Development of a Layer-Type Vertical-Axis Wind Power System(I)
|關鍵字:||垂直式風機;複合材料;有限元素;葉片;Composite materials;finite element method;wind turbine;wind power|
風力發電為一主要的再生能源，它將大自然的風速動能轉換成電能，不需要石化燃料的能量轉換，成本低廉,亦不會產生二氧化碳與其他廢氣等公害, 為一潔淨能源。風力發電可分為垂直軸式與水平軸式两種, 目前大型風機多為水平式, 但中小型則傾向採用垂直軸式, 因為垂直軸式風力發電具有設計方法先進、風能利用率高、起動風速低、基本不易產生氣動噪音等優點，具有廣泛市場應用的前景，因此垂直軸式風力發電機將越受重視。在實際環境中風向是經常變化的，水平軸式風機的迎風面不可能始終對著風，容易引起“對風損失＂ 即無法充份吸取風能的缺點，而垂直式風機則不容易存在這個問題。另一方面,垂直軸式風機的葉片在旋轉過程中的受力情況要比水平軸式的好，由於慣性力與重力的方向始終不變，所受的是恆定載荷，因此疲勞壽命要比水平軸式風機長。同時，垂直式風機可以放在風機的下部或是地面，便於安裝和維護。雖然垂直軸式風機有上述的優點, 但目前的設計方式存在着不少缺點, 以致其發電效率不彰, 影响其經濟價值。一般阻力型(Savonius)垂直軸式風機在低風速時便可啓動發電, 但只能在慢轉速下發電, 風速變高後發電效率便會變差。若改為升力型(Darrieus) 者, 則只適合在高風速下發電, 低風速時發電效率不佳。將两者合在一起來發電, 則可能會有慣性牽累及擋風的問題發生, 影响發電效果。本研究將提出一新的設計理念, 以排除目前垂直軸式風機的缺點。本計畫所研發的垂直式風機系統包括一多層圓盤式吸能機構、發電機、電控系統(含市電併網) 和蓄電元件等。第一年先以一1kW的新型垂直軸式層狀型風機系統作為模擬對象, 分別研究葉輪的空氣動力特性及流場形態、複合材料葉輪的結構設計及壽命評估、複合材料葉輪的成型方法及模具設計、永磁式發電機的發電特性及可靠度、電力的最佳管控方法、儲電系统的建立、轉動機構的行為、系统的整合技術、元件及結構的測試方法與允收標準、系统的試騐方法及效率與可靠性評估等。第二年延續第一年的工作, 改善及提升第一年所建立之研究方法和技術, 並用於研製一實用型及具商品化潛力的5kW垂直軸式風機系统。本計畫將設計並製作發電系统的轉動機構, 然後整合子計畫或廠商提供之葉輪、發電機、電控系统及儲電元件以組裝整座風力發電系统, 進行風機系统運轉的功能、穩定性及可靠度試騐, 分析測試結果, 識別影響風機效率及導致風機系统失效之重要因子, 並提出改善對策。本計畫之研究將作為將來研發中型風力機系统的奠基工作, 所開發之設計、製造、測試、保固等程序和技術都可提供給產業界作為將來生產小型或開發中型風力機系统的依據。|
Because wind energy is cheap, clean and easy to attain, it has thus become an important renewable energy source. Wind turbines can be classified into two main categories, namely, horizontal- and vertical-axis wind turbines [HAWT and VAWT]. Presently most of the big wind turbines are HAWT. But for wind turbines of mid to small sizes, VAWT has the potential to become the better choice. This is because VAWT may have many advantages such as wind direction independent, easy absorption of wind energy, low startup wind speed, low noise level etc. The current design of VAWT, however, cannot fully reveal the merits of such power system and thus lowers the competitiveness and hinders the applications of the system. For instance, Savonius which is one the most commonly used VAWT absorbs wind energy by using S shaped blades to directly resist wind pressure. It can start to turn and generate power at low wind speed. But at high wind speed, the rotational speed of the blades cannot build up as expected because high wind pressure to resist the rotation of the blades is also generated. Therefore, the efficiency of the power system becomes poor at high wind speed. Another popular type of VAWT is Darrieus. It uses vertical airfoil shaped wind blades to absorb energy. At high wind speed, it can have pretty good efficiency to generate power. But at low wind speed, it has difficulty to start rotation and thus has poor efficiency for power generation. The combination of Savonius and Darrieus produces a new type of VAWT. The shortcoming of this type of system is that its efficiency becomes poor at high wind speed because the Savonius part becomes a burden to the Darrieus parts and thus lower the rotational speed of the system. To circumvent the existing shortcomings of the current design of VAWT, a new design concept for fabricating a VAWT of high efficiency and reliability is proposed in this project. The proposed VAWT comprises a layer-type composite wind energy absorber which consists of a number of circular trays stacking up in the axial direction, a permanent magnet-type power generator, a frame to support the energy absorber and the generator, an electricity control and management system, and power storage system. The high stiffness and light weight of composite materials make the wind energy absorber have less mass moment of inertia for rotation and thus increase the efficiency of the power system. In the first year, a 1kW power system is used as a tool to establish the methods and technologies for power system design, structural design, mold design, rotational mechanism design, power generation design, electricity control and management system design, components testing, system integration and assembling, system reliability testing and life assessment. In the second year, the methods and technologies developed in the first year are improved and applied to fabricate a 5kW power system of high efficiency and reliability. In this project, the rotational mechanism of the power system is designed and the system integration technology of assembling the power system is developed. The power system is subjected to functional as well as reliability tests to verify the suitability of the design. The tests results are analyzed to identify the factors that can have significant effects on the efficiency, stability, and reliability of the power system. Appropriate actions are taken to improve the performance and enhance the reliability of the power system. The methods and technologies developed in this project will become the strong foundation for developing VAWT with higher power in the future. The technologies attained in this project will be transferred to the industry to produce small or develop medium VAWTs.
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