scispace - formally typeset
Search or ask a question

Showing papers on "Power-flow study published in 2002"


Journal ArticleDOI
TL;DR: The p-q-r theory as discussed by the authors provides two degrees of freedom to control the system currents by only compensating the instantaneous imaginary power without using any energy storage element, and the definition of powers maintains power conservation, and agrees well with the general understanding of power.
Abstract: This paper proposes a novel power compensation algorithm in three-phase four-wire systems by using p-q-r theory. The p-q-r theory is compared with two previous instantaneous power theories, p-q theory and cross vector theory. The p-q-r theory provides two-degrees of freedom to control the system currents by only compensating the instantaneous imaginary power without using any energy storage element. The definition of powers maintains power conservation, and agrees well with the general understanding of power. Simulation results show the superiority of p-q-r theory both in definition and compensation.

251 citations


Journal ArticleDOI
TL;DR: In this paper, an adaptive distributed power flow solution method based on the compensation-based method is proposed for simulation of slow dynamics in a distributed system model with three-phase nonlinear loads, lines, capacitors and transformers.
Abstract: Recently, there has been great interest in the integration of dispersed generation units at the distribution level. This requires new analysis tools for understanding system performance. This paper presents an adaptive distributed power flow solution method based on the compensation-based method. The comprehensive distributed system model includes three-phase nonlinear loads, lines, capacitors, transformers, and dispersed generation units. The numerical properties of the compensation-based power flow method are compared and analyzed under different situations, such as load unbalance, sudden increase of one-phase loads, degree of meshed loops, number of generator nodes and so on. Based on these analyses, an adaptive compensation-based power flow method is proposed that is fast and reliable while maintaining necessary accuracy. It is illustrated that this adaptive method is especially appropriate for simulation of slow dynamics.

248 citations


Book
01 Jan 2002

248 citations


Journal ArticleDOI
Jen-Hao Teng1
TL;DR: A novel approach to solve the three-phase power flow problem for large-scale distribution systems is introduced, based on the optimal ordering scheme and triangular factorization of Y -bus matrix, which not only takes advantage of the sparsity of system equations but also is insensitive to network topology.

118 citations


Journal ArticleDOI
TL;DR: A power system simulation environment in MATLAB/Simulink is presented and the developed Power Analysis Toolbox (PAT) is a very flexible and modular tool for load flow, transient and small signal analysis of electric power systems.
Abstract: A power system simulation environment in MATLAB/Simulink is presented in this paper. The developed power analysis toolbox (PAT) is a very flexible and modular tool for load flow, transient, and small-signal analysis of electric power systems. Standard power system component models and a wide range of flexible AC transmission systems (FACTS) devices are included. Its data structure and block library have been tested to confirm its applicability to small-to-medium-sized power systems. Its advantages over an existing commercial package are given.

98 citations


Patent
17 Jun 2002
TL;DR: The modular power supply of the present invention provides a new device and method for powering multiple portable and/or small devices each requiring an AC or DC current source at one of various lowvoltage levels as mentioned in this paper.
Abstract: The modular power supply of the present invention provides a new device and method for powering multiple portable and/or small devices each requiring an AC or DC current source at one of various low-voltage levels. The invention comprises a main power base that is capable of converting AC power levels in common use internationally into a main low-level DC bus, which may, for example, be 24VDC. The AC input source and the derived DC voltage are then supplied via separate buses to smaller power “blocks” of two distinct designs, one for transforming the AC bus voltage to a low-voltage AC output, and one for converting the DC bus voltage to a low-voltage DC output. The DC blocks are of a common design, but are differentiated in that their respective output voltages are set by a “programming” element. The AC blocks are of a second common design, but are differentiated in that their respective output voltages are set by a “programming” transformer. All of these power “blocks” are of such a physical design that any DC block can only make contact with the DC bus and any AC block can only make contact with the AC bus. All of the blocks share a common output connector type and a common shape. In this way, a certain number of blocks, set by the size and output power of the power base unit, may be chosen from the group of all AC and DC blocks. Such blocks can be interchanged in placement on the power base unit in various permutations so as to meet the AC or DC input requirements of the various equipment that is to be powered by the invention.

