Showing papers on "Power-flow study published in 2001"

Modeling and simulation of a distribution STATCOM using Simulink's Power System Blockset

Abstract: This paper presents a study on the modeling of a STATCOM (Static Synchronous Compensator) used for reactive power compensation on a distribution network. The power circuits of the D-STATCOM and the distribution network are modeled by specific blocks from the Power System Blockset while the control system is modeled by Simulink blocks. Static and dynamic performance of a /spl plusmn/3 MVar D-STATCOM on a 25-kV network is evaluated. An "average modeling" approach is proposed to simplify the PWM inverter operation and to accelerate the simulation for control parameters adjusting purpose. Simulation performance obtained with both modeling approaches are presented and compared.

Mobile power generation system

Abstract: A power generation system is described for supplying electrical power to a load (128) from at least one of a generator (108) and a battery (110). The power generation system includes a power bus (116) coupled to the generator and a bidirectional conversion unit (106) coupled between the power bus and the battery. The bidirectional conversion unit is capable of transitioning between a first direction wherein electrical power flows from the power bus to the battery and a second direction wherein electrical power flows from the battery to the power bus.

Comparison of voltage security constrained optimal power flow techniques

Abstract: This paper compares two different optimal power flow (OPF) formulations that consider voltage security in power systems. The techniques are both based on multi-objective optimization methodologies, so that operating costs and losses can be minimized while maximizing the "distance" to voltage collapse. The techniques are described in detail and compared to study their similarities, as well as advantages and disadvantages. The comparisons are based on the results obtained by applying these two methods to a modified version of the 118-bus IEEE test system.

Voltage control devices models for distribution power flow analysis

Abstract: This paper presents the development of mathematical models for thyristor controlled series compensator (TCSC), for voltage regulator devices and for remote bus voltage control that are suitable to be used with the three-phase current injection method (TCIM) for power flow calculation. TCIM is a Newton method where the equations are written in rectangular coordinates resulting in a 6n/spl times/6n Jacobian matrix. The representation of a control device requires an augmented system of equations to incorporate the additional relationship between each control action and the controlled variable, resulting in an augmented Jacobian matrix. Practical distribution systems are tested and the effectiveness of the proposed formulation is demonstrated.

Microturbine/capacitor power distribution system

Abstract: A power generation system is disclosed. In one embodiment, the power generation system includes a fuel source to provide fuel, a turbogenerator, coupled to the fuel source, to generate AC power, and a power controller electrically coupled to the turbogenerator. The power controller includes a first power converter to convert the AC power to DC power on a DC bus, and a second power converter to convert the DC power on the DC bus to an output power to supply a load. The power controller to regulate the fuel to the turbogenerator, independent of a DC voltage on the DC bus. A capacitor, such as an electrochemical capacitor or a hybrid capacitor, is coupled to the DC bus to source instantaneous power to and sink instantaneous power from the DC bus, due to load changes, to stabilize the DC voltage on the DC bus.

Damping algorithm based on phasor estimation

Abstract: The paper describes a new method to generate the reactance reference for a TCSC, which has been installed in order to provide damping in a power system. The knowledge of the expected oscillation frequency in the power system is used to create a coordinate system, which rotates with that frequency. In this coordinate system a phasor representing the power swing is being extracted from the input power signal. A reactance reference signal with arbitrary gain and phase shift can easily be created using the phasor. The phase of the reactance reference is preserved during limiting. Gain and phase-shift may comfortably be scheduled due to measured parameters like average power, power swing amplitude etc. Frequency compensation has been implemented, and adapts the frequency in the measuring system when a power oscillation occurs. The new approach has been implemented and successfully tested in the North-South Interconnection in Brazil in March 1999 and has been in operation since then. The scheme is applicable for PSS and other FACTS damping systems.

Power generators and method and device for generating power

Abstract: In order to coordinate power generators (32-35) and consumers (36,37) in a power network using intelligent management, a method for generating power is provided wherein at least two decentralized power generators(32-35) are connected to an electric network (31), supplying said network (31) with power. A value for the current output of at least one power generator(32-35) is detected and compared to a theoretical output and according to the result, the output of the power generators (32-35) connected to the electric network (31)is adapted correspondingly.

