Multiple Harmonic Sources Research Articles

Methodology of calculating harmonic distortion from multiple traction loads

This paper presents a methodology for studying and specifying incremental and aggregated harmonic distortion emission limits from multiple harmonic sources that are connected to the utility network in close proximity and/or electrically are close to each other. The methodology specifically concentrates on traction loads and includes the development of combined equivalent circuits for the harmonic sources for evaluating their impact on power quality. This methodology has been used successfully to represent an electrified traction load and can be extended and applied to the assessment of multiple embedded generators such as from PV solar or wind farms.

不平衡接続された単相分散型電源による三相系統の高調波電流抑制

As a result of the progress in renewable energy technologies, distributed generation (DG) with harmonic compensation capability has become an attractive topic. If photovoltaic (PV) systems have harmonic compensation functionality, they can help suppress the harmonic currents produced by multiple harmonic sources like energy-saving household appliances. This paper proposes harmonic circulate control, which is a harmonic suppression method that uses DG units. Using the proposed method, the current distortion in three-phase distribution grids can be suppressed by a smaller number of harmonic compensators than with conventional methods. In order to verify the validity of the proposed control strategy, experimental results using a laboratory system are presented.

Using Wavelet Hybrid Self-Organizing Feature Map Network for V-I Based Multiple Harmonic Sources Classification

This paper proposes a method using non-linear voltage-current characteristics for multiple harmonic sources classification using wavelet hybrid neural network (WHNN). Typical voltage-current characteristics of harmonic sources are non-linear closed curves in the time-domain, referring to the converters, reactors, and non-linear loads. The hybrid neural network is a two-subnetwork architecture, consisting of wavelet layer and a self-organizing feature map (SOFM) network connected in cascade. The effectiveness of the proposed method is demonstrated by numerical tests. The results of multiple harmonic sources show the computational efficiency and accurate classification.

Phasor-based assessment for harmonic sources in distribution networks

Phasor-based interdependencies of multiple harmonic sources, especially Distributed Energy Resources, on distribution networks are analyzed in this paper. A new index, Phasor Harmonic Index (IPH), is proposed by the authors. IPH considers both harmonic source magnitude and phase angle for different harmonic orders. Other commonly used harmonic indices are based solely on magnitude of waveforms. A very detailed model of a distribution network is used in the harmonic assessment. With the help of the detailed distribution network model, the phase couplings and the phase balancing impacts on harmonic propagation between three phases are investigated. Moreover, effects of harmonic source phase angle deviations are analyzed at both the customer side and the substation side. This paper investigates the importance of phase angles in harmonic assessment and how distribution network characteristics can be analyzed appropriately with phasor-based harmonic studies. In addition to device level harmonics, system level harmonic propagation need to be considered.

Identification of Multiple Harmonic Sources in Power System Using Optimally Placed Voltage Measurement Devices

This paper presents an effective methodology to identify the multiple harmonic sources along with their harmonic injection levels in a power system using optimally placed harmonic measurement devices (HMDs). Binary particle swarm optimization is used to find the optimal locations of HMDs to collect harmonic data. The proposed harmonic identification approach is based on the direction of harmonic power flow at system nodes to categorize and rank the suspected buses. The method is simple and can be used for locating the multiple harmonic sources in the presence of load modeling errors and measurement errors. The effectiveness of the proposed methodology is tested on 18-bus radial as well as nonradial distribution systems under different scenarios.

Comparative in-flight and wind tunnel investigation of the development of natural and controlled disturbances in the laminar boundary layer of an airfoil

This paper describes in-flight and wind tunnel research into laminar-turbulent transition. Measurements were carried out with a laminar wing glove for a glider (Twin II Grob G103), which could also be used in the large laminar wind tunnel at the Institute for Aerodynamics and Gasdynamics in Stuttgart. The central aspect of the investigation was the survey of the temporal–spatial development and propagation of natural as well as controlled generated waves. For the experiments performed, varied sensor arrays were used which allowed the two-dimensional acquisition of flow information on the glove (surface hot-wire and piezo foil sensors). Thus the amplification and the spatial distribution of the disturbances could be measured and compared in flight as well as in the wind tunnel, beginning with the very early linear amplification stage to the early non-linear stage of transition. For the investigation of controlled transition, multiple spanwise adjacent harmonic point sources were used which were operated independently.

