Radio-Communications Architectures

Wireless communications, i.e. radio-communications, are widely used for our different daily needs. Examples are numerous and standard names like BLUETOOTH, WiFI, WiMAX, UMTS, GSM and, more recently, LTE are well-known [Baudoin et al. 2007]. General applications in the RFID or UWB contexts are the subject of many papers. This chapter presents radio-frequency (RF) communication systems architecture for mobile, wireless local area networks (WLAN) and connectivity terminals. An important aspect of today's applications is the data rate increase, especially in connectivity standards like WiFI and WiMAX, because the user demands high Quality of Service (QoS). To increase the data rate we tend to use wideband or multi-standard architecture. The concept of software radio includes a self-reconfigurable radio link and is described here on its RF aspects. The term multi-radio is preferred. This chapter focuses on the transmitter, yet some considerations about the receiver are given. An important aspect of the architecture is that a transceiver is built with respect to the radio-communications signals. We classify them in section 2 by differentiating Continuous Wave (CW) and Impulse Radio (IR) systems. Section 3 is the technical background one has to consider for actual applications. Section 4 summarizes state-of-the-art high data rate architectures and the latest research in multi-radio systems. In section 5, IR architectures for Ultra Wide Band (UWB) systems complete this overview; we will also underline the coexistence and compatibility challenges between CW and IR systems

Towards Very Large Scale Analog (VLSA): Synthesizable Frequency Generation Circuits.

Driven by advancement in integrated circuit design and fabrication technologies, electronic systems have become ubiquitous. This has been enabled powerful digital design tools that continue to shrink the design cost, time-to-market, and the size of digital circuits. Similarly, the manufacturing cost has been constantly declining for the last four decades due to CMOS scaling. However, analog systems have struggled to keep up with the unprecedented scaling of digital circuits. Even today, the majority of the analog circuit blocks are custom designed, do not scale well, and require long design cycles. This thesis analyzes the factors responsible for the slow scaling of analog blocks, and presents a new design methodology that bridges the gap between traditional custom analog design and the modern digital design. The proposed methodology is utilized in implementation of the frequency generation circuits – traditionally considered analog systems. Prototypes covering two different applications were implemented. The first synthesized all-digital phase-locked loop was designed for 400-460 MHz MedRadio applications and was fabricated in a 65 nm CMOS process. The second prototype is an ultra-low power, near-threshold 187-500 kHz clock generator for energy harvesting/autonomous applications. Finally, a digitally-controlled oscillator frequency resolution enhancement technique is presented which allows reduction of quantization noise in ADPLLs without introducing spurs.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/109027/1/mufaisal_1.pd

Contributions to Modulation and Control Algorithms for Multilevel Converters

Las actuales tendencias de la red eléctrica han lanzado a la industria a la búsqueda de sistemas de generación, distribución y consumo de energía eléctrica más eficientes. Generación distribuida, reducción de componentes pasivos, líneas DC de alta tensión son, entre otras, las posibles líneas de investigación que están actualmente siendo consideradas como el futuro de la red eléctrica. Sin embargo, nada de esto sería posible si no fuera por los avances alcanzados en el campo de la electrónica de potencia. El trabajo aquí presentado comienza con una breve introducción a la electrónica de potencia, concretamente a los convertidores de potencia conectados a red, sus estrategias de control más comunes y enfoques ante redes desbalanceadas. A continuación, las contribuciones del autor sobre el control y modulación de una topología particular de convertidores, conocidos como convertidores multinivel, se presentan como el principal contenido de este trabajo. Este tipo de convertidores mejoran la eficiencia y ciertas prestaciones, en comparación con convertidores más tradicionales, a costa de una mayor complejidad en el control al incrementar la cantidad de los componentes hardware. A pesar de que existen numerosas topologías de convertidores multinivel y algunas de ellas son brevemente expuestas en este trabajo, la mayoría de las aportaciones están enfocadas para convertidores del tipo diode-clamped converter. Adicionalmente, se incluye una aportación para convertidores del tipo multinivel modular, y otra para convertidores en cascada. Se espera que el contenido de la introducción de este trabajo, junto a las contribuciones particulares para convertidores multinivel sirva de inspiración para futuros investigadores del campo

