Doping of Organic Semiconductors: Effects of Crosslinking and Dopant Substituents

Doping is the process of addition of dopants to host semiconductors to improve their conductivity and charge transport behavior. Organic solids are held together by weak van der Waals interactions between the molecules and Coulombic attractions between the charged species. Because of these weaker interactions in organic materials, the molecules themselves have higher mobilities within the host material, and therefore, have a higher tendency to move. In most of the devices, the diffusion of the dopants in device stacks is detrimental and therefore, minimizing dopant diffusion within device interlayers is a very important topic to be consider. Considering the widespread usage of DMBI-H derivatives for doping of organic semiconductors, this work will focus on two aspects of doping; investigation of different approaches to address the diffusion of DMBI-H derivatives and studying the effect of dopant substituents on charge transport behavior. The first and second chapters of this thesis, will focus on crosslinking as new approaches for minimizing the dopant diffusion in the solid state. Chapter 2 will discuss electrostatic crosslinking in which the restriction of dopant ion movement by forming multiple electrostatic sites between the multiply charged ions and ionized host segments. Chapter 3 will discuss chemical crosslinking and chemical bond formation to decrease the diffusion of dopant and the corresponding dopant ions. Chapter 4 will focus on a study in which the effect of a polar side chain on DMBI-H for doping of a donor-acceptor polymer. The final chapter summarizes the findings of the thesis, puts them in a broader perspective, and suggests future directionsPh.D

E-Mobility -- Advancements and Challenges

Mobile platforms cover a broad range of applications from small portable electric devices, drones, and robots to electric transportation, which influence the quality of modern life. The end-to-end energy systems of these platforms are moving toward more electrification. Despite their wide range of power ratings and diverse applications, the electrification of these systems shares several technical requirements. Electrified mobile energy systems have minimal or no access to the power grid, and thus, to achieve long operating time, ultrafast charging or charging during motion as well as advanced battery technologies are needed. Mobile platforms are space-, shape-, and weight-constrained, and therefore, their onboard energy technologies such as the power electronic converters and magnetic components must be compact and lightweight. These systems should also demonstrate improved efficiency and cost-effectiveness compared to traditional designs. This paper discusses some technical challenges that the industry currently faces moving toward more electrification of energy conversion systems in mobile platforms, herein referred to as E-Mobility, and reviews the recent advancements reported in literature

Efficient model for modular multi-level converter simulation

Detailed models of modular multi-level converters (MMCs) are cumbersome for electromagnetic transient simulation programs because of their high number of components which involve large simulation times. In this work, the modeling of an MMC is addressed with the objective of reducing the simulation time. First, the MMC structure is presented, including the modulation technique, the voltage balancing algorithm and the circulating current control used to validate the model. Next, an efficient simplified model is proposed. This is formed by just one variable voltage source, one variable capacitor and one variable resistor per arm, regardless of the number of submodules. This simplified model allows the simulation time to be reduced while keeping the dynamics of the MMC. The comparison through several PSCAD simulations with a detailed 5-level MMC model proves its validity during both steady-state and transient conditions (ac and dc short-circuits).The authors acknowledge the financial support of the Spanish Ministry of Economy and EU FEDER Funds under Grant DPI2014-53245-R and the Universitat Jaume I under Grants P1.1B2013-51 and E-2014-24.Vidal-Albalate, R.; Belenguer, E.; Beltrán, H.; Blasco Gimenez, R. (2015). Efficient model for modular multi-level converter simulation. Mathematics and Computers in Simulation. 99(1):1-15. https://doi.org/10.1016/j.matcom.2015.10.001S11599

Space Vector Modulation of Multi-level and Multi-module Converters for High Power Applications

This thesis presents and investigates Space Vector Modulation (SVM) switching strategies for (i) a multi-level Diode-Clamped Converter (DCC) and (ii) a multi-module Voltage-Sourced Converter (VSC) system in which each module is a conventional two-level VSC. Although the SVM strategies are general and applicable for n-level DCC and n-module VSC systems, this text only concentrates on five-level DCC and four-module VSC systems. For a five-level DCC, a computationally efficient SVM algorithm is proposed. The algorithm, that is based on a classifier Neural Network (NN), reduces the computational time for the SVM realization. Therefore, adequate saving of processor execution time, in each sampling period of SVM, is provided to carry out other functions, e.g. the calculations required for DC-capacitor voltage balancing task. The thesis also proposes a DC-capacitor voltage balancing strategy to counteract the voltage drift phenomenon of (i) a passive-front-end five-level DCC, and (ii) a back-to-back connected five-level DCC system. The proposed balancing strategy, that is based on augmenting the proposed SVM algorithm, takes advantage of the redundant switching states to minimize a quadratic cost function associated with voltage deviations of the DC-capacitors. The salient features of the proposed balancing strategy are (i) online calculation of SVM to select the best switching states, (ii) minimization of switching frequency, (iii) minimization of the THD content of the AC-side voltage, and (iv) no requirement for additional power circuitry. For a four-module VSC system a sequential sampling SVM strategy is proposed. The proposed strategy (i) provides harmonic cancellation/minimization at the net AC-side voltage of the multi-module VSC system, and (ii) offers a low switching frequency for each VSC module. Technical feasibility of the proposed SVM strategies for a five-level DCC and a four-module VSC system, as a STATCOM and a back-to-back HVDC system, are investigated and presented. The studies are conducted in the time-domain, in the PSCAD/EMTDC software environment.Ph

Sequential Tripping of Hybrid DC Circuit Breakers to Enhance the Fault Interruption Capability in Multi-Terminal DC Grids

Presented at the CIGRE US National Committee 2018 Grid of the Future Symposiumhe hybrid solid-state DC circuit breakers (DC CBs) have become one of the most promising technologies to address the protection challenges within multi-terminal DC (MTDC) grids. Those breakers are designed in such a way that a large number of identical modules are connected in series to enable extinguishing the fault current with the arresters embedded in them. Conventionally, these modules are commanded to trip simultaneously, creating significant overvoltage and overcurrent stresses for the rest of the system. To attenuate these adverse impacts, in this paper, a sequential tripping method is proposed to improve the performance of hybrid DC CBs through commanding the main breakers to trip in a sequential manner. It has been verified that by the proposed method, fault clearance is expedited while the maximum overcurrent is reduced. To address the unbalanced energy absorptions among the different modules of the CB, a modified sequential tripping scheme is also proposed. By rescheduling the sequential tripping sequence, this method enables an equal redistribution of energy, which greatly reduces the risk of thermal overloading. Both of the proposed methods are evaluated and tested under a practical six-terminal DC grid in the PSCAD/EMTDC software environment. The performance and effectiveness of the proposed methods are confirmed by simulation results