequency and damping. These estimates are then compared with results from a Prony analysis on a ringdown resulting from a 1400 MW brake insertion under the same operating conditions as the ambient data. Results show that estimates are consistent between the ambient and ringdown analysis indicating that it is possible to estimate a power system's electromechanical characteristics simply from ambient data. These results demonstrate that it may be possible to provide power system control and operation algorithms with a real-time estimate of modal frequency and damping.

Neural network based estimation of maximum power generation from PV module using environmental information

Abstract: This paper presents an application of an artificial neural network for the estimation of maximum power generation from PV module. The output power from a PV module depends on environmental factors such as irradiation and cell temperature. For the operation planning of power systems, the prediction of the power generation is inevitable for PV systems. For this purpose, irradiation, temperature and wind velocity are utilized as the input information to the proposed neural network. The output is the predicted maximum power generation under the condition given by those environmental factors. The efficiency of the proposed estimation scheme is evaluated by using actual data on daily, monthly and yearly bases. The proposed method gives highly accurate predictions compared with predictions using the conventional multiple regression model.

Transaction analysis in deregulated power systems using game theory

Abstract: The electric power industry is in transition to a deregulated marketplace for power transactions. In this environment, all power transactions are made based on price rather than cost. A regional power pool is noted as the most straightforward path to a deregulated electricity marketplace. However, many questions remain unanswered regarding the economics of power pool participation. In a deregulated energy marketplace, participants are interested in maximizing their own profits, regardless of the system-wide profits. It is perceived that competition will reduce the price of electricity for retail customers, however, the key issue for participants is related with the price definition to remain competitive. In this paper, the authors use game theory to simulate the decision making process for defining offered prices in a deregulated environment. The outcome of this study may be used by power pool coordinators to discourage unfair coalitions. A modified IEEE 30 bus power system is used as a deregulated power pool to illustrate the main features of the proposed method.

Automatic Learning Techniques in Power Systems

Abstract: From the Publisher: Automatic Learning Techniques in Power Systems is dedicated to the practical application of automatic learning to power systems Power systems to which automatic learning can be applied are screened and the complementary aspects of automatic learning, with respect to analytical methods and numerical simulation, are investigated This book presents a representative subset of automatic learning methods - basic and more sophisticated ones - available from statistics (both classical and modern), and from artificial intelligence (both hard and soft computing) The text also discusses appropriate methodologies for combining these methods to make the best use of available data in the context of real-life problems Automatic Learning Techniques in Power Systems is a useful reference source for professionals and researchers developing automatic learning systems in the electrical power field

Maximum loadability of power systems using interior point nonlinear optimization method

Abstract: This paper proposes a nonlinear optimization interior point (IP) method for the determination of maximum loadability in a power system. Details of the implementation of pure primal-dual and predictor-corrector primal-dual IP algorithms are presented. It is shown that most of the computational effort of the algorithm is taken by the formation and factorization of the augmented Hessian matrix of the IP algorithm. The size of this matrix can be as large as ten times the number of buses in the system. Comparisons of the two IP implementations with large scale power systems with as many as 4000 buses are presented. It is shown that the IP algorithm constitutes an effective method for the determination of the maximum loadability in a power system.

Improving power system dynamics by series-connected FACTS devices

Abstract: This paper examines improvement of power system dynamics by use of unified power flow controllers, thyristor controlled phase shifting transformers and thyristor controlled series capacitors. Models suitable for incorporation in dynamic simulation programs for studying angle stability are analysed. A control strategy for the damping of electromechanical power oscillations using an energy function method is derived. The achieved control laws are shown to be effective both for the damping of large signal and small signal disturbances and are robust with respect to loading condition, fault location and network structure. Furthermore, the control inputs are easily attainable from locally measurable variables. The effectiveness of the controls are demonstrated for model power systems.

Reactive power pricing and management

Abstract: This paper explores the technical and economic issues of determining reactive power pricing structures in an open-access environment. It is believed that reactive power pricing and management under open-access will depend upon two important developments: (1) the functional unbundling of facilities that support the reactive power and voltage control service, and (2) grid rules to facilitate the coordination between generation and transmission systems for reliable system operation. The paper discusses the characteristics of reactive power that must be considered in order to develop a framework for reactive power pricing and management. Several cost allocation methods for valuing reactive power are presented. Two workable reactive power pricing structures are also proposed. The first is based on performance standards and the second is based on the local reactive power market concept.

