Harmonic Related Problems Research Articles

NEW ITERATIVE SCHEMES FOR GENERAL HARMONIC VARIATIONAL INEQUALITIES

Some new classes of general harmonic convex sets and convex functions are introduced and studied in this paper. The optimality criteria of the differentiable general harmonic functions is characterized by the general harmonic variational inequalities. Special cases are also pointed out as applications of the new concepts. Auxiliary principle technique involving an arbitrary operator is applied to suggest and analysis several inertial type methods are suggested. Convergence criteria is investigated of the proposed methods under weaker conditions. The results obtained in this paper may inspire further research along with implementable numerical methods for solving the general harmonic variational inequalities and related optimization problems.

Some New Classes of Harmonic Hemivariational Inequalities

Some new classes of harmonic hemivariational inequalities are introduced and investigated in this paper. It has been shown that the optimality conditions of the sum of two harmonic convex functions can be characterized by the harmonic hemivariational inequalities. Several special cases such as harmonic complementarity problems and related harmonic problems are discussed. The auxiliary principle technique is applied to suggest and analyze some iterative schemes for harmonic hemivariational inequalities. We prove the convergence of these iterative methods under some weak conditions. Our method of proof of the convergence criteria is simple compared to other techniques. Results obtained in this paper continue to hold for new and known classes of harmonic variational inequalities and related optimization problems. The ideas and techniques of this paper may inspire further research in various branches of pure and applied sciences.

A Comparative Study on Power System Harmonics for Offshore Plants

The field of power system harmonics has been receiving a great deal of attention recently. This is primarily due to the fact that non-linear (or harmonic-producing) loads comprise an ever-increasing portion of what is handled at a typical industrial plant. The incidence rate of harmonic-related problems is low, but awareness of harmonic issues can still help increase offshore power plant system reliability. On the rare occasion that harmonics become a problem, this is either due to the magnitude of harmonics produced or power system resonance. This harmonic study used an electrical configuration for the offloading scenario of a Floating LNG (FLNG) unit, considering power load. This electrical network configuration is visible in the electrical network load flow study part of the project. This study has been carried out to evaluate the performance of an electric power system, focusing on the harmonic efficiency of an electrically driven motor system to ensure offshore plant safety. In addition, the design part of this study analyzed the electric power system of an FLNG unit to improve the safety of operation and maintenance.

Influence of phasor adjustment of harmonic sources on the allowable penetration level of distributed generation

Harmonic distortion caused by increasing size of inverter-based distributed generation (DG) can give rise to power quality problems in distribution power networks. Therefore, it is very important to determine allowable DG penetration level by considering the harmonic related problems. In this study, an optimization methodology is proposed for maximizing the penetration level of DG while minimizing harmonic distortions considering different load profiles. The methodology is based on updating the voltage magnitude and angle at point of common coupling depending on the size of DG to be utilized in the harmonic power flow modeling. The harmonic parameters are determined by using decoupled harmonic power flow method, in which the harmonic source modeling with harmonic current spectrum angle adjustment is embedded, while the nonlinear loads and inverter-based DGs are connected to the distribution power network. The allowable penetration level of DGs is determined based on power quality constraints including total harmonic voltage distortion, individual harmonic voltage distortion, and RMS bus voltage limits in the optimization framework. Fuzzy-c means clustering method is also applied to decrease the computational effort of the optimization process in the long-term load profile. The effectiveness of the proposed method is illustrated on the IEEE 33-bus radial distribution network for different scenarios.

Analysing of Harmonics Affecting the Energy Quality in Opium Alkaloids Plant's Power System

The quality of energy has been defined to control harmonics caused by non-linear loads and international standards were brought to overcome the harmonic related problems. In determining the power quality, parameters like current-voltage harmonic, transient, flicker, current and voltage imbalance between phases, K factor are examined according to these international standards. The biggest disadvantage of harmonics is that they do not affect the power quality over an individual network but also affect the entire energy system primarily neighbouring facilities. Therefore, the energy system of Opium Alkaloids Plant was examined by using measurements information of current and voltage harmonics affecting the energy quality. And, it has been determined that the harmonics have a negative impact on energy quality. According to these findings, it has been proposed to install a well-designed filter for elimination of harmonics. Besides, it has been emphasised that new hardwares and devices should be chosen to support this harmonic filtering system in the future.

