A 2kW interleaved ZCS-FM boost rectifier digitally controlled by FPGA device

This paper presents a 2kW single-phase high power factor boost rectifier with four cells in interleave connection, operating in critical conduction mode, and employing a soft-switching technique, controlled by Field Programmable Gate Array (FPGA). The soft-switching technique Is based on zero-current-switching (ZCS) cells, providing ZC (zero-current) turn-on and ZCZV (zero-current-zero-voltage) turn-off for the active switches, and ZV (zero-voltage) turn-on and ZC (zero-current) turn-off for the boost diodes. The disadvantages related 'to reverse recovery effects of boost diodes operated in continuous conduction mode (additional losses, and electromagnetic interference (EMI) problems) are minimized, due to the operation in critical conduction mode. In addition, due to the Interleaving technique, the rectifer's features include the reduction in the input current ripple, the reduction in the output voltage ripple, the use of low stress devices, low volume for the EMI input filter, high input power factor (PF), and low total harmonic distortion (THD) In the input current, in compliance with the TEC61000-3-2 standards. The digital controller has been developed using a hardware description language (VHDL) and implemented using a XC2S200E-SpartanII-E/Xilinx FPGA device, performing a true critical conduction operation mode for four interleaved cells, and a closed-loop to provide the output voltage regulation, like as a pre-regulator rectifier. Experimental results are presented for a 2kW implemented prototype with four interleaved cells, 400V nominal output voltage and 220V(rms) nominal input voltage, in order to verify the feasibility and performance of the proposed digital control through the use of a FPGA device.

A novel HPF voltage source rectifier for variable speed refrigeration systems

A novel single-phase voltage source rectifier capable to achieve High-Power-Factor (HPF) for variable speed refrigeration system application, is proposed in this paper. The proposed system is composed by a single-phase high-power-factor boost rectifier, with two cells in interleave connection, operating in critical conduction mode, and employing a soft-switching technique, controlled by a Field Programmable Gate Array (FPGA), associated with a conventional three-phase IGBT bridge inverter (VSI - Voltage Source Inverter), controlled by a Digital Signal Processor (DSP). The soft-switching technique for the input stage is based on zero-current-switching (ZCS) cells. The rectifier's features include the reduction in the input current ripple, the reduction in the output voltage ripple, the use of low stress devices, low volume for the EMI input filter, high input power factor (PF), and low total harmonic distortion (THD) in the input current, in compliance with the EEC61000-3-2 standards. The digital controller for the output stage has been developed using a conventional voltage-frequency control (scalar V/f control), and a simplified stator oriented Vector control, in order to verify the feasibility and performance of the proposed digital controls for continuous temperature control applied at a refrigerator prototype.

A multi-cell variable frequency interleaved ZCS boost rectifier digitally controlled by FPGA

This paper presents a multi-cell single-phase high power factor boost rectifier in interleave connection, operating in critical conduction mode, employing a soft-switching technique, and controlled by Field Programmable Gate Array (FPGA). The soft-switching technique is based on zero-current-switching (ZCS) cells, providing ZC (zero-current) turn-on and ZCZV (zero-current-zero-voltage) turn-off for the active switches, and ZV (zero-vohage) turn-on and ZC (zero-current) turn-off for the boost diodes. The disadvantages related to reverse recovery effects of boost diodes operated in continuous conduction mode (additional losses, and electromagnetic interference (EMI) problems) are minimized, due to the operation in critical conduction mode. In addition, due to the interleaving technique, the rectifier's features include the reduction in the input current ripple, the reduction in the output voltage ripple, the use of low stress devices, low volume for the EMI input filter, high input power factor (PF), and low total harmonic distortion (THD) in the input current, in compliance with the IEC61000-3-2 standards. The digital controller has been developed using a hardware description language (VHDL) and implemented using a XC2S200E-SpartanII-E/Xilinx FPGA device, performing a true critical conduction operation mode for all interleaved cells, and a closed-loop to provide the output voltage regulation, like as a preregulator rectifier. Experimental results are presented for a implemented prototype with two and with four interleaved cells, 400V nominal output voltage and 220V(rms) nominal input voltage, in order to verify the feasibility and performance of the proposed digital control through the use of a FPGA device.

