Speed Horizontal Axis Wind Turbines Research Articles

Combined effects of pitch angle, rotational speed and site wind distribution in small HAWT performance

Constant speed horizontal axis wind turbines operate at power coefficients different than its maximum due to operation at different tip speed ratios (TSRs). Whereas rotational speed and the site wind speed distribution determine the TSR range of the operation, the pitch angle is significant for the aerodynamic performance of the wind turbine. In this paper, a blade element momentum approach is used to study the power production effects of pitch angle and rotational speed of NREL Phase VI wind turbine at different site wind distributions (characterized by Weibull distributions). It is shown that the best combination of rotational speed and pitch angle always occurs at the same pitch angle, but for different rotational speeds (other than the best one) the best pitch angle may vary. The best rotational speed is found to be dependent on both form and scale factors of Weibull wind speed distribution. Improvements in turbine pitch angle and rotational speed are found to increase generated energy up to four times, but the increasing factor is highly dependent on wind speed distribution: For the studied turbine, high-wind-speeds sites can benefit more from the adjustment of these parameters than low-speed ones.

Analysis of Vector Controlled Variable Speed DFIG for Wind Turbines

Double Fed Induction Generators (DFIG) has been widely used for the past two decades in large wind farms. This paper presents control and analysis of the doubly fed induction generator (DFIG) connected to variable speed horizontal axis wind turbine (HAWT). The detailed wind turbine (WT) model, DFIG dynamic model in d-q-synchronous reference frame, power electronic converters, and controllers are presented. The reactive and active power of the DFIG can be precisely decoupled by controlling the rotor side converter (RSC). The field-oriented control (FOC) strategy and the proportional-integral (PI) controllers were used to control the RSC of the DFIG. Furthermore, a space vector pulse width modulation (SVPWM) was utilized to generate pulsing signals required to drive three phases DC-AC converter (inverter). The proposed control method of DFIG based on HAWT was verified by simulation in MATLAB-SIMULINK software. The obtained simulation results showed the capability and effectiveness of the proposed control method.

Economically optimal configuration of onshore horizontal axis wind turbines

During the recent years, the use of new materials and enhanced production processes led to successively increasing sizing parameter – namely rotor diameter, rated power and hub height – of wind turbines as well as decreasing initial and running costs. The thereby risen market share shows that wind energy projects are an interesting field for financial investors. In this connection the question arises, how investors benefit from the mentioned technical developments. Regarding the utility maximization of investors in turbine projects, goal of this survey is to determine the economically optimal turbine configuration in contrast to the technically feasible by maximizing the net present value. For this purpose, a generalized approximation of the power curve of three-bladed, direct-driven, variable speed horizontal axis wind turbines is applied. For estimation of the economic parameters, a complex mass-cost-model is used for determination of the initial costs as a function of the sizing parameter. Thereby, a method is shown for adjustment of this model to several differences in price levels of the different turbine components. Furthermore, detailed relationships for running costs as well as the estimation of the cost of equity capital are shown. Due to the current importance of feed-in tariff, revenues for electricity sale depend on the German “Renewable Energy Act”. The calculation of economically optimal sizing parameter first is done for a reference site in conjunction with a sensitivity analysis to determine the most influential sizing parameter with respect to economic viability. Afterwards, a range of typically onshore wind speeds in Germany is considered.

Optimum Blade Profiles for a Variable-Speed Wind Turbine in Low Wind Area

A Blade-Element Momentum (BEM) based software was used to design a 300kW, variable speed Horizontal Axis Wind Turbine (HAWT). Chord lengths, blade twist angles and rotational speeds were allowed to change independently so as to achieve a maximum energy output, while design constraints were also being met. Computational Fluid Dynamic (CFD) was use to validated the BEM calculation. According to low wind area, the rated wind speed was set quite low at 10 m/s. The optimal design of wind turbine reaches 50.5% efficiency at the design tip speed ratio of 7.5. The wind turbine can maintain 50.5% efficiency level over wind speeds range of 4-9 m/s by changing the rotating speeds from 16-36 RPM. Beyond the rated wind speed, the turbine can regulate its power by changing the rotating speed to decrease its efficiency and maintain the power output at 300kW. Results from CFD agree well with the BEM calculation. It verifies that the optimum designed blade from the BEM was reliable.

