| Marine current energy, as a kind of ocean energy, has made significant technical progress in the past decades. Various novel devices are developed to collect marine current energy by researchers, among which the horizontal axis marine current turbine (HAMCT) is regarded as the most technical, competitive, and the commercial one and some demonstration and commercialized turbines have been operating at home and abroad nowadays. The HAMCT works in the sea water as well as the complex ocean environment, and is required that the HAMCT can operate more than 20 years, so this is a challenge of load calculation and analysis for the generator and on the basis of load calculation for the generator components design.Based on the analysis of the HAMCT load conditions under the effect of current, and in the same time focused on researching the load characteristics under special operating modes, such as ocean wave and current flow shear. The table of design load cases are formulated and load analysis of the HAMCT has been carried out of all load cased. After load analysis, the independent variable pitch control method based on Fuzzy PID controller to reduce the asymmetric loads of the turbine rotor. The method of theoretical model analysis, FEM simulation analysis, computer simulation analysis and experimental study will be adopted. The main content of this paper is as follows:(1) Using the blade element moment (BEM) theory to analyse the power capture principle of the HAMCT by both in macro-perspective and micro-perspective, the calculation method of axial and tangential inducing factor is given to calculate the local loads and overall laods of the turbine. The load analysis models are built by the BEM method and CFD method respectively, the results show that the calculated results of BEM method is less than that of the CFD method due to the neglect of three dimension flow effect. So this paper improves the BEM method by the correction chord and the lift and drag coefficient of the blade foil in three-dimensional flow field, the improved BEM method is verified by simulation.(2) In order to use the load caculation method easier in the standardization and the industrialization of the HAMCT, a design software based on the above load calculation method is developed. It can be used in the design and strength check of the components of the turbine, such as the rotor blade, hub, low-speed shaft, gear box and so on. A 60 kW HAMCT is developed using the software, and by the towing tests in factory and field tests in ocean environment of a long time, the design method is verified.(3) The table of design load cases is formulated, and the marine current velocity models considering current turbulence, ocean wave, current shear and yaw error are built. Through the method of rain cycly count, the influence of these factors to the fatigue loads are analyzed. The results show that all these factors will increase the fatigue loads of the turbine, but the influence of the ocean wave is unconspicuous unless the frequency and wave height is very large. But the influence of the current turbulence, current shear and yaw error must be taken into consideration. According to the load case table, load calculation and analysis under all the load cases are carried out on the prototype of a 120kW turbine.(4) Aiming at the nonlinearity an the incomprehensibility of the HAMCT model, control strategy based on Fuzzy PID is adopted to reduce the asymmetrical loads caused by the asymmetrical current profile through individual pitch control (IPC) system. The decoupling between the tilt moment and yaw moment of the turbine rotor is realized by Coleman coordinate transformation. The turbie is modeled in Matlab/Simulink to verify the control system, the results show that, the adopted IPC strategy can reduce the asymmetrical loads of the turbine rotor effectively. (5) Aiming at the predictability of ocean current characteristics derived from the ocean tide,blade pitch control strategy based on current velocity preview is adopted to avoid the continuous pitch action. The simulation model is built in Matlab/Simulink, the results show that, the blade pitch control strategy based current velocity preview can convert the continuous pitch action to intermittent pitch action without reduction of the generated power. The accumulated blade pitch angle of a tide cycle is decreased remarkably though the stability of the generated power is sacrificed a little. Thus the wear of the sealing structure at the blade root is reduced and the life of the sealing structure is extended. (6) Blade pitch system are often used in power control and load control of the HAMCT, as the hub space is little and pitch load is high for the HAMCT, the actuator based on pinion and rack and driving system based on hydraulic transmission is designed. The dynamics of the pitch system is researched both by simulation in AMESim and factory tests.(7) The major work of the study is summarized, and the conclusions and innovations are expounded. Besides, the future work is also lised at the end. |
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