System Integration of the Horizontal-Axis Wind Turbine: The Design of Turbine Blades with an Axial-Flux Permanent Magnet Generator

Chi-Jeng Bai, Wei-Cheng Wang, Po-Wei Chen, Wen-Tong Chong
2014 Energies  
In designing a horizontal-axis wind turbine (HAWT) blade, system integration between the blade design and the performance test of the generator is important. This study shows the aerodynamic design of a HAWT blade operating with an axial-flux permanent magnet (AFPM) generator. An experimental platform was built to measure the performance curves of the AFPM generator for the purpose of designing the turbine blade. An in-house simulation code was developed based on the blade element momentum
more » ... ement momentum (BEM) theory and was used to lay out the geometric shape of the turbine blade, including the pitch angle and chord length at each section. This simulation code was combined with the two-dimensional (2D) airfoil data for predicting the aerodynamic performance of the designed blades. In addition, wind tunnel experiments were performed to verify the simulation results for the various operating conditions. By varying the rotational speeds at four wind speeds, the experimental and simulation results for the mechanical torques and OPEN ACCESS Energies 2014, 7 7774 powers presented good agreement. The mechanical power of the system, which maximizes at the best operating region, provided significant information for designing the HAWT blade. Keywords: wind turbine; horizontal-axis wind turbine (HAWT); axial-flux permanent magnet (AFPM) generator; blade element momentum (BEM) theory; airfoil; wind tunnel experiment Introduction A small-scale horizontal-axis wind turbine (HAWT) system which provides less than 10 kW output is relatively simpler than large-scale ones in both design and construction because there is no gear box and pitch control system, but traditionally it has drawn little attention due to its low power capacity and economic concerns [1] [2] [3] . Nonetheless, to have an effective HAWT system, some practical problems still exist in the system integration of the force and moment/torque distributions between the turbine blades and the electric generators. Recently, studies on small-scale HAWT systems are focused on the developments in the fields of aerodynamics, mechanical/electrical engineering, control technology, and electronics. The optimal HAWT blade shape design and the performance analysis, characterized as parts of aerodynamics, are intensively analyzed using the blade element momentum (BEM) theory [4] [5] [6] [7] [8] [9] [10] . This models turbine blades as a set of isolated two-dimensional (2D) airfoils and then performs an integration to find the thrust and torque. Goundar and Ahmed [4] designed a 3-bladed horizontal-axis tidal current turbine (HATCT) blade with a 10 m diameter using the BEM theory. This theory is applied to predict the aerodynamic performance, resulting in the maximum efficiency of 47.6% at the rated wind speed of 2 m/s and tip speed ratio (TSR) of 4. Lanzafame and Messina [9] built a mathematical model through BEM theory to calculate the aerodynamic performance for the NREL Phase III turbine. The lift and drag coefficient curves of the wind turbine system were successfully characterized for the evaluation of the axial and angular induction factors. Dai et al. [10] has also predicted the aerodynamic loads for the MW scale HAWT blade using the BEM theory. This model was modified by Prandtl and Buhl based on the B-L semi-empirical dynamic stall (DS) model, developed for calculating the NACA63-4xx airfoil. The DS model is currently appropriate for engineering applications. Hirahara et al. [11] and Koki et al. [12] have proposed a method for experimentally determining the mechanical torque generated from the turbine blade using a torque transducer installed between the turbine blade and the electric generator inside a wind tunnel. Hsiao et al. [5] has designed a HAWT blade with a radius of 0.36 m using the improved BEM theory and tested the aerodynamic performance in a wind tunnel. Previous studies related to the aerodynamic tests have provided useful information for measuring the turbine blade performance including the behavior of airfoils, blades and wakes, which helped not only in understanding the aerodynamic characteristics, but also the mathematical models [13] [14] [15] . Recently, variable-speed HAWT systems have gradually replaced constant-speed ones, which have fairly low system efficiencies at most of the wind speeds. To improve the system efficiency, many modern wind turbine systems adapt the variable-speed systems with an electronic control system [16, 17] . For example, the small-scaled HAWT system takes advantage of the variable-speed
doi:10.3390/en7117773 fatcat:7byrybt3uzgdfmgkdelukvmhma