Least squares-based methods

The objective of this paper is to present an approach for isolating the harmonic contents in both voltage and current waveforms of the montage feeder of Gharb Talkha substation (60/11 KV). A novel technique using Discrete Wavelet transform (DWT) for the analysis of the waveforms harmonics content At the beginning the substation is simulated using Simulink toolbox in Matlab program with and without the presence of capacitor bunk. The obtained voltage and current waveforms are compared to the actual data. The proposed model is used to study the effect of replacing the capacitor bank with single tuned parallel passive filter. The resulting current and voltage waveforms are analyzed using the proposed DWT technique. The analysis showed that the Total Harmonic Distortion (THD) of both voltage and current waveforms is improved as well as the power factor.

Pantograph arcing with AC supply generates transients, cause asymmetries and distortion in supply voltage and current waveforms and can damage the pantograph and the overhead contact line. The asymmetry generates a net dc component and harmonics, which propagate within the traction power and signalling system and causes electromagnetic interference. Unlike DC-fed systems (Part I), the arcing in ac supply is complex because of the zero crossing of currents and voltages. In this paper, we discuss the mechanisms of sliding contact and arcing between pantograph-contact wire using the experimental setup described in Part I. Influences of various parameters and test conditions on arcing phenomenon and their signature patterns on the supply voltage and current waveforms are presented. It is shown how the arcing mechanism and corresponding asymmetry in the voltage and current waveforms are governed by line speed, current, supply voltage, inductive load, and pantograph material. The asymmetry in the current waveform is mainly due to the difference in the duration of successive zero-current regions and uneven distortion of the waveshapes. This, in turn, creates the asymmetry in the voltage waveform. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the electromagnetic interference due to pantograph arcing in AC traction systems.

Voltage source inverter (VSI) had been used in dc traction power substation to deliver the trains braking energy back to the utility grid. To mitigate low order harmonics components, pulse-width-modulation (PWM) technique is commonly used in VSI controlled. As a result, the ac voltage and current waveforms may contain high frequency ripples. This paper proposes to mitigate the high frequency harmonics using LCL-filter with series <em>R</em>-damper. This filter offers good attenuation on harmonics with smaller size compare to other passive filter topologies. Theoretical analysis and simulation verification are conducted in designing the proposed filter. System level simulation had also been carried out. Sinusoidal grid current and voltage waveforms are recorded (THD<2%). This paper also includes damping losses analysis in conjunction with resonance peak suppression in designing the <em>R</em>-damper.

An experimental investigation of a TRAPATT diode with its oscillator circuit is presented. The measurements of current and voltage waveforms were made with a sampling oscilloscope (3 dB bandwidth, 14 GHz)and an improved capacitive voltage-divider probe. Design information is given for this type of probe which can have an almost unlimited bandwidth. Voltage and current waveforms across the semiconductor chip are presented for a diode that oscillated at 1 GHz with an efficiency of 49%. It is shown that the mode of operation and the waveforms are explained well by a simple theoretical model that has been developed.

When the soil invaded by water as the grounding medium in green power generation sites near river basins, on the coast, is dominantly characterized in terms of its resistivity, the characteristics of the voltage and current waveforms on transient discharges such as the soil can be experimentally investigated using the liquid gap, reproducing the resistivity of the soil. The transient discharge characteristics is available information on the surge withstand rating of surge protective devices used in the green power generation sites. Experimental results on the behaviour of lightning impulse discharges in a tap-water gap are reported; these results show that the resistivity of tap water is nearly equal to those of a river and cultivated and marshy land. Further, (1) the discharge voltage and current waveforms indicate the periodic attenuated waveforms for one period, and the voltage waveforms indicate amplitude distortions; (2) the discharge impedance obtained using the fitting curves to the discharge waveforms ranges from 1 to 2.5 times that of the tap-water resistance, i.e., 80Ω, and from 8 to 3.2 times that for positive and negative rod discharges.

