Showing papers on "Power-flow study published in 1994"

Power analysis of embedded software: a first step towards software power minimization

Abstract: Embedded computer systems are characterized by the presence of a dedicated processor and the software that runs on it Power constraints are increasingly becoming the critical component of the design specification of these systems At present, however, power analysis tools can only be applied at the lower levels of the design-the circuit or gate level It is either impractical or impossible to use the lower level tools to estimate the power cost of the software component of the system This paper describes the first systematic attempt to model this power cost A power analysis technique is developed that has been applied to two commercial microprocessors-Intel 486DX2 and Fujitsu SPARClite 934 This technique can be employed to evaluate the power cost of embedded software This can help in verifying if a design meets its specified power constraints Further, it can also be used to search the design space in software power optimization Examples with power reduction of up to 40%, obtained by rewriting code using the information provided by the instruction level power model, illustrate the potential of this idea >

Peak electrical power conversion system

Abstract: An electrical power conversion system that supplies the maximum available output power from a power source such as a solar array to a plurality of loads such as rechargeable batteries. The output power of the solar array peaks at an optimum current that is less than is maximum available output current. The system includes a controller and a plurality of dc-to-dc converters that charge the batteries. The controller monitors the solar array's output power and adjusts the battery charging by generating a current control signal that tracks a peak of the solar array's available output power and sets a current limit such that the combined current draw of the plurality of dc-to-dc converters is substantially equal to the solar array's optimum current at which it provides its maximum available power. The electrical power and control signals are transmitted from the power source and controller to the power converters on three bus bars, including a power bus, a control bus, and a common bus. The current control signal and the voltage control signal are multiplexed onto the single control bus. The controller and the dc-to-dc converters are mounted on planar printed circuit boards having clips arranged in a triangular pattern that allow the dc-to-dc converters to be easily attached to and removed from the buses.

Parallel connection of different types of AC power supplies of differing capacities

Abstract: A power inverting method and system for connecting a plurality of AC power supplies to a common bus line in parallel wherein the AC power supplies are independently controlled so that power supplies with different rating characteristics can be coupled to the common bus line without adverse effects such as the existence of cross currents flowing between the different power supplies. In each AC power supply there is provided a system parameter calculating unit for calculating optimum load current, system impedance and output voltage parameters of the power supply which are then output to a reference data producing unit which generates appropriate feedback voltage and phase signals for output to a voltage controller and a phase synchronization controller, respectively. The voltage controller and phase synchronization controller output feedback signals to a power inverter which varies the power supply output. Using such feedback control in each of the plurality of power supply units enables a constant current to be output to a load on the system and eliminates the possibility of cross currents between the various power supply units.

Congeneration power system

Abstract: A secondary power system eliminates the need for an automatic transfer switch and permits simultaneous supply from different sources. Primary power is rectified and connected to a DC bus, an AC generator has its output rectified and connected to the DC bus, and a storage battery is also connected to the DC bus. Current on the DC bus is inverted to AC to provide an uninterrupted power supply. The system is connected to a household electrical system by a power distribution panel which can be installed in a home prior to the secondary power system and can facilitate installation of the secondary system. The distribution panel can selectively bypass the secondary system and can disconnect non-vital loads when primary power is not available. The generator is powered by an engine using gasoline, natural gas or water, which can also power other systems, such as air conditioning, with exhaust heat or rotary motion.

Short term operation and power exchange planning of hydro-thermal power systems

Abstract: This paper considers a unified problem of short-term operation planning and power exchange scheduling of large hydro-thermal power systems including: unit commitment, hydro power plant operation planning, pumped-storage hydro power plant operation planning and scheduling of power exchange with other power utilities. The criterion function is the total variable profit incurred by energy production, sales of energy to the users inside the power system, sales of energy to other power companies and purchase of energy from them, or from other sources. The overall problem is solved using the Lagrangian relaxation method. A decomposition technique is applied to solve the dual (mixed-integer) and primal (continuous programming) problem. Dynamic programming, feasible direction method and linear programming method are used for the solution of subproblems. The results of the application of the method to a numerical example are given. >

Power system harmonics. Part 1. Harmonic sources

Abstract: Harmonics have been present in power systems since the very early stages of AC system development. The first part in this series of tutorials deals with harmonics from nonlinear power converters. Future parts will cover measurements, calculation, harmonic problems and harmonic reduction.

