Energy and conductance state modeling of power electronic converters for DC microgrids

This document will demonstrate the methodology used to create an energy and conductance based model for power electronic converters. The work is intended to be a replacement for voltage and current based models which have limited applicability to the network nodal equations. Using conductance-based modeling allows direct application of load differential equations to the bus admittance matrix (Y-bus) with a unified approach. When applied directly to the Y-bus, the system becomes much easier to simulate since the state variables do not need to be transformed. The proposed transformation applies to loads, sources, and energy storage systems and is useful for DC microgrids. Transformed state models of a complete microgrid are compared to experimental results and show the models accurately reflect the system dynamic behavior.

Influence of directionality and maximal power output on speech understanding with bone anchored hearing implants in single sided deafness

Bone-anchored hearing implants (BAHI) are routinely used to alleviate the effects of the acoustic head shadow in single-sided sensorineural deafness (SSD). In this study, the influence of the directional microphone setting and the maximum power output of the BAHI sound processor on speech understanding in noise in a laboratory setting were investigated. Eight adult BAHI users with SSD participated in this pilot study. Speech understanding in noise was measured using a new Slovak speech-in-noise test in two different spatial settings, either with noise coming from the front and noise from the side of the BAHI (S90N0) or vice versa (S0N90). In both spatial settings, speech understanding was measured without a BAHI, with a Baha BP100 in omnidirectional mode, with a BP100 in directional mode, with a BP110 power in omnidirectional and with a BP110 power in directional mode. In spatial setting S90N0, speech understanding in noise with either sound processor and in either directional mode was improved by 2.2-2.8 dB (p = 0.004-0.016). In spatial setting S0N90, speech understanding in noise was reduced by either BAHI, but was significantly better by 1.0-1.8 dB, if the directional microphone system was activated (p = 0.046), when compared to the omnidirectional setting. With the limited number of subjects in this study, no statistically significant differences were found between the two sound processors.

Nuclear power plants and childhood leukaemia: lessons from the past and future directions

In the 1980s, leukaemia clusters were discovered around nuclear fuel reprocessing plants in Sellafield and Dounreay in the United Kingdom. This raised public concern about the risk of childhood leukaemia near nuclear power plants (NPPs). Since then, the topic has been well-studied, but methodological limitations make results difficult to interpret. Our review aims to: (1.) summarise current evidence on the relationship between NPPs and risk of childhood leukaemia, with a focus on the Swiss CANUPIS (Childhood cancer and nuclear power plants in Switzerland) study; (2.) discuss the limitations of previous research; and (3.) suggest directions for future research. There are various reasons that previous studies produced inconclusive results. These include: inadequate study designs and limited statistical power due to the low prevalence of exposure (living near a NPP) and outcome (leukaemia); lack of accurate exposure estimates; limited knowledge of the aetiology of childhood leukaemia, particularly of vulnerable time windows and latent periods; use of residential location at time of diagnosis only and lack of data on address histories; and inability to adjust for potential confounders. We conclude that risk of childhood leukaemia around NPPs should continue to be monitored and that study designs should be improved and standardised. Data should be pooled internationally to increase the statistical power. More research needs to be done on other putative risk factors for childhood cancer such as low-dose ionizing radiation, exposure to certain chemicals and exposure to infections. Studies should be designed to allow examining multiple exposures.

Power Games in Strategy Formation Processes – A Performative Interpretation

The article approaches an understanding of power within strategy formation processes established by verbal and bodily communication. On this note, we examined concepts of power constituted by hierarchy and developed a conceptual framework for a performative interpretation of power. In line with Austin’s (1962) and Butler’s (1990, 1993, 1997) concept of performativity as well as strategy-as-practice research (Balogun et al., 2007; Jarzabkowski & Spee, 2009) we ask: How is persuasion achieved by strategic actors during strategy formation processes? To explore verbal and bodily communication empirically we developed an experimental setting in a small high-tech company located in Germany in December, 2012. The Results indicate that (1) during critical incidents – when perspectives clash – actors use arguments to gain persuasion. (2) The data illustrates that independently of their hierarchical position within the company, strategic actors show an equal distribution of argumentative techniques.

The role of workplace absence as an organizational mechanism in predicting employee alcohol and drug disorders

Background. EAP programs for airline pilots in companies with a well developed recovery management program are known to reduce pilot absenteeism following treatment. Given the costs and safety consequences to society, it is important to identify pilots who may be experiencing an AOD disorder to get them into treatment. ^ Hypotheses. This study investigated the predictive power of workplace absenteeism in identifying alcohol or drug disorders (AOD). The first hypothesis was that higher absenteeism in a 12-month period is associated with higher risk that an employee is experiencing AOD. The second hypothesis was that AOD treatment would reduce subsequent absence rates and the costs of replacing pilots on missed flights. ^ Methods. A case control design using eight years (time period) of monthly archival absence data (53,000 pay records) was conducted with a sample of (N = 76) employees having an AOD diagnosis (cases) matched 1:4 with (N = 304) non-diagnosed employees (controls) of the same profession and company (male commercial airline pilots). Cases and controls were matched on the variables age, rank and date of hire. Absence rate was defined as sick time hours used over the sum of the minimum guarantee pay hours annualized using the months the pilot worked for the year. Conditional logistic regression was used to determine if absence predicts employees experiencing an AOD disorder, starting 3 years prior to the cases receiving the AOD diagnosis. A repeated measures ANOVA, t tests and rate ratios (with 95% confidence intervals) were conducted to determine differences between cases and controls in absence usage for 3 years pre and 5 years post treatment. Mean replacement costs were calculated for sick leave usage 3 years pre and 5 years post treatment to estimate the cost of sick leave from the perspective of the company. ^ Results. Sick leave, as measured by absence rate, predicted the risk of being diagnosed with an AOD disorder (OR 1.10, 95% CI = 1.06, 1.15) during the 12 months prior to receiving the diagnosis. Mean absence rates for diagnosed employees increased over the three years before treatment, particularly in the year before treatment, whereas the controls’ did not (three years, x = 6.80 vs. 5.52; two years, x = 7.81 vs. 6.30, and one year, x = 11.00cases vs. 5.51controls. In the first year post treatment compared to the year prior to treatment, rate ratios indicated a significant (60%) post treatment reduction in absence rates (OR = 0.40, CI = 0.28, 0.57). Absence rates for cases remained lower than controls for the first three years after completion of treatment. Upon discharge from the FAA and company’s three year AOD monitoring program, case’s absence rates increased slightly during the fourth year (controls, x = 0.09, SD = 0.14, cases, x = 0.12, SD = 0.21). However, the following year, their mean absence rates were again below those of the controls (controls, x = 0.08, SD = 0.12, cases, x¯ = 0.06, SD = 0.07). Significant reductions in costs associated with replacing pilots calling in sick, were found to be 60% less, between the year of diagnosis for the cases and the first year after returning to work. A reduction in replacement costs continued over the next two years for the treated employees. ^ Conclusions. This research demonstrates the potential for workplace absences as an active organizational surveillance mechanism to assist managers and supervisors in identifying employees who may be experiencing or at risk of experiencing an alcohol/drug disorder. Currently, many workplaces use only performance problems and ignore the employee’s absence record. A referral to an EAP or alcohol/drug evaluation based on the employee’s absence/sick leave record as incorporated into company policy can provide another useful indicator that may also carry less stigma, thus reducing barriers to seeking help. This research also confirms two conclusions heretofore based only on cross-sectional studies: (1) higher absence rates are associated with employees experiencing an AOD disorder; (2) treatment is associated with lower costs for replacing absent pilots. Due to the uniqueness of the employee population studied (commercial airline pilots) and the organizational documentation of absence, the generalizability of this study to other professions and occupations should be considered limited. ^ Transition to Practice. The odds ratios for the relationship between absence rates and an AOD diagnosis are precise; the OR for year of diagnosis indicates the likelihood of being diagnosed increases 10% for every hour change in sick leave taken. In practice, however, a pilot uses approximately 20 hours of sick leave for one trip, because the replacement will have to be paid the guaranteed minimum of 20 hour. Thus, the rate based on hourly changes is precise but not practical. ^ To provide the organization with practical recommendations the yearly mean absence rates were used. A pilot flies on average, 90 hours a month, 1080 annually. Cases used almost twice the mean rate of sick time the year prior to diagnosis (T-1) compared to controls (cases, x = .11, controls, x = .06). Cases are expected to use on average 119 hours annually (total annual hours*mean annual absence rate), while controls will use 60 hours. The cases’ 60 hours could translate to 3 trips of 20 hours each. Management could use a standard of 80 hours or more of sick time claimed in a year as the threshold for unacceptable absence, a 25% increase over the controls (a cost to the company of approximately of $4000). At the 80-hour mark, the Chief Pilot would be able to call the pilot in for a routine check as to the nature of the pilot’s excessive absence. This management action would be based on a company standard, rather than a behavioral or performance issue. Using absence data in this fashion would make it an active surveillance mechanism. ^

