bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactions and co‐ordination of multiple‐function FACTS controllers
Authors: Wang H. F. 
Published: July 2007

AbstractThis paper presents two study cases of interaction analysis of multiple‐function FACTS (flexible AC transmission systems) controllers: ‐ the contradiction between the voltage and the damping control of a SVC (static VAr compensator); ‐ the interaction between the voltage control of the DC link capacitor and the damping control of a UPFC (unified power‐flow controller). In the paper, an algorithm is proposed for the co‐ordinated design of these two multiple‐function FACTS controllers. Examples are presented to confirm the analytical conclusions obtained and to demonstrate the effectiveness of the algorithm of the co‐ordination proposed.
High power factor ac/dc/ac converter with h‐bridge cascade five‐level pwm inverter
Authors: Lin B.‐R. 
Published: July 2007

AbstractThis paper presents an AC/DC/AC converter which consists of a three‐phase switch‐mode rectifier (SMR) and a three‐phase multilevel inverter with separate isolated DC power supplies. Based on a hysteresis current control scheme in the stationary reference frame, the three‐phase SMR is controlled to supply sinusoidal currents with high power factor and low current distortion. The separate DC bus voltages are provided by regulated switch‐mode DC/DC converters. The series connection of H‐bridge cells is adopted to provide multilevel phase voltage. The control scheme of the three‐phase multilevel inverter is based on a look‐up table with sine‐triangular pulse‐width‐modulation (PWM) method. The voltage unbalance problem between the separate isolated DC bus voltages is improved by using the proposed control scheme. The proposed control algorithm of the AC/DC/AC converter is verified by simulation and experimental results.
New control system for an ac‐excited synchronous machine to achieve a wide field weakening range and a high overload capability
Authors: Haag J. , Rees S. , Gutemann M. 
Published: July 2007

AbstractIn the conventional AC‐excited synchronous machine operated with mains excitation [1,2], the commutation conditions in the machine‐side thyristor converter do not allow the drive to be notably overloaded. In addition operation with field weakening and full four‐quadrant operation are not possible due to the principle. If on the other hand the AC‐excited synchronous machine is excited by a small insulated gate bipolar transistor inverter (IGBT), then the commutation conditions in the machine‐side thyristor converter can be improved with the control system presented here. Therefore a considerable overload capability and a field weakening range of 1:2 and more can be realized with the AC‐excited synchronous machine. Areas of application previously excluded are thus opened up to the AC‐excited synchronous machine.
Comparison of electromagnetic field for two different lightning pulse current models
Authors: Andreotti A. , De Martinis U. , Verolino L. 
Published: July 2007

AbstractIn this paper the electromagnetic field produced by a lightning current analytically described by the so called double exponential model is compared with the field produced by the same current (same peak, rise and decay time) analytically described by the model proposed by Heidler. The exponential model has been widely used in literature for its simplicity and its relatively good accuracy. The Heidler model is more complex, but removes the main problem shown by the double exponential: the non‐zero derivative at the beginning of the lightning pulse in contrast with the physical phenomenon. In the lightning electromagnetic pulse (LEMP) simulations both models are now used. In the paper we aim to make a comparison between the two. In particular we show that the two models are fairly equivalent in the frequency range up to 2 MHz, namely the range of interest of typical lightning phenomena. In addition, the double exponential model is shown to be conservative for higher frequencies.
An advanced methodology for steady‐state security assessment of power systems
Authors: Popovic D. P. , Dobrijevic D. M. , Mijuskovic N. A. , Vlaisavljevic D. J. 
Published: July 2007

