Showing papers on "Power-flow study published in 1993"

A flexible active and reactive power control strategy for a variable speed constant frequency generating system

Abstract: Variable-speed constant-frequency generating systems are used in wind power, hydroelectric power, aerospace, and naval power generation applications to enhance efficiency and reduce friction. In these applications, an attractive candidate is the slip power recovery system comprising a doubly excited induction machine or doubly excited brushless reluctance machine and PWM power converters with a DC link. In this paper, a flexible active and reactive power control strategy is developed, such that the optimal torque-speed profile of the turbine can be followed and overall reactive power can be controlled, while the machine copper losses have been minimized. At the same time, harmonics injected into the power network have also been minimized. In this manner, the system can function as both a highly-efficient power generator and a flexible reactive power compensator. >

A novel single-phase power factor correction scheme

Abstract: A single-phase power factor correction scheme is proposed based on the power flow analysis. It is found that the conventional power factor correction (PFC) circuit must be designed to handle the rated power, although its purpose is only for power factor correction. With the proposed scheme, the PFC circuit is in parallel with the major power flow path, thus reducing its size and weight compared to a conventional two-cascade-stage scheme. A prototype circuit is built and tested to verify this concept. >

Power flow control by use of controllable series components

Abstract: Power flow control in electric power systems by use of controllable series power capacitors and phase shifters is discussed. Models suitable for incorporation in power flow programs are developed and analyzed. The power flow control problem is defined in a stringent way, and a method for solving the power flow control problem is proposed based on decomposition. This method is applied on test systems and the convergence rate of the algorithm is discussed. Simplified models of the components are also derived. These simplified models are shown to be quite accurate in most situations, and are used to construct regions of feasible power flows of the controlled lines. >

An optimal procedure for placing sensors and estimating the locations of harmonic sources in power systems

Abstract: The problem of where best to take measurements to estimate the locations of harmonic sources in power systems is addressed. Sensitivity analysis and the minimum variance criterion are utilized to solve this problem. The underdetermined case dealing with a few measurements in a large system is analyzed. Three examples are provided to prove that while the optimal sensor placement problem does not necessarily possess a sequential solution, the sequential solution yields a very good approximation solution. >

Voltage stability: analysis needs, modelling requirement, and modelling adequacy

Abstract: The importance of representing dynamic loads by valid dynamic models in dynamic analyses of voltage stability is demonstrated. Several dynamic load models reported in the literature are reviewed. It is shown that, for loads with slow dynamics or when the system voltage may be assumed constant, small signal stability is independent of the load model used, provided the model parameter values are correctly chosen. The same results can also be predicted by steady-state analysis by appropriately modifying the conventional power flow model. In large disturbance situations, and when the load dynamics exhibit fast response characteristics, a detailed system modelling is needed. An argument is presented in favour of using the theoretically rigorous and well established models for loads with fast dynamic response, when detailed analyses are warranted.

Phase-shifting transformers in load flow and short-circuit analysis: modelling and control

Abstract: A new accurate model representing phase-shifting transformers for both load flow and fault analysis is introduced. The model is simple, efficient and numerically stable. The theoretical basis of the model and the practical procedures of implementation for the fast-decoupled load flow method and short-circuit calculation are presented. The model described was implemented in the Interactive Power System Analysis program, and the results of verification for various transformer arrangements in typical practical power networks are presented.

Power System Models, Objectives and Constraints in Optimal Power Flow Calculations

Abstract: The principal goal of the Optimal Power Flow (OPF) program is to provide the electric utility with suggestions (setpoints) to optimize the current power system state online with repect to various objectives. Typical objectives are minimization of the total generation cost, minimization of the total (or regional) active power network losses, maximization of the degree of security of a network or even a combination of some of them. The achievement of these goals is important to utilities, since often they are obliged by law to operate the network with consumption of minimal resoures and a maximum degree of security.

Robust redesign of power system damping controllers

Abstract: This paper presents a procedure based on H/sub /spl infin// optimization for the design of robust power system stabilizers (PSS). The approach used is a mixed model matching and robustness design. The objective is to improve the robustness of a control law designed for a single operating condition. >

Power-by-wire aircraft secondary power systems

Abstract: This paper describes the secondary power sources available on a large transport aircraft that supply power for the aircraft operating and payload systems. The benefits expected from integrating all of the engine-based hydraulic and pneumatic power sources into the electrical system are identified in qualitative terms. The estimated capacity of an all-electric secondary power system for a tri-jet and a new large transport are compared. An integration architecture of the pneumatic, hydraulic, and electrical power using one type of distributed power is illustrated, Particular emphasis is given to the flight control system and the electrical power system needs to ensure integrity of power and data for critical flight control functions. The data bus and power source redundancy for flight control actuation is discussed using an integrated power and cable concept in conjunction with an intelligent power controller. The need for the industry to develop comprehensive data bus architectures that network the entire vehicle information infrastructure is discussed. >

Power bus digital communication system

Abstract: A power bus digital communication system reduces power and signal cabling in a space satellite by transformer coupling digital signal sources to power bus circuits, the transformer coupling devices in all power bus circuits being in parallel relation and electrically isolated from a power supply whereby the digital communication sources may communicate among themselves at a DC power level using a square wave modulated according to a Manchester code.

