A speed estimation, obtained from a model reference adaptive system (MRAS) , is used to control the elec- trical torque of the induction machine. A V/F control strategy is used in the low-speed region for starting and driving the WECS set into the speed operating range. In order to tune the MRAS system and compensate for the variation of the machine parameters, an estimation of the rotational speed is obtained from the rotor slot harmonics (RSH) [7,8]. The spectral analysis method used in this publication can track the rotational speed not only in steady state but also when the WECS is subjected to fast dynamic changes.
At wind speeds below 6m/s the PAC is switched off for all three strategies. It is only turned on again if the wind turbine has returned to its normal operating point and the estimated wind speed rises above 7m/s. This hysteresis prevents chattering from occurring. Figure 9 demonstrates this, showing the output from one wind turbine at a mean wind speed of 6.5m/s. The estimated wind speed does not rise above 7m/s until approximately 65 seconds. At this point the PAC switches on and a change in power output is requested. At approximately 90 seconds the wind speed drops below 6m/s and the PAC switches off again. Although the estimated wind speed rises above 7m/s at approximately 115 seconds, the wind turbine has not yet returned to normal operation. Only once it has done so,
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wind speed estimation problem  such as power balance estimator method , Kalman filter (KF)-based estimator –, disturbance accommodating control (DAC) , unknown input observer (UIO)  and the immersion and invariance (I&I) estimator . In this paper, three algorithms are used to estimate the effective wind speed by solving power balance equations. The estimated wind speed is used to determine the optimal speed reference for generator control system. Several model based control approaches have been studied for the wind turbine system, such as linear-quadratic regulator (LQR), pole-placement and PID, which provides convenience to implement such controllers in practical applications , .
However, the sparkle mitigation technique shows its limits in some distribution networks wherever the grid electric resistance angle is low . once the wind speed is high and also the grid electric resistance angle is 10◦, the reactive power required for flicker mitigation is three.26 per unit . it's tough for a grid- side convertor (GSC) to come up with this quantity of reactive power, particularly for the doubly fed induction generator (DFIG) system, of that the convertor capability is simply around zero.3 per unit. The STATCOM that receives a lot of attention is additionally adopted to scale back flicker emission. However, it's unlikely to be financially variable for distributed generation applications. Active power management by varied the dc-link voltage of the consecutive convertor is conferred to attenuate the sparkle emission .
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Abstract:- The documented investigation in this paper examines main power quality for wind turbines and its connection with the public grid. This main goal has been to investigate most popular type of wind turbines which are grid connected using doubly-fed induction generators (DFIG) at normal operation, as well as voltage control of these wind turbines after clearing a lines short circuit in the utility grid. This paper introduces the configuration of main portions of grid connected turbines, which have an importance in the wind power plants operation. It also proposes a new compact modeling of these wind turbines, which has a feature that the expressions of most plant portions are free of any complex or details that described in other past models.
Dr. Sajjad Tohidi was born in Meshkinshahr, Iran, in 1984. He received the B.Sc. degrees, from Iran University of science and technology, and the M.Sc. and Ph.D. degree in Electrical engineering from sharif university of technology, Iran. He is currently faculty member in University of Tabriz. His research interests include power systems dynamics, electrical machines and wind power generation.
Due to the wind speed variation, wind shear and tower shadow effects, grid connected wind turbines are the sources of power fluctuations which may produce flicker during continuous operation. This paper presents a model of an MW-level variable speed wind turbine with a doubly fed induction generatorto investigate the flicker emission and mitigation issues. An individual pitch control (IPC) strategy is proposed to reduce the flicker emission at different wind speed conditions. The IPC scheme is proposed and the individual pitch controller is designed according to the generator active power and the azimuth angle of the wind turbine. The simulations are performed on the NREL (National Renewable Energy Laboratory) 1.5-MW upwind reference wind turbine model. Simulation results show that damping the generator active power by IPC is an effective means for flicker mitigation of variable speed wind turbines during continuous operation.
Abstract. This paper addresses the preliminary robust multi-disciplinary design of small wind turbines. The turbine to be designed is assumed to be connected to the grid by means of power electronic converters. The main input parameter is the yearly wind distribution at the selected site, and it is represented by means of a Weibull distribution. The objective function is the electrical energy delivered yearly to the grid. Aerodynamic and electrical characteristics are fully coupled and modelled by means of low- and medium-fidelity models. Uncertainty affecting the blade geometry is considered, and a multi-objective hybrid evolutionary algorithm code is used to maximise the mean value of the yearly energy production and minimise its variance.