Aerospace power control system for monitoring and reliably transferring power buses

Abstract: An aerospace power control system switches an aerospace load from a faulty ac power bus to a good ac power bus of two or more ac power buses if the currently connected ac power bus is about to fail. The voltage level and frequency of the power provided on the buses are monitored to determine which of the power buses are within required limits to provide power to the aerospace load. If monitoring of the currently connected ac power bus indicates that the bus is not within the required limits and may be shut down in the immediate future, the connection of the aerospace load is switched to another ac power bus which is within the required limits. The current provided to the load is monitored to determine zero-crossing points of the current with the switch from the currently connected faulty bus to a good bus being performed at a zero-crossing point of the load current. The level of the current being provided to the aerospace load is also monitored to detect a faulty load condition. If the load current exceeds defined limits, the load will be disconnected from all ac power buses to shut down the faulty load. The aerospace power control system is generally applicable to single phase and three phase ac power, with switch over at zero-crossing points being performed on a phase-by-phase basis for three phase ac power.

Power electronics transforms aircraft systems

Abstract: This paper describes the secondary power sources available on a large transport aircraft and discusses expectation that power electronics will enable the transforming of present aircraft systems into new highly integrated systems. The benefits expected from integrating all of the engine-based hydraulic and pneumatic power sources into a single 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. A power system architecture that eliminates the need for a pneumatic and hydraulic power distribution system 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. >

Performance comparison of output power estimators used in AC/DC/AC converters

Abstract: In the paper various methods of power estimation used in AC/DC/AC converters are compared. To maintain constant DC bus voltage using only small electrolytic capacitors which is one of the design targets in these systems, the input bridge reference currents must be generated on the basis of the system power flow. Since this method is not sufficient for tight regulation, an inner DC bus voltage control loop is usually added. The design procedure of the DC bus voltage regulator is also presented. The performance of three estimation methods is compared in terms of DC bus voltage fluctuation in dynamic conditions for a 15 kW AC/DC/AC converter. >

Analysis of the instability of PFC power supplies with various AC sources

Abstract: Certain AC sources and line conditioners are not compatible with all power factor corrected (PFC) power supplies The resulting combination can lead to system instability and cause complete loss of power control The mathematical models of different types of AC sources and of a typical PFC power supply are presented and the interaction between them is described both qualitatively and in terms of stability requirements Examples of unstable systems are shown and solutions to the stability problem from both ends of the power cord are discussed >

Modeling and measurement of a high-performance computer power distribution system

Abstract: This paper describes a study whose purpose was to provide a methodology to accurately model entire high-performance computer power distribution systems, from power supply to load. Simulation and measurement results for a CMOS microprocessor system are shown to compare favorably. >

Power flow analysis in mtdc-ac systems—a new approach

Abstract: This paper presents a new approach to the power flow analysis in steady state for multiterminal DC-AC power systems. A flexible and practical choice of per unit system is used to formulate the DC network and power converter equations. A converter is represented by Norton's equivalent of a current source in parallel with a commutation resistance. Unlike in previous literature, the DC network equations are used to derive the controller equations for the DC system using a subset of specifications. The specifications considered are current or power at all terminals except the slack terminal where the DC voltage is specified. The control equations are solved by Newton's method, using the current injections at the converter terminals as state variables. Further, a systematic approach to the handling of constraints is proposed by identifying the priorities in rescheduling of the specified variables. The methodology is illustrated by example of a 5 terminal DC system (11 refs.)

Power analysis for semi-custom design

Abstract: We present a power analysis system for semi-custom hardware design that operates on a cell level making it a faster alternative to the currently available transistor level systems. Our system allows for the calculation of static and dynamic power consumption of a circuit. Measuring the power consumption is critical for low power design as it enables the designer to meet power specifications, drive power optimization tools, distribute power effectively through a design and choose appropriate packages. Implementation results show that the power analysis system is 4 orders of magnitude faster than circuit-level simulation, with accuracy within 10%. >

A graphical user interface for design, simulation, and analysis of power plant electrical auxiliary systems

Abstract: An interactive graphical user interface (GUI) package for the design, simulation and analysis of a power plant electrical auxiliary system is presented in this paper. The purpose of this package is to assist the engineer in performing nonreal-time, what-if, analysis in an interactive and intuitive environment. The package, AUXSYS, is capable of performing load flow and motor starting simulations. It provides a graphical interface for designing the one-line diagram of the plant and analyzing the output of the simulations. It is currently used for modelling Wisconsin Electric Power Company's (WEPCO) power plant electrical auxiliary systems and is implemented for use on PCs. >

Reactive power-real or imaginary?

