22 resultados para Pulse width modulation
Resumo:
An EMI lter for a three-phase buck-type medium power pulse-width modulation rectier is designed. This lter considers differential mode noise and complies with MIL-STD- 461E for the frequency range of 10kHz to 10MHz. In industrial applications, the frequency range of the standard starts at 150kHz and the designer typically uses a switching frequency of 28kHz because the fth harmonic is out of the range. This approach is not valid for aircraft applications. In order to design the switching frequency in aircraft applications, the power losses in the semiconductors and the weight of the reactive components should be considered. The proposed design is based on a harmonic analysis of the rectier input current and an analytical study of the input lter. The classical industrial design does not consider the inductive effect in the lter design because the grid frequency is 50/60Hz. However, in the aircraft applications, the grid frequency is 400Hz and the inductance cannot be neglected. The proposed design considers the inductance and the capacitance effect of the lter in order to obtain unitary power factor at full power. In the optimization process, several lters are designed for different switching frequencies of the converter. In addition, designs from single to ve stages are considered. The power losses of the converter plus the EMI lter are estimated at these switching frequencies. Considering overall losses and minimal lter volume, the optimal switching frequency is selected
Resumo:
An EMI filter for a three-phase buck-type medium power pulse-width modulation rectifier is designed. This filter considers differential mode noise and complies with MIL-STD-461E for the frequency range of 10kHz to 10MHz. In industrial applications, the frequency range of the standard starts at 150kHz and the designer typically uses a switching frequency of 28kHz because the fifth harmonic is out of the range. This approach is not valid for aircraft applications. In order to design the switching frequency in aircraft applications, the power losses in the semiconductors and the weight of the reactive components should be considered. The proposed design is based on a harmonic analysis of the rectifier input current and an analytical study of the input filter. The classical industrial design does not consider the inductive effect in the filter design because the grid frequency is 50/60Hz. However, in the aircraft applications, the grid frequency is 400Hz and the inductance cannot be neglected. The proposed design considers the inductance and the capacitance effect of the filter in order to obtain unitary power factor at full power. In the optimization process, several filters are designed for different switching frequencies of the converter. In addition, designs from single to five stages are considered. The power losses of the converter plus the EMI filter are estimated at these switching frequencies. Considering overall losses and minimal filter volume, the optimal switching frequency is selected.
Resumo:
Pulse-width modulation is widely used to control electronic converters. One of the most topologies used for high DC voltage/low DC voltage conversion is the Buck converter. It is obtained as a second order system with a LC filter between the switching subsystem and the load. The use of a coil with an amorphous magnetic material core instead of air core lets design converters with smaller size. If high switching frequencies are used for obtaining high quality voltage output, the value of the auto inductance L is reduced throughout the time. Then, robust controllers are needed if the accuracy of the converter response must not be affected by auto inductance and load variations. This paper presents a robust controller for a Buck converter based on a state space feedback control system combined with an additional virtual space variable which minimizes the effects of the inductance and load variations when a not-toohigh switching frequency is applied. The system exhibits a null steady-state average error response for the entire range of parameter variations. Simulation results are presented.
Resumo:
La ptica anidlica es una rama de la ptica cuyo desarrollo comenz a mediados de la dcada de 1960. Este relativamente nuevo campo de la ptica se centra en la transferencia eficiente de la luz, algo necesario en muchas aplicaciones, entre las que destacamos los concentradores solares y los sistemas de iluminacin. Las soluciones de la ptica clsica a los problemas de la transferencia de energa de la luz slo son adecuadas cuando los rayos de luz son paraxiales. La condicin paraxial no se cumple en la mayora de las aplicaciones para concentracin e iluminacin. Esta tesis contiene varios diseos free-form (aquellos que no presentan ninguna simetra, ni de rotacin ni lineal) cuyas aplicaciones van destinadas a estos dos campos. El trmino nonimaging viene del hecho de que estos sistemas pticos no necesitan formar una imagen del objeto, aunque no formar la imagen no es una condicin necesaria. Otra palabra que se utiliza a veces en lugar de nonimaging es la palabra anidlico, viene del griego "an+eidolon" y tiene el mismo significado. La mayora de los sistemas pticos diseados para aplicaciones anidlicas no presentan ninguna simetra, es decir, son free-form (anamrficos). Los sistemas pticos free-form estn siendo especialmente relevantes durante los ltimos aos gracias al desarrollo de las herramientas para su fabricacin como mquinas de moldeo por inyeccin y el mecanizado multieje. Sin embargo, solo recientemente se han desarrollado tcnicas de diseo anidlicas capaces de cumplir con estos grados de libertad. En aplicaciones de iluminacin el mtodo SMS3D permite disear dos superficies free-form para controlar las fuentes de luz extensas. En los casos en que se requiere una elevada asimetra de la fuente, el objeto o las restricciones volumtricos, las superficies free-form permiten obtener soluciones de mayor eficiencia, o disponer de menos elementos en comparacin con las soluciones de simetra de rotacin, dado que las superficies free-form tienen ms grados de libertad y pueden realizar mltiples funciones debido a su naturaleza anamrfica. Los concentradores anidlicos son muy adecuados para la captacin de energa solar, ya que el objetivo no es la reproduccin de una imagen exacta del sol, sino sencillamente la captura de su energa. En este momento, el campo de la concentracin fotovoltaica (CPV) tiende hacia sistemas de alta concentracin con el fin de compensar el gasto de las clulas solares multi-unin (MJ) utilizadas como receptores, reduciendo su rea. El inters en el uso de clulas MJ radica en su alta eficiencia de conversin. Para obtener sistemas competitivos en aplicaciones terrestres se recurre a sistemas fotovoltaicos de alta concentracin (HCPV), con factores de concentracin geomtrica por encima de 500x. Estos sistemas se componen de dos (o ms) elementos pticos (espejos y/o lentes). En los sistemas presentados a lo largo de este trabajo se presentan ejemplos de concentradores HCPV con elementos reflexivos como etapa primaria, as como concentradores con elementos refractivos (lente de Fresnel). Con la necesidad de aumentar la eficiencia de los sistemas HCPV reales y con el fin de proporcionar la divisin ms eficiente del espectro solar, clulas conteniendo cuatro o ms uniones (con un potencial de alcanzar eficiencias de ms del 45% a una concentracin de cientos de soles) se exploran hoy en da. En esta tesis se presenta una de las posibles arquitecturas de divisin del espectro (spectrum-splitting en la literatura anglosajona) que utilizan clulas de concentracin comercial. Otro campo de aplicacin de la ptica nonimaging es la iluminacin, donde es necesario proporcionar un patrn de distribucin de la iluminacin especfico. La iluminacin de estado slido (SSL), basada en la electroluminiscencia de materiales semiconductores, est proporcionando fuentes de luz para aplicaciones de iluminacin general. En la ltima dcada, los diodos emisores de luz (LED) de alto brillo han comenzado a reemplazar a las fuentes de luz convencionales debido a la superioridad en la calidad de la luz emitida, elevado tiempo de vida, compacidad y ahorro de energa. Los colimadores utilizados con LEDs deben cumplir