An Adaptive Single Neural Control for Variable Step-Size P&O MPPT of Marine Current Turbine System

Marine current energy has been increasingly used because of its predictable higher power potential.Owing to the external disturbances of various flow velocity and the high nonlinear effects on the marine current turbine(MCT)system,the nonlinear controllers which rely on precise mathematical models show poor performance under a high level of parameters’uncertainties.This paper proposes an adaptive single neural control(ASNC)strategy for variable step-size perturb and observe(P&O)maximum power point tracking(MPPT)control.Firstly,to automatically update the neuron weights of SNC for the nonlinear systems,an adaptive mechanism is proposed to adaptively adjust the weighting and learning coefficients.Secondly,aiming to generate the exact reference speed for ASNC to extract the maximum power,a variable step-size law based on speed increment is designed to strike a balance between tracking speed and accuracy of P&O MPPT.The robust stability of the MCT control system is guaranteed by the Lyapunov theorem.Comparative simulation results show that this strategy has favorable adaptive performance under variable velocity conditions,and the MCT system operates at maximum power point steadily.

Performance Analysis of the Effects of Microgrooved Surface on A Marine Current Turbine with Underwater Mooring Platform

Marine current turbine(MCT),which is designed for the power supply of underwater mooring platform(UMP),is investigated in this article.To reduce its flow noise,the microgrooved surface is applied at the suction surface of the turbine blades.Comprehensive analyses of the effects of the UMP on MCT with microgrooved surface in different working conditions are presented.The transient turbulent flow field is obtained by incompressible large eddy simulation(LES),and then the Ffowcs Williams and Hawkings(FW-H)acoustic analogy is adopted to forecast the flow noise generated from the pressure fluctuations and loadings of the UMP shell and MCT blade surfaces.The numerical methods are first validated with experimental data and good agreements are obtained.Then,the influence of several key parameters on the performance of the MCT is then systematically studied,including interval distance,angle of pitch and angle of sideslip.For each case,the hydrodynamic parameters(thrust coefficient,torque coefficient and power coefficient),the vortical structures behind the model and the overall sound pressure level(OASPL)directionality are analyzed.Additionally,the noise reduction effect of the microgrooved surface is also presented.The present investigation could provide an overall understanding for the performance of MCT combined with UMP.

Optimal Feedback Control of Nonlinear Variable-Speed Marine Current Turbine Using a Two-Mass Model

This paper presents a contribution related to the control of nonlinear variable-speed marine current turbine(MCT)without pitch operating below the rated marine current speed.Given that the operation of the MCT can be divided into several operating zones on the basis of the marine current speed,the system control objectives are different for each zone.To deal with this issue,we develop a new control approach based on a linear quadratic regulator with variable generator torque.Our proposed approach enables the optimization of the rotational speed of the turbine,which maximizes the power extracted by the MCT and minimizes the transient loads on the drivetrain.The novelty of our study is the use of a real profile of marine current speed from the northern coasts of Morocco.The simulation results obtained using MATLAB Simulink indicate the effectiveness and robustness of the proposed control approach on the electrical and mechanical parameters with the variations of marine current speed.

Marine Current Turbine Simulator Development Based on Hardware in the Loop Simulation Concept

This paper is a contribution to the development of real time simulators for energy conversion research with respects to the ＂hardware in the loop simulation＂ concept. The focus is on the study of marine current kinetics energy conversion from into electrical energy using a marine current turbine simulator, developed in three stages. In the first stage the marine current turbine is emulated with the help of an induction drive who reproduces at its shaft the characteristics of a real turbine. It is connected with a load break used to force the emulator to respect on its shaft the characteristics of the real turbine. In the second stage, the induction drive is connected on the shaft with a doubly feed induction generator, for the study of energy conversion. The emulator respects the working regime, developed in the previous step, of a real turbine due to the control of the drive. In the third stage the induction machine emulating the turbine is interconnected with the generator and the load break. This assembly is used for the dynamic study of the marine current turbine. The break is used to create extra loads on the shaft and a variable inertial moment.

Multi-point design optimization of hydrofoil for marine current turbine

The comprehensive performance of the marine current turbine is an important issue in the ocean energy development. Its key is the performance of the hydrofoil, which is used to form the turbine blade. A multi-point optimization method of the hydrofoil is proposed in this paper. In this method, the Bezier curve is used to parameterize the hydrofoil. The geometrical parameters are used as variables while the lift-drag ratio and the cavitation performance of the hydrofoil are used as the objective functions. The NSGA-II algorithm is chosen as the optimization algorithm. In order to resolve the difficulty of this high-dimensional multi-objective optimi- zation problem, the conception of the distance metric in the metric space is introduced to unify the lift-drag ratio and the cavitation performance under different working conditions. And then, the above optimization method is applied in the NACA63-815 hydro- foil＇s optimal design under three typical conditions. Finally, the results from the performance comparison of the original and optimi- zed hydrofoils obtained by using the CFD simulation are analyzed in detail. It is indicated that the optimized hydrofoils enjoy a better hydrodynamic performance than the original ones under the three conditions. The feasibility and the theoretical validity of this optimization method are confirmed by the results.

A new biomimicry marine current turbine: Study of hydrodynamic performance and wake using software OpenFOAM

Inspired by Dryobalanops aromatica seed, a new biomimicry marine current turbine is proposed. Hydrodynamic performance and wake properties are two key factors determining whether a new marine current turbine design is practical or not. Thus, a study of hydrodynamic performance and wake of the proposed biomimicry turbine is conducted. The computational fluid dynamics（CFD） software, Open FOAM is used to generate the required results for the mentioned study. The hydrodynamic performance and wake properties of the proposed biomimicry turbine is compared to two conventional turbines of Bahaj et al. and Pinon et al. respectively. The simulation results showed that the proposed biomimicry marine current turbine gives optimum power output with its power coefficient, 0.376 PC ≈ at the tip speed ratio（TSR） of 1.5. Under the same boundary conditions, the maximum torque produced by the proposed biomimicry turbine at zero rotational speed is 38.71 Nm which is 1110% greater than the torque generated by the turbine of Bahaj et al.. The recovery distance for the wake of the biomimicry turbine is predicted to be 10.6% shorter than that of IFREMER-LOMC turbine. The above-mentioned results confirm the potential application of the proposed biomimicry marine current turbine in the renewable energy industry.

Numerical investigation of the power generation of a ducted composite material marine current turbine

In the hostile and highly corrosive marine environment,advanced composite materials can be used in marine current turbines due to their high strength-to-weight ratios and excellent resistance to corrosion.A composite material marine current turbine(CMMCT),which has significant advantages over traditional designs,has been developed and investigated numerically.A substantial improvement in turbine performance is achieved by placement of a duct to concentrate the energy.Computational fluid dynamics(CFD) results show that the extracted power of a ducted CMMCT can be three to four times the power extracted by a bare turbine of the same turbine area.The results provide an insight into the hydrodynamic design and operation of a CMMCT used to shorten the design period and improve technical performance.

Numerical Investigation of Flow Motion and Performance of A Horizontal Axis Tidal Turbine Subjected to A Steady Current

Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k-ε model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.