Showing papers on "Power-flow study published in 2005"

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

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

Usefulness of DC power flow for active power flow analysis

Abstract: In recent days almost every study concerning the analyses of power systems for market related purposes uses DC power flow. DC power flow is a simplification of a full power flow looking only at active power flows. Aspects as voltage support and reactive power management are not considered. However, such simplifications cannot always be justified and might sometimes be unrealistic. In this paper authors analyze the assumptions of DC power flow, and make an attempt at quantifying these using indexes. Among other, the paper answers the question of how low the X/R ratio of line parameters can be, and what is the maximal deviation from the perfect flat voltage which still allows DC power flow to be acceptably accurate.

Simultaneous coordinated tuning of PSS and FACTS damping controllers in large power systems

Abstract: This work deals with the simultaneous coordinated tuning of the flexible AC transmission systems (FACTS) power oscillation damping controller and the conventional power system stabilizer (PSS) controllers in multi-machine power systems. Using the linearized system model and the parameter-constrained nonlinear optimization algorithm, interactions among FACTS controller and PSS controllers are considered. Furthermore, the parameters of the damping controllers are optimized simultaneously. Simulation results of multi-machine power system validate the efficiency of this approach. The proposed method is effective for the tuning of multi-controllers in large power systems.

Benders decomposition: applying Benders decomposition to power systems

Abstract: It is apparent that power system restructuring provides a major forum for the application of decomposition techniques - including the Benders decomposition algorithm - to coordinate the optimization of various objectives among self-interested entities. It is used for solving large-scale, mixed-integer programming (MIP) problems. Benders decomposition has been successfully applied to take advantage of underlying problem structures for various optimization problems, such as restructured power systems operation and planning. This paper shows how Benders decomposition works in the power system.

Optimal power flow as a tool for fault level-constrained network capacity analysis

Abstract: The aim of this paper is to present a new method for the allocation of new generation capacity, which takes into account fault level constraints imposed by protection equipment such as switchgear. It simulates new generation capacities and connections to other networks using generators with quadratic cost functions. The coefficients of the cost functions express allocation preferences over connection points. The relation between capacity and subtransient reactance of generators is used during the estimation of fault currents. An iterative process allocates new capacity using optimal power flow mechanisms and readjusts capacity to bring fault currents within the specifications of switchgear. The method was tested on a 12-bus LV meshed network with three connection points for new capacity and one connection to an HV network. It resulted in significantly higher new generation capacity than existing first-come-first-served policies.

Convexity of the set of feasible injections and revenue adequacy in FTR markets

Abstract: The feasible set of power injections for the constrained power flow equations is nonconvex when practical transmission capacity and bus voltage limits are imposed. The projection onto the space of active power injections may be "close" to convex, but this is not sufficient to guarantee revenue adequacy for the settlement of financial transmission rights.

Sensitivity-based security-constrained OPF market clearing model

Abstract: This paper proposes a novel technique for representing system security constraints that properly include voltage stability limits in the operation of competitive electricity markets. The market-clearing algorithm is modeled as a voltage stability constrained optimal power flow (OPF) problem, while the distance to the closest critical power flow solution is represented by means of a loading parameter and evaluated using a continuation power flow (CPF) technique. Sensitivities obtained at the OPF step are used to estimate power directions for the CPF method, while the CPF analysis provides the loading parameter to be used in the OPF problem based on an N-1 contingency criterion. The OPF and the CPF steps are repeated until the maximum loading parameter is found, thus providing optimal solutions considering both proper market conditions and security margins. Two benchmark systems with both supply and demand bidding are used to illustrate and test the proposed technique

Continuation three-phase power flow: a tool for voltage stability analysis of unbalanced three-phase power systems

Abstract: In this paper, a continuation three-phase power flow (CTPFlow) approach in polar coordinates, which can be used to analyze voltage stability of unbalanced three-phase power systems, is proposed. Using CTPFlow, the PV curves of unbalanced three-phase power systems can be obtained. It is found that the patterns of the PV Curves of unbalanced three-phase power systems are quite different from that of balanced three-phase power systems or positive-sequence power systems. The investigations indicate that a CTPFlow is needed where there are unbalanced network or loads existing in a system. Numerical examples are given to illustrate the approach.

Locomotive power train architecture

Abstract: The present invention is directed to a power control architecture for a vehicle, particularly a locomotive, in which a number of energy sources (105, 111, 115) are connected to a common electrical bus (101, 102) and selectively provide energy to the bus (101, 102) based on the relationship between their respective output voltages and the bus voltage

Method and apparatus for providing economic analysis of power generation and distribution

Abstract: An economic dispatch program optimally allocates load demand specifying real power and reactive power to be generated by a power plant among various power generators in a manner so that each of the power generators are operated within its optimal operating space as defined by a reactive capability curve. Allocating a power demand with consideration of the reactive capability curves of the power generators results in optimal generation of real power and reactive power as specified by the load demand. Alternatively, the economic dispatch program allocates load demand specifying real power and reactive power to be delivered by a power grid among various power plants wherein one or more of the various power plants have capacity limits exhibited by reactive capability curves.