con requisitos tales como tener una alta eficiencia, un alto control del haz de luz, una mezcla de color espacial y una gran compacidad. Presentamos un colimador de luz free-form con microestructuras capaz de conseguir buena colimacin y buena mezcla de colores con una fuente de LED RGGB. Una buena mezcla de luz es importante no slo para simplificar el diseo ptico de la luminaria sino tambin para evitar hacer binning de los chips. La mezcla de luz ptica puede reducir los costes al evitar la modulacin por ancho de pulso y otras soluciones electrnicas patentadas para regulacin y ajuste de color. Esta tesis consta de cuatro captulos. Los captulos que contienen la obra original de esta tesis son precedidos por un captulo introductorio donde se presentan los conceptos y definiciones bsicas de la ptica geomtrica y en el cual se engloba la ptica nonimaging. Contiene principios de la ptica no formadora de imagen junto con la descripcin de sus problemas y mtodos de diseo. Asimismo se describe el mtodo de Superficies Mltiples Simultneas (SMS), que destaca por su versatilidad y capacidad de controlar varios haces de rayos. Adicionalmente tambin se describe la integracin Khler y sus aplicaciones en el campo de la energa fotovoltaica. La concentracin fotovoltaica y la iluminacin de estado slido son introducidas junto con la revisin de su estado actual. El Segundo y Tercer Captulo contienen diseos pticos avanzados con aplicacin en la concentracin solar principalmente, mientras que el Cuarto Captulo describe el colimador free-form con surcos que presenta buena mezcla de colores para aplicaciones de iluminacin. El Segundo Captulo describe dos concentradores pticos HCPV diseados con el mtodo SMS en tres dimensiones (SMS3D) que llevan a cabo integracin Khler en dos direcciones con el fin de proporcionar una distribucin de irradiancia uniforme libre de aberraciones cromticas sobre la clula solar. Uno de los diseos es el concentrador XXR free-form diseado con el mtodo SMS3D, donde el espejo primario (X) y la lente secundaria (R) se dividen en cuatro sectores simtricos y llevan a cabo la integracin Khler (proporcionando cuatro unidades del array Khler), mientras que el espejo intermedio (X) presenta simetra rotacional. Otro concentrador HCPV presentado es el Fresnel-RXI (FRXI) con una lente de Fresnel funcionando como elemento primario (POE) y una lente RXI como elemento ptico secundario (SOE), que presenta configuracin 4-fold con el fin de realizar la integracin Khler. Las lentes RXI son dispositivos nonimaging conocidos, pero su aplicacin como elemento secundario es novedosa. Los concentradores XXR y FRXI Khler son ejemplos acadmicos de muy alta concentracin (ms de 2,000x, mientras que los sistemas convencionales hoy en da no suelen llegar a 1,000x) preparados para las clulas solares N-unin (con N>3), que probablemente requerirn una mayor concentracin y alta uniformidad espectral de irradiancia con el fin de obtener sistemas CPV terrestres eficientes y rentables. Ambos concentradores estn diseados maximizando funciones de mrito como la eficiencia ptica, el producto concentracin-aceptancia (CAP) y la uniformidad de irradiancia sobre la clula libre de la aberracin cromtica (integracin Khler). El Tercer Captulo presenta una arquitectura para la divisin del espectro solar basada en un mdulo HCPV con alta concentracin (500x) y ngulo de aceptancia alto (>1) que tiene por objeto reducir ambas fuentes de prdidas de las clulas triple unin (3J) comerciales: el uso eficiente del espectro solar y la luz reflejada de los contactos metlicos y de la superficie de semiconductor. El mdulo para la divisin del espectro utiliza el espectro solar ms eficiente debido a la combinacin de una alta eficiencia de una clula de concentracin 3J (GaInP/GaInAs/Ge) y una de contacto posterior (BPC) de concentracin de silicio (Si), as como la tcnica de confinamiento externo para la recuperacin de la luz reflejada por la clula 3J con el fin de ser reabsorbida por la clula. En la arquitectura propuesta, la clula 3J opera con su ganancia de corriente optimizada (concentracin geomtrica de 500x), mientras que la clula de silicio trabaja cerca de su ptimo tambin (135x). El mdulo de spectrum-splitting consta de una lente de Fresnel plana como POE y un concentrador RXI free-form como SOE con un filtro paso-banda integrado en l. Tanto POE como SOE realizan la integracin Khler para producir homogeneizacin de luz sobre la clula. El filtro paso banda enva los fotones IR en la banda 900-1,150nm a la clula de silicio. Hay varios aspectos prcticos de la arquitectura del mdulo presentado que ayudan a reducir la complejidad de los sistemas spectrum-splitting (el filtro y el secundario forman una sola pieza slida, ambas clulas son coplanarias simplificndose el cableado y la disipacin de calor, etc.). Prototipos prueba-de-concepto han sido ensamblados y probados a fin de demostrar la fabricabilidad del filtro y su rendimiento cuando se combina con la tcnica de reciclaje de luz externa. Los resultados obtenidos se ajustan bastante bien a los modelos y a las simulaciones e invitan al desarrollo de una versin ms compleja de este prototipo en el futuro. Dos colimadores slidos con surcos free-form se presentan en el Cuarto Captulo. Ambos diseos pticos estn diseados originalmente usando el mtodo SMS3D. La segunda superficie pticamente activa est diseada a posteriori como una superficie con surcos. El diseo inicial de dos espejos (XX) est diseado como prueba de concepto. En segundo lugar, el diseo RXI free-form es comparable con los colimadores RXI existentes. Se trata de un diseo muy compacto y eficiente que proporciona una muy buena mezcla de colores cuando funciona con LEDs RGB fuera del eje ptico como en los RGB LEDs convencionales. Estos dos diseos son dispositivos free-form diseados con la intencin de mejorar las propiedades de mezcla de colores de los dispositivos no aplanticos RXI con simetra de revolucin y la eficiencia de los aplanticos, logrando una buena colimacin y una buena mezcla de colores. La capacidad de mezcla de colores del dispositivo no-aplantico mejora aadiendo caractersticas de un aplantico a su homlogo simtrico sin prdida de eficiencia. En el caso del diseo basado en RXI, su gran ventaja consiste en su menor coste de fabricacin ya que el proceso de metalizacin puede evitarse. Aunque algunos de los componentes presentan formas muy complejas, los costes de fabricacin son relativamente insensibles a la complejidad del molde, especialmente en el caso de la produccin en masa (tales como inyeccin de plstico), ya que el coste del molde se reparte entre todas las piezas fabricadas. Por ltimo, las ltimas dos secciones son las conclusiones y futuras lneas de investigacin. ABSTRACT Nonimaging optics is a branch of optics whose development began in the mid-1960s. This rather new field of optics focuses on the efficient light transfer necessary in many applications, among which we highlight solar concentrators and illumination systems. The classical optics solutions to the problems of light energy transfer are only appropriate when the light rays are paraxial. The paraxial condition is not met in most applications for the concentration and illumination. This thesis explores several free-form designs (with neither rotational nor linear symmetry) whose applications are intended to cover the above mentioned areas and more. The term nonimaging comes from the fact that these optical systems do not need to form an image of the object, although it is not a necessary condition not to form an image. Another word sometimes used instead of nonimaging is anidolic, and it comes from the Greek an+eidolon and has the same meaning. Most of the optical systems designed for nonimaging applications are without any symmetry, i.e. free-form. Free-form optical systems become especially relevant lately with the evolution of free-form tooling (injection molding machines, multi-axis machining techniques, etc.). Nevertheless, only recently there are nonimaging design techniques that are able to meet these degrees of freedom. In illumination applications, the SMS3D method allows designing two free-form surfaces to control very well extended sources. In cases when source, target or volumetric constrains have very asymmetric requirements free-form surfaces