93 citations


Patent
20 Dec 2002
TL;DR: In this article, a novel system and methodology of electrical power regulation, conditioning and distribution on an aircraft is described, which consists of an alternator adapted to directly connect to an engine on the aircraft and generate variable frequency AC power, a variable-frequency AC bus coupled directly to the alternator, and at least one variable-fraction AC load at low performance coupled to the variable-level AC bus.
Abstract: A novel system and methodology of electrical power regulation, conditioning and distribution on an aircraft is disclosed. The system comprises an alternator adapted to directly connect to an engine on the aircraft and generate variable frequency AC power, a variable frequency AC bus coupled directly to the alternator, and at least one variable frequency AC load at low performance, coupled to the variable frequency AC bus. At least one bi-directional power converter may be coupled directly to the variable frequency AC bus and adapted to convert the variable frequency AC raw power to a fully regulated adjustable-frequency and adjustable-voltage power to control AC motors and other high performance variable frequency AC loads. A bi-directional power converter is coupled directly to the variable frequency AC bus and adapted to convert the variable frequency AC power generated by the alternator into constant frequency AC power. At least one constant frequency AC load is coupled to a constant frequency AC bus which is in turn coupled between the constant frequency AC load and the bi-directional power converter. A first bi-directional power bus controller is coupled between the bi-directional power converter and the constant frequency AC bus. The system further comprises an AC/DC bi-directional power converter coupled to a DC bus and at least one DC load coupled thereto. A second bi-directional power bus controller is coupled between the AC/DC power converter and the DC bus. The first and second bi-directional controllers provide for the selective and automatic reconfiguration of the flow of power through the system. A novel high-level subsystem interconnection architecture is also disclosed.

91 citations


Patent
23 Jul 2002
TL;DR: In this article, a control system for a power converter designed to convert DC power from a source such as a battery, flywheel or fuel cell into AC power is described, where an impedance current regulator is used to provide an impedance signal to a summing unit where it may be combined with real and reactive current command signals provided from respective sources.
Abstract: A control system (20) for a power converter (22) designed to convert DC power from a source (30) such as a battery, flywheel or fuel cell into AC power. The control system includes an impedance current regulator (106) for providing an impedance current signal to a summing unit (110) where it may be combined with real and reactive current command signals provided from respective sources (62, 64). The resultant current signal provided by the summing unit is provided to a voltage correction unit (112) that uses the resultant current signal in developing a correction voltage signal provided to the power converter. The correction voltage signal contains information used by the power converter in adjusting the real and reactive currents in its output AC power based on the ability of the AC power network to accept changes in current. Multiple power converters having the control system of the present invention may be connected in parallel to a single AC load or multiple AC loads, without the need for a separate control system interconnecting the power converters. The control system may be advantageously incorporated into a distributed generation network and in uninterruptible power systems, whether or not such systems are included in a distributed generation network.

89 citations


Dissertation
01 Jan 2002
TL;DR: In this article, the authors proposed a voltage droop control scheme for DC distributed power systems, which does not require any high-speed communication between sources and loads, and is considered the most suitable for DC distribution power systems.
Abstract: Renewable energy systems are likely to become wide spread in the future due to environmental demands. As a consequence of the dispersed nature of renewable energy systems, this implies that there will be a distributed generation of electric power. Since most of the distributed electrical energy sources do not provide their electric power at line frequency and voltage, a DC bus is a useful common connection for several such sources. Due to the differences in output voltage among the sources, depending on both the type of source and their actual operating point, the sources are connected to the DC power system via power electronic converters. The intention behind the presented work is not to replace the existing AC power system, but to include local DC power systems. The AC and DC power systems are connected at some points in the network. The renewable energy sources are weak compared to the present hydro power and nuclear power plants, resulting in a need of power conditioning before the renewable energy is fed to the transmission lines. The benefit of such an approach is that power conditioning is applied on a central level, i.e. at the interface between the AC and DC power systems. Present DC transmission systems are discussed and investigated in simulations. Then, different methods for load sharing and voltage control are discussed. Especially, the voltage droop control scheme is examined thoroughly. Since the droop control method does not require any high-speed communication between sources and loads, this is considered the most suitable for DC distributed power systems. The voltage feed back design of the controller also results in a specification of the DC bus capacitors (equivalents to DC link capacitors of single converters) needed for filtering. If the converters in the DC distribution system are equipped with capacitors selected from this design criterion and if the DC bus impedance is neglected, the source converters share the total load equally in per unit. The same DC distribution bus configuration is studied in a wind power application. Especially the dynamic properties of load-source interactions are highlighted. They are interesting since the sources are considered weak for a distributed power system. This is illustrated with simulations where the power is fed from wind turbines only and constant power loads are controlled at the same time as the DC bus voltage level. Personal safety and prevention of property damage are important factors of conventional AC power systems. A grounding scheme for the DC distribution system together with algorithms for detection of ground faults, are presented. The proposed method detects ground faults on both the AC and DC sides and is extended to cover short circuit faults with a minor work effort. Experimental verifications follow the theoretical investigations introduced above. First, dynamic properties are studied and the behavior predicted from theoretical analysis and simulations is verified. Then, load sharing is investigated. Also in this investigation, the experimental results agree with the simulated. (Less)

