Stability and Control of Power Systems using Vector Lyapunov Functions and Sum-of-Squares Methods

Recently sum-of-squares (SOS) based methods have been used for the stability analysis and control synthesis of polynomial dynamical systems. This analysis framework was also extended to non-polynomial dynamical systems, including power systems, using an algebraic reformulation technique that recasts the system's dynamics into a set of polynomial differential algebraic equations. Nevertheless, for large scale dynamical systems this method becomes inapplicable due to its computational complexity. For this reason we develop a subsystem based stability analysis approach using vector Lyapunov functions and introduce a parallel and scalable algorithm to infer the stability of the interconnected system with the help of the subsystem Lyapunov functions. Furthermore, we design adaptive and distributed control laws that guarantee asymptotic stability under a given external disturbance. Finally, we apply this algorithm for the stability analysis and control synthesis of a network preserving power system.Comment: to appear at the 14th annual European Control Conferenc

Physical and Chemical Approaches to Improving the Stability of Perovskite Solar Cells

In recent years, perovskite solar cells (PSCs) have emerged as one of the most promising photovoltaic technologies. Their compatibility with low cost, simple fabrication techniques, high performance, and industrial scalability make them attractive for commercialization. However, moisture can cause serious damage to PSCs, resulting in complete device failure in a period of hours to days. Improved lifetimes are necessary for their future success. This thesis focuses on my efforts to improve the moisture stability of PSCs using two different approaches. The first approach focuses on applying hydrophobic barrier layers as hole-transport layers (HTLs) to improve the lifetime of PSCs, whereas the second approach is to find a stable perovskite composition. The first section of this thesis focuses on polythiophene-based HTLs. According to previous studies, hydrophobic HTLs like poly(3-hexylthiophene) improve the stability of the underlying perovskite layer by blocking moisture ingress. This section discusses the synthesis of four poly(3-alkoxythiophenes) with different side chains having different degrees of hydrophobicity. The effect of the side chain is discussed in terms of its ability to protect thin films of MAPbI3. The second section builds on this work. Here, the problems with the poor device performance of the polythiophene HTLs are addressed. A new device architecture is introduced which uses a poly(3-hexylthiophene) nanowire network in a poly(methyl methacrylate) matrix as the HTL. Due to the incorporation of the poly(methyl methacrylate) matrix, there was a large increase in the stability of the device towards both liquid and vapor-phase water. The third portion of this thesis investigates the decomposition processes of different well-known perovskite compositions. It focuses on the perovskites themselves and screens different perovskites for their moisture stability using in situ absorption spectroscopy and in situ grazing iii incidence wide angle x-ray scattering. It provides a better understanding of perovskite degradation processes and takes us one step closer to PSCs with longer lifetimes. This thesis discusses two approaches to improve the lifetime of PSCs. As moisture instability is an intrinsic problem of the PSCs, a stable perovskite composition is necessary for longer-lived devices. Similarly, it is also essential to develop better barrier layers to prevent moisture ingress

Physical and Chemical Approaches to Improving the Stability of Perovskite Solar Cells

In recent years, perovskite solar cells (PSCs) have emerged as one of the most promising photovoltaic technologies. Their compatibility with low cost, simple fabrication techniques, high performance, and industrial scalability make them attractive for commercialization. However, moisture can cause serious damage to PSCs, resulting in complete device failure in a period of hours to days. Improved lifetimes are necessary for their future success. This thesis focuses on my efforts to improve the moisture stability of PSCs using two different approaches. The first approach focuses on applying hydrophobic barrier layers as hole-transport layers (HTLs) to improve the lifetime of PSCs, whereas the second approach is to find a stable perovskite composition. The first section of this thesis focuses on polythiophene-based HTLs. According to previous studies, hydrophobic HTLs like poly(3-hexylthiophene) improve the stability of the underlying perovskite layer by blocking moisture ingress. This section discusses the synthesis of four poly(3-alkoxythiophenes) with different side chains having different degrees of hydrophobicity. The effect of the side chain is discussed in terms of its ability to protect thin films of MAPbI3. The second section builds on this work. Here, the problems with the poor device performance of the polythiophene HTLs are addressed. A new device architecture is introduced which uses a poly(3-hexylthiophene) nanowire network in a poly(methyl methacrylate) matrix as the HTL. Due to the incorporation of the poly(methyl methacrylate) matrix, there was a large increase in the stability of the device towards both liquid and vapor-phase water. The third portion of this thesis investigates the decomposition processes of different well-known perovskite compositions. It focuses on the perovskites themselves and screens different perovskites for their moisture stability using in situ absorption spectroscopy and in situ grazing iii incidence wide angle x-ray scattering. It provides a better understanding of perovskite degradation processes and takes us one step closer to PSCs with longer lifetimes. This thesis discusses two approaches to improve the lifetime of PSCs. As moisture instability is an intrinsic problem of the PSCs, a stable perovskite composition is necessary for longer-lived devices. Similarly, it is also essential to develop better barrier layers to prevent moisture ingress

Resilience of Traffic Networks with Partially Controlled Routing

This paper investigates the use of Infrastructure-To-Vehicle (I2V) communication to generate routing suggestions for drivers in transportation systems, with the goal of optimizing a measure of overall network congestion. We define link-wise levels of trust to tolerate the non-cooperative behavior of part of the driver population, and we propose a real-time optimization mechanism that adapts to the instantaneous network conditions and to sudden changes in the levels of trust. Our framework allows us to quantify the improvement in travel time in relation to the degree at which drivers follow the routing suggestions. We then study the resilience of the system, measured as the smallest change in routing choices that results in roads reaching their maximum capacity. Interestingly, our findings suggest that fluctuations in the extent to which drivers follow the provided routing suggestions can cause failures of certain links. These results imply that the benefits of using Infrastructure-To-Vehicle communication come at the cost of new fragilities, that should be appropriately addressed in order to guarantee the reliable operation of the infrastructure.Comment: Accepted for presentation at the IEEE 2019 American Control Conferenc