Showing papers on "Power-flow study published in 1999"

Power System Oscillations

Abstract: 1. Introduction. 2. The Nature of Power System Oscillations. 3. Modal Analysis of Power Systems. 4. Modal Analysis for Control. 5. Power System Structure and Oscillations. 6. Generator Controls. 7. Power System Stabilizers. 8. Power System Stabilizers - Problems and Solutions. 9. Robust Control. 10. Damping by Electronic Power System Devices. A1. Model Data Formats and Block Diagrams. A2. Equal Eigenvalues. Index.

Dispersed generation impact on distribution networks

Abstract: The insertion of dispersed generation into existing electric power systems has a great impact on real-time operation and planning. Several uncertainties characterize the ability of the existing power system to integrate this form of generation, Hence, dispersed generation must be taken into consideration in power system performance so that operation and security are not disturbed. Dispersed generation increases the complexity of controlling, protecting and maintaining power distribution systems. This article focuses on some technical aspects, but not on the impact on the quality of supply and on tariff signals.

Unified modeling of hybrid electric vehicle drivetrains

Abstract: Hybridizing automotive drivetrains, or using more than one type of energy converter, is considered an important step toward very low pollutant emission and high fuel economy. The automotive industry and governments in the United States, Europe, and Japan have formed strategic initiatives with the aim of cooperating in the development of new vehicle technologies. Efforts to meet fuel economy and exhaust emission targets have initiated major advances in hybrid drivetrain system components, including: high-efficiency high-specific power electric motors and controllers; load-leveling devices such as ultracapacitors and fly-wheels; hydrogen and direct-methanol fuel cells; direct injection diesel and Otto cycle engines; and advanced batteries. The design of hybrid electric vehicles is an excellent example of the need for mechatronic system analysis and design methods. If one is to fully realize the potential of using these technologies, a complete vehicle system approach for component selection and optimization over typical driving situations is required. The control problems that arise in connection with hybrid power trains are significant and pose additional challenges to power-train control engineers. The principal aim of the paper is to propose a framework for the analysis, design, and control of optimum hybrid vehicles within the context of energy and power flow analysis. The approaches and results presented in the paper are one step toward the development of a complete toolbox for the analysis and design of hybrid vehicles.

The theory of instantaneous power in three-phase four-wire systems: a comprehensive approach

Abstract: This paper describes a holistic approach to the theory of instantaneous power in three-phase four-wire systems, focusing on the original theory created in 1983 and a modified theory presented in 1994. The two theories are perfectly identical if no zero-sequence voltage is included in a three-phase three-wire system. However, they are different in the instantaneous active and reactive power in each phase if a zero-sequence voltage and current are included in a three-phase four-wire system. Theory and computer simulations in this paper lead to the following conclusions: an active filter without energy storage components can fully compensate for the neutral current even in a three-phase four-wire system including a zero-sequence voltage and current, when a proposed control strategy based on the original theory is applied. However, the active filter cannot compensate for the neutral current fully, when an already-proposed control strategy based on the modified theory is applied.

AEP unified power flow controller performance

Abstract: The installation of the world's first unified power flow controller (UPFC) has been completed and a series of commissioning tests were conducted at the Inez Substation of American Electric Power (AEP) in eastern Kentucky. The project is a collaborative effort between AEP, the Westinghouse Electric Corporation, and the Electric Power Research Institute (EPRI). Comprising two /spl plusmn/160 MVA voltage-sourced GTO-thyristor-based inverters, this installation is the first large-scale practical demonstration of the UPFC concept, and its completion is a significant milestone in the progress of power electronics technology for flexible AC transmission system (FACTS). This paper briefly reviews the main features of the Inez installation and discusses the operation of the equipment. A collection of measured performance characteristics is presented to illustrate the unique capabilities of the UPFC. These dynamic measurements were made in the course of commissioning, and they graphically illustrate the ability of the UPFC to independently control the real and reactive power on a transmission line, while also regulating the local bus voltage. The results include a demonstration of the series inverter at Inez, operating in stand-alone mode. This test constitutes the first practical large-scale demonstration of the static synchronous series compensator (SSSC) concept.

