Alexandre B. Nassif

An Investigation on the Selection of Filter Topologies for Passive Filter Applications

Passive filters have been a very effective solution for power system harmonic mitigation. These filters have several topologies that give different frequency response characteristics. The current industry practice is to combine filters of different topologies to achieve a certain harmonic filtering goal. However, there is a lack of information on how to select different filter topologies. This decision is based on the experience of present filter designers. The goal of this paper is to investigate the filter topology selection issue. It presents our research results on the effectiveness and costs of various filter topologies for harmonic mitigation. The research results show that the association of three single-tuned filters is a very appropriate solution for most typical harmonic problems.

A Frequency-Domain Harmonic Model for Compact Fluorescent Lamps

Compact fluorescent lamps (CFLs) are gaining widespread acceptance due to energy conservation concerns. The CFL is a significant harmonic source since its current total harmonic distortion can exceed 100%. Although each CFL consumes only a small amount of power, mass-deployed CFLs could become a significant harmonic source. This paper presents a frequency-domain harmonic model for the CFL. This model is suitable for assessing the collective impact of a large number of CFLs since it includes the impact of supply-voltage harmonics on the harmonic currents produced by the CFLs. The model is subsequently simplified and two variations are proposed. The model and its variations are verified by comparing their results with the measurements taken from various CFLs. Furthermore, the attenuation characteristics of CFLs are investigated. The results reveal the conditions in which the simplified models can be applied with acceptable errors.

An investigation on the harmonic attenuation effect of modern compact fluorescent lamps

In recent years, awareness of energy conservation and environmental protection has promoted the use of energy efficient home appliances. Compact fluorescent lamps (CFLs) are expected to replace incandescent bulbs as they consume comparatively less energy and their useful life is longer. However, compact fluorescent lamps absorb extremely distorted current waveforms, resulting in high current harmonic injections on the electrical grid. Like other electronic devices based on single-phase rectification, CFLs are susceptible to the attenuation effect. If this effect is not taken into consideration, the cumulative harmonic current produced by the lamps can be significantly overestimated and the results obtained using the current-source model can be too conservative to be useful. This paper focuses on the harmonic characterization of modern compact fluorescent lamps. It presents experimental analysis investigation on the attenuation effect of CFLs, which is caused by the influence of distorted supply voltage on nonlinear load harmonic current injections.

Characterizing the Harmonic Attenuation Effect of Compact Fluorescent Lamps

This letter proposes an index called the equivalent lamp index to characterize the harmonic attenuation effect of the compact fluorescent lamps (CFLs). The index can be used to facilitate the assessment of the collective harmonic impact of multiple CFLs. The proposed index is given in the form of a family of curves established by experimental studies. The implication of the results is that when N CFLs are installed in a house, the actual harmonic current injected by that house to the power system is equivalent to M lamps modeled as ideal current sources, where M is smaller than N.

Flicker source identification by interharmonic power direction

Flicker is an important power quality index and is currently receiving increasing concern. The identification of the flicker source is necessary for the utility company to find who is the responsible for measured flicker, and so to act accordingly to improve power quality. Nevertheless, not much work has been done in this field. This paper analyzes the correlation between flicker and interharmonics, and proposes a novel method based on interharmonic power direction for flicker source identification. Simulations and field tests are provided for some typical flicker sources, such as an induction motor and a variable frequency drive (VFD). The results validate the effectiveness of the proposed method

A V-I slope-based method for flicker source detection

Flicker can be defined as the impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time. The flicker source detection is an important step in the power quality evaluation process as only after the information about the disturbance location is available, the diagnosis and troubleshooting can be accordingly carried out. This paper is concerned about the flicker source detection subject. The problem is described, the method is proposed and shown to be comprehensive enough to diagnose stationary and random flicker. Analytical proof, a simulation and a practical case assembled in laboratory are presented to show the validity of the method. Its principle is based in the relationship between voltage and current rms values, and it is possible to show that the behavior of this relationship permits one to draw conclusions about the flicker source.

Impacts of FACTS controllers on damping power systems low frequency electromechanical oscillations

This paper presents a study comparing the effects of four flexible ac transmission systems (FACTS) controllers, the static var compensator (SVC), the static synchronous compensator (STATCOM), the thyristor controlled series compensator (TCSC) and the static synchronous series compensator (SSSC) on power systems small-signal angle stability. This investigation is carried out for a single generator connected to an infinite bus via a loss-less transmission line. The study is based on the investigation of the critical eigenvalues of the power system linearized model in the framework of the dynamic bifurcation theory. The presented simulation results allow a comparative analysis of the effects of these four controllers and reveal that the SSSC exhibits the best effectiveness on damping power systems low frequency electromechanical oscillations.

An Impedance-Based Approach for Identifying Interharmonic Sources

This paper proposes a new method for identifying the interharmonic source location in power systems. The method is based on the interharmonic impedances measured at the metering points, and is inspired by the fact that the impedance of interharmonic-generating loads at that frequency is much higher than that of the utility system. This method represents an improvement over the traditional power-direction method, as the new method is more robust and less prone to erroneous identification. The issues associated with data reliability are addressed, and a set of data reliability criteria is presented. The effectiveness of the new method has been verified through simulation studies and field measurements.

Modeling, measurement and mitigation of power system harmonics

Power system harmonics and interharmonics are power quality concerns that have received a great deal of attention in recent years. These phenomena can have several adverse effects on power system operation. The main harmonic and interharmonic sources are devices based on power electronics. An emerging class of harmonic sources is comprised of power electronic-based home appliances. These appliances are dispersed throughout the low-voltage distribution system, and their collective impact can result in unacceptable levels of voltage distortion. The characterization of home appliances based on their harmonic currents is an important step toward understanding the impact of these devices. This thesis presents an evaluation of the relative severity of the harmonic currents from these devices, and the impact of the disparity of the harmonic current phase angles. Typically, the voltage supplied to each harmonic source is already distorted. This distortion causes a change of the harmonic current magnitudes (traditionally referred to as the attenuation effect). Common harmonic analysis methods cannot take this variation into account because they use a typical harmonic current source model specified by a supply voltage having little or no distortion. This thesis characterizes the harmonic attenuation effect of power electronic-based appliances. One of the findings is that harmonic amplification, rather than attenuation, can occur under credible voltage conditions. This finding had not been made previously. In order to include the harmonic attenuation/amplification in appliance modeling, a measurement-based harmonic modeling technique is proposed. One of the most economic and effective ways to mitigate harmonics in power systems is through the use of harmonic shunt passive filters. These filters can be of many topologies. Selecting these topologies is a task that, today, depends on the experience and judgment of the filter designer. An investigation is carried out on the common filter topologies, and the most cost-effective topologies for mitigating harmonics are identified. As many of the larger harmonic loads also generate interharmonics, interharmonics have become prevalent in todays medium-voltage distribution system. Mitigation cannot be carried out until the interharmonic-source location is known. A method for interharmonic source determination is proposed and then verified through simulation and field measurement studies.

H 2 Norm-Oriented STATCOM Tuning for Damping Power System Oscillations

This work is mainly concerned with the effects of the static synchronous compensator (STATCOM), a flexible AC transmission system (FACTS) controller, on small-signal power system angle stability. This investigation is carried out for both inter-area and local oscillations mode. The study is based on the investigation of the eigenvalues of the linearized power system models in the framework of dynamic bifurcation theory. The tuning method of the STATCOM gains aiming the H 2 norm minimization is briefly explained, and the presented simulation results are sufficient to provide a comprehensive analysis of the effects of this controller for damping power systems low frequency electromechanical oscillations.