Control Strategy Of Turbine Research Articles

Comparative Study of Different Pitch Angle Control Strategies for DFIG Based on Wind Energy Conversion System

Abstract- This paper presents an advanced pitch angle control for large scale Wind Energy Conversion System (WECS) based on a Doubly-Fed Induction Generator (DFIG). Blade Pitch angle control is the extremely popular techniques for regulating the aerodynamic power of the wind turbine and minimize aerodynamic fatigue when the wind speed is higher than its rated value. The traditional control technique is based on the proper system modeling and analytical analysis of the transfer function which are not always available and the non-linearity of the control system. To overcome the problems in the traditional control, the adaptive fuzzy-PID control is proposed in this work. The process of the blade pitch control using adaptive fuzzy-PID control strategy is featured with nonlinearity, multi-variable, time variation and time delay. The simulation results are enclosed which prove the effectiveness of the auto-tuning adaptive fuzzy-PID (AF-PID) controller in improving the dynamic performance of the wind turbine (WT). This article emulated comparative analysis of 1.5 MW Doubly-fed induction generator wind turbine control strategies based on computer modeling in MATLAB/Simulink software.

Near-wake behaviour of a utility-scale wind turbine

Super-large-scale particle image velocimetry (SLPIV) and the associated flow visualization technique using natural snowfall have been shown to be effective tools to probe the turbulent velocity field and coherent structures around utility-scale wind turbines (Hong et al.Nat. Commun., vol. 5, 2014, article 4216). Here, we present a follow-up study using the data collected during multiple deployments from 2014 to 2016 around the 2.5 MW turbine at the EOLOS field station. These data include SLPIV measurements in the near wake of the turbine in a field of view of 115 m (vertical) $\times$ 66 m (streamwise), and the visualization of tip vortex behaviour near the elevation corresponding to the bottom blade tip over a broad range of turbine operational conditions. The SLPIV measurements provide velocity deficit and turbulent kinetic energy assessments over the entire rotor span. The instantaneous velocity fields from SLPIV indicate the presence of intermittent wake contraction states which are in clear contrast with the expansion states typically associated with wind turbine wakes. These contraction states feature a pronounced upsurge of velocity in the central portion of the wake. The wake velocity ratio $R_{w}$, defined as the ratio of the spatially averaged velocity of the inner wake to that of the outer wake, is introduced to categorize the instantaneous near wake into expansion ($R_{w}<1$) and contraction states ($R_{w}>1$). Based on the $R_{w}$ criterion, the wake contraction occurs 25 % of the time during a 30 min time duration of SLPIV measurements. The contraction states are found to be correlated with the rate of change of blade pitch by examining the distribution and samples of time sequences of wake states with different turbine operation parameters. Moreover, blade pitch change is shown to be strongly correlated to the tower and blade strains measured on the turbine, and the result suggests that the flexing of the turbine tower and the blades could indeed lead to the interaction of the rotor with the turbine wake, causing wake contraction. The visualization of tip vortex behaviour demonstrates the presence of a state of consistent vortex formation as well as various types of disturbed vortex states. The histograms corresponding to the consistent and disturbed states are examined over a number of turbine operation/response parameters, including turbine power and tower strain as well as the fluctuation of these quantities, with different conditional sampling restrictions. This analysis establishes a clear statistical correspondence between these turbine parameters and tip vortex behaviours under different turbine operation conditions, which is further substantiated by examining samples of time series of these turbine parameters and tip vortex patterns. This study not only offers benchmark datasets for comparison with the-state-of-the-art numerical simulation, laboratory and field measurements, but also sheds light on understanding wake characteristics and the downstream development of the wake, turbine performance and regulation, as well as developing novel turbine or wind farm control strategies.

Study on Power Angle Stability of Wind-fire Hybrid Transmission System Controlled by Virtual Synchronous Machine

Wind-fire hybrid transmission system stability has always been a research hot spot, and as the wind turbine control strategy is more and more complex, the stability is more complicated. In recent years, the idea of virtual synchronous machine applied to the control scheme of wind turbines has been popularized, so it is necessary to discuss the power angle stability of wind-fire hybrid system considering the additional control of the wind turbines with the virtual synchronous machine. In this paper, a typical wind-fire hybrid transmission system model is established, and the operating characteristics of the wind turbine are analyzed and the wind turbine model is established. Then, a control strategy of virtual synchronous machine is proposed. At last, the power equivalence function of wind-fire hybrid transmission system is analyzed by Extended Area Equity Criterion (EEAC), and the simulation results in PSASP show that when the receiver is a strong system, the higher the wind-fire ratio, the better the system's angle stability is. The control of the virtual synchronous machine has less effect on the stability of the power angle. When the receiver is a weak system, with the increase of wind power ratio, the power angle stability first increases and then decreases, there is an optimal ratio, and the application of the virtual synchronous machine control can effectively enhance the system's power angle stability, thereby improving the optimal wind-fire ratio.

Wind field effect on the power generation and aerodynamic performance of offshore floating wind turbines

This study is aimed at investigating wind field effect on the power generation and the aerodynamic performance of offshore floating wind turbines. For this purpose, three comparative wind fields are generated: a uniform wind field, a steady wind field with wind shear, and a turbulent wind field. Aero-hydro-servo coupled analysis is performed in time-domain to estimate how a referenced semisubmersible offshore floating wind turbine behaves in the three wind fields. The results reveal the importance of wind shear and inflow turbulence to the performance of the floating wind turbine. Thrust force and power generation become very unstable in the presence of inflow turbulence. Due to the control strategy of the wind turbine, the power generation is also correlated with operational state and turbulence frequency. Although wind shear has a tiny effect on the rotor performance, the local aerodynamic load applied at a single blade experiences fluctuation with the presence of wind shear. It is also shown that the ultimate structural and fatigue damage loads at blade root are augmented by inflow turbulence and wind shear.

Small wind turbine effectiveness in the urban environment

Abstract The aerodynamic design of small wind turbines for the urban setting attracts increasing interest within the scientific community, but the adoption of a proper control strategy may be just as important, especially in high turbulent winds, where such energy conversion devices should ideally operate. As a matter of fact, the mere rotor efficiency is meaningless unless the system has also the capability of rapidly changing its angular speed in case of a sudden variation of the wind velocity, to reach a new optimal operating condition. This work will attempt neither to develop dynamic simulation models nor to examine possible turbine control strategies, being the focus much broader, namely, the investigation of operational contexts where the peculiar inertial characteristics of wind turbines would compromise any form of robust control. Inertial and operational data of commercially available turbines (characterized by both horizontal and vertical-axis architectures), as well as the results disseminated in various literature sources, operational experiences and design best practices, are here collected under one cover and compared, thus deriving some basic and fundamental relations between rotor inertia and angular acceleration, highlighting how, in several cases, a control strategy based on the continuous tracking of the optimal operating condition is most unlikely. Such considerations raise the question of whether the problem of inertia renders futile many prevailing theories about small wind turbine operation and plans for implementing new control strategies, especially as far as vertical axis architectures are concerned. On the other hand, some constructive advice is also presented, in the form of a means to compare the effective performances of different turbines, in a given installation site, with respect to their nominal (i.e. steady state, or wind tunnel) behaviour. As a final result, a new bound for a reliable estimation of the amount of energy a wind turbine will generate in a specific site is suggested, based on the comparison between a representative time scale of the installation site and the response time of the candidate wind turbine.

The typhoon effect on the aerodynamic performance of a floating offshore wind turbine

The wind energy resource is considerably rich in the deep water of China South Sea, where wind farms have to face the challenge of extreme typhoon events. In this work, the typhoon effect on the aerodynamic performance of the 5MW OC3-Hywind floating offshore wind turbine (FOWT) system has been investigated, based on the Aero-Hydro-Servo-Elastic FAST code. First, considering the full field observation data of typhoon “Damrey” is a long duration process with significant turbulence and high wind speed, so one 3-h representative truncated typhoon wind speed time history has been selected. Second, the effects of both the (variable-speed and collective-pitch) control system of NREL 5 MW wind turbine and the motion of the floating platform on the blade aerodynamic performance of the FOWT system during the representative typhoon time history has been investigated, based on blade element momentum (BEM) theory (coupled with potential theory for the calculation of the hydrodynamic loads of the Spar platform). Finally, the effects of different wind turbine control strategies, control parameter (KP–KI) combinations, wave heights and parked modes on the rotor aerodynamic responses of the FOWT system have been clarified. The extreme typhoon event can result in considerably large extreme responses of the rotor thrust and the generated power due to the possible blade pitch angle error phenomenon. One active-parked strategy has been proposed for reducing the maximum aerodynamic responses of the FOWT system during extreme typhoon events.

