Browsing by Subject "Hybrid"

Now showing 1 - 8 of 8
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    Allocation policy analysis for cache coherence protocols for STT-MRAM-based caches
    (2014-10) Nandkar, Pushkar Shridhar
    Spintronic devices have demonstrated promising results to replace the traditional CMOS devices in Last Level Caches. Recent research have focussed on STT-CMOS hybrid caches and presented techniques to reduce leakage power and achieve performance benefit due to larger caches size that can be accommodated in the same footprint. Instead of using such hybrid caches, we use in-place STT-MRAM replacements for the complete cache hierarchy and show that we can achieve increased performance due to larger caches and significant power benefits due to decreased leakage. Further, we study different cache coherence protocols and with different allocation policies. Our preliminary results show that Non-inclusive protocols save write dynamic energy mostly due to reduced number of line fills compared to an inclusive protocol. We study the complete parsec benchmark suite and discuss the best allocation policy for each benchmark while considering the energy-delay trade off.
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    Building-integrated solar energy devices based on wavelength selective films
    (2013-06) Ulavi, Tejas U.
    A potentially attractive option for building integrated solar is to employ hybrid solar collectors which serve dual purposes, combining solar thermal technology with either thin film photovoltaics or daylighting. In this study, two hybrid concepts, a hybrid photovoltaic/thermal (PV/T) collector and a hybrid `solar window', are presented and analyzed to evaluate technical performance. In both concepts, a wavelength selective film is coupled with a compound parabolic concentrator (CPC) to reflect and concentrate the infrared portion of the solar spectrum onto a tubular absorber. The visible portion of the spectrum is transmitted through the concentrator to either a thin film Cadmium Telluride (CdTe) solar panel for electricity generation or into the interior space for daylighting. Special attention is given to the design of the hybrid devices for aesthetic building integration. An adaptive concentrator design based on asymmetrical truncation of CPCs is presented for the hybrid solar window concept. The energetic and spectral split between the solar thermal module and the PV or daylighting module are functions of the optical properties of the wavelength selective film and the concentrator geometry, and are determined using a Monte Carlo Ray-Tracing (MCRT) model. Results obtained from the MCRT can be used in conjugation with meteorological data for specific applications to study the impact of CPC design parameters including the half-acceptance angle θ_c, absorber diameter D and truncation on the annual thermal and PV/daylighting efficiencies. The hybrid PV/T system is analyzed for a rooftop application in Phoenix, AZ. Compared to a system of the same area with independent solar thermal and PV modules, the hybrid PV/T provides 20% more energy, annually. However, the increase in total delivered energy is due solely to the addition of the thermal module and is achieved at an expense of a decrease in the annual electrical efficiency from 8.8% to 5.8% due to shading by the absorber tubes. For this reason, the PV/T hybrid is not recommended over other options in new installations. The hybrid solar window is evaluated for a horizontal skylight and south and east facing vertical windows in Minneapolis, MN. The predicted visible transmittance for the solar window is 0.66 to 0.73 for single glazed systems and 0.61 to 0.67 for double glazed systems. The solar heat gain coefficient and the U-factor for the window are comparable to existing glazing technology. Annual thermal efficiencies of up to 24% and 26% are predicted for the vertical window and the horizontal skylight respectively. Experimental measurements of the solar thermal component of the window confirm the trends of the model. In conclusion, the hybrid solar window combines the functionality of an energy efficient fenestration system with hybrid thermal energy generation to provide a compelling solution towards sustainable design of the built environment.
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    Collection of Heat Loss in Photovoltaic System by Parallelly Connected Thermoelectric Network
    (2022-06) Erickson, Joel
    The goal of this work is to increase solar cell efficiency by efficiently combining the electric power of a solar cell and a thermoelectric generator into a single two terminal hybrid device. This work presents a method of achieving this by dividing the thermoelectric generator into smaller thermoelectric generators, forming a parallelly connected network with them, and connecting this network in series with the solar cell. An equivalent circuit model was developed for this device scheme and compared with experimental data. The data show some support of the model, but fine evaluation of the model’s accuracy was hindered by limitations in the experimental setup. If thermoelectric generator efficiency increases in the future, it may become practical to combine thermoelectric generators with solar cells. Providing a method for combining the two power sources at the cellular level may be important for simplifying and improving systems that use these photovoltaic/thermoelectric hybrids.
