When a wind park is sited offshore, compact, lightweight and reliable components are important requirements. In this Master's thesis a wind energy conversion system has been proposed, where the objective is to meet the requirements of an offshore environment. The system consists of a permanent magnet generator, a reduced matrix converter, a high frequency transformer and a full-bridge converter. It is the reduced matrix converter which is the main focus of the thesis. The reduced matrix converter (RMC) provides direct AC-AC conversion without the need of a bulky DC link capacitor, it is thus a compact solution. It is built with six bi-directional switches. Each switch consists of two reverse blocking IGBTs in antiparallel. The reverse blocking IGBT is different from the conventional IGBT because it blocks voltage of both polarities.Due to the direct AC-AC conversion of the RMC it is necessary to implement a special protection scheme for the circuit. The scheme provides reliable operation of the RMC so the switches are not damaged. This is achieved by the introduction of a clamp circuit. The clamp circuit has been studied during normal operation and the operation during faults has been described. The entire WECS has been implemented in the simulation program PSIM to simulate behavior of the clamp circuit during normal operation and to calculate switching and clamp circuit losses. Both losses are related to the RMC, and are important for the study of the overall energy efficiency of the converter. Total losses have been compared for two different modulation techniques, these are carrier based modulation and space vector modulation. The simulation results indicated that space vector modulation is the most energy efficient solution for the system.

Boiling two-phase flow is found in many industrial applications such as boiling water reactors, two-phase flow heat exchangers and refrigeration systems. The physics of two-phase gas-liquid flow may lead to undesirable system instabilities, and in the literature density wave oscillations (DWO) is reported to be the most commonly observed instability phenomenon. However, the literature alsoprovides two opposing views on what the fundamental mechanism of DWO is. The so-called classical description of DWO focuses on the variation in mixture density as the governing mechanism, and the oscillation period will consequently be about one to two times the channel residence time. The findings presented in citet{Rizwan-Uddin1994} show that it is the variation in mixture velocity that hasthe dominating effect, and the oscillation period was reported to be closer to four times the channel residence time. citet{Ambrosini2000} united the two opposing views by stating that the governing mechanismdepends on the level of system subcooling. The classical description of DWO is based on a lower level of subcooling, while citet{Rizwan-Uddin1994} considered higher subcooling. Here, the fundamental mechanisms of DWO and the effect of system subcooling is investigated further by performing a numerical analysis using a one dimensional homogenous equilibrium flow model. The modeled system consists of a horizontal uniformlyheated boiling channel with an inlet- and exit restriction. The system is exposed to constant externally imposed pressure drop. The effect of system subcooling is investigated by comparing the self-sustained periodicoscillations which make out the modeled stability threshold. The flow model is validated by observing the above mentioned effects of subcooling on DWO. Further, it is found that the change from a density dominated exit restriction towards a velocity dominated exit restriction is a smooth transition for increased subcooling. The amplitude of the variations in exit mixture velocity increases continuously with subcooling, anddue to the squared relationship between the exit restriction pressure drop and the exit mixture velocity, velocity becomes the governing mechanism at high subcooling.The modeled stability threshold approaches a straight line at high subcooling. This line represents operating conditions which have the same mean boiling boundary location. However, the amplitude of the variations about this mean limit grows exponentially at high subcooling. The oscillation period of the observed DWO grows continuously with higher subcooling, and the period increases exponentially at high subcooling. In contrast, the mean boiling channel residence time approaches an upper mean limit at high subcooling. It is postulated that it is the transition towards a more mixture velocity dominated system that causes the oscillation period to evolve as it does with respect to the level of subcooling.

Electricity generation, along with motor vehicles, is one of the biggest sources of pollution for the planet. Renewable energies are not able to replace massively polluting power plants but they can at least alleviate for it. Biomass and hydro power are the main source of renewable energy but wind power is developing to high extent, increasing by 30% its installed capacity every year in the world. Norway is increasing its wind power production since every hydro power areas are already used. The shallow Norwegian waters along with the increase of energy demand leads to offshore wind project.The aim of this thesis is to study the integration of large scale offshore wind farms into the grid. The biggest offshore wind farm is currently installed in the United Kingdom (Thanet) and its capacity is 300 MW. The wind farm studied here has a capacity of 1000 MW. HVAC and HVDC transmission are investigated in order to connect the wind farm to Norway. Case faults are performed in order to study the system stability. The connection points are located in the most populated areas of Norway, where there is a real need for new power plants: Sørlandet and Vestlandet.Statnett is the Norwegian transmission system operator and thus the focus was made on the connection with power flow and stability analysis and not on the full description of the wind farm. For simulations, Statnett is mainly using PSS®E (Power System Simulator) from Siemens but as much of the help was providing by SINTEF, the largest independent research organisation in Scandinavia, it was more convenient to use their tool: SIMPOW from STRI AB.

This master thesis studies the possible pathways to support military vehicles and ground troops with electrical power a more efficient way, than the present solution. Present energy solution is based on generation of electrical power from internal combustion engines and/or stored energy in batteries. The usage of the vehicles engine for generation of electricity in static positions, results in several disadvantages on a modern battlefield. The batteries specific energy increase every year, but the soldier’s energy need has increased even faster, resulting in a problematic weight load for the dismounted soldier. In the thesis several new or improved solutions are investigated. The solutions are based on technology available today or within the next decade (2020) and selected on the basis of military criteria. A flexible model has been made in an energy simulating program capable to simulate a number of different energy configurations based on future electrical power consumption. Modelling and simulation of the soldiers power system has been recommended by earlier studies [10], but similar models have not been found by the author. The simulation results reveal that improvements of soldiers’ energy solution are feasible. By implementing new or better batteries in the current energy system, considerable improvement can be achieved. Introduction of fuel cells based on methanol fuel starts to become mature, and can result in several advantages on the battlefield. Solar harvesting can give an additional energy supply, but depend highly on insolation and available time for harvesting.