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This paper, explores the connection of a wind farm to the grid through high voltage direct current system on voltage source converter VSC-HVDC. 12 MW wind farm consisting of 6 individual 2 MW permanent magnet synchronous generators is presented. In this paper we proposed a new particle swarm optimization algorithm (PSO) based PI controller in order to optimize the gains of PI controller of VSC-HVDC link, which consequently improve the stability of the link after a strict faults. Different results are obtained to show the efficiency of the proposed PSO algorithm for the conception of optimal controller for a VSC-HVDC link connected to a wind farm. MATLAB/Similink simulations are provided to illustrate the performance of the proposed approach under serious perturbation as single AC fault and DC fault.

The recent developments in semiconductors and control equipment have made the voltage source converter based high voltage direct current (VSC-HVDC) feasible. This new DC transmission is known as "HVDC Light or "HVDC Plus by leading vendors. Due to the use of VSC technology and pulse width modulation (PWM) the VSC-HVDC has a number of potential advantages as compared with classic HVDC. In this paper, the scenario of back-to-back VSC-HVDC link connecting two adjacent asynchronous AC networks is studied. Control strategy is implemented and its dynamic performances during disturbances are investigated in MATLAB/Simulink program. The simulation results have shown good performance of the proposed system under balanced and unbalanced fault conditions. The availability of the modern semiconductor devices such as the Insulated Gate Bipolar Transistor (IGBT) [1] has led to the development of a new generation of power electric converters. These devices, unlike the conventional thyristors which have no intrinsic turn-off ability, are of the fully controlled type. The most common converters, which employ the self commutating, high voltage, high current, and high switching frequency power electronic devices, are the Voltage Source Converters (VSC). A number of FACTS controllers which use VSC as their basic building block have been already in operation in various parts of the world. The most popular controllers are: the STATCOM, the SSSC, the UPFC, and the voltage source converter based HVDC transmission (VSC-HVDC) [2,3].The VSC-HVDC system is the most recent HVDC technology. It consists of two VSC, one of which operates as a rectifier and the other as an inverter. The two converters are connected either back-to-back or joined by a DC cable, depending on the application. Its main function is to transmit a constant DC power from the rectifier station to the inverter station, with high controllability. The VSC-HVDC has several main advantages against the conventional HVDC based on thyristors. They are [4, 5]:1. Independent control of the active and reactive power output from each terminal.2. Reduced requirements for harmonic filters.3. Improvements of the power quality and system stability.4. Elimination of the requirement for a local power generation.These features make the VSC-HVDC attractive for connection of weak AC system, island networks, and renewable energy sources, which may be located in remote area, to a main grid.This paper presents the elements of back-to-back VSC-HVDC where the converter stations are located at the same site and transmission line or cable is not needed. The paper wills first give a brief description about the VSC-HVDC transmission system and its terminal control functions. Following that, typical operating contingency scenarios are simulated in order to evaluate transient performance. The simulation results confirm that the control strategy has fast response and strong stability.

The Static Synchronous Compensator (STATCOM) devices are pure power electronics devices that use voltage source, IGBT, IGCT or GTO based converters to generate reactive current. This paper illustrates the effect of STATCOM connected whit an HVDC inverter feeding a weak AC network, on the recovery from commutation failures following AC side disturbances. MATLAB/SIMULINK simulation results have demonstrated the robust performance of the proposed system based on the first CIGRÉ HVDC Benchmark model against commutation failures.

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