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    Development of a Hydraulic Energy Storage System for Hybrid Wind Turbine Transmissions
    (2021-05) Mohr, Eric
    Mid-size wind turbines are an under-recognized means to help prevent irreversible climate damage caused by unprecedented human-made carbon emissions. A high-power hydraulic energy storage system can be added to turbine transmissions to capture energy in high wind speeds, and release energy in low wind speeds. The hybrid system stabilizes the output power of the transmission, and increases reliability while offering ancillary benefits such as fault-ride through and pitch and yaw control in severe weather. The hybrid system was constructed. Experimental characterization of hybrid parameters determined that a modified heat transfer model of the accumulator is realistic, and that the thermal time constant of the accumulator is around 80 seconds. A high fidelity simulation is produced which is experimentally validated. The simulation is then used to find the additional annual energy production compared to the non-hybrid system is 3.5%. This value can only be attained with the addition of a clutch and directional valve.
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    The development of a power management strategy for a hydraulic hybrid passenger vehicle
    (2014-07) Meyer, Jonathan James
    The amount of energy being consumed is increasing each year, with the highest sector being the transportation industry. Within the transportation sector, the highest area of oil consumption is in the small and lightweight vehicle category. With increasing oil prices and decreasing supply, methods of reducing oil consumption have been studied. One is by developing a hybrid vehicle, which combines the internal combustion engine with an additional power source. For lightweight vehicles, electric hybrid vehicles have been thoroughly studied. While hydraulic hybrids have been studied for larger applications such as delivery trucks and buses, little research has been done in the area of small, lightweight vehicles. Hydraulics have a higher power density than electronics, so hydraulic hybrids can get better performance than electric hybrids while reducing fuel consumption.In this research, a series and power-split architecture is studied for a passenger vehicle. Because of the additional hydraulic power source along with energy storage, the optimal way to control these vehicles is not known. Therefore, an energy management strategy must be developed to determine the optimal strategy for splitting the power between the engine and the hydraulics.Three different methods are used to develop the energy management strategy - a rule-based strategy based on dynamic programming results, stochastic dynamic programming, and model predictive control. An experimental hardware-in-the-loop setup is used to replicate a series hybrid in which the different energy management strategies are tried. Through simulation and experimentation, it was found that not one strategy works best in all scenarios, and variables such as knowledge of duty cycle and energy storage must be taken into account when developing the strategy.An input-coupled power-split hybrid was also studied, which combines the mechanical efficiency of the parallel hybrid with the engine management of a series hybrid. Through a series of simulations, a strategy that declutched the engine from the drivetrain while the vehicle is stopped gave a significant reduction in fuel consumption. Another advantage of the power-split architecture is the ability to operate the vehicle in different modes by declutching the engine and removing hydraulic units by the use of valves. By using this strategy, the fuel economy can be almost doubled over a baseline strategy which operates only in power-split mode. Finally, the size of the accumulator can have an effect on the fuel consumption, with a smaller accumulator leading to less fuel consumed; however, if the accumulator is too small, the performance starts to degrade with a downsized engine.The results of this research can be used to develop a toolbox that can be used for developing energy management strategies by having the user enter a model, objective function, and duty cycle for a system. By using other information, such as knowledge of duty cycle, the toolbox can determine the best method of developing the control strategy, reducing the amount of time and resources for developing an optimal control strategy.