Abstract: No matter how abstract the concept of reactive power is, requiring as it does the use of `imaginary' algebra to calculate, it plays a vital role in the stable operation of power systems. The author explains what reactive (or imaginary) power is and its effects on components and generator design. The author then discusses the early generator developments of Charles Parsons, high voltage transmission, reactive power control in transmission systems, and measurement of reactive power.

Voltage reactive security analysis in power systems with automatic secondary voltage control

Abstract: The complete methodology for the steady-state voltage/reactive security analysis of power systems with automatic secondary voltage control is proposed. Both the decentralised and the co-ordinated control concepts are incorporated in a comprehensive procedure, consisting of three principal steps: contingency selection, contingency analysis and corrective control. The contingency selection stage is based on the extended load flow model and a new voltage/reactive performance index. The contingency analysis is performed next, by using either the extended load flow model (for decentralised control), or the optimum power flow model (for co-ordinated control). Finally, a simplified linear programming model for corrective resetting of pilot-bus set-point voltages is proposed with the aim to increase voltage security margins. The complete methodology was verified on the eastern part of high-voltage power system of former Yugoslavia.

Voltage stability assessment of isolated power systems with power electronic converters

Abstract: This paper extends the concept of small signal models to the frequency domain and then presents a new method for isolated power system voltage stability analysis. An approximation for the voltage and reactive power relationship of the cycloconverter is proposed and verified by time domain simulation. Small signal models for various nonlinear, power system components including power electronic converters are derived, based upon which, the incremental network of the system is formed. The voltage stability indices of various buses, which are defined in the bus impedance matrix of the incremental network, can be calculated using the conventional factorisation method without the need to determine the matrix eigenvalues and eigenvectors. The model and algorithm can also be used to predict the stiffness of the system with respect to voltage fluctuations during operation.

Modeling the protection system components of the space station electric power system

Abstract: To facilitate protection system studies on the space station electric power system, there is a need to develop a model that can accurately and conveniently simulate both the power system and the protection system. Models for two major protective devices, the remote bus isolator and the remote power controller, are described. These models have been installed in a power system model resembling one channel of the space station power system. The usefulness of these models in protection system studies Is demonstrated. >

A probabilistic approach to control variable adjustment for power system planning applications

Abstract: This paper applies probabilistic load flow techniques to network constrained setting of control variables based on sensitivity analysis. The method determines operating constraint violations for a whole planning period together with the probability of each violation and leads to the satisfaction of these constraints with a minimum number of control corrective actions in a desired order. The paper investigates the effects of high dispersion in the input variables in order to assess the effectiveness of the method for long-term planning applications. >

An Overview of Flexible AC Transmission Systems

Abstract: Preface FACTS or "flexible AC transmission systems" is a term that has been suggested for the use of solid state devices to control bulk power flow in transmission systems. The Electric Power Research Institute supported this idea, and many researchers have invested efforts on the value and potential of FACTS. At this time, it appears that the main value of FACTS lies in improving transmission capability; increasing the flexibility of power flow control (e.g., for wheeling or for economic dispatch); for controlling voltage (and var flow); and possibly additional advantages in lower voltage systems (e.g., distributioli systems). This report is an overview of FACTS. It was produced by the EE 532 class ("Computer Analysis of Power Systems") at Purdue Ur~iversity in the Fall, 1994 semester. The student in this class always prepare a term report which is issued by the School of Electrical Engineering as a technical report. The cost of printing was paid by the Purdue Electric Power Center (PEPC) which forms a base of the povver engineering program at Purdue. The students also presented their work in the form of a videotape. I was the class instructor for the semester.

Development of fuzzy excitation control system

Abstract: Power system stability is essential to reliable and economical operation of power systems. The quick-response excitation control with PSS is used as a power system stability improvement measure at the generator. However, this method is not always sufficient to apply in a wide operation range of power system configuration, load flow, and so on. This paper includes results of experiments of fuzzy excitation control system on the ac/dc Power System Simulator of CRIEPI. This control system is verified to improve power system stability and has better performance than the conventional excitation control on a one-and two-machine to infinite bus system.