76 citations


Journal ArticleDOI
TL;DR: In this paper, the application of interval arithmetic technique for balanced radial distribution system power flow analysis is reported. But uncertainties only in the input load parameters are considered, and the results are compared with the results obtained from repeated load-flow simulations.

75 citations


Proceedings ArticleDOI
25 Jul 2002
TL;DR: In this paper, a methodology based on a parametric study is proposed to investigate distributed generation impacts when interconnected to distribution networks and validated for a particular case of voltage profile (LV/MV).
Abstract: Utility power systems are faced to an increasing number of small size producers requiring interconnection particularly to the low voltage (LV) network. Since most distribution systems are not designed to "receive" large scale power injections, these small generation units may impact these networks specifically in terms of quality of the energy delivered, reliability and safety of the whole distribution system from LV to medium voltage (MV) levels. In this paper, a methodology, based on a parametric study, is proposed to investigate distributed generation (DG) impacts when interconnected to distribution networks. The proposed methodology has been validated for a particular case of voltage profile (LV/MV). The test system used for this study is a real urban network containing 11 feeders with 2 transformers of 36 MVA.

Journal ArticleDOI
TL;DR: In this paper, an approximate model for power flow studies that takes into consideration modeling of lossless UPFC-embedded transmission lines including the effect of line charging susceptance is presented.
Abstract: The unified power flow controller (UPFC) integrates properties of both shunt and series compensations and can effectively alter power system parameters in a way that increases power transfer capability and stabilizes the system. This paper presents an approximate model for power flow studies that takes into consideration modeling of lossless UPFC-embedded transmission lines including the effect of line charging susceptance. The approximate model is then simplified to a dc load flow model that takes into account the modeling of the UPFC. The equations derived in this paper are applied to an optimal power flow of a small test system, where the results obtained by approximate load flow method are compared to those of dc load flow method. The results presented in the paper show valuable impacts of putting UPFC in service on out-of-merit costs and locational marginal prices (LMPs) in a restructured power system environment. The results show that the dc load flow relations can be modified to reflect the effects of the UPFC. In addition, results show that UPFC may reduce generation out-of-merit costs and let LMPs regain uniformity.

Patent
21 Nov 2002
TL;DR: In this paper, an isolated DC bus architecture was proposed to enable bi-directional power flow among interconnected elements. But the architecture is not suitable for the use of a turbogenerator to provide power to the primary energy source.
Abstract: A continuous power supply may include a turbogenerator to provide power to supply the load and or an energy storage element and possibly also to the primary energy source. Utilizing an isolated DC bus architecture permits bi-directional power flow among interconnected elements.

Proceedings ArticleDOI
07 Aug 2002
TL;DR: In this article, a railway static power conditioner (RPC) is proposed to balance the effective power of different phases and compensate reactive power and harmonics in high-speed AC electric railways.
Abstract: High-speed AC electric railways, such as Shinkansen, require large single-phase AC electric power. So, if the short circuit capacity of the power system is not large enough, therefore, railway operation causes large voltage unbalance at the three-phase side. In this paper, a railway static power conditioner (RPC), a new system for reducing voltage unbalance and fluctuation, is described. To reduce voltage unbalance and fluctuation, the RPC balances effective power of different phase and compensates reactive power and harmonics. It enables operation of high-speed AC electrified railways even if the short circuit capacity of the power system is rather small.