AbstractThe basic objective of this paper is to present the relevant aspects of an advanced methodology for steady‐state security assessment of power systems. This methodology consists of the following relevant parts: procedure for forming the unified external network equivalents, with adaptive buffer system selection, procedure for fast contingency selection and simple method for the fast and sufficiently accurate assessment of dynamic variation of power system frequency during the time of its primary control. For the potentially critical contingency, the continuation of iterative procedure is performed. Full contingency analysis is based on specially developed method, which enables successive solution of the load‐flow problem for a set of characteristic post‐dynamic quasi‐stationary states. The characteristics of the developed methodology are tested on the example of the existing electric power interconnection in the Balkans.
An approach to the non‐active power concept in terms of the poynting‐park vector
Authors: Ferrero A. , Leva S. , Morando A. P. 
Published: July 2007

AbstractThis paper reconsiders the approach to the electric systems in terms of Maxwell equations, and reconsiders in particular the energy transfer involved in an electric system in terms of the flux of the Poynting vector. This approach is extended to the three‐phase systems, and the Park transformation is reconsidered by applying it to the Poynting vector. In this way a correct physical meaning can be assigned to the non‐active components of the Park instantaneous power by tracing them back to the components of the Poynting vector.
On techniques for the localisation of multiple distortion sources in three‐phase networks: Time domain verification
Authors: Rens A. P. J. , Swart P. H. 
Published: July 2007

AbstractFrequency domain network modelling techniques have shown that the localisation of steady‐state distortion sources by monitoring the direction of active power in the harmonic components can not be accomplished through continuous single‐point measurements in the presence of multiple distortion sources. Because frequency domain models of line commutated AC/DC converters could so easily be susceptible to error, the same analysis in the time domain will enhance the credibility of the findings. A time‐domain approach has therefore been adopted by generating the equivalent power system data through repeated ATP (alternative transients programme) simulations and interpreting the resulting trends by means of a Mathcad package. The results obtained confirm the previous findings.
Measurements for the characterization of quasi‐periodic waveforms
Authors: Peretto L. , Sasdelli R. 
Published: July 2007

AbstractQuasi‐periodic signals feature discrete‐spectrum waveforms with lines located at frequencies expressed by non‐rational numbers. In this paper, a new digital method for the spectral analysis of quasi‐periodic bi‐tone signals is proposed. The results of some simulations showing its good performance are reported and discussed.
Frequency coupling matrices for multi‐stage conversion system analysis
Authors: Carbone R. , Lo Schiavo A. , Marino P. , Testa A. 
Published: July 2007

AbstractA general approach for harmonic and interharmonic analysis of multi‐stage conversion systems is formalized. The approach is based on frequency coupling matrices (FCMs) relating voltage and current harmonics and interharmonics. Each component of the conversion system is classified as linear time—invariant or non‐linear time—invariant or non‐linear time variant and a systematic procedure to build up its FCM is presented. Then, according to the specific topology of the conversion system, single‐component FCMs are opportunely combined to deduce a whole‐system FCM. This matrix allows to estimate the absorbed current due to voltage interharmonics, to analyze the admittance of the conversion system and to investigate the current amplitude dependence on the supply voltage phase; such possibilities are shown with reference to a test system.
Simulation and digital implementation of a simple technique of active filter for elimination of switching ripples/distortion in the supply current
Authors: Singh B. N. , Chandra A. , Rastgoufard P. 
Published: July 2007

AbstractThis paper deals with a digital signal processor (DSP) based implementation of a three‐phase shunt active filter (AF) to compensate harmonics and reactive power of nonlinear loads. A three‐phase diode bridge rectifier with R‐L and R‐C loads is taken as the nonlinear load. It is observed that the AF systems suffer from the problems of switching ripples (in case of R‐L nonlinear load) and distortion (in case of R‐C nonlinear load). The switching ripples and distortion in the supply currents contribute considerably to its Total Harmonics Distortion (THD). This investigation proposes a new, cost free and simple approach for the elimination of switching ripples and distortion in the supply current. A pulse width modulation (PWM) current controlled voltage source inverter (CCVSI) is used as the AF. The AF system is tested with two types of PWM switching techniques, namely, carrier‐less (hysteresis) and carrier based techniques. Two types of current control techniques, namely, direct current control and indirect current control are designed to obtain PWM switching signals for the devices of the AF. The capability of the indirect current control technique towards the elimination of switching ripples and distortion is established. Simulated and experimental results for steady state and transient operating conditions of the AF for R‐L as well as R‐C nonlinear loads are given and discussed in detail.
Some remarks concerning the measurement of the ferromagnetic losses under non‐sinusoidal conditions
Authors: Ţugulea Andrei 
Published: July 2007

