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Accurate predictions of the annual energy yield from wave energy converters are essential to the development of the wave industry. The current method based on power matrices uses only a small part of the data available from sea state estimations and it is consequently prone to inaccuracies. The research presented in this work investigates the issue of energy yield prediction and questions the power matrix method. This is accomplished by quantifying the influence of several directional sea states parameters on the performances of wave energy converters. The approach taken was to test several wave energy converters in the Edinburgh Curved tank with a large set of sea states. The selected wave energy converters are a fix OWC, a set of two OWCs acting as a weak directional device and the desalination duck model. Uni-modal and bi-modal sea states were used. For the uni-modal sea states, parameters related to the wave system shape were considered. For the bi-modal sea states, the relative position of the wave system peaks was investigated and the uni-modality index was introduced to quantify the degree to which sea states could be considered bi-modal. For all sea states, the significant wave height was kept constant. The experimental work required good spectral estimates. The MLM and MMLM were adapted to deterministic waves to improve their stability and accuracy. A routine to isolate wave systems was also developed in order to estimate parameters with respect to each wave systems. For uni-modal spectra, parametric models of the observed performances of the devices could be devised. The frequency spreading and its interaction with the energy period proved to be as important as the energy period itself, which suggests that the frequency spreading should be used for energy production prediction. For bi-modal spectra, evidence of the duck sensitivity to directionality was found while the OWCs were not affected.

Transient stability studies are primarily concerned with the generator response of ac power systems and use only steady state type equations to model HVdc converter terminals. These equations are adequate for small disturbances at the converter terminals but cannot accurately represent a converters behaviour during, and through its recovery of, a significant transient disturbance. A detailed three phase electromagnetic analysis is necessary to describe the converters correct behaviour. This thesis describes an accurate and effective hybrid method combining these two types of studies, for analyzing dynamically fast devices such as HVdc converters within ac power systems. Firstly, conventional techniques are reviewed for both a transient stability analysis of power systems and for an electromagnetic transient analysis of HVdc converters. This review deals in particular with the two programs that constitute the hybrid developed in this thesis. Various techniques are then examined to efficiently and accurately pass the dynamic effects of an HVdc link to an ac system stability study, and the dynamic effects of an ac system to a detailed HVdc link study. An optimal solution is derived to maximise the inherent advantages of a hybrid. Finally, the hybrid is applied to a test system and its effectiveness in performing its task is shown.

Switching device power losses place critical limits on the design and performance of high-frequency integrated DC-DC converters. Especially, the layout of metal interconnects in lateral power MOSFETs has a profound effect on their on-resistances and conduction power losses. This thesis presents an analytical interconnect modeling and layout optimization technique for large-area power MOSFETs. The layout optimization of 24V LDMOS transistors in the area of 1 mm2 has achieved an improvement of 55 % in its on-resistance. The simulation result has been verified by experimental measurements on a test chip fabricated in TSMC 0.25 µm HV CMOS technology. In addition, this thesis presents an optimized output stage design methodology for the implementation of a 4 MHz, 12V to 1V integrated DC-DC converter. A segmented output stage scheme is employed to increase the converter efficiency at light load conditions. The peak efficiency of 84% was achieved at load current of 2 A.

Switching device power losses place critical limits on the design and performance of high-frequency integrated DC-DC converters. Especially, the layout of metal interconnects in lateral power MOSFETs has a profound effect on their on-resistances and conduction power losses. This thesis presents an analytical interconnect modeling and layout optimization technique for large-area power MOSFETs. The layout optimization of 24V LDMOS transistors in the area of 1 mm2 has achieved an improvement of 55 % in its on-resistance. The simulation result has been verified by experimental measurements on a test chip fabricated in TSMC 0.25 µm HV CMOS technology. In addition, this thesis presents an optimized output stage design methodology for the implementation of a 4 MHz, 12V to 1V integrated DC-DC converter. A segmented output stage scheme is employed to increase the converter efficiency at light load conditions. The peak efficiency of 84% was achieved at load current of 2 A.

An Electrolyser is a part of a renewable energy system (RES) and generates hydrogen from water electrolysis that is used in fuel cells. A dc-to-dc converter is required to couple the Electrolyser to the system DC bus. This thesis presents an extensive comparison of three soft-switched high-frequency transformer isolated dc-to-dc converters for this application. It is shown that LCL-type series resonant converter (SRC) with capacitive output filter is suitable for this application. Due to the wide variation in input voltage and load current, no converter can maintain zero-voltage switching (ZVS) for the complete operating range. To overcome this problem, two new converter configurations are proposed. Proposed Configuration 1 is a two-stage boost-LCL SRC with capacitive output filter and Proposed Configuration 2 is a transient-boost dual half-bridge LCL SRC with capacitive output filter. Operating principle, design, simulation and experimental results of the newly proposed converters are also presented.

This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Diode bridge rectifiers are considered for rectification to avoid the complex linear generator control at the input side. To reduce the size and the cost of energy storage elements, DC voltage regulation is done using a DC/DC converter. To achieve smooth and high power, many WECs need to be connected to a common DC link. A neutral point clamped inverter is considered for the DC/AC conversion due to its advantages over conventional topologies. Various pulse width modulation schemes are tested for the inverter to choose the optimum PWM method. The harmonics in the inverter output voltage is derived numerically and compared with simulation and experiment to understand the effect of dead-time in the inverter operation. Depending on the load current drawn from the inverter, the voltages in the two input capacitors of a three-level neutral point clamped inverter deviates from equilibrium unless the neutral point is grounded. To avoid this voltage imbalance as well as to regulate the DC link voltage a dual output boost converter with pulse delay control is proposed. The modeling, simulation and experiments show an improvement in the compensation voltage using pulse delay control compared to the previously proposed methods in the literature. The synchronous current control and the grid connection of the three-level converter have been accomplished in the laboratory.  Finally, the three-level power converter system has been tested with a linear permanent magnet generator at Lysekil to analyze the controller requirements.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaf 41). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 105-106). Also available on the World Wide Web.