RMS Value Of Current Research Articles

The effectiveness of a current flattening circuit as countermeasure against DPA attacks

This paper presents an on-chip current flattening circuit designed in 0.18-μm CMOS technology, which can be integrated with secure microsystems, such as smart cards, as a countermeasure against power analysis attacks. The robustness of the proposed countermeasure is evaluated by measuring the number of current traces required for a differential power analysis attack. We analyze the relationship between the required number of current traces and the dynamic current variations, and we show empirically that the required numbers of current traces is proportional to an inverse of the square of the rms value of the flattened current. Finally, we evaluate the effectiveness of the proposed design by using the experimental results of the fabricated chip. The analysis of the experimental results confirms the effectiveness of the current flattening circuit.

A resonant driver with functionally shared devices for plasma display panels

A sustain circuit with energy recovery and injection circuit is proposed based on reduced number of low-cost and low-rating devices for plasma display panels (PDPs). The proposed driver configures the sustain circuit and the resonant network in such a way that some of circuit components can function for both sustain and energy recovery/injection operations. Due to the semiconductor devices shared in common as well as simplified arrangement, the developed structure can be designed with fewer devices than the conventional approaches with all devices operated individually. Moreover, since the proposed driver is designed with low voltage-rating devices compared with the conventional 2 and 3 level based driver, it can take advantages of semiconductor devices with lower conduction and switching losses as well as cheaper costs. The proposed driver generates such five-level sustain voltage waveforms as a cascaded Weber-type driver, which results in reduced rms values of panel displacement currents and lowered power losses. As a result, the PDP driver presented in this paper can feature reduced number of low voltage rating devices, smaller size, and high efficiency.

Symmetrization of asymmetrical nonlinear three‐phase load supplied from non‐ideal sinusoidal voltage source

PurposeThe purpose of this paper is to deal with the problem of symmetrization of asymmetrical three‐phase delta connected nonlinear load. In the model of the three‐phase sinusoidal voltage source have also been included inner impedances. The purpose is to obtain symmetrical line currents of the voltage source, to minimize RMS values of currents and to minimize higher harmonics generated by nonlinear loads.Design/methodology/approachThis symmetrization of the system is realized by means of a symmetrizing system, which is composed of LC one‐ports. In order to solve the problem the symmetrical component theory is applied. The structure of symmetrizing system is consisted of two components: parameters determined for the basic harmonic and the filter for elimination of the higher harmonics generated by nonlinear loads.FindingsAfter symmetrization line currents of the source will be symmetrical with lower RMS values than before symmetrization, and the source will generate the greater active power than beforehand.Research limitations/implicationsThis approach can be used for inertialess (non‐reactive) elements in systems, where currents are periodical.Practical implicationsThe results of symmetrization can be useful for high‐power systems where LC one‐ports can be used, e.g. for arc furnaces.Originality/valueApplication of presented methods makes possible to improve the working point of the system, i.e. voltage source can generate greater active power than before symmetrization and line currents can be symmetrical.

On the Implementation of Time-frequency Transforms for Defining Power Components in Non-sinusoidal Situations: A Survey

Power quality indices play an important role in decision making in deregulated competitive environments. Useful power quality indices require clear and accepted definitions of power components as well as the RMS values of voltage and current. This is especially true in case of non-stationary distorted waveforms, where neither a frequency-domain–based approach using fast Fourier transform tools nor a time-domain–based approach using real-time data give satisfactory results. Wavelet transform is able to represent any distorted waveform in a time-frequency spectrum while preserving relevant information in both time and frequency domains. Different methods have been proposed in an attempt to define power components in the wavelet domain. This article offers a critical evaluation of the current state-of-the-art concerning this topic. The article also offers conclusions and suggested future work.

Improvements of protective characteristics of automatic low-voltage circuit breakers

Suggestions on how to improve the protective characteristics of automatic low-voltage breakers, namely, to increase the sensitivity to remote short-circuits (faults), to raise the speed of selective protection, and to enhance the reliability by long-distance (remote) backup are considered. The use of the power function of a current to quickly identify the reason for a circuit disturbance and determine the rms current value of the current’s periodic component is grounded. Advantages of the use of the Joule integral as a criterion to selectively operate breakers are shown.

