2kW風力發電機被動螺距控制之分析模擬與設計

Abstract

風力發電機大致可分為簡易型無控制設計風力機、局部控制風力機(具備電力控制功能但無機械控制功能)、被動控制風力機(具備電力控制功能及被動機械控制功能)、主動控制風力機(具備電力控制功能及主動機械控制功能)等四大類。小型風力機由於成本考量，大多採用沒有控制設計風力機或局部控制風力機，但兩者的發電性能表現上都有許多成長空間。故本文研究的目的即是改善由東元電機所提供2 kW局部控制風力機之固定螺距(pitch)在高風速條件下的性能表現，採用被動控制風力機之機構，並針對此機構進行參數設計靈敏度分析與研究，進而提高發電效能，其成本可透過大量生產的方式降低。 本研究之數值模擬分析主要是採用MATLAB/SimMechanics與NREL(National Renewable Energy Laboratory)之FAST (Fatigue, Aerodynamics, Structures, and Turbulence)所提供之Aerodynamics相輔使用。首先參考西班牙Windspot之被動螺距控制機構進行研究，再提出新型被動控制機構的概念進行分析，可得知利用離心力的原理，在高風速的情況下，風力發電機組將利用螺距控制以限制截風能量並協助使風力發電機轉速慢下，在部分荷載範圍，螺距控制允許葉片依據風速轉動到最佳角度，如此將可有效利用風能。 由結果可看出，經由被動螺距改良之東元電機2 kW風力機，Windspot機構所設計的彈簧常數6200 N/m、配重桿長度20公分，以及新型機構所設計的參數為彈簧常數9000 N/m、配重桿長度25公分，藉由適當之彈簧常數與配重桿長度互相搭配，同時達成在高風速下保護葉片的效果以及維持正常發電，在低風速也能維持正常的功率輸出，此結果有助於小型風力機的應用與發展。

Generally, wind turbines can be categorized into four types: the simplest one called no control, the one with local control containing electrical power control without functions of mechanical control, the one with passive control that has the power control and passive mechanical control, and the one with active control having the power control and active mechanical control. Most of the small wind turbines are designed with no control or local control due to cost effectiveness issues. Both of these two types, however, remain rooms for improvement in terms of performance. The purpose of the present study is to improve the performance of fixed-pitch TECO 2 kW wind turbine with additional passive pitch control mechanism along with parametric and sensitivity study. The cost of the proposed system can be reduced with standardization and mass production. Software packages MATLAB/SimMechanics combining with FAST (Fatigue, Aerodynamics, Structures, and Turbulence), developed by NREL (National Renewable Energy Laboratory), are used for investigation in the present study. Based on the concept from the Spain made wind turbine, Windspot, that the over-speed control with passive pitch mechanism can be achieved by utilizing the centrifugal force, we propose and design a new passive control mechanism and investigate the feasibility of adding the mechanism onto the fixed-pitch TECO 2kW wind turbine. Under high wind conditions, the pitch control mechanism reduces the rotation speed of the wind turbine and limits the capture of wind energy for the purpose of adjusting output power, achieving higher utilization efficiency of wind power and providing protection for rotor blades. Both the Windspot and the new-designed passive mechanism are modeled and parametrically studied. The optimal designs that give better performance are summarized and suggested as follows: (1) For the TECO 2kW wind turbine with Windspot passive control mechanism, the spring constant is 6200 N/m and weight stick length is 20 cm. (2) For the turbine with new design mechanism, the spring constant and stick length are 9000 N/m and 25 cm, respectively. It is shown that the cut-out wind speed can be extended with proper selection of the spring constant and stick length. As a results, the present study successfully demonstrate that the TECO 2 kW fixed-pitch wind turbine is improved by two types of passive pitch control mechanisms.