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Two versions of separability of aerodynamic torque for variable speed wind turbines are investigated; the separated function, related to wind speed, in the first version is only dependent on that variable and not on rotor speed and in the second version is only dependent on tip speed ratio. Both provide very good approximations to the aerodynamic torque over extensive neighbourhoods of , at least from 0 to . If anything, the wind speed separability is the more accurate but has the least analytic support being purely empirically motivated. The two versions of separability are illustrated by application to a 3MW HAWT.
Throughout history the use of wind energy has been a constant for human kind. Such energy comes from a renewable source, namely, the natural and continuous atmospheric processes . The use of wind energy has increase notably in recent years, especially for generation of electric power . This is because the increasing need of finding less polluting alternatives for energy production has found in wind power system a realizable option, with the power-electronic controlled variable speed wind turbines as the most efficient scheme. The speed and the pitch angle of the blades of these turbines are controlled by digital algorithms in all time .
In Previous day’s power generation is mostly based on the non-renewable sources but now-a-days power generation with renewable energy is more efficient and growing one. Variable speed wind turbines employing Doubly Fed Induction Generator (DFIG) is the most popular technology in currently installed wind turbines .With the continuous increase in penetration level of DFIG wind turbines, power system stability becomes an important issue which needs to be properly investigated ,.Wind power generation with DFIG is optimal one and high penetration of this DFIG creates some instability in rotor and grid side. By replacing Variable Speed Wind Turbine (VSWT) generation with equivalently rated synchronous units, the small-signal stability and transient stability of the system was assessed. But efficiency of the system is reduced and it creates more stress in gear system. Power electronic converter of the DFIG acts as an interface between DFIG generator and the grid. And increased penetration of DFIG, the effective inertia of the system will be reduced. DFIGs are not synchronously coupled to the power systems, the wind turbines do not participate in electromechanical oscillations. This DFIG frequency of the stator is based on the frequency of the rotor and it is varied by the controllers.
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Due to the wind speed variation, wind shear and tower shadow effects, grid connected wind turbines are the sources of power fluctuations which may produce flicker during continuous operation. This paper presents a model of an MW-level variable speed wind turbine with a doubly fed induction generator to investigate the flicker emission and mitigation issues. An individual pitch control (IPC) strategy is proposed to reduce the flicker emission at different wind speed conditions. The IPC scheme is proposed and the individual pitch controller is designed according to the generator active power and the azimuth angle of the wind turbine. The simulations are performed on the NREL (National Renewable Energy Laboratory) 1.5-MW upwind reference wind turbine model. Simulation results show that damping the generator active power by IPC is an effective means for flicker mitigation of variable speed wind turbines during continuous operation.
Although wind turbines are able to turn to face the wind, it has been suggested that the relationship between wind power and wind speed is, to some extent, dependent on the wind direction. Potter et al. (2007) find that the uncertainty in the relationship depends on the wind direction. Nielsen et al. (2006) include a wind direction variable into the relationship to explain turbine wake effects and direction dependent bias of the meteorological forecasts. nche (2006) recognizes that wind direction influences the performance of a wind farm, and so uses it in a wind power prediction model. In Figure 5, we plot wind power against wind speed using different symbols to show the data points for selected wind directions. The plots suggest that the variability in the relationship can depend on wind direction. For Aeolos, south-westerly wind seems to produce a higher degree of variability in the relationship, and for Rokas, south-westerly wind shows higher variability than north-westerly when the wind speed is below about 13 m/s.
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The goal of our study was to investigate the uncertainty in predicting potential wind-energy production under such landscape conditions. Juneau, Alaska served as a testbed. Frequent storms moving into the Gulf of Alaska govern Juneau’s climate . Being located in a fjord landscape that belongs to the Tongass National Forest, the terrain has strong impact on the wind speed. Juneau is surrounded by mountains covered by about 30 glaciers that make up the Juneau Icefield. Thus, any construction of a windfarm atop of the mountains is hardly reasona- ble. The frequent avalanches prohibit any icefree potential locations. The high tidal differences make any off- shore location challenging from a technical point of view. Furthermore, whales and other marine mammals dis- like the infra-sound created by wind turbines and stay away from these areas . However, the tourists, among glacier viewing, also come to see and watch these animals. Consequently, an offshore location is prohibitive from an economic point of view. The complex terrain allows installing a windfarm at lower elevation where the fjord widens and joins other fjords.