are offering solutions with higher efficiency or with fewer elements in comparison with rotationally symmetric solutions, as free-forms have more degrees of freedom and they can perform multiple functions due to their free-form nature. Anidolic concentrators are well suited for the collection of solar energy, because the goal is not the reproduction of an exact image of the sun, but instead the collection of its energy. At this time, Concentration Photovoltaics (CPV) field is turning to high concentration systems in order to compensate the expense of multi-junction (MJ) solar cells used as receivers by reducing its area. Interest in the use of MJ cells lies in their very high conversion efficiency. High Concentration Photovoltaic systems (HCPV) with geometric concentration of more than 500x are required in order to have competitive systems in terrestrial applications. These systems comprise two (or more) optical elements, mirrors and/or lenses. Systems presented in this thesis encompass both main types of HCPV architectures: concentrators with primary reflective element and concentrators with primary refractive element (Fresnel lens). Demand for the efficiency increase of the actual HCPV systems as well as feasible more efficient partitioning of the solar spectrum, leads to exploration of four or more junction solar cells or submodules. They have a potential of reaching over 45% efficiency at concentration of hundreds of suns. One possible architectures of spectrum splitting module using commercial concentration cells is presented in this thesis. Another field of application of nonimaging optics is illumination, where a specific illuminance distribution pattern is required. The Solid State Lighting (SSL) based on semiconductor electroluminescence provides light sources for general illumination applications. In the last decade high-brightness Light Emitting Diodes (LEDs) started replacing conventional light sources due to their superior output light quality, unsurpassed lifetime, compactness and energy savings. Collimators used with LEDs have to meet requirements like high efficiency, high beam control, color and position mixing, as well as a high compactness. We present a free-form collimator with microstructures that performs good collimation and good color mixing with RGGB LED source. Good light mixing is important not only for simplifying luminaire optical design but also for avoiding die binning. Optical light mixing may reduce costs by avoiding pulse-width modulation and other patented electronic solutions for dimming and color tuning. This thesis comprises four chapters. Chapters containing the original work of this thesis are preceded by the introductory chapter that addresses basic concepts and definitions of geometrical optics on which nonimaging is developed. It contains fundamentals of nonimaging optics together with the description of its design problems, principles and methods, and with the Simultaneous Multiple Surface (SMS) method standing out for its versatility and ability to control several bundles of rays. Khler integration and its applications in the field of photovoltaics are described as well. CPV and SSL fields are introduced together with the review on their background and their current status. Chapter 2 and Chapter 3 contain advanced optical designs with primarily application in solar concentration; meanwhile Chapter 4 portrays the free-form V-groove collimator with good color mixing property for illumination application. Chapter 2 describes two HCPV optical concentrators designed with the SMS method in three dimensions (SMS3D). Both concentrators represent Khler integrator arrays that provide uniform irradiance distribution free from chromatic aberrations on the solar cell. One of the systems is the XXR free-form concentrator designed with the SMS3D method. The primary mirror (X) of this concentrator and secondary lens (R) are divided in four symmetric sectors (folds) that perform Khler integration; meanwhile the intermediate mirror (X) is rotationally symmetric. Second HCPV concentrator is the Fresnel-RXI (FRXI) with flat Fresnel lens as the Primary Optical Element (POE) and an RXI lens as the Secondary Optical Element (SOE). This architecture manifests 4-fold configuration for performing Khler integration (4 array units), as well. The RXI lenses are well-known nonimaging devices, but their application as SOE is novel. Both XXR and FRXI Khler HCPV concentrators are academic examples of very high concentration (more than 2,000x meanwhile conventional systems nowadays have up to 1,000x) prepared for the near future N-junction (N>3) solar cells. In order to have efficient and cost-effective terrestrial CPV systems, those cells will probably require higher concentrations and high spectral irradiance uniformity. Both concentrators are designed by maximizing merit functions: the optical efficiency, concentration-acceptance angle (CAP) and cell-irradiance uniformity free from chromatic aberrations (Khler integration). Chapter 3 presents the spectrum splitting architecture based on a HCPV module with high concentration (500x) and high acceptance angle (>1). This module aims to reduce both sources of losses of the actual commercial triple-junction (3J) solar cells with more efficient use of the solar spectrum and with recovering the light reflected from the 3J cells grid lines and semiconductor surface. The solar spectrum is used more efficiently due to the combination of a high efficiency 3J concentration cell (GaInP/GaInAs/Ge) and external Back-Point-Contact (BPC) concentration silicon (Si) cell. By employing external confinement techniques, the 3J cells reflections are recovered in order to be re-absorbed by the cell. In the proposed concentrator architecture, the 3J cell operates at its optimized current gain (at geometrical concentration of 500x), while the Si cell works near its optimum, as well (135x). The spectrum splitting module consists of a flat Fresnel lens (as the POE), and a free-form RXI-type concentrator with a band-pass filter embedded in it (as the SOE), both POE and SOE performing Khler integration to produce light homogenization. The band-pass filter sends the IR photons in the 900-1,150nm band to the Si cell. There are several practical aspects of presented module architecture that help reducing the added complexity of the beam splitting systems: the filter and secondary are forming a single solid piece, both cells are coplanar so the heat management and wiring is simplified, etc. Two proof-of-concept prototypes are assembled and tested in order to prove filter manufacturability and performance, as well as the potential of external light recycling technique. Obtained measurement results agree quite well with models and simulations, and show an opened path to manufacturing of the Fresnel RXI-type secondary concentrator with spectrum splitting strategy. Two free-form solid V-groove collimators are presented in Chapter 4. Both free-form collimators are originally designed with the SMS3D method. The second mirrored optically active surface is converted in a grooved surface a posteriori. Initial two mirror (XX) design is presented as a proof-of-concept. Second, RXI free-form design is comparable with existing RXI collimators as it is a highly compact and a highly efficient design. It performs very good color mixing of the RGGB LED sources placed off-axis like in conventional RGB LEDs. Collimators described here improve color mixing property of the prior art rotationally symmetric no-aplanatic RXI devices, and the efficiency of the aplanatic ones, accomplishing both good collimation and good color mixing. Free-form V-groove collimators enhance the no-aplanatic device's blending capabilities by adding aplanatic features to its symmetric counterpart with no loss in efficiency. Big advantage of the RXI design is its potentially lower manufacturing cost, since the process of metallization may be avoided. Although some components are very complicated for shaping, the manufacturing costs are relatively insensitive to the complexity of the mold especially in the case of mass production (such as plastic injection), as the cost of the mold is spread in many parts. Finally, last two sections are conclusions and future lines of investigation.
