The increasing penetration of renewable energy in the power system grid makes it one of the most important topics in electricity generation, now and into the future. Tidal current energy is one of the most rapidly growing technologies for generating electric energy. Within that frame, tidal current energy is surging to the fore. Forecasting is the first step in dealing with future generations of the tidal current power systems. The doubly-fed induction generator (DFIG) and the direct drive permanent magnet synchronous generator (DDPMSG) are the most commonly used generators associated with tidal current turbines. The aim of the present work is to propose a forecasting technique for tidal current speed and direction and to develop dedicated control strategies for the most commonly used generators, enabling the turbines to act as an active component in the power system. This thesis is divided into two parts. The first part proposes a hybrid model of an artificial neural network (ANN) and a Fourier series model based on the least squares method (FLSM) for monthly forecasting of tidal current speed magnitude and direction. The proposed hybrid model is highly accurate and outperforms both the ANN and the FLSM alone. The model is validated and shown to perform better than other models currently in use. This study was done using data collected from the Bay of Fundy, Nova Scotia, Canada, in 2008. The second part of the thesis describes the overall dynamic models of the tidal current turbine driving either a DFIG or a DDPMSG connected to a single machine infinite bus system, including controllers used to improve system stability. Two models are tested and validated, and two proportional integral (PI) controllers are proposed for each machine to control the output power of the tidal current turbine. The controllers are tested using a small signal stability analysis method for the models, and prove the robustness of the tidal current turbine using two different types of generators over those without controllers. The controller gain ranges are also investigated to establish zones of stability. Overall results show the advantages of using a DDPMSG over a DFIG.

Channel constrictions in which strong currents are mainly driven by tidal processes represent sites with high potential for harvesting renewable and predictable tidal stream energy. Tidal Current Turbines (TCTs) deployed in arrays appear to be the most promising solution to efficiently capturing this carbon neutral energy resource. However to ensure the sustainable character of such projects, the balance between power extraction maximization and environmental impact minimization must be found so that device layout optimization takes into account environmental considerations. This is particularly appropriate since both resource and impact assessments go intrinsically hand in hand. The present method proposes the use and adaptation of ocean circulation models as an assessment tool framework for tidal current turbine (TCT) array-layout optimization. By adapting both momentum and turbulence transport equations of an existing model, the present TCT representation method is proposed to extend the actuator disc concept to 3-D large scale ocean circulation models. Through the reproduction of physical experiments to reasonable accuracy, grid and time dependency tests and an up-scaling exercise, this method has shown its numerical validity as well as its ability to simulate accurately both momentum and turbulent turbine-induced perturbations in the wake. These capabilities are demonstrated for standalone devices and device arrays, and are achieved with a relatively short period of computation time. Consequently the present TCT representation method is a very promising basis for the development of a TCT array layout optimization tool. By applying this TCT representation method to realistic cases, its capability is demonstrated for power capture assessment and prediction of hydrodynamic interactions as would be required during the layout deployment optimization process. Tidal energy has seen considerable development over the last decade and the first commercial deployments are likely to take place within the next 5 years. It is hoped that this new tool and the numerical approaches described herein will contribute to the development of TCT array power plants around the world.

Tidal currents can be used as a predictable source of sustainable energy, and have the potential to make a useful contribution to the energy needs of the UK and other countries with such a resource. One of the technologies which may be used to transform tidal power into mechanical power is a vertical axis turbine, the hydrodynamic analysis of which this thesis is concerned with. The aim of this analysis is to gain a better understanding of the power transformation process, from which position there is the possibility of improving the conversion efficiency. A second aim is to compare the results from different modelling approaches. Two types of mathematical modelling are used: a basic blade element momentum model and a more complex Reynolds-averaged Navier Stokes (RANS) model. The former model has been programmed in Matlab by the present author while the latter model uses a commercial computational fluid dynamics (CFD) code, ANSYS CFX. This RANS model uses the SST k-! turbulence model. The CFD analysis of hydrofoils (equally airfoils), for both fixed and oscillating pitch conditions, is a significant proportion of the present work. Such analysis is used as part of the verification and validation of the CFD model of the turbine. It is also used as input to the blade element momentum model, thereby permitting a novel comparison between the blade element momentum model and the CFD model of the turbine. Both types of turbine model were used to explore the variation in turbine efficiency (and other factors) with tip speed ratio and with and without an angle of attack limiting variable pitch strategy. It is shown that the use of such a variable pitch strategy both increases the peak efficiency and broadens the peak. The comparison of the results from the two different turbine modelling approaches shows that when the present CFD hydrofoil results are used as input to the blade element model, and when dynamic effects are small and the turbine induction factor is low, there is generally good agreement between the two models.