Visualization of an electric power transmission system

Abstract: Visualization techniques are applied to an electric power system transmission network to create a graphical picture of network power flows and voltages. A geographic data map is used. Apparent power flow is encoded as the width of an arrow, with direction from real power flow. Flows are superposed on flow limits. Contour plots and color coding failed for representing bus voltages. A two-color thermometer encoding worked well. The resulting visualization is a significant improvement over current user interface practice in the power industry. >

Power system security with the consideration of economic dispatch

Abstract: Operation of power systems demands a high degree of security to keep the system satisfactorily operating, if it is subjected to a disturbance. On the other hand, systems operation requires attention to economy. In this work, the proposed approach reconciled the possible conflict between dynamic security and economy requirements. Firstly, the pattern recognition technique was used to assess dynamic security. Linear classifiers, that determine the stability of the electric power system were developed and presented. This set of classifiers were added to the other system stability and operational constraints, in the quadratic programming, that has been traditionally used in economic studies. The problem was then formulated to satisfy a secure-economic preventative strategy. This strategy directly presented a solution, that ensured economy and security of the power system. The method has been tested by applying it to two test systems, usually used in the literature. The technique showed ease and applicability to different areas of power system analysis. >

An adaptive SOR algorithm and its parallel implementation for power system applications

Abstract: In our earlier papers,we investigated the parallelization and implementation of Gauss-Seidel (G-S) and Successive Overrelaxation (SOR) power flow analysis on shared memory, (SM) and distributed (DM) machines. For the SOR case, constant acceleration factors obtained from experiments are used to speedup convergence. In this paper, we introduce a new adaptive nonlinear SOR (ANSOR) algorithm which uses an approximated optimal acceleration factor obtained during the iteration process. The algorithm is shown to be faster due to the significant reduction in the number of iterations, and to converge robustly under heavily-loaded conditions on large power systems. We also implement parallel and sequential versions of our ANSOR algorithm on the nCUBE2 machine, and show that our algorithm is competitive with the fast decoupled load flow (FDLF) algorithm. Moreover, the portability of the parallel ANSOR code is demonstrated by porting the code to the Intel iPSC/860 hypercube and the Paragon mesh MIMD machines. However, our new algorithm is not a panacea for all problems, as we demonstrate with an example from transient stability analysis. >

Stabilization of power system using variable structure output feedback control

Abstract: This paper presents a new output feedback variable structure power system stabilizer for a single-machine infinite-bus system The stabilizer design is accomplished using extra dynamics in the form of a dynamic compensator The method of equivalent control is used to describe the "augmented reduced order system" in the "sliding mode" Due to the reduction of order of the system in the sliding mode, the order of the compensator is usually less than the order of the compensator given by the Kimura-Davison formula A numerical example is worked out and the performance of the machine is investigated using different stabilizers to illustrate the effectiveness of the proposed design

A 12 kW switching mode power supply with free input-voltage

Abstract: Phase-controlled AC to DC power conversion has the disadvantages of low power factor and harmonic pollution on the utility side, particularly in the case where DC voltage regulation is required. This paper presents a 12 kW switching mode power supply for a telecom power system. The scheme employs a buck-type power converter in the front-end resulting in high input power factor and less harmonics to the utility. A two-loop controller with a feedback and a feedforward loop is used to minimize the effects of the rectified ripple voltages and to improve the system dynamics. Since it also has a very wide input-voltage range, it can be directly applied for both the input systems of AC 220 V and 380 V. >

Power factor and harmonic compensation in industrial power systems with nonlinear loads

Abstract: Industrial power systems are often characterized as large consumers of reactive power and significant generators of harmonics because most of the load is generally composed of induction motors and static power converters. Consequently, this article analyzes a typical power system configuration where is it desirable to install power factor capacitors and tuned harmonic filters for reactive power compensation and harmonic control. The resonant conditions for a given power factor correction or a harmonic frequency are determined directly from the roots of a quadratic expression. This formulation also allows a quick evaluation of power factor range with excessive harmonic levels, as well as effects of tuned reactors on the resonant frequencies. >

A meter placement algorithm for the enhancement of state estimation function in an energy management system

Abstract: A meter placement algorithm, that uses the variances of the state estimation (SE) errors as indices, is proposed to enhance the accuracy and robustness of the SE solutions. The algorithm provides a list of buses with low local redundancy in any observable area of a power network and a list of candidate measurements to reduce the SE error variances. The candidate measurements have the potential to increase the local redundancy around a certain bus on the list, thus improving its SE solution. Certain heuristics are applied to make sure that a minimum number of leverage points is introduced into the measurement set by the additional measurements. Test results on the IEEE 30 bus system are provided. >

On line tracking state estimation in power system

Abstract: In this paper the tracking of the time varying power system state is analysed. A tracking state estimator is a digital feedback loop (a computer algorithm) which uses real time measurements of voltage magnitudes, real power flows and reactive power flows to track the static state as it varies during the daily load cycle. Two different tracking algorithms were tested: suitable to Snapshot scan and Sequential scan mode of measurement system. Results are presented for AEP-30 bus power system