Abstract-The potential of electric power generation from marine tidal currents is enormous. Tidal currents are being recognized as a resource to be exploited for the sustainable generation of electrical power. The high load factors resulting from the fluid properties and the predictable resource characteristics make marine currents particularly attractive for power generation and advantageous when compared to other renewable energies. Moreover, international treaties related to climate control have triggered resurgence in development of renewable ocean energy technology. Therefore, several demonstration projects in tidal power are scheduled to capture the tidal generated coastal currents. Regarding this emerging and promising area of research, this paper reviews marine tidal power fundamental concepts and main projects around the world. It also report issues regarding electrical generator topologies associated to tidal turbines. Moreover, attempts are made to highlight future issues so as to index some emerging technologies mainly according to relevant works that have been carried out on wind turbines and on ship propellers.Index Terms-Tidal current, marine technology, electric power generation, energy converter systems, state of the art.

Abstract-This paper deals with the development of a Matlab-Simulink model of a marine current turbine system through the modeling of the resource and the rotor. The simulation model has two purposes: performances and dynamic loads evaluation in different operating conditions and control system development for turbine operation based on pitch and speed control. In this case, it is necessary to find a compromise between the simulation model accuracy and the control-loop computational speed. The blade element momentum (BEM) approach is then used for the turbine modeling. As the developed simulation model is intended to be used as a sizing and site evaluation tool for current turbine installations, it has been applied to evaluate the extractable power from the Raz de Sein (Brittany, France). Indeed, tidal current data from the Raz de Sein are used to run the simulation model over various flow regimes and yield the power capture with time.

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This paper deals with the speed control of a variable speed DFIG-based marine current turbine. Indeed, to increase the generated power and therefore the efficiency of a marine current turbine, a nonlinear controller has been proposed. DFIG has been already considered for similar applications particularly wind turbine systems using mainly PI controllers. However, such kinds of controllers do not adequately handle some of tidal resource characteristics such as turbulence and swell effects. Indeed, these may decrease marine current turbine performances. Moreover, DFIG parameter variations should be accounted for. Therefore, a robust nonlinear control strategy, namely high-order sliding mode control, is proposed. This control strategy relies on the resource and the marine turbine models that were validated by experimental data. The sensitivity of the proposed control strategy is analyzed regarding the swell effect as it is considered as the most disturbing one for the resource model. Tidal current data from the Raz de Sein (Brittany, France) are used to run simulations of a 7.5-kW prototype over various flow regimes. Simulation results are presented and fully analyzed. Index Terms-Marine current turbine (MCT), doubly-fed induction generator (DFIG), modeling, nonlinear control, highorder sliding mode. NOMENCLATURE DFIG = Doubly-Fed Induction Generator; MCT = Marine Current Turbine; ρ = Fluid density; A = Cross-sectional area of the marine turbine; V tide = Fluid speed; C p = Power coefficient; C = Tide coefficient; V st (V nt ) = Spring (neap) tide current speed; s, (r) = Stator (rotor) index; d, q = Synchronous reference frame index; V (I) = Voltage (Current); P (Q) = Active (Reactive) power; φ = Flux; T em (T m ) = Electromagnetic torque (Mechanical torque); R = Resistance L (M) = Inductance (Mutual inductance); θ r = Rotor position; This work is supported by Brest Métropole Océane (BMO) and the European Social Fund (ESF). It is also supported by the GDR SEEDS CNRS N°2994 under the Internal Project HYDROLE. It is done within the framework of the Marine Renewable Energy Commission of the Brittany Maritime Cluster (Pôle Mer Bretagne).ω r (ω s ) = Angular speed (Synchronous speed); f = Viscosity coefficient; J = Rotor Inertia; p = Pole pair number.

International audienceThis paper deals with the speed control of a variable speed doubly-fed induction generator (DFIG)-based marine current turbine (MCT). To increase the generated power and therefore the efficiency of an MCT, a nonlinear controller has been proposed. DFIG has been already considered for similar applications, particularly wind turbine systems using mainly proportional-integral (PI) controllers. However, such kinds of controllers do not adequately handle some tidal resource characteristics such as turbulence and swell effects. These may decrease MCT performances. Moreover, DFIG parameter variations should be accounted for. Therefore, a robust nonlinear control strategy, namely high-order sliding mode (HOSM) control, is proposed. This control strategy relies on the resource and the marine turbine models that were validated by experimental data. The sensitivity of the proposed control strategy is analyzed regarding the swell effect as it is considered as the most disturbing one for the resource model. Tidal current data from the Raz de Sein (Brittany, France) are used to run simulations of a 7.5-kW prototype over various flow regimes. Simulation results are presented and fully analyzed