Design and Optimization of Power Delivery and Distribution Systems Using Evolutionary Computation Techniques

Nowadays computing platforms consist of a very large number of components that require to be supplied with diferent voltage levels and power requirements. Even a very small platform, like a handheld computer, may contain more than twenty diferent loads and voltage regulators. The power delivery designers of these systems are required to provide, in a very short time, the right power architecture that optimizes the performance, meets electrical specifications plus cost and size targets. The appropriate selection of the architecture and converters directly defines the performance of a given solution. Therefore, the designer needs to be able to evaluate a significant number of options in order to know with good certainty whether the selected solutions meet the size, energy eficiency and cost targets. The design dificulties of selecting the right solution arise due to the wide range of power conversion products provided by diferent manufacturers. These products range from discrete components (to build converters) to complete power conversion modules that employ diferent manufacturing technologies. Consequently, in most cases it is not possible to analyze all the alternatives (combinations of power architectures and converters) that can be built. The designer has to select a limited number of converters in order to simplify the analysis. In this thesis, in order to overcome the mentioned dificulties, a new design methodology for power supply systems is proposed. This methodology integrates evolutionary computation techniques in order to make possible analyzing a large number of possibilities. This exhaustive analysis helps the designer to quickly define a set of feasible solutions and select the best trade-off in performance according to each application. The proposed approach consists of two key steps, one for the automatic generation of architectures and other for the optimized selection of components. In this thesis are detailed the implementation of these two steps. The usefulness of the methodology is corroborated by contrasting the results using real problems and experiments designed to test the limits of the algorithms.

Spherical collectors versus bare tethers for drag, thrust, and power generation

Performances of ED-tethers using either spherical collectors or bare tethers for drag, thrust, or power generation, are compared. The standard Parker-Murphy model of current to a full sphere, with neither space-charge nor plasmamotion effects considered, but modified to best fit TSS1R results, is used (the Lam, Al'pert/Gurevich space-charge limited model will be used elsewhere) In the analysis, the spherical collector is assumed to collect current well beyond its random-current value (thick-heath). Both average current in the bare-tether and current to the sphere are normalized with the short-circuit current in the absence of applied power, allowing a comparison of performances for all three applications in terms of characteristic dimensionless numbers. The sphere is always substantially outperformed by the bare-tether if ohmic effects are weak, though its performance improves as such effects increase.

Limits of the power of Tissue P systems with cell division

Tissue P systems generalize the membrane structure tree usual in original models of P systems to an arbitrary graph. Basic opera- tions in these systems are communication rules, enriched in some variants with cell division or cell separation. Several variants of tissue P systems were recently studied, together with the concept of uniform families of these systems. Their computational power was shown to range between P and NP ? co-NP , thus characterizing some interesting borderlines between tractability and intractability. In this paper we show that com- putational power of these uniform families in polynomial time is limited by the class PSPACE . This class characterizes the power of many clas- sical parallel computing models

High data rate modulation of high power 1060-nm DBR tapered lasers with separate contacts

Direct optical modulation at 2.5 Gb/s with amplitude of more than 0.5 W has been demonstrated in single longitudinal mode distributed Bragg reflector tapered lasers emitting at 1060 nm with separated injection of the ridge waveguide and tapered sections. The modulating signal of ~110 mA peak to peak was applied to the ridge waveguide section, yielding a high modulation efficiency of ~5 W/A. The large-signal frequency response of the experimental set-up was limited by the bandwidth of the electrical amplifier rather than by the internal dynamics of the laser, indicating that higher bit rates could be achieved with improved driving electronics.

Wide bandwidth envelope trackers with reduced switching frequency for RF power amplifier

El requerimiento de proveer alta frecuencia de datos en los modernos sistema de comunicación inalámbricos resulta en complejas señales 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 típicamente entre 4 y 10 dB de back-o_ desde la máxima potencia de salida, ocasionando una baja eficiencia del sistema. La eliminación y restauración de la evolvente (EER) y el seguimiento de la evolvente (ET) son dos prometedoras técnicas para resolver el problema de la eficiencia. Tanto en EER como en ET, es complicado diseñar un amplificador de potencia que sea eficiente para señales de RF de alto ancho de banda y alto PAPR. Una propuesta común para los amplificadores de potencia es incluir un convertidor de potencia de muy alta eficiencia operando a frecuencias más altas que el ancho de banda de la señal RF. En este caso, la potencia perdida del convertidor ocasionado por la alta frecuencia desaconseja su práctica cuando el ancho de banda es muy alto. La solución a este problema es el enfoque de esta disertación que presenta dos arquitecturas de amplificador evolvente: convertidor híbrido-serie con una técnica de evolvente lenta y un convertidor multinivel basado en un convertidor reductor multifase con control de tiempo mínimo. En la primera arquitectura, una topología híbrida está compuesta de una convertidor reductor conmutado y un regulador lineal en serie que trabajan juntos para ajustar la tensión de salida para seguir a la evolvente con precisión. Un algoritmo de generación de una evolvente lenta crea una forma de onda con una pendiente limitada que es menor que la pendiente máxima 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 conmutación, porque la forma de onda no sólo tiene una pendiente reducida sino también un menor ancho de banda. De esta forma, el regulador lineal se usa para filtrar la forma de onda tiene una pérdida de potencia adicional. Dependiendo de cuánto se puede reducir la pendiente de la evolvente para producir la forma de onda, existe un trade-off entre la pérdida de potencia del convertidor reductor relacionada con la frecuencia de conmutación y el regulador lineal. El punto óptimo referido a la menor pérdida de potencia total del amplificador de evolvente es capaz de identificarse con la ayuda de modelo preciso de pérdidas que es una combinación de modelos comportamentales y analíticos de pérdidas. Además, 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 oscilación resonante del filtro de salida porque el convertidor reductor opera en lazo abierto. La segunda arquitectura es un amplificador de evolvente de seguimiento de tensión multinivel. Al contrario que los convertidores que usan multi-fuentes, un convertidor reductor multifase se emplea para generar la tensión multinivel. En régimen permanente, el convertidor reductor opera en puntos del ciclo de trabajo con cancelación completa del rizado. El número de niveles de tensión es igual al número de fases de acuerdo a las características del entrelazamiento del convertidor reductor. En la transición, un control de tiempo mínimo (MTC) para convertidores multifase es novedosamente propuesto y desarrollado para cambiar la tensión de salida del convertidor reductor entre diferentes niveles. A diferencia de controles convencionales de tiempo mínimo 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 régimen permanente después de la transición para que la siguiente transición pueda empezar muy pronto, lo que es muy favorable para la aplicación de seguimiento de tensión multinivel. Además, 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 función, conectada en serie con el convertidor reductor multifase. Dado que tanto el régimen permanente como el estado de transición del convertidor no están fuertemente relacionados con la frecuencia de conmutación, la frecuencia de conmutación puede ser reducida para el alto ancho de banda de la evolvente, la cual es la principal consideración de esta arquitectura. La optimización de la segunda arquitectura para más alto anchos de banda de la evolvente es presentada incluyendo el diseño del filtro de salida, la frecuencia de conmutación y el número de fases. El área de diseño del filtro está restringido por la transición rápida y el mínimo pulso del hardware. La rápida transición necesita un filtro pequeño pero la limitación del pulso mínimo del hardware lleva el diseño en el sentido contrario. La frecuencia de conmutación del convertidor afecta principalmente a la limitación del mínimo pulso y a las pérdidas de potencia. Con una menor frecuencia de conmutación, el ancho de pulso en la transición es más pequeño. El número de fases relativo a la aplicación específica puede ser optimizado en términos de la eficiencia global. Otro aspecto de la optimización es mejorar la estrategia de control. La transición permite seguir algunas partes de la evolvente que son más rápidas de lo que el hardware puede soportar al precio de complejidad. El nuevo método de sincronización de la transición incrementa la frecuencia de la transición, permitiendo que la tensión multinivel esté más cerca de la evolvente. Ambas estrategias permiten que el convertidor pueda seguir una evolvente con un ancho de banda más alto que la limitación de la etapa de potencia. El modelo de pérdidas del amplificador de evolvente se ha detallado y validado mediante medidas. El mecanismo de pérdidas de potencia del convertidor reductor tiene que incluir las transiciones en tiempo real, lo cual es diferente del clásico modelos de pérdidas de un convertidor reductor síncrono. Este modelo estima la eficiencia del sistema y juega un papel muy importante en el proceso de optimización. 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 energía 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.

