Magnitude Of Harmonic Currents Research Articles

Residential Harmonic Injection Models Based on Field Measurements

In recent years, harmonic current levels have increased in residential distribution networks due to the growing penetration of nonlinear loads at customer premises. To properly model the harmonic current injection of residences, probabilistic models that account for the stochastic behavior of domestic loads are needed. As a part of the study reported in this paper, a field measurement campaign was performed in 24 dwellings during a one-week period with a one-minute resolution. Harmonic current magnitudes and phase angles of odd harmonic orders up to the 25th as well as the active and reactive power demanded were recorded. By applying two different unsupervised learning techniques (i.e., nonparametric density estimation and Gaussian mixture models) to these measurements, two probabilistic models of harmonic injection of individual residential sites have been derived. Statistical probability distributions have been determined for the magnitude and phase of each harmonic order segmented in different power demand intervals. The developed models are validated on a test feeder by comparing harmonic voltages caused by the injection of the synthetically generated currents with those obtained from measurements. Both field measurement results and the detailed data defining the probabilistic harmonic current models are made public in an Open Science database repository.

Including uncertainties in harmonic hosting capacity calculation of a fast EV charging station utilizing Bayesian statistics and harmonic correlation

• High correlation is observed between fundamental current and some low order harmonic currents. • Considering correlation between fundamental and harmonic current magnitude improves the accuracy of the sample generation for harmonic stochastic studies. • A new method, based on Bayesian statistics and the correlation between harmonic magnitude and fundamental magnitude for the currents, is proposed for the generation of stochastic samples. • The harmonic hosting capacity is obtained for a fast EV charging station using a stochastic model of the harmonic charging currents. The harmonic emission from an electric vehicle fast charger depends on factors like charger topology, EV type, initial state of charge of EV battery, as well as supply voltage and background distortion. This paper presents the results from harmonic current measurement of a fast charger for a period of one month in Sweden that has charged a variety of EVs from different brands under different state of charge and background distortion. Besides the common harmonic emission pattern, a high level of variation in emission is observed that can affect the aggregation of the emission from multiple chargers. To include such uncertainties, the harmonic hosting capacity is obtained for a fast EV charging station in a stochastic way. A new method, based on Bayesian statistics and the correlation between harmonic magnitude and fundamental magnitude, is proposed for the generation of stochastic samples. It is shown that the proposed method, to a high extent, can model the stochastic behavior of harmonic emission from a fast charger. Furthermore, the results show that neglecting the correlation between harmonic magnitude and fundamental magnitude can underestimate the harmonic hosting capacity.

THD reduction in measurement of H - Bridge multilevel inverter using pulse modulated switching integrated with linear quadratic Regulator

In this paper, the proposed Pulse Modulated Switching Cascaded H-bridge Multilevel Inverter (PM-SCHM) can be utilized for the reduction of Total Harmonic Distortion (THD). In high and medium power applications, multilevel inverters are commonly used. Because of the presence of harmonics in this scenario, THD has an impact on the overall efficiency of power electronics devices. The frequency analysis of a multilevel inverter is based on frequency spectra and numerical computation. A squared multilevel voltage waveform can be obtained by using an infinite range of switching harmonics. The proposed PM-SCHM scheme consists of a multi-level inverter arranged in an H-bridge sensor Cascaded manner. To compensate harmonic current magnitude in opposite direction Shunt Active Power Filter (APF) is used. A pulse modulation scheme is applied to the proposed PM-SCHM scheme for the arrangement of components using Linear Quadratic Regulator (LQR). The constructed LQR scheme utilizes a load for compensation with source voltage. This research focused on 5th order harmonics with a fundamental frequency of 50Hz. The comparative analysis of simulation results exhibited that the proposed Pulse Modulated Switching based Cascaded H bridge sensor Multilevel Inverter PM-SCHM scheme exhibits significant performance rather than the conventional technique.

Computation of Nonlinear Load Harmonic Currents in the Presence of External Distortions

This paper deals with the issues of computation of the nonlinear load harmonic currents in the presence of external distortions based on the real measurements with help of passive harmonic. Such values are necessary when modeling an equivalent nonlinear load as current sources in the presence of external distortions. The passive filter allows to separate external and internal distortions, which is necessary when determining the harmonic currents of a single consumer. The influence of various parameters on the computation of harmonic currents of a nonlinear load, such as the parameters of a passive harmonic filter, the impedance of the power supply transformer, the load parameters of the consumer, taking into account the harmonic generation from the grid side, and from the consumer side, is considered. It is shown that an external source of distortion has practically no effect on the error in estimating the harmonic current magnitudes of a nonlinear load. The obtained simulation results were confirmed experimentally on a laboratory test bench. Recommendations for the selection of passive harmonic filter parameters have been developed to minimize the error in determining the harmonic current magnitudes of a nonlinear load.

