1,011 research outputs found
New trends in active filters for improving power quality
No full textSince their basic compensation principles were proposed around 1970, active filters have been studied by many researchers and engineers aiming to put them into practical applications. Shunt active filters for harmonic compensation with or without reactive power compensation, flicker compensation or voltage regulation have been put on a commercial base in Japan, and their rating or capacity has ranged from 50 kVA to 60 MVA at present. In near future, the term of active filters will cover a much wider sense than that of active filters in the 1970s did. The function of active filters will be expanded from voltage flicker compensation or voltage regulation into power quality improvement for power distribution systems as the capacity of active filters becomes larger. This paper describes present states of the active filters based on state-of-the-art power electronics technology, and their future prospects toward the 21st century, including the personal view and expectation of the author</p
INTERPRETACIÓN DE LA POTENCIA ELECTRICA TRIFÁSICA BAJO CONDICIONES NO SINUSOIDALES BASADO EN LA TEORIA DE AKAGI-NABAE.
No full textEn este articulo se presenta la formulación teorica de la Potencia Activa y Reactiva instantanea según Akagi-Nabae y se plantea una interpretación física de esta
Y. Ishii, Ae. Nidhi, O. Akagi, W. Aroonrut, E. Noriko : A Glossarial Index of the Sukhothai Inscriptions
No full textPou-Lewitz. Y. Ishii, Ae. Nidhi, O. Akagi, W. Aroonrut, E. Noriko : A Glossarial Index of the Sukhothai Inscriptions. In: Bulletin de l'Ecole française d'Extrême-Orient. Tome 78, 1991. pp. 349-351
Suppression of common-mode voltage in a PWM rectifier/inverter system
No full textThis paper proposes a PWM rectifier/inverter system capable of suppressing not only supply harmonic currents but also electromagnetic interference (EMI). An active common-noise canceler (ACC) developed for this system is characterized by sophisticated connection of a common-mode transformer which can compensate for common-mode voltages produced by both PWM rectifier and inverter. As a result, the size of the common-mode transformer can be reduced to 1/3, compared with the previously proposed ACC. A prototype PWM rectifier/inverter system (2.2 kW) has been implemented and tested. Some experimental results show reduction characteristics of the supply harmonic current and EMI</p
Control óptimo de un filtro activo para la reducción de armónicos en la red eléctrica de distribución, utilizando la teoría de AKAGI.
No full textThe present research has as main objective to review the harmonic correction of an electrical
distribution system to analyze the implementation of an algorithm based on the Non-Linear
Optimization and Akagi theory, which deals with instantaneous active and reactive power
where the currents and voltages of a Three-phase three-wire system were expressed vectorially
through the use of the Clarke and Park transform while the other theory is based on getting an
optimal lambda that formulate the Non-Linear Optimization model and applying the Lagrange
theory, using conditions of (KKT). This research was carried out by a base model desing of a
simulated electrical system in SIMULINK program implementing an active power filter that
has as its main function the harmonics reduction in the electric power distribution networks.
The simulations were carried out to give optimal results when the active power filter was
applied, correcting notoriously the harmonics produced by the different loads that cause
disturbances to the electric network.La presente investigación tiene como objetivo estudiar la corrección de armónicos de un sistema
eléctrico de distribución para analizar la implementación de un algoritmo basado en la
Optimización No Lineal y Teoría de Akagi, cual trata sobre la potencia activa y reactiva
instantánea donde las corrientes y los voltajes de un sistema trifásico de tres hilos se expresaban
vectorialmente mediante el uso de la transformada de Clarke y Park mientras la otra teoría se
basa en obtener un lambda optimo formulando el modelo de optimización no lineal y aplicando
la teoría del Lagrange, aplicando las condiciones de (KKT). Este estudio se realizó diseñando
un modelo base de un sistema eléctrico simulado en el programa SIMULINK implementando
al sistema un filtro activo de potencia que tiene como principal función la reducción de los
armónicos en las redes de distribución de energía eléctrica. Las simulaciones realizadas dan
resultados óptimos al implementar el filtro activo de potencia corrigiendo de manera notoria los
armónicos producidos por las diferentes cargas que ocasionan perturbaciones a la red eléctrica
A hybrid active filter for damping of harmonic resonance in industrial power systems
No full textThis paper proposes a hybrid active filter for damping of harmonic resonance in industrial power systems. The hybrid filter consists of a small-rated active filter and a 5th tuned passive filter. The active filter is characterized by detecting the 5th harmonic current flowing into the passive filter. It is controlled in such a way as to behave as a negative or positive resistor by adjusting a feedback gain from a negative to positive value, and vice versa. The negative resistor presented by the active filter cancels a positive resistor inherent in the passive filter, so that the hybrid filter acts as an ideal passive filter with infinite quality factor. This significantly improves damping the harmonic resonance, compared with the passive filter used alone. Moreover, the active filter acts as a positive resistor to prevent an excessive harmonic current from flowing into the passive filter. Experimental results obtained from a 20 kW laboratory model verify the viability and effectiveness of the hybrid active filter proposed in this paper </p
