bluuebunny/crossref_metadata_2025_split huggingface dataset:
Harmonic distortion in three‐phase inverters controlled by synchronous sigma‐delta‐modulation
Authors: Mertens A. 
Published: July 2010

AbstractSeveral soft switching three‐phase inverters have been proposed in the literature, using a resonant AC or DC voltage link in order to reduce switching losses. This allows operation with higher switching frequencies. In these inverters, the switching instances have to be synchronized with the periodic zero crossings of the link voltage. Thus synchronous pulse modulation strategies like Sigma‐Delta‐Modulation have to be used for control. The benefit of high switching frequency has to be considered in the light of performance of the modulation scheme, which can be measured by determining the r.m.s. value of the distortion current. In this paper, this magnitude is calculated analytically for three‐phase inverters controlled by synchronous Sigma‐Delta Modulation. The derivation is based on the assumptions of constant link frequency and large ratio of link‐ to output frequency. The solutions allow to calculate the r.m.s. distortion current for any periodic shape of the link voltage including DC. Simulations show that the results hold for link‐ to output frequency ratios down to 100. The spectral performance of synchronous Sigma‐Delta‐Modulation is compared with conventional pulse width modulation.
Frequency domain analysis of brushless dc motor performance
Authors: Ackermann B. , Bolte E. , Howe D. , Jenkins M. K. , Zhu Z. Q. 
Published: July 2010

AbstractThe steady‐state performance of three‐phase brushless DC motors supplied from bipolar drive circuits is analysed using frequency domain techniques. The drive system model caters for arbitrary waveforms of the induced voltage, delta‐ and star‐connected windings, advanced and retarded commutation, the on‐time of each transistor within one cycle ranging from 120o to 180o (electrical degrees), transistor and diode voltage drops and an average switch resistance in the on‐state. Predictions from the analysis are compared with previously published results.
Some remarks to active and fictitious power in polyphase and single‐phase systems
Authors: Depenbrock M. 
Published: July 2010

AbstractA generally applicable method to analyze the relations connecting currents, voltages, instantaneous‐, active‐, non‐active‐ and apparent power quantities is described. By introducing a special m‐conductor equivalent scheme a unified treatment of non‐sinusoidal, unbalanced polyphase systems is possible and a simple definition of unsymmetrical loads can be derived. It is explained why it is necessary to distinguish between the decomposition of quantities into components or into portions. The method includes other ones well known and approved in the past as more special cases.
An evaluation of the instantaneous calculation of load current components
Authors: Marshall D. A. , Venter F. P. , van Wyk J. D. 
Published: July 2010

AbstractThe development of theoretical techniques for the instantaneous calculation of load current components is evaluated. The associated instantaneous calculation of load power components is also evaluated since it is used in the calculation of the currents. The generation of these different power components with respect to compensation are pointed out. Further implementation of the instantaneous power theory is discussed. A three‐phase vector approach to the instantaneous calculation of power components is also discussed. Experimental results obtained by using the instantaneous power theory are illustrated.
Current compensation in three‐phase power systems
Authors: Willems J. L. 
Published: July 2010

AbstractIn this paper the compensation of reactive and unbalanced currents in three‐phase power systems is discussed. The main result proved is that in sinusoidal steady state any current which corresponds to zero total active power can be compensated by means of a reactive element; the compensation of the reactive currents and the compensation of the unbalanced currents in three‐phase power systems are special cases of this result. The explicit expression of the compensating reactances is derived and the multiplicity of the solutions is discussed. The result is illustrated on some examples.
Power factor improvement of three‐phase unbalanced loads with non‐sinusoidal supply voltage
Authors: Czarnecki L. S. 
Published: July 2010

