Showing papers on "Power-flow study published in 2000"

Trajectory sensitivity analysis of hybrid systems

Abstract: The development of trajectory sensitivity analysis for hybrid systems, such as power systems, is presented in the paper. A hybrid system model which has a differential-algebraic-discrete (DAD) structure is proposed. This model forms the basis for the subsequent sensitivity analysis. Crucial to the analysis is the development of jump conditions describing the behavior of sensitivities at discrete events, such as switching and state resetting. The efficient computation of sensitivities is discussed. A number of examples are presented to illustrate various aspects of the theory. It is shown that trajectory sensitivities provide insights into system behavior which cannot be obtained from traditional simulation.

Control of parallel inverters in distributed AC power systems with consideration of line impedance effect

Abstract: The authors have developed a new control technique which allows paralleled inverters to share linear or nonlinear load in a distributed AC power supply system. This technique does not require control interconnections and automatically compensates for inverter parameter variations and line impedance imbalances. Experimental results are provided in the paper to prove the concept.

Modeling of wind farms in the load flow analysis

Abstract: Two methods are proposed, for the simulation of wind farms with asynchronous generators in the load flow analysis. Both methods are based on the steady-state model of the induction machine. The first involves improving the conventional PQ bus, and the second involves modeling the generators in steady-state in the bus where the wind farm is located. The two sets of results are then compared.

Voltage instability: phenomena, countermeasures, and analysis methods

Abstract: A power system may be subject to (rotor) angle, frequency or voltage instability. Voltage instability takes on the form of a dramatic drop of transmission system voltages, which may lead to system disruption. During the past two decades it has become a major threat for the operation of many systems and, in the prevailing open access environment, it is a factor leading to limit power transfer. The objective of this paper is to describe voltage instability phenomena, to enumerate preventive and curative countermeasures, and to present in a unified and coherent way various computer analysis methods used or proposed.

The Electric Power Engineering Handbook

Abstract: Electric Power. Electric Power Utilization. Transformers. Transmission Systems. Substations. Distribution Systems. Electric Power Utilization. Power System Analysis and Simulation. Power System Protection. Power System Transients. Power System Dynamics/Stability. Power System Operation/Control. Power System Planning (Reliability). Power Electronics. Power Quality.

Power transfer allocation for open access using graph theory-fundamentals and applications in systems without loopflow

Abstract: In this paper, graph theory is used to calculate the contributions of individual generators and loads to line flows and the real power transfer between individual generators and loads that are significant to transmission open access. Related lemmas are proved which present necessary conditions required by the method. Based on AC load flow solution a novel method is suggested which can decide downstream and upstream power flow tracing paths very fast and can calculate the contribution factors of generations and loads to the line flows efficiently. The power transfer between generators and loads can also be determined. The suggested method is suitable for both active and reactive power tracings of real power systems.

Voltage contours for power system visualization

Abstract: Power system engineers are presented with vast amounts of information to analyze during daily operations. In systems containing thousands of buses, it can be very difficult to assess the state of the power system in an intuitive and rapid manner. The paper discusses the use of contours for visualizing power system voltage data. Also, because of the low computation requirements of the contouring algorithm, the algorithm is implemented into a real-time animation of the voltage profile of a power system. The contouring routines are implemented into the PowerWorld/sup TM/ Simulator software package, with results shown for systems with up to several thousand buses. Experiments and interviews with system engineers are also discussed to measure the applicability of voltage contouring as an add-on to practical EMS systems.

Providing premium power through distributed resources

Abstract: The modern industrial facility depends on sensitive electronic equipment that can be shut down suddenly by severe power system disturbances. A large number of these disturbances on the power system are a result of line faults which can cause momentary voltage sags. This results in equipment malfunctioning and high restart cost. This papers describes the control of distributed resources as a solution to such problems. In particular the focus is on systems of distributed resources that can switch from grid connection to island operation without causing problems for critical loads.

Low power bus coding techniques considering inter-wire capacitances

Abstract: The power dissipation associated with driving data buses can be significant, especially considering the increasing component of inter-wire capacitance. Previous work on bus encoding has focused on minimizing transitions to reduce power dissipation. In this paper, it is shown that transition reduction is not necessarily the best approach for reducing power when the effects of inter-wire capacitance are considered. An electrical model for data buses designed with submicron technologies is presented and a family of coding techniques is proposed that can reduce the average power consumption of the bus by 40%.