A shunt active power filter adopting Lyapunov control approach

The rising price of oil, the reduction of cheap energy sources, and growing global environmental concerns have drawn greater attention to suppressing harmonicrelated problems resulting from nonlinear load pollution like diode rectifiers in traditional ac drives. To solve these problems, the use of active power filters (APFs) to mitigate harmonic proliferation has drawn much attention in recent years. Most studies only show control block diagrams with classic control methods. These control schemes look very attractive for their simplicity and ease of implementation, but lack in presenting an adequate compensation algorithm or stability analysis of active power filters. In this paper, a Lyapunov‐based current control method for an APF system is proposed. The control law is derived from directly applying the Lyapunov stability theory to the integral controller, so that the closed‐loop systems possess better harmonic current elimination. The proposed APF controller forces the supply current to be sinusoidal, with low current harmonics, and to be in phase with the line voltage. Computer simulations and experimental results obtained from a laboratory system developed in this paper verify the viability and effectiveness of the full‐digital‐controlled active filter.

Application of IGCT in High-Power Rectifiers

This paper investigates the possibility of applying an integrated gate commutated thyristor (IGCT) into high-current high-power rectifier systems. The optimal power converter topology that fully utilizes the functionality of the IGCT is proposed. The proposed power converter consists of a front-end diode rectifier and three-level step-down dc/dc converter. As compared to two-level operation, half the input dc voltage and twice the effective switching frequency of three-level operation can provide a wider operation range of continuous conduction mode resulting in a higher average output current of less ripple size than two-level case. A laboratory prototype of a 5-kA 3.1-MW rectifier has been simulated and tested to confirm the feasibility of the IGCT in the proposed power converter topology. The proposed solution generates a relatively smooth output dc current with less contents of high-frequency harmonics, thereby avoiding the high-frequency harmonic-related problems found in insulated-gate-bipolar-transistors-based high-current rectifiers. The IGCT would play a significant role to improve the cost-effective performance and reliability in low- and medium-ranged high-current high-power rectifier systems.

Space and time harmonics related problems and their mitigation for position and speed sensorless slip-ring induction motor drives applications

There have been renewed interests in slip-ring induction machines due to their increasing use in both grid connected and stand-alone wind power generation schemes. Despite the squirrel cage induction generators’ advantages of being brushless, low-cost, needing less maintenance and having inherent overload protection, the biggest advantage of variable-speed wound rotor induction machines is in its doubled energy capture. Also in high power induction motor drives such as static Kramer drives or static Scherbius drives use of wound rotor induction motors is a must. Thus it becomes necessary to measure the speed of the machine for closed loop control for such high performance drives. Recently, a sensorless position and speed estimation scheme was proposed for wound rotor wind power generator. In this paper, the limitation of the scheme caused by space and time harmonics have been investigated. Simulation results have been presented to explain the mechanism of the space and time harmonics caused distortion of current. Experimental results showing the deterioration of speed detection scheme at light load for a slip-ring induction motor have been presented. Finally, improvements have been applied experimentally to obtain better speed estimation.

Partial regularity for harmonic maps and related problems

AbstractVia gauge theory, we give a new proof of partial regularity for harmonic maps in dimensionsm≥ 3 into arbitrary targets. This proof avoids the use of adapted frames and permits us to consider targets of “minimal”C2‐regularity. The proof we present extends to a large class of elliptic systems. © 2007 Wiley Periodicals, Inc.

Power monitoring and harmonic problems in the modern building

Personal computers are responsible for generating the majority of harmonic-related problems in the modern building. It is becoming increasingly problematic in commercial buildings, especially where large quantities of computers are present. The problems caused by personal computers can now be quantified by the use of digital power monitoring systems. Current and voltage values are no longer adequate to understand the characteristics of electrical loads, as it is important to understand the complexity of the load. Therefore, a graphical picture of the load can reveal move answers to apparently complex problems.

Developing a harmonics education facility in a power system simulator for power engineering education

This paper describes a newly installed harmonics education facility in detail to teach students about harmonics related problems in a power system. A nonlinear load, which produces harmonic currents, and a harmonic filter, which is a mitigation facility, are merged into an existing power system simulator for advanced power engineering education. The nonlinear load is a widely used three-phase, 6-pulse controlled rectifier. The filter bank is designed to eliminate the characteristic harmonic currents. This paper also shows the resonant condition caused by shunt capacitors which are usually used for power factor correction. Several suggested experiments are given to teach students about harmonics related problems including harmonic sources, measurement, resonance, limitation, and mitigation. The harmonics education facility greatly extends and promotes the performance of the power system simulator.