Resumo:
In recent years, interest in light-emitting diode (LED) lighting has been growing because of its high efficacy, lifetime and ruggedness. This paper proposes a better adaptation of LED lamps to the technical requirements of photovoltaic lighting domestic systems, whose main quality criteria are reliability and that behave as voltage power supplies. As the key element of reliability in LED lamps is temperature, a solution is proposed for driving LED lamps using voltage sources, such as photovoltaic system batteries, with a control architecture based on pulse width modulation signal that regulates the current applied according to the LED lamp temperature. A prototype of the LED lamp has been implemented and tested to show its good performance at different temperatures and at different battery voltages.
Resumo:
Pulse-width modulation is widely used to control electronic converters. One of the most frequently used topologies for high DC voltage/low DC voltage conversion is the Buck converter. These converters are described by a second order system with an LC filter between the switching subsystem and the load. The use of a coil with an amorphous magnetic material core rather than an air core permits the design of smaller converters. If high switching frequencies are used to obtain high quality voltage output, then the value of the auto inductance L is reduced over time. Robust controllers are thus needed if the accuracy of the converter response must be preserved under auto inductance and payload variations. This paper presents a robust controller for a Buck converter based on a state space feedback control system combined with an additional virtual space variable which minimizes the effects of the inductance and load variations when a switching frequency that is not too high is applied. The system exhibits a null steady-state average error response for the entire range of parameter variations. Simulation results and a comparison with a standard PID controller are also presented.
Resumo:
A method of unpolarized laser pulses shaping is reported. The basis of the method is the use of an hybrid optical bistable device with nematic liquid-crystals, similar to the one previously reported by us. A sample of the input light constrols, by an asymmetrical electronic comparator, a 1 x 2 electro-optical total switch. The output pulses are reshaped and maintain the same polarization properties as the input light. From triangular input light signals, symmetriacl and asymmetrical output pulses have been obtained. The minimum pulse width achieved was 0.1 msec. A representation of the output versus input light signals gives an hysteresys cycle in the asymmetrical case.
Resumo:
Esta tesis se centra en el estudio y desarrollo de algoritmos de guerra electrnica {electronic warfare, EW) y radar para su implementacin en sistemas de tiempo real. La llegada de los sistemas de radio, radar y navegacin al terreno militar llev al desarrollo de tecnologas para combatirlos. As, el objetivo de los sistemas de guerra electrnica es el control del espectro electomagntico. Una de la funciones de la guerra electrnica es la inteligencia de seales {signals intelligence, SIGINT), cuya labor es detectar, almacenar, analizar, clasificar y localizar la procedencia de todo tipo de seales presentes en el espectro. El subsistema de inteligencia de seales dedicado a las seales radar es la inteligencia electrnica {electronic intelligence, ELINT). Un sistema de tiempo real es aquel cuyo factor de mrito depende tanto del resultado proporcionado como del tiempo en que se da dicho resultado. Los sistemas radar y de guerra electrnica tienen que proporcionar informacin lo ms rpido posible y de forma continua, por lo que pueden encuadrarse dentro de los sistemas de tiempo real. La introduccin de restricciones de tiempo real implica un proceso de realimentacin entre el diseo del algoritmo y su implementacin en plataformas hardware. Las restricciones de tiempo real son dos: latencia y rea de la implementacin. En esta tesis, todos los algoritmos presentados se han implementado en plataformas del tipo field programmable gate array (FPGA), ya que presentan un buen compromiso entre velocidad, coste total, consumo y reconfigurabilidad. La primera parte de la tesis est centrada en el estudio de diferentes subsistemas de un equipo ELINT: deteccin de seales mediante un detector canalizado, extraccin de los parmetros de pulsos radar, clasificacin de modulaciones y localization pasiva. La transformada discreta de Fourier {discrete Fourier transform, DFT) es un detector y estimador de frecuencia quasi-ptimo para seales de banda estrecha en presencia de ruido blanco. El desarrollo de algoritmos eficientes para el clculo de la DFT, conocidos como fast Fourier transform (FFT), han situado a la FFT como el algoritmo ms utilizado para la deteccin de seales de banda estrecha con requisitos de tiempo real. As, se ha diseado e implementado un algoritmo de deteccin y anlisis espectral para su implementacin en tiempo real. Los parmetros ms caractersticos de un pulso radar son su tiempo de llegada y anchura de pulso. Se ha diseado e implementado un algoritmo capaz de extraer dichos parmetros. Este algoritmo se puede utilizar con varios propsitos: realizar un reconocimiento genrico del radar que transmite dicha seal, localizar la posicin de dicho radar o bien puede utilizarse como la parte de preprocesado de un clasificador automtico de modulaciones. La clasificacin automtica de modulaciones es extremadamente complicada en entornos no cooperativos. Un clasificador automtico de modulaciones se divide en dos partes: preprocesado y el algoritmo de clasificacin. Los algoritmos de clasificacin basados en parmetros representativos calculan diferentes estadsticos de la seal de entrada y la clasifican procesando dichos estadsticos. Los algoritmos de localization pueden dividirse en dos tipos: triangulacin y sistemas cuadrticos. En los algoritmos basados en triangulacin, la posicin se estima mediante la interseccin de las rectas proporcionadas por la direccin de llegada de la seal. En cambio, en los sistemas cuadrticos, la posicin se estima mediante la interseccin de superficies con igual diferencia en el tiempo de llegada (time difference of arrival, TDOA) o diferencia en la frecuencia de llegada (frequency difference of arrival, FDOA). Aunque slo se ha implementado la estimacin del TDOA y FDOA mediante la diferencia de tiempos de llegada y diferencia de frecuencias, se presentan estudios exhaustivos sobre los diferentes algoritmos para la estimacin del TDOA, FDOA y localizacin pasiva mediante TDOA-FDOA. La segunda parte de la tesis est dedicada al diseo e implementacin filtros discretos de respuesta finita (finite impulse response, FIR) para dos aplicaciones radar: phased array de banda ancha mediante filtros retardadores (true-time delay, TTD) y la mejora del alcance de un radar sin modificar el hardware existente para que la solucin sea de bajo coste. La operacin de un phased array de banda ancha mediante desfasadores no es factible ya que el retardo temporal no puede aproximarse mediante un desfase. La solucin adoptada e implementada consiste en sustituir los desfasadores por filtros digitales con retardo programable. El mximo alcance de un radar depende de la relacin seal a ruido promedio en el receptor. La relacin seal a ruido depende a su vez de la energa de seal transmitida, potencia multiplicado por la anchura de pulso. Cualquier cambio hardware que se realice conlleva un alto coste. La solucin que se propone es utilizar una tcnica de compresin de pulsos, consistente en introducir una modulacin interna a la seal, desacoplando alcance y resolucin. ABSTRACT This thesis is focused on the study and development of electronic warfare (EW) and radar algorithms for real-time