Analysis of asymmetrical faults in power systems using dynamic phasors

Abstract: Summary form only given, as follows. This paper presents application of the dynamic phasor modeling technique to unbalanced polyphase power systems. The proposed technique is a polyphase generalization of the dynamic phasor approach, and it is applicable to nonlinear power system models. In a steady-state, the dynamic phasors reduce to standard phasors from AC circuit theory. The technique produces results that are very close to those obtained from time-domain simulations. Simulations in terms of dynamic phasors typically allow larger integration steps than the standard time-domain formulation. The authors present simulations of unbalanced faults involving a three-phase synchronous generator connected to an infinite bus through a transmission line, and demonstrate that models based on dynamic phasors provide very accurate descriptions of observed transients.

Generation maintenance scheduling considering transmission constraints

Abstract: This paper describes a new approach for establishing power systems scheduled generators outages for maintenance purposes. The time frame considered refers to power systems short-term operations planning horizon (i.e. one month ahead). The paper's main contribution is focused on modeling grid operational constraints, which are dealt with by a DC optimal power flow. The resulting large-scale optimization problem is solved by mixed-integer programming techniques aided by Benders decomposition strategy. The obtained results clearly show that representing transmission influence is essential for the establishment of a sound set of scheduled outages for the system's generators, especially in the case of hydrothermal systems.

Function-level power estimation methodology for microprocessors

Abstract: We have developed a function-level power estimation methodology for predicting the power dissipation of embedded software. For a given microprocessor core, we empirically build the “power data bank”, which stores the power information of the built-in library functions and basic instructions. To estimate the average power of an embedded software on this core, we first get the execution information of the target software from program profiling/tracing tools. Then we evaluate the total energy consumption and execution time based on the “power data bank”, and take their ratio as the average power. High efficiency is achieved because no power simulator is used once the “power data bank” is built. We apply this method to a commercial microprocessor core and get power estimates with an average error of 3%. With this method, microprocessor vendors can provide users the “power data bank” without releasing details of the core to help users get early power estimates and eventually guide power optimization.

Controlling generator power

Abstract: A power controller for controlling an engine-driven generator includes a high voltage DC bus interconnecting various power modules. In electrical communication with the DC bus are: a bi-directional DC-DC converter constructed to transfer electrical power from the DC bus to a battery to charge the battery, and from the battery to the DC bus; a rectifier constructed to rectify electrical power from the generator and to supply the rectified power to the DC bus; an invester constructed to convert DC bus electrical power to AC electrical power and to supply the AC power to an output connector; and an AC-DC constructed to convert AC electrical power, supplied via an input connector, to DC bus electrical power. The controller may be employed in a power supply on a mobile vehicle or boat, for example. The power modules of the controller cooperate in various combinations to provide a wide variety of power transfer functions.

Power supply system for distributed source

Abstract: PROBLEM TO BE SOLVED: To provide a power supply system for a distributed source, installing a distributed power source system in a plot of a power user by a power supply provider to perform power supply to the user, diagnosis of system operation, etc. SOLUTION: This system includes a distributed power source system 16, supplying power of commercial frequency to a load 8 of a specific user, additionally performing system linkage and a system managing means 15 connected to each distributed power source system via a communication network 12; the distributed power source system 16 includes a solar battery 1, a fuel cell 2, a storage battery 3, a power converter means 4 for system-linking power output from these power-generating means, a power condition monitor means 6, and a system control means 7; and the system control means 7 communicates operating information of the distributed power source system 16 to the system managing means 15 and controls the operating condition of the power converter means 4, according to the indication received from the system-managing means 15.

Power acceptability and voltage sag indices in the three phase sense

Abstract: The electric power acceptability curves are an empirical set of curves that represent the intensity and duration of bus voltage disturbances. These curves are discussed with regard to the energy delivered to the load, and alternatives for the assessment and measurement of bus voltage sags. Special attention is given to the three phase case.

Placement of FACTS devices in open power market

Abstract: The ongoing power system restructuring requires an opening of unused potentials of transmission systems due to environmental, right-of-way and cost problems which are major hurdles for power transmission network expansion. FACTS devices can be an alternative to reduce the flows in heavily loaded lines, resulting in an increased loadability, low system loss, improved stability of the network, reduced cost of production and fulfilled contractual requirement by controlling the power flows in the network. This paper suggests, first, the few optimal locations of FACTS devices and then determines the best optimal location in order to reduce the production cost along with the device cost. The allocation and requirement are also discussed. The effectiveness of the purposed methods is demonstrated on IEEE 14-bus system.