New family of zero-current-switching PWM converter

A new family of dc-to-dc pulse-width-modulated (PWM) converters is presented. These converters feature soft-commutation at zero-current (ZC) in the active switches. The new ZCS-PWM Boost and new ZCS-PWM Zeta converters, both based on the new ZCS-PWM soft-commutation cell proposed, are used as examples to illustrate the operation of the new family of converters.

Um novo sistema de refrigeração com controle de temperatura, compressor aberto, máquina de indução trifásica com velocidade variável e correção ativa do fator de potência do estágio de entrada

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparação de aluminas porosas hierarquicamente estruturadas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Pré-regulador retificador entrelaçado (Interleaved) ZCS-FM boost, com controle digital através de dispositivo FPGA e linguagem VHDL

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A novel single-phase ZCS-PWM high power factor boost rectifier

This paper presents a novel single-phase high power factor PWM boost rectifier, featuring soft commutation of the active switches at zero-current (ZCS). It incorporates the most desirable properties of the conventional PWM and the soft-switching resonant techniques. The input current shaping is achieved with average current mode control, and continuous inductor current mode. This new PWM converter provides ZCS turn-on and turn-off of the active switches, and it is suitable for high power applications employing IGBTs. Principle of operation, theoretical analysis, a design example, and experimental results from a laboratory prototype rated at 1600 W with 400 Vdc output voltage are presented. The measured efficiency and power factor were 96.2% and 0.99 respectively, with an input current THD equal to 3.94%, for an input voltage THD equal to 3.8%, at rated load.

A new family of zero-current-switching PWM converters and a novel HPF-ZCS-PWM boost rectifier

A new family of direct current (DC) to DC converters based on a zero current switching pulse width modulated (ZCS-PWM) soft commutation cell is presented. This ZCS-PWM cell is consists of two transistors, two diodes, two inductors and one capacitor; and provides zero voltage turn-on to the diodes, a zero-current turn-on and a zero-current zero-voltage turn-off to the transistors. In addition, a new commutation cell in a new ZCS-PWM boost rectifier is developed, obtaining a structure with power factor near the unity, high efficiency at wide load range and low total harmonic distortion in the input current.

Charge separation and recombination in novel polymeric absorber materials for organic solar cells : a photophysical study

In dieser Dissertation wird die Ladungsträgergeneration und -rekombination in neuen polymeren Absorbermaterialien für organische Solarzellen untersucht. Das Verständnis dieser Prozesse ist wesentlich für die Entwicklung neuer photoaktiver Materialsysteme, die hohe Effizienzen erzielen und organische Solarzellen konkurrenzfähig im Bereich der erneuerbaren Energien machen. Experimentell verwendet diese Arbeit hauptsächlich die Methode der transienten Absorptionsspektroskopie, die sich für die Untersuchung photophysikalischer Prozesse auf einer Zeitskala von 100 fs bis 1 ms als sehr leistungsfähig erweist. Des Weiteren wird eine soft-modeling Methode vorgestellt, die es ermöglicht, photophysikalische Prozesse aus einer gemessenen transienten Absorptions-Datenmatrix zu bestimmen, wenn wenig a priori Kenntnisse der Reaktionskinetiken vorhanden sind. Drei unterschiedliche Donor:Akzeptor-Systeme werden untersucht; jedes dieser Systeme stellt eine andere Herangehensweise zur Optimierung der Materialien dar in Bezug auf Lichtabsorption über einen breiten Wellenlängenbereich, effiziente Ladungstrennung und schnellen Ladungstransport. Zuerst wird ein Terpolymer untersucht, das aus unterschiedlichen Einheiten für die Lichtabsorption und den Ladungstransport besteht. Es wird gezeigt, dass es möglich ist, den Fluss angeregter Zustände vom Chromophor auf die Transporteinheit zu leiten. Im zweiten Teil wird der Einfluss von Kristallinität auf die freie Ladungsträgergeneration mit einer Folge von ternären Mischungen, die unterschiedliche Anteile an amorphem und semi-kristallinem Polymer enthalten, untersucht. Dabei zeigt es sich, dass mit steigendem amorphen Polymeranteil sowohl der Anteil der geminalen Ladungsträgerrekombination erhöht als auch die nicht-geminale Rekombination schneller ist. Schlussendlich wird ein System untersucht, in dem sowohl Donor als auch Akzeptor Polymere sind, was zu verbesserten Absorptionseigenschaften führt. Die Rekombination von Ladungstransferzuständen auf der unter 100 ps Zeitskala stellt hier den hauptsächliche Verlustkanal dar, da freie Ladungsträger nur an Grenzflächen erzeugt werden können, an denen Donor und Akzeptor face-to-face zueinander orientiert sind. Darüber hinaus wird festgestellt, dass weitere 40-50% der Ladungsträger durch die Rekombination von Grenzflächenzuständen verloren gehen, die aus mobilen Ladungsträgern geminal gebildet werden.