Spectral analysis of permanent magnet electric machines

PurposeThis paper aims to provide the mathematical background for representation of permanent magnet AC machines in terms of rotating magnetic field waves of any shape instead of being restricted to the sinusoidal. The general idea is to replace the inductances in the mathematical model of the machine by means of adequate time functions of the flux linkage.Design/methodology/approachOn the basis of several 2D or 3D solutions obtained by the finite element (FE) approach, the set of basis functions is generated for further post‐processing. These functions enable fast and accurate computations of back EMF time shape at any load conditions, which in turn gives the instantaneous values of terminal quantities like torque or voltage, depending on the regime of interest.FindingsThe permanent magnet machine (PMM) has been represented by means of the traveling non‐dispersive waves of the flux density in the air gap rotating with specified group velocity. The conversion between distributions of the flux density in space and flux linkage in time is obtained through filtering in the spectral domain using 2D or 3D discrete Fourier transform. The change of magnetic saturation due to arbitrary value of the machine load is incorporated by the interpolation between known magnitudes of the basis functions at given a priori RMS values of phase currents. It has been proved that a sinusoidal field machine is particular to the presented theory.Research limitations/implicationsThe paper deals with the steady state of PMM; however, the extension towards the transient analysis is possible.Practical implicationsThe paper presents a fast and accurate model of PMM for the analysis of its basic electromagnetic quantities.Originality/valueThe analysis of terminal quantities being different in time from sinusoidal or constant distributions, both electrical and mechanical, is usually performed by means of a time stepping approach. The required computing effort is still too high for real time applications. The presented method starts from single FE solutions and converts their accuracy on the set of mutually orthogonal functions having the clear representation in the spectral, mode‐frequency domain. The magnitudes of these basic functions enable one to express the electromagnetic power in a form equivalent to classic dq representation, but not constrained by sinusoidal input quantities.

Optimal Reactive Compensators in Power Systems Under Asymmetrical and Nonsinusoidal Conditions

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Based on the condition for the minimum rms value of line currents, a method for improving the power factor in power systems under asymmetrical and nonsinusoidal conditions is presented. This paper offers straightforward and convenient formulations of active currents for the three-phase four-wire, three-phase three-wire, and single-phase systems. Owing to the transformation matrix introduced in this paper, the formulation of active currents is valid regardless of whether the voltages and currents are balanced or unbalanced and it permits any point of the system to be chosen for the voltage reference. Observing the constraints related to the reactive compensators, the line current minimization procedure is used for the determination of optimal compensating capacitances for the three-phase four-wire, three-phase three-wire, and single-phase systems. The optimal reactive compensators based on up to six capacitors are proposed. The definitions of power factors before and after compensation are introduced. The influence analysis of nonactive power compensation on harmonic distortion of line currents has been also performed. Experimental results are obtained to confirm the validity and applicability of the proposed compensation procedure. </para>

A simple instant‐estimation method for time‐average quantities of single‐phase power and application to single‐phase power grid connection by inverter

AbstractThis paper presents and analyzes a new simple instant‐estimation method for time‐average quantities such as rms values of voltage and current, active and reactive powers, and power factor for single‐phase power with the fundamental component of constant or nearly constant frequency by measuring instantaneous values of voltage and current. According to the analyses, the method can instantly estimate time‐average values with accuracy of the fundamental frequency, and estimation accuracy of the power factor is about two times better than that of voltage, current, and powers. The instant‐estimation method is simple and can be easily applied to single‐phase power control systems that are expected to control instantly and continuously power factor on a single‐phase grid by inverter. Based on the proposed instant‐estimation method, two methods for such power control systems are also proposed and their usefulness is verified through simulations. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 34–43, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20236

Influence of Machine Specific Instantaneous Current Wave Form on Resistance Spot Welding Process

The influence of the machine specific instantaneous current wave forms on weld nugget dimensions and weld strength is investigated over six spot welding machines. It is observed that the nature of the real-time current wave forms corresponding to a common rms value can vary in different ac spot welding machines. The variations exist in the values of peak current and in the current-on and -off times in every ac cycle. It is observed that real-time current wave form involving higher peak current leads to slightly larger weld nugget diameter compared to wave form with smaller peak current even if the overall rms value remains similar. The real-time current wave form from a medium frequency dc confirms to a fast rise to the set weld current and remains steady for the complete weld time. A detailed experimental study has depicted that the real-time ac wave forms especially with high peak values and sharp rise characteristics offer a relatively smaller permissible range of weld currents compared to the wave forms with relatively flatter characteristics. The steady instantaneous current wave form confirming to the medium frequency dc machine has facilitated a larger permissible range of weld current. A numerical analysis of the spot welding process based on finite element process is carried out using both the instantaneous current wave forms and the corresponding rms values of weld current. The predicted weld dimensions using instantaneous current wave forms have showed slightly better agreement with the corresponding measured weld dimensions.