Efficient approach to characterising harmonic currents generated by a cluster of three-phase AC∕DC converters

An efficient approach to characterising harmonic currents generated by a cluster of parallel-operated AC/DC converters in the steady state is presented. The approach is carried out in the time domain and the interactions between converters are considered. In calculating harmonic currents generated by a single converter, the Poincaré map-based approach is applied to increase the computational efficiency. A solution procedure that is sequentially solving a single-converter problem with detailed model in the time domain, while the others are fixed as equivalent AC current sources, is proposed to find the overall source-side harmonic currents. The computed AC-side harmonic components of each converter current are then extracted via FFT. Solutions obtained by the proposed method are compared with those obtained by using a brute-force time-domain simulation tool, Simulink. It is shown that the AC-side harmonic currents determined by the proposed approach agree well with those obtained by the time-domain simulation tool, but the solution time is significantly reduced. Therefore, the proposed approach is useful for quantifying harmonic currents generated by a cluster of AC/DC converters and to facilitate the harmonic mitigation implementations, such as passive and active harmonic filter designs, for complying with harmonic standards such as IEC 61000-3-4 and IEEE-519. In addition, the proposed approach is suitable for characterising harmonic currents generated by other types of power-electronic devices, such as AC and/or DC drives, operated in parallel simultaneously. The solution algorithm can also be integrated into a harmonic power flow program for penetration studies to provide a fast quantification of the impact of multiple harmonic sources on the power system.

Multiple Harmonic Source Detection and Equipment Identification With Cascade Correlation Network

This paper presents the design of a harmonic source detection system with a cascade correlation network (CCN). Current-injection-based harmonic power flow was used to calculate bus voltages and total harmonic distortion (THD). THD of voltages is used as indices for meter placement in the power network. At metering buses, it shows that the harmonic components of voltages under various loads would form particular patterns in the frequency domain, and can be used to create training examples for CCN. Good meter planning is helpful to reduce the number of meters and training examples. With an IEEE 14-bus power system, computer simulations were conducted to show the effectiveness of the proposed system.

Modal Analysis of Industrial System Harmonics Using the s-Domain Approach

This paper describes the use of modal analysis of s-domain network models in the solution of harmonic distortion problems of industrial systems. Modal analysis involves the computation of the system poles, transfer function zeros as well as their sensitivities to changes in network parameters. A new modal sensitivity coefficient and a new modal observability index are introduced. These new coefficient and index are used to solve harmonic problems in a practical industrial system having multiple harmonic sources. The results obtained are believed to demonstrate the practical value of the proposed method.

Determination of location of multiple harmonic sources in a power system

In this paper, a methodology for accurate determination of multiple harmonic sources in a power system is presented. In the proposed methodology, assuming that no prior information regarding the possible locations of the harmonic sources in the system is available, the problem of determination of location of harmonic sources is solved in two stages. In the first stage, weighted least square estimation technique is used to find possible candidate buses (where the harmonic sources may be connected) among the system buses. In the second stage, using the concept of Euclidean norm, the exact buses (where the harmonic sources are present) among the possible candidate buses are obtained. To demonstrate the effectiveness of the proposed technique, the IEEE-14 and IEEE-30 bus test systems are used.

A simple method for incorporating transformer phase-shifts in a sparsity-oriented single-phase harmonic penetration algorithm

Abstract Transformer phase-shifts can play an important role in the study of harmonic penetration within a power system. The incorporation of these quantities in the conventional Linear Frequency Domain Analysis (LFDA) technique, which is widely used for large-scale power systems harmonic analysis, leads to the problem of unnecessary additional computation time and memory requirements. The problem is sought to be due to the asymmetry in the system admittance matrix when the transformer phase-shifts are included in the algorithm. A new method is described that solves the problem by retaining the system admittance matrix symmetrical throughout the computation process, thus enabling the use of efficient symmetrical sparsity techniques for solving the system unknowns. The validity of the method is substantiated by comparing our results with the results of conventional LFDA technique for a small 4-bus system and the IEEE 40-bus industrial system. The study of the results also demonstrates the importance of transformer phase-shifts in determining the correct harmonic distortion level in a system with multiple harmonic sources.