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This paper represents dynamic modeling and simulation of variable speed wind turbine (VSWT) with grid and without grid connection using MATLAB/SIMULINK, a widely used power system analysis and dynamic tool. The variable speed wind turbine with single fed induction generator (IG) and power electronic converter, controller is modeled for dynamic analysis. Component model and equations are represented and implemented in MATLAB/SIMULINK. Controllable power inverter strategy is applied for capturing maximum power under varying speed of wind turbine and controlled reactive power for voltage regulation. Simulation studies give control performance analysis of a gearless VSWT under varying wind speeds.
Abstract: Diffusers have been used to augment the wind speed in diffuser augmented wind turbines. However, there is no known method to estimate the wind speed augmentation by these diffusers. This study presents a mathematical model that estimates the wind speed augmentation by empty conical diffusers for use in diffuser augmented wind turbines (DAWT). The model is used by DAWT wind energy systems engineers in optimizing the power output of the DAWT. The model is based on the diffuser length (L), diffuser expansion angle (θ) and the diffuser inlet diameter (D). The model equation and the experimental data are correlated with R 2 = 0.9751 and RMSE = 0.034. It was shown that the diffuser expansion angle (θ), a predictor contributes more to the desired output as compared to the non-dimensional length (L/D) .
Increasing wind power penetration levels to the power systems of many regions and countries has led to the elaboration of specific technical requirements for the connection of wind farms to the grids. These requirements are concerned with grid codes issued by the system operators . The grid codes specifies that wind farms should contribute to power system control (frequency and also voltage), much as the conventional power generation stations, and withstand on wind farm behaviour in case of abnormal operating conditions of the network (such as in case of voltage dips due to network faults) . Grid code requirements have been a major driver for the development of Wind turbine (WT) technology.
ABSTRACT: This paper presents the results of variable speed wind power generation system using permanent magnet synchronous generator. The Sepic converters are utilized as converters for variable speed wind power generation system. The inverter is designed with space vector modulation (SVM) to reduce total harmonic distortion. Wind power generation system simulated using Matlab consisting of wind turbine, PMSG, diode rectifier, PWM controlled Sepic converter, inverter with SVM and AC load.
charging voltage to it, and in case the charge falls below the lower set threshold, the circuit will connect, and initiate the charging process. Here the IC 555 is configured as a comparator for comparing the battery low and high voltage conditions at pin#2 and pin#6 respectively. As per the internal circuit arrangement, a 555 IC will make its output pin#3 high when the potential at pin#2 goes below 1/3 of supply voltage. The above position sustains even if the voltage at pin#2 tends to drift a little higher. This happens due to the internal set hysteresis level of the IC. However if the voltage continues to drift higher, pin#6 gets hold of the situation and the moment it senses a potential difference higher than 2/3rd of supply voltage, it instantly reverts the output from high to low at pin#3. In this lead acid battery charger circuit design, it simply means that, the pre-sets R2 and R6 should be set such that the relay just deactivates when the battery voltage goes below say 11.3V (for 12V batts) and activates when the battery voltage reaches above 14.2V. Rectifier is connected to Charging circuit through a 15V voltage regulator. Rectifier gets the supply from the wind turbine. These charging circuits prevent the battery from overcharging and backflow of current when there is no supply.
between the mechanical and electrical frequency by injecting a rotor current with a variable frequency. Both during normal operation and faults the behaviour of the generator is thus governed by the power converter and its controllers. The power converter consists of two converters, the rotor-side converter and grid-side converter, which are controlled independently of each other. The rotor-side converter controls the active and reactive power by controlling the rotor current components, while the line-side converter controls the DC- link voltage and ensures a converter operation at unity power factor. In both cases – sub synchronous and over synchronous – the stator feeds energy into the grid. The DFIG has several advantages. It has the ability to control reactive power and to decouple active and reactive power control by independently controlling the rotor excitation current. The DFIG has not necessarily to be magnetized from the power grid, it can be magnetized from the rotor circuit, too. It is also capable of generating reactive power that can be delivered to the stator by the grid-side converter. In the case of a weak grid, where the voltage may fluctuate, the DFIG may be ordered to produce or absorb an amount of reactive power to or from the grid, with the purpose of voltage control. The converter used in DFIG is back to back converter