Development of an active power filter based on wide-bandgap semiconductors

Pla de Doctorat Industrial, Generalitat de CatalynuaElectrical and electronic equipment needs sinusoidal currents and voltages to function properly. Equipment such as computers, household appliances, electric vehicle chargers, and LED lights can distort the grid and worsen grid quality. Distorted electrical grids can cause malfunctions, reduce service life, and decrease the performance of connected equipment. Industry commonly solves these problems using active power filters, which can minimise the harmonics of the grid, eliminate undesirable reactive power, and restore balance to unbalanced power grids. This thesis deals with the design and implementation of an active power filter based on wide-bandgap semiconductors, which have properties that are superior to classical silicon devices. An active power filter’s design must take advantage of these benefits to build converters that are smaller, more efficient, and consume fewer resources. However, wide-bandgap semiconductors also present design challenges. Because the most commonly used active power filters in the industry are based on two-level voltage source converters, the research for this doctoral thesis focuses on this converter topology. Moreover, its main objective is to contribute new modulation techniques that are specially designed to work with wide-bandgap semiconductors. The proposed modulations consider different aspects, such as the computational cost of the algorithms, converter losses, and the electromagnetic distortion generated. First, this thesis presents a hexagonal sigma-delta (H-S¿) modulation based on sigma-delta (S¿) modulation. The properties of this modulation are studied, and the technique is compared with other widely used modulations. The comparison considers efficiency, harmonic distortion, the electromagnetic compatibility of the converter, and the type of wideband semiconductor used. In addition, a fast algorithm is mathematically developed to simplify the presented modulation and reduce its computational cost. Secondly, this thesis presents a family of sigma-delta modulations specially designed to improve electromagnetic compatibility: the reduced common-mode voltage sigma-delta (RCMV-S¿) modulations. These modulations avoid using the vectors that generate the maximum common-mode voltage, which significantly reduces the generated electromagnetic distortion without affecting the performance of the converter and its harmonic distortion. Finally, the proposed modulations are applied in a wide-bandgap power converter working as an active filter. Thus, it is verified that the techniques presented in this thesis will obtain satisfactory results when implemented in commercial active power filters.Els equips elèctrics i electrònics necessiten corrents i tensions sinusoïdals per funcionar correctament. Existeixen equips com els ordinadors, els electrodomèstics, els carregadors de vehicle elèctric o les llums LED, que poden distorsionar la xarxa i empitjorar la qualitat d'aquesta. Les xarxes elèctriques distorsionades poden causar el mal funcionament dels equips que s'hi connecten, reduir la seva vida útil i també empitjorar la seva eficiència. A la industria és habitual utilitzar filtres actius per a solucionar aquests problemes. Els filtres actius permeten minimitzar els harmònics presents a la Δxarxa, eliminar la potència reactiva no desitjada i equilibrar xarxes elèctriques desequilibrades. Aquesta tesi tracta sobre el disseny i la implementació d'un filtre actiu basat en semiconductors de banda ampla. Aquests semiconductors presenten propietats superiors als clàssics dispositius de silici. El disseny d'un filtre actiu ha d'aprofitar aquests avantatges per a construir convertidors més petits, eficients i que consumeixin menys recursos. Tanmateix, els semiconductors de banda ampla també presenten problemes que el disseny ha de solucionar. Els filtres actius més utilitzats en la indústria són els basats en convertidors de font de tensió (voltatge source converters) amb dos nivells. La recerca d'aquesta tesi doctoral està focalitzada en aquesta topologia de convertidor, i el seu principal objectiu és l’aportació de noves tècniques de modulació especialment dissenyades per treballar amb semiconductors de banda ampla. Les modulacions proposades tenen en compte diferents aspectes: el cost computacional dels algoritmes, les pèrdues del convertidor i la distorsió electromagnètica generada. En primer lloc, es presenta una modulació sigma-delta hexagonal (H-__) que es basa en la modulació sigma-delta (ΣΔ). S'estudien les propietats d'aquesta modulació i la tècnica es compara amb altres modulacions àmpliament usades. La comparativa realitzada considera l’eficiència, la distorsió harmònica, la compatibilitat electromagnètica del convertidor i el tipus de semiconductor de banda ampla emprat. Addicionalment, es desenvolupa matemàticament un algoritme ràpid per simplificar la modulació presentada i reduir el seu cost computacional. En segon lloc, es presenta una família de modulacions sigma-delta especialment dissenyades per millorar la compatibilitat electromagnètica: les modulacions sigmadelta amb tensió en mode comú reduïda (RCMV-ΣΔ ). Aquestes modulacions eviten fer servir els vectors que generen la màxima tensió en mode comú. D'aquesta manera es redueix significativament la distorsió electromagnètica generada sense afectar de forma notable al rendiment del convertidor ni a la seva distorsió harmònica. Finalment, les modulacions proposades s'apliquen en un convertidor de potència, basat en semiconductors de banda ampla, que treballa com a filtre actiu. Això es verifica que les tècniques presentades en aquesta tesi poden ser implementades en filtres actius comercials obtenint resultats satisfactoris.Postprint (published version

Contributions on spectral control for the asymmetrical full bridge multilevel inverter

