الفهرس 
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Abstract
The HVDC system is realized as the most practicable solution for the enormous integration of transmission power systems, the interconnection between power systems positioned in remote areas and the interconnection of asynchronous ac grids. Nevertheless, there are several remaining issues and it is essential to additional research before its growth. One of the research areas which create greater helpfulness is the operation and control of such grids. A system of these features must be accomplished of maintaining the power balance, allocating the load flows between converters after a change in load or generation conditions and achieving security desires. In this thesis, the three most widespread strategies for its control, integrated and droop are described, and their influence on the network operation is calculated. The first controller was studied in this thesis but this controller has some problems such as deviations with reference to the nominal values, maximum overshoot and large settling time. Thus, it is not possible to control the inserted power in each of the stations. The PI Conventional problems can be solved with secondary controller PSO-PI which lets following references values improved than traditional one, minimizing in the maximum overshoot and settling time. A Discrete Time Controller DTC tertiary control was suggested by using Fast Output Sampling FOS which allows the system optimization agreeing to the minimization of losses and good trajectory for the reference values. This controller is based on the droop characteristic and, therefore, the system does not require critical communications for its stability and it’s satisfies. In order to confirm and study the behavior on the process, simulations of the control are done by means of the power systems study tool MATLAB / SIMULINK. The main objectives of this thesis are : The main benefits of using HVDC when compared with HVAC. The main types of HVDC and the difference between them. The main system components that we will design the controller on it. The design of the first controller by using proportional Integral PI and make different cases studies to show how the system trajectory the reference values. The design of the second controller by using Particle Swarm Optimization-PI (PSO-PI) to show how the system performance is better than using traditional one. The design of the third controller by using Discrete Time Controller (DTC-FOS) then show that it’s the best one for trajectory the reference values in different cases , and minimizing the overshoot and settling time values to the best values. Comparison were made between two level converter and three level converter to show that the reduction in total harmonics contents by using three level converter. Finally the application of HVDC on Egyptian Electrical Network and KSA network was presented to show the benefits of using VSC-HVDC in connection between two countries Electrical Network.