Energy-based Fair Queuing: Energy-centric Processor Scheduling Algorithm for Battery-limited Mobile Systems

Los dispositivos móviles modernos disponen cada vez de más funcionalidad debido al rápido avance de las tecnologías de las comunicaciones y computaciones móviles. Sin embargo, la capacidad de la batería no ha experimentado un aumento equivalente. Por ello, la experiencia de usuario en los sistemas móviles modernos se ve muy afectada por la vida de la batería, que es un factor inestable de difícil de control. Para abordar este problema, investigaciones anteriores han propuesto un esquema de gestion del consumo (PM) centrada en la energía y que proporciona una garantía sobre la vida operativa de la batería mediante la gestión de la energía como un recurso de primera clase en el sistema. Como el planificador juega un papel fundamental en la administración del consumo de energía y en la garantía del rendimiento de las aplicaciones, esta tesis explora la optimización de la experiencia de usuario para sistemas móviles con energía limitada desde la perspectiva de un planificador que tiene en cuenta el consumo de energía en un contexto en el que ésta es un recurso de primera clase. En esta tesis se analiza en primer lugar los factores que contribuyen de forma general a la experiencia de usuario en un sistema móvil. Después se determinan los requisitos esenciales que afectan a la experiencia de usuario en la planificación centrada en el consumo de energía, que son el reparto proporcional de la potencia, el cumplimiento de las restricciones temporales, y cuando sea necesario, el compromiso entre la cuota de potencia y las restricciones temporales. Para cumplir con los requisitos, el algoritmo clásico de fair queueing y su modelo de referencia se extienden desde los dominios de las comunicaciones y ancho de banda de CPU hacia el dominio de la energía, y en base a ésto, se propone el algoritmo energy-based fair queueing (EFQ) para proporcionar una planificación basada en la energía. El algoritmo EFQ está diseñado para compartir la potencia consumida entre las tareas mediante su planificación en función de la energía consumida y de la cuota reservada. La cuota de consumo de cada tarea con restricciones temporales está protegida frente a diversos cambios que puedan ocurrir en el sistema. Además, para dar mejor soporte a las tareas en tiempo real y multimedia, se propone un mecanismo para combinar con el algoritmo EFQ para dar preferencia en la planificación durante breves intervalos de tiempo a las tareas más urgentes con restricciones temporales.Las propiedades del algoritmo EFQ se evaluan a través del modelado de alto nivel y la simulación. Los resultados de las simulaciones indican que los requisitos esenciales de la planificación centrada en la energía pueden lograrse. El algoritmo EFQ se implementa más tarde en el kernel de Linux. Para evaluar las propiedades del planificador EFQ basado en Linux, se desarrolló un banco de pruebas experimental basado en una sitema empotrado, un programa de banco de pruebas multihilo, y un conjunto de pruebas de código abierto. A través de experimentos específicamente diseñados, esta tesis verifica primero las propiedades de EFQ en la gestión de la cuota de consumo de potencia y la planificación en tiempo real y, a continuación, explora los beneficios potenciales de emplear la planificación EFQ en la optimización de la experiencia de usuario para sistemas móviles con energía limitada. Los resultados experimentales sobre la gestión de la cuota de energía muestran que EFQ es más eficaz que el planificador de Linux-CFS en la gestión de energía, logrando un reparto proporcional de la energía del sistema independientemente de en qué dispositivo se consume la energía. Los resultados experimentales en la planificación en tiempo real demuestran que EFQ puede lograr de forma eficaz, flexible y robusta el cumplimiento de las restricciones temporales aunque se dé el caso de aumento del el número de tareas o del error en la estimación de energía. Por último, un análisis comparativo de los resultados experimentales sobre la optimización de la experiencia del usuario demuestra que, primero, EFQ es más eficaz y flexible que los algoritmos tradicionales de planificación del procesador, como el que se encuentra por defecto en el planificador de Linux y, segundo, que proporciona la posibilidad de optimizar y preservar la experiencia de usuario para los sistemas móviles con energía limitada. Abstract Modern mobiledevices have been becoming increasingly powerful in functionality and entertainment as the next-generation mobile computing and communication technologies are rapidly advanced. However, the battery capacity has not experienced anequivalent increase. The user experience of modern mobile systems is therefore greatly affected by the battery lifetime,which is an unstable factor that is hard to control. To address this problem, previous works proposed energy-centric power management (PM) schemes to provide strong guarantee on the battery lifetime by globally managing energy as the first-class resource in the system. As the processor scheduler plays a pivotal role in power management and application performance guarantee, this thesis explores the user experience optimization of energy-limited mobile systemsfrom the perspective of energy-centric processor scheduling in an energy-centric context. This thesis first analyzes the general contributing factors of the mobile system user experience.Then itdetermines the essential requirements on the energy-centric processor scheduling for user experience optimization, which are proportional power sharing, time-constraint compliance, and when necessary, a tradeoff between the power share and the time-constraint compliance. To meet the requirements, the classical fair queuing algorithm and its reference model are extended from the network and CPU bandwidth sharing domain to the energy sharing domain, and based on that, the energy-based fair queuing (EFQ) algorithm is proposed for performing energy-centric processor scheduling. The EFQ algorithm is designed to provide proportional power shares to tasks by scheduling the tasks based on their energy consumption and weights. The power share of each time-sensitive task is protected upon the change of the scheduling environment to guarantee a stable performance, and any instantaneous power share that is overly allocated to one time-sensitive task can be fairly re-allocated to the other tasks. In addition, to better support real-time and multimedia scheduling, certain real-time friendly mechanism is combined into the EFQ algorithm to give time-limited scheduling preference to the time-sensitive tasks. Through high-level modelling and simulation, the properties of the EFQ algorithm are evaluated. The simulation results indicate that the essential requirements of energy-centric processor scheduling can be achieved. The EFQ algorithm is later implemented in the Linux kernel. To assess the properties of the Linux-based EFQ scheduler, an experimental test-bench based on an embedded platform, a multithreading test-bench program, and an open-source benchmark suite is developed. Through specifically-designed experiments, this thesis first verifies the properties of EFQ in power share management and real-time scheduling, and then, explores the potential benefits of employing EFQ scheduling in the user experience optimization for energy-limited mobile systems. Experimental results on power share management show that EFQ is more effective than the Linux-CFS scheduler in managing power shares and it can achieve a proportional sharing of the system power regardless of on which device the energy is spent. Experimental results on real-time scheduling demonstrate that EFQ can achieve effective, flexible and robust time-constraint compliance upon the increase of energy estimation error and task number. Finally, a comparative analysis of the experimental results on user experience optimization demonstrates that EFQ is more effective and flexible than traditional processor scheduling algorithms, such as those of the default Linux scheduler, in optimizing and preserving the user experience of energy-limited mobile systems.

