New PhD theses
Arvind Parwal, "Grid Integration and Impact of a Wave Power System", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214, 1842
Abstract:
Increasing energy consumption and concern for carbon emissions has boosted the demand for renewable energy production. The focus on renewable energy has gained much attention in wind, solar, hydro and wave power generations. Wave power has great potential due to its high energy density but there are challenges as well. This thesis addresses some of the challenges involved in the grid integration of wave energy and in maintaining power quality. In this thesis a grid connection of permanent magnet linear generator (PMLG) based wave energy converter (WEC) as a renewable energy source is evaluated at the Division of Electricity, Uppsala University.
The grid impact of a wave energy park in terms of flicker, voltage variations and harmonic distortion at the grid-connection point are investigated extensively. The short-term flicker level generated by the WEC and a wave energy park (WEP) related to the rated WEP power and grid impedance angle at the PCC are evaluated.[...]
Mohd Nasir Ayob, "Adaptation of wave power plants to regions with high tides", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214, 1795
Abstract:
The wave energy converter (WEC) developed at Uppsala University is based on the concept of a heaving point absorber with a linear generator placed on the seafloor. The translator inside the generator oscillates in a linear fashion and is connected via a steel wire to a point absorbing buoy. The power production from this device is optimal when the translator’s oscillations are centered with respect to the stator. However, due to the tides, the mean translator position may shift towards the upper or lower limits of the generator’s stroke length, thereby affecting the power production. This effect will be severe if the WEC operates in an area characterized by a high tidal range. The translator may be stuck at the top or rest at the bottom of the generator for a considerable amount of time daily.[...]
Maria Angeliki Chatzigiannakou, "Offshore deployments of marine energy converters", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214, 1792
Abstract:
The depletion warning of non-renewable resources, such as gas, coal and oil, and the imminent effects of climate change turned the attention to clean and fossil fuel-free generated electricity. University research groups worldwide are studying solar, wind, geothermal, biomass and ocean energy harvesting. The focus of this thesis is the wave and marine current energy researched at the division of Electricity at Uppsala University (UU).
The main drawbacks that hinder the commercialization of marine energy converter devices is a high installation, operation, maintenance and decommissioning cost. Furthermore, these processes are highly weather dependent and thus, can be time consuming beyond planning. In this thesis, an evaluation of the cost, time and safety efficiency of the devices’ offshore deployment (both wave and marine current), and a comparative evaluation regarding the safety in the use of divers and remotely operated vehicles (ROVs) are conducted.[...]
Francisco Francisco, "Adapting sonar systems for monitoring ocean technologies", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214, 1752
Abstract:
The global energy sector is under profound reforms aiming towards renewable energy sources, clean technologies and expansion of smart grids, all with the additional aim of providing affordable and dependable electricity for everyone. A reduction of carbon dioxide emissions is a priority on the global agenda, and to achieve that, cleaner energy technologies has to be more integrated into the energy mix. This thesis focus on a sustainable implementation of wave, tidal and offshore wind power, wherefore there is a need to investigate more about the prerequisites and consequences ocean energy can have on the marine environment. For that, reliable, cost effective and continuous environmental monitoring framework is necessary in order to support and safeguard ocean energy operations.[...]
Petter Eklund, "Design of Rare Earth Free Permanent Magnet Generators", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1746
Abstract:
Low speed permanent magnet (PM) synchronous generators (SGs) are commonly used in renewable energy. Rare earth (RE) PMs such as neodymium-iron-boron are a popular choice due to their high performance. In 2011 supply and cost issues were added to the previously existing environmental concerns regarding REPM raw materials as the world's major producer China imposed export restrictions. This thesis aims to investigate and propose design solutions for PMSGs that do not use REPMs. Two approaches are used: to design generators using the cheaper and more abundant ferrite PM materials, and to investigate how properties of new PM materials influence SG design.[...]
Johan Forslund, "Studies of a Vertical Axis Turbine for Marine Current Energy Conversion: Electrical system and turbine performance", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1739
Abstract:
Ocean energy is a field of growing interest when it comes to renewable energy thanks to its high density of energy per unit area, and to the high predictability. Conversion of hydrokinetic energy, found in marine currents, is the utilization of the energy in free-flowing water for conversion to electric energy. This thesis presents experimental data from a test site with a marine current converter. The converter system features a vertical axis turbine directly connected to a permanent magnet synchronous generator placed on the riverbed. The converter is controlled by an electrical system. The focus of the work is to evaluate power control methods and turbine performance. Results of a simple voltage control system is presented and compared with operation without control. The turbine type in the converter system is not self-starting. The startup power and energy has been investigated through experiments. The converter system has been connected to the local electric utility grid and the first experimental results are presented. [...]