Optimal distributed generation allocation in distribution network using Hereford Ranch algorithm

Abstract: The necessity for flexible electric systems, energy saving, loss reducing and environmental impact are providing impetus to the development of distributed generation (DG). DG includes the application of small generators, scattered throughout a power system, to provide the electric power needed by electrical customer. Such locally distributed generation, has several merits from the viewpoint of environmental restriction and location limitations, as well as transient and voltage stability in the power system. The exact solution of the DG allocation can be obtained by a complete enumeration of all feasible combinations of sites and sizes of DGs in the network. The number of alternatives could be very large, however load flow should be performed for each feasible combination and selection of the optimized solution among these alternatives is an important task. The problem is to determine site and size of DG that minimizes the distribution power losses under the condition that number of DGs and total capacity of DGs are known. Artificial intelligence techniques have come to be most widely used tool for solving optimal DG allocation. Genetic algorithm (GA) is an efficient tool to solve optimization problems. Generally, GA's ability to find a correct solution in a variety of problems, to preserve diversity for preventing premature convergence and to improve convergence time is affected by parent selection algorithm for generating offspring. In this paper, to overcome the defects of existing simple genetic algorithm (SGA), Hereford Ranch algorithm (HRA), is applied to search optimal site and size of DG in distribution feeders. HRA uses sexual differentiation and selective breeding in choosing parents for genetic string. The proposed method was tested for 34-node IEEE distribution test feeder

Method for calculating power flow solution of a power transmission network that includes unified power flow controllers

Abstract: A method for calculating power flow solution of a power transmission network with unified power flow controllers is adapted to calculate the power flow on a large-scale power transmission network. The unified power flow controller has a series transformer, a series converter, a direct current coupling capacitor, a shunt converter, and a series transformer. The shunt transformer is connected electrically to a sending-end bus. The series transformer is connected electrically to the sending-end bus and a receiving-end bus. The unified power flow controller is represented by equivalent active and reactive loads on the sending-end and receiving-end buses of the power transmission network.

Evaluation and performance comparison of power swing detection algorithms

Abstract: This paper presents performance comparisons and evaluations of several power swing detection algorithms. Any sudden change in the configuration or the loading of an electrical network causes power swing between the load concentrations of the network. In order to prevent the distance protection from tripping during such conditions, a power swing blocking is utilized. The decreasing impedance, the Vcos/spl phi/ and the superimposed currents methods are conventional algorithms for power swing detection. In this paper, the behavior of these algorithms is evaluated. Different conditions have been generated by EMTDC software and voltage and current waveforms have been given to the power swing detectors. Operation of the power swing detectors has been investigated for different conditions and the operation of different algorithms are compared.

Electrothermal coordination part II: case studies

Abstract: The concept of electrothermal coordination (ETC) in power system operation introduced in Part I proposes to exploit thermal inertia to coordinate line temperature dynamics with existing power system controls, thus increasing power transfer capability and enhancing system security and economic performance. In this Part II, the characteristics of ETC and its benefits in operational functions such as augmenting power transfer capability, emergency control, congestion management, and system loadability are numerically analyzed through a number of case studies. This paper also examines some practical issues concerning the deployment of ETC.

Power emulation: a new paradigm for power estimation

Abstract: In this work, we propose a new paradigm called power emulation, which exploits hardware acceleration to drastically speedup power estimation. Power emulation is based on the observation that most power estimation tools typically perform the following sequence of operations: simulating the circuit to obtain value traces or statistics for the inputs of its constituent components, evaluating power models for each circuit component based on the input values seen during simulation, and aggregating the power consumption of individual components to compute the circuit's power consumption. We further recognize that the steps involved in power estimation (power model evaluation, aggregation) can themselves be thought of as synthesizable functions and implemented as hardware circuits. Thus, any given design can be enhanced by adding to it "power estimation hardware", and the resulting power model enhanced circuit can be mapped onto a hardware prototyping platform. While drastic speedups in power estimation (orders of magnitude) are possible using this approach, a significant challenge arises due to the increase in circuit size as a result of adding power estimation hardware. We propose a systematic methodology to reduce the size of the power model enhanced circuit through a suite of techniques, including power model reuse across different circuit components, regulating the granularity of components for power modeling, exploiting inter-component power correlations, resource sharing for power model computations, and the use of block memories for efficient storage within power models. We demonstrate the benefits of the proposed power emulation paradigm by applying it to register-transfer level (RTL) power estimation for industrial designs, resulting in speedups from around 10X to over 500X compared to state-of-the-art commercial power estimation tools.