Charge generation and recombination in solid-state dye-sensitized solar cells

Diese Doktorarbeit befasst sich mit Ladungsgeneration und – rekombination in Feststoff-Farbstoffsolarzellen, die spiro-OMeTAD als Lochleiter verwenden. Die vorliegende Arbeit ist in drei Fallstudien unterteilt: i.) Kern-erweiterte Rylen-Farbstoffe, ii.) ein Perylenmonoimid-Farbstoff und iii.) Donor-π verbrückte (Cyclopentadithiophen)-Akzeptor-Farbstoffe. Trotz ihres hohen molaren Extinktionskoeffizienten und der hohen Absorbanz der sensibilisierten Filme, zeigen einige dieser Farbstoffmoleküle nur geringe photovoltaischen Effizienzen. Um den Ursprung des geringen Wirkungsgrades herauszufinden, wurde breitbandige, ultraschnelle transiente Absorptionsspektroskopie an Solarzellen durchgeführt.rnInsbesondere die Auswirkungen verschiedender Ankergruppen, Dipolmomente, Photolumineszenzlebenszeiten, Lithium-Kationensensitivität und Ladungsträgerdynamik, die alle einen großen Einfluss auf den Wirkungsgrad der Solarzelle besitzen, wurden untersucht. In der ersten Fallstudie zeigte ein kurzer Rylen-Farbstoff aufgrund deutlich verlängerter Lebenszeiten die beste Effizienz im Vergleich zu größeren Kern-erweiterten Rylen-Farbstoffen. Die Lebenszeit wurde weiter reduziert, wenn Maleinsäure als Ankergruppe unter einer Ringöffnungsreaktion an die mesoporöse Oberfläche des Metalloxid-Halbleiters adsorbierte. Dies konnte mit Hilfe von Berechnungen mittels der Dichtefunktionaltheorie (DFT, B3LYP) auf die Differenz des Dipolmoments zwischen Grundzustand und angeregtem Zustand zurückgeführt werden. Die Berechnungen bekräftigen die unvorteilhafte Injektion von Ladungen durch die Änderung der Richtung des Dipolmoments, wenn eine Ringöffnung der Anhydridgruppe stattfindet. In der zweiten Studie zeigte das Perylenmonoimid-Derivat ID889 einen Wirkungsgrad von 4.5% in Feststoff-Farbstoffsolarzellen, wobei ID889 sogar ohne Zuhilfenahme eines Additivs in der Lage ist langlebige Farbstoffkationen zu bilden. Die Verwendung von Lithium-Kationen stabilisiert jedoch sowohl den Prozess der Ladungsgeneration als auch den der Ladungsregeneration. Des Weiteren wurde in ID889-sensitivierten Bauteilen kein reduktives Löschen beobachtet. Dabei wurde die Dynamik der Exzitonen mittels einer soft-modelling Methode Kurvenanalyse aus den Daten der transienten Absorptionsspektroskopie gewonnen. Zuletzt wurden Strukturen mit Cyclopentadithiophen(CPDT)-Baustein untersucht, die eine typische D-π-A Molekülstruktur bilden. FPH224 und 233 zeigten dabei eine bessere Effizienz als FPH231 und 303 aufgrund einer großen Injektionseffizienz (IE) und längerer Lebenszeit der angeregten Zustände. Dies kann auf reduktives Löschen in FPH231 und 303 zurückgeführt werden, wohingegen FPH224 und 233 einen moderaten Zerfall des Spirokationensignals zeigten.