This paper introduces the power quality analysis of unidirectional and bidirectional ac voltages controllers. An AC voltage regulator coupled between the power supply and the load is a device having major components of two thyristors connected in inverse parallel manner and the power flow is controlled by varying the firing angle of thyristors. For each configuration, the experimental setup is implemented on Feedback Power Electronics Trainer and simulation is done using MATLAB/Simulink. The simulated and experimental waveforms of current and voltage in case of resistive and inductive loads are obtained by taking different firing angles and are correlated, which demonstrate the effectiveness of model and its configurations. Due to switching operations of power electronic converters, they contain nonlinearities and generate harmonics which not only disturb the performance of converters but also the quality of input power system is badly affected. The power quality factor is observed by Fluke Power Quality Analyzer that can monetize the cost of energy waste due to poor quality. In this research, the performance evaluation of controller with industrial inductive loads under different delaying angle is investigated and detailed comparative analysis is done by experimental readings and simulation results. Total Harmonic Distortion (THD) analysis for different waveforms of voltage and current, its calculation and comparison for change in loads have been presented in this paper.

The present methods used to calibrate an active power or energy meter device under test (DUT) under nonsinusoidal conditions are based on a limited number of current and voltage waveforms and do not exercise the dynamic range of the DUT. After reviewing a method recently developed at the National Physical Laboratory (NPL) to exercise the dynamic range of a DUT under sinusoidal and nonsinusoidal conditions for specified current and voltage waveforms, the paper reports on the performance of the DUT under nonsinusoidal conditions measured using the NPL method. Experimental results: 1) verify theoretical predictions that the active power fractional full-scale (FS) error depends on both the phase-angle group between the current and voltage waveforms and the phase angle between the harmonics and the fundamental of both the current and voltage waveforms and 2) show that the active power fractional FS error for sinewave excitation can be larger than that for nonsinusoidal conditions

Steady-state operation of a load commutated inverter (LCI) fed synchronous motor drive is analysed by means of a digital computer based solution of the synchronous machine equations. The solution permits calculation of current, voltage, and torque waveforms and includes the effects of finite DC link inductance, saliency of the rotor and all machine resistances. The continuity constraints for steady-state operation are exploited to enable the proper initial conditions to be calculated directly, without the need for iteration. Operating points are described by the firing angle yo, and the overlap angle μ, and are computed for an assumed DC supply voltage of 1.0 per unit. The linearity of the state equations allows the normalised solutions to be scaled to obtain any desired value of torque, DC link current etc. Sample calculations are provided, showing the influence of the DC link inductance on the torque, DC link current and voltage waveforms. These are then compared with experimentally measured data taken from a 3 kVA LCI fed synchronous motor drive, and a good level of agreement is achieved.

The operating power frequency fluctuates around its nominal value under normal conditions based on the dynamic balance between load demand and generation levels. This frequency variation creates a challenge in computing and analyzing voltage and current root-mean-square values over time, since sliding windows may not cover an integer number of cycles of the sampled voltage and/or current data. The overall objective of this paper is to present an adaptive resampling technique for the voltage and current waveforms, such that each sliding window used for computation of power quality parameters always cover an exact integer number of cycles. This technique is illustrated for a capacitor de-energizing operation, which is detected through a step change in the rms voltage profile. Once this de-energizing operation has been detected, the voltage waveform is resampled and the rms voltage profile with a high time resolution is obtained through a fast and recursive approach. Finally, the exact capacitor de-energizing instant is estimated. The proposed approach is shown to be simple, yet robust and accurate.

ESD on GaN-based LEDs: An analysis based on dynamic electroluminescence measurements and current waveforms

Harmonics in current and voltage waveforms produced by nonlinear loads in a distribution system can be minimised using passive filters; however, implementing these filters requires the calculation of several suitable parameters for filter components. This work aimed to simulate and analyse the harmonics in the Al-Itihad 11 kV distribution system that branches off from Zubayr substation (33/11 kV) in Basra in Iraq using MATLAB/SIMULINK. Five non-linear loads were simulated to generate harmonics in the simulated Al-Itihad distribution system, and for each non-linear load three types of filters were tested: a single tuned filter (STF), double tuned filter (DTF), and C-type filter. The objectives of these filters to minimise the total harmonic distortion (THD) in the voltage and current waveforms, to minimise the total current, and to improve the power factor of the distribution system. The simulation results showed a reduction in total harmonic distortion, a reduction in the current at the main distribution feeder, and an improvement in the power factor of the feeder.

