Browsing by Author "Barroso Estébanez, Jorge Ángel"

The objective of this research is to analyze the performance of a passive hybrid powerplant control system to be implemented in a lightweight unmanned aerial vehicle capable to ascend up to the high troposphere (10,000 m). The powerplant is based on a high-temperature PEM fuel cell connected in parallel to a set of lithium-polymer batteries and regulated by two power diodes. Test performed in steady state demonstrates that the use of the hybrid system increases the efficiency of the stack by more than 7% because the voltage at the main DC bus is limited by the batteries. The robustness of the passive control system is proved in a long-term test in which random perturbations of ±15% are applied to the average power that would be demanded during the ascent flight. The hybridization of the stack with the batteries eliminates sudden peaks in the current generated by the stack, which are responsible for prompt degradation phenomena that drastically reduce its useful lifetime. The study demonstrates that with the passive hybrid powerplant it is possible to reach the target height with the gas storage system considered in the application, contrary to what happens with the simple power plant.

En los últimos años, la industria aeronáutica está mostrando un creciente interés en el desarrollo y uso de vehículos aéreos no tripulados (UAV). Los UAV son cada vez más empleados en el sector militar, donde destacan las plataformas destinadas al reconocimiento de terrenos, las comunicaciones y el espionaje. No obstante, también están aumentando las aplicaciones en el sector industrial y civil, en tareas tales como el mantenimiento de grandes infraestructuras, la vigilancia de cultivos y bosques, la protección de parques naturales, el control de fronteras o para realizar mediciones meteorológicas. Propulsar estos dispositivos mediante sistemas eléctricos es preferible por su mayor eficiencia comparada con la de los motores de combustión interna y la práctica ausencia de emisiones contaminantes. La presente tesis se centra en la investigación de una nueva planta de potencia basada en pila de combustible con membrana polimérica (PEMFC), estudiando una solución hibridada con un banco de baterías de litio-polímero comercial que permita a un prototipo de UAV ligero elevar su cota de vuelo hasta la alta troposfera (10.000 m). La tesis se presenta como un compendio de artículos publicados, dividida en tres partes. En la primera, distribuida en seis secciones, se realiza un resumen de todas las investigaciones que han dado lugar a las publicaciones. La segunda contiene el texto adaptado de las publicaciones que conforman la tesis, mientras que en la tercera se incluyen como anexos algunos documentos adicionales, así como la información técnica de la MEA (del inglés Membrane Electrode Assembly) utilizada y los planos de las placas diseñadas para la pila. Para cumplir el objetivo propuesto, durante la tesis se han escrito códigos numéricos específicos que permitieron resolver el problema aerodinámico y realizar un completo análisis energético, obteniendo como resultado la distribución de pesos de los diferentes elementos que conforman el UAV. Las difíciles condiciones de vuelo debidas a la baja presión en la troposfera imponen que la pila de combustible sea de alta temperatura (HT-PEMFC) y cátodo cerrado, ensamblada con membranas de PBI (polibencimidazol) dopadas con ácido fosfórico, lo que permite una temperatura de trabajo de 160ºC. Se ha desarrollado una HT-PEMFC ligera con diseño propio de todos los elementos mecánicos (las placas monopolares, de presión y terminales, el sistema de sellado y el sistema de cierre), excepto los sistemas membranaelectrodo, que son componentes comerciales. Asimismo, se ha resuelto el problema térmico combinando medidas experimentales y simulaciones numéricas con un código propio y se ha diseñado un sistema de refrigeración pasivo con un consumo mínimo de potencia. Los estudios han concluido que la planta de potencia más eficiente y estable es una híbrida formada por la HT-PEMFC y un banco de baterías de litio-polímero. Finalmente, para minimizar el peso total del sistema, se ha propuesto una planta de potencia híbrida con un sistema electrónico de potencia con regulación pasiva. / In recent years, the aeronautical industry has shown growing interest in the development and use of unmanned aerial vehicles (UAVs). UAVs are increasingly used in the military sector for different missions such as reconnaissance, communications and espionage. However, applications in the industrial and civil sectors are also increasing in tasks such as maintenance of large infrastructures, monitoring crops and forests, etc. Propelling these devices with electrical systems is preferable because they are more efficient than internal combustion engines, and are essentially free of pollutant emissions. The present thesis is focused on research with respect to a new power plant (PP) based on a polymer electrolyte membrane fuel cell (PEMFC), considering a hybrid solution with commercial lithium-polymer (LiPo) batteries that allow an existing prototype of light UAV to reach an altitude of 10,000 m. The thesis is presented as a compendium of published articles, structured in three parts. In the first part, divided into six sections, all the research developed to reach the proposed objectives is summarized. The second part encloses the adapted text of the three published papers. Meanwhile, the third part contains some additional documents, the technical information of the membrane electrode assembly (MEA) used (provided by the manufacturer), and the plans of the designed plates that comprise the PEM fuel cell stack. During the research performed, specific numerical codes have been developed to solve the aerodynamic problem and to perform a complete energy analysis. The mass distribution of the different components that make up the UAV have been obtained. With these results, the maximum mass that can be carried on board has been calculated, as well as the mass distribution among the different elements that form the power plant. The very harsh flight conditions due to the low troposphere pressure impose a closed-cathode high-temperature PEM fuel cell (HT-PEMFC). It is formed of PBI polybenzimidazole) membranes doped with phosphoric acid, with a working temperature of 160ºC. At the same time, both hydrogen and oxygen have to be carried on board. In this thesis, all the mechanical elements of the stack (the monopolar, pressure and end plates, the sealing system, and the closing system) have been specifically designed, except the membrane-electrode assemblies, which are commercially available. Besides, the thermal problem has been solved by combining experimental measurements and numerical simulations with a proprietary code. As a result, a passive cooling system with minimum power consumption has been designed. The studies have concluded that the most efficient and stable power plant is a hybrid one, formed by the HT-PEMFC and a bank of lithium-polymer batteries. Finally, in order to minimize the total weight of the system, an HPP with passive power electronics has been considered.