Time-varying harmonics. II. Harmonic summation and propagation

This paper represents the second part of a two-part article reviewing the state of the art of probabilistic aspects of harmonics in electric power systems. It includes tools for calculating probabilities of rectangular and phasor components of individual as well as multiple harmonic sources. A procedure for determining the statistical distribution of voltages resulting from dispersed and random current sources is reviewed. Some applications of statistical representation of harmonics are also discussed.

Time-Varying Harmonics: Part II-Harmonic Summation and Propagation

This paper represents the second part of a two-part article reviewing the state-of-the-art of probabilistic aspects of harmonics in electric power systems. It includes tools for calculating probabilities of rectangular and phasor components of individual as well as multiple harmonic sources. A procedure for determining the statistical distribution of voltages resulting from dispersed and random current sources is reviewed. Some applications of statistical representation of harmonics are also discussed.

Application of algorithms and artificial-intelligence approach for locating multiple harmonics in distribution systems

A new method is proposed for locating multiple harmonic sources in distribution systems. The proposed method first determines the proper locations for metering measurement using fuzzy clustering. Next, an artificial neural network based on the back-propagation approach is used to identify the most likely location for multiple harmonic sources. A set of systematic algorithmic steps is developed until all harmonic locations are identified. The simulation results for an 18-busbar system show that the proposed method is very efficient in locating the multiple harmonics in a distribution system.

Experiences in the investigation of harmonic penetrations: case studies

This paper discusses experiences in the analysis of harmonic penetrations. The discussion includes the following considerations: (1) a small linear load bus without a harmonic source is more likely to render the voltage distortion therein the most severe; (2) the variation of linear loads at the harmonic source bus will lead to a change in harmonic voltages around the system; (3) multiple harmonic sources may decrease the impact of voltage distortions; (4) there exists an optimal compensation to reduce harmonics for one special load pattern and network configuration; improper compensation will result in severe voltage distortions; and (5) an improper estimation of shunt admittance at the swing bus will render an insignificant harmonic power flow solution. Linear algebra is used to provide a mathematical background for interpreting the above phenomena. Two power systems are used to serve as samples to illustrate the numerical results.

Modelling the interaction of multiple small harmonic current sources in an isolated power distribution system

Modelling the interaction of multiple small harmonic current sources in an isolated power distribution system

Optimum distribution system harmonic filter design using a genetic algorithm

This paper presents a technique for the anticipation of harmonic distortion as well as selection and placement of filters on distribution systems which have multiple harmonic sources and constantly changing characteristics caused by compensating capacitor switching and load impedance changes. The purpose is to predict and reduce harmonic voltage distortion for all buses in the system to comply with IEEE Standard 519. A genetic algorithm is used in this technique and shows itself an effective tool in optimizing a multivariable objective function.

Predicting voltage distortion in a system with multiple random harmonic sources

A method for statistically describing power system harmonic voltages in terms of the parameters of the harmonic current sources is presented. It is shown that for a large enough number of sources, a complete probabilistic characterization of the harmonic voltages can be found in terms of the second order moments of each current phasor's rectangular components. The method is tested on an existing distribution system by using both simulation and field measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distribution system harmonic worst case design using a genetic algorithm

IEEE Standard 519 suggests that utility distribution buses should provide a voltage harmonic distortion level of less than 5% provided customers on the distribution feeder limit their load harmonic current injections to a prescribed level. It is desirable to anticipate voltage harmonics on distribution lines that have constantly changing characteristics due to line switching, capacitor switching, and load impedance changes, and are also subject to multiple harmonic sources with changing magnitudes and spectra. A technique is outlined for finding worst case combinations of these distribution system variables in order to design solutions to potential harmonic excesses. The number of harmonic source-load combinations makes it desirable to use a genetic algorithm for this purpose. >

Optimum filter design for distribution feeders with multiple harmonic sources

A procedure is developed for selection and placement of optimum filters on distribution feeders that have distributed and balanced or unbalanced harmonic sources and variable compensating capacitors. The objective is to minimize voltage harmonic distortion for all buses on the feeder. Analysis of an example feeder system shows that optimum filters chosen and placed in this manner may produce results superior to the filter designed to reduce distortion at a single bus and other multibus filter design procedures.