Application of evolutionary programming to reactive power planning-comparison with nonlinear programming approach

Abstract: This paper proposes an application of evolutionary programming (EP) to reactive power planning (RPP). Several techniques have been developed to make EP practicable to solve a real power system problem and other practical problems. The proposed approach has been used in the IEEE 30-bus system and a practical power system. For illustration purposes, only results for the IEEE 30-bus system are given. Simulation results, compared with those obtained by using a conventional gradient-based optimization method, Broyden's method, are presented to show that the present method is better for power system planning. In the case of optimization of noncontinuous and nonsmooth functions, EP is much better than nonlinear programming. The comprehensive simulation results show a great potential for applications of EP in power system economical and secure operation, planning and reliability assessment.

Estimation of power system inertia constant and capacity of spinning-reserve support generators using measured frequency transients

Abstract: A procedure for estimating the inertia constant M(=2H) of a power system and total on-line capacity of spinning-reserve support generators, using transients of the frequency measured at an event such as a generator load rejection test, is presented. A polynomial approximation with respect to time is applied to the waveform of the transients in estimating the inertia constant, and a simple model based on the idea of average system frequency is assumed in estimating the capacity of the generators. Results of the estimation using the transients at 10 events show that the inertia constant of the 60 Hz power system of Japan is around 14 to 18 seconds in the system load base, and the capacity of the spinning-reserve support generators is 20 to 40% of the system load. The proposed procedure is expected to be tested by Kansai Electric Power Company with increased number of events. This effort will contribute to estimate and evaluate the dynamic behavior of the system frequency in loss of generation or load.

A unified model for the analysis of FACTS devices in damping power system oscillations. I. Single-machine infinite-bus power systems

Abstract: The static VAr compensator (SVC), controllable series compensator (CSC) and phase shifter (PS) are three of the options of power electronic devices, referred to as FACTS (flexible AC transmission systems) devices. They are becoming of increasing importance in suppressing power system oscillations and improving system damping. In this paper, a unified model of a power system installed with these three FACTS devices is established. Their effectiveness in suppressing power system oscillations is investigated by analysing their damping torque contributions to the power system. The work in this paper relies on the theoretical analysis of a general single-machine infinite-bus power system where the objective is to present an insight into the operation of the damping control of the FACTS devices.

Transient power quality problems analyzed using wavelets

Abstract: In the literature, wavelet techniques have been proposed for the identification of power system transient signals (e.g., lightning impulse, and capacitor switching transients). In this paper, the wavelet technique is proposed for the analysis of the propagation of transients in power systems. The advantages and disadvantages of the method are discussed and the way in which these analysis methods complement previously reported identification methods is described. An example based on the discretized solution of a differential equation is given.

Method for generating electrical power from fuel cell powered cars parked in a conventional parking lot

Abstract: The present invention provides a method and apparatus for generating electrical power from multiple vehicles (10) powered by fuel cells while the vehicles are parked in a parking lot. A plurality of spaced-apart electrical receptacles (25) are provided for receiving an electric cable (22) for connection to a parked vehicle for electrically connecting the fuel cell in each of the parked vehicles to the plurality of electrical receptacles. An electric power grid (12) is electrically connected to the plurality of electrical receptacles for transferring D.C. electrical power from the fuel cells in the parked vehicles to the electric power grid. At least one electric power collection station is electrically connected to the electric power grid for collecting at a common point the D.C. electric power in the electric power grid. In addition, at least one inverter is electrically connected to the electric power collection station for converting the D.C. electric power to A.C. electric power. Apparatus is provided for supplying the A.C. electric power to a load or a utility grid.