Power Flow Analysis of the Swedish Railway Electrical System

Abstract: This thesis deals with analysis of the steady state power flow in the Swedish railway electrical system. Finding the steady state of the system means that all voltages and power flows in the system ...

Power flow analysis and efficiency optimization of a doubly fed synchronous machine

Abstract: This paper deals with the energy balance of the doubly fed synchronous machine (DFSM). The proposed method is based on the principle which consider that the electro–mechanical conversion takes place between stator circuits and the machine shaft, so that the electrical power applied to rotor circuits is taken as a command. From this point of view, the study stresses are: Stability, A low ratio of the rotor command referred to the converted energy, High efficiency. Results are presented in the rms value of rotor applied voltage (V2a) – angle between the stator and the rotor voltages vectors (5) plane. We have found, when we vary the slip (s), that the high efficiency areas move in such way that the ratio of s over V2a remains constant (which means a constant rotor flux).

Extended Ward equivalent of external system for on-line security analysis

Abstract: Today's power systems are more and more intensively interconnected. The monitored part of the power system that these measurements cover normally consists of the energy control centre's own system which is called the internal system, and the neighbouring system which is called the external system. Usually, the external system is far bigger than the internal system and a modern energy control centre for a number of the interconnections is responsible for the control of the internal system. So external network modelling is becoming an important component of on-line security analysis. This paper investigates the extended Ward equivalent method. A new equivalent modelling, with sparsity technique, for on-line power system security analysis is presented. The extended Ward equivalent has been tested by simulation on the IEEE 30-bus, IEEE 118-bus load flow test system, and the 706-bus interconnected power system of the NGC. The results show that extended Ward equivalent has suitable properties for practical use and further development. >

100 kHz distributed power system for aircraft engine modular control

Abstract: A distributed power system based on a 100-kHz trapezoidal bus voltage has been designed, constructed, and operated. Lower current harmonics result from using a trapezoidal source rather than a sine wave source. The overall system efficiency is 70-72%. High frequency AC distributed power systems should be considered for low power systems having cable lengths of up to tens of meters. >

Unity power factor scheme using cascade converters

Abstract: This work presents detailed theoretical and experimental results of a novel means of obtaining sinusoidal input current and unity power factor cascade buck-boost power converter. Using the new configuration, available sinusoidal line current in phase with the bus voltage is achieved, while its amplitude can be varied within a wide range. The buck operation has the same performance as the boost operation. The influence of the circuit parameters is investigated and validated by experimental results. Full theoretical analysis, simulation and experimental results are presented. >

On-line transient stability assessment in operation-DEEAC in Northeast China Power System

Abstract: Achievements in on-line transient stability assessment of the Northeast China Power System are reported in this paper. The improved dynamic extended equal area criterion (DEEAC) is interfaced to a state estimator with DBMS in an advanced EMS environment. Thousands of DEEAC results, recorded from snapshots of on-line estimations have been thoroughly checked with an off-line numerical integration method. For first swing stability assessment of both symmetrical and asymmetrical faults, there are only less than 1% of cases whose errors exceed 10%. Moreover, all large errors occur with mild contingencies only. Each critical clearing time (CCT) calculation takes about 10 s CPU time of a VAX-11/785 computer. In an HABITAT environment (developed by ESCA Corp.), the on-line EEAC package is very user-friendly. >

Robustness issues in stability control of large electric power systems

Abstract: Controller based alternatives to direct power system reinforcements can be very attractive, but they raise some difficult issues. The uncertainties that attend large scale power system applications preclude complete demonstrations of controller robustness. Functional reliability must be assessed more broadly, in ways that incorporate engineering judgment and are fortified through sound practice. Uncertainty which cannot be mitigated should be accommodated in controller design, and in controller operation. Necessary countermeasures include examination of power system dynamics, expanded development and use of mathematical tools, and more aggressive use of information technology at all stages of the engineering process. These should be supplemented by an in depth dialog, between the control engineering and power communities, as to what actually constitutes acceptable risk and sound practice. >

Application of a genetic algorithm to meter allocation in electric power systems

Abstract: This paper presents a genetic algorithm (GA)-based approach to meter allocation in electric power systems. State estimation plays a key role in power system security control. The accuracy of the state estimation is highly influenced by meter allocation. In this paper, meter allocation of redundant measurements are examined to improve the accuracy. The proposed method has been successfully applied to the IEEE 14-node system that has about 1.313/spl times/10/sup 11/ combinations of redundant measurements.

