This paper deals with a modern approach of controlling the power flow in AC transmission lines. The control and distribution of power flow in two parallel transmission lines can be implemented by applying one of the flexible AC transmission system (FACTS), which is static compensator (STATCOM) device. The STATCOM device is installed on one line of the two parallel transmission lines to design the controllers for such a system using Electromagnetic Transients Program (EMTP). The closed-loop STATCOM system as a terminal line voltage regulator is designed with two types of controllers, PI with gain scheduling and fuzzy logic. The dynamic performance of the two controllers is tested and compared. It is found that, the fuzzy logic controller forces the system to settle to the steady state value faster than the PI controller with gain scheduling. The fuzzy logic controller is robust; it has a fast response during disturbance and parameters variation. Whereas, the PI controller with gain scheduling has a higher overshoot percentage during transient behavior. Tuning the PI controller with gain scheduling is time consuming and difficult in EMTP, it has a limited range of changing the operating voltage condition due to the tuning difficulty. In the other hand, the fuzzy logic controller can be tuned much faster. Finally, It is claimed that the fuzzy logic controller is a better choice for the STATCOM system compared to the PI controller with gain scheduling.  

FACTS technology has considerable applications in power systems, such as; improving the steady state performance, damping the power system oscillations, controlling the power flow, and etc. STATCOM is one of the most important FACTS devices used in the parallel compensation, enhancing transient stability and etc. Since three phase fault is widespread in power systems, in this paper STATCOM is used to improve the transient stability of power system when three phase fault occurred. Neural Network has been used for adjusting the gain of the supplementary controller of STATCOM. The simulation performed in MATLAB / Simulink software. Simulation results showed when STATCOM combines with proposed Neural Network based supplementary controller; the transient stability of power system improves.

A large number of single-phase loads and sources create unbalanced voltage in microgrids. Voltage unbalance reduces the power quality, which results in misoperation or failure of customer equipment and microgrid. Also, voltage unbalance negatively impacts induction motors, power electronic converters, and adjustable speed drives.  Static synchronous compensator (STATCOM), as an influential segment of the Flexible Alternative Current Transmission Systems (FACTS), has been extensively utilized as shunt compensators for controlling reactive power and regulation voltage in transmission and distribution networks. Under unbalanced conditions, an oscillating couple between the positive and negative sequence components of control loops emerge in the d-q frame. This paper suggests an innovative point of common coupling (PCC) voltage controller in Decoupled Double Synchronous Reference Frame (DDSRF) to compensate for an unbalanced PCC voltage and reduce the oscillating couple using STATCOM. Implementation of the proposed DDSRF involves several steps. Firstly, unbalance signals are rotated counterclockwise to split up the positive sequences. Secondly, those signals are rotated clockwise to separate negative sequences. Finally, by utilizing mathematical equations, the proposed DDSRF is introduced, which enables independent control of positive and negative sequence components. This study controls DC capacitor voltage for unbalanced conditions. Furthermore, the regulation voltage at PCC is performed. The control system scheme is also designed under unbalanced conditions, and simulation results guarantee the suggested control strategy.