Theory and applications of power system blockset, a MATLAB/Simulink-based simulation tool for power systems

Abstract: This paper presents a unified framework for power system simulation using a Simulink environment. The modeling and simulation of power systems under Simulink are described and discussed. Application examples for power systems including power networks, power electronics and electric machines are presented and compared with two popular simulation packages (EMTP, PSpice).

A new continuation power flow tool for investigating the nonlinear effects of transmission branch parameter variations

Abstract: This paper presents a new computational tool for investigating the nonlinear effects of varying multiple branch parameters. This is a new continuation power flow tool since this is the first time continuation has been applied to branch parameters, not bus junctions. The applications for the new tool include: (i) contingency analysis due to the loss of any transmission facilities, (ii) investigation of the existence of a power flow solution under severe contingencies that might not "converge" using standard power flow solvers, and (iii) examination of the nonlinear effects of various control devices (e.g., unified power flow controllers) on the state of a power system. Simulation results are presented for a large-scale system with 3493 buses and 6689 branches.

Re-dispatching generation to increase power system security margin and support low voltage bus

Abstract: This article proposes a new method to increase a power system's security margin and/or support its low voltage bus by re-dispatching generator outputs, using a normal vector found at a voltage collapse boundary or a low voltage boundary (LVB). This method uses the normal vector as an indicator to change the generation direction so that more power can be transferred before reaching a boundary of a critical limit such as the voltage collapse boundary or LVB, etc. The method has been tested in the simulation on several systems and shows predicted results. It can be applied to many practical power systems to enhance the system's security, or to increase the system's transfer capability. It also provides technical guidance for an open access transmission in a deregulated environment, when bidding results are shown as generation patterns.

Hybrid systems view of power system modelling

Abstract: The large disturbance behaviour of power systems often involves complex interactions between continuous dynamics and discrete events. The paper proposes a differential-algebraic-discrete (DAD) model structure which captures those interactions in a systematic way. It is shown that the model is a realization of a general hybrid system model. The DAD model opens up opportunities for the application to power systems of hybrid system results in stability analysis and control. The paper presents a practical approach to implementing the DAD model structure.

An LVDC industrial power distribution system without central control unit

Abstract: This paper develops a scheme to control a parallel connected, multiterminal DC power distribution system without the need of central control unit for fast communication. The described scheme utilizes superconductors on the DC bus and incorporates UPS properties with the ability to supply large passive loads than conventional UPSs. A five terminal, mesh connected study system is used to demonstrate the basic characteristics of DC power distribution system such as the ability to ride through an AC system outage. In this paper, a simulation model of the study system is developed and the simulation results show that the proposed DC power distribution system has a high power quality performance.

A new approach to islanding detection of dispersed generators with self-commutated static power converters

Abstract: In this paper, an islanding detection approach for dispersed generators with a self-commutated static power converter is proposed. This method is suggested based on the monitoring of the magnitude and sign change in /spl part/f/sub B//|/spl part/P/sub L/. To facilitate the detection process, a designated circuit for generating the output power deviation is also developed. The proposed method has been tested under various scenarios in order to examine the detection performance and operation reliability. It is found that the proposed method effectively detects the islanding event when different amount of power mismatch is considered. Moreover, by employing the simulated disturbances to the test system, the outcome reveals that the probability of false alarm is low. Test results solidify the feasibility of the method for the application considered.

Identification of voltage collapse through direct equilibrium tracing

Abstract: This paper describes an approach for identifying power system voltage collapse. Unlike the conventional two-step procedure, it simultaneously solves the system differential and algebraic equations (at steady state) to obtain the equilibrium points. Combined with a parameterized continuation technique, the methodology identifies voltage collapse during the direct equilibrium tracing, without rebuilding system dynamic Jacobian and checking its singularity. This significantly reduces the computational cost. All the assumptions of slack and PV buses are removed. The generator field and armature current limits are also accurately implemented. Numerical test results with the New England 39-bus system are presented. Three more systems with up to 8267 buses and 1112 machines are employed to demonstrate the capability of the approach.