Patent
04 Jun 2002
TL;DR: In this article, the phase angle of the power drawn and a combination of capacitors (32) to connect to the power line were calculated to compensate for a measured level of reactive power.
Abstract: An automatic power factor correction system (1), for an electrical power installation (3) drawing varying levels of reactive power, measures an electrical parameter of the power drawn by a load (5) of the power installation (3) which is capable of indicating a level of reactive power drawn by the load (5) and couples a combination of capacitors (32) to the power line (4) to compensate for the level of reactive power indicated by the electrical parameter measured. In particular, the system (1) measures the phase angle of the power drawn and calculates a combination of capacitors (32) to connect to the power line (4) to compensate for a measured level of reactive powre.

Patent
10 Jan 2002
TL;DR: In this article, a turbogenerator with a motor/generator and a turbine coupled to a common shaft is coupled with a DC bus, and a power controller regulates a speed of the turbine independent of the DC voltage on the DC bus.
Abstract: A power generation system includes a turbogenerator having a motor/generator and a turbine coupled to a common shaft, and generates AC power. A first power converter is coupled to the turbogenerator and a DC bus and converts the AC power to DC power on the DC bus. A second power converter is coupled to the DC bus and is couple-able to a load. The second power converter converts the DC power on the DC bus to an output power for coupling to the load. Also coupled to the DC bus are a battery and a capacitor to stabilize a DC voltage on the DC bus during load changes. The power generation system further includes a power controller coupled to the turbogenerator and the first and second power converters. The power controller regulates a speed of the turbine, independent of the DC voltage on the DC bus.

Patent
10 Jan 2002
TL;DR: In this article, a power generation system includes a turbogenerator having a motor/generator and a turbine coupled to a common shaft, and generates AC power, a first power converter is coupled to the turbine and a DC bus and converts the AC power to DC power on the DC bus, and the second power converter converts the DC power to an output power for coupling to the load.
Abstract: A power generation system includes a turbogenerator having a motor/generator and a turbine coupled to a common shaft, and generates AC power A first power converter is coupled to the turbogenerator and a DC bus and converts the AC power to DC power on the DC bus A second power converter is coupled to the DC bus and is couple-able to a load The second power converter converts the DC power on the DC bus to an output power for coupling to the load Also coupled to the DC bus are a battery and a capacitor to stabilize a DC voltage on the DC bus during load changes The power generation system further includes a power controller coupled to the turbogenerator and the first and second power converters The power controller regulates a speed of the turbine, independent of the DC voltage on the DC bus

Journal ArticleDOI
10 Dec 2002
TL;DR: An approach to paralleling optimal power flow is described that is applicable to very large interconnected power systems and is suitable for distributed implementation and a useful guide to the choice of control parameters that are highly problem dependent and sensitive to problem data.
Abstract: An approach to paralleling optimal power flow is described that is applicable to very large interconnected power systems and is suitable for distributed implementation. The proposed scheme is based on an augmented Lagrangian approach using the 'auxiliary problem principle'. The objective is to find a set of control parameters with which the auxiliary problem principle can be best implemented in solving distributed optimal power flow problems. The paper is a useful guide to the choice of control parameters that are highly problem dependent and sensitive to problem data. Several IEEE Reliability Test Systems and the Korea Electric Power System demonstrate alternative parameter sets that are the key elements in achieving fast convergence.

Journal ArticleDOI
TL;DR: In this article, the authors presented a methodology based on AC power transfer distribution factors to allocate the MW loading on transmission lines and group of lines is the basis of NERC's "flow-based" transmission allocation system.
Abstract: The ability to allocate the MW loading on transmission lines and group of lines is the basis of NERC's "flow-based" transmission allocation system. In such a system, MW flows must be allocated to each line or group of lines in proportion to MWs being transmitted by each transaction. This letter presents a methodology based on AC power transfer distribution factors to allocate the MW loading on transmission lines. The AC power transfer distribution factors have been derived using sensitivity properties of Newton Raphson load flow Jacobian at a base case load flow result. A 75-bus Indian power system network has been used to demonstrate the effectiveness of the proposed method.