Two cases of malignant glaucoma unresolved by pars plana vitrectomy
No full textYoshikatsu Hosoda, Tadamichi Akagi, Nagahisa YoshimuraDepartment of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, Kyoto, JapanAbstract: Malignant glaucoma, which is characterized by a shallow or flat anterior chamber with high intraocular pressure, can usually be resolved by pars plana vitrectomy with anterior hyaloidectomy. We describe two cases in which malignant glaucoma was refractory to conventional treatment and complete vitrectomy. Case one an 88-year-old woman with pseudoexfoliation glaucoma underwent trabeculotomy and subsequently developed malignant glaucoma. Four months after transient recovery by pars plana vitrectomy, the malignant glaucoma recurred. She underwent peripheral iridectomy and local zonulectomy with successful control of her intraocular pressure. In case two, an 85-year-old man had a history of pseudoexfoliation glaucoma. Seven months after phacoemulsification and intraocular lens implantation, he developed malignant glaucoma that was refractory to pars plana vitrectomy. He underwent peripheral iridectomy, goniosynechialysis and trabectome surgery resulting in the successful control of his intraocular pressure. In rare cases of malignant glaucoma refractive to vitrectomy, peripheral iridectomy with or without local zonulectomy is a reasonable and minimally invasive surgical procedure.Keywords: malignant glaucoma, pars plana vitrectomy, peripheral iridectom
Relationships of the Duration from Onset and Macular Morphology with Metamorphopsia After Surgery for Macula-Off Rhegmatogenous Retinal Detachment
No full textTadanobu Sato,1 Tadamichi Akagi,1 Daigo Kobayashi,1 Akiko Anraku,2 Yohei Nozaki,1 Takumi Ando,1 Hiromitsu Yoshida,1 Hiroko Terashima,1 Hiruma Hasebe,2 Takeo Fukuchi1 1Division of Ophthalmology and Visual Science, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan; 2Department of Ophthalmology, Saiseikai Niigata Hospital, Niigata, JapanCorrespondence: Tadamichi Akagi, Division of Ophthalmology and Visual Science, Graduate School of Medical and Dental Sciences, Niigata University, 1-757, Asahimachi-dori, Chuo-ku, Niigata, 951-8510, Japan, Tel +81-25-227-2296, Fax: +81-25-227-0785, Email [email protected]: To investigate the relationships among postoperative metamorphopsia and postoperative macular morphological changes and the duration from the onset of visual field disturbance to surgery (DVD) in patients who underwent surgery for macula-off rhegmatogenous retinal detachment (RRD).Patients and Methods: We retrospectively reviewed 33 eyes of 33 patients who underwent pars plana vitrectomy (PPV) for macula-off RRD with known onset of symptoms of visual field disturbance at Niigata University Medical and Dental Hospital or Saiseikai Niigata Hospital and were followed up for at least 6 months postoperatively. Optical coherence tomography images of the macula obtained at 6 months postoperatively and DVD were analyzed, and the associations of the DVD with vertical metamorphopsia (vM) and horizontal metamorphopsia (hM) at 6 months postoperatively were evaluated using M-CHARTS.Results: vM was significantly correlated with the DVD and ellipsoid zone (EZ) disruption (P = 0.004 and P = 0.008, respectively), while hM was significantly correlated only with the DVD (P = 0.018). vM was significantly smaller in eyes with a DVD ≤ 7 days (0.34 ± 0.35)) than in eyes with a DVD ≥ 8 days (0.69 ± 0.32) (P = 0.005). In the multivariate analyses, postoperative vM was significantly associated with EZ disruption and the DVD (≤ 7 or ≥ 8 days) (P = 0.012 and P = 0.014, respectively).Conclusion: Metamorphopsia after PPV for macula off RRD was associated with the DVD and EZ disruption.Keywords: pars plana vitrectomy, optical coherence tomography, vision disorders, macula-off rhegmatogenous retinal detachmen
Control and analysis of a unified power flow controller
No full textThis paper presents a control scheme and comprehensive analysis for a unified power flow controller (UPFC) on the basis of theory, computer simulation and experiment. This developed theoretical analysis reveals that a conventional power feedback control scheme makes the UPFC induce power fluctuation in transient states. The conventional control scheme cannot attenuate the power fluctuation, and so the time constant of damping is independent of active and reactive power feedback gains integrated in its control circuit. This paper proposes an advanced control scheme which has the function of successfully damping out the power fluctuation. A UPFC rated at 10 kVA is designed and constructed, which is a combination of a series device consisting of three single-phase pulsewidth modulation (PWM) converters and a shunt device consisting of a three-phase diode rectifier. Although the dynamics of the shunt device are not included, it is possible to confirm and demonstrate the performance of the series device. Experimental results agree well with both analytical and simulated results and show viability and effectiveness of the proposed control scheme </p
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