AbstractThe present standards concerning the measurement of the losses in ferromagnetic media, namely the IEC publications 404‐2 (1978), 404‐;3 (1982) and 404–10 (1988), refer only to the magnetic flux densities between 1 T and 1.85 T, if the magnetic sheets are grain oriented, and 1 T and 1.5 T if the magnetic sheets are nonoriented. The time variation of the magnetic fluxes must be almost sinusoidal at industrial frequencies of 50 Hz or 60 Hz and medium frequencies between 400 Hz and 10,000 Hz. In the above‐mentioned standards there are no references concerning the measurement of losses under non‐sinusoidal conditions. The paper deals with some theoretical aspects concerning the power‐flows under non‐sinusoidal time variation of the electromagnetic fields. The theoretical conclusions are applied to the study of the losses in ferromagnetic media. It is shown that new norms or standards are necessary. Some practical suggestions are given at the end.
A class of analytical functions to study the lightning effects associated with the current front
Authors: Heidler F. , Cvetić J. 
Published: July 2007

AbstractThe lightning currents are measured on tall structures and by artificially initiated lightning. Additionally they are deduced from the remote electric or magnetic field radiated during the so‐called return stroke phase, when the lightning current is flowing to earth. For this purpose return stroke models were developed giving the dependency between the field data and the current along the ionized return stroke channel. The most frequently employed models use the so‐called channel‐base currents, which are commonly expressed by analytical functions to simplify the calculation procedure. A review is given about a class of analytical functions being very convenient in such calculations. The special attention is given to the type of current function most frequently used in lightning research and standardization. With these functions the fine structure in the current front can be studied, which is of basic interest with respect to the lightning protection.
A novel non‐linear TCSC control scheme for a multi‐machine power system
Authors: Zheng S. L. , Lei X. , Li X. Y. , Povh D. , Retzmann D. 
Published: July 2007

AbstractIn this paper, a novel non‐linear thyristor controlled series compensation (TCSC) control scheme for damping power oscillations and improving transient stability of a multi‐machine power system is presented. Based on the analysis of TCSC power modulation in a two‐machine system, a non‐linear control law for the TCSC is established via local measurements. With the help of the feedback linearization technique, the non‐linear model of a multi‐machine power system is transferred to an equivalent linearization model. To this equivalent linear system a well‐developed optimal linear design methodology with integral‐of‐time‐multiplied‐absolute error criterion (ITAE) is adopted to achieve optimal control performance. The effectiveness and robustness of the non‐linear control scheme proposed are demonstrated with a three‐machine system equipped with a TCSC. In comparison with a conventional control scheme, significant improvements in dynamic performance are achieved by the proposed TCSC control strategy.
Reduction of operating frequency for power cables
Authors: Steinbrich K. 
Published: July 2007

AbstractThe article describes the effects of operating frequency reduction on the transmission behaviour of high power cables. Strongly reduced current losses, lowered induced voltages in the sheaths and lower charging currents offer new solutions for the transmission of energy by cables. The following facts can be obtained by reduction of the operating frequency: an increase of the current carrying capacity, an enlargement of the transmission distance, lower thermal stress of the cable and better efficiency of the power transmission. The above mentioned advantaes are typical for direct current (d.c.) transmission systems, but can now also be achieved for usual alternating current (a.c.) cables by reduction of the operating frequency. The positive effects of frequency reduction are represented for four different types of power cables.
Load‐prediction with neural and statistical components in power systems with instationary load patterns
Authors: Wilfert H.‐H. , Voigtländer K. 
Published: July 2007

