Reset control for DC-DC converters: an experimental application

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Power converters in grid connected systems are required to have fast response to ensure the stability of the system. The standard PI controllers used in most power converters are capable of fast response but with significant overshoot. In this paper a hybrid control technique for power converter using a reset PI + CI controller is proposed. The PI + CI controller can overcome the limitation of its linear counterpart (PI) and ensure a fast flat response for power converter. The design, stability and cost of feedback analysis for a DC-DC boost converter employing a PI + CI controller is explored in this work. The simulation and experimental results which confirm the fast, flat response will be presented and discussed.Peer ReviewedPostprint (published version

Effect of organic amendments on soils, drainage waters and ground waters in the state of Bahrain

This research examined the effects of different types of organic amendments at different rates of addition and with different quantities of irrigation water on two major soil types of Bahrain. The aim was to quantify potential improvements in soil quality, the accumulation of trace metals in the soil, and the release of metals and nutrients to drainage waters, and leaching of nutrients and metals to ground water. Organic amendments, cow manure, chicken manure and sewage sludge were analysed for various physical and chemical properties. Pot experiments, field soil and water analysis in areas of organic amendment were carried out. Drainage waters close to intensive agricultural production, where mineral fertilizers and organic amendments were used, were analysed for nutrients and heavy metals. Run-off water from major farms and local ground waters were also analysed. From the pot experiments it was found that soil water holding capacity did not change much after the addition of organic amendments except in the case of sewage sludge addition. Total organic carbon and total kjeldhal nitrogen content Increased in the 0-5 cm layer. Low TDS water and sewage sludge applications improved aggregate stability to some extent. Extractable phosphorus was enhanced by the chicken manure treatment more than any others. Addition of different organic amendments did not affect exchangeable cations. pH values did not show appreciable changes and soils were neutral. Among the trace metals Investigated, cadmium, lead, zinc and copper, all were found in the 0-5 cm layer and none were present at toxic levels in soils. Zinc and Copper were the only metals showing a tendency to leach to the lower soil layer. In all cases, the metal concentrations in the surface soil were proportional 'to the quantities added in the amendments. Concentration of trace metals in the leachate from pot experiments were very low. Field studies indicated that, use of organic amendments resulted in increased N, P and C in the surface soil. Nitrogen, phosphorus and potassium concentrations in drainage waters near agricultural areas were higher than at other non-agricultural areas. Ground water nutrients did not show any correlation between fertilizer addition and their proximity to the agricultural land except at Al-Akr. Nitrogen, phosphorus and potassium levels in the soil profile indicated that nutrients are present mainly at the 0-5 cm levels and downward movement was minimum. Application of organic manure before the fertilizer addition apparently retarded the leaching process. Soil surface run-off water from agricultural land also showed high concentrations of nitrate (NO3). All fertilizer amended plots had lower metal concentrations than the two sites amended with sewage sludge.The sewage sludge treated sites contained elevated levels of heavy metals at the 0-5 cm layer and plants grown on the sludge treated sites had higher concentrations of heavy metals than the control sites using inorganic fertilizers. Cadmium content of plant materials grown on sludge application sites exhibited higher levels than allowed in plants meant for feeding the animals

Control Strategies for Improving Reliability and Efficiency in Modular Power Converters

The significance of modular power converters has escalated drastically in various applications such as electrical energy distribution, industrial motor drives and More Electric Aircraft (MEA) owing to the benefits such as scalability, design flexibility, higher degree of fault tolerance and better maintenance. One of the main advantages of modular systems is the ability to replace the faulty converter cells during maintenance instead of the entire system. However, such maintenance cycles can result in a system of converter cells with different aging. A system with cells having different aging arises the threats of multiple maintenance, lower reliability and availability, and high maintenance costs. For controlling the thermal-stress based aging of modular power converters, power routing strategy was proposed. The thesis focuses on the different implementation strategies of power routing for modular converters. Power semiconductors are one of the most reliability critical components in power converters, and thermal-stress has been identified as the main cause of their failure. This thesis work concentrates on the power semiconductor reliability improvement algorithms. For improving system lifetime, virtual resistor based power routing algorithms for single stage and multi-stage modular architectures have been investigated through simulations and validated with experiment. A unified framework for routing the power in complex modular converter architectures is defined based on graph theory. Popular converter architectures for Smart Transformer (ST) and MEA applications are modeled as graphs to serve as the basis for developing power flow optimization. The effectiveness of graph theory for optimizing the power flow in modular systems is demonstrated with the help of proposed algorithms

The role of transcription factor dFoxO in regulating tracheal terminal cell plasticity of the fruit fly Drosophila melanogaster

Plasticity is a fundamental biological process that ensures that individuals' morphology, behavior, and physiology adapt to match their environment. Understanding the mechanisms that regulate trait plasticity is important because knowledge of how phenotypic plasticity is regulated has significant consequences for the study of diseases that result from changes in plasticity. Reduced O2 levels—or hypoxia, can lead to irreversible cellular damage in organisms, and therefore, organisms have evolved adaptive responses to compensate for the lack of O2. Drosophila melanogaster is highly resistant to oxygen deficiency and its respiratory (tracheal) system has features in common with the vertebrate vascular system. The tracheal terminal cells (TTCs) are plastic in nature, and they respond to hypoxia and different dietary conditions by sprouting out new branches, a process that can be compared to angiogenesis in mammals. Here we elucidate the role of the transcription factor, Forkhead box protein O(dFoxO) in regulating TTC plasticity. Deregulation of FoxO activity in the TTCs achieved by deficiency and overexpression of FoxO led to the loss of plasticity of the terminal cells. However, partial reduction of expression of FoxO via RNAi led to hyperbranching phenotype, suggesting that FoxO need to be expressed at a physiologically relevant level to maintain plasticity of the terminal cells. Suppressing JNK activity in the terminal cells did not affect the plasticity of the terminal cells, suggesting that the FoxO regulation in the terminal cells is independent of JNK activity. On the other hand, the induced release of Insulin from the insulin producing cells positively regulated the terminal branching, implying dFoxO might be regulated via IIS signaling

Seeds of change: How current structure shapes the type and timing of reorganizations

Research Summary: This article develops theory on how an organization's structure affects future reorganizations. I highlight that a firm's structure shapes not only the locus of decision-making power (i.e., centralization and decentralization) but also the employees' interaction structure. I develop microlevel theory that connects the firm's structure to the interactions among its employees—for instance, its influence on the time employees spend adjusting their behavior after a reorganization. This theory predicts that some structures are more likely than others to promote a reorganization to occur sooner. I use a unique, hand-collected data set of reorganizations in the cell-phone manufacturing industry to test and find directional support for this theory. Managerial Summary: I examine the effect of a firm's current structure on its corporate reorganization decisions, which are defined as the addition and/or removal of business units. I posit that the way employees are grouped into those business units may affect both the type and timing of subsequent reorganizations; the reason is that employees of similar (resp. different) backgrounds should need less (resp. more) time to achieve effective collaboration. Using data on the reorganizations of cell-phone manufacturing firms during 1983–2008, I find directional support for the theory. This result implies that managers may need to watch closely any reorganization that shifts the firm toward more heterogeneous interaction structures—because its implementation may well require additional time