Sudden Change In Wind Speed Research Articles

Development of Novel Robust Regulator for Maximum Wind Energy Extraction Based upon Perturbation and Observation

This paper develops a robust regulator design approach to maximum power point tracking (MPPT) of a variable-speed wind energy conversion system (WECS) under the concept of perturbation and observation. The proposed perturb and observe regulators (PORs) rooted on the sliding mode method employs the optimal power curve (OPC) to realize MPPT operations by continuously adjusting rotor speeds and the duty cycles, which can ensure control performance against system parameter variations. The proposed PORs can detect sudden wind speed changes indirectly through the mechanical power coefficient, which is used to acquire the rotor speed reference by comparing it with the optimal power constant. For the speed and duty cycle regulation, two novel controllers based on the proposed POR, i.e., an MPPT controller and a speed controller, are devised in this research. Moreover, by applying the small-signal analysis on a nonlinear wind turbine system, the convergence of the proposed speed controller is proven for the first time based on the Lyapunov theory, and meanwhile, a single-pole transfer function, to describe the effect of duty cycle variations on rotor speeds, is designed to ensure its stability. The proposed strategy is verified by simulation cases operated in MATLAB/Simulink and experimental results performed from a 0.5-kW wind turbine generator simulator.

Continuous variation of wind drift and evaporation losses under a linear move irrigation system

The traditional catch-can technique for measuring water depth application under sprinkler irrigation systems has the limitation of being unable to monitor the continuous variation of wind drift and evaporation losses (WDEL) under changing weather conditions. Such information is essential to better manage the agricultural water by improving the global water application uniformity under moving irrigation machines. Three parallel, long, impermeable water collection strips were constructed underneath a stationary linear move irrigation system to address this issue. The sprinkler discharge efficiency (SDE≈1- WDEL) was monitored over 5-min intervals (SDE5min) during Apr-Aug of 2014-on a bare experimental plot. Experiments were conducted on a discrete basis for about 1040h total in order to collect more than 11,600 SDE5min data points. It was found that the SDE5min is very dynamic and can experience abrupt changes up to 16.5% as a result of sudden changes in wind speed and direction. The maximum and minimum observed SDE5min during the study period were 97.5 and 73.6%, respectively. The difference between maximum and minimum SDE5min during a day/night cycle was controlled by solar radiation and maximum wind speed. The average hourly SDE (SDEhr) for data collected at predawn, morning, afternoon, and evening were 89.5, 87.7, 86.9 and 88.8%, respectively. Overall, the daily SDE was mainly controlled by air temperature and varied between 81.8 and 91.8%, indicating that ∼8–18% of the daily applied water was lost on average. A multiple linear regression model was developed to help predict the SDEhr as a function of weather parameters. The model indicated wind speed, temperature and relative humidity as the best explanatory variables and predicted the SDEhr with an absolute error just over 4%. Because the difference between maximum and minimum SDEhr over a full experimental day could be as high as 22%, this magnitude of error was considered to be acceptable for wind drift and evaporation loss estimation.

A second-order sliding mode and fuzzy logic control to optimal energy management in wind turbine with battery storage

The optimal control of large-scale wind turbine has become a critical issue for the development of renewable energy systems and their integration into the power grid to provide reliable, secure and efficient electricity, despite any possible constraints such as sudden changes in wind speed. This paper deals with the modeling and control of a hybrid system integrating a permanent magnet synchronous generator (PMSG) in variable speed wind turbine (VSWT) and batteries as energy storage system (BESS). Moreover a new supervisory control system for the optimal management and robust operation of a VSWT and a BESS is described and evaluated by simulation under wind speed variation and grid demand changes. In this way, the proposed coordinated controller has three subsystems (generator side, BESS side and grid side converters). The main function of the first one is to extract the maximum wind power through controlling the rotational speed of the PMSG, for this a maximum power point tracking algorithm based on fuzzy logic control and a second-order sliding mode control (SOSMC) theory is designed. The task of the second one is to maintain the required direct current (DC) link voltage level of the PMSG through a bidirectional DC/DC converter, whereas in the last, a (SOSMC) is investigated to achieve smooth regulation of grid active and reactive powers quantities, which provides better results in terms of attenuation of the harmonics present in the grid courant compared with the conventional first-order sliding controller. Extensive simulation studies under different conditions are carried out in MATLAB/Simulink, and the results confirm the effectiveness of the new supervisory control system.