Design of a Two-Phase buck converter with fourth-order output filter for envelope amplifiers of limited bandwidth

The use of techniques such as envelope tracking (ET) and envelope elimination and restoration (EER) can improve the efficiency of radio frequency power amplifiers (RFPA). In both cases, high-bandwidth DC/DC converters called envelope amplifiers (EA) are used to modulate the supply voltage of the RFPA. This paper addresses the analysis and design of a modified two-phase Buck converter optimized to operate as EA. The effects of multiphase operation on the tracking capabilities are analyzed. The use of a fourth-order output filter is proposed to increase the attenuation of the harmonics generated by the PWM operation, thus allowing a reduction of the ratio between the switching frequency and the converter bandwidth. The design of the output filter is addressed considering envelope tracking accuracy and distortion caused by the side bands arising from the nonlinear modulation process. Finally, the proposed analysis and design methods are supported by simulation results, as well as demonstrated by experiments obtained using two 100-W, 10-MHz, two-phase Buck EAs capable of accurately tracking a 1.5-MHz bandwidth OFDM signal.

3D simulation of complex shading affecting PV systems taking benefit from the power of graphics cards developed for the video game industry

Shading reduces the power output of a photovoltaic (PV) system. The design engineering of PV systems requires modeling and evaluating shading losses. Some PV systems are affected by complex shading scenes whose resulting PV energy losses are very difficult to evaluate with current modeling tools. Several specialized PV design and simulation software include the possibility to evaluate shading losses. They generally possess a Graphical User Interface (GUI) through which the user can draw a 3D shading scene, and then evaluate its corresponding PV energy losses. The complexity of the objects that these tools can handle is relatively limited. We have created a software solution, 3DPV, which allows evaluating the energy losses induced by complex 3D scenes on PV generators. The 3D objects can be imported from specialized 3D modeling software or from a 3D object library. The shadows cast by this 3D scene on the PV generator are then directly evaluated from the Graphics Processing Unit (GPU). Thanks to the recent development of GPUs for the video game industry, the shadows can be evaluated with a very high spatial resolution that reaches well beyond the PV cell level, in very short calculation times. A PV simulation model then translates the geometrical shading into PV energy output losses. 3DPV has been implemented using WebGL, which allows it to run directly from a Web browser, without requiring any local installation from the user. This also allows taken full benefits from the information already available from Internet, such as the 3D object libraries. This contribution describes, step by step, the method that allows 3DPV to evaluate the PV energy losses caused by complex shading. We then illustrate the results of this methodology to several application cases that are encountered in the world of PV systems design. Keywords: 3D, modeling, simulation, GPU, shading, losses, shadow mapping, solar, photovoltaic, PV, WebGL

Low Work-Function Thermionic Emission and Orbital-Motion-Limited Ion Collection at Bare-Tether Cathodic Contact

Una amarra electrodinámica (electrodynamic tether) opera sobre principios electromagnéticos intercambiando momento con la magnetosfera planetaria e interactuando con su ionosfera. Es un subsistema pasivo fiable para desorbitar etapas de cohetes agotadas y satélites al final de su misión, mitigando el crecimiento de la basura espacial. Una amarra sin aislamiento captura electrones del plasma ambiente a lo largo de su segmento polarizado positivamente, el cual puede alcanzar varios kilómetros de longitud, mientras que emite electrones de vuelta al plasma mediante un contactor de plasma activo de baja impedancia en su extremo catódico, tal como un cátodo hueco (hollow cathode). En ausencia de un contactor catódico activo, la corriente que circula por una amarra desnuda en órbita es nula en ambos extremos de la amarra y se dice que ésta está flotando eléctricamente. Para emisión termoiónica despreciable y captura de corriente en condiciones limitadas por movimiento orbital (orbital-motion-limited, OML), el cociente entre las longitudes de los segmentos anódico y catódico es muy pequeño debido a la disparidad de masas entre iones y electrones. Tal modo de operación resulta en una corriente media y fuerza de Lorentz bajas en la amarra, la cual es poco eficiente como dispositivo para desorbitar. El electride C12A7 : e−, que podría presentar una función de trabajo (work function) tan baja como W = 0.6 eV y un comportamiento estable a temperaturas relativamente altas, ha sido propuesto como recubrimiento para amarras desnudas. La emisión termoiónica a lo largo de un segmento así recubierto y bajo el calentamiento de la operación espacial, puede ser más eficiente que la captura iónica. En el modo más simple de fuerza de frenado, podría eliminar la necesidad de un contactor catódico activo y su correspondientes requisitos de alimentación de gas y subsistema de potencia, lo que resultaría en un sistema real de amarra “sin combustible”. Con este recubrimiento de bajo W, cada segmento elemental del segmento catódico de una amarra desnuda de kilómetros de longitud emitiría corriente como si fuese parte de una sonda cilíndrica, caliente y uniformemente polarizada al potencial local de la amarra. La operación es similar a la de una sonda de Langmuir 2D tanto en los segmentos catódico como anódico. Sin embargo, en presencia de emisión, los electrones emitidos resultan en carga espacial (space charge) negativa, la cual reduce el campo eléctrico que los acelera hacia fuera, o incluso puede desacelerarlos y hacerlos volver a la sonda. Se forma una doble vainas (double sheath) estable con electrones emitidos desde la sonda e iones provenientes del plasma ambiente. La densidad de corriente termoiónica, variando a lo largo del segmento catódico, podría seguir dos leyes distintas bajo diferentes condiciones: (i) la ley de corriente limitada por la carga espacial (space-charge-limited, SCL) o (ii) la ley de Richardson-Dushman (RDS). Se presenta un estudio preliminar sobre la corriente SCL frente a una sonda emisora usando la teoría de vainas (sheath) formada por la captura iónica en condiciones OML, y la corriente electrónica SCL entre los electrodos cilíndricos según Langmuir. El modelo, que incluye efectos óhmicos y el efecto de transición de emisión SCL a emisión RDS, proporciona los perfiles de corriente y potencial a lo largo de la longitud completa de la amarra. El análisis muestra que en el modo más simple de fuerza de frenado, bajo condiciones orbitales y de amarras típicas, la emisión termoiónica proporciona un contacto catódico eficiente y resulta en una sección catódica pequeña. En el análisis anterior, tanto la transición de emisión SCL a RD como la propia ley de emisión SCL consiste en un modelo muy simplificado. Por ello, a