AbstractThree‐phase load asymmetry causes a useless current loading of the supply source and this loading increases even more if the supply voltage is non‐sinusoidal. This loading can be expressed quantitatively with the unbalanced current iuof RMS value ||iu||. A whole compensation of the unbalanced current iuwas proved to be possible with reactive balancing circuits, however, it may be very complex. This paper shows that a substantial minimization of the unbalanced current iumay be achieved with such a circuit, but of much lower complexity. The method suggested requires that the unbalanced admittances Anof the load for harmonic frequencies are known. A harmonic analysis that provides the complex RMS values of the phase voltages and currents harmonics in a cross‐section between the load and the source enables us to determine these admittances and design the balancing circuit. It was shown, moreover, that the reduction of the unbalanced current iucan be integrated with the reactive current irminimization.
A new method for reduction of current and voltage harmonic distortion in power systems
Authors: Mikolajuk K. , Tobola A. 
Published: July 2010

AbstractThe paper shows that it is possible to design such a switched 1 ‐port which ‐ excited by a sinusoidal voltage ‐draws desired current harmonics. The circuit switched twice within a period can generate odd current harmonics and the circuit switched once within a period generates even harmonics. This new kind of compensator has advantages of active filters such as good compensation characteristics. On the other hand it is easier to realize a large VA compensator based on the presented idea than to realize a high switching frequency static power compensator. Most established active and hybrid filters are based on a load current measurement. The compensator presented in the paper can be used to eliminate current distortion as well as voltage distortion. The two‐step optimization with the use of the harmonic voltage measurement allows to eliminate harmonic voltage. The results of numerical simulation and experimental results are presented.
Influence of the pulse‐width modulation control method on the performance of frequency inverter induction motor drives
Authors: Ch. Andresen E. , Haun A. 
Published: July 2010

AbstractThe methods of sinusoidal PWM voltage control, current hysteresis control, predictive current control and direct stator flux and torque control are briefly presented. The different operation principles are explained by block and structure diagrams. Their staiorflux and stator current trajectories are compared. The effect on the characteristic operational performance of induction squirrel cage motors is investigated. The harmonic losses of the stator and rotor winding and the torque oscillations are compared while considering the skin effect of the windings. Finally the torque response times are presented. The results are achieved by digital simulation and proved on a test stand with 22 kW induction motor and 30 kVA GTO frequency inverter.
Measures to raise brush life of modern DC machines
Authors: Binder A. 
Published: July 2010

AbstractThe maintenance periods of DC motors can be raised significantly if brush wear is reduced effectively. This is accomplished by improving commutation. The measures to reach this goal are: reducing the commutating inductance of the armature coils, minimizing dissymmetries of the magnetic circuit as well as the influence of the main flux on the compole flux, improving the mechanical performance of the commutators, using brushes which are insensitive to high brush current densities and avoiding harmful mechanical vibrations. By long‐time tests of several converter‐fed DC machines it is proved that brush life of typically 15000 h (at 1500 rpm) and rated current (up to 100 kW output power) may be realized nowadays as a standard.
Stabilizers enhancing the frequency regulation action of HVDC links supplying weak AC systems
Authors: Maris T. I. , Lygdis A. D. , Vovos N. A. , Giannakopoulos G. B. 
Published: July 2010

AbstractPower System Stabilizers (PSS) superimposed to the basic control system of an HVDC link supplying a weak AC system, in order to enhance its frequency regulation action, are proposed. To decrease the AC voltage sensitivity at the inverter side, the basic control system of the HVDC link is proposed to operate with the rectifier under Minimum Ignition Angle (MIA) control and the inverter under Constant Current (CC) control. Inputs to the PSS are the frequency and the AC voltage deviations at the inverter side and their constant parameters are calculated using modal control technique. Detailed simulation results for a practical integrated AC/DC system are presented to evaluate the performance of the proposed control scheme.
The modern space‐phasor theory, Part II: Comparison with the generalized machine theory and the space‐vector theory
Authors: Serrano‐Iribarnegaray L. 
Published: July 2010