AbstractA hybrid pattern algorithm is presented combining statistical and neural methods to forecast hourly load of an electrical power supplying system. Compared with ordinary neural techniques which require a large stationary data‐set for the parametrization of the huge number of net‐weights, the algorithm yields to a sufficient prediction even with a small reference data‐set and is especially suited for power utilities with instationary load patterns. In this sense the choice of appropriate model structures and parsimonious parametrization are considered in particular. The presented modular design yields to a high transparency of the entire prediction algorithm. Furthermore a clear assessable performance measure of the prediction accuracy of the four individual steps of the forecasting algorithm is presented.
Technical and economical analysis of 3‐LIMB and 4‐LIMB three phase transformers in YN/YN network
Authors: Elleuch M. , Poloujadoff M. 
Published: July 2007

AbstractThis paper deals with the behaviour of the three phase three limb transformer (with or without tertiary winding) as well as the four limb transformer under unbalanced steady states in a YN/yn network. Technical and economical comparative analysis has been established among the different configurations of the transformers. The opportunity of the replacement of the four limb transformer, currently used in the Tunisian distribution network, by a three limb transformer equipped by a tertiary winding has been discussed. During the analysis, the example of a 20 KVA transformer with a tertiary winding and a fourth limb (which could be removed) has been tested. A satisfactory concurrent is obtained between theoretical and experimental results.
System management of a wind energy converter to control a wind specific power fluctuation
Authors: Sourkounis C. , Kanakis A. , Lemogo‐Kana Ch. 
Published: July 2007

AbstractThe fluctuating production of electric energy converters caused by the dynamic changing wind velocity leads to a system perturbation which can be called flicker. Apart from this system perturbation the quality of the electric power is also reduced because of the tower shadow effect. The periodic appearance of this effect overlaps and intensifies the flicker. Within the scope of this contribution a system management will be introduced, which reduces the tower shadow effect and which damps the short‐term power fluctuation caused by the changing wind velocity. The mode of operation of this system management will be shown on a simulated test model (7.5 kW) of a real wind energy converter (Ventis 100/20). In this simulation, the model of the aerodynamic behaviour of the wind rotor and the mechanical subsystem reproduces the real stationary and dynamic behaviour. The control of power is realised by the system management based on a microcontroller and a three phase A.C. power controller.
A black box identification in frequency domain
Authors: Mercorelli P. , Terwiesch P. 
Published: July 2007

AbstractHarmonic oscillations as integer multiples of the fundamental frequency in a power system are caused by nonlinear physical effects such as switching or saturation. Modelling and detection of these harmonics are crucial for power system control and protection. The present paper proposes the use of wavelet networks with smooth local trigonometric functions as activation functions. A new algorithm is proposed, together with the use of the Cross Entropy function as a tool for evaluating the model quality. The algorithm consists of recursive dual iterations with biorthogonal smooth local sine and cosine wavelet packets in order to calculate the adjustable parameters related to the activation functions. The algorithm efficiently minimizes the Shannon Entropy function by adoptively choosing the best time‐frequency cells on the wavelet packet tree. During every loop the Cross Entropy function between estimated outputs and target outputs is checked. A procedure by using trigonometric wavelet packets is proposed as an effective tool for disturbance detection, power quality analysis and non‐linear harmonic circuit modelling. Simulations of a converter bridge for traction drives are included to illustrate the effectiveness of the algorithm and the choice of the activation function.
Numerical determination of characteristic temperatures in directly loaded power oil transformer
Authors: Radakovic Z. 
Published: July 2007

AbstractThe paper presents the application results of original non‐linear non‐stationary thermal model of the oil power transformers. The main advantage of the model is precise treatment of non‐linear convection heat transfer influence to the transient thermal process. It is convenient to calculate the model parameters from the short‐circuit heating experiment. The aim of this paper is to investigate the precision of such obtained parameters application to a transformer in normal operation. For that purpose, the precise calculation of power losses distribution is needed and is proposed in the paper. For experimental verification of the model accuracy the measuring method for continuous monitoring of mean winding temperature of directly loaded transformer is developed.
New passive filter design for neutral current cancellation in balanced 3‐phase 4‐wire non‐linear distribution systems
Authors: El‐Saadany E. F. , Salama M. M. A. , Chikhani A. Y. 
Published: July 2007

AbstractDifferent types of non‐linear loads are expected to proliferate into the distribution system, causing the harmonic distortion levels on these systems to increase. Third harmonic and all other triplen harmonic currents have little diversity among different loads and add in the neutral. The neutral current in a low voltage three‐phase four‐wire distribution system is expected to increase resulting in significant problems. The factors that affect the neutral current magnitude as well as the phase currents distortion are investigated. A new technique, namely, reactance one‐port compensator is presented in order to cancel the neutral current and improve the overall system distortion levels. The attenuation and diversity effects are considered during performing this study. The analysis uses the electromagnetic transient program (EMTP) to model the loads as well as the overall system. The proposed filter drastically improves the system performance and substantially reduces the neutral current.
An economic parallel processing technology for faster than real‐time transient stability simulation
Authors: Beaudin S. , Marceau R. J. , Bois G. , Savaria Y. , Kandil N. 
Published: July 2007

AbstractThe need to increase power flows is forcing electric power companies to consider the rapid determination of transfer and security limits in energy management centers. At the present time, transient stability transfer limits are generally calculated off‐line due to the limitations of numerical computers. This paper introduces an innovative approach for simulating transient stability based on the use of a new type of chip technology designed for real‐time image processing. Power system equations in matrix form are solved by means of rapid matrix operation techniques on the PULSE (parallel ultra large scale engine) technology, resulting in outstanding low cost performance. This paper confirms the efficiency of this approach on the 9 bus Western Systems Coordinating Council (WSCC) test power system. Simulation results based on a preliminary version of the PULSE technology clearly indicate that economic, faster than real‐time transient stability simulation is feasible for large networks.
Fast analytical short‐circuit current calculation of rectifier‐fed auxiliary subsystems
Authors: Kunz M. , Herold G. 
Published: July 2007

AbstractThe course of time of a three‐phase rectifier system which its alternating valve participation can be interpreted as a continuous sequence of alternating switching states. To allow a more convenient calculation, the substitutional circuit with the converter is transformed into state‐space coordinates. Hereby each operational mode of the rectifier can be represented by two linear independent space‐phasor component networks. In the state‐space, an analytical solution for this boundary value system can be carried out. After a retransformation back into the time domain, its time functions can be derived. In contrast to other calculation methods, no assumptions or simplifications have to be made like ideal smooth DC currents. Furthermore, all states of operation of the rectifier bridge can be easily calculated, which cover DC side idle‐running to DC short‐circuit.
MPP control of a photovoltaic energy system
Authors: Hua C. , Lin J. , Tzou H. 
Published: July 2007

AbstractPhotovoltaic (PV) power converters are used to convert the electrical energy from the PV modules to a stable and reliable power source. The object of this paper is to analyse and design a DC/DC converter with current regulation for PV energy systems. An on‐line tracking method with a discrete time control and a Pl compensator is used to track the maximum power points (MPPs) of the PV modules. With the temperature‐loop and insolation‐loop control, the proposed MPPT control features accurate MPPT and fast transient response. The large‐ and small‐signal model and transfer function for the system are developed by using the principle of energy conservation. The Tl320C25 digital signal processor (DSP) was used to implement the proposed on‐line MPPT control. Simulations and experimental results show excellent performance.