Tracing active and reactive power between generators and loads using real and imaginary currents

Abstract: In a competitive environment, usage allocation questions must be answered clearly and unequivocally To help answer such questions, this paper proposes a method for determining how much of the active and reactive power output of each generator is contributed by each load This method takes as its starting point a solved power flow solution All power injections are translated into real and imaginary currents to avoid the problems arising from the nonlinear coupling between active and reactive power flows caused by losses The method then traces these currents to determine how much current each source supplies to each sink These current contributions can then be translated into contributions to the active and reactive power output of the generators It is also shown that the global contribution of a load can be decomposed into contributions from its active and reactive parts This decomposition is reasonably accurate for the reactive power generation To determine the contributions to active power generation, the previously-described method based on the active power flows is recommended

The instantaneous power theory on the rotating p-q-r reference frames

Abstract: This paper proposed the rotating p-q-r reference frames where one instantaneous active power p, and two instantaneous reactive powers q/sub q/, q/sub r/ were defined in 3-phase 4-wire systems. The three power components are linearly independent, so that compensating for the two instantaneous reactive powers leads to control the two components of the current space vector independently. With the theory, this paper shows that the neutral current of a 3-phase 4-wire system can be eliminated by only compensating for the instantaneous reactive power using no energy storage element. Simulation results verify the theory very well.

Available transfer capability and first order sensitivity

Abstract: A method of calculating available transfer capability and the exploration of the first order effects of certain power system network variables are described. The Federal Energy Regulatory Commission has ordered that bulk electrical control areas must provide to market participants a "commercially viable" network transfer capability for the import, export and throughput of energy. A practical method for deriving this transfer capability utilizing both linear and nonlinear power flow analysis methods is developed that acknowledges both thermal and voltage system limitations. The available transfer capability is the incremental transfer capability derived by the method reduced by margins. A procedure for quantifying the first order effect of network uncertainties such as load forecast error and simultaneous transfers on the calculated transfer capability of a power system snapshot are explored. The quantification of these network uncertainties can provide information necessary for system operation, planning and energy market participation.

High efficiency power system with plural parallel DC/DC converters

Abstract: A distributed staged power system for use in electric and hybrid electric vehicles, and the like. The system comprises a plurality of parallel DC-to-DC power modules that are controlled by way of input and output control signal interfaces using a smart controller. The distributed staged power system provides higher efficiency because of smart staging of the power modules. The distributed staged power system enables or disables each of the modules as determined by a smart controller to provide the highest possible conversion efficiency.

Multi-tier service restoration through network reconfiguration and capacitor control for large-scale radial distribution networks

Abstract: A fast and effective service restoration algorithm allowing multi-tier or system-wide switching and capacitor control actions is developed for large-scale, radial distribution networks. The service restoration problem is formulated as a constrained multiple-objective optimization problem. A solution algorithm designed to consider networks with predominately manual switches is developed which utilizes information calculated from three-phase power flow analysis to restore as much priority and total load as possible while requiring a minimal number of control actions and amount of geographic travel distance. Simulation results are presented for a 399 bus distribution network and compared to the service restoration algorithm which avoided multi-tier switching.

Optimal power flow incorporating voltage collapse constraints

Abstract: The paper presents applications of optimization techniques to voltage collapse studies. First a "maximum distance to voltage collapse" algorithm that incorporates constraints on the current operating conditions is presented. Second, an optimal power flow formulation that incorporates voltage-stability criteria is proposed. The algorithms are tested on a 30-bus system using a standard power flow model, where the effect of limits on the maximum loading point is demonstrated.

Model reduction for analysis of cascading failures in power systems

Abstract: In this paper, we apply a principal-orthogonal decomposition based method to the model reduction of a hybrid, nonlinear model of a power network. The results demonstrate that the sequence of fault events can be evaluated and predicted without necessarily simulating the whole system.

Power estimation for architectural exploration of HW/SW communication on system-level buses

Abstract: The power consumption due to the HW/SW communication on system-level buses represents one of the major contributions to the overall power budget. A model to estimate the switching activity of the on-chip and off-chip buses at the system-level has been defined to evaluate the power dissipation and to compare the effectiveness of power optimization techniques. The paper aims at providing a framework for architectural exploration of a system design, focusing on the power consumption estimation of memory communication. Experimental results, conducted on bus streams generated by a real microprocessor and a stream generator, show how the variation of cache parameters and the introduction of bus encoding at the different levels on the memory hierarchy can affect the system power dissipation. Therefore, the proposed model can be effectively adopted to appropriately configure the memory hierarchy and the system bus architecture from the power standpoint.

