In this paper investigations on a fixed speed wind farm with squirrel cage induction generators directly connected to the grid in combination with a StatCom under unbalanced grid voltage fault are given by means of theory and simulations. The stability of fixed speed wind turbines can be improved by a StatCom, which is well known and documented in literature for balanced grid voltage dips. Under unbalanced grid voltage dips the negative sequence voltage causes additional generator torque oscillations. A StatCom control structure with the capability to control the positive or negative sequence of the voltage is used. The simulation results clarify the effect of positive and negative sequence voltage compensation by a StatCom on the operation of a fixed speed wind farm. The influence of different StatCom control targets is investigated that lead to an increased network voltage stability and lower torque pulsations.

This paper presents a graphical user interface (GUI) uses Particle Swarm Optimization (PSO), which is used to find the optimal locations and sizing parameters of multi type Flexible AC transmission systems (FACTS) devices in complex power systems. The GUI toolbox, offers user to choose a power system network, PSO settings and the type and number of FACTS devices for the selected network. In this paper, three different FACTS devices are implemented: SVC, TCSC and TCPST. FACTS devices are used to increase the system loadability, by reducing power flow on overloaded lines, transmission line losses, improving system stability and security. With this can make the transmission system more energy-efficient. PSO used here for optimally allocating and sizing the multiple type FACTS in a standardized power network (IEEE 30 bus system) in order to improve voltage profile, minimizing power system total losses and maximizing system loadability with respect to the size of FACTS.