Development, characterization, and application of flowing atmospheric-pressure afterglow ionization for mass spectrometric analysis of ambient organic aerosols

Addressing current limitations of state-of-the-art instrumentation in aerosol research, the aim of this work was to explore and assess the applicability of a novel soft ionization technique, namely flowing atmospheric-pressure afterglow (FAPA), for the mass spectrometric analysis of airborne particulate organic matter. Among other soft ionization methods, the FAPA ionization technique was developed in the last decade during the advent of ambient desorption/ionization mass spectrometry (ADI–MS). Based on a helium glow discharge plasma at atmospheric-pressure, excited helium species and primary reagent ions are generated which exit the discharge region through a capillary electrode, forming the so-called afterglow region where desorption and ionization of the analytes occurs. Commonly, fragmentation of the analytes during ionization is reported to occur only to a minimum extent, predominantly resulting in the formation of quasimolecular ions, i.e. [M+H]+ and [M–H]– in the positive and the negative ion mode, respectively. Thus, identification and detection of signals and their corresponding compounds is facilitated in the acquired mass spectra. The focus of the first part of this study lies on the application, characterization and assessment of FAPA–MS in the offline mode, i.e. desorption and ionization of the analytes from surfaces. Experiments in both positive and negative ion mode revealed ionization patterns for a variety of compound classes comprising alkanes, alcohols, aldehydes, ketones, carboxylic acids, organic peroxides, and alkaloids. Besides the always emphasized detection of quasimolecular ions, a broad range of signals for adducts and losses was found. Additionally, the capabilities and limitations of the technique were studied in three proof-of-principle applications. In general, the method showed to be best suited for polar analytes with high volatilities and low molecular weights, ideally containing nitrogen- and/or oxygen functionalities. However, for compounds with low vapor pressures, containing long carbon chains and/or high molecular weights, desorption and ionization is in direct competition with oxidation of the analytes, leading to the formation of adducts and oxidation products which impede a clear signal assignment in the acquired mass spectra. Nonetheless, FAPA–MS showed to be capable of detecting and identifying common limonene oxidation products in secondary OA (SOA) particles on a filter sample and, thus, is considered a suitable method for offline analysis of OA particles. In the second as well as the subsequent parts, FAPA–MS was applied online, i.e. for real time analysis of OA particles suspended in air. Therefore, the acronym AeroFAPA–MS (i.e. Aerosol FAPA–MS) was chosen to refer to this method. After optimization and characterization, the method was used to measure a range of model compounds and to evaluate typical ionization patterns in the positive and the negative ion mode. In addition, results from laboratory studies as well as from a field campaign in Central Europe (F–BEACh 2014) are presented and discussed. During the F–BEACh campaign AeroFAPA–MS was used in combination with complementary MS techniques, giving a comprehensive characterization of the sampled OA particles. For example, several common SOA marker compounds were identified in real time by MSn experiments, indicating that photochemically aged SOA particles were present during the campaign period. Moreover, AeroFAPA–MS was capable of detecting highly oxidized sulfur-containing compounds in the particle phase, presenting the first real-time measurements of this compound class. Further comparisons with data from other aerosol and gas-phase measurements suggest that both particulate sulfate as well as highly oxidized peroxyradicals in the gas phase might play a role during formation of these species. Besides applying AeroFAPA–MS for the analysis of aerosol particles, desorption processes of particles in the afterglow region were investigated in order to gain a more detailed understanding of the method. While during the previous measurements aerosol particles were pre-evaporated prior to AeroFAPA–MS analysis, in this part no external heat source was applied. Particle size distribution measurements before and after the AeroFAPA source revealed that only an interfacial layer of OA particles is desorbed and, thus, chemically characterized. For particles with initial diameters of 112 nm, desorption radii of 2.5–36.6 nm were found at discharge currents of 15–55 mA from these measurements. In addition, the method was applied for the analysis of laboratory-generated core-shell particles in a proof-of-principle study. As expected, predominantly compounds residing in the shell of the particles were desorbed and ionized with increasing probing depths, suggesting that AeroFAPA–MS might represent a promising technique for depth profiling of OA particles in future studies.