AbstractIt has been shown in the first part of this article that any transient state of a converted‐fed symmetrical machine can be represented in the Space‐Phasor Theory (SPhTh) by a very simple phasorial diagram. This second part discusses in detail why this is not possible in the Generalized Machine Theory (GMTh). It makes clear that the SPhTh and the GMTh are two complementary but different methods, based on the two existing “natural” approaches for analyzing electrical machines, according to the way in which the flux is split. Thereafter, relying on the comparison of both theories, other practical advantages which clearly support choosing the SPhTh are explained. The paper also includes a review of the Space‐Vector Theory by Kovacs and Racz which, in accordance with the work of other authors, is shown to be a modified version of the GMTh for the particular case of three‐phase machines.
Electric field calculation combined with a CAD system for the personal computer
Authors: Okubo H. , Maehara H. , Kato K. , Hikita M. , Kito Y. 
Published: July 2010

AbstractA Personal‐Computer‐based CAD (PC‐CAD) system combined with the electric field analysis was developed and is referred to as “CADEF” (CAD system with Electric Field analysis). To construct such a system, both software and hardware need to be upgraded and the related conversion programs have to be developed. In the CADEF, the CAD drawings are fully utilized for the input data processing and the output expression of the electric field analysis. A Charge Simulation Method (CSM) is adopted as an analysis software. In the calculation process, singular points on the CSM such as the triple junctions are automatically recognized and processed. By introducing the expert knowledge and the experiential factors on the charge arrangements as the rules, the automatic calculation system is accomplished.
Some considerations on active compensation devices
Authors: Lauria D. , Tironi E. 
Published: July 2010

AbstractThe knowledge of the methodologies and devices bothtavoiding the disturbing injections in electrical networks and limiting the effects of disturbances existing before is a well‐known problem. In the present paper the results expected by using some active apparatuses for disturbances compensation are examined. The limits of different solutions are detected and some design elements are provided as well.
An approach to the direct analysis of transient stability
Authors: Djukanovic M. B. , Sobajic D. J. , Pao Y.‐H. 
Published: July 2010

AbstractThe Transient Energy Function (TEF) method has been intensely investigated over the last decade as a reliable and accurate tool for transient stability assessment of multimachine power systems. In this paper we propose the Potential Energy Boundary Surface (PEBS) based method for direct analysis of transient stability. The critical value of transient energy and the Critical Clearing Time (TCCT) are evaluated without the need for successive calculation and memorization of the system kinetic and potential energy values along the sustained fault trajectory. The method is used for determination of output features in the training phase of the neural‐net based transient security assessment. The proposed approach is tested on the well‐known ten‐generator New England test system demonstrating the validity and accuracy of obtained results.
Basic areas of research preceding design and commissioning of 1200 kV AC power transmission lines: Some key problems and solutions
Authors: Tikhodeev N. N. 
Published: July 2010

AbstractIn the paper is reported the experience of studies that preceded the planning, construction and operation of 1200 kV lines in Russia and Kazakhstan in the former USSR in areas peculiar to UHV power transmission, including the switching surge dielectric strength of long air gaps, selection of line insulation, profound limitation of resonance and switching overvoltages, environmental effects, corona losses of bundles with eight and more subconductors, radio interference. Both implemented and contemplated alternatives of UHV lines are discussed.
A general solution to the harmonics summation problem
Authors: Lehtonen M. 
Published: July 2010

AbstractA general solution is presented for the probability density function of the amplitude of the sum of a number of harmonics from different sources. In the solution, the phase angles and amplitudes of component vectors may vary randomly in any given range. If these variation ranges are the same for all the component vectors, then ‐ in addition to them ‐ only arithmetic and geometric sums of the maximum amplitudes need to be known in order to calculate the parameters of the probability density function.
Computer‐aided calculation of the steady‐state thermal performance characteristics of low‐voltage circuit breakers
Authors: Völker F. 
Published: July 2010

AbstractA discrete thermal network is given as an equivalent circuit of the steady‐state thermal performance characteristics of circuit breakers. The immediate environment of the enclosure and the feeders of the unenclosed switching device are the boundaries of the equivalent circuit, which specifically models the central phase of a three‐phase circuit breaker. Computer simulations make it possible to analyse the thermal system performance in rated service. Selected examples prove the high quality of the model and the efficiency of the described method of calculation.
Steady‐state modelling of a uniform pulse‐width modulated single‐phase AC‐to‐DC converter‐fed DC motor drive
Authors: Hamed S. A. 
Published: July 2010

AbstractWith the increasing availability of power transistor switches, PWM controlled rectifiers can efficiently and economically be employed in low and medium power applications of DC drive systems. In this paper, steady‐state modelling and solution of a uniform pulse‐width modulated single‐phase AC‐to‐DC converter‐fed DC motor drive is accomplished. The developed model is presented in a generalized form that is applicable irrespective of the number of pulses per supply half‐cycle. Measured and predicted parameters are shown to be very close and the model is proved to be efficient and accurate. Both continuous and discontinuous modes of operation are covered, and critical operating conditions at which the system moves from one mode to the other are thoroughly investigated. The effects of the armature inductance‐to‐resistance ratio and the chopping frequency on these critical conditions, load and line harmonics, and on the ripple contents of the armature current are also thoroughly investigated.
Solid‐liquid interface of an inductively heated metal sphere
Authors: Bex H. , Greuel K. 
Published: July 2010

AbstractIn this paper inductive melting in a metal sphere is investigated, whereby the temperature dependence of the sample 's most important material parameters is considered. The solid‐liquid interface in the sphere is determined in consideration of heat conduction. The melting process takes place in a vacuum with zero gravity under the influence of a homogeneous, magnetic alternating field. For the numerical solution of the heat conduction equation, homogeneous, isotropic conditions are assumed in discrete toroidal volumes. This approach simplifies, at the same time, the use of Maxwell's equations. Using the method of finite differences, the procedure yields not only the spatial location of the solid‐liquid interface but also the corresponding time and absorbed active power as a function of frequency, radius of the sphere and intensity of the exciting field. And not least, the total required melting time for melting the sphere can be determined.
Simple robust adaptive control of static VAR compensator
Authors: Machowski J. , Nelles D. 
Published: July 2010

AbstractA study of power system transient stability enhancement through effective use of static VAR compensator is presented. It is shown that optimal state‐variable control can be approximately realized as a simple closed‐loop control based on locally measurable electric quantities. In order to make this regulation more effective and insensitive to the changes of the network parameters and loading condition it is proposed to use simple adaptive control with dynamic gain tuned by additional control loops. Tests done for two‐machine and multi‐machine systems have confirmed the validity and robustness of the proposed control method.
The rms method and its application to the evaluation of errors of instrument transformers at non‐sinusoidal waveforms
Authors: Bojna I. , Jahn P. 
Published: July 2010

AbstractThe paper describes a general method, the so called RMS‐value method, which allows to analyse the current, voltage and power conditions in circuits with non‐sinusoidal periodic currents and voltages, without knowledge of the content of their harmonic components. Using this method the errors of the instrument transformers, including the power measurement in circuits with non‐sinusoidal periodic currents and voltages, are defined. The suggested method is illustrated by measurements of the current transformers with specified non‐sinusoidal currents.
Novel approach to numerical equivalence investigations on synthetic circuits for circuit‐breaker testing
Authors: Witte G. , Möller K. 
Published: July 2010

AbstractThe paper addresses to the calculation of the interruption limit of circuit breakers in connection with equivalence studies on synthetic test circuits. After a presentation of the applied arc‐equation, a method is presented to detect the calculated interruption limit by the rate of rise of the conductance minimum as a function of the current slope. Thus, a range of decision can be defined, in order to reduce the effort for equivalence studies of synthetic test circuits.
Study of the neutral‐to‐ground voltage in a compensated power system
Authors: Leitloff V. , Pierrat L. , Feuillet R. 
Published: July 2010