Symmetrization of asymmetrical three‐phase load supplied from non‐ideal periodic non‐sinusoidal voltage source using simplified structure of the compensator

PurposeThe problems presented in the paper concern a three‐phase four‐wire system with periodical non‐sinusoidal voltage sources with inner impedances and asymmetrical linear three‐phase loads. Generally, the line currents of the system are asymmetrical. The purpose of the paper is to improve the working conditions of the system by means of symmetrization.Design/methodology/approachA method of symmetrization of these systems has been proposed. In this paper, the symmetrization problem has been solved by using the symmetrical components theory and compensation of reactive power for each of voltage harmonics under consideration.FindingsAfter symmetrization currents become symmetrical and their RMS values and active power on source impedances become lower. The realization of symmetrization makes possible: reduction of RMS values of source currents, an assurance of equal loads for individual phases of the system supplied from sources with inner impedances, after symmetrization the voltage source generates and load consumes greater useful active power.Originality/valueThe simplified structure of the compensator has been proposed in the paper. The symmetrization has been presented with reference to new structure of the compensator.

Optimal non-active power compensation under non-sinusoidal conditions

This paper presents a new method of non-active power compensation in power systems under non-sinusoidal conditions. The basic idea of the compensation procedure stems from the condition for the minimum rms value of line currents. The application of optimization procedure, observing the above criterion, results in the required compensator. Three different compensators are derived: total non-active power compensator, compensator without energy storage, and reactive compensator. The paper introduces the factors which define the amount of active power in total power before and after the non-active power compensation. The compensation procedure is valid for single-phase and polyphase systems. Simulation results confirm the validity and applicability of the compensation procedure for a diversity of load currents.

High-Impedance Fault Detection Using Discrete Wavelet Transform and Frequency Range and RMS Conversion

High-impedance faults (HIFs) are faults which are difficult to detect by overcurrent protection relays. Various pattern recognition techniques have been suggested, including the use of wavelet transform . However this method cannot indicate the physical properties of output coefficients using the wavelet transform. We propose to use the Discrete Wavelet Transform (DWT) as well as frequency range and rms conversion to apply a pattern recognition based detection algorithm for electric distribution high impedance fault detection. The aim is to recognize the converted rms voltage and current values caused by arcs usually associated with HIF. The analysis using discrete wavelet transform (DWT) with the conversion yields measurement voltages and currents which are fed to a classifier for pattern recognition. The classifier is based on the algorithm using nearest neighbor rule approach. It is proposed that this method can function as a decision support software package for HIF identification which could be installed in an alarm system.

Extending the constant power speed range of the brushless DC motor through dual-mode inverter control

An inverter topology and control scheme has been developed and tested to demonstrate that it can drive low-inductance, surface mounted permanent magnet motors over the wide constant power speed range (CPSR) required in electric vehicle applications. This new controller, called the dual-mode inverter controller (DMIC) , can drive both the Permanent Magnet Synchronous Machine with sinusoidal back emf, and the brushless dc machine (BDCM) with trapezoidal emf as a motor or generator. Here we concentrate on the application of the DMIC to the operation of the BDCM in the motoring mode. Simulation results, supported by closed form analytical expressions, show that the CPSR of the DMIC driven BDCM is infinite when all of the motor and inverter loss mechanisms are neglected. The expressions further show that the ratio of high-to-low motor inductances accommodated by the DMIC is 11 making the DMIC compatible with both low- and high-inductance BDCMs. Classical hysteresis-band motor current control used below base speed is integrated with DMICs phase advance above base speed. The power performance of the DMIC is then simulated across the entire speed range. Laboratory testing of a low-inductance, 7.5-hp BDCM driven by the DMIC demonstrated a CPSR above 6:1. Current peak and rms values remained controlled below rated values at all speeds. A computer simulation accurately reproduced the results of lab testing showing that the limiting CPSR of the test motor is 8:1.

Neutral Currents in Large Public Lighting Networks

The modern large public lighting networks are characterized by two major aspects that rise problems from both power quality and neutral current point of view in low voltage wye-connected three-phase electrical systems: (i) the supply system is unbalanced loaded; (ii) the presence of discharge sources. It is important to underline that nowadays, these aspects are not taken into account in the proper sizing of neutral conductors. The paper presents a simplified but enough accurate methodology to estimate the RMS value of neutral currents in lighting networks. The theoretical relationships are illustrated for a three-phase public lighting network that contains high pressure sodium lamps.