A microturbine based power generation system and method

Abstract: A power electrical system (37) is disclosed to connect a microturbine (12) and an electrical machine (14) to electrical power sources (18, 44) and a load (16). The invention permits the microturbine to be started using an external DC power source (18) and/or an external AC power source (44). DC power is converted to AC power by means of a buck-boost chopper (30), DC bus (24) and a DC-to-AC converter (42). AC power, from the AC power source, is converted to frequencies and voltages suitable to start a microturbine by a pair of DC-to-AC converters (42, 46) and the DC bus (24). The frequency and voltage levels of the AC power are gradually increased to accelerate the microturbine to startup speed. Once the microturbine is started, the external power sources are disconnected, and the DC bus and the DC-to-AC converters produce output AC power at a voltage level and frequency to match an electrical load.

MV network planning under uncertainties on distributed generation penetration

Abstract: The necessity for flexible electric systems, changing regulatory and economic scenarios, energy savings and environmental impact are providing impetus to the development of distributed generation, which is predicted to play an increasing role in the future electric power system; with so much new distributed generation being installed, it is critical that the power system impacts be assessed accurately so that DG can be applied in a manner that avoids causing degradation of power quality, reliability and control of the utility system. Considering that uncertainties on DG power production are very relevant and different scenarios should be taken into consideration, traditional deterministic planning techniques cannot be sufficient to take the right decisions. For these reasons, this paper proposes a new three steps procedure, based on an heuristic optimization algorithm for the optimal network planning, considering all technical constraints, like feeder capacity limits, feeder voltage profile and three-phase short circuit current in the network nodes and on the application of the decision theory. Finally a case study is proposed and discussed to show the applicability of the proposed methodology and its main advantages.

Temperature Effect to Distribution System Load Profiles and Feeder Losses

Abstract: A systematic procedure is proposed to study the effect of temperature change to the power system load demand by using the typical load patterns of customer classes. The billing data of all service customers are retrieved to derive the daily load profile of the selected Taipower district. To verify the accuracy of the estimated load composition, the simulation results are compared to the actual load profile collected by the SCADA system. The sensitivity analysis of load demand with respect to the temperature change for each customer class is performed by statistic regression according to the actual customer power consumption and temperature data. The load contribution by each customer class is updated by the corresponding temperature sensitivity and integrated together to form the new load profile of a service district with temperature change. To investigate the temperature effect to the distribution system operation, one of the Taipower distribution feeders is selected for computer simulation. The power demand at each load bus of the distribution feeder is calculated by applying the temperature sensitivity and the three-phase load flow analysis is then executed to find the new feeder loading and power loss with the temperature change.

Static transfer switch: analysis of switching conditions and actual transfer time

Abstract: The operation of a static transfer switch is analyzed in this paper. Control system requirements for performing fast transfer between two power supplies without affecting the operation of the healthy source are explained. Maximum detection times and system conditions for fast transfer are analytically evaluated.

Turbine power unit for hybrid electric vehicle applications

Abstract: A power generation system for a hybrid electric vehicle is disclosed. The system includes a fuel source, a turbogenerator coupled to the fuel source, and a power controller. The power controller is electrically coupled to the turbogenerator, and includes first and second power converters. The first power converter converts AC power from the turbogenerator to DC power on a DC bus, and the second power converter converts the DC power on the DC bus to an operating DC power on output lines. The power controller regulates the fuel to the turbogenerator, independent of DC voltage on the DC bus. The system further includes an electric motor, a drive control unit coupled between the output lines and the electric motor, and a traction battery. The traction battery is coupled across the output lines, and provides an additional source of current, upon demand, to the electric motor.

Selecting ANN structures to find transmission faults

Abstract: Programming models based on artificial neural networks (ANN) have seen increased usage. ANNs are used in various fields (industry, medicine, finance, or new technology, among others). There is a wide range of possible power system applications of neural networks in operation and control processes, including stability assessment, security monitoring, load forecasting, state estimation, load flow analysis, contingency analysis, emergency control actions, HVDC system design, etc. This article features an automatic system that selects the most adequate ANN structure to solve any type of problem. The ANN Automatic Selection System (SARENEUR) was implemented in a specific case in order to obtain a neural network structure that shows better results in fault location within a two-terminal transmission line. The fault location is obtained according to the values of steady-state voltages and currents measured at one end.

Power mode based macro-models for power estimation of electronic circuits

Abstract: A method of creating models for power estimation of a circuit comprising generating an input space for the circuit. The input space is separated into multiple power modes corresponding to regions that display similar power behavior. Separate power models are generated for each of said multiple power modes. A power mode identification function is created that selects an appropriate power model from the separate power models based on the present and past values of the circuit inputs.