Autonomic control of power subsystems in a redundant power system

Abstract: A power management system and method for multiple redundant power supplies. The present invention provides management and control of N+M power supplies, where N represents the minimum number of power supplies required and where M is the number of redundant power supplies (M>1), where any one of the power supplies may be capable of supplying power to all the loads of the power subsystems. In the preferred embodiment each power subsystem includes a power supply and a controller coupled to a power bus. A communication bus is provided common to each power subsystem. During reset or power-on periods, the controllers are programmed to uniquely delay the start time of each power supply, thereby protecting against an overcurrent/overvoltage condition on the power bus during reset periods. A master controller is provided to monitor normal operating conditions of the power subsystems and communication bus. The master controller is programmed to ensure that a predetermined number of power supplies are coupled to the power bus, even in the event of total or partial communication failure.

Contingency ranking for on-line voltage stability assessment

Abstract: Voltage stability has become a challenging problem for many power systems. Contingency screening and ranking (CS&R) is one of the important components of on-line voltage stability assessment. The objective of CS&R is to quickly and accurately select a short list of critical contingencies from a large list of potential contingencies and rank them according to their severity. Suitable preventive control actions can be implemented considering contingencies that are likely to affect the power system performance. An effective method for contingency ranking is proposed in this paper. This method calculates the voltage stability margin considering branch outages. Test results based on the IEEE 300 bus power system, a 600 bus power system as well as two utility systems (197 bus and 1254 bus) are presented.

Computation of bifurcation boundaries for power systems: a new /spl Delta/-plane method

Abstract: This paper is devoted to the problems of finding the load flow feasibility saddle node, and Hopf bifurcation boundaries in the space of power system parameters. The first part contains a review of the existing relevant approaches including not-so-well-known contributions from Russia. The second part presents a new robust method for finding the power system load flow feasibility boundary on the plane defined by any three vectors of dependent variables (nodal voltages), called the /spl Delta/ plane. The method exploits some quadratic and linear properties of the load flow equations and state matrices written in rectangular coordinates. An advantage of the method is that it does not require an iterative solution of nonlinear equations (except the eigenvalue problem). In addition to benefits for visualization, the method is a useful tool for topological studies of power system multiple solution structures and stability domains. Although the power system application is developed, the method can be equally efficient for any quadratic algebraic problem.

Computer system with hybrid power distribution

Abstract: A power supply for a computer is disclosed. The power supply is capable of providing power in both a DC domain and a high frequency AC domain. A first power consuming component can be coupled to the power supply to receive power in the DC domain, and a second power consuming component can be coupled to the power supply to receive power in the high frequency AC domain.

Existence, uniqueness, and monotonic properties of the feasible power flow solution for radial three-phase distribution networks

Abstract: This paper analytically investigates the steady-state properties of a practical power distribution system with unbalanced loads, single-, two-, and three-phase lines and transformers of different connection types. It is shown that the three-phase power flow solution with feasible voltage magnitude for radial three-phase distribution networks with nonlinear load modeling always exists and is unique. Also, motivated by the practical use of three-phase power flow analysis as a basic tool for distribution system application functions, monotonic properties of the voltage magnitude at each node with respect to load changes are established. Implications and applications of these analytical results to distribution system analysis and design are discussed.

A New Approach for Power Flow Analysis of Balanced Radial Distribution Systems

Abstract: Power flow analysis is perhaps the most useful technique in the design and operation of a power system. This paper reports on a new method of power flow analysis for solving balanced radial distribution systems. The proposed method models the radial distribution system as a series of interconnected ladder networks. Using Kirchoff's laws, a set of iterative power flow equations was developed to conduct the power flow studies. It is very efficient and has excellent convergence characteristics. The radial topology of distribution networks has been fully exploited such that a unique branch and node numbering scheme is utilized to achieve storage and computational economy. Due to the voltage dependency of loads in distribution systems, various static load models are incorporated in the power flow algorithm to obtain better and more accurate results. The computer software implemented in this power flow method was then developed using C++ and successfully applied to several practical radial distribution networks...

Power flow control with FACTS devices

Abstract: A new method of power flow calculation considering FACTS devices is developed in the paper from a view of general approach of nonlinear system. The power flow equations of a power system with FACTS devices are presented. This method can also be used when there are some other nonlinear devices in a system. Testing results show that this method costs less time in power flow calculation than other methods. The power flow control range of UPFC in a power system is employed in the discussion. Examples are presented to show and verify what this paper specifies.