Optimal power flows of interconnected power systems

Abstract: The work presented in this paper seeks to provide a theoretically sound, yet practical foundation for the implementation of inter-utilities power exchanges based on spot pricing. The proposed approach allows the operational independence of each utility. Using decomposition-coordination techniques, a multi-area optimal power flow problem is reformulated as a master problem and a set of area-OPF subproblems, each associated with one area. An interior-point/cutting-plane method is used to reduce the number of iterations in the numerical solution of the nondifferentiable master problem. The paper includes test results on IEEE-based systems.

Control setting of unified power flow controllers through a robust load flow calculation

Abstract: The unified power flow controller (UPFC) provides a promising means to control power flow in modern power systems. Essentially, the performance depends on proper control setting achievable through a power flow analysis program. The paper presents a reliable method to meet the requirements by developing a Newton–Raphson based load flow calculation program through which control setting of the UPFC can be determined directly. Case studies have been performed on standard IEEE 14-bus and 57-bus systems to show that the proposed method is robust and effective.

Maximum power operating inverter system

Abstract: PROBLEM TO BE SOLVED: To solve the problem in an AC output solar cell power generating system for taking out maximum power from solar cells and superimposing it on the power from an AC power supply, that the power conversion loss is increased because power is converted twice when a DC/DC converter having a maximum power point tracking function is combined with an inverter in order to realize maximum power point tracking and total efficiency of the power generating system is lowered. SOLUTION: Maximum power point tracking is realized without employing a DC/DC converter by keeping optimal operating conditions of an inverter from the waveform of pulse voltage and current generated from solar cells when the instantaneous output power from the inverter varies over time.

Reactive power considerations in linear ATC computation

Abstract: The paper presents some initial concepts on including reactive power in linear methods for computing Available Transfer Capability (ATC). It proposes a new approach that first determines the reactive power flows using the exact circle equation for the transmission line complex flow, and then determines ATC using active power distribution factors. The ideas are demonstrated on 3-bus and 7-bus systems, and the results are discussed and compared with those obtained without reactive power considerations, and full nonlinear solutions.

The generation of ZIP-V curves for tracing power system steady state stationary behavior due to load and generation variations

Abstract: The P-V Curve, Q-V Curve, or P-Q-V Curve have been widely used to analyze power system behaviors under varying loading conditions. These curves have been generated under the condition that tire constant P-Q load component of a bus (or a collection of buses) varies, with the constant current load and constant impedance load being kept indeed "constant". As such, the physical meaning of these curves can be easily explained. Motivated by the facts that load models have profound impacts on power system behaviors and that the nonlinear load model ZIP-model is popular in modeling nonlinear behaviors of loads, this paper proposes a new class of curves, called ZIP-V curves, to better trace power system steady-state stationary behavior due to load and generation variations. The ZIP-V curves encompass the traditional P-V, Q-V, P-Q-V curves (constant P-Q load), I-V curve (constant current load), Z-V curve (constant impedance load), or generalized curves such as IP-V (constant current and constant power load), ZP-V (constant impedance and constant power load) or IZ-V (constant current and constant impedance load) curve when the values of corresponding components are kept constant. A tool based on the continuation power flow (CPFLOW) method useful for generating the ZIP-V curves is developed and its application to generate ZIP-V curves of a 4561-bus interconnected power system is illustrated.

System and method using phase detection to equalize power from multiple power sources

Abstract: A system and a method may use variable-frequency power sources for supplying power to a load The system and method use phase detection in order to automatically and substantially equalize the currents supplied to a load by each of the variable-frequency power sources, and to cancel a ripple component of the input current drawn by the system First and second power sources supply power to the load The power sources have a similar relationship between their respective variable switching frequencies and the power that they supply to the load First and second switching frequencies of, respectively, the first and second power sources are locked to one another using phase detection to substantially equalize the power supplied to the load by each power source The system and method are advantageously utilized to provide a power factor correction front-end for a switch-mode power supply Power sources with non-linear and/or inverse relationships between power supplied and switching frequency can be used In alternate embodiments power from series power sources is equalized by equalizing voltages supplied by each power source to a load

An active bus conditioner for a distributed power system

Abstract: In a distributed power system with many power converters on the DC bus, there is always the concern of the possible interactions between the system building blocks, which are designed at the individual box level. This paper presents a novel concept, the DC bus conditioner, which compensates the harmonic and reactive current on the DC bus and actively damps the oscillations in a DC power system. With a certain amount of extra energy storage, the bus conditioner can provide the large signal variable frequency ripple current as required by the load and actively shape the small signal impedance characteristics of the DC bus interface at the mid-frequency range to increase the system stability margin. The breadboard experimental results are presented.