Patent
01 Jul 2002
TL;DR: In this paper, a power authority manages power usage levels in computer systems by monitoring power consumption levels and providing power consumption information to the various systems, such as power tables and power consumption graphs.
Abstract: According to the present invention, methods and apparatus are provided for static and dynamic power management of computer systems. A power authority manages power usage levels in computer systems by monitoring power consumption levels and providing power consumption information to the various systems. In one example, the power authority updates power tables to vary aggregate power consumption levels.

Journal ArticleDOI
07 Aug 2002
TL;DR: In this paper, an alternative for electronically controlled capacitive compensation of a transmission line is presented, which incorporates an AC-AC power converter utilising pulse width modulation and provides accurate power flow control through the transmission line.
Abstract: In recent years, several power electronics based technologies, such as the thyristor controlled series capacitor and the unified power flow controller, have been introduced to provide active control of power flow through transmission lines. They have been prompted by the need to utilise existing lines up to their thermal limits to feed power to an increasing load demand, while maintaining adequate stability margins. In this paper, an alternative for electronically controlled capacitive compensation of a transmission line is presented. The proposed compensator incorporates an AC-AC power converter utilising pulse width modulation and provides accurate power flow control through the transmission line. Operating principles of the compensator are presented along with EMTP simulations demonstrating operation of the compensator.

Journal ArticleDOI
TL;DR: Bulk-power systems are fundamentally different from other Permitting and large infrastructure systems, such as air-traffic control centers, natural gas least some re pipelines, and long-distance telephone networks as mentioned in this paper.
Abstract: Bulk-power systems are fundamentally different from other Permitting and large infrastructure systems, such as air-traffic control centers, natural-gas least some re pipelines, and long-distance telephone networks. Electric systems to face til have two unique characteristics: . . Need for continuous and near electricity pl instantaneous balancing of geneconomic, ei eration and load, consistent with transmission-network conand reliabi straints Because the transmission network is largely passive, controlling flows on individual lines is limited primarily to adjusting generation output and to opening and closing switches to add or remove transmission lines from service. Because of these two characteristics, bulk-power system operators rely primarily on changes in generation output (MW movements up or down) to keep the system in balance and comply with transmission limits. In principle, changes in electricity consumption could serve as well as generator movements in meeting these reliability requirements, but the use of customer loads for reliability purposes is the exception rather than the rule. The traditional, vertically integrated utility managed short-term reliability by dispatching its generating units as well

Proceedings ArticleDOI
07 Aug 2002
TL;DR: Linear analysis techniques are analysis tools that provide valuable engineering insights into the dynamic characteristics of a power system that are often not easily obtainable by other means of analysis as mentioned in this paper, and they can be used to acquire a more complete understanding of power system dynamic phenomena.
Abstract: Linear analysis techniques are analysis tools that provide valuable engineering insights into the dynamic characteristics of a power system that are often not easily obtainable by other means of analysis. Their importance is underlined by frequent new developments and applications. One of the objectives of this panel session is to highlight the practical value of linear analysis methods as a means to acquiring a more complete understanding of power system dynamic phenomena.

Journal ArticleDOI
TL;DR: In this paper, two lemmas have been proved first which show the reasons for circulating power and then graph theory is applied to detect the existence of circulating power, and an optimal power flow (OPF) approach is suggested to eliminate circulating power.

Proceedings ArticleDOI
13 Oct 2002
TL;DR: In this paper, the authors present an overview on the recent trend of small signal stability analysis of power systems, focusing mainly on the experience, applications and achievements, and the challenges facing the power industry in this area.
Abstract: This paper presents an overview on the recent trend of small-signal stability analysis of power systems, focusing mainly on the experience, applications and achievements, and the challenges facing the power industry in this area. Issues discussed include experiences and lessons learnt from real-life incidents, modelling and study requirements, analysis tools available and their performances, and the possible future developments. The paper shows the importance of addressing small signal stability of power systems in all stages of planning and operation, as well as the viability of analysing and mitigating these problems with the advanced tools available to the industry today.