implementation. The arrival of radar, radio and navigation systems to the military sphere led to the development of technologies to fight them. Therefore, the objective of EW systems is the control of the electromagnetic spectrum. Signals Intelligence (SIGINT) is one of the EW functions, whose mission is to detect, collect, analyze, classify and locate all kind of electromagnetic emissions. Electronic intelligence (ELINT) is the SIGINT subsystem that is devoted to radar signals. A real-time system is the one whose correctness depends not only on the provided result but also on the time in which this result is obtained. Radar and EW systems must provide information as fast as possible on a continuous basis and they can be defined as real-time systems. The introduction of real-time constraints implies a feedback process between the design of the algorithms and their hardware implementation. Moreover, a real-time constraint consists of two parameters: Latency and area of the implementation. All the algorithms in this thesis have been implemented on field programmable gate array (FPGAs) platforms, presenting a trade-off among performance, cost, power consumption and reconfigurability. The first part of the thesis is related to the study of different key subsystems of an ELINT equipment: Signal detection with channelized receivers, pulse parameter extraction, modulation classification for radar signals and passive location algorithms. The discrete Fourier transform (DFT) is a nearly optimal detector and frequency estimator for narrow-band signals buried in white noise. The introduction of fast algorithms to calculate the DFT, known as FFT, reduces the complexity and the processing time of the DFT computation. These properties have placed the FFT as one the most conventional methods for narrow-band signal detection for real-time applications. An algorithm for real-time spectral analysis for user-defined bandwidth, instantaneous dynamic range and resolution is presented. The most characteristic parameters of a pulsed signal are its time of arrival (TOA) and the pulse width (PW). The estimation of these basic parameters is a fundamental task in an ELINT equipment. A basic pulse parameter extractor (PPE) that is able to estimate all these parameters is designed and implemented. The PPE may be useful to perform a generic radar recognition process, perform an emitter location technique and can be used as the preprocessing part of an automatic modulation classifier (AMC). Modulation classification is a difficult task in a non-cooperative environment. An AMC consists of two parts: Signal preprocessing and the classification algorithm itself. Featurebased algorithms obtain different characteristics or features of the input signals. Once these features are extracted, the classification is carried out by processing these features. A feature based-AMC for pulsed radar signals with real-time requirements is studied, designed and implemented. Emitter passive location techniques can be divided into two classes: Triangulation systems, in which the emitter location is estimated with the intersection of the different lines of bearing created from the estimated directions of arrival, and quadratic position-fixing systems, in which the position is estimated through the intersection of iso-time difference of arrival (TDOA) or iso-frequency difference of arrival (FDOA) quadratic surfaces. Although TDOA and FDOA are only implemented with time of arrival and frequency differences, different algorithms for TDOA, FDOA and position estimation are studied and analyzed. The second part is dedicated to FIR filter design and implementation for two different radar applications: Wideband phased arrays with true-time delay (TTD) filters and the range improvement of an operative radar with no hardware changes to minimize costs. Wideband operation of phased arrays is unfeasible because time delays cannot be approximated by phase shifts. The presented solution is based on the substitution of the phase shifters by FIR discrete delay filters. The maximum range of a radar depends on the averaged signal to noise ratio (SNR) at the receiver. Among other factors, the SNR depends on the transmitted signal energy that is power times pulse width. Any possible hardware change implies high costs. The proposed solution lies in the use of a signal processing technique known as pulse compression, which consists of introducing an internal modulation within the pulse width, decoupling range and resolution.
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Enhancement-mode (E-mode) high electron mobility transistors (HEMTs) based on a standard AlGaN/GaN heterostructure have been fabricated using two different methods: 19F implantation and fluorine-based plasma treatment. The need of a thermal annealing after both treatments has been proven in order to restore the ID and gm levels. DC characterization at high temperature has demonstrated that ID and gm decrease reversibly due to the reduction of the electron mobility and the drift velocity. Pulsed measurements (state period and variable pulse width) have been performed to study the self-heating effects.
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An envelope amplifier for an EER (Envelope Elimination and Restoration) and ET (Envelope Tracking) techniques is shown in this paper. The amplifier is based on a high speed two phases buck converter and employs RF LDMOS technology for the switching stage. A DPWM (Digital Pulse With Modulation) signal is used to control the amplifier by means of a functions generator. Simulations and measurements on a circuit prototype are presented showing a good agreement. Up to 125W output peak power can be delivered over a 5 load resistor. About 80% efficiency has been obtained. And at the two tone test, the third order intermodulation products (IP3) remain below 45dBc over a 2MHz bandwidth.
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In the Laser-Fired Contact (LFC) process, a laser beam fires a metallic layer through a dielectric passivating layer into the silicon wafer to form an electrical contact with the silicon bulk [1]. This laser technique is an interesting alternative for the fabrication of both laboratory and industrial scale high efficiency passivated emitter and rear cell (PERC). One of the principal characteristics of this promising technique is the capability to reduce the recombination losses at the rear surface in crystalline silicon solar cells. Therefore, it is crucial to optimize LFC because this process is one of the most promising concepts to produce rear side point contacts at process speeds compatible with the final industrial application. In that sense, this work investigates the optimization of LFC processing to improve the back contact in silicon solar cells using fully commercial solid state lasers with pulse width in the ns range, thus studying the influence of the wavelength using the three first harmonics (corresponding to wavelengths of 1064 nm, 532 nm and 355 nm). Previous studies of our group focused their attention in other processing parameters as laser fluence, number of pulses, passivating material [2, 3] thickness of the rear metallic contact [4], etc. In addition, the present work completes the parametric optimization by assessing the influence of the laser wavelength on the contact property. In particular we report results on the morphology and electrical behaviour of samples specifically designed to assess the quality of the process. In order to study the influence of the laser wavelength on the contact feature we used as figure of merit the specific contact resistance. In all processes the best results have been obtained using green (532 nm) and UV (355 nm), with excellent values for this magnitude far below 1 mcm2.