Las topologías de circuitos inversores multinivel pueden trabajar a tensiones y potencias mayores que las alcanzadas por convertidores convencionales de dos niveles. Además, la conversión multinivel reduce la distorsión armónica de las variables de salida y en algunos casos, a pesar del aumento de elementos de conmutación, también reduce las pérdidas de conversión al incrementarse el número de niveles. La reducción de distorsión alcanzada por el número de niveles puede aprovecharse para reducir las pérdidas de conmutación disminuyendo la frecuencia de las señales portadoras. Para reducir aún más esta frecuencia sin degradar el espectro, nosotros controlamos las pendientes de las portadoras triangulares. Primero se han desarrollado dos modelos analíticos para predecir el espectro del voltage de salida, dependiendo de: el índice de modulación MA, la razón de distribución de voltaje K de las fuentes de alimentación , y las cuatro pendientes de las portadoras{r1, r2, r3, r4}. El primer modelo considera el Muestreo Natural y se basa en Series Dobles de Fourier (SDF) mientras que el segundo modelo, utiliza la Serie Sencilla de Fourier (SSF) introduciendo el concepto de Muestreo Pseudo-Natural, una aproximación digital de la modulación natural. Ambos modelos son programados en Matlab, verificados con Pspice y validados con un prototipo experimental que contiene un modulador digital implementado con DSP.La concordancia entre las modulaciones natural y pseudo-natural, asi como entre sus respectivos modelos, es aprovechada por un algorítmo genético (AG) donde la THD es la función costo a reducir. Después de varios ensayos y de sintonizar el AG, se genera una matriz que contiene conjuntos de portadoras optimizadas dentro un rango específico de las variables {MA,K} y es probada con un segundo prototipo en lazo cerrado. Un lazo lento digital modifica las portadoras creadas por un dsPIC en modulaciones PWM; estas son demoduladas y sus amplitudes corregidas por un lazo de acción anticipada. Estas portadoras se comparan con una referencia sinusoidal que a su vez es modificada por variables de estado, generando finalmente la modulación multinivel en lazo cerrado. Los resultados finales demuestran la fiabilidad de la reducción de armónicos usando la programación de las pendientes de las portadoras. Palabras claves: inversor multinivel, PWM, distorsión armónica, modelo espectral, pendiente de portadora, conjunto de portadoras, distribución de niveles, Serie Doble de Fourier, Serie Simple de Fourier, muestreo natural, muestreo regular, muestreo pseudo-natural , Algoritmos Genéticos.Multilevel inverter (MI) topologies can work at higher voltage and higher power than conventional two-level converters. In addition, multilevel conversion reduces the output variables harmonic distortion and, sometimes, in spite of the devices-count increment, the conversion losses can also decrease by increasing the number of levels. The harmonic distortion reduction achieved by increasing the number of levels, can be used to further reducing the switching losses by decreasing the inverter carrier frequencies. To reduce even more the switching frequency without degrading output spectrum, we control the triangular carrier waveforms slopes. First, to achieve this target, two analytical models have been created in order to predict the inverter output voltage spectrum, depending on diverse parameters: the amplitude modulation index MA, the voltage distribution K of the inverter input sources, and the four carrier slopes {r1, r2, r3, r4}. The first model considers Natural Sampling and is based on Double Fourier Series (DFS) whereas the second model based on Simple Fourier Series (SFS), introduces the concept of Pseudo-Natural Sampling, as a digital approximation of the natural modulation. Both models are programmed in Matlab, verified with Pspice simulations and validated with a first experimental prototype with a DSP digital modulator.The good agreement between natural and pseudo-natural modulations, as well as their respective DFS and SFS models, is exploited by a Genetic Algorithm (GA) application where THD is the cost function to minimize. After testing and properly tuning the GA, a framework matrix containing the optimized carriers set for a specific range of variables {MA,K} is generated and then, tested with a second, closed-loop prototype. A slow digital loop modifies the carrier slopes created by dsPIC microcontroller as PWM modulations, whose amplitude, once demodulated, are affected by a feed-forward loop. These carriers, compared with a sinusoidal reference, state-feedback modified, generate finally the closed-loop multilevel modulation. The final results demonstrates the feasibility of harmonic reduction by means of carrier slopes programming. Keywords: multilevel inverter, PWM, harmonic distortion, spectral modeling, carrier slope, carriers set, level distribution, Double Fourier Series, Simple Fourier Series, natural sampling, regular sampling, pseudo-natural sampling, Genetic Algorithms

Grid integration of renewable power generation

This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation.This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation

Direct imaging of a digital-micromirror device for configurable microscopic optical potentials

Programable spatial light modulators (SLMs) have significantly advanced the configurable optical trapping of particles. Typically, these devices are utilized in the Fourier plane of an optical system, but direct imaging of an amplitude pattern can potentially result in increased simplicity and computational speed. Here we demonstrate high-resolution direct imaging of a digital micromirror device (DMD) at high numerical apertures (NA), which we apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a (1200 x 1920) pixel DMD and commercially available 0.45 NA microscope objectives, finding that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue-detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5% of the diffraction limit. The result is near arbitrary control of the density the BEC without the need for expensive custom optics. We also introduce the technique of time-averaged DMD potentials, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud, by utilising the high switching speed (20 kHz maximum) of the DMD. These techniques will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases. The performance of this system in a direct imaging configuration has wider application for optical trapping at non-trivial NAs.Comment: 9 page