continuación se ha estudiado con detalle la solución de vaina estacionaria de una sonda con emisión termoiónica polarizada negativamente respecto a un plasma isotrópico, no colisional y sin campo magnético. La existencia de posibles partículas atrapadas ha sido ignorada y el estudio incluye tanto un estudio semi-analítico mediante técnica asintóticas como soluciones numéricas completas del problema. Bajo las tres condiciones (i) alto potencial, (ii) R = Rmax para la validez de la captura iónica OML, y (iii) potencial monotónico, se desarrolla un análisis asintótico auto-consistente para la estructura de plasma compleja que contiene las tres especies de cargas (electrones e iones del plasma, electrones emitidos), y cuatro regiones espaciales distintas, utilizando teorías de movimiento orbital y modelos cinéticos de las especies. Aunque los electrones emitidos presentan carga espacial despreciable muy lejos de la sonda, su efecto no se puede despreciar en el análisis global de la estructura de la vaina y de dos capas finas entre la vaina y la región cuasi-neutra. El análisis proporciona las condiciones paramétricas para que la corriente sea SCL. También muestra que la emisión termoiónica aumenta el radio máximo de la sonda para operar dentro del régimen OML y que la emisión de electrones es mucho más eficiente que la captura iónica para el segmento catódico de la amarra. En el código numérico, los movimientos orbitales de las tres especies son modelados para potenciales tanto monotónico como no-monotónico, y sonda de radio R arbitrario (dentro o más allá del régimen de OML para la captura iónica). Aprovechando la existencia de dos invariante, el sistema de ecuaciones Poisson-Vlasov se escribe como una ecuación integro-diferencial, la cual se discretiza mediante un método de diferencias finitas. El sistema de ecuaciones algebraicas no lineal resultante se ha resuelto de con un método Newton-Raphson paralelizado. Los resultados, comparados satisfactoriamente con el análisis analítico, proporcionan la emisión de corriente y la estructura del plasma y del potencial electrostático. ABSTRACT An electrodynamic tether operates on electromagnetic principles and exchanges momentum through the planetary magnetosphere, by continuously interacting with the ionosphere. It is a reliable passive subsystem to deorbit spent rocket stages and satellites at its end of mission, mitigating the growth of orbital debris. A tether left bare of insulation collects electrons by its own uninsulated and positively biased segment with kilometer range, while electrons are emitted by a low-impedance active device at the cathodic end, such as a hollow cathode, to emit the full electron current. In the absence of an active cathodic device, the current flowing along an orbiting bare tether vanishes at both ends and the tether is said to be electrically floating. For negligible thermionic emission and orbital-motion-limited (OML) collection throughout the entire tether (electron/ion collection at anodic/cathodic segment, respectively), the anodic-to-cathodic length ratio is very small due to ions being much heavier, which results in low average current and Lorentz drag. The electride C12A7 : e−, which might present a possible work function as low as W = 0.6 eV and moderately high temperature stability, has been proposed as coating for floating bare tethers. Thermionic emission along a thus coated cathodic segment, under heating in space operation, can be more efficient than ion collection and, in the simplest drag mode, may eliminate the need for an active cathodic device and its corresponding gas-feed requirements and power subsystem, which would result in a truly “propellant-less” tether system. With this low-W coating, each elemental segment on the cathodic segment of a kilometers-long floating bare-tether would emit current as if it were part of a hot cylindrical probe uniformly polarized at the local tether bias, under 2D probe conditions that are also applied to the anodic-segment analysis. In the presence of emission, emitted electrons result in negative space charge, which decreases the electric field that accelerates them outwards, or even reverses it, decelerating electrons near the emitting probe. A double sheath would be established with electrons being emitted from the probe and ions coming from the ambient plasma. The thermionic current density, varying along the cathodic segment, might follow two distinct laws under different con ditions: i) space-charge-limited (SCL) emission or ii) full Richardson-Dushman (RDS) emission. A preliminary study on the SCL current in front of an emissive probe is presented using the orbital-motion-limited (OML) ion-collection sheath and Langmuir’s SCL electron current between cylindrical electrodes. A detailed calculation of current and bias profiles along the entire tether length is carried out with ohmic effects considered and the transition from SCL to full RDS emission is included. Analysis shows that in the simplest drag mode, under typical orbital and tether conditions, thermionic emission provides efficient cathodic contact and leads to a short cathodic section. In the previous analysis, both the transition between SCL and RDS emission and the current law for SCL condition have used a very simple model. To continue, considering an isotropic, unmagnetized, colissionless plasma and a stationary sheath, the probe-plasma contact is studied in detail for a negatively biased probe with thermionic emission. The possible trapped particles are ignored and this study includes both semianalytical solutions using asymptotic analysis and complete numerical solutions. Under conditions of i) high bias, ii) R = Rmax for ion OML collection validity, and iii) monotonic potential, a self-consistent asymptotic analysis is carried out for the complex plasma structure involving all three charge species (plasma electrons and ions, and emitted electrons) and four distinct spatial regions using orbital motion theories and kinetic modeling of the species. Although emitted electrons present negligible space charge far away from the probe, their effect cannot be neglected in the global analysis for the sheath structure and two thin layers in between the sheath and the quasineutral region. The parametric conditions for the current to be space-chargelimited are obtained. It is found that thermionic emission increases the range of probe radius for OML validity and is greatly more effective than ion collection for cathodic contact of tethers. In the numerical code, the orbital motions of all three species are modeled for both monotonic and non-monotonic potential, and for any probe radius R (within or beyond OML regime for ion collection). Taking advantage of two constants of motion (energy and angular momentum), the Poisson-Vlasov equation is described by an integro differential equation, which is discretized using finite difference method. The non-linear algebraic equations are solved using a parallel implementation of the Newton-Raphson method. The results, which show good agreement with the analytical results, provide the results for thermionic current, the sheath structure, and the electrostatic potential.