Aerodynamics performance of continuously variable speed horizontal axis wind turbine with optimal blades

For conventional HAWT (horizontal axis wind turbines), the rotor speed is maintained constant while the blade tip speed changes continuously. This reduces considerably the power performance of the wind turbine particularly at high wind speeds where the tip speed ratio is small. With growth of variable speed generators, a compact BEM (blade element momentum) analysis is derived to design optimal blades for continuously variable speed HAWTs. First, a generalized quadratic equation on the angular induction factor is introduced which is related to local axial induction factor, blade local speed ratio, and drag to lift ratio. Second, the optimal blade geometry is obtained for which the maximum power coefficient is calculated at different design tip speed ratios and drag to lift ratios by assuming variable operational speed. Third, it is demonstrated that the power performance of the variable speed wind turbine is significantly higher than the conventional constant speed wind turbines. In addition, the present BEM modeling may be useful to reduce the computational effort of iterative numerical methods used in determining off-design power performance of conventional wind turbines with constant speed.

Experimental and Numerical Studies on a Low Reynolds Number Airfoil for Wind Turbine Blades

Testing of a low Reynolds number airfoil designed for low speed horizontal axis wind turbine (HAWT) blades was performed to study its aerodynamic characteristics. Experiments were conducted at Reynolds numbers (Re) of 38,000 to 200,000 at angles of attack from -2 o to 20 o . The airfoil geometry was chosen after testing a number of profiles with XFOIL software. The pressure distribution, lift and drag coefficients and the flow characteristics were also studied with ANSYS-CFX software. The freestream turbulence level was increased from 1% to 5% and 10% which shifted the transition point on the upper surface upstream, resulting in increased skin friction drag for lower angles of attack due to a larger turbulent boundary layer region. The slope of the lift curve did not change much at higher turbulence levels; however, for higher angles of attack, the separation from the upper surface was delayed resulting in an increase in lift and a reduction in drag. The lift to drag ratio increased by 8% to 15% as a result of increasing the turbulence level in the angles of attack-range of interest.

Vortex specification and horizontal axis wind turbine design

SYNOPSIS Free vortex specification for axial turbomachines is applied to high speed horizontal axis wind turbines. The approach is shown to yield values of interference coefficients and coefficient of performance, which are either optimum or very close to the optimum. An energy loss coefficient is then used to determine the range of values for the output power coefficient of a HAWT turbine.

Horizontal axis wind turbine control: Comparison of classical, LQG andH ∞ designs

A comparison between classical, LQG andH∞ design procedures is presented for the design of the power regulator in a fixed speed horizontal axis wind turbine. The relative merits of the different approaches are discussed regarding both the procedures and the resulting controllers.

Classical control of active pitch regulation of constant speed horizontal axis wind turbines

Owing to current concern over the environment, there is much interest in renewable sources of electrical power generation of which one of the most promising is wind power. However, it is not yet a mature technology and many basic issues have yet to be resolved. One such issue is the best means of regulating the wind turbines. Many horizontal axis grid-connected wind turbines have the capability to vary the angle of pitch of the blades which can be exploited to provide regulation. The purpose of this paper is to report on an extensive investigation into the control of active pitch regulation of constant speed, grid-connected horizontal axis wind turbines. The performance attainable by PI control design and classical Nyquist-Bode loop shaping is determined and compared

On Aerodynamic Performance of Low Speed Horizontal Axis Wind Turbine (In the Case of Optimum Chord Length)

On Aerodynamic Performance of Low Speed Horizontal Axis Wind Turbine (In the Case of Optimum Chord Length)