[Medium-term results after m. vastus medialis obliquus-plasty for lateral patellar dislocation]

Progressive retropatellar arthrosis is often seen in dated rigid distal realignment (i.e. osteotomy of tuberositas) at long-term follow-ups. Therefore, operations for lateral dislocation of the patella are still discussed controversially. Dynamic, proximal realignments seem to have lower rates of arthrosis but higher rates of redislocation. Recently, in anatomic and biomechanic studies, the m. vastus medialis obliquus (vmo) was found to be one of the most important proximal restraints to lateral dislocation of the patella.A total of 28 patients (mean age 21.5 years) were treated between 1994 and 2003 with a plasty of the vmo for lateral patellar dislocation. The technique was performed for most etiologies of femoropatellar instability.For this proximal soft tissue technique, the muscle tendon is detached from its patellar insertion. Subsequently, the tendon is reinserted at the patella 10-15 mm more distally and fixed with Mitek anchors. Full weight bearing in extension is possible immediately after surgery. An active vastus medialis training is started after 6 weeks.Of the patients, 27 were evaluated clinically and radiologically in 2004 (a mean of 5 years postoperatively). A total of 83% of the patients estimated the result to be good or excellent, 10% were satisfied and 7% were discontent. The mean Lysholm-Knee-Score was 83.1 points. Two patients suffered a patella redislocation (7%). A statistically significant improvement of the congruence angle was noted in the radiographs, even in medium-term controls. In 89% of the cases no or only little retropatellar arthrosis was observed. These 5 year results are comparable to those of other techniques for distal or proximal realignments. The rate of redislocation was below average. Compared to the rate of retropatellar arthrosis in long-term results of rigid distal realignment, our patients demonstrated a relative low rate after 5 years. We attribute this to the minimal interference in physiological joint mechanics and to the restored anatomy. In terms of future long-term results, our findings are promising. The idea of a proximal dynamic stabilization and the causal operative approach at the origin of pathology using vmo-plasty was confirmed in recent anatomic and biomechanic studies. Over or under correction of soft tissues could be adapted. More rigid techniques of distal realignment do not allow an adaptation to this extent and can lead to prearthrotic hyperpression in the medial femoropatellar and femorotibial joints.

Kassandra, la niña pirata

Trabajo realizado con la técnica de pastel o soft pastel, con soltura de trazos con carácter como si fuesen pinceladas, hacen resaltar la figura de la niña y sus atuendos tratados con efumino, que por contraste se enriquecen (figurativo, libre y gestual).

Characterization of BaTi1-xZrxO3 thin films obtained by a soft chemical spin-coating technique

Single-phase perovskite structure BaZrxTi1-xO3 (BZT) (0.05less than or equal toxless than or equal to0.25) thin films were deposited on Pt-Ti-SiO2-Si substrates by the spin-coating technique. The structural modifications in the thin films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice (a axis) with the increasing content of zirconium in these films. Such Zr substitution also result in variations of the phonon mode wave numbers, especially those of lower wave numbers, for BaZrxTi1-xO3 thin films, corroborate to the structural change caused by the zirconium doping. on the other hand, Raman modes persist above structural phase transition, although all optical modes should be Raman inactive in the cubic phase. The origin of these modes must be interpreted as a function of a local breakdown of the cubic symmetry, which could be a result of some kind of disorder. The BZT thin films exhibited a satisfactory dielectric constant close to 181-138, and low dielectric loss tan delta<0.03 at the frequency of 1 kHz. The leakage current density of the BZT thin films was studied at elevated temperatures and the data obey the Schottky emission model. Through this analysis the Schottky barrier height values 0.68, 1.39, and 1.24 eV were estimated to the BZT5, BZT15, and BZT25 thin films, respectively. (C) 2004 American Institute of Physics.