Identification of severe multiple contingencies in electric power networks

Abstract: In this paper we propose a two-stage screening and analysis process for identifying multiple contingencies that may result in very severe disturbances and blackouts. In a screening stage we form an optimization problem to find the minimum change in the network to move the power flow feasibility boundary to the present operating point and that will cause the system to separate with a user-specified power imbalance. The lines identified by the optimization program are used in a subsequent analysis stage to find combinations that may lead to a blackout. This approach is applied to a 30-bus system with encouraging results.

A network-based distributed slack bus model for DGs in unbalanced power flow studies

Abstract: This paper revisits the concept of a single slack bus in power flow solvers for distribution systems to accommodate the anticipated growth of distributed generators (DGs) in unbalanced distribution systems. It introduces a distributed slack bus model through scalar participation factors by applying the concept of generator domains. The participation factors are incorporated into the three-phase power flow equations, and a Newton-Raphson solver is discussed and implemented. Simulation results on systems with a different number of DGs and different levels of DG penetration are obtained and studied.

A modified particle swarm optimization algorithm and its application in optimal power flow problem

Abstract: A modified particle swarm optimization (MPSO) algorithm is presented. In the new algorithm, particles not only studies from itself and the best one but also from other individuals. By this enhanced study behavior, the opportunity to find the global optimum is increased and the influence of the initial position of the particles is decreased At last, the method adopting MPSO algorithm to solve the optimal power flow problem is given. The numeric simulation for a 5-bus system shows that this algorithm is feasible to solve optimal power flow problem.

Power monitors: a framework for system-level power estimation using heterogeneous power models

Abstract: Power analysis early in the design cycle is critical for the design of low power systems. With the move to system-level specifications and design methodologies, there has been significant research interest in system-level power estimation. However, as demonstrated in this paper, the addition of power estimation capabilities to system-level simulation tools can significantly degrade simulation efficiency (up to 8.5/spl times/), limiting the use of power estimation during long simulation rum, and the ability to perform extensive design space exploration. Some power modeling techniques for system components provide "local" tradeoffs between power estimation accuracy and computational cost This work addresses a complementary problem - the optimized integration and usage of heterogeneous component power models within a system-level simulation framework. We view system-level power estimation as a global deployment of computational effort (the effort required to perform power estimation) over space (the different components) and time (the duration of the simulation). We illustrate the advantages of optimizing the allocation of power estimation effort based on run-time variations of component-level, as well as system-level power consumption characteristics. To achieve this, we have developed a novel power estimation framework, based on a network of power monitors. Power monitors observe component- and system-level execution and power statistics at run time, based on which they (I) select between multiple alternative power models for each component, and/or (II) configure the component power models, to best negotiate the trade-off between efficiency and accuracy. In effect, the power monitor network performs a coordinated, adaptive, spatio-temporal allocation of computational effort for power estimation. Experiments conducted on a commercial system-level simulation framework and system-on-chip platform demonstrate that the proposed techniques yield large reductions in power estimation overhead (nearly an order of magnitude), while minimally impacting power estimation accuracy.

A predictor/corrector scheme for obtaining Q-limit points for power flow studies

Abstract: This work proposes a new continuation power flow method tracing QV constraint exchange points (CEP), at which generators regulating voltages hit the reactive power limits. The proposed method is based on a predictor/corrector scheme to obtain CEPs in succession. The condition for Q-limit immediate instability is derived and used in the algorithm, where the stability of the obtained CEP is checked in each iteration. The point of collapse method is also combined in the algorithm to detect a saddle node bifurcation. The effectiveness of the proposed method is demonstrated through numerical examinations in IEEE 118 bus systems.

Method and system for ac power grid monitoring

Abstract: A method and system allows for substantially real-time monitoring of the operational dynamics of power plants (16, 18, 20) and other components comprising an AC power grid, by using information collected from a network of power grid frequency detection and reporting devices (22, 24, 26). The invention allows for the substantially real-time detection and reporting of certain power grid events such as power plant trips.

Power generation system, and administration apparatus and administration method of power generation system

Abstract: In a power generation system which includes a plurality of sets of direct current power sources and power converters which are connected to the direct current power sources to convert a direct current power into an alternating current power, the power converters being connected in parallel to supply the alternating current power to a system power supply, from the plurality of power converters in the system, one power converter is set as a master machine which detects an islanding operation state in which power supply from the system power supply is stopped, and setting is executed so as to cause the remaining power converters not to detect the islanding operation state. When the master machine is not present among the power converters in operation, the master machine is selected from the power converters in operation in accordance with a predetermined condition.