Field Oriented Control of DFIG Based Wind Energy System Using Battery Energy Storage System

Wind power is the fastest growing source of electrical energy in the world today due to the increasing awareness of the environmental problems together with the rapid increase in the fuel cost and the power demand. Wind energy conversion using Doubly Fed Induction Generator (DFIG) is one of the most important types of renewable energy generations. The wind farm power output has large fluctuations due to sudden wind speed changes. Fluctuate power can often cause the violation of voltage and frequency limits in the weak system. It can be severe problem for the system stability also. The control system in the proposed arrangement of DFIG is able to reduce power fluctuation with the help of Battery Energy Storage System (BESS). In order to decouple the active and reactive powers generated by the machine, field oriented control is applied. As a result, high performance control of power can be achieved. The developed method has been tested through modelling a DFIG based wind energy system with BESS using SimPower System tools of MATLAB and simulated for operation as a grid connected system. The performance of DFIG based wind energy system demonstrates satisfactory performance under different wind speed conditions.

A Maximum Power Tracking Technique for Grid-Connected DFIG-Based Wind Turbines

In this paper, a maximum power tracking technique is presented for doubly fed induction generator-based wind turbines. The presented technique is a novel version of the conventional method, i.e., the electrical torque is proportional to the square of the rotor speed, in which the proportional coefficient is adaptively adjusted in real-time through three control laws. The first control law calculates the desired electrical torque using feedback linearization, assuming that the power capture coefficient and the desired rotor speed are instantaneously identified. The second control law estimates the real-time values of the power capture coefficient from a Lyapunov-based analysis, and the third control law provides the desired rotor speed. These control laws cause the turbine to adaptively adjust the rotor speed toward a desired speed in which the operating point moves in the direction of increasing the power capture coefficient. The proposed maximum power tracking method differs distinctly from the perturb-and-observe scheme by eliminating a need for adding a dither or perturbation signal, and robustly tracks the trajectory of maximum power points even in the event of a sudden wind speed change that can cause the perturb-and-observe technique to fail. In this paper, the National Renewal Energy Laboratory 5-MW reference wind turbine model is used to demonstrate the validity and robustness of the proposed method.

System Identification through Nonstationary Response: Wavelet and Transformed Singular Value Decomposition—Based Approach

AbstractThe full-scale data measured from tall buildings and long-span bridges are usually nonstationary due to transient earthquake ground motion, sudden changes in wind speed and/or direction, or time-varying motion of vehicles. The dynamic properties (i.e., frequency, damping, etc.) of these structures during nonstationary events closely relate to their operational safety, so their accurate identification is critical. Traditional system identification methods may fail to provide reliable results (especially for damping estimation) in these situations due to a lack of long segments of stationary data. In addition, these methods are not able to track the time-varying system properties caused by large amplitude response due to strong earthquakes or winds. This highlights the necessity of developing system identification methods suitable for nonstationary/transient data. In response to this need, this paper proposes a new nonstationary system identification scheme which first utilizes the wavelet transform...

The art and science of forensic meteorology

When weather factors into a legal dispute, meteorologists use eyewitness accounts, troves of atmospheric data, and simulated reenactments to figure out what went awry.

Design and Analysis of an MPPT Technique for Small-Scale Wind Energy Conversion Systems

This paper proposes a maximum power point tracking (MPPT) algorithm for small-scale wind energy conversion systems. The proposed algorithm uses the dc current as the perturbing variable. The algorithm detects sudden wind speed changes indirectly through the dc-link voltage slope. The voltage slope is also used to enhance the tracking speed of the algorithm and to prevent the generator from stalling under rapid wind speed slowdown conditions. The proposed method uses two modes of operation: A perturb and observe (P&O) mode with adaptive step size under slow wind speed fluctuation conditions, and a prediction mode employed under fast wind speed change conditions. The dc-link capacitor voltage slope reflects the acceleration information of the generator, which is then used to predict the next step size and direction of the current command. The proposed algorithm shows enhanced stability and fast tracking capability under both high and low rate of change wind speed conditions and is verified using a 1.5 kW prototype hardware setup.

A sensitivity based approach to assess the impacts of integration of variable speed wind farms on the transient stability of power systems

The impact of large penetration of wind power on the transient stability of multi-machine power systems is discussed in this paper. Variable speed wind farms with doubly fed induction generators (DFIG) are considered. A new index based on the sensitivity of the DFIG terminal voltage is used to assess the transient stability margin of power systems, both for constant wind speed condition and during a sudden change in wind speed. Suitable locations for connecting the DFIG to an existing power system are identified with the help of this index. The effect of increase in wind power penetration on the transient stability condition of the existing power system is studied. The proposed index is also used to select the optimum crowbar resistance during fault ride-through operation.

Horizontal axis wind turbine dynamic stall predictions based on wind speed and direction variability

The onset of dynamic stall in horizontal axis wind turbines (HAWTs) is related to the rapid increase in the angle of attack caused by sudden changes in wind speed and direction. In order to relate the changes in wind speed and direction with the variations in the blade-section angle of attack, an analytical model is proposed to determine the regions of the blade affected by dynamic stall. The so-called threshold radius has been identified and defined as the percentage of the blade length from the horizontal axis wind turbines hub beyond which the probability of dynamic stall occurrence falls to zero. High quality wind data were acquired to determine the average wind conditions that serve as the model inputs. It is shown that the rate of change of wind speed, due to gusts or the average turbulence, can cause large regions of dynamic stall on the wind turbine blade. Other parameters, such as the yaw misalignment and the rate of change of yaw angle are shown to be the cause of asymmetrical distribution of threshold radius with azimuth and also serve to increase the affected regions. Finally it is shown that the type of airfoil used in the turbine blade also has a significant effect on the threshold radius due to the different limiting reduced frequencies.

Dynamic Response of a Grid Connected Wind Farm with Different Types of Generators

For a wide areas wind farm, which composed of different zones of different wind turbines and different generators , this paper aims to simulate a wind farm model that icludes a wind turbine and three different types of generators , which are three phase synchronous generator, three phase squirrel-cage induction generator and three phase doubly-fed induction generator ,these generators are the main machines that generally used in the field of wind energy generation. All generators are connected in parallel at the point of common coupling (pcc) and connected to the utility grid . This model is a simple representation of the actual model of zafarana wind farm, which is the biggest wind farm in Egypt and further to use it in different kinds of simulations, and display the difference in response among all generators, where all generators are 500 kw power rating , and subjected to the same operating conditions . After modeling the system, the transient response of the system will be studied and analyzed at different operating cases as: Case.1 constant wind speed operation Case.2 variable wind speed operation Case.3 sudden change in turbine mechanical power Case.4 sudden change in wind speed. So this paper introduces a survey on the dynamic response of a large wind farm of different generators at different operating conditions Keywords: modeling, synchronous generator, induction generator, wind farm, simulation model, transient analysis. DOI: http://dx.doi.org/10.11591/ijpeds.v2i1.175

Design of a multilevel control strategy for integration of stand-alone wind/diesel system

Control of variable speed wind turbines coupled with squirrel cage induction generators situated in remote areas is difficult and suffers from some fundamental problems. These systems cannot stabilize frequency and voltage of the grid in acceptable ranges. Changes in the load during 1 day and sudden changes in wind speed also make this problem harder to deal with. In this paper, a system consisting of three wind turbines integrated with two types of diesel generator connected to a variable load is analyzed, and a new multilevel control strategy is proposed. A new load model is implemented by changing power demand based on load curve. This control method adjusts a controller based on past system and environmental data. Simulations based on PSCAD/EMTDC software show the ability of the proposed control system to provide high quality power for this type of load.

Feedforward Pitch Control Using Wind Speed Estimation

The dynamic response of a multi-MW wind turbine to a sudden change in wind speed is usually slow, because of the slow pitch control system. This could cause a large excursion of the rotor speed and an output power over the rated. A feedforward pitch control can be applied to minimize the fluctuations of these parameters. This paper introduces the complete design steps for a feedforward pitch controller, which consist of three stages, i.e. the aerodynamic torque estimation, the 3-dimensional lookup table for the wind seed estimation, and the calculation of the feedforward pitch amount. The effectiveness of the feedforward control is verified through numerical simulations of a multi-MW wind turbine.

Control Strategy to Mitigate the Impact of Reduced Inertia Due to Doubly Fed Induction Generators on Large Power Systems

The present work is based on developing a control strategy to mitigate the impact of reduced inertia due to significant DFIG penetration in a large power system. The paper aims to design a supplementary control for the DFIG power converters such that the effective inertia contributed by these wind generators to the system is increased. The paper also proposes the idea of adjusting pitch compensation and maximum active power order to the converter in order to improve inertial response during the transient with response to drop in grid frequency. Results obtained on a large realistic power system indicate that the frequency nadir following a large power impact in the form of generators dropping out is effectively improved with the proposed control strategy. The proposed control is also validated against the sudden wind speed change in the form of wind gust downs and wind ramp downs occurring in conjunction with the generators dropping out. A beneficial impact in terms of damping power system oscillations is also observed, which is validated by eigenvalue analysis. The affected mode is then excited with a large disturbance in time domain. The damping improvement observed in time domain and subsequent Prony analysis support the result obtained from eigenvalue analysis.

Evaluating and modelling the response of an individual to a sudden change in wind speed

The response of an individual to a sudden increase in wind velocity is important in terms of wind comfort and wind safety. This paper is concerned with the latter issue and outlines a series of physical and numerical experiments undertaken in order to evaluate the response of an individual to a sudden change in wind speed. The physical experiments were undertaken in the dynamic circuit of the Jules Verne Climatic Wind Tunnel at CSTB in Nantes, France and subjected 31 people to wind speeds up to 20 m/s. In all cases the wind speed increased from a mean value of zero to the target value in approximately 0.2 s. The wind speed required to cause loss of balance is shown to be a function of orientation and weight. In an attempt to understand the influence that gust frequency and mean velocity exert on wind safety criteria, a simple numerical model has been developed. The model is shown to agree reasonably well with the data pertaining to the physical experiments. Furthermore the model has been used in a predictive sense to evaluate response of a 50th percentile child to sudden changes in wind speed. It is shown that such a child is potentially very wind sensitive, with 30% reduction in the wind velocity required to cause loss of balance when compared to the 50th percentile adult male.

Neural network controller for a permanent magnet generator applied in a wind energy conversion system

In this paper a neural network controller for achieving maximum power tracking as well as output voltage regulation, for a wind energy conversion system (WECS) employing a permanent magnet synchronous generator, is proposed. The permanent magnet generator (PMG) supplies a DC load via a bridge rectifier and two buck–boost converters. Adjusting the switching frequency of the first buck–boost converter achieves maximum power tracking. Adjusting the switching frequency of the second buck–boost converter allows output voltage regulation. The on-times of the switching devices of the two converters are supplied by the developed neural network (NN). The effect of sudden changes in wind speed, and/or in reference voltage on the performance of the NN controller are explored. Simulation results showed the possibility of achieving maximum power tracking and output voltage regulation simultaneously with the developed NN controller. The results proved also the fast response and robustness of the proposed control system.

Adjustment of Wind Waves to Sudden Changes of Wind Speed

An experiment was conducted in a small wind-wave facility at the Ocean Engineering Laboratory, California, to address the following question: when the wind speed changes rapidly, how quickly and in what manner do the short wind waves respond? To answer this question we have produced a very rapid change in wind speed between Ulow (4.6 m s−1) and Uhigh (7.1 m s−1). Water surface elevation and air turbulence were monitored up to a fetch of 5.5 m. The cycle of increasing and decreasing wind speed was repeated 20 times to assure statistical accuracy in the measurement by taking an ensemble mean. In this way, we were able to study in detail the processes by which the young laboratory wind waves adjust to wind speed perturbations. We found that the wind-wave response occurs over two time scales determined by local equilibrium adjustment and fetch adjustment, Δt1/T = O(10) and Δt2/T = O(100), respectively, in the current tank. The steady state is characterized by a constant non-dimensional wave height (H/gT2 or equivalently, the wave steepness for linear gravity waves) depending on wind speed. This equilibrium state was found in our non-steady experiments to apply at all fetches, even during the long transition to steady state, but only after a short initial relaxation Δt1/T of O(10) following a sudden change in wind speed. The complete transition to the new steady state takes much longer, Δt2/T of O(100) at the largest fetch, during which time energy propagates over the entire fetch along the rays (dx/dt = cg) and grows under the influence of wind pumping. At the same time, frequency downshifts. Although the current study is limited in scale variations, we believe that the suggestion that the two adjustment time scales are related to local equilibrium adjustment and fetch adjustment is also applicable to the ocean.