Wave-to-Wire Model of a Wave Energy Converter equipped with an All-Electric Power Take-Off

The purpose of the thesis is to develop a detailed wave-to-wire model of a point absorber wave energy converter (WEC) with grid connection. The software used is MATLAB-Simulink. An electrical machine driven by an ideal inverter has been chosen and subsequently the detailed wave-to-wire model of the point absorber WEC is tested. The final part of the project includes the grid connection of the detailed wave-to-wire mode

Performance Evaluation and Life Cycle Cost Analysis of the Electrical Generation Unit of a Wave Energy Converter

The main focus of this work is the performance and the economical assessment of a radialflux generator that is used in wave power applications. The wave energy converter (WEC) usedin this work is a point absorber, that is considered to move only in heave. The generation unitof the WEC consists of a permanent magnet machine and a power electronic converter.The straight and v-shaped interior mounted permanent magnet generators, surface mountedpermanent magnet generator and neodymium and ferrite assisted synchronous reluctance generatorsare selected as the main generator designs to be studied in this work. These designs areanalysed using finite element method (FEM) and the annual energy productions and losses arequantified. Furthermore, some design variations such as, different iron materials, stator slot geometriesand a SiC MOSFET based converter are investigated, in order to assess the impact ofa specific design variation on the energy efficiency. An economical evaluation of these variantsusing the life cycle cost (LCC) analysis is performed, in order to quantify the economical consequencesof the energy losses during the operational life time, as well as determining the costsof the initial generator investment. The results obtained suggest favorableWEC generator typesand design alterations for LCC improvements.An important finding is that the PM assisted SRM generator provides the best energy performance,given the same geometry and material limitations. The annual energy productionachieved by the SMPM generator is fairly similar to that of the IPM generator, despite not beingable to provide the required torque at high speed operations, since the high speed operationsoccur rarely. Moreover, it is found that the poor field weakening trajectory of the SMPM can beimproved by placing iron pieces at magnet sides. Another interesting result is that even thoughthe annual energy production is increased when the rotor material is replaced by a cobalt-iron,due to its high costs, this design was not found economically favorable. The design variationthat improves the electric generation system of theWEC to the highest degree is found to be theSiC MOSFET based converter design, rather than the IGBT variant. The annual energy lossesdecrease by 5 MWh, due to up to 3 times lower converter losses. Owing to the substantialenergy improvement, the SiC MOSFET case is the economically favorable choice compared tothe generation system that uses an IGBT converter, despite theMOSFET modules being 7 timesmore costly than its IGBT counterpart

Optimization and Energy Maximizing Control Systems for Wave Energy Converters

In recent years, we have been witnessing great interest and activity in the field of wave energy converters’ (WECs) development, striving for competitiveness and economic viability via increasing power conversion while decreasing costs and ensuring survivability [...

Optimal control of wave energy converters

Wave Energy Converters (WECs) are devices designed to absorb energy from ocean waves. The particular type of Wave Energy Converter (WEC) considered in this thesis is an oscillating body; energy conversion is carried out by means of a structure immersed in water which oscillates under forces exerted by waves. This thesis addresses the control of oscillating body WECs and the objective of the control system is to optimise the motion of the devices that maximises the energy absorption. In particular, this thesis presents the formulation of the optimal control problem for WECs in the framework of direct transcription methods, known as spectral and pseudospectral optimal control. Direct transcription methods transform continuous time optimal control problems into Non Linear Programming (NLP) problems, for which the literature (and the market) offer a large number of standard algorithms (and software packages). It is shown, in this thesis, that direct transcription gives the possibility of formulating complex control problems where realistic scenarios can be taken into account, such as physical limitations and nonlinearities in the behaviour of the devices. Additionally, by means of spectral and pseudospectral methods, it is possible to find an approximation of the optimal solution directly from sampled frequency and impulse response models of the radiation forces, obviating the need for finite order approximate models. By implementing a spectral method, convexity of the NLP problem, associated with the optimal control problem for a single body WEC described by a linear model, is demonstrated analytically. The solution to a nonlinear optimal control problem is approximated by means of pseudospectral optimal control. In the nonlinear case, simulation results show a significant difference in the optimal behaviour of the device, both in the motion and in the energy absorption, when the quadratic term describing the viscous forces are dominant, compared to the linear case. This thesis also considers the comparison of two control strategies for arrays of WECs. A Global Control strategy computes the optimal motion by taking into account the complete model of the array and it provides the global optimum for the absorbed energy. In contrast, an Independent Control strategy implements a control system on each device which is independent from all the other devices. The final part of the thesis illustrates an approach for the study of the effects of constraints on the total absorbed energy. The procedure allows the feasibility of the constrained energy maximisation problem to be studied, and it provides an intuitive framework for the design of WECs relating to the power take-off operating envelope, thanks to the geometrical interpretation of the functions describing both the total absorbed energy and the constraints

Optimization and Energy Maximizing Control Systems for Wave Energy Converters

The book, “Optimization and Energy Maximizing Control Systems for Wave Energy Converters”, presents eleven contributions on the latest scientific advancements of 2020-2021 in wave energy technology optimization and control, including holistic techno-economic optimization, inclusion of nonlinear effects, and real-time implementations of estimation and control algorithms