Transmission loss allocation through a modified Ybus

Abstract: A methodology to allocate the active power transmission loss among agents of a power pool is proposed. The approach is based on the inclusion of the admittances equivalent to bus power injections in the bus admittance matrix. For a given power-flow solution, the relationship between the branch currents and the load/generator current injections is determined using a modified bus admittance matrix, which allows the power loss of each transmission line to be expressed in terms of bus current injections. The proposed technique is simple to implement and flexible enough to allow the assignment of loss parcels to a preselected set of buses. An example, with a six-bus system illustrates the main steps of the proposed allocation strategy, and numerical results obtained with the IEEE 57-bus system are used to assess the quality of the loss allocation.

Dispersed generation modeling for object-oriented distribution load flow

Abstract: The interest in dispersed generation (DG) is world-widely increasing. The connection of small generating units affects the operation of distribution systems and classical modeling and analyzing techniques must be revised. Recently, a novel approach to the distribution load-flow problem has been proposed: the object-oriented (OO) paradigm has been applied both to the system modeling and to the Newton-Raphson solving algorithm in the cases of radial and weakly meshed distribution systems. In this paper, the OO load-flow modeling and algorithm are extended to account for the inclusion of DG. The OO paradigm allows easily introducing accurate models of DG interfacing to the network by various electric devices (synchronous generators, induction machines, power electronics converters). Numerical applications are presented to evidence the features of the algorithm evaluating the effects of DG on the operation of two test systems.

Voltage stability limit of electric power systems with Generator reactive power constraints considered

Abstract: This paper investigates the smoothness of the transfer limit surface, or the loadability surface, of power systems. The reactive power output constraints of generators are taken into consideration. A new methodology employed for the investigation is based on characterizing each maximum loading point by the state of the generators (PV or PQ). Then the transfer limit surface is investigated through careful observation of nose curves. In those special cases with only one constraint, the transfer limit surface is smooth. However, in the more general case of multiple constraints, the transfer limit surface is nonsmooth. These properties have been confirmed in a numerical example using a system with two constraints and three load parameters.

Power manager and power managing method for battery-powered application

Abstract: A power manager is configured to manage power for a battery-powered application. A power source, a load and a battery are interconnected through a circuit path. Power from the power source is provided to the load and battery by a switching regulator. Various implementations are presented.

Power supply system for vehicle with improved energy efficiency and vehicle including the same

Abstract: A matrix converter (38) converts three-phase AC power input from a first motor-generator (MG1) directly to three-phase AC power for driving a second motor-generator (MG2) and outputs the resultant three-phase AC power, without rectifying the three-phase AC power generated by the first motor-generator (MG1) once to DC power as in an example using a conventional three-phase full-wave rectification inverter. In a power supply system for a vehicle (14), the three-phase AC power is transmitted and received between two motor-generators (MG1, MG2) more directly, by means of the matrix converter (38). Therefore, power loss can be reduced, as compared with a conventional example in which the three-phase AC power is once converted to DC power. Thus, a power supply system for a vehicle with improved energy efficiency and a vehicle including the same can be provided.

Power flow controller responsive to power circulation demand for optimizing power transfer

Abstract: A power flow controller responsive to power circulation demand for optimizing power transfer is disclosed. When a power flow controller operates at its rated capacity, it can no longer regulate from-bus voltage set-points, line power flow set-points, or both. In such cases, the power flow controller switches to power circulation set-point control without exceeding the rated capacities of the voltage-sourced converters in the power flow controller. Power-voltage (PV) curves associated with voltage stability analysis for maximizing power transfer can be generated and stored for use with a power flow controller operating in automatic power flow control mode.

Operational and topological optimization of multi-carrier energy systems

Abstract: This paper presents an approach for the combined optimization of energy systems including multiple energy carriers such as electricity, natural gas, and district heat. Power flow and conversion between the different energy infrastructures is described as multi-input multi-output coupling, what enables simple analysis and optimization of the flows. While previous work deals with operational optimization (multi-carrier optimal dispatch and power flow), this paper focuses on optimization of the couplings between the different systems

Identify the impact of distributed resources on congestion management

Abstract: Due to dispersed locations and various capacities, emerging Distributed Resources (DR's) have diverse and highly nonlinear impact (Contribution Factor, CF) on transmission operation constraints, thereafter on congestion management in electricity markets. From the perspective of Independent System Operators (ISO's) and DIStribution COmpanies (DISCO's), it is crucial to address such impacts in order to identify the "desirable" and "undesirable" DR's. This paper introduces a straightforward-partitioning space, ITDA, developed by a fuzzy c-means clustering approach based on accurate CF's derived from AC power flow. Case studies with 6-bus and 30-bus test systems demonstrate that the proposed technique is simple and applicable.