الفهرس 
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Abstract
Due to the percentage increase of wind generation penetration in the electric utility grid, new grid codes have been issued that require Low-Voltage Ride-Through capability (LVRT) for wind turbines so that they can remain online and support the electric grid instead of direct tripping of the wind turbines. The objective of the thesis is to develop an integrated control and protection system for modern wind turbines to fulfill the revised grid code requirements. The settings of the wind turbine protection system are coordinated with the turbine control system to satisfy the grid codes and Transmission System Operators (TSO) requirements. The main objectives of the thesis are: 1- Determining the requirements of the TSO and the grid owners on the wind farms. 2- Determining how the protection and control systems that have been constructed on Doubly Fed Induction Generator (DFIG) wind turbine also known as Type 3 and Full converter (FC) wind turbine also known as Type 4 to satisfy existing requirements and identify failure to achieve this. 3- Developing a protection system of DFIG wind turbine by replacing the active CROWBAR used by wind turbine manufacturers with Series Dynamic Resistance (SDR) as a LVRT circuit. 4- Developing control systems of the FC wind turbine by replacing the control strategy (A) used by wind turbine manufacturers for LVRT by control strategy (B) in order to satisfy the requirements on the wind turbines. The work is mainly about the protection schemes and the control strategies for the DFIG and FC wind turbines in order to keep the wind turbines connected to the network during grid faults, which cause voltage dips at the generator terminal. The models are implemented using PSCAD/ EMTDC transient simulation package. The active CROWBAR is LVRT protection circuit used mostly by DFIG wind turbine manufacturers. It was found by the simulation results that the active CROWBAR has drawbacks such as disconnection of the Rotor Side Converter (RSC) which make the generator operates as Single Fed Induction Generator (SFIG) and absorbs reactive power from the grid. To overcome this, Series Dynamic Resistance (SDR) is proposed as a LVRT protection circuit for DFIG. It is connected in series with the rotor winding. SDR has the advantage that when it operates during the fault, the RSC is not disconnected and the DFIG is under control and can supply reactive power during the voltage dip in order to facilitate voltage recovery. The simulation results show that the developed hybrid LVRT protection scheme (SDR+ DC chopper) provides better LVRT performance in comparison with hybrid scheme (active CROWBAR+ DC chopper), by making the generator has the ability to inject reactive power to the grid during grid faults. On the other hand the commonly LVRT control strategy (A) used by wind turbine manufacturers for FC is discussed and evaluated. The simulation results show that the control strategy (A) has drawbacks such as formation of a high DC voltage at DC-Link which may destroy the power electronic components of the FC turbine. So a DC Chopper must be connected to smooth the DC voltage. To overcome this, it has been proposed a LVRT control strategy (B) to provide better LVRT performance for FC. The simulation results with different grid faults including symmetrical and unsymmetrical faults show that the proposed control strategy (B) gives better LVRT performance in comparison with control strategy (A), by keeping the DC link voltage nearly constant without using DC chopper. The developed techniques will be then tested on Zafarana wind farm. The protection schemes used in Gamesa 850 KW (DFIG) wind turbine which is the most used WT in Zafarana wind farm will be reviewed and evaluated. The active CROWBAR and SDR are proposed as LVRT protection circuits for the Gamesa 850 KW wind turbine. The proposed active CROWBAR connected in parallel with the rotor winding and SDR connected in series with the rotor wind make the turbine able to stay on-line during grid faults. The simulation results with different grid faults including symmetrical and unsymmetrical faults show that the developed hybrid LVRT protection scheme (SDR+ DC chopper) provides better LVRT performance in comparison with hybrid scheme (active CROWBAR+ DC chopper), by making the generator has the ability to inject reactive power to the grid during grid faults. The Egyptian Grid codes as well as the E.ON grid code (Transmission Provider in Germany) requirements for wind farms is considered as the grid code for this thesis.