AbstractThis paper presents an extension of the theory of compensated systems taking into account general admittances between the three phases and earth at steady‐state condition. First, an introduction to the theory and history of compensated systems is given. The influence of reactances in the voltage source and the influence of a single phase resistive earth fault on the neutral‐to‐ground voltage are studied. As an illustration of the possibilities of the extended theory, the introduction of source impedances and the detection of high‐resistive earth faults by observing the neutral‐to‐ground voltage are examined.
Inductive ultra‐wide band detection and location of partial discharges in high‐voltage cables
Authors: Wouters P. A. A. F. , Van Der Laan P. C. T. , Steennis E. F. 
Published: July 2010

AbstractIn medium‐ and high‐voltage cables with a helical structure of the earth screen current pulses from partial discharges travelling along the cable are observed to follow the spiralling structure. The resulting tangential current produces an axial magnetic field which can be detected by an inductive sensor without having to make any change to the cable. A specially developed inductive sensor placed around the outer sheath of an intact cable is made selectively sensitive to the high‐frequency signals (± 100 MHz) arising from the partial discharges. The discharge pulses are recorded by a fast digitizer (bandwidth of 600 MHz). In laboratory experiments partial discharges with a minimum magnitude of about 5 pCfrom electrical treeing in short, medium‐voltage cables could be detected. Location by means of transit time measurements was performed with an accuracy of about 5 cm. In one case, the polarity of the discharge signal was successfully used to locate the discharge to within 1 cm.
Adaptive algorithm for estimation of voltage phasor, frequency and rate of change of frequency
Authors: Terzija V. , Djurié M. 
Published: July 2010

AbstractThis paper presents results in the design of an adaptive algorithm for real‐time estimation of voltage phasor, frequency and its rate of change. The new algorithm, separated in two stages, is based on the non‐recursive “Least Error Squares Technique” (LS Technique). The estimation of the unknown parameters of the voltage signal is improved by means of an update procedure in the first stage. The update procedure is iteratively provided by the algorithm adaptation to the actual estimated frequency so that the frequency measurement range and accuracy are significantly improved and sensibility to the noise is reduced. The rate of change of frequency, estimated in the second stage using a common LS Technique, is represented by the linearly time‐dependent observation model. To demonstrate the performance of the algorithm developed, computer simulated, experimentally obtained and real‐life data records tests are presented.
Non‐linear control of induction motors via input‐output decoupling
Authors: Frick A. , Von Westerholt E. , De Fornel B. 
Published: July 2010

AbstractAn original two‐step input‐output decoupling approach aimed at the design of a non‐linear controller/or induction machines is described. The resulting scheme is compared to both the non‐linear control by exact linearization and the classical field‐oriented vector control. The performance of the three controllers, which are implemented in discrete time, is evaluated and compared in the framework of a realistically simulated variable speed drive. The proposed approach provides excellent flux‐speed decoupling, and it allows for a straightforward and exact limitation of the machine currents. The latter represents the major advantage to most other non‐linear control schemes, where the inaccessibility of the currents, which prevents their correct limitation, is a mayor drawback.
Performance of three‐phase fully‐controlled bridge rectifiers with non‐ideal supply feeding static active loads
Authors: Ahmed F. I. , Abdel‐Halim I. A. M. , Hassaneen K. M. 
Published: July 2010

AbstractThe paper presents an analysis of the performance of a three‐phase, fully‐controlled bridge rectifier feeding static active loads, when the AC supply feeding the bridge is non‐ideal. The modes of operation of the system, which depend on the overlap angle, are fully investigated. Closed‐form analytical expressions from which the performance characteristics can be obtained are derived without any approximation either in the shape of the load‐current waveforms or in the in the shape of the current during the overlap periods.