A tidal current turbine is a device functioning in a manner similar to wind turbine for harnessing energy from tidal currents, a group of which is called a farm. The existing approaches used to predict power from tidal current turbine farms oversimplify the hydrodynamic interactions between turbines, which significantly affects the results. The major focus of this dissertation is to study the relationship between turbine distribution (the relative position of the turbines) and the hydrodynamic interactions between turbines, and its impact on the power from a farm. A new formulation of the discrete vortex method (DVM-UBC) is proposed to describe the behavior of turbines and unsteady flow mathematically, and a numerical model is developed to predict the performance, the unsteady wake and acoustic emission of a stand-alone turbine using DVM-UBC. Good agreement is obtained between the results obtained with DVM-UBC and published numerical and experimental results. Then, another numerical model is developed to predict the performance, wake and acoustic emission of a two-turbine system using DVM-UBC. The results show that the power of a two-turbine system with optimal relative position is about 25% more than two times that of a stand-alone turbine under the same conditions. The torque such a system may fluctuate 50% less than that of a stand-alone turbine. The acoustic emission of such a system may be 35% less than that of a stand-alone turbine. As an extension, a numerical procedure is developed to estimate the efficiency of an N-turbine system by using a linear theory together with the two-turbine system model. By integrating above hydrodynamic models for predicting power and a newly-developed Operation and Maintenance (O&M) model for predicting the cost, a system model is framed to estimate the energy cost using a scenario-based cost-effectiveness analysis. This model can estimate the energy cost more accurately than the previous models because it breaks down turbine’s components and O&M strategies in much greater detail when studying the hydrodynamics and reliability of the turbine. This dissertation provides a design tool for farm planners, and shed light on other disciplines such as environmental sciences and oceanography.

A tidal current turbine is a device functioning in a manner similar to wind turbine for harnessing energy from tidal currents, a group of which is called a farm. The existing approaches used to predict power from tidal current turbine farms oversimplify the hydrodynamic interactions between turbines, which significantly affects the results. The major focus of this dissertation is to study the relationship between turbine distribution (the relative position of the turbines) and the hydrodynamic interactions between turbines, and its impact on the power from a farm. A new formulation of the discrete vortex method (DVM-UBC) is proposed to describe the behavior of turbines and unsteady flow mathematically, and a numerical model is developed to predict the performance, the unsteady wake and acoustic emission of a stand-alone turbine using DVM-UBC. Good agreement is obtained between the results obtained with DVM-UBC and published numerical and experimental results. Then, another numerical model is developed to predict the performance, wake and acoustic emission of a two-turbine system using DVM-UBC. The results show that the power of a two-turbine system with optimal relative position is about 25% more than two times that of a stand-alone turbine under the same conditions. The torque such a system may fluctuate 50% less than that of a stand-alone turbine. The acoustic emission of such a system may be 35% less than that of a stand-alone turbine. As an extension, a numerical procedure is developed to estimate the efficiency of an N-turbine system by using a linear theory together with the two-turbine system model. By integrating above hydrodynamic models for predicting power and a newly-developed Operation and Maintenance (O&M) model for predicting the cost, a system model is framed to estimate the energy cost using a scenario-based cost-effectiveness analysis. This model can estimate the energy cost more accurately than the previous models because it breaks down turbine’s components and O&M strategies in much greater detail when studying the hydrodynamics and reliability of the turbine. This dissertation provides a design tool for farm planners, and shed light on other disciplines such as environmental sciences and oceanography.

A tidal current turbine is a device functioning in a manner similar to wind turbine for harnessing energy from tidal currents, a group of which is called a farm. The existing approaches used to predict power from tidal current turbine farms oversimplify the hydrodynamic interactions between turbines, which significantly affects the results. The major focus of this dissertation is to study the relationship between turbine distribution (the relative position of the turbines) and the hydrodynamic interactions between turbines, and its impact on the power from a farm. A new formulation of the discrete vortex method (DVM-UBC) is proposed to describe the behavior of turbines and unsteady flow mathematically, and a numerical model is developed to predict the performance, the unsteady wake and acoustic emission of a stand-alone turbine using DVM-UBC. Good agreement is obtained between the results obtained with DVM-UBC and published numerical and experimental results. Then, another numerical model is developed to predict the performance, wake and acoustic emission of a two-turbine system using DVM-UBC. The results show that the power of a two-turbine system with optimal relative position is about 25% more than two times that of a stand-alone turbine under the same conditions. The torque such a system may fluctuate 50% less than that of a stand-alone turbine. The acoustic emission of such a system may be 35% less than that of a stand-alone turbine. As an extension, a numerical procedure is developed to estimate the efficiency of an N-turbine system by using a linear theory together with the two-turbine system model. By integrating above hydrodynamic models for predicting power and a newly-developed Operation and Maintenance (O&M) model for predicting the cost, a system model is framed to estimate the energy cost using a scenario-based cost-effectiveness analysis. This model can estimate the energy cost more accurately than the previous models because it breaks down turbine’s components and O&M strategies in much greater detail when studying the hydrodynamics and reliability of the turbine. This dissertation provides a design tool for farm planners, and shed light on other disciplines such as environmental sciences and oceanography. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate