This work provides a signal-processing and statistical-error analysis methodology to assess key performance indicators for a floating Doppler wind lidar. The study introduces the raw-to-clean data processing chain, error assessment indicators and key performance indicators, as well as two filtering methods at post-processing level to alleviate the impact of angular motion and spatial variability of the wind flow on the performance indicators. Towards this aim, the study mainly revisits horizontal wind speed (HWS) and turbulence intensity measurements with a floating ZephIR 300 lidar buoy during a 38 day nearshore test campaign in Pont del Petroli (Barcelona). Typical day cases along with overall statistics for the whole campaign are discussed to illustrate the methodology and processing tools developed.
Vortex generators (VGs) are used increasingly by the wind turbine industry as flow control devices to improve rotor blade performance. According to experimental observations, the vortices generated by VGs have previously been observed to be self-similar for both the axial (uz) and azimuthal (u¿) velocity components. Furthermore, the measured vortices have been observed to obey the criteria for helical symmetry. These are powerful results, as it reduces the highly complex 3-D flow to merely four parameters and therefore significantly facilitates the modeling of this type of flow, which in a larger perspective can assist in parametric studies to increase the total power output of wind turbines. In this study, corresponding computer simulations using Reynolds-averaged Navier-Stokes equations have been carried out and compared with the experimental observations. The main objective is to investigate how well the simulations can reproduce these aspects of the physics of the flow, i.e., investigate if the same analytical model can be applied and therefore significantly facilitate the modeling of this type of flow, which in a larger perspective can assist in parametric studies to increase the total power output of wind turbines. This is especially interesting since these types of flows are notoriously difficult for the turbulence models to predict correctly. Using this model, parametric studies can be significantly reduced, and moreover, reliable simulations can substantially reduce the costs of the parametric studies themselves.
Stereoscopic particle image velocimetry (SPIV) has been used to characterize the flow around the blade of a yawed horizontal axis wind turbine model. The goal was to assess the possibility of obtaining the 3D velocity field around the blade, the pressure distribution, and the aerodynamic loads being exerted on the blade under unsteady flow conditions. The SPIV equipment was mounted on a traverse system and provided with phase-locked velocity planes perpendicular to the blade axis, scanning the blade from the root to the tip, at three different azimuthal positions, so as to have information of the time variation of the flow. The pressure distribution and the aerodynamic loads on each plane were obtained via 3D formulation. Main differences encountered when measuring loads in yawed flow compared with axial flow have been discussed. Finally, the consistency of the results with similar results obtained computationally with a panel model was assessed. The proposed methodology presents one step further in the application of SPIV to measure forces on a horizontal axis wind turbine, assessing the possibility of estimating the blade loads when the turbine is operating under non-axial flow conditions, with the goal of better simulating real working operating regimes in a wind farm, where the flow is typically not uniform. The proposed methodology could be developed and used to better understand relevant wind energy issues such as dynamic loading and active load control efficiency, in the future. The processed and averaged flow fields from the experimental SPIV data are made available online to the reader. See appendix for description of the files
The flow around the blade of a horizontal axis wind turbine wind tunnel model, operating at its optimal tip speed ratio in axial flow, has been investigated by means of stereoscopic particle image velocimetry (SPIV). The aim was to assess the possibility of measuring the loads impinged on the blade, using the acquired velocity field and its spatial derivatives. Thus, the three-dimensional (3D) velocity field and the pressure distribution surrounding the blade, as well as the aerodynamic loads, responsible for thrust and torque, were obtained with a non-intrusive method. The SPIV equipment was mounted on a traverse system and provided with phase-locked velocity planes perpendicular to the blade axis, scanning the blade from the root to the tip, at a fixed azimuthal position. The obtained velocity fields were used to estimate the pressure distribution and the aerodynamic loads on each plane, using a 3D formulation. Finally, these results were compared and discussed with similar results obtained computationally with a panel method model, showing good consistency. In the future, the proposed methodology could be used to study relevant topics such as active load control techniques, rotational augmentation, dynamic stall phenomena and the aerodynamics of small wind turbines operating at low Re numbers, among others. The processed and averaged flow fields from the experimental SPIV data are made available online to the reader. See appendix for description of the files.
Recently, the concept of wind power plant has been introduced as a result of the increment of wind power penetration in power systems. A wind power plant can be defined as a wind farm, which is expected to behave similar to a conventional power plant in terms of power generation, control and ancillary services. Transmission system operators are requiring wind power generation to help to power system with some ancillary services such as fault ride through or power system stabilizer capability. Therefore, it is important to study the power system stabilizer capability of wind power plants. In this paper, a comparison of various power system stabilizer schemes is presented. The effect of the distance from the tie line to the wind farm on the controller response and the influence of wind power plants proximity to synchronous generators are also evaluated. These studies show that wind power plants have promising power system stabilizer capability even using local input signals. However, the location of the wind power plant on the power system is a critical factor.
In this paper, a novel coordination and control strategy for capacitor banks and on-load tap changer for a wind power
plant is introduced. The capacitor banks are controlled in such way that the steady-state usage of the converters for reactive
power injection is driven below to a maximum desired value of 0.1 pu. Additionally, the control transients because of the
capacitor bank switching are minimized by using a suitable control structure. The tap changer control is coordinated with
the plant control to decrease the impact of the capacitors reactive power in the line drop calculation, thus reducing the
amount of tap operations and improving the accuracy of the line drop voltage estimation.
The coordination of the central controller with the plant components is analysed and tested through electromagnetic
transient program simulations.
Modern wind power plants are required and designed to ride through faults in electrical networks, subject to fault clearing.
Wind turbine fault current contribution is required from most countries with a high amount of wind power penetration.
In order to comply with such grid code requirements, wind turbines usually have solutions that enable the turbines
to control the generation of reactive power during faults. This paper addresses the importance of using an optimal injection
of active current during faults in order to fulfi l these grid codes. This is of relevant importance for severe faults,
causing low voltages at the point of common coupling. As a consequence, a new wind turbine current controller for
operation during faults is proposed. It is shown that to achieve the maximum transfer of reactive current at the point
of common coupling, a strategy for optimal setting of the active current is needed.
This paper addresses the representation of the wound rotor asynchronous generators by an equivalent synchronous generator,
valid for short circuit current calculations.
Modern wind power plants are required and designed to ride through faults in the network, subjected to fault clearing.
Accurate knowledge of the wind turbine short circuit current contribution is needed for component sizing and protection
relay settings during faults within the wind power plant collector system or in the external networks.
When studying fault currents and protection settings for wind power installations, the industry standard is to employ
software packages where generators are represented by their equivalent synchronous generator operational impedances.
Hence, it is of importance to represent non-synchronous wind generators by an equivalent synchronous generator.