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Resumen En la ltima dcada la tecnologa lser se ha convertido en una herramienta imprescindible en la fabricacin de dispositivos fotovoltaicos, muy especialmente en aquellos basados en tecnologa de lmina delgada. Independientemente de crisis coyunturales en el sector, la evolucin en los prximos aos de estas tecnologas seguir aprovechndose de la flexibilidad y calidad de proceso de la herramienta lser para la consecucin de los dos objetivos bsicos que harn de la fotovoltaica una opcin energtica econmicamente viable: la reduccin de costes de fabricacin y el aumento de eficiencia de los dispositivos. Dentro de las tecnologas fotovoltaicas de lmina delgada, la tecnologa de dispositivos basados en silicio amorfo ha tenido un gran desarrollo en sistemas estndar en configuracin de superestrato, pero su limitada eficiencia hace que su supervivencia futura pase por el desarrollo de formatos en configuracin de substrato sobre materiales flexibles de bajo coste. En esta aproximacin, las soluciones industriales basadas en lser actualmente disponibles para la interconexin monoltica de dispositivos no son aplicables, y desde hace aos se viene investigando en la bsqueda de soluciones apropiadas para el desarrollo de dichos procesos de interconexin de forma que sean transferibles a la industria. En este contexto, esta Tesis propone una aproximacin completamente original, demostrando la posibilidad de ejecutar una interconexin completa de estos dispositivos irradiando por el lado de la lmina (es decir de forma compatible con la opcin de configuracin de substrato y, valga la redundancia, con el substrato del dispositivo opaco), y con fuentes lser emitiendo en UV. Este resultado, obtenido por primera vez a nivel internacional con este trabajo, aporta un conocimiento revelador del verdadero potencial de estas fuentes en el desarrollo industrial futuro de estas tecnologas. Si bien muy posiblemente la solucin industrial final requiera de una solucin mixta con el empleo de fuentes en UV y, posiblemente, en otras longitudes de onda, esta Tesis y su planteamiento novedoso aportan un conocimiento de gran valor a la comunidad internacional por la originalidad del planteamiento seguido, los resultados parciales encontrados en su desarrollo (un nmero importante de los cuales han aparecido en revistas del JCR que recogen en la actualidad un nmero muy significativo de citas) y porque saca adems a la luz, con las consideraciones fsicas pertinentes, las limitaciones intrnsecas que el desarrollo de procesos de ablacin directa selectiva con lseres UV en parte de los materiales utilizados presenta en el rango temporal de interaccin de ns y ps. En este trabajo se han desarrollado y optimizado los tres pasos estndar de interconexin (los habitualmente denominados Pl, P2 y P3 en la industria fotovoltaica) demostrando las ventajas y limitaciones del uso de fuentes en UV tanto con ancho temporal de ns como de ps. En particular destaca, por el xito en los resultados obtenidos, el estudio de procesos de ablacin selectiva de xidos conductores transparentes (en este trabajo utilizados tanto como contacto frontal as como posterior en los mdulos) que ha generado resultados, de excelente acogida cientfica a nivel internacional, cuya aplicacin trasciende el mbito de las tecnologas de silicio amorfo en lmina delgada. Adems en este trabajo de Tesis, en el desarrollo del objetivo citado, se han puesto a punto tcnicas de anlisis de los procesos lser, basadas en mtodos avanzados de caracterizacin de materiales (como el uso combinado de la espectroscopia dispersiva de rayos X y la microscopa confocal de barrido) que se presentan como autnticos avances en el desarrollo de tcnicas especficas de caracterizacin para el estudio de los procesos con lser de ablacin selectiva de materiales en lmina delgada, procesos que no solo tienen impacto en el mbito de la fotovoltaica, sino tambin en la microelectrnica, la biotecnologa, la microfabricacin, etc. Como resultado adicional, parte de los resultados de este trabajo, han sido aplicados exitosamente por el grupo de investigacion en la que la autora desarrolla su labor para conseguir desarrollar procesos de enorme interes en otras tec-nologas fotovoltaicas, como las tecnologas estandar de silicio amorfo sobre vidrio en configuracion de superestrato o el procesado de capas delgadas en tecnologas convencionales de silicio cristalino. Por ultimo decir que este trabajo ha sido posible por una colaboracion muy estrecha entre el Centro Laser de la UPM, en el que la autora desarrolla su labor, y el Grupo de Silicio Depositado del Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, CIEMAT, que, junto al Grupo de Energa Fotovoltaica de la Universidad de Barcelona, han preparado la mayor parte de las muestras utilizadas en este estudio. Dichas colaboraciones se han desarrollado en el marco de varios proyectos de investigacion aplicada con subvencion publica, tales como el proyecto singular estrategico PSE-MICROSIL08 (PSE-120000-2006-6), el proyecto INNDISOL (IPT-420000-2010-6), ambos financiados porel Fondo Europeo de Desarrollo Regional FEDER (UE) Una manera de hacer Europa y el MICINN, y los proyectos de Plan Nacional AMIC (ENE2010-21384-C04- 02) y CLASICO (ENE2007-6772-C04-04), cuya financiacion ha permitido en gran parte llevar a termino este trabajo Abstract In the last decade, the laser technology has turned into an indispensable tool in the production of photovoltaic devices, especially of those based on thin film technology. Regardless the current crisis in the sector, the evolution of these technologies in the upcoming years will keep taking advantage of the flexibility and process quality of the laser tool for the accomplishment of the two basic goals that will convert the photovoltaic energy into economically viable: the manufacture cost reduction and the increase in the efficiency of the devices. Amongst the thin film laser technologies, the technology of devices based on amorphous silicon has had a great development in standard systems of superstrate configuration, but its limited efficiency makes its survival dependant on the development of formats in substrate configuration with low cost flexible materials. In this approach, the laser industrial solutions currently available for the monolithic interconnection are not applicable, and in the last few years the investigations have been focused on the search of appropriate solutions for the development of such interconnection processes in a way that the same are transferable to the industry. In this context, this Thesis proposes a totally original approach, proving the possibility of executing a full interconnection of these devices by means of irradiation from the film side, i.e., compatible with the substrate configuration, and with UV laser sources. This result, obtained for the first time at international level in this work, provides a revealing knowledge of the true potential of these sources in the future industrial development of these technologies. Even though very probably the final industrial solution will require a combination of the use of UV sources along with other wavelengths, this Thesis and its novel approach contribute with a high value to the international community because of the originality of the approach, the partial results found throughout its development (out of which, a large number has appeared in JCR journals that currently accumulate a significant number of citations) and brings to light, with the pertinent scientific considerations, the intrinsic limitations that the selective direct ablation processes with UV laser present in the temporal range of interaction of ns and ps for part of the materials used in this study. More particularly, the three standard steps of interconnection (usually denominated P1, P2 and P3 in the photovoltaic industry) have been developed and optimized, showing the advantages as well as the limitations of the use of UV sources in both the ns and ps pulse-width ranges. It is highly remarkable, because of the success in the obtained results, the study of selective ablation processes in transparent conductive oxide (in this work used as a front and back contact), that has generated results, of excellent international scientific reception, whose applications go beyond the scope of thin film photovoltaic technologies based on amorphous silicon. Moreover, in this Thesis, with the development of the mentioned goal, different techniques of analysis of laser processes have been fine-tuned, basing the same in advanced methods for material characterization (like the combined use of EDX Analysis and Confocal Laser Scanning Microscopy) that can be presented as true breakthroughs in the development of specific techniques for characterization in the study of laser processes of selective ablation of materials in thin film technologies, processes that not only have impact in the photovoltaic field, but also in those of microelectronics, biotechnology, micro-fabrication, etc. As an additional outcome, part of the results of this work has been successfully applied, by the investigation group to which the author belongs, to the development of processes of enormous interest within other photovoltaic technologies, such as the standard technologies on amorphous silicon over glass in superstrate configuration or the processing of thin layers in conventional technologies using crystalline silicon. Lastly, it is important to mention that this work has been possible thanks to the close cooperation between the Centro Laser of the UPM, in which the author develops her work, and the Grupo de Silicio Depositado of Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, CIEMAT, which, along with the Grupo de Energa Fotovoltaica of Universidad de Barcelona, has prepared the largest part of the samples utilized in this study. Such collaborations have been carried out in the context of several projects of applied investigation with public funding, like Proyecto Singular Estrategico PSE-MICROSIL08 (PSE-120000-2006-6), Proyecto IN-NDISOL (IPT-420000-2010-6), both funded by the European Regional Development Fund (ERDF), Una manera de hacer Europa and MICINN, and the projects of Plan Nacional AMIC (ENE2010-21384-C04-02) and CLASICO (ENE2007-6772-C04-04), whose funds have enabled the devel-opment of large part of this work.