Power fluctuation and power loss of wind turbines due to wind shear and tower shadow

The magnitude and stability of power output are two key indices of wind turbines. This study investigates the effects of wind shear and tower shadow on power output in terms of power fluctuation and power loss to estimate the capacity and quality of the power generated by a wind turbine. First, wind speed models, particularly the wind shear model and the tower shadow model, are described in detail. The widely accepted tower shadow model is modified in view of the cone-shaped towers of modern large-scale wind turbines. Power fluctuation and power loss due to wind shear and tower shadow are analyzed by performing theoretical calculations and case analysis within the framework of a modified version of blade element momentum theory. Results indicate that power fluctuation is mainly caused by tower shadow, whereas power loss is primarily induced by wind shear. Under steady wind conditions, power loss can be divided into wind farm loss and rotor loss. Wind farm loss is constant at 3α(3α–1)R2/(8H2). By contrast, rotor loss is strongly influenced by the wind turbine control strategies and wind speed. That is, when the wind speed is measured in a region where a variable-speed controller works, the rotor loss stabilizes around zero, but when the wind speed is measured in a region where the blade pitch controller works, the rotor loss increases as the wind speed intensifies. The results of this study can serve as a reference for accurate power estimation and strategy development to mitigate the fluctuations in aerodynamic loads and power output due to wind shear and tower shadow.

Control Strategy of DC Link Voltage Flywheel Energy Storage for Non Grid Connected Wind Turbines Based on Fuzzy Control

The large-scale development of wind power is an important means to reduce greenhouse gas emissions, alleviate environmental pollution and improve the utilization rate of renewable energy. At the same time, large-scale non grid connected wind power generation theory avoids the technical difficulties of wind power integration [1]. However, due to the randomness and uncontrollability of wind energy, the output power of the wind power generation system will fluctuate accordingly [2]. Therefore, the corresponding energy storage devices are arranged in the non-grid-connected wind power generation system to ensure the power quality, and it has become the key to full utilization of renewable energy. In the case of wind speed fluctuation, the DC bus control strategy of the wind turbine is proposed in this paper. It can reduce the impact on the unit converter and the power load; this ensures safe and stable operation of non-grid connected wind turbines.

Nacelle LiDAR online wind field reconstruction applied to feedforward pitch control

This paper presents innovative filtering and reconstruction techniques of nacelle LiDAR data, and exploitation of obtained wind anticipation capabilities for wind turbine control strategy. The implemented algorithms are applied under industrial constraints, on a MAIA EOLIS wind turbine, equipped with a LEOSPHERE 5-beams pulsed LiDAR, during experimental campaigns of SMARTEOLE collaborative project.

Random bounce algorithm: real-time image processing for the detection of bats and birds

Wind energy plants generate an impact on wildlife with significant fatality rates for various bat and bird species, e.g. due to a collision with the rotor blades. Monitoring approaches, such as vision-based systems, are needed to reduce their mortality by means of an optimized turbine control strategy as soon as flying animals are detected. Since manual analysis of the video data is ineffective, automatic video processing with real-time capabilities is required. In this paper, we propose the random bounce algorithm (RBA) as a novel real-time image processing method for vision-based detection of bats and birds. The RBA is combined with object tracking in order to extract flight trajectories. Its performance is compared with connected components object detection. Results from a laboratory flight tunnel as well as from a field study at a 2 MW wind energy plant in Southern Germany will be presented and discussed. We have successfully detected and tracked objects both in laboratory experiments with many animals and in field experiments with individual animals at a frame rate of 10 fps.

Predictive control strategy of a gas turbine for improvement of combined cycle power plant dynamic performance and efficiency.

This paper presents a novel strategy for implementing model predictive control (MPC) to a large gas turbine power plant as a part of our research progress in order to improve plant thermal efficiency and load–frequency control performance. A generalized state space model for a large gas turbine covering the whole steady operational range is designed according to subspace identification method with closed loop data as input to the identification algorithm. Then the model is used in developing a MPC and integrated into the plant existing control strategy. The strategy principle is based on feeding the reference signals of the pilot valve, natural gas valve, and the compressor pressure ratio controller with the optimized decisions given by the MPC instead of direct application of the control signals. If the set points for the compressor controller and turbine valves are sent in a timely manner, there will be more kinetic energy in the plant to release faster responses on the output and the overall system efficiency is improved. Simulation results have illustrated the feasibility of the proposed application that has achieved significant improvement in the frequency variations and load following capability which are also translated to be improvements in the overall combined cycle thermal efficiency of around 1.1 % compared to the existing one.