Torque Ripple Reduction Method for Permanent Magnet Synchronous Machine Drives With Novel Harmonic Current Control

Torque ripple reduction has become an active research area for permanent magnet synchronous machine (PMSM) drives. This paper presents a novel torque ripple reduction method based on harmonic current control. In the proposed method, the optimal harmonic current solution based on the torque ripple model with minimum stator resistive loss is derived in the rotor reference frame (RRF). The optimal harmonic currents are injected by the proposed harmonic current controller (HCC), wherein the magnitude of harmonic currents are defined as controller variables. To estimate the harmonic currents, the proposed method also utilizes the least mean square (LMS) based adaptive filter (AF), wherein the coefficients are defined as feedback to the proposed HCC. The proposed methodology is demonstrated using both simulations and experiments and is verified to reduce torque ripples of PMSM drives over a wide range of speeds.

Optimal probabilistic planning of passive harmonic filters in distribution networks with high penetration of photovoltaic generation

In recent years, distribution networks have been increasingly affected by the random nature of harmonic sources introduced by nonlinear load and renewable energy sources (RES) such as photovoltaic (PV) systems. This paper presents an approach based on Genetic Algorithm (GA) and Monte-Carlo Simulation (MCS) for the optimal planning of single-tuned passive harmonic filters (PHFs) in a distribution network. The resistance and inductance of the lines within the network are modeled by frequency dependent characteristics. The probabilistic characteristics of the load and PV system currents are also considered for optimal planning of PHFs. In our optimization model, the objective function minimizes the total PHF installation cost and the energy losses, by considering the total harmonic distortion (THD) of bus voltages and maximum capacity of PHF as constraints. The proposed method is validated by a simulation study using an unbalanced three-phase real distribution system. An advantage of this method over most of the conventional approaches is that both harmonic current magnitude and phase angle of real PV systems are taken into account. Numerical results show the applicability and effectiveness of the proposed method.

Genetic Algorithm-Based Current Optimization for Torque Ripple Reduction of Interior PMSMs

This paper investigates the torque ripple modeling and minimization for interior permanent magnet synchronous machines (PMSMs). At first, a novel torque ripple model is proposed in which the torque ripples resulted from the spatial harmonics of permanent magnet flux linkage, time harmonics of stator currents and the cogging torque are included. Based on the torque ripple model, a genetic algorithm (GA)-based harmonic current optimization approach is proposed for torque ripple minimization. In this approach, GA is applied to optimize both the magnitude and phase angle of the stator harmonic currents to minimize the peak-to-peak torque ripple, minimize the sum of squares of the harmonic currents, and maximize the average torque component produced by the injected harmonic currents. The results demonstrate that the magnitude of the harmonic current can be significantly reduced by optimizing the phase angles of these harmonic currents. This leads to further suppression of the torque ripple when compared with that of a case where phase angles are not considered in the optimization. Also, an increase of the average torque is achieved when the optimum harmonic currents are injected. The proposed model and approach are evaluated through both numerical and experimental investigations on a laboratory interior PMSM.

Identification of Harmonic Current Contributions of Iron and Steel Plants Based on Time-Synchronized Field Measurements—Part I: At PCC

This is the second of a two-paper series, in which the field-data-based analytical method proposed in Part I has been extended to determine the amount of harmonic currents absorbed by the shunt harmonic filters of the iron and steel (I&S) plants from the rest of the system. The nonlinear characteristics of the plants and the utility are modeled as harmonic current sources, whereas the linear parts of the proposed extended model consist of passive circuit elements, with the harmonic filter RLC circuit parameters also integrated into the model. This extended method, which can be also used for harmonic contribution assessments, requires sample-by-sample time-synchronized harmonic current measurements inside the plants and at the point of common coupling (PCC). It eliminates the need for harmonic voltage measurements at the expense of the need for inside-plant measurements. It has been verified both by computer simulations and by application on field data. The results have shown that the proposed method is a successful tool to determine the magnitude of harmonic currents that are absorbed by the harmonic filters of I&S plants connected to the PCC, particularly when measured harmonic currents of I&S plants exceed the actual contributions.

Statistical characterisation of harmonic current emission for large photovoltaic plants

SUMMARY Harmonic current emission of photovoltaic (PV) systems is a well-known problem. However, its quantitative characterisation, which requires the compilation and use of abundant statistical data, had never been satisfactorily dealt with. This paper discusses the multifaceted statistical characterisation of these emissions in a large PV plant. The topics addressed are harmonic current magnitude and its phase angle in relation to PV power output level and background harmonic voltages. Harmonic current emission in PV systems should be recorded during any single 1-week period throughout a full year. Because power quality metres are expensive, it is more economical to measure this type of emission with simple, cost-effective equipment. This paper thus presents a new assessment method for harmonic emission based on PV power output level, which is the main parameter affecting the emission, and which is easily monitored by most PV inverters. This new method uses statistical data to define a dependence model for the PV power output of PV harmonic current emissions. Such a model is rarely provided by PV inverter manufacturers. However, the simpler dependence model required for this method can be obtained by inexpensive power quality metres. This new method also produces accurate results at low process costs. Copyright © 2013 John Wiley & Sons, Ltd.