Flore Rémouit, "Automation of underwater operations on wave energy converters using remotely operated vehicles", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1695
Abstract:
In the last fifteen years, the Division of Electricity at Uppsala University has been developing a wave energy converter (WEC) concept. The concept is based on a point-absorbing buoy with a directly driven linear generator placed on the seabed. Several units are connected to a marine substation, whose role is to collect and smooth the power absorbed from the waves and then bring it to the shore through one single cable.
A big challenge in the project is to reduce the costs related to the deployment and maintenance of the WECs and substation. Currently, those operations are performed by divers, which is costly and entail considerable risks. A possibility is to replace divers with automated solutions using small robots called remotely operated vehicles (ROVs). This PhD thesis proposes and analyses a method for deployment and maintenance of underwater devices with no use of diving operations.[...]
Nattakarn Suntornwipat, "Diamond devices based on valley polarization", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214; 1670
Abstract:
Diamond is a wide bandgap semiconductor with extreme properties such as high thermal conductivity, high breakdown field, high carrier mobilities and chemical inertness. These properties together with the possibility to synthesize high purity Single-Crystalline (SC) diamond by Chemical Vapor Deposition (CVD), make it a very interesting material and a candidate for use in power electronics and in hazardous environments. The low impurity concentration achieved when fabricating diamond by CVD allows for a detailed study of the intrinsic electronic properties.
Diamond has six equivalent conduction band valleys oriented along the {100} axes with a uniquely low scattering rate between them. At low temperatures, the intervalley phonon scattering rate in diamond becomes negligible, which leads to a stable valley polarization state. We have observed non-equilibrium valley populations (valley-polarized electron ensembles), which in turn have been found to result in a Negative Differential Mobility (NDM).[...]
Victor Mendoza, "Aerodynamic studies of vertical axis turbines using the actuator line model", Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1671
Abstract:
This thesis addresses the unsteady aerodynamics involved in the operation of vertical axis wind turbines (VAWTs). The main focus is to represent and understand the most relevant phenomena within the resulting flow pattern as the wake structure, loads on the different turbine components and the performance of the rotor. An actuator line model has been used for this purpose.
This model has been validated against experimental measurements from diverse cases with different operating conditions in both confined wind tunnels and open site locations. Numerical works were carried out considering a wide range of tip speed ratios (TSRs), and therefore covering from the no stall to the deep stall regime. The latter requires the implementation of a dynamic stall model for the proper representation of the unsteady forces on the blades. Also, different inlet conditions such as a uniform flow, a logarithmic wind shear and an atmospheric boundary layer (ABL) have been tested. The so-called recycling method technique was used to produce the fully developed ABL flow. Additionally, the resulting wake and performance of interacting turbines has been studied.[...]
Kaspars Siliņš, "Plasma Enhanced Chemical- and Physical- Vapor Depositions Using Hollow Cathodes", Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1629
Abstract:
Development of coating deposition technologies, in terms of performance and costs, is an ongoing process. A promising class of deposition technologies are based on hollow cathode discharges.
This thesis investigates performance of selected hollow cathode plasma sources developed at the Plasma group, at Uppsala University for coating deposition at moderate pressures. Amorphous carbon film deposition was investigated by Radio frequency (RF) Hollow Cathode Plasma Jet (RHCPJ) and Magnets-in-Motion (M-M) linear hollow cathode plasma sources. Titanium nitride (TiN) films were deposited by a magnetized Hollow Cathode Enhanced magnetron Target (HoCET). Aluminium nitride (AlN) deposition by RHCPJ was compared with High Power Impulse Magnetron Sputtering (HiPIMS).[...]
Pasan Hettiarachchi, "Measurements of X-ray emission from laboratory sparks and upward initiated lightning", Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1618
Abstract:
In 1925 Nobel laureate R. C. Wilson predicted that high electric fields of thunderstorms could accelerate electrons to relativistic energies which are capable of generating high energetic radiation. The first detection of X-rays from lightning was made in 2001 and from long sparks in 2005. Still there are gaps in our knowledge concerning the production of X-rays from lightning and long sparks, and the motivation of this thesis was to rectify this situation by performing new experiments to gather data in this subject.[...]