A novel control strategy approach to optimally design a wind farm layout

Recently wind energy has become one of the most important alternative energy sources and is growing at a rapid rate because of its renewability and abundancy. For the clustered wind turbines in a wind farm, significant wind power losses have been observed due to wake interactions of the air flow induced by the upstream turbines to the downstream turbines. One approach to reduce power losses caused by the wake interactions is through the optimization of wind farm layout, which determine the wind turbine positions and control strategy, which determine the wind turbine operations. In this paper, a new approach named simultaneous layout plus control optimization is developed. The effectiveness is studied by comparison to two other approaches (layout optimization and control optimization). The results of different optimizations, using both grid based and unrestricted coordinate wind farm design methods, are compared for both ideal and realistic wind conditions. Even though the simultaneous layout plus control optimization is theoretically superior to the others, it is prone to the local minima. Through the parametric study of crossover and mutation probabilities of the optimization algorithm, the results of the approach are generally satisfactory. For both simple and realistic wind conditions, the wind farm with the optimized control strategy yield 1–3 kW more power per turbine than that with the self-optimum control strategy, and the unrestricted coordinate method yield 1–2 kW more power per turbine than the grid based method.

Dispatching and Frequency Control Strategies for Marine Current Turbines Based on Doubly Fed Induction Generator

This paper presents the modeling and development of a dispatchable large-scale marine current turbine (MCT)farm equipped with power fluctuation compensation and primary frequency control schemes. The proposed control strategies rely on the regular and highly predictable power extraction from the marine currents, which are essentially governed by astronomical forces. Therefore, a mathematical model for prediction of marine current speed is developed and validated with the recorded measurements. Subsequently, the effect of velocity disturbances caused by the swell effect is studied and a battery energy storage station (BESS)control strategy for power fluctuation mitigation is proposed with reduced BESS capacity. Additionally, the provision of frequency control for MCT based on BESS has been discussed. The performance of the BESS-based frequency control strategy has been analyzed and compared with that of frequency control based on the combination of inertial response and deloaded operation. The simulation results depict that both these strategies can effectively enable MCTs to participate in primary frequency control, however, provision of frequency control based on BESS is more feasible in terms of profitability and reduction in fossil fuel consumption.

Cooperative wind turbine control for maximizing wind farm power using sequential convex programming

This paper describes the use of a cooperative wind farm control approach to improve the power production of a wind farm. The power production by a downstream wind turbine can decrease significantly due to reduced wind speed caused by the upstream wind turbines, thereby lowering the overall wind farm power production efficiency. In spite of the interactions among the wind turbines, the conventional (greedy) wind turbine control strategy tries to maximize the power of each individual wind turbine by controlling its yaw angle, its blade pitch angle and its generator torque. To maximize the overall wind farm power production while taking the wake interference into account, this study employs a cooperative control strategy. We first derive the wind farm power as a differentiable function of the control actions for the wind turbines in a wind farm. The wind farm power function is then maximized using sequential convex programming (SCP) to determine the optimum coordinated control actions for the wind turbines. Using an example wind farm site and available wind data, we show how the cooperative control strategy improves the power production of the wind farm.

Sliding Mode Control of a Wind Turbine with Exponential Reaching Law

This paper presents a novel control strategy of a wind turbine based on Doubly Fed Induction Generator (DFIG) to maximize the electrical power generated by the DFIG, for low wind speed. To achieve this objective, the nonlinear sliding mode control with exponential reaching law (ERL ), the Bees algorithm and the fuzzy maximum power point tracking MPPT are applied to the system. The ERL and the Bees algorithm are used to obtain a good reference tracking and to suppress the chatter phenomenon. The effectiveness of this control strategy is proven through the simulation results.

Study on the Low Voltage Ride-Through of Doubly-Fed Induction Generator Based on BP Neural Network

In order to ensure that wind turbines could be online under the condition of power grid transient fault, the technology of low voltage ride-through (LVRT) for wind turbine has become a research focus of experts and scholars at home and abroad. In current wind turbine control strategy, the PI parameters of the control system keep unchanged when the wind turbine is in the process of LVRT, which affects the performance of the control system. Therefore, the adaptive PI parameter adjustment system based on BP neural network is proposed, which realize the adaptive adjustment of PI parameters in the process of LVRT. The simulation model of the LVRT process was built, the simulation results show that this control algorithm can effectively restrain the current oscillation caused by the voltage sag, shorten the fault recovery time of the system, and has a good dynamic performance. Besides, the adaptability and robustness of the system has been increased, which has improved the low voltage ride-through capability of the system.