A new method for measuring power system frequency

Abstract: The algorithms of numerical protective relays are very sensitive to variations in the power system frequency during operation. Even slight changes of the power frequency can lead to large calculation errors in the values for impedances, the power factor, etc. Implementing an adaptive sampling rate requires knowing the actual system frequency at all times with high accuracy. A new frequency measurement method has been successfully implemented. Since the method is not dependent upon zero-crossings of the measured current, it can calculate the frequency after every sample. In addition, the necessary signal-window is approximately 3 cycles, which means that the calculation is faster than all classical methods. The new method has made possible the development of a full-featured generator protection relay that can operate over a frequency range of 15 Hz-70 Hz. The accuracy of the frequency calculation is better then 10 mHz for a nominal frequency of 60 Hz.

Simultaneous power supply source

Abstract: A power transfer system for applying backup electrical power to electrical systems is described which applies backup power automatically without power interruption and which is straightforward to implement and inexpensive to manufacture. The power transfer system has a direct current (DC) power bus as a common supply point for protected electrical equipment, thereby making prior art systems which provide power transfer between alternating current (AC) power sources and typically provide an AC power bus in common with the protected equipment no longer necessary.

Tracing the flow of power in transmission networks for use-of-transmission-system charges and congestion management

Abstract: With the separate pricing of generation and transmission, it has become necessary to find the capacity usage of different transactions occuring at the same time so that a fair use-of-transmission-system charge can be given separately to individual customers. It is also helpful to transmission congestion management if the power produced by each generator and consumed by each load could be tracked through the network, The existing proportional sharing and circuits based methods, and the newly developed power flow comparison method are introduced and compared in this paper. Calculations are illustrated in an example 6-bus power system. The new power flow comparison method and the existing proportional sharing method are also tested on the IEEE 57-bus system to show their capabilities. The power flow comparison method offers more alternatives in using available transmission capacity and pricing line flows, and provides the user with sensitivity information on how proposed corrections will affect the flows in other critical lines.

Analysis of interarea oscillations in the European electric power system in synchronous parallel operation with the Central-European networks

Abstract: In the European power system UCPTE in parallel operation with the Central-European power systems, called CENTREL, slowly damped inter-area oscillations have been observed The swings occurred especially when long distance power transactions were carried out The paper presents results of a small signal stability analysis, focused on power transits in the European power system In a detailed model the critical swing modes, their mode shapes and the participation factors were investigated In the East-West-direction two swing modes with wide area effect are significant To make clear the causes for insufficient damped interarea swings a sensibility analysis relating to power transits, network voltage level and generator voltage controller gains has been carried out

Zone branch reliability methodology for analyzing industrial power systems

Abstract: There are many methods available for evaluating the frequency and duration of load point interruptions within a given industrial power system configuration. As systems become larger and more interconnected, these existing methods can become computationally bound and limited in their ability to assess the impact of unreliable protective equipment and unreliable protection-coordination schemes on individual load point reliability indexes within a given plant configuration. These methods also can often not account for complex isolation and restoration procedures within an industrial plant configuration. This paper presents a zone-branch methodology that overcomes many of these limitations and applies the methodology to a large industrial plant power system configuration. The primary advantage of the zone-branch methodology is that it can readily identify faulty protection schemes involving all the components of an industrial power system and evaluate load point reliability indexes.

Solving power flow problems with a Matlab implementation of the power system applications data dictionary

Abstract: This paper implements a power flow application and variations using the IEEE Power System Application Data Dictionary within a Matlab environment. It describes a number of useful data and implementation techniques for a variety of applications. The techniques include the use of very compact and efficient code for the computation of Power Transfer Distribution Factors. Power Transfer Distribution Factors are all important element of present and proposed congestion management strategies for power systems, particularly, when these systems must operate in a deregulated environment.

Several schemes of alleviating bus voltage stress in single stage power factor correction converters

Abstract: High DC bus voltage stress is an important issue for the single stage PFC converters in practical application. This paper analyzes the inherent reason of the high bus voltage stress of single-stage power-factor-correction (PFC) AC/DC converters. Four possible resolving schemes are analyzed and discussed, and some of practical implementation circuits topologies are also given. Theoretical analysis and simulation results show that the both series-charging, parallel-discharging capacitors (SCPDC) scheme and bus-voltage-feedback (BVF) method are deemed to be more viable than the other two methods.