الفهرس 
chapter 1Only 14 pages are availabe for public view
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Abstract
Wind power generators represent a prominent facility for generating renewable and clean bulk power to utility grids. Basically, there are many good reasons for using more wind energy on electricity systems. For instance, wind generation is supported by not only being clean and renewable but also having minimal running cost requirements. Although wind energy has many benefits, their utilization in the electrical grid doesn’t come without cost. The main drawbacks of wind power generation industry are due to the wind itself. Because of the capricious and stochastic nature of the wind, the wind speed changes over moments, hours, days and seasons.
The induction (asynchronous) generator is widely used for many years in wind generation applications. The reliability, rugged construction, low price, and low maintenance made this type of machines the most suitable for wind turbines. In addition to these favorable aspects, the flexibility of rotational speed (slip) of the induction generator, compared to the absolutely fixed speed of synchronous generators, reduces the current spikes due to wind gusts. Yet, the main drawback of induction generators is that they consume reactive power. Double Fed Induction Generator (DFIG) technology is widely used in large and modern wind turbines (1 to 10 MW) since it permits variable speed operation at reasonable cost and provides a reactive power control
The wind speed variability definitely affects the wind power production. So, to get the optimum benefits of the bulk wind power produced by the interesting DFIG scheme, a Maximum Power Point Tracking (MPPT) strategy has been required. The peak power tracking control can have the wind turbine system achieve optimum wind energy utilization and maintain the maximal aerodynamic efficiency.
In this thesis, comprehensive models of grid connected DFIG – based wind turbines are implemented where the power generated from wind is transferred to the gird via two paths. The main path is the direct-connected stator link, whereas the secondary path is the rotor circuit which supplies the power via two back-to-back converters. It is worth mentioning that most of the power is transmitted via the stator and only small portion is fed via the rotor circuit and the converters.
The main objectives of this control are to fulfill the optimum wind power tracking, reactive power control, and blades’ pitch control in case of higher rotor speeds. The control decouples the active and reactive power control by controlling the direct and quadrature current components independently. Park transformation is used to convert the abc stator quantities to their equivalent in the synchronous dq reference.
Different methods (MPPT) Techniques like Optimal Torque (OT) Control are used, further Adaptive Neuro -Fuzzy Inference System (ANFIS) is implemented. Based on the simulation results, DFIG based wind turbine is capable to achieve MPPT, further the simulation results gives better performance using artificial intelligent technique. Various methods of optimization techniques are applied on the control schemes of rotor and grid side converters. Control actions are simulated with detailed model using MATLAB/SIMULINK environment.
The controller is so simple that it needs only online values of DFIG voltages and currents which can be obtained easily by using just current and voltage sensors. To optimize the system response, ANFIS based PI controller parameters tuning is presented to search the optimal PI controller parameters
Two control schemes are implemented in the developed grid-connected wind turbine model: speed control and pitch control. The speed control scheme is composed by two vector- control schemes designed respectively for the rotor-side and grid-side PWM voltage source converters. Cascade control is used in the vector-control schemes. Two design methods, pole- placement and internal model control, are applied for designing the PI-controllers in the vector-control schemes. The pitch control scheme is employed to regulate the aerodynamic power from the turbine. The performances of the control schemes, respectively current control loops, power control loops, DC-link voltage control loop and pitch control loop, are illustrated, which meet the design requirements. Simulation results show that the wind turbine is capable of providing satisfactory steady state and dynamic performances, which makes it possible that the wind turbine model can be applied to study the power quality issues of such kind of grid-connected wind turbines and their interaction with the grid.
Experimental and theoretical studies of Pitch Angle control are implemented in the laboratory (Smart Systems Labs) based on the results there are large agreement between them. Both experimental and simulation results shows that as pitch angle increase the Cp decrease which cause decrease in active power and rotor speed with different wind speed profile. The experimental results were in a good agreement with the simulated results.