AGC simulator for price-based operation. I. A model

Abstract: This paper deals with automatic generation control (AGC) in a deregulated electric industry. Through the passage of new public utility regulatory policies, the Federal Energy Regulatory Commission (FERC) encourages an open market system for price based operation. The FERC has issued a notice of proposed rulemaking seeking comments on various ancillary services. One of these ancillary services is load following. This paper suggests the modifications required in the conventional AGC software to prepare students to study load following in price-based market operation. The details of implementing an academic power system are used to highlight the differences between the AGC operation in a vertically integrated industry (conventional paradigm) and a horizontally integrated industry (new paradigm). The future business environment for electric utilities is incompletely defined as of this writing. Therefore, a framework for price-based operation is developed to assist students in understanding AGC implementation in the new market structure. The proposed market structure is kept generic enough to capture all possibilities in marketing load following capability.

Basic control of unified power flow controller

Abstract: A unified power flow controller (UPFC) is a typical FACTS device capable of instantaneous control of three power system parameters. This paper presents a basic control system which enables the UPFC to follow the changes in reference values of the active and reactive power supplied from the outer system controller. The analysis is based on the transformation of the three-phase power system to the rotating reference frame. As a step closer to a practical application of the UPFC, a modified control structure with a predictive control loop and precontrol signal for a DC-voltage control was designed. The new control system offers better stability and transient performance in comparison with the classical decoupled strategy, especially considering the harmonic distortion of the current being controlled. The derived basic control of the UPFC was tested with the NETOMAC program system.

Dynamic reduction of large power systems for stability studies

Abstract: This paper documents experience with applications of dynamic reductions to large power system models for stability studies. The main factors that affect the quality of the reduced models are discussed. The quality of reduced models and the benefits of dynamic reductions are demonstrated for three large interconnected power systems.

Feasibility of micro power supplies for MEMS

Abstract: Most microelectromechanical systems (MEMS) designed today use macroscopic power supplies, thereby placing limits on the functionality of MEMS in many applications. An alternative to this approach is to design MEMS with integral microscopic distributed power supplies. This paper examines the feasibility of creating micro power supplies by considering three functions common to MEMS power systems: (1) capture energy; (2) store energy; and (3) drive actuation, of these, only the capture energy function is highly dependent on the specific application. For each of the three functions, a table is presented which compares various means of performing the function. This information makes it possible to determine what design alternatives are feasible for the creation of a micro power supply for any specific application of MEMS. We use smart bearings with active surface features as an example application and develop a design for a micro power supply suitable for this work.

Cascade multilevel inverters for utility applications

Abstract: Cascade multilevel inverters have been developed by the authors for utility applications. A cascade M-level inverter consists of (M-1)/2 H-bridges in which each bridge has its own separate DC source. The new inverter: (1) can generate almost sinusoidal waveform voltage while only switching one time per fundamental cycle, (2) can eliminate transformers of multipulse inverters used in conventional utility interfaces and static VAr compensators, and (3) makes possible direct parallel or series connection to medium- and high-voltage power systems without any transformers. In other words, the cascade inverter is much more efficient and suitable for utility applications than traditional multipulse and pulse width modulation (PWM) inverters. The authors have experimentally demonstrated the superiority of the new inverter for reactive power (VAr) and harmonic compensation. This paper summarizes features, feasibility, and control schemes of the cascade inverter for utility applications including utility interface of renewable energy, voltage regulation, VAr compensation, and harmonic filtering in power systems. Analytical, simulated, and experimental results demonstrate the superiority of the new inverters.

A unity power factor PWM rectifier with DC ripple compensation

Abstract: This paper presents a new topology for a pulsewidth modulation (PWM) rectifier which achieves unity power factor on the AC supply side and ripple reduction on the DC output side. The main circuit of this rectifier consists of a conventional PWM rectifier and a pair of additional switches. The switches and PWM rectifier are controlled such that the ripple current on the DC line is reduced, and unity power factor is achieved on the AC line. As a result, this circuit does not require a large DC capacitor or a passive LC resonant circuit. Furthermore, control of the additional switches and PWM rectifier requires only a simple control circuit. The effectiveness of this circuit was confirmed by experiments and analysis. The rectifier is useful for uninterruptible power systems (UPSs) and DC power supplies, especially for cases in which batteries are connected to the DC line.