Developing utility harmonic regulations based on IEEE STD 519-B.C, Hydro's approach

Application of existing harmonic standards to an electric utility power system involves many practical issues. They include designing an efficient procedure to evaluate the acceptability of an installation, specifying rational conditions to perform evaluation, and defining equitable limits to check acceptability. In this paper, how BC Hydro addresses these problems in its recently developed harmonic guide is described. The purpose is to share BC Hydro's experiences with other electric utilities on the development of practical regulations to prevent harmonic-related problems. >

Computer based harmonic simulation and testing for directional-overcurrent relays

This paper discusses a unique simulation method to study harmonics using a computer based three-phase harmonic source, programmable three-phase voltage and current amplifiers, a digital-to-analog interface board, and a computer program. This paper can be useful for educational purposes and in research facilities to teach and perform research on harmonic related problems. This simulation method has been used in the Center for Energy Studies at Wichita State University for the past three years in many research projects. One application of this method was to test the performance of electromechanical and microprocessor protective relays. By using this simulation method, extensive experiments have been performed in which the relays were subjected to a matrix of distortion frequencies, magnitudes, and phases. The results of testing one relay are discussed, and suggestions for the application of the relay are given.

Effects of harmonic sources on customer loads

This paper provides practical guidelines that would help power system engineers analyze certain harmonic related problems heuristically. The interaction between a given harmonic source and any other harmonic source(s) on line is studied. Two important factors pertaining to the injected harmonic currents, harmonic order and phase, are considered in the evaluation of the effects of one harmonic load on another. A harmonic load flow program based on the bus admittance matrix method was developed for purposes of this study. While this study suggests the use of a quantitative metric, the real power P, to correctly determine the effects of one customer on another, it is obvious that a study like this has immediate applications which include the design of power factor correction schemes, filter design and power system planning.

Computer based harmonic simulation and testing for protective relays

This paper discusses a unique simulation method to study harmonics using a computer-based three phase harmonics source, programmable three phase voltage and current amplifiers, a digital-to-analog interface board, and a computer program. This paper can be useful for educational purposes and in research facilities to teach and perform research on harmonic related problems. This simulation method has been used in the center for energy studies for the past 3 yr in many research projects.

Cumulant-based approach to harmonic retrieval and related problems

A frequently encountered problem in signal processing is that of estimating the frequencies and amplitudes of harmonics observed in additive colored Gaussian noise. In practice, the observed signals are contaminated with spatially and temporally colored noise of unknown power spectral density. A cumulant-based approach to these problems is proposed. The cumulants of complex processes are defined, and it is shown that specific 1-D slices of the fourth-order cumulant of the noisy signal for the direction of arrival (DOA) and retrieval of harmonics in noise (RHN) problems are identical to the autocorrelation of a related noiseless signal. Hence correlation-based high-resolution methods may be used with fourth-order cumulants as well. The effectiveness of the proposed methods is demonstrated through standard simulation examples.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer Based Harmonic Generator Facilities to Study Harmonic Related Problems

Unique educational and research facilities for teaching and performing research on harmonic-related problems in power systems are discussed. The facilities consist mainly of computer-based three-phase harmonic generators, a data acquisition system to process the data digitally, and a computer control system to control the harmonics levels. Application of the system in teaching, studying and investigating appropriate solutions to harmonic-related problems is the primary objective. The assistance of power industry representatives in formulating the different problems is discussed. A brief summary of six teaching projects and concepts of the computer-based system are included. >

Computer based harmonic generator facilities to study harmonic related problems

Unique educational and research facilities for teaching and performing research on harmonic-related problems in power systems are discussed. The facilities consist mainly of computer-based three-phase harmonic generators, a data acquisition system to process the data digitally, and a computer control system to control the harmonics levels. Application of the system in teaching, studying and investigating appropriate solutions to harmonic-related problems is the primary objective. The assistance of power industry representatives in formulating the different problems is discussed. A brief summary of six teaching projects and concepts of the computer-based system are included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Benefits of an Automated On-Line Harmonic Measurement System

Any industrial plant that has a considerable amount of rectification may experience harmonic-related problems (e.g., solid-state control circuit malfunctioning, communication noise, etc.). The application of power-factor correction capacitor banks to such a system will generally increase the likelihood of such problems occurring. To properly identify the cause of such problems and, in some cases, recommend solutions, an on-line analysis of the system may be necessary. This usually involves a harmonic analysis of the current or voltage waveforms observed in the electrical system. A description of an automated on-line harmonic measurement system used by the authors will be presented along with the advantages of using such a system. In addition, two specific examples showing the application of an automated on-line harmonic measurement system will also be presented.