Evaluación de las Consecuencias de la Nueva Regulación de la OMI sobre Combustibles Marinos

El 10 de octubre de 2008 la Organización Marítima Internacional (OMI) firmó una modificación al Anexo VI del convenio MARPOL 73/78, por la que estableció una reducción progresiva de las emisiones de óxidos de azufre (SOx) procedentes de los buques, una reducción adicional de las emisiones de óxidos de nitrógeno (NOx), así como límites en las emisiones de dióxido de Carbono (CO2) procedentes de los motores marinos y causantes de problemas medioambientales como la lluvia ácida y efecto invernadero. Centrándonos en los límites sobre las emisiones de azufre, a partir del 1 de enero de 2015 esta normativa obliga a todos los buques que naveguen por zonas controladas, llamadas Emission Control Area (ECA), a consumir combustibles con un contenido de azufre menor al 0,1%. A partir del 1 de enero del año 2020, o bien del año 2025, si la OMI decide retrasar su inicio, los buques deberán consumir combustibles con un contenido de azufre menor al 0,5%. De igual forma que antes, el contenido deberá ser rebajado al 0,1%S, si navegan por el interior de zonas ECA. Por su parte, la Unión Europea ha ido más allá que la OMI, adelantando al año 2020 la aplicación de los límites más estrictos de la ley MARPOL sobre las aguas de su zona económica exclusiva. Para ello, el 21 de noviembre de 2013 firmó la Directiva 2012 / 33 / EU como adenda a la Directiva de 1999. Tengamos presente que la finalidad de estas nuevas leyes es la mejora de la salud pública y el medioambiente, produciendo beneficios sociales, en forma de reducción de enfermedades, sobre todo de tipo respiratorio, a la vez que se reduce la lluvia ácida y sus nefastas consecuencias. La primera pregunta que surge es ¿cuál es el combustible actual de los buques y cuál será el que tengan que consumir para cumplir con esta Regulación? Pues bien, los grandes buques de navegación internacional consumen hoy en día fuel oil con un nivel de azufre de 3,5%. ¿Existen fueles con un nivel de azufre de 0,5%S? Como hemos concluido en el capítulo 4, para las empresas petroleras, la producción de fuel oil como combustible marino es tratada como un subproducto en su cesta de productos refinados por cada barril de Brent, ya que la demanda de fuel respecto a otros productos está bajando y además, el margen de beneficio que obtienen por la venta de otros productos petrolíferos es mayor que con el fuel. Así, podemos decir que las empresas petroleras no están interesadas en invertir en sus refinerías para producir estos fueles con menor contenido de azufre. Es más, en el caso de que alguna compañía decidiese invertir en producir un fuel de 0,5%S, su precio debería ser muy similar al del gasóleo para poder recuperar las inversiones empleadas. Por lo tanto, el único combustible que actualmente cumple con los nuevos niveles impuestos por la OMI es el gasóleo, con un precio que durante el año 2014 estuvo a una media de 307 USD/ton más alto que el actual fuel oil. Este mayor precio de compra de combustible impactará directamente sobre el coste del trasporte marítimo. La entrada en vigor de las anteriores normativas está suponiendo un reto para todo el sector marítimo. Ante esta realidad, se plantean diferentes alternativas con diferentes implicaciones técnicas, operativas y financieras. En la actualidad, son tres las alternativas con mayor aceptación en el sector. La primera alternativa consiste en “no hacer nada” y simplemente cambiar el tipo de combustible de los grandes buques de fuel oil a gasóleo. Las segunda alternativa es la instalación de un equipo scrubber, que permitiría continuar con el consumo de fuel oil, limpiando sus gases de combustión antes de salir a la atmósfera. Y, por último, la tercera alternativa consiste en el uso de Gas Natural Licuado (GNL) como combustible, con un precio inferior al del gasóleo. Sin embargo, aún existen importantes incertidumbres sobre la evolución futura de precios, operación y mantenimiento de las nuevas tecnologías, inversiones necesarias, disponibilidad de infraestructura portuaria e incluso el desarrollo futuro de la propia normativa internacional. Estas dudas hacen que ninguna de estas tres alternativas sea unánime en el sector. En esta tesis, tras exponer en el capítulo 3 la regulación aplicable al sector, hemos investigado sus consecuencias. Para ello, hemos examinado en el capítulo 4 si existen en la actualidad combustibles marinos que cumplan con los nuevos límites de azufre o en su defecto, cuál sería el precio de los nuevos combustibles. Partimos en el capítulo 5 de la hipótesis de que todos los buques cambian su consumo de fuel oil a gasóleo para cumplir con dicha normativa, calculamos el incremento de demanda de gasóleo que se produciría y analizamos las consecuencias que este hecho tendría sobre la producción de gasóleos en el Mediterráneo. Adicionalmente, calculamos el impacto económico que dicho incremento de coste producirá sobre sector exterior de España. Para ello, empleamos como base de datos el sistema de control de tráfico marítimo Authomatic Identification System (AIS) para luego analizar los datos de todos los buques que han hecho escala en algún puerto español, para así calcular el extra coste anual por el consumo de gasóleo que sufrirá el transporte marítimo para mover todas las importaciones y exportaciones de España. Por último, en el capítulo 6, examinamos y comparamos las otras dos alternativas al consumo de gasóleo -scrubbers y propulsión con GNL como combustible- y, finalmente, analizamos en el capítulo 7, la viabilidad de las inversiones en estas dos tecnologías para cumplir con la regulación. En el capítulo 5 explicamos los numerosos métodos que existen para calcular la demanda de combustible de un buque. La metodología seguida para su cálculo será del tipo bottom-up, que está basada en la agregación de la actividad y las características de cada tipo de buque. El resultado está basado en la potencia instalada de cada buque, porcentaje de carga del motor y su consumo específico. Para ello, analizamos el número de buques que navegan por el Mediterráneo a lo largo de un año mediante el sistema AIS, realizando “fotos” del tráfico marítimo en el Mediterráneo y reportando todos los buques en navegación en días aleatorios a lo largo de todo el año 2014. Por último, y con los datos anteriores, calculamos la demanda potencial de gasóleo en el Mediterráneo. Si no se hace nada y los buques comienzan a consumir gasóleo como combustible principal, en vez del actual fuel oil para cumplir con la regulación, la demanda de gasoil en el Mediterráneo aumentará en 12,12 MTA (Millones de Toneladas Anuales) a partir del año 2020. Esto supone alrededor de 3.720 millones de dólares anuales por el incremento del gasto de combustible tomando como referencia el precio medio de los combustibles marinos durante el año 2014. El anterior incremento de demanda en el Mediterráneo supondría el 43% del total de la demanda de gasóleos en España en el año 2013, incluyendo gasóleos de automoción, biodiesel y gasóleos marinos y el 3,2% del consumo europeo de destilados medios durante el año 2014. ¿Podrá la oferta del mercado europeo asumir este incremento de demanda de gasóleos? Europa siempre ha sido excedentaria en gasolina y deficitaria en destilados medios. En el año 2009, Europa tuvo que importar 4,8 MTA de Norte América y 22,1 MTA de Asia. Por lo que, este aumento de demanda sobre la ya limitada capacidad de refino de destilados medios en Europa incrementará las importaciones y producirá también aumentos en los precios, sobre todo del mercado del gasóleo. El sector sobre el que más impactará el incremento de demanda de gasóleo será el de los cruceros que navegan por el Mediterráneo, pues consumirán un 30,4% de la demanda de combustible de toda flota mundial de cruceros, lo que supone un aumento en su gasto de combustible de 386 millones de USD anuales. En el caso de los RoRos, consumirían un 23,6% de la demanda de la flota mundial de este tipo de buque, con un aumento anual de 171 millones de USD sobre su gasto de combustible anterior. El mayor incremento de coste lo sufrirán los portacontenedores, con 1.168 millones de USD anuales sobre su gasto actual. Sin embargo, su consumo en el Mediterráneo representa sólo el 5,3% del consumo mundial de combustible de este tipo de buques. Estos números plantean la incertidumbre de si semejante aumento de gasto en buques RoRo hará que el transporte marítimo de corta distancia en general pierda competitividad sobre otros medios de transporte alternativos en determinadas rutas. De manera que, parte del volumen de mercancías que actualmente transportan los buques se podría trasladar a la carretera, con los inconvenientes medioambientales y operativos, que esto produciría. En el caso particular de España, el extra coste por el consumo de gasóleo de todos los buques con escala en algún puerto español en el año 2013 se cifra en 1.717 millones de EUR anuales, según demostramos en la última parte del capítulo 5. Para realizar este cálculo hemos analizado con el sistema AIS a todos los buques que han tenido escala en algún puerto español y los hemos clasificado por distancia navegada, tipo de buque y potencia. Este encarecimiento del transporte marítimo será trasladado al sector exterior español, lo cual producirá un aumento del coste de las importaciones y exportaciones por mar en un país muy expuesto, pues el 75,61% del total de las importaciones y el 53,64% del total de las exportaciones se han hecho por vía marítima. Las tres industrias que se verán más afectadas son aquellas cuyo valor de mercancía es inferior respecto a su coste de transporte. Para ellas los aumentos del coste sobre el total del valor de cada mercancía serán de un 2,94% para la madera y corcho, un 2,14% para los productos minerales y un 1,93% para las manufacturas de piedra, cemento, cerámica y vidrio. Las mercancías que entren o salgan por los dos archipiélagos españoles de Canarias y Baleares serán las que se verán más impactadas por el extra coste del transporte marítimo, ya que son los puertos más alejados de otros puertos principales y, por tanto, con más distancia de navegación. Sin embargo, esta no es la única alternativa al cumplimiento de la nueva regulación. De la lectura del capítulo 6 concluimos que las tecnologías de equipos scrubbers y de propulsión con GNL permitirán al buque consumir combustibles más baratos al gasoil, a cambio de una inversión en estas tecnologías. ¿Serán los ahorros producidos por estas nuevas tecnologías suficientes para justificar su inversión? Para contestar la anterior pregunta, en el capítulo 7 hemos comparado las tres alternativas