Influence of Harmonics in Laboratory due to Nonlinear Loads

This research was focused on the customer’s side of the meter which is the effect of harmonics on a laboratory in Electrical System Engineering School at K.Wai Perlis. Harmonic currents in equipments can cause them to experience overheating and increased losses, while harmonic voltage produces magnetic fields rotating at a speed corresponding to the harmonic frequency. This also results in equipments heating, mechanical vibrations and noise, reduced efficiency, reduced life, and voltage stress on insulation of equipment windings. The loads in this research are computers, Compact Fluorescent Lamps CFLs), Air Conditions and printers,which all of the loads are harmonic significant The instrument to measure and monitoring is Fluke 435 Power Quality Analyzer. With the operation of varying nonlinear loads, the injected harmonic current magnitudes and phase angles vary in a random way. This research offers the advantage of providing the utility a wealth of information on the effects of harmonics in their equipments. This will subsequently make them aware of the causes of increased cost and reduced efficiency that may be experienced by using these equipments. This paper describes the investigation cost of harmonic effect as THD, and harmonic energy losses cost. Keywords : harmonics, nonlinear loads, Energy losses cost, THD. DOI: http://dx.doi.org/10.11591/ijpeds.v2i2.142

Effects of Voltage Supply Unbalance on AC Harmonic Current Components Produced by AC/DC Converters

This paper examines the main factors affecting amplitudes of the harmonic current components generated by HVDC converters operating under unbalanced voltage supply. A symmetrical firing scheme is considered and emphasis is placed on operation of the six-pulse full bridge rectifiers, which are used as the basic arrangement for assembling the twelve pulse converter widely used in HVDC transmission and as a field voltage supply for synchronous generators in large power plants. Several computer simulation results are shown in order to illustrate the effect produced by the unbalanced voltage supply on the characteristic ac harmonic current magnitudes when considering different operating conditions characterized by changes on dc current amplitudes and on the firing delay angle. Special attention is placed on the noncharacteristic triple harmonic currents arisen basically as a result of the different commutation time on phase currents produced by the negative sequence components of the phase-to-phase voltages.

Preventing substation tripping

This article describes an actual case history of substation nuisance tripping caused by a transformer differential relay due to rolled-out current-transformer (CT) connections. One set of differential relay CTs was installed averse order, and it's wiring was installed as if the CTs were stalled in the correct order. It was after several weeks of substation initial energization, when all plant auxiliary loads, such as lighting and small 480-V equipment, were in operation, the substation main transformer tripped on a line-to-ground arcing fault on the 480 V-system. Transformer differential relay settings, which caused tripping of the transformer for this through fault, were suspected to be in error. It was thought that perhaps arcing ground fault on the 480-V system contained a relatively higher magnitude of harmonic currents. Relay-setting calculations, especially the harmonic restraint, percent slope, tap ratio adjustment, and percent mismatch were reviewed and found to be within acceptable ranges. After thorough checking of relay settings and visual inspection of the substation transformer and switchgear, the field crew reenergized the substation while the technical investigation by the author was still in progress.

An investigation of harmonics attenuation and diversity among distributed single-phase power electronic loads

Widely distributed single-phase power electronic loads are an increasingly important source of harmonics in power distribution systems. The objective of this paper is to investigate the cumulative harmonic current characteristics of a large number of such loads. A complete analytical model for the most common load type is derived. This model is then used to investigate the impact of: (1) interaction due to a shared source impedance; (2) variation in power level; and (3) variations in circuit parameters, on individual and cumulative current harmonics. The key findings of the paper are that diversity and attenuation are very important factors in predicting the behavior of distributed single-phase power electronic loads, especially for the higher-order harmonics, and that due to these two factors, the commonly-used fixed current injection method, using arithmetic sums of harmonic current magnitudes, can significantly overestimate the cumulative harmonic currents produced by these loads.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An Analysis of the Harmonic Impedance of a Saturated Induction Machine

Design of inverters for use with induction motors requires a knowledge of the impedances of the machine to harmonics of the supply frequency. This paper presents an harmonic equivalent circuit and describes how its parameters may be obtained. It shows that, when the harmonic current magnitudes and relative phase angles are such as to produce phase modulation of the rotating field, the harmonic magnetizing inductance is equal to the fundamental saturated magnetizing inductance. When the current harmonics produce amplitude modulation of the rotating field, the harmonic magnetizing inductance is equal to the incremental slope of the fundamental magnetization curve at the point of operation. Measurements made with phase currents having controllable harmonic content are presented to corroborate the theory.

Harmonics and 3-phase thyristor drives

As industry employs more a.c./d.c. thyristor drives, the effect and magnitude of harmonic currents injected into the supply become more significant. However, many people not conversant with convertor system design do not understand how the equipment they are using generates harmonics