Journal ArticleDOI
R. Stoicescu1, K. Miu2, Chika O. Nwankpa2, D. Niebur2, Xiaoguang Yang2 
TL;DR: A three-phase steady state model of a power converter (ac/dc-dc/ac) composed of a diode rectifier, a loss-less dc link, and a pulse-width-modulated inverter is presented.
Abstract: This paper presents a power converter model intended for both balanced and unbalanced radial power flow studies. A three-phase steady state model of a power converter (ac/dc-dc/ac) composed of a diode rectifier, a loss-less dc link, and a pulse-width-modulated inverter is presented. Both the three-phase rectifier and the three-phase inverter are modeled as three equivalent Y-connected single-phase rectifiers and single-phase inverters, respectively. The model is implemented within a three-phase power flow solver with phase representation. Simulation results on a balanced and an unbalanced 15-bus system are presented.

Proceedings ArticleDOI
25 Jul 2002
TL;DR: In this article, an evaluation of the North American Electric Reliability Council's (NERC) new control performance standards, as they might be applied to the Western Japanese 60 Hz system, is presented.
Abstract: Summary form only given as follows. This paper presents an evaluation of the North American Electric Reliability Council's (NERC) new control performance standards, as they might be applied to the Western Japanese 60 Hz system. Dynamic simulation of the system frequency response, including the effects of primary and secondary frequency control, power plant response, and load fluctuation characteristic were performed using a load flow program during normal system operation. Parameter sensitivities have been studied for some of the pertinent control parameters influencing the generation control performance, including power plant and AGC response parameters, and amounts of generation under control for governor and AGC.

Proceedings ArticleDOI
25 Jul 2002
TL;DR: In this paper, the modeling of TCSC for power flow studies has been discussed and presented in detail, and the performance of the proposed algorithm has been tested for IEEE-30 bus systems.
Abstract: The thyristor controlled series capacitor (TCSC) is one of the most effective flexible AC transmission system (FACTS) devices. It offers smooth and flexible control of the line impedance with much faster response compared to the traditional control devices. While numerous studies concerning the utilization of these devices, have been carried out so far, most of the research has focused on issues such as transient stability improvement, sub-synchronous resonance (SSR) mitigation, damping of power swings, voltage collapse, etc. In his paper, the modeling of TCSC for power flow studies has been discussed and presented in detail. The Newton-Raphson AC power flow method was used to perform the above studies. The performance of the proposed algorithm has been tested for IEEE-30 bus systems. It has also been observed that the proposed algorithm can be applied to larger systems and do not suffer with computational difficulties.

Proceedings ArticleDOI
25 Jul 2002
TL;DR: A parallel Newton-GMRES (generalised minimal residual) power flow solution algorithm based on a message-passing distributed-memory multiprocessor architecture such as a cluster of workstations and it is shown that the parallel GMRES method is more scalable than the parallel direct method in a low latency network.
Abstract: This paper presents a parallel Newton-GMRES (generalised minimal residual) power flow solution algorithm based on a message-passing distributed-memory multiprocessor architecture such as a cluster of workstations. The results show that the new algorithm can achieve good performance for two large-scale power system cases on a small cluster of GNU/Linux single-processor workstations. The workstations are connected via 1.0 Gbit/s Ethernet. The comparison between iterative methods and direct methods for the parallel solution of large sparse linear systems is also presented. It is shown that the parallel GMRES method is more scalable than the parallel direct method in a low latency network. Based on the presented parallel iterative linear solver, it is possible to exploit any parallelism in the Newton power flow solution process. For a workstation cluster on 1.0 Gbit/s Ethernet, which has high latency, the speedup appears to saturate. Nevertheless, when a low latency network, such as Myrinet, is available, the power flow algorithm with an iterative linear solver is expected to be more scalable than that with a direct linear solver.

Proceedings ArticleDOI
25 Jul 2002
TL;DR: In this paper, the authors discuss the impact of HVDC on power system stability and propose a control mechanism to augment the system angle stability, which is the same as used in power flow studies.
Abstract: This paper discusses the impact of HVDC on Power System Stability and proposes a control mechanism to augment the system angle stability. At first, the authors discuss the HVDC model used in transient studies. Basically, it is the same as used in power flow studies, details of which have been given in Section II of the paper. The model considers the limits of HVDC lines, which consists of many control modes. A case has been studied where the HVDC tends to make the system unstable if the setting of the line is not changed during and after a fault. They then propose a control mechanism to strengthen the system stability. Two types of controllers, namely proportional control and proportional-integral control have been studied and compared. Also they have shown their effects on the system stability.