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A design for obtaining memory in optical bistability with liquid crystals is reported. This design uses optical feedback on a twisted nematie liquid crystal ( TNLC ) through an optoelectronic system. A constant input light is the read-out and its value depends on the desired initial working point, usually at the bottom of the T(V) vs. V curve. Light levels depend on the feedback. An input light pulse change the working point to the top of the transmission curve. When this pulse vanishes, the working point remains at the upper part of the curve. Hence a memory function is obtained. Minimum pulse width needed was 1msec. ON-OPF ratio was 100:3.
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El requerimiento de proveer alta frecuencia de datos en los modernos sistema de comunicacin inalmbricos resulta en complejas seales moduladas de radio-frequencia (RF) con un gran ancho de banda y alto ratio pico-promedio (PAPR). Para garantizar la linealidad del comportamiento, los amplificadores lineales de potencia comunes funcionan tpicamente entre 4 y 10 dB de back-o_ desde la mxima potencia de salida, ocasionando una baja eficiencia del sistema. La eliminacin y restauracin de la evolvente (EER) y el seguimiento de la evolvente (ET) son dos prometedoras tcnicas para resolver el problema de la eficiencia. Tanto en EER como en ET, es complicado disear un amplificador de potencia que sea eficiente para seales de RF de alto ancho de banda y alto PAPR. Una propuesta comn para los amplificadores de potencia es incluir un convertidor de potencia de muy alta eficiencia operando a frecuencias ms altas que el ancho de banda de la seal RF. En este caso, la potencia perdida del convertidor ocasionado por la alta frecuencia desaconseja su prctica cuando el ancho de banda es muy alto. La solucin a este problema es el enfoque de esta disertacin que presenta dos arquitecturas de amplificador evolvente: convertidor hbrido-serie con una tcnica de evolvente lenta y un convertidor multinivel basado en un convertidor reductor multifase con control de tiempo mnimo. En la primera arquitectura, una topologa hbrida est compuesta de una convertidor reductor conmutado y un regulador lineal en serie que trabajan juntos para ajustar la tensin de salida para seguir a la evolvente con precisin. Un algoritmo de generacin de una evolvente lenta crea una forma de onda con una pendiente limitada que es menor que la pendiente mxima de la evolvente original. La salida del convertidor reductor sigue esa forma de onda en vez de la evolvente original usando una menor frecuencia de conmutacin, porque la forma de onda no slo tiene una pendiente reducida sino tambin un menor ancho de banda. De esta forma, el regulador lineal se usa para filtrar la forma de onda tiene una prdida de potencia adicional. Dependiendo de cunto se puede reducir la pendiente de la evolvente para producir la forma de onda, existe un trade-off entre la prdida de potencia del convertidor reductor relacionada con la frecuencia de conmutacin y el regulador lineal. El punto ptimo referido a la menor prdida de potencia total del amplificador de evolvente es capaz de identificarse con la ayuda de modelo preciso de prdidas que es una combinacin de modelos comportamentales y analticos de prdidas. Adems, se analiza el efecto en la respuesta del filtro de salida del convertidor reductor. Un filtro de dampeo paralelo extra es necesario para eliminar la oscilacin resonante del filtro de salida porque el convertidor reductor opera en lazo abierto. La segunda arquitectura es un amplificador de evolvente de seguimiento de tensin multinivel. Al contrario que los convertidores que usan multi-fuentes, un convertidor reductor multifase se emplea para generar la tensin multinivel. En rgimen permanente, el convertidor reductor opera en puntos del ciclo de trabajo con cancelacin completa del rizado. El nmero de niveles de tensin es igual al nmero de fases de acuerdo a las caractersticas del entrelazamiento del convertidor reductor. En la transicin, un control de tiempo mnimo (MTC) para convertidores multifase es novedosamente propuesto y desarrollado para cambiar la tensin de salida del convertidor reductor entre diferentes niveles. A diferencia de controles convencionales de tiempo mnimo para convertidores multifase con inductancia equivalente, el propuesto MTC considera el rizado de corriente por cada fase basado en un desfase fijo que resulta en diferentes esquemas de control entre las fases. La ventaja de este control es que todas las corrientes vuelven a su fase en rgimen permanente despus de la transicin para que la siguiente transicin pueda empezar muy pronto, lo que es muy favorable para la aplicacin de seguimiento de tensin multinivel. Adems, el control es independiente de la carga y no es afectado por corrientes de fase desbalanceadas. Al igual que en la primera arquitectura, hay una etapa lineal con la misma funcin, conectada en serie con el convertidor reductor multifase. Dado que tanto el rgimen permanente como el estado de transicin del convertidor no estn fuertemente relacionados con la frecuencia de conmutacin, la frecuencia de conmutacin puede ser reducida para el alto ancho de banda de la evolvente, la cual es la principal consideracin de esta arquitectura. La optimizacin de la segunda arquitectura para ms alto anchos de banda de la evolvente es presentada incluyendo el diseo del filtro de salida, la frecuencia de conmutacin y el nmero de fases. El rea de diseo del filtro est restringido por la transicin rpida y el mnimo pulso del hardware. La rpida transicin necesita un filtro pequeo pero la limitacin del pulso mnimo del hardware lleva el diseo en el sentido contrario. La frecuencia de conmutacin del convertidor afecta principalmente a la limitacin del mnimo pulso y a las prdidas de potencia. Con una menor frecuencia de conmutacin, el ancho de pulso en la transicin es ms pequeo. El nmero de fases relativo a la aplicacin especfica puede ser optimizado en trminos de la eficiencia global. Otro aspecto de la optimizacin es mejorar la estrategia de control. La transicin permite seguir algunas partes de la evolvente que son ms rpidas de lo que el hardware puede soportar al precio de complejidad. El nuevo mtodo de sincronizacin de la transicin incrementa la frecuencia de la transicin, permitiendo que la tensin multinivel est ms cerca de la evolvente. Ambas estrategias permiten que el convertidor pueda seguir una evolvente con un ancho de banda ms alto que la limitacin de la etapa de potencia. El modelo de prdidas del amplificador de evolvente se ha detallado y validado mediante medidas. El mecanismo de prdidas de potencia del convertidor reductor tiene que incluir las transiciones en tiempo real, lo cual es diferente del clsico modelos de prdidas de un convertidor reductor sncrono. Este modelo estima la eficiencia del sistema y juega un papel muy importante en el proceso de optimizacin. Finalmente, la segunda arquitectura del amplificador de evolvente se integra con el amplificador de clase F. La medida del sistema EER prueba el ahorro de energa con el amplificador de evolvente propuesto sin perjudicar la linealidad del sistema. ABSTRACT The requirement of delivering high data rates in modern wireless communication systems results in complex modulated RF signals with wide bandwidth and high peak-to-average ratio (PAPR). In order to guarantee the linearity performance, the conventional linear power amplifiers typically work at 4 to 10 dB back-off from the maximum output power, leading to low system efficiency. The envelope elimination and restoration (EER) and envelope tracking (ET) are two promising techniques to overcome the efficiency problem. In both EER and ET, it is challenging to design efficient envelope amplifier for wide bandwidth and high PAPR RF signals. An usual approach for envelope amplifier includes a high-efficiency switching power converter operating at a frequency higher than the RF signal's bandwidth. In this case, the power loss of converter caused by high switching operation becomes unbearable for system efficiency when signal bandwidth is very wide. The solution of this problem is the focus of this dissertation that presents two architectures of envelope amplifier: a hybrid series converter with slow-envelope technique and a multilevel converter based on a multiphase buck converter with the minimum time control. In the first architecture, a hybrid topology is composed of a switched buck converter and a linear regulator in series that work together to adjust the output voltage to track the envelope with accuracy. A slow envelope generation algorithm yields a waveform with limited slew rate that is lower than the maximum slew rate of the original envelope. The buck converter's output follows this waveform