Modelling Turbine Loads during an Extreme Coherent Gust using Large Eddy Simulation

A group of wind turbines operating in extreme transient wind conditions has been simulated using LES and an actuator model. An extreme wind event is introduced into the simulation domain using transient boundary conditions. The event is based on the extreme coherent gust (ECG) structure from the International Wind Turbine Design Standard IEC61400-1:2005 which consists of a simultaneous gust and wind direction change. Details of the implementation are discussed with regard to adapting the analytical functions described in the standard. A recently developed actuator sector method is used to represent the wind turbines in the simulation. The actuator method is coupled to the aero-elastic wind turbine simulation code FAST to allow dynamic control of the wind turbines based on the ambient flow conditions. Standard baseline controllers are used to regulate generator torque, actuate blade pitch angle and control yaw direction. A span-wise periodic array of turbines operating in a steady atmospheric boundary layer is simulated before the introduction of the ECG structure. The convection of the wind event is analysed, along with the subsequent response of the wind turbines and loading during the wind event is quantified. The simulations demonstrate a methodology for modelling groups of turbines operating in transient wind conditions that can be used to study turbine loads or test new turbine control strategies.

Control development for floating wind

Control of a floating wind turbine has proven to be challenging, but essential for lowering the cost of floating wind energy. Topic of a recent joint R&D project by GustoMSC, MARIN and ECN, is the concept design and verification with coupled simulations and model tests of the GustoMSC Tri-Floater. Only using an integral design approach, including mooring and control design, a cost effective system can be obtained. In this project, ECN developed a general floating wind turbine control strategy and applied this in a case study to the GustoMSC Tri-Floater and the OC3Hywind spar, both equipped with the NREL 5MW RWT. The designed controller ensures stable operation, while maintaining proper speed and power regulation. The motions of the floating support are reduced and substantial load reduction has been achieved.

The key technologies and development of offshore wind farm in China

Abstract China is one of the largest energy consumers in the world. Excessive consumption of coal and other primary energy causes serious environmental pollution and energy crisis. China must wean from the over-reliance on coal and needs to make great efforts to develop clean and efficient renewable energy. In recent years, offshore wind energy has been developing rapidly with the advantages of not taking up land resources and high utilization rate. By the end of 2012, the total installed capacity of offshore wind power was 389.6 MW in China. The planning capacity will be 5 GW by 2015 and 30 GW by 2020 [1] , [2] . Compared to onshore wind power, the development of offshore wind power is facing some new problems and challenges, for example power transmission, offshore harsh natural environments, multi-sectoral coordination and management, and so on. This paper firstly analyzes the irrationality of China׳s energy consumption structure and the necessity for developing offshore wind power. Secondly, an overview of offshore wind farm access, AC (Alternating Current) and DC (Direct Current) transmission technologies and offshore wind turbine control strategies are given. The development status and future plans of offshore wind power are also introduced. Finally, we analyze the existing problems and obstacles during the construction process of offshore wind farms from three aspects, including technical, economic, and national policies. And some corresponding recommendations to accelerate the development of offshore wind farm are also proposed.

Structural health and prognostics management for the enhancement of offshore wind turbine operations and maintenance strategies

ABSTRACTOffshore wind turbines are an attractive source for clean and renewable energy for reasons including their proximity to population centers and higher capacity factors. One obstacle to the more widespread installation of offshore wind turbines in the USA, however, is that recent projections of offshore operations and maintenance costs vary from two to five times the land‐based costs. One way in which these costs could be reduced is through use of a structural health and prognostics management (SHPM) system as part of a condition‐based maintenance paradigm with smart loads management. This paper contributes to the development of such strategies by developing an initial roadmap for SHPM, with application to the blades. One of the key elements of the approach is a multiscale simulation approach developed to identify how the underlying physics of the system are affected by the presence of damage and how these changes manifest themselves in the operational response of a full turbine. A case study of a trailing edge disbond is analysed to demonstrate the multiscale sensitivity of damage approach and to show the potential life extension and increased energy capture that can be achieved using simple changes in the overall turbine control and loads management strategy. The integration of health monitoring information, economic considerations such as repair costs versus state of health, and a smart loads management methodology provides an initial roadmap for reducing operations and maintenance costs for offshore wind farms while increasing turbine availability and overall profit. Copyright © 2013 John Wiley & Sons, Ltd.