This research work will examine singular value decomposition (SVD), Fast Fourier Transform (FFT) and least square technique for the estimation of harmonics in power system. Harmonics in power system disturbs the quality of energy supplied to load, increased energy losses and reduce the reliability of the power system. In some cases, the large power converter systems produce not only typical harmonics but also a significant amount of inter harmonics which can significantly deteriorate the quality of power supply voltage. Inter harmonics are those components of current or voltage waveform which are not integer multiple of fundamental frequency component. Since poor power quality cause losses in power system that's why researchers are working to find techniques to estimate and control the harmonics in power system. Singular value decomposition approach is an ideal technique to estimate harmonics in power system located far away. Since in most of the cases, power system produce over determine equations which can easily be solved using SVD for optimal solution. Singular vector decomposition, SVD is really a mathematical method to lessen a dataset containing an extensive number of qualities to a dataset containing fundamentally less values, yet which still contains a huge portion of the variability introduce in the first information. SVD investigation brings about a more reduced representation of correlations, particularly with multivariate datasets and can give knowledge into spatial and temporal variations exhibited in the fields of data being analysed under different circumstance. Similarly traditional least square method is also one of the most prominent method to estimate the line of best fit. This research work will show the analysis of said techniques to find the optimal approximation of noisy and distorted wave form. To investigate effectiveness of said techniques; simulations will be carried out in MATLAB with same parameters.

An analytical method to study the discharge-radiation dynamics (DRD) in alternating current plasma display panels was developed. The input parameters for this DRD analysis were experimentally determined panel voltage and current wave forms. Discharge voltage, current, and power wave forms in the discharge volume of a cell were first obtained from the measured panel voltage and current wave forms using known geometrical configurations and electric circuit calculations. Intrinsic discharge parameters, such as electron temperature and density, were then determined to satisfy these discharge wave forms under the assumption of a hydrodynamic approach. A one-dimensional discharge structure with two regions (cathode fall and positive column) and several other assumptions which are plausible from the discharge physics point of view were also adopted. These assumptions took account of known cross sections and energies of electron-impact excitation and ionization of discharge gas atoms, and a secondary electron emission coefficient of the dielectric surface at the cathode side induced by ion bombardment. Radiation intensities from the discharge were calculated using the determined intrinsic discharge parameters, and the results were compared with those measured for the respective panel conditions used in the calculations, yielding a fair agreement. The luminous efficiency, defined as the radiation intensity divided by the discharge power, was also determined using the intrinsic discharge parameters. Discussion on the luminous efficiency change for different panel operating conditions revealed that the efficiency improvement at a lower voltage was attributable to a lower electron temperature for this condition.

Field tests were conducted at an industrial plant to see whether the voltage and current waveforms at the input transformer supplying power to the plant would agree with computer generated predictions. The latter were made by using a simple simulation procedure, previously published, for analysing a power system that supplies a substantial nonlinear load. The plant demand was about 300 kW. Very good agreement was obtained between the measured waveforms and those predicted using the simulation procedure, from the presumed composition of the load. However, in many practical situations the composition of the load is not known. In general, in such cases, the load composition may be deduced from the known current waveforms of the individual load components. This is achieved by adding them together in the proper proportions so that the RMS difference between the measured current waveform and the predicted one is minimised. The work described provides the basis for a next step: integration of the simulation scheme into a large multibus system so that a standard load-flow program may be used to account for the effects of harmonics on the system.

This article presents a new idea that enables direct, high-precision, in-situ, and in-operation core loss measurement in experiment. Coupled with the improved dual-curve derivative (iDCD) method that provides accurate in-situ total magnetic loss measurement, this article can accurately and experimentally disentangle the core and winding losses from the lumped magnetic loss in-situ and in-operation for practical power electronic converters. Historically, the timing skew between measurement channels has plagued direct power loss measurement approaches, especially for switched-mode power electronics whose voltage and current waveforms are both alternating current (ac) (e.g., excited by rectangular and triangular stimuli). This unknown timing skew severely hinders the application of the conventional “two-winding method” for magnetic core loss measurement, introducing challenges when attempting to measure the power loss under desired operating conditions. This article builds a comprehensive mathematical model to analyze the effect of the timing skew on the direct core loss measurement and presents a novel approach based on a capacitor branch to eliminate the measurement error caused by the unknown timing skew. The proposed method provides an extremely tight error tolerance at a sub-1% level. A new cross-validation method—though is only suitable in highly controlled lab settings and is less accurate—is developed to demonstrate the proposed method’s efficacy and prove that the proposed method can be freely applied beyond lab settings. Theoretical analysis is verified in simulation and experiment with a conventional dc-dc step-down buck converter with nonsinusoidal voltage and current waveforms under a range of practical circuit parameters.