instead of the original envelope using lower switching frequency, because the waveform has not only reduced slew rate but also reduced bandwidth. In this way, the linear regulator used to filter the waveform has additional power loss. Depending on how much reduction of the slew rate of envelope in order to obtain that waveform, there is a trade-off between the power loss of buck converter related to the switching frequency and the power loss of linear regulator. The optimal point referring to the lowest total power loss of this envelope amplifier is identified with the help of a precise power loss model that is a combination of behavioral and analytic loss model. In addition, the output filter's effect on the response is analyzed. An extra parallel damping filter is needed to eliminate the resonant oscillation of output filter L and C, because the buck converter operates in open loop. The second architecture is a multilevel voltage tracking envelope amplifier. Unlike the converters using multi-sources, a multiphase buck converter is employed to generate the multilevel voltage. In the steady state, the buck converter operates at complete ripple cancellation points of duty cycle. The number of the voltage levels is equal to the number of phases according the characteristics of interleaved buck converter. In the transition, a minimum time control (MTC) for multiphase converter is originally proposed and developed for changing the output voltage of buck converter between different levels. As opposed to conventional minimum time control for multiphase converter with equivalent inductance, the proposed MTC considers the current ripple of each phase based on the fixed phase shift resulting in different control schemes among the phases. The advantage of this control is that all the phase current return to the steady state after the transition so that the next transition can be triggered very soon, which is very favorable for the application of multilevel voltage tracking. Besides, the control is independent on the load condition and not affected by the unbalance of phase current. Like the first architecture, there is also a linear stage with the same function, connected in series with the multiphase buck converter. Since both steady state and transition state of the converter are not strongly related to the switching frequency, it can be reduced for wide bandwidth envelope which is the main consideration of this architecture. The optimization of the second architecture for wider bandwidth envelope is presented including the output filter design, switching frequency and the number of phases. The filter design area is restrained by fast transition and the minimum pulse of hardware. The fast transition needs small filter but the minimum pulse of hardware limitation pushes the filter in opposite way. The converter switching frequency mainly affects the minimum pulse limitation and the power loss. With lower switching frequency, the pulse width in the transition is smaller. The number of phases related to specific application can be optimized in terms of overall efficiency. Another aspect of optimization is improving control strategy. Transition shift allows tracking some parts of envelope that are faster than the hardware can support at the price of complexity. The new transition synchronization method increases the frequency of transition, allowing the multilevel voltage to be closer to the envelope. Both control strategies push the converter to track wider bandwidth envelope than the limitation of power stage. The power loss model of envelope amplifier is detailed and validated by measurements. The power loss mechanism of buck converter has to include the transitions in real time operation, which is different from classical power loss model of synchronous buck converter. This model estimates the system efficiency and play a very important role in optimization process. Finally, the second envelope amplifier architecture is integrated with a Class F amplifier. EER system measurement proves the power saving with the proposed envelope amplifier without disrupting the linearity performance.
Resumo:
Hybrid Stepper Motors are widely used in open-loop position applications. They are the choice of actuation for the collimators in the Large Hadron Collider, the largest particle accelerator at CERN. In this case the positioning requirements and the highly radioactive operating environment are unique. The latter forces both the use of long cables to connect the motors to the drives which act as transmission lines and also prevents the use of standard position sensors. However, reliable and precise operation of the collimators is critical for the machine, requiring the prevention of step loss in the motors and maintenance to be foreseen in case of mechanical degradation. In order to make the above possible, an approach is proposed for the application of an Extended Kalman Filter to a sensorless stepper motor drive, when the motor is separated from its drive by long cables. When the long cables and high frequency pulse width modulated control voltage signals are used together, the electrical signals difer greatly between the motor and drive-side of the cable. Since in the considered case only drive-side data is available, it is therefore necessary to estimate the motor-side signals. Modelling the entire cable and motor system in an Extended Kalman Filter is too computationally intensive for standard embedded real-time platforms. It is, in consequence, proposed to divide the problem into an Extended Kalman Filter, based only on the motor model, and separated motor-side signal estimators, the combination of which is less demanding computationally. The efectiveness of this approach is shown in simulation. Then its validity is experimentally demonstrated via implementation in a DSP based drive. A testbench to test its performance when driving an axis of a Large Hadron Collider collimator is presented along with the results achieved. It is shown that the proposed method is capable of achieving position and load torque estimates which allow step loss to be detected and mechanical degradation to be evaluated without the need for physical sensors. These estimation algorithms often require a precise model of the motor, but the standard electrical model used for hybrid stepper motors is limited when currents, which are high enough to produce saturation of the magnetic circuit, are present. New model extensions are proposed in order to have a more precise model of the motor independently of the current level, whilst maintaining a low computational cost. It is shown that a significant improvement in the model It is achieved with these extensions, and their computational performance is compared to study the cost of model improvement versus computation cost. The applicability of the proposed model extensions is demonstrated via their use in an Extended Kalman Filter running in real-time for closed-loop current control and mechanical state estimation. An additional problem arises from the use of stepper motors. The mechanics of the collimators can wear due to the abrupt motion and torque profiles that are applied by them when used in the standard way, i.e. stepping in open-loop. Closed-loop position control, more specifically Field Oriented Control, would allow smoother profiles, more respectful to the mechanics, to be applied but requires position feedback. As mentioned already, the use of sensors in radioactive environments is very limited for reliability reasons. Sensorless control is a known option but when the speed is very low or zero, as is the case most of the time for the motors used in the LHC collimator, the loss of observability prevents its use. In order to allow the use of position sensors without reducing the long term reliability of the whole system, the possibility to switch from closed to open loop is proposed and validated, allowing the use of closed-loop control when the position sensors function correctly and open-loop when there is a sensor failure. A different approach to deal with the switched drive working with long cables is also presented. Switched mode stepper motor drives tend to have poor performance or even fail completely when the motor is fed through a long cable due to the high oscillations in the drive-side current. The design of a stepper motor output fillter which solves this problem is thus proposed. A two stage filter, one devoted to dealing with the diferential mode and the other with the common mode, is designed and validated experimentally. With this ?lter the drive performance is greatly improved, achieving a positioning repeatability even better than with the drive working without a long cable, the radiated emissions are reduced and the overvoltages at the motor terminals are eliminated.