Computational Methods for Large Sparse Power Systems Analysis: An Object Oriented Approach

Abstract: Preface. Acknowledgments. 1. Introduction. 2. Object Orientation for Modeling Computations. 3. Data Structure for Sparse Matrix Computation. 4. Sparse Symmetric Linear System Solver. 5. Sparse QR Decomposition. 6. Optimization Methods. 7. Sparse LP and QP Solvers. 8. Load Flow Analysis. 9. Short Circuit Analysis. 10. Power System State Estimation. 11. Optimal Power Flow. 12. Power System Dynamics. Appendices. References. Index.

Optimal power flow control by converter based FACTS controllers

Abstract: In this paper, general mathematical models for power converter-based FACTS controllers such as STATCOM, SSSC and UPFC suitable for optimal power flow study are established. There are several solution methods for OPF available, which include interior point methods. In this paper, the optimal power flow problem with these converter based FACTS controllers is solved by the newly developed nonlinear interior point methods, since they have been the most successful OPF methods.

Impact of voltage sags in practical power system networks

Abstract: Voltage sags are momentary dips in voltage that may cause misoperations to the customer's sensitive loads of the power utility and are recognised as the most important power quality problems. The scope of the work presented in this paper includes: (i) critical awareness on the importance of characterization and impact of voltage sags, (ii) identification of a suitable algorithm for voltage sag analysis, and (iii) demonstration of the chosen methodology on a practical power system case study. The ability to estimate voltage sag characteristics offers an opportunity to evaluate alternate configurations. The overall methodology proposed utilizes the standard software packages of load flow analysis, short circuit studies and interface modules developed specifically for this problem. Methodology for sag analysis includes the characteristics of sag, like magnitude, duration, phase angle jump, sag frequency, some of the important factors affecting sag magnitude, and area of vulnerability for radial distribution systems.

Multiple power sources control system

Abstract: A multiple power sources control system has several power input sides can switch a power source to other power sources of power input sides as original power source of one of power input sides has an abnormal phenomenon (such as no power supply, too low or high voltage and abnormal frequency, etc.) such that loads can keep obtaining supplied power. In addition, power of loads has better protection because of multiple input power supply.

A Case-Based Windows Graphic Package for the Education and Training of Power System Restoration

Abstract: This paper presents a case-based Windows graphic package developed by the authors for the education and training ofpower system restoration. In order to overcome the inherent complexities associated with a restoration switching sequence, a case-based reasoning (CBR) algorithm has been developed. An object-oriented Windows-based graphical user interface (GUI) has been developed to communicate with the expert system and to visualize outputs. Simulation results on a part of the Saskatchewan Power (SaskPower) network have been presented in this paper. The restoration practices of the SaskPower network have been collected and stored in a knowledge database called case library. The power flow and the implementation risk analysis tools have been incorporated into the expert system. A risk analysis tool has been used to determine the implementation risk due to the imperfect switching actions. Using the GUI, a user can simulate a blackout event on the system under study. The expert system proposes a restoration proposal after reasoning with the past solutions available in the case library. Using the power flow analysis tool, the user can check the system scenarios after the restoration proposal is implemented.

Location of FACTS devices for enhancing power systems' security

Abstract: A stressed power system, either due to increased loading or due to severe contingencies, often lead to situations where the system no longer remains in the secure operating region. Under these situations, it is a primary objective of the operator to apply control action to bring the power system into a secure region. Any delay or unavailability of suitable control, and the system may become unstable. FACTS devices can play a very important role in power system security enhancement. Due to high capital investment, it is necessary to locate these devices optimally in the power system. In this paper, a suitable approach has been suggested based on the sensitivity analysis on FACTS device control parameters with respect to reduction in a real power flow performance index to enhance the security of the power system. The proposed approach has been illustrated on a sample system.

Reducing power bus impedance at resonance with lossy components

Abstract: Power bus structures in printed circuit boards with solid power and ground planes exhibit resonances. When the power bus is resonant, the power bus impedance can increase dramatically. This paper explores the effect of component equivalent series resistance (ESR) on power bus resonances. General guidelines for selecting an optimum ESR are provided and are supported by laboratory measurements and numerical simulations.

Power wheeling pricing using power tracing and MVA-KM method

Abstract: This paper introduces a new wheeling pricing technique called the MVA-KM method, which applies AC power flow and considers apparent power. A technique of buses sorting with ordering is incorporated with the proportional sharing principle and the upstream looking algorithm to trace the flow of electricity. An application example is illustrated. Computational results obtained by applying the proposed MVA-KM method are compared with that applying the MW-MILE method.