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    Modeling, Optimization, and Detailed Design of a Hydraulic Flywheel-Accumulator
    (2014-07) Strohmaier, Kyle Glenn
    Improving mobile energy storage technology is an important means of addressing concerns over fossil fuel scarcity and energy independence. Traditional hydraulic accumulator energy storage, though favorable in power density, durability, cost, and environmental impact, suffers from relatively low energy density and a pressure-dependent state of charge. The hydraulic flywheel-accumulator concept utilizes both the hydro-pneumatic and rotating kinetic energy domains by employing a rotating pressure vessel. This thesis provides an in-depth analysis of the hydraulic flywheel-accumulator concept and an assessment of the advantages it offers over traditional static accumulator energy storage.After specifying a practical architecture for the hydraulic flywheel-accumulator, this thesis addresses the complex fluid phenomena and control implications associated with multi-domain energy storage. To facilitate rapid selection of the hydraulic flywheel-accumulator dimensions, computationally inexpensive material stress models are developed for each component. A drive cycle simulation strategy is also developed to assess the dynamic performance of the device. The stress models and performance simulation are combined to form a toolset that facilitates computationally-efficient model-based design.The aforementioned toolset has been embedded into a multi-objective optimization algorithm that aims to minimize the mass of the hydraulic flywheel-accumulator system and to minimize the losses it incurs over the course of a drive cycle. Two optimizations have been performed - one with constraints that reflect a vehicle-scale application, and one with constraints that reflect a laboratory application. At both scales, the optimization results suggest that the hydraulic flywheel-accumulator offers at least an order of magnitude improvement over traditional static accumulator energy storage, while operating at efficiencies between 75% and 93%. A particular hydraulic flywheel-accumulator design has been selected from the set of laboratory-scale optimization results and subjected to a detailed design process. It is recommended that this selection be constructed and tested as a laboratory prototype.
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    Novel optimal control algorithms with application to the parallel hydraulic hybrid vehicle power train.
    (2010-10) Ertel, Robert Gregory
    The parallel Hydraulic Hybrid Vehicle (HHV) power train is quickly becoming a viable option among large (class 7-10) vehicles. This is due to its potentially vast improvements in fuel economy over non-hybrid power trains. Optimal control of the parallel HHV power train is critical to overall vehicle performance and is largely responsible for gains in efficiency. The research presented in this thesis aims to answer the question of how to best operate the power train to achieve maximum efficiency during driving intervals when vehicle speed is unspecified, except at boundary points. A state-space model of the parallel HHV power train is derived in the energy domain using a classical Lagrangian approach. Two optimal control algorithms are developed and applied to the vehicle. The first algorithm is gradient descent based and is derived using the calculus of variations. The second algorithm discretizes the optimal control problem in time and converts it to a non-linear program. Several optimal control problems are solved and the results offer valuable insight into efficient operation of the parallel HHV power train.
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    Sustainable Development of Polymers Using Hybrid Process of Biosynthesis and Chemical Reactions
    (2022-02) Wu, Yuxiao
    Natural and synthetic polymers can be found everywhere in our everyday lives. Polymer materials contribute to crucial roles in sophisticated applications such as electronics, medical devices and implants. They are also found in parts of every trivial thing in modern life such as clothing, food packaging, housing, and transportation. We rely more on synthetic polymers over natural polymers since the prosperity of petrochemical industry after the Second Industrial Revolution. The cheap and abundant fossil fuel allowed the development of a wide array of synthetic polymers in the 20th century. However, environmental concerns associated with using petroleum feedstock as the raw material received more and more attention. Over the past several decades researchers have focused on replacing petroleum feedstock with renewable feedstock to produce sustainable polymers. The abundant biomass is often used as the renewable raw material and one important way to breakdown biomass is through microbial fermentation. The development of genetic engineering allowed successful expansion of the natural metabolic pathways of microorganisms. Many industrial chemicals and novel chemicals were produced from microbial fermentation. The advantage of microbial fermentation is that it is carried out in mild reaction conditions and generates environmentally benign byproducts. However, microbial fermentation lacks the economic viability and utility due to long fermentation time and productivity. A hybrid synthesis process combining microbial fermentation and chemical reaction is a highly efficient approach to produce sustainable polymers. With this in mind, my PhD research has focused on developing hybrid chemical engineering process for the production of novel or existing polymer precursors and implement them for material applications. Using metabolic engineering and simple chemical reaction, I have produced N-acetyldopamine which can be used as a precursor for catechol functionalized polymers. By optimizing the fermentation pathway of mesaconic acid, the yield and productivity have reached an industrially practical level. The hybrid synthesis process to isoprene, the monomer for natural rubber, was established combining this optimized fermentation route with preciously developed one-pot cascade thermal chemical reaction. Finally, I implemented a heterologous pathway to produce citramalic acid. I have worked to establish a C5 diacid platform from microbial fermentation. Combining with a thermocatalytic decarboxylation reaction, an integrated hybrid process for the conversion of glucose to poly(methyl methacrylate) was achieved.