5MW離岸浮動半潛式風力發電機整合雙饋式感應發電機與併網之全機組運轉分析及控制之研究

Abstract

本篇研究旨在發展半潛式之浮動式離岸型風力發電機全機組運轉模擬分析及控制，整合空氣動力、波浪力、風機機組動態、半潛式載台動態、錨碇系統動態、風機子系統及控制系統等，進行全機組建模及動態模擬分析。本論文以軟體FAST結合軟體WAMIT以及軟體MATLAB/SIMULINK建立5MW風機、OC4半潛式載台及錨碇系統進行全機組動態模擬與分析。首先於FAST建立風力發電機之運動模型，包含半潛式載台、錨碇系統、塔架、葉片及機艙模型等，並進行葉片氣動力分析(Aerodynamic Analysis)，再輸入由WAMIT預先計算的浮台水動力係數來進行水動力分析(Hydrodynamic Analysis)，以及在MATLAB/SIMULINK建立風機之子系統，包含：雙饋式感應發電機控制系統、併網側控制系統、變旋角控制系統(pitch angle)及變轉速控制系統等閉迴路控制系統。整合風機之運轉控制策略與控制理論，使風機能在額定風速下執行變轉速控制，控制風機轉速再不超過額定轉速為前提下追蹤最佳尖速比，擷取所能擷取的最大風能。在額定風速上同時執行變轉速控制與葉片變旋角控制，使風機能保持轉速於額定轉速，並調節發電功率維持於額定功率5MW。最後探討浮動式風機載台之移動性(Mobility)對發電功率之影響，在低於額定風速區，發電功率振盪與正向相對風速呈現正相關，在高於額定風速區，葉片變旋角系統之啟動將使風機塔頂受力改變，進而影響輸出功率呈現二次過衝之現象，本研究對此提出主動式平衡系統做為改善策略。

The objective of this study is to develop the co-simulation analysis of aerodynamics, wave force, mechanism dynamics and control system dynamics for the semi-submersible floating wind turbine. This paper investigates the dynamic simulation and analysis for the OC4-DeepCwind semi-submersible floating wind turbine by combining the software of FAST, WAMIT and MATLAB/SIMULINK. FAST serves to build the motion models of floating foundation, mooring system, tower, blades and nacelle of the wind turbine, and the aerodynamic analysis of blade. WAMIT executes the hydrodynamic analysis of floating foundation. MATLAB/SIMULINK is used to establish the subsystem dynamic models for analysis and design of wind turbines. The subsystems comprise the closed-loop control systems of the doubly-fed induction generator, the grid side control, the variable-pitch control system and the variable-speed control system. By integrating the operation control strategy, we can realize the maximum power output while the wind speed is above cut-in speed and under the rated wind speed through the generator-side control for tracking the desired rotor rotational speed calculated according to the optimal tip-speed ratio. To avoid damage, the rotor rotational speed is limited to avoid exceeding the rated rotational speed. While the wind speed is above the rated wind speed, the hydraulic pitch control system starts to adjust the pitch angle of the blades to maintain the rated output power. The variable-pitch control and the variable-speed control of the semi-submersible offshore wind turbine can be achieved under different wind conditions. Finally, the impact of the floating turbine mobility on the power output is discussed. While the wind speed is under the rated wind speed, the power oscillation is positively related to the perpendicular relative wind speed. While the wind speed is above the rated wind speed, the hydraulic pitch control system starts to adjust the pitch angle of the blades and changes the force and moment of the tower top. The power output is affected and exhibit the phenomenon of secondary power overshoot. The study proposes the active floating foundation balance control system to improve the impact of floating wind turbine mobility on power output.