الفهرس 
Direct torque control of machine side multilevel converter
DC voltage Control with Fuzzy Logic ControllersOnly 14 pages are availabe for public view
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Abstract
Nowadays, wind turbine capacities are increasing rapidly. New capacities of 5 MW wind turbines now exist and yet are still increasing continuously, especially for offshore wind turbines. Generation voltage has been increased to comply with the new power demand. Multilevel converter is used to decrease switching voltage to an acceptable level.
In this thesis, maximum power point tracking for variable speed wind turbine with two techniques are used. The first technique uses optimum maximum power curve fitting Pmax(Wmax) to generate an optimal reference speed. The second maximum power point tracking for variable speed wind turbine is based on adaptive neural fuzzy inference system algorithm. It predicts the optimal reference speed of squirrel cage induction generator (input of direct torque controller for the machine side multilevel converter) with wind speed variations
The diode clamped three, four and five level converters with direct torque controller for the machine side converter with proportional integral controller are used. The high level converter enhances the performance of the induction generator torque, current, flux, speed, active and reactive power during start up and wind speed variations. Moreover, the total harmonic distortion is decreased compared with the classical two levels converter without the need of using complex controllers.
The diode clamped three, four and five level converters with direct power controller for the grid side converter with proportional integral controller is used. This topology is used to improve the performance of the delivered power flowing from the dc-link to the electric utility-grid. It decreases ripples of the DC-link voltage and total harmonic distortion and improves the power factor of the injected power to the utility-grid. The proposed system r is done using Matlab/SimulinkSimscape Power Systems. Comparison is done between the multilevel converter and the two-level converter.
Fuzzy logic controller for both direct torque control of machine side converter and direct power control of grid side converter with diode clamped three, four and five-level converter is carried out. The use of the proportional integral controller for both direct torque control and direct power control with multilevel converters to decreases the steady-state error, but it may increase peak overshoot and steady state time. It cannot handle uncertainty (system parameters and sensor measurement). While replacing proportional integral controller with fuzzy logic controller decreases peak overshoot, steady state time and it can handle uncertainty. The use of direct torque control with fuzzy speed controller for multilevel converters will improve the performance of wind turbine and despite squirrel cage induction generator wind variation. Direct power control with fuzzy dc voltage controller for multilevel converters improves power quality of injected power delivered to utility-grid.
The proposed technique in balancing internal capacitors voltage for back to back diode clamped multilevel converters based on switching redundancy of space vector voltage is implemented. The switching redundancy of space vector voltage is used for direct power control with grid side multilevel converter based on fuzzy logic control. The proposed system is evaluated for three and four level converters with the cases of wind speed variations and grid voltage dips. Simulation is carried out using Matlab-Simulink Sim Power Systems.