y hemos calculado tanto los costes de inversión como los gastos operativos correspondientes a equipos scrubbers o propulsión con GNL para una selección de 53 categorías de buques. La inversión en equipos scrubbers es más conveniente para buques grandes, con navegación no regular. Sin embargo, para buques de tamaño menor y navegación regular por puertos con buena infraestructura de suministro de GNL, la inversión en una propulsión con GNL como combustible será la más adecuada. En el caso de un tiempo de navegación del 100% dentro de zonas ECA y bajo el escenario de precios visto durante el año 2014, los proyectos con mejor plazo de recuperación de la inversión en equipos scrubbers son para los cruceros de gran tamaño (100.000 tons. GT), para los que se recupera la inversión en 0,62 años, los grandes portacontenedores de más de 8.000 TEUs con 0,64 años de recuperación y entre 5.000-8.000 TEUs con 0,71 años de recuperación y, por último, los grandes petroleros de más de 200.000 tons. de peso muerto donde tenemos un plazo de recuperación de 0,82 años. La inversión en scrubbers para buques pequeños, por el contrario, tarda más tiempo en recuperarse llegando a más de 5 años en petroleros y quimiqueros de menos de 5.000 toneladas de peso muerto. En el caso de una posible inversión en propulsión con GNL, las categorías de buques donde la inversión en GNL es más favorable y recuperable en menor tiempo son las más pequeñas, como ferris, cruceros o RoRos. Tomamos ahora el caso particular de un buque de productos limpios de 38.500 toneladas de peso muerto ya construido y nos planteamos la viabilidad de la inversión en la instalación de un equipo scrubber o bien, el cambio a una propulsión por GNL a partir del año 2015. Se comprueba que las dos variables que más impactan sobre la conveniencia de la inversión son el tiempo de navegación del buque dentro de zonas de emisiones controladas (ECA) y el escenario futuro de precios del MGO, HSFO y GNL. Para realizar este análisis hemos estudiado cada inversión, calculando una batería de condiciones de mérito como el payback, TIR, VAN y la evolución de la tesorería del inversor. Posteriormente, hemos calculado las condiciones de contorno mínimas de este buque en concreto para asegurar una inversión no sólo aceptable, sino además conveniente para el naviero inversor. En el entorno de precios del 2014 -con un diferencial entre fuel y gasóleo de 264,35 USD/ton- si el buque pasa más de un 56% de su tiempo de navegación en zonas ECA, conseguirá una rentabilidad de la inversión para inversores (TIR) en el equipo scrubber que será igual o superior al 9,6%, valor tomado como coste de oportunidad. Para el caso de inversión en GNL, en el entorno de precios del año 2014 -con un diferencial entre GNL y gasóleo de 353,8 USD/ton FOE- si el buque pasa más de un 64,8 % de su tiempo de navegación en zonas ECA, conseguirá una rentabilidad de la inversión para inversores (TIR) que será igual o superior al 9,6%, valor del coste de oportunidad. Para un tiempo en zona ECA estimado de un 60%, la rentabilidad de la inversión (TIR) en scrubbers para los inversores será igual o superior al 9,6%, el coste de oportunidad requerido por el inversor, para valores del diferencial de precio entre los dos combustibles alternativos, gasóleo (MGO) y fuel oil (HSFO) a partir de 244,73 USD/ton. En el caso de una inversión en propulsión GNL se requeriría un diferencial de precio entre MGO y GNL de 382,3 USD/ton FOE o superior. Así, para un buque de productos limpios de 38.500 DWT, la inversión en una reconversión para instalar un equipo scrubber es más conveniente que la de GNL, pues alcanza rentabilidades de la inversión (TIR) para inversores del 12,77%, frente a un 6,81% en el caso de invertir en GNL. Para ambos cálculos se ha tomado un buque que navegue un 60% de su tiempo por zona ECA y un escenario de precios medios del año 2014 para el combustible. Po otro lado, las inversiones en estas tecnologías a partir del año 2025 para nuevas construcciones son en ambos casos convenientes. El naviero deberá prestar especial atención aquí a las características propias de su buque y tipo de navegación, así como a la infraestructura de suministros y vertidos en los puertos donde vaya a operar usualmente. Si bien, no se ha estudiado en profundidad en esta tesis, no olvidemos que el sector marítimo debe cumplir además con las otras dos limitaciones que la regulación de la OMI establece sobre las emisiones de óxidos de Nitrógeno (NOx) y Carbono (CO2) y que sin duda, requerirán adicionales inversiones en diversos equipos. De manera que, si bien las consecuencias del consumo de gasóleo como alternativa al cumplimiento de la Regulación MARPOL son ciertamente preocupantes, existen alternativas al uso del gasóleo, con un aumento sobre el coste del transporte marítimo menor y manteniendo los beneficios sociales que pretende dicha ley. En efecto, como hemos demostrado, las opciones que se plantean como más rentables desde el punto de vista financiero son el consumo de GNL en los buques pequeños y de línea regular (cruceros, ferries, RoRos), y la instalación de scrubbers para el resto de buques de grandes dimensiones. Pero, por desgracia, estas inversiones no llegan a hacerse realidad por el elevado grado de incertidumbre asociado a estos dos mercados, que aumenta el riesgo empresarial, tanto de navieros como de suministradores de estas nuevas tecnologías. Observamos así una gran reticencia del sector privado a decidirse por estas dos alternativas. Este elevado nivel de riesgo sólo puede reducirse fomentando el esfuerzo conjunto del sector público y privado para superar estas barreras de entrada del mercado de scrubbers y GNL, que lograrían reducir las externalidades medioambientales de las emisiones sin restar competitividad al transporte marítimo. Creemos así, que los mismos organismos que aprobaron dicha ley deben ayudar al sector naviero a afrontar las inversiones en dichas tecnologías, así como a impulsar su investigación y promover la creación de una infraestructura portuaria adaptada a suministros de GNL y a descargas de vertidos procedentes de los equipos scrubber. Deberían además, prestar especial atención sobre las ayudas al sector de corta distancia para evitar que pierda competitividad frente a otros medios de transporte por el cumplimiento de esta normativa. Actualmente existen varios programas europeos de incentivos, como TEN-T o Marco Polo, pero no los consideramos suficientes. Por otro lado, la Organización Marítima Internacional debe confirmar cuanto antes si retrasa o no al 2025 la nueva bajada del nivel de azufre en combustibles. De esta manera, se eliminaría la gran incertidumbre temporal que actualmente tienen tanto navieros, como empresas petroleras y puertos para iniciar sus futuras inversiones y poder estudiar la viabilidad de cada alternativa de forma individual. ABSTRACT On 10 October 2008 the International Maritime Organization (IMO) signed an amendment to Annex VI of the MARPOL 73/78 convention establishing a gradual reduction in sulphur oxide (SOx) emissions from ships, and an additional reduction in nitrogen oxide (NOx) emissions and carbon dioxide (CO2) emissions from marine engines which cause environmental problems such as acid rain and the greenhouse effect. According to this regulation, from 1 January 2015, ships travelling in an Emission Control Area (ECA) must use fuels with a sulphur content of less than 0.1%. From 1 January 2020, or alternatively from 2025 if the IMO should decide to delay its introduction, all ships must use fuels with a sulphur content of less than 0.5%. As before, this content will be 0.1%S for voyages within ECAs. Meanwhile, the European Union has gone further than the IMO, and will apply the strictest limits of the MARPOL directives in the waters of its exclusive economic zone from 2020. To this end, Directive 2012/33/EU was issued on 21 November 2013 as an addendum to the 1999 Directive. These laws are intended to improve public health and the environment, benefiting society by reducing disease, particularly respiratory problems. The first question which arises is: what fuel do ships currently use, and what fuel will they have to use to comply with the Convention? Today, large international shipping vessels consume fuel oil with a sulphur level of 3.5%. Do fuel oils exist with a sulphur level of 0.5%S? As we conclude in Chapter 4, oil companies regard marine fuel oil as a by-product of refining Brent to produce their basket of products, as the demand for fuel oil is declining in comparison to other products, and the profit margin on the sale of other petroleum products is higher. Thus, oil companies are not interested in investing in their refineries to produce low-sulphur fuel oils, and if a company should decide to invest in producing a 0.5%S fuel oil, its price would have to be very similar to that of marine gas oil in order to recoup the investment. Therefore, the only fuel which presently complies with the new levels required by the IMO is marine gas oil, which was priced on average 307 USD/tonne higher than current fuel oils during 2014. This higher purchasing price for fuel will have a direct impact on the cost of maritime transport. The entry into force of the above directive presents a challenge for the entire maritime sector. There are various alternative approaches to this situation, with different technical, operational and financial implications. At present three options are the most widespread in the sector. The first option consists of “doing nothing” and simply switching from fuel oil to marine gas oil in large ships. The second option is installing a scrubber system, which would enable ships to continue consuming fuel oil, cleaning the combustion gases before they are released to the atmosphere. And finally, the third option is using Liquefied Natural Gas (LNG), which is priced lower than marine gas oil, as a fuel. However, there is still significant uncertainty on future variations in prices, the operation and maintenance of the new technologies, the investments required, the availability of port infrastructure and even future developments in the international regulations themselves. These uncertainties mean that none of these three alternatives has been unanimously accepted by the sector. In this Thesis, after discussing all the regulations applicable to the sector in Chapter 3, we investigate their consequences. In Chapter 4 we examine whether there are currently any marine fuels on the market which meet the new sulphur limits, and if not, how much new fuels would cost. In Chapter 5, based on the hypothesis that all ships will switch from fuel oil to marine gas oil