| The difference between front-end speed controlled wind turbine and traditional wind turbine lies in their transmission system. Firstly, wind energy can be absorbed by wind wheel, and then be changed through hydraulic mechanical transmission system of front-end speed controlled wind turbine into a stable electrical energy output with constant speed. However, the working principle of traditional wind turbine is different, and generators are driven firstly and then fit the grid connection by converter. Because the combination of hydraulic and mechanical transmission in new wind turbine can adjust wind speed to be stable in front of wind turbine, the inverter between the turbine and grid will be removed through this combine method. Therefore, without harmonic produced by converter, new generation of wind turbine can generate high quality of electrical energy and increase reliability of the system. Moreover, the method of hydraulic mechanical transmission as the primary speed control system applied in wind power transmission technology will be firstly presented, and hydraulic speed adjusting system is one of the key technologies needed.Based on the basic theories of front-end speed controlled wind turbine, this thesis expounds the structure of the turbine, illuminates the process of adjusting the output speed to maintain a constant in hydraulic transmission system, deduces the relationship between different parts in the turbine, and calculates the efficiency of hydraulic transmission system.Model of hydraulic transmission system of front-end speed controlled wind turbine will be built and analyzed in details. By researching on structure and working principle of the various parts of transmission system, speed and torque relationships and internal power change between them are derived speed ratio floor plans, power diagram, characteristic curves of hydraulic torque converter and hydraulic transmission system can be obtained by analyzing characteristics of speed planetary gear and hydraulic torque converter.Considering the nonlinearity of wind speed, two kinds of fuzzy controller are designed in this thesis. Coarse control and fine-tune control will be applied firstly according to the error of the double-mode parameter-adjustable fuzzy controller and automatic switching fuzzy control rules. Then weighting factors will be adjusted at real-time according to error level at different modes. Futhermore accurate control of hydraulic speed control system will be realized. Particle swarm optimization algorithm with faster convergence speed, strong robustness and can find optimal solutions of optimization objective function with high probability. Fuzzy controller based on particle swarm optimization can optimize quantization scale factor in fuzzy controller quickly and accurately. Finally, through simulation analysis, fuzzy controller based on either double-mode parameter-adjust or particle swarm optimization algorithm is better than conventional PID controller in control performance. |
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