A Simple Instant-Estimation Method for Time-Average Quantities of Single-Phase Power and Application to Single-Phase Power Grid Connection by Inverter

This paper presents and analyzes a new simple instant-estimation method for time-average quantities such as rms-values of voltage and current, active and reactive powers, and power factor for single-phase power with the fundamental component of constant or nearly-constant frequency by measuring instantaneous values of voltage and current. According to the analyses, the method can instantly estimate time average values with accuracy of the fundamental frequency, and estimation accuracy of power factor is about two times better than that of voltage, current, and powers. The instant-estimation method is simple and can be easily applied to single-phase power control systems that are expected to control instantly and continuously power factor on a single-phase grid by inverter. Based on the proposed instant-estimation method, two-methods for such power control systems are also proposed and their usefulness is verified through simulations.

Electromigration induced resistance decrease in Sn conductors

The resistance of thick film (2 μm) Sn conductors deposited onto Ni/Cr underlays was found to decrease several percent during electromigration stressing. The application of dc was necessary to initiate the resistance decrease. Equivalent ac current (rms values equal) did not produce the effect and extensive aging at elevated temperature did not either, indicating that the effect is not purely thermally induced. It is suggested that the reduction in the electromigration induced chemical potential from reductions in resistivity associated with reorientation of the microstructure is responsible for the effect.

Analysis of the neutral conductor current in a three-phase supplied network with nonlinear single-phase loads

This paper describes what factors (i.e., load and supply) have an important effect on the neutral conductor current. It is shown that an asymmetry up to 10/spl deg/ or an unbalance of 10% in the power supply has only a minor effect on the RMS value of the neutral conductor current. An unbalance in load conditions increases the neutral conductor current. Harmonics in the power supply voltage highly affect the RMS value of the neutral conductor current.

Line current characteristics of three-phase uncontrolled rectifiers under line voltage unbalance condition

Three-phase uncontrolled rectifiers with capacitive filters are highly sensitive to line voltage unbalance, drawing significantly unbalanced line current even under slightly unbalanced voltage condition. This paper presents an analysis of this amplification effect for an ideal rectifier circuit without AC- and DC-side inductors. A novel way of modeling the voltage unbalance is established by introducing a deviation voltage superimposed on balanced three-phase line voltages, which allows simplified analysis of the rectifier operation. With proper approximations, closed-form expressions for symmetrical components of the fundamental line current and correspondingly the current unbalance factor are derived in terms of the voltage unbalance factor, filter reactance, and load current. The equivalent RMS value of the third harmonic current is also derived. The analysis clearly shows high sensitivity of the current unbalance to the voltage unbalance, and provides a basic guideline for rectifier circuit design. The validity of the analysis is confirmed by simulation.

Stator current harmonics and their causal vibrations: a preliminary investigation of sensorless vibration monitoring applications

This paper presents an initial study into the relationship between vibration and current harmonics of electric motors, including the effect of externally induced vibrations. This relationship was investigated experimentally on both new motors, on a vibration stand, and a motor with bearing wear. Both theory and experimental results show that a change in the RMS value of the stator current is directly related to the change in vibration magnitude, for a known vibration frequency. The paper shows this result both for a new motor with an externally induced vibration and for a motor with vibration caused by progressive bearing wear.

The design of a hand-held K-factor meter using an air-core current transformer

This paper describes in detail the design of a portable microcontroller-based K-factor meter, or transformer harmonic derating factor meter. This innovative instrument is based on the recently developed time domain method for K-factor determination. K-factor is measured from the ratio of the rms value of the time derivative of a current to the rms value of this same current. The meter employs the properties of an air-core current transformer, or Rogowski coil, to acquire the time derivative of a current and then numerical integration, of this digitized signal, to obtain the current waveform itself. This method avoids the noise of the numeric differentiation, characteristic of the time domain approach to K-factor measurement, as well as the computational effort of the fast Fourier transform in the frequency domain approach. In addition, the instrument incorporates thermal demand models for both K-factor and rms current to assess transformer harmonic heating over a user selected time interval. A prototype meter, using a MC68HC16 microcontroller, was built and tested with a variety of actual and synthesized power system waveforms.