Automatic analog power distribution synthesis in rail

Abstract: The move to higher levels of integration has increased the fraction of application specific integrated circuit (ASIC) designs containing both analog and digital circuits. While the die area for the analog portion of these chips is modest, the design time is often significant. This has motivated the development of automated analog physical design tools for cell-level place-and-route and system-level signal-integrity-routing. To date, we are aware of no tool that has specifically addressed the critical design task of synthesizing the power distribution for the analog portion of an analog or mixed-signal ASIC. In this thesis, we describe algorithms for analog power distribution synthesis and demonstrate their effectiveness. Existing digital power bus synthesis algorithms have failed to address critical concerns for analog circuitry, thus yielding unacceptable results. These tools synthesize only the bus component of power distribution networks and only consider simplified DC aspects of macros and busses. In this research, we present a new formulation for the analog power distribution synthesis problem which synthesizes both the power busses and power I/O cell assignment by evaluating DC, AC, and transient interaction between the macros, busses, chip substrate, and package. Further, we introduce algorithms which simultaneously optimize power I/O cell assignment, power bus topology selection, and power bus sizing. RAIL, the power distribution synthesis tool developed in the course of this research, addresses many of the concerns in supplying power to analog circuits. RAIL iteratively improves the design by optimizing the power I/O cell assignment, the power bus topology selection, and the power bus sizing simultaneously via simulated annealing algorithms. With each iteration, RAIL evolves the design evaluating the static and dynamic behavior of circuits containing linearized resistors, capacitors, inductors, dependant sources, and time-varying independent sources, using Asymptotic Waveform Evaluation (AWE). We have found our formulation effective on several synthetic, industrial, and university analog and mixed-signal examples. For example, we have synthesized the analog power distribution for a 7.5mm x 7.5mm chip, consisting of 25 macrocells, modeled with 304 power bus segments, 618 electrical nodes, a 10 x 10 x 1 substrate grid to meet 361 DC, AC, and transient electrical constraints.

Power system static voltage stability limit and the identification of weak bus

Abstract: This paper develops a new approach to find the power system static voltage stability limit using the conventional load flow solution method The developed approach proposes a load admittance model to replace the load injection only on the heaviest load bus Tested results in several systems show that the approach has advantages in terms of simplicity, flexibility, rapidity and accuracy Based on the investigation of the voltage stability limits for the load buses, it is easy to identify the weak bus of the power system >

The parameter identification of power system and its application for transient stability analysis

Abstract: Mathematical models of power system elements are fundamental to power system studies such as planning, design, operation and control. It is necessary to improve the accuracy of power system simulation by means of identification techniques to obtain more realistic parameters of the elements in real power systems. In this paper, field tests to obtain the parameters and field tests to validate the models and their parameters are briefly described with emphasis on the comparison of test and simulation results. Transient stability studies show that the dynamic characteristics of power systems can be more exactly represented by using the models and parameters obtained from field test data. They also show that the total power output of the concerned power plant can be increased by 4-6 percent. Thus the economic benefit is considerable. >

Use of FACTS devices for power system stability enhancement

Abstract: This paper describes research in progress on the development of new techniques for analysis and control of power systems using FACTS (Flexible AC Transmission System) devices during both the voltage and transient stability time frames. These methods are shown to offer the potential for enhancing the system's stability margin. >

Power system load forecasting with ann and fuzzy logic control

Abstract: Power system load forecasting is an important subject both in power system planning as well as in online power system operation The authors show that for both long term forecasting for planning and short term forecasting for online power system operation, simpler speedy and robust forecasting software is very useful For this purpose, an artificial neural network plus fuzzy logic is shown to be very appealing >

The Network Subsystem Implementation of the Energy Management System of the Public Power Corporation of Greece

Abstract: This paper describes the implementation of the network subsystem of the Energy Management System (EMS) for the Public Power Corporation (PPC) of Greece, which is presently at the stage of field installation and final testing. Specifically, it describes the interconnected network model, the User Interface, the real-time network sequence (topology processing, State Estimation, loss sensitivity calculations, Contingency Analysis), and the study network environment (Powerflow, Optimal Powerflow and Contingency Analysis).

Optimal Power Flow Application to Composite Power System Reliability Analysis

Abstract: This paper presents a method which applies an efficient optimal power flow model to composite power system reliability analysis. It is based on the contingency enumerative approach. The optimal power flow is the premier tool for contingency effects analysis. The method used here incorporates the process of economic dispatch, observes the operating constraints and determines tlie amount of load curtailment after exhaustion of all other options. The optimization problem is solved either with the simplex method or with an interior point algorithm. Tlie perforniiance evaluation of the optimal powcr flow model for a large power system is provided. Finally, the reliability computations are illustrated w i h a simple example.