to comply with the regulations, we calculate the increase in demand for marine gas oil this would lead to, and analyse the consequences this would have on marine gas oil production in the Mediterranean. We also calculate the economic impact such a cost increase would have on Spain's external sector. To do this, we also use the Automatic Identification System (AIS) system to analyse the data of every ship stopping in any Spanish port, in order to calculate the extra cost of using marine gas oil in maritime transport for all Spain's imports and exports. Finally, in Chapter 6, we examine and compare the other two alternatives to marine gas oil, scrubbers and LNG, and in Chapter 7 we analyse the viability of investing in these two technologies in order to comply with the regulations. In Chapter 5 we explain the many existing methods for calculating a ship's fuel consumption. We use a bottom-up calculation method, based on aggregating the activity and characteristics of each type of vessel. The result is based on the installed engine power of each ship, the engine load percentage and its specific consumption. To do this, we analyse the number of ships travelling in the Mediterranean in the course of one year, using the AIS, a marine traffic monitoring system, to take “snapshots” of marine traffic in the Mediterranean and report all ships at sea on random days throughout 2014. Finally, with the above data, we calculate the potential demand for marine gas oil in the Mediterranean. If nothing else is done and ships begin to use marine gas oil instead of fuel oil in order to comply with the regulation, the demand for marine gas oil in the Mediterranean will increase by 12.12 MTA (Millions Tonnes per Annum) from 2020. This means an increase of around 3.72 billion dollars a year in fuel costs, taking as reference the average price of marine fuels in 2014. Such an increase in demand in the Mediterranean would be equivalent to 43% of the total demand for diesel in Spain in 2013, including automotive diesel fuels, biodiesel and marine gas oils, and 3.2% of European consumption of middle distillates in 2014. Would the European market be able to supply enough to meet this greater demand for diesel? Europe has always had a surplus of gasoline and a deficit of middle distillates. In 2009, Europe had to import 4.8 MTA from North America and 22.1 MTA from Asia. Therefore, this increased demand on Europe's already limited capacity for refining middle distillates would lead to increased imports and higher prices, especially in the diesel market. The sector which would suffer the greatest impact of increased demand for marine gas oil would be Mediterranean cruise ships, which represent 30.4% of the fuel demand of the entire world cruise fleet, meaning their fuel costs would rise by 386 million USD per year. ROROs in the Mediterranean, which represent 23.6% of the demand of the world fleet of this type of ship, would see their fuel costs increase by 171 million USD a year. The greatest cost increase would be among container ships, with an increase on current costs of 1.168 billion USD per year. However, their consumption in the Mediterranean represents only 5.3% of worldwide fuel consumption by container ships. These figures raise the question of whether a cost increase of this size for RORO ships would lead to short-distance marine transport in general becoming less competitive compared to other transport options on certain routes. For example, some of the goods that ships now carry could switch to road transport, with the undesirable effects on the environment and on operations that this would produce. In the particular case of Spain, the extra cost of switching to marine gas oil in all ships stopping at any Spanish port in 2013 would be 1.717 billion EUR per year, as we demonstrate in the last part of Chapter 5. For this calculation, we used the AIS system to analyse all ships which stopped at any Spanish port, classifying them by distance travelled, type of ship and engine power. This rising cost of marine transport would be passed on to the Spanish external sector, increasing the cost of imports and exports by sea in a country which relies heavily on maritime transport, which accounts for 75.61% of Spain's total imports and 53.64% of its total exports. The three industries which would be worst affected are those with goods of lower value relative to transport costs. The increased costs over the total value of each good would be 2.94% for wood and cork, 2.14% for mineral products and 1.93% for manufactured stone, cement, ceramic and glass products. Goods entering via the two Spanish archipelagos, the Canary Islands and the Balearic Islands, would suffer the greatest impact from the extra cost of marine transport, as these ports are further away from other major ports and thus the distance travelled is greater. However, this is not the only option for compliance with the new regulations. From our readings in Chapter 6 we conclude that scrubbers and LNG propulsion would enable ships to use cheaper fuels than marine gas oil, in exchange for investing in these technologies. Would the savings gained by these new technologies be enough to justify the investment? To answer this question, in Chapter 7 we compare the three alternatives and calculate both the cost of investment and the operating costs associated with scrubbers or LNG propulsion for a selection of 53 categories of ships. Investing in scrubbers is more advisable for large ships with no fixed runs. However, for smaller ships with regular runs to ports with good LNG supply infrastructure, investing in LNG propulsion would be the best choice. In the case of total transit time within an ECA and the pricing scenario seen in 2014, the best payback periods on investments in scrubbers are for large cruise ships (100,000 gross tonnage), which would recoup their investment in 0.62 years; large container ships, with a 0.64 year payback period for those over 8,000 TEUs and 0.71 years for the 5,000-8,000 TEU category; and finally, large oil tankers over 200,000 deadweight tonnage, which would recoup their investment in 0.82 years. However, investing in scrubbers would have a longer payback period for smaller ships, up to 5 years or more for oil tankers and chemical tankers under 5,000 deadweight tonnage. In the case of LNG propulsion, a possible investment is more favourable and the payback period is shorter for smaller ship classes, such as ferries, cruise ships and ROROs. We now take the case of a ship transporting clean products, already built, with a deadweight tonnage of 38,500, and consider the viability of investing in installing a scrubber or changing to LNG propulsion, starting in 2015. The two variables with the greatest impact on the advisability of the investment are how long the ship is at sea within emission control areas (ECA) and the future price scenario of MGO, HSFO and LNG. For this analysis, we studied each investment, calculating a battery of merit conditions such as the payback period, IRR, NPV and variations in the investors' liquid assets. We then calculated the minimum boundary conditions to ensure the investment was not only acceptable but advisable for the investor shipowner. Thus, for the average price differential of 264.35 USD/tonne between HSFO and MGO during 2014, investors' return on investment (IRR) in scrubbers would be the same as the required opportunity cost of 9.6%, for values of over 56% ship transit time in ECAs. For the case of investing in LNG and the average price differential between MGO and LNG of 353.8 USD/tonne FOE in 2014, the ship must spend 64.8% of its time in ECAs for the investment to be advisable. For an estimated 60% of time in an ECA, the internal rate of return (IRR) for investors equals the required opportunity cost of 9.6%, based on a price difference of 244.73 USD/tonne between the two alternative fuels, marine gas oil (MGO) and fuel oil (HSFO). An investment in LNG propulsion would require a price differential between MGO and LNG of 382.3 USD/tonne FOE. Thus, for a 38,500 DWT ship carrying clean products, investing in retrofitting to install a scrubber is more advisable than converting to LNG, with an internal rate of return (IRR) for investors of 12.77%, compared to 6.81% for investing in LNG. Both calculations were based on a ship which spends 60% of its time at sea in an ECA and a scenario of average 2014 prices. However, for newly-built ships, investments in either of these technologies from 2025 would be advisable. Here, the shipowner must pay particular attention to the specific characteristics of their ship, the type of operation, and the infrastructure for supplying fuel and handling discharges in the ports where it will usually operate. Thus, while the consequences of switching to marine gas oil in order to comply with the MARPOL regulations are certainly alarming, there are alternatives to marine gas oil, with smaller increases in the costs of maritime transport, while maintaining the benefits to society this law is intended to provide. Indeed, as we have demonstrated, the options which appear most favourable from a financial viewpoint are conversion to LNG for small ships and regular runs (cruise ships, ferries, ROROs), and installing scrubbers for large ships. Unfortunately, however, these investments are not being made, due to the high uncertainty associated with these two markets, which increases business risk, both for shipowners and for the providers of these new technologies. This means we are seeing considerable reluctance regarding these two options among the private sector. This high level of risk can be lowered only by encouraging joint efforts by the public and private sectors to overcome these barriers to entry into the market for scrubbers and LNG, which could reduce the environmental externalities of emissions without affecting the competitiveness of marine transport. Our opinion is that the same bodies which approved this law must help the shipping industry invest in these technologies, drive research on them, and promote the creation of a port infrastructure which is adapted to supply LNG and handle the discharges from scrubber systems. At present there are several European incentive programmes, such as TEN-T and Marco Polo, but we do not consider these to be sufficient. For its part, the International Maritime Organization should confirm as soon as possible whether the new lower sulphur levels in fuels will be postponed until 2025. This would eliminate the great uncertainty among shipowners, oil companies and ports regarding the timeline for beginning their future investments and for studying their viability.