Active filter for power distribution system with selectable harmonic elimination

Abstract: A power distribution system includes an ac power source; a power bus connected to the ac power source; a capacitor bank shunt-connected to the power bus; and an active filter shunt-connected to the power bus. The active filter includes current sensors, an inverter and an inverter control. Each current sensor senses current flowing through a corresponding capacitor of the capacitor bank. The inverter control, in response to the current sensors, controls the inverter to inject harmonic currents into the power bus.

Uniqueness of static voltage stability analysis in power systems

Abstract: Diverse theories have been established in voltage stability analysis since various aspects have been observed during voltage collapse phenomena. Through rigorous mathematical investigation, this paper shows that all the major methods used in static voltage stability analysis, i.e. Jacobian method, voltage sensitivity method, real and reactive power loss sensitivity method and energy function method-provide an identical result to show the uniqueness of static voltage stability analysis in theory. The tests for sample systems have shown that an identical result can be obtained from the various analysis methods.

Transaction based power flow analysis for transmission utilization allocation

Abstract: This paper proposes a framework of transaction based power flow analysis (TBPF) for transmission utilization allocation. The TBPF utilizes distributed purchase-sale pairs to replace the role of a single slack bus on energy imbalance during power flow calculation iterations. To compare with conventional power flow analysis, accurate allocation of use-of-transmission is part of a TBPF solution. In particular, the TBPF is able to identify interaction components among transactions as well as the effect of reactive power on transmission losses and active power flows. Two allocation rules for cross terms are proposed to hedge firm or existing transactions against market risk. The standard WSCC 9 bus system is used to demonstrate the performance of the TBPF.

Implementation of nonuniform reliability in a deregulated power market

Abstract: Power system deregulation has introduced some fundamental problems regarding system security and customer reliability. This paper presents some reliability models for different market players in an arbitrary power market. A generation system is represented by an equivalent multi-state generation provider and a transmission system is represented by an equivalent multistate transmission provider. The parameters of the equivalent service providers are determined using reliability network equivalent techniques. The determination and implementation of nonuniform reliability are illustrated. A test system is used to illustrate the application of these techniques.

Unified power quality conditioner based on current source converter topology

Abstract: Nonlinear devices, such as power electronics converters, inject harmonic currents in the AC system and increase overall reactive power demanded by the equivalent load. Also, the number of sensitive loads that require ideal sinusoidal supply voltages for their proper operation has increased. In order to keep power quality under limits proposed by standards, it is necessary to include some sort of compensation. Different types of power quality compensators of higher or lower complexity have been reported. The aim of this paper is to present a unified power quality conditioner (UPQC) that consists of two three-phase current-source converters connected on the same inductive DC link. Such system has faster phase voltage control loop than its voltage-source converter based counterpart, as well as the inherent short circuit protection capability. Also, in this case passive filter connection between UPQC and the load is not needed, which minimizes the cost of the system.

Damping power system oscillations by unidirectional control of alternative power generation plants

Abstract: The paper shows the potential that alternative power generation plants have to damp oscillations in large electrical power systems. Electrochemical fuel cell, gas turbine, wind turbine, solar, photovoltaic, etc. power plants can provide local damping when they inject power in proportion to the frequency deviation from the standard reference. The damping is introduced through the power electronic converters that most alternative power plants use to interface with the power system. Another important contribution of the paper is the use of a unidirectional damping strategy with only absorption (or injection) of power. As a feasibility study, the goal of the paper is to evaluate the necessary size (as a fraction of the overall power) that the alternative power generation plants (APGP) must have to damp out system oscillations in a few seconds. Examples on power systems of two, six and thirty-nine nodes are presented for illustration.

A new method for handling PV nodes in backward/forward power flow for radial and weakly meshed networks

Abstract: Besides the good convergence characteristics and robustness, an effective handling of PV nodes is a desirable feature of any power flow method. This paper proposes a new approach for handling PV nodes in the power flow methods for radial and weakly meshed transmission and distribution networks. It concerns the class of power flow methods where backward and forward procedures are the main part. The new approach has been developed without additional assumptions. It automatically determines whether the control generator at PV node should inject current at 90 degrees leading the corresponding node voltage or at 90 degrees lagging the corresponding node voltage. It does not introduce any additional active power at PV nodes and exactly keeps the voltage magnitudes on their scheduled values (if reactive power limits